CA1074519A - Method and apparatus for producing undercut tubular synthetic plastic articles - Google Patents
Method and apparatus for producing undercut tubular synthetic plastic articlesInfo
- Publication number
- CA1074519A CA1074519A CA258,002A CA258002A CA1074519A CA 1074519 A CA1074519 A CA 1074519A CA 258002 A CA258002 A CA 258002A CA 1074519 A CA1074519 A CA 1074519A
- Authority
- CA
- Canada
- Prior art keywords
- core
- article
- fitting
- mold
- combination
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C57/00—Shaping of tube ends, e.g. flanging, belling or closing; Apparatus therefor, e.g. collapsible mandrels
- B29C57/02—Belling or enlarging, e.g. combined with forming a groove
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C37/00—Component parts, details, accessories or auxiliary operations, not covered by group B29C33/00 or B29C35/00
- B29C37/0003—Discharging moulded articles from the mould
- B29C37/0014—Discharging moulded articles from the mould by flexibly or permanently deforming undercut portions of the articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/26—Moulds
- B29C45/261—Moulds having tubular mould cavities
- B29C45/2612—Moulds having tubular mould cavities for manufacturing tubular articles with an annular groove
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
- B29C45/17—Component parts, details or accessories; Auxiliary operations
- B29C45/40—Removing or ejecting moulded articles
- B29C45/44—Removing or ejecting moulded articles for undercut articles
- B29C45/4407—Removing or ejecting moulded articles for undercut articles by flexible movement of undercut portions of the articles
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Injection Moulding Of Plastics Or The Like (AREA)
- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
ABSTRACT
Undercut tubular synthetic plastic articles, such as fit-tings, are formed in the mold cavity of an injection molding machine on a two-piece core a tubular component of which is surrounded by the undercut portion of the article and a first smaller-diameter portion at one side of the undercut portion. A cylindrical compon-ent of the core slidably guides the tubular component and is sur-rounded by a second smaller-diameter portion of the article at the other side of the undercut portion. When the injection of plastic-ized material is completed, the housing of the mold is opened to expose the undercut portion and the first smaller-diameter portion of the article on the core, the first smaller-diameter portion and the undercut portion are heated to or maintained at a temperature at which they can undergo elastic deformation, and the tubular com-ponent is moved axially of the article and of the cylindrical com-ponent so that the first smaller-diameter portion of the article is expanded by an external ring-shaped projection which forms part of the tubular component and was surrounded by the undercut portion.
The first smaller-diameter portion of the article thereupon con-tracts so that its inner diameter is again less than the inner di-ameter of the undercut portion. The article is allowed to harden prior to complete separation from the core, and the first smaller-diameter portion is held against excessive contraction during hard-ening of the article.
Undercut tubular synthetic plastic articles, such as fit-tings, are formed in the mold cavity of an injection molding machine on a two-piece core a tubular component of which is surrounded by the undercut portion of the article and a first smaller-diameter portion at one side of the undercut portion. A cylindrical compon-ent of the core slidably guides the tubular component and is sur-rounded by a second smaller-diameter portion of the article at the other side of the undercut portion. When the injection of plastic-ized material is completed, the housing of the mold is opened to expose the undercut portion and the first smaller-diameter portion of the article on the core, the first smaller-diameter portion and the undercut portion are heated to or maintained at a temperature at which they can undergo elastic deformation, and the tubular com-ponent is moved axially of the article and of the cylindrical com-ponent so that the first smaller-diameter portion of the article is expanded by an external ring-shaped projection which forms part of the tubular component and was surrounded by the undercut portion.
The first smaller-diameter portion of the article thereupon con-tracts so that its inner diameter is again less than the inner di-ameter of the undercut portion. The article is allowed to harden prior to complete separation from the core, and the first smaller-diameter portion is held against excessive contraction during hard-ening of the article.
Description
The present invention relates to a method and appaxatus for the production of plastic articles which constitute tubes ~r in-clude! tubular portions, and more particularly to improvements in a method and apparatus for the production of plastic articles which exhibit one or more undercuts in the form o$ internal grooves or re-cesses provided in a tubular portion which is flanked by tubular por-tions having smaller inner diameters. Such undercuts are often nec-essary in fittings in order to receive sealing elements in the form of gaskets or packings. Still more particularly, the invention re-lates to improvements in the molds of injection molding or analog-ous machines, and in a method which can be practiced by resorting to such molds.
Flanged fittings or pipe connectors (e.g., elbows, return bends, tees, crosses, reducing couplings or straight unions) are often provided with undercuts to accommodate sealing elements for the ends of flexible or rigid pipes which are inserted into the fit-tings. In accordance with a presently prevailing technique, under-cuts in the flanges of fittings which are produced in injection molding machines are fonmed by resorting to one or more secondary operations which contribute to the cost of such articles. For ex-ample, it is known to provide a flange of a fitting with a relative-ly ~hick circumferentially complete rib or bead which is thereupon treated from within (e.g., by resorting to milling or turning tools) in order to form therein a ring-shaped internal recess or groove for reception of a sealing element. The formation of such internal groove takes place subsequent to ejection of the article from an in-jection molding machine so that the interval which is required for completion of an undercut fitting is much longer than the interval which is required for completion of the injection molding cycle.
It was further proposed to make undercut fittings in spe-
Flanged fittings or pipe connectors (e.g., elbows, return bends, tees, crosses, reducing couplings or straight unions) are often provided with undercuts to accommodate sealing elements for the ends of flexible or rigid pipes which are inserted into the fit-tings. In accordance with a presently prevailing technique, under-cuts in the flanges of fittings which are produced in injection molding machines are fonmed by resorting to one or more secondary operations which contribute to the cost of such articles. For ex-ample, it is known to provide a flange of a fitting with a relative-ly ~hick circumferentially complete rib or bead which is thereupon treated from within (e.g., by resorting to milling or turning tools) in order to form therein a ring-shaped internal recess or groove for reception of a sealing element. The formation of such internal groove takes place subsequent to ejection of the article from an in-jection molding machine so that the interval which is required for completion of an undercut fitting is much longer than the interval which is required for completion of the injection molding cycle.
It was further proposed to make undercut fittings in spe-
- 2 - ~
107~S19 cially designed injection moLding machines wherein the injection molding cycle precedes a blowing cycle serving for the formation of an undercut in one or more flanges of the fitting. It is also known to produce fittings in conventional injection molding machines which furnish fittings with flanges having internal surfaces of constant diameter, and to thereupon introduce such fittings into a blow mold-ing machine which expands a selected portion of a flange so as to provide the internal surface of the flange with a groove for recep-tion of sealing means. Such procedures are not satisfactory because the wall thickness of a blow molded undercut portion invariably de-viates from the wall thickness of neighboring portions of the fin-ished article.
In accordance with still another presently known technique, that flange of a fitting which i8 to be provided with an undercut resembles an outwardly flaring hollow frustum of a cone, and the outermost portion of such flange is thereupon treated to reduce its dimensions, i.e., the inner diameter Gf the thus contracted portion is less than the inner diameter of the neighboring portion. The neighb~ring portion can receive a sealing element which is held against axial movement by the contracted portion of the flange. The just described procedure shares the ~rawbac~8 of previously outlin-ed techniques, i.e., the internal groove of the undercut portion must be formed in a separate operation which follows the making of the fitting. Moreover if a fitting, whose flange has been formed with an undercut in accordance with the last mentioned prior pro-cedure, is used in pipe lines for hot fluids, the connection between the flange and a flexible or rLg~d cnnduit rapidly develops a leak.
This is attributable to a peculiarity of thermoplastic synthetic plastic materials which is known as thermal restoration. Briefly stated, the molecules of thermoplastic material assume a predetermin-1 [)74S:19 ed orientation during introduction of pLasticized material into amold. Thus, the orientation of molecules in a flange which, at the time of introduction of plasticized material into the molding cav-ity, resembles a hollow conical frustum is different from the or-ientation of molecules in a cylindrical flange. When the flange is heated subsequent to formation of an undercut therein (by causing the free end of the flange to shrink), the molecules tend to assume the original orientation which is characteristic of a hollow frusto-con~ ~1 flange with theresult that the flange opens up and permits communication between the confined fluid and the surrounding atmo-sphere.
~ n object of the invention is to provide a novel and im-proved method of producing fittings or other hollow articles which consist of synthetic plastic material and include undercut tubular portions flanked by smaller-diameter tubular portions.
~ nother object of the invention is to provide a method wh~ch renders it possible to form undercut portions simultaneously wlth the making of hollow articLes, i.e., wherein the undercuts de-velop at the time the respective articles are formed in an injection molding or like machine.
A further object of the invention is to provide a method which can be used ~or mass-production of undercut hollow articles with a high degree of reproducibility, within short intervals of time, and by resorting to relativeLy simple apparatus.
An additional object of the invention is to provide a method of making synthetic plastic fittings or other holl~w articles which can be practiced by resorting to retrofitted apparatus.
Still another object of the invention is to provide a nov-el die or mold which can be used for the production of undercut hol low synthetic plastic articles in accordance with the improved method.
Another object of the invention is to provide an apparatus, especially an injection molding machine, which em-bodies the improved mold.
An ancillary object of the invention is to provide an improved core or plug which forms part of the above-outlined mold.
A further object of the invention is to provide a novel and improved housing for the core of the above-outlined mold.
Another object of the invention is to provide an undercut fitting or another undercut hol.low synthetic plastic article which is produced in accordance with the above-outlined method and by resorting to the improved mold.
According to one aspect of the invention, there is provided a method of making a tubular pipe fitting of the type having a longitudinally extending axis and a predetermined wall thickness throughout and wherein two circumferentially extending outer annular portions having first inner diameters flank a circumferentially extending intermediate annular portion having a larger second inner diameter and defining a circumferentially extending annular groove for reception of a sealing element, the difference between the radii of said outer annular portions and the radius of said intermediate annular portion being at least equal to said thickness, comprising the steps of introducing plasticized synthetic plastic material into a mold whose cavity has a configuration matching that of the fitting, the mold being shiftable between an open position to facilitate removal of the fitting and a closed position to form the cavity and facilitate formation of the fitting, the mold cavity being defined by a core having a first core part for cooperating in forming one of the outer annular portions and a second core part for cooperating in forming the other of the outer annular portions together with the intermediate annular portion, the core parts being axially shiftable relative to one another between a first position in which the core parts cooperate in forming the mold cavity and second position in which the second core part is adapted to be stripped from the intermediate annular portion of the fitting, the mold cavity also being defined by a first outer mold part radially shiftable between a first position in which it cooperates in forming part of the cavity for one of the outer annular portions and part of the intermediate annular portion and second radial position away from the fitting to permit stripping of the core, the mold cavity also being defined by a second outer mold part shiftable axially between a first axial position in which it cooperates in forming part of the cavity for the other of the outer annular portions and the remainder of the intermediate annular portion and a second axial position away from the fitting to permit stripping of the core, the mold cavity around the core including a larger portion with an outer diameter corresponding to said second inner diameter and two smaller portions flanking said larger portion and having outer diameters corresponding to said first diameters whereby the introduced material is converted into said fitting;
exposing the exterior of the fitting by shifting the first and second outer mold parts to their respective second positions, at least in the region of said intermediate portion and one of said outer portions; maintaining the exposed outer portion of the fitting in a state in which it can undergo elastic deform-ation; and moving the fitting and the second core part relative to each other in a direction to force the larger portion of the core through said exposed outer portion of the fitting whereby such outer portion expands during the passage of said larger portion therethrough and thereupon contracts so that its inner diameter is again less than the inner diameter of said ~ _ intermediate portion.
The method preferably further comprises a first additional step of causing the material of the entire article to set or harden subsequent to the aforementioned moving step, and a second additional step of completely withdrawing the core from the article upon completion of the setting or hardening step.
The one outer portion of the article can be supported from within in the course of the first additional step to prevent excessive reduction of its inner diameter due to shrinkage; this can be achieved by maintaining a portion of the core in the interior of the one outer portion subsequent to forcible movement of the larger portion of the core through the one outer portion of the article.
If the material of the article is a synthetic thermo-plastic substance, the temperature of the one outer portion of the article preferably exceeds the temperature of the other outer portion of the article in the course of the moving step.
A layer of gaseous fluid (e.g., compressed air) can be establish-ed and maintained between the exterior of the core and theinterior of the article in the course of the moving step; this facilitates the movement of art~cle relative to the core and/or vice versa. Such layer can be established by providing the periphery of the core with ports which discharge compressed air in the course of relative movement between the core and the article. The temperature of compressed air can be selected and regulated with a view to insure that the one outer portion of the article remains elastically deformable during forcible passage of the larger core portion therethrough. Since the intermediate portion of the article is likely to undergo at least some expansion during passage of the larger core portion through the one outer portion, the intermediate portion is ~ _ 7 _ ~074519 preferably treated in the same way as the one outer portion, i.e., it is elastically deformable so that it can contract upon withdrawal of the larger portion from its internal groove or recess.
According to another aspect of the invention, in an apparatus for the production of tubular articles of the type wherein two outer annular portions having first inner diameter flank an undercut intermediate annular portion having a larger second inner diameter, particularly in an injection molding machine for thermoplastic synthetic plastic materials, there is provided a combination comprising a mold having an open-and-shut housing and a core including components movable relative to each other, said core being spacedly surrounded by and defining with said housing an annular cavity having a configuration matching the configuration of said articles, said core including a larger portion with an outer diameter corresponding to said second inner diameter and two smaller portions flanking said larger portion and having outer diameters corresponding to said first inner diameters; means for introducing into said cavity a charge of plasticized synthetic plastic material which fills said cavity and is thus converted into an article of said type;
means for maintaining at least one outer portion of the article on said core in a state in which said one outer portion can undergo elastic deformation in open position of said housing;
and means for moving said core and the article thereon relative to each other in a direction to force said larger portion through said one outer portion whereby said one outer portion expands and thereupon contracts so that its inner diameter is again less than said second inner diameter.
The novel features which are considered as character-istic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both ~ - 7a -1074$19 as to its construction and its mode of operation, together with adclitional features and advantages thereof, will be best under-stood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.
FIG. 1 is a schematic elevational view of an injection molding machine having a mold which embodies one form of the invention, two plate-like sections of the housing of the mold being shown in open positions;
FIG. 2 is an enlarged transverse vertical sectional view, substantially as seen in the direction of arrows from the line II-II of FIG. l;
- 7b -~10745~9 FIG. 3 is a fragmentary central sectional view of the mold in the machine of FIG. 1, with the mold in closed position;
FIG. 4 illustrates the structure of FIG. 3, but with the plate-like sections of the housing of the mold in-partly open posi-tion and with a sleeve of the housing in partly retracted position;
FIG. 5 illustrates the structure o~ FIG. 4, but with the sleeve of the housing of the mold in ~ully retracted position; and FIG. 6 is a fragmentary central sectional view of a modi-~ied mold.
Referring first to FIGS. 1 and 2, the injection molding machine 23 comprises a base 27 supporting a mold opening, closing and locking unit 25, a plasticizing cylinder 26 with a hopper 26a and injection nozzle 26b, horizontal tie rods 30 for the platen 28 of an interchangeable mold section 101, another interchangeable mold section 1 which is movable between the positions shown in FIGS. 3 and 4 and is mounted on a platen 29, and a hydraulically operated actuating unit 124 for a reciprocable third section or sleeve 8 of the mold. The mold section 101 carries centering pins 32 which en-ter complementary sockets 33 of the mold section 1 when the mold is closed. The sections 1, 101 and 8 can be said to constitute a hous-ing or shell of the mold, and the latter ~urther comprises a compos-ite first core including a cylindrical main component 3 and a sleeve-like tubular component 7 (FIGS. 3 to 5) which is slidable, within limits, relative to the main component 3. ~ second core 8a is mov-able by a second hydraulically operated actuating unit 24.
In order to close the mold, the unit 25 moves the section 1 from the position shown in ~IG. 4 to that shown in FIG. 3 (while the unit 124 maintains the sleeve 8 in the end position shown in FIG. 3), and the unit 25 also moves the section 1 toward the section 101 so that the centering pins 32 enter the sockets 33 of the sec-., . ~ , . . .
:~74515~
tion L. The unit 25 comprises means for Locking the sections 1, 101 against movement away from each other. The machlne 23 is then ready for injection of plasticized synthetic plastic material into a mo]Ld cavity 31 which is defined by the parts L, 101, 8~ 3, 7 and 8a and whose configuration matches that of an article which is to be produced. The article is assumPd to be a fitting or connector having a first part including an undercut (larger-diameter) inter-mediate portion S, a first outer portion 6 which is located at one side of the intermediate portion 5 and whose inner diameter is less than the inner diameter of the portion 5, and a second outer portion 4 which is located at the other side of the intermediate portion 5 and whose inner diameter is also less than the inner diameter of the portion 5 (the inner diameter of the outer portion 4 may e~ual that of the outer portion 6). When the mold is closed (FIG. 3), the nozzle 26b of the cylinder 26 injects plasticized material into the cavity 31 whereby such material fills the cavity and is converted into a hollow article including the portions 4, 5 and 6. The illus-trated article includes a second part which is integral with the portion 4, remote from the outer portion 6 and makes an acute, right or obtuse angle with the common axis 2 of the portions 4, 5, 6 and first core 3, 7. The second part of the artLcle surrounds the core 8a. If the second part of the article is tn be provided with an undercut, the second core 8a is replaced with a core which is an-alogous to or identical wi~h the first core. The actuating unit 24 then moves the components of tha second core in the same or sim-ilar way as will be describPd in connection with the actuating unit 124 and the first core.
The manner in which an article including the portions 4, 5 and 6 is formed in the mold cavity 31, and the manner in which the article is thereupon treated and separated from the first core 10~45i9 including the components 3 and 7, is shown in FIGS. 3, 4 and 5. As stated above, FIG. 3 shows the mold in closed position in which the left-hand end portion 18 of the tubular component 7 of the composite first core abuts against an external shoulder 9 of the cylindrical main component 3. A collar 7a at the right-hand end of the tubular component 7 is engaged by an internal shoulder 10 of the sleeve 8 with a force which suffices to insure that the end portion 18 remains in abutment with the shoulder 9. The outer diameter of the end portion 18 equals the outer diameter of an enlarged portion 3a of the main component, and the portions 3a, 18 determine the inner diameter of the outer portion 4 of the article which is formed in the mold cavity 31. The inner diameter of the undercut intermediate portion 5 of the article is determined by the outer diameter of a ring-shaped larger portion or projection 13 of the tubular component 7, and the inner diameter of the outer portion 6 is determined by an intermediate portion 7b of the component 7. It will be noted that the radius of the projection 13 exceeds the radius of the portion 7b or 18 to an extent which is greater than the wall thickness of the article in the mold cavity 31; in fact, the difference between the radius of projection 13 and the radii of portions 7b, 18 may be several times the wall thickness of an article.
The mold section 101 has been omitted in FIGS, 3 to 5 for the sake of clarity. The mold section 1 has a substantially semi-circular wedge-like locking member 12 which extends into a circum-ferential groove 11 of the sleeve 8 to maintain the sleeve in the position of FIG. 3. The locking member 12 is optional; it can be omitted if the motion transmitting member 15 of the actuating unit 124 is capable of holding the sleeve 8 in the end position of FIG.
107~S19 cially designed injection moLding machines wherein the injection molding cycle precedes a blowing cycle serving for the formation of an undercut in one or more flanges of the fitting. It is also known to produce fittings in conventional injection molding machines which furnish fittings with flanges having internal surfaces of constant diameter, and to thereupon introduce such fittings into a blow mold-ing machine which expands a selected portion of a flange so as to provide the internal surface of the flange with a groove for recep-tion of sealing means. Such procedures are not satisfactory because the wall thickness of a blow molded undercut portion invariably de-viates from the wall thickness of neighboring portions of the fin-ished article.
In accordance with still another presently known technique, that flange of a fitting which i8 to be provided with an undercut resembles an outwardly flaring hollow frustum of a cone, and the outermost portion of such flange is thereupon treated to reduce its dimensions, i.e., the inner diameter Gf the thus contracted portion is less than the inner diameter of the neighboring portion. The neighb~ring portion can receive a sealing element which is held against axial movement by the contracted portion of the flange. The just described procedure shares the ~rawbac~8 of previously outlin-ed techniques, i.e., the internal groove of the undercut portion must be formed in a separate operation which follows the making of the fitting. Moreover if a fitting, whose flange has been formed with an undercut in accordance with the last mentioned prior pro-cedure, is used in pipe lines for hot fluids, the connection between the flange and a flexible or rLg~d cnnduit rapidly develops a leak.
This is attributable to a peculiarity of thermoplastic synthetic plastic materials which is known as thermal restoration. Briefly stated, the molecules of thermoplastic material assume a predetermin-1 [)74S:19 ed orientation during introduction of pLasticized material into amold. Thus, the orientation of molecules in a flange which, at the time of introduction of plasticized material into the molding cav-ity, resembles a hollow conical frustum is different from the or-ientation of molecules in a cylindrical flange. When the flange is heated subsequent to formation of an undercut therein (by causing the free end of the flange to shrink), the molecules tend to assume the original orientation which is characteristic of a hollow frusto-con~ ~1 flange with theresult that the flange opens up and permits communication between the confined fluid and the surrounding atmo-sphere.
~ n object of the invention is to provide a novel and im-proved method of producing fittings or other hollow articles which consist of synthetic plastic material and include undercut tubular portions flanked by smaller-diameter tubular portions.
~ nother object of the invention is to provide a method wh~ch renders it possible to form undercut portions simultaneously wlth the making of hollow articLes, i.e., wherein the undercuts de-velop at the time the respective articles are formed in an injection molding or like machine.
A further object of the invention is to provide a method which can be used ~or mass-production of undercut hollow articles with a high degree of reproducibility, within short intervals of time, and by resorting to relativeLy simple apparatus.
An additional object of the invention is to provide a method of making synthetic plastic fittings or other holl~w articles which can be practiced by resorting to retrofitted apparatus.
Still another object of the invention is to provide a nov-el die or mold which can be used for the production of undercut hol low synthetic plastic articles in accordance with the improved method.
Another object of the invention is to provide an apparatus, especially an injection molding machine, which em-bodies the improved mold.
An ancillary object of the invention is to provide an improved core or plug which forms part of the above-outlined mold.
A further object of the invention is to provide a novel and improved housing for the core of the above-outlined mold.
Another object of the invention is to provide an undercut fitting or another undercut hol.low synthetic plastic article which is produced in accordance with the above-outlined method and by resorting to the improved mold.
According to one aspect of the invention, there is provided a method of making a tubular pipe fitting of the type having a longitudinally extending axis and a predetermined wall thickness throughout and wherein two circumferentially extending outer annular portions having first inner diameters flank a circumferentially extending intermediate annular portion having a larger second inner diameter and defining a circumferentially extending annular groove for reception of a sealing element, the difference between the radii of said outer annular portions and the radius of said intermediate annular portion being at least equal to said thickness, comprising the steps of introducing plasticized synthetic plastic material into a mold whose cavity has a configuration matching that of the fitting, the mold being shiftable between an open position to facilitate removal of the fitting and a closed position to form the cavity and facilitate formation of the fitting, the mold cavity being defined by a core having a first core part for cooperating in forming one of the outer annular portions and a second core part for cooperating in forming the other of the outer annular portions together with the intermediate annular portion, the core parts being axially shiftable relative to one another between a first position in which the core parts cooperate in forming the mold cavity and second position in which the second core part is adapted to be stripped from the intermediate annular portion of the fitting, the mold cavity also being defined by a first outer mold part radially shiftable between a first position in which it cooperates in forming part of the cavity for one of the outer annular portions and part of the intermediate annular portion and second radial position away from the fitting to permit stripping of the core, the mold cavity also being defined by a second outer mold part shiftable axially between a first axial position in which it cooperates in forming part of the cavity for the other of the outer annular portions and the remainder of the intermediate annular portion and a second axial position away from the fitting to permit stripping of the core, the mold cavity around the core including a larger portion with an outer diameter corresponding to said second inner diameter and two smaller portions flanking said larger portion and having outer diameters corresponding to said first diameters whereby the introduced material is converted into said fitting;
exposing the exterior of the fitting by shifting the first and second outer mold parts to their respective second positions, at least in the region of said intermediate portion and one of said outer portions; maintaining the exposed outer portion of the fitting in a state in which it can undergo elastic deform-ation; and moving the fitting and the second core part relative to each other in a direction to force the larger portion of the core through said exposed outer portion of the fitting whereby such outer portion expands during the passage of said larger portion therethrough and thereupon contracts so that its inner diameter is again less than the inner diameter of said ~ _ intermediate portion.
The method preferably further comprises a first additional step of causing the material of the entire article to set or harden subsequent to the aforementioned moving step, and a second additional step of completely withdrawing the core from the article upon completion of the setting or hardening step.
The one outer portion of the article can be supported from within in the course of the first additional step to prevent excessive reduction of its inner diameter due to shrinkage; this can be achieved by maintaining a portion of the core in the interior of the one outer portion subsequent to forcible movement of the larger portion of the core through the one outer portion of the article.
If the material of the article is a synthetic thermo-plastic substance, the temperature of the one outer portion of the article preferably exceeds the temperature of the other outer portion of the article in the course of the moving step.
A layer of gaseous fluid (e.g., compressed air) can be establish-ed and maintained between the exterior of the core and theinterior of the article in the course of the moving step; this facilitates the movement of art~cle relative to the core and/or vice versa. Such layer can be established by providing the periphery of the core with ports which discharge compressed air in the course of relative movement between the core and the article. The temperature of compressed air can be selected and regulated with a view to insure that the one outer portion of the article remains elastically deformable during forcible passage of the larger core portion therethrough. Since the intermediate portion of the article is likely to undergo at least some expansion during passage of the larger core portion through the one outer portion, the intermediate portion is ~ _ 7 _ ~074519 preferably treated in the same way as the one outer portion, i.e., it is elastically deformable so that it can contract upon withdrawal of the larger portion from its internal groove or recess.
According to another aspect of the invention, in an apparatus for the production of tubular articles of the type wherein two outer annular portions having first inner diameter flank an undercut intermediate annular portion having a larger second inner diameter, particularly in an injection molding machine for thermoplastic synthetic plastic materials, there is provided a combination comprising a mold having an open-and-shut housing and a core including components movable relative to each other, said core being spacedly surrounded by and defining with said housing an annular cavity having a configuration matching the configuration of said articles, said core including a larger portion with an outer diameter corresponding to said second inner diameter and two smaller portions flanking said larger portion and having outer diameters corresponding to said first inner diameters; means for introducing into said cavity a charge of plasticized synthetic plastic material which fills said cavity and is thus converted into an article of said type;
means for maintaining at least one outer portion of the article on said core in a state in which said one outer portion can undergo elastic deformation in open position of said housing;
and means for moving said core and the article thereon relative to each other in a direction to force said larger portion through said one outer portion whereby said one outer portion expands and thereupon contracts so that its inner diameter is again less than said second inner diameter.
The novel features which are considered as character-istic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both ~ - 7a -1074$19 as to its construction and its mode of operation, together with adclitional features and advantages thereof, will be best under-stood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.
FIG. 1 is a schematic elevational view of an injection molding machine having a mold which embodies one form of the invention, two plate-like sections of the housing of the mold being shown in open positions;
FIG. 2 is an enlarged transverse vertical sectional view, substantially as seen in the direction of arrows from the line II-II of FIG. l;
- 7b -~10745~9 FIG. 3 is a fragmentary central sectional view of the mold in the machine of FIG. 1, with the mold in closed position;
FIG. 4 illustrates the structure of FIG. 3, but with the plate-like sections of the housing of the mold in-partly open posi-tion and with a sleeve of the housing in partly retracted position;
FIG. 5 illustrates the structure o~ FIG. 4, but with the sleeve of the housing of the mold in ~ully retracted position; and FIG. 6 is a fragmentary central sectional view of a modi-~ied mold.
Referring first to FIGS. 1 and 2, the injection molding machine 23 comprises a base 27 supporting a mold opening, closing and locking unit 25, a plasticizing cylinder 26 with a hopper 26a and injection nozzle 26b, horizontal tie rods 30 for the platen 28 of an interchangeable mold section 101, another interchangeable mold section 1 which is movable between the positions shown in FIGS. 3 and 4 and is mounted on a platen 29, and a hydraulically operated actuating unit 124 for a reciprocable third section or sleeve 8 of the mold. The mold section 101 carries centering pins 32 which en-ter complementary sockets 33 of the mold section 1 when the mold is closed. The sections 1, 101 and 8 can be said to constitute a hous-ing or shell of the mold, and the latter ~urther comprises a compos-ite first core including a cylindrical main component 3 and a sleeve-like tubular component 7 (FIGS. 3 to 5) which is slidable, within limits, relative to the main component 3. ~ second core 8a is mov-able by a second hydraulically operated actuating unit 24.
In order to close the mold, the unit 25 moves the section 1 from the position shown in ~IG. 4 to that shown in FIG. 3 (while the unit 124 maintains the sleeve 8 in the end position shown in FIG. 3), and the unit 25 also moves the section 1 toward the section 101 so that the centering pins 32 enter the sockets 33 of the sec-., . ~ , . . .
:~74515~
tion L. The unit 25 comprises means for Locking the sections 1, 101 against movement away from each other. The machlne 23 is then ready for injection of plasticized synthetic plastic material into a mo]Ld cavity 31 which is defined by the parts L, 101, 8~ 3, 7 and 8a and whose configuration matches that of an article which is to be produced. The article is assumPd to be a fitting or connector having a first part including an undercut (larger-diameter) inter-mediate portion S, a first outer portion 6 which is located at one side of the intermediate portion 5 and whose inner diameter is less than the inner diameter of the portion 5, and a second outer portion 4 which is located at the other side of the intermediate portion 5 and whose inner diameter is also less than the inner diameter of the portion 5 (the inner diameter of the outer portion 4 may e~ual that of the outer portion 6). When the mold is closed (FIG. 3), the nozzle 26b of the cylinder 26 injects plasticized material into the cavity 31 whereby such material fills the cavity and is converted into a hollow article including the portions 4, 5 and 6. The illus-trated article includes a second part which is integral with the portion 4, remote from the outer portion 6 and makes an acute, right or obtuse angle with the common axis 2 of the portions 4, 5, 6 and first core 3, 7. The second part of the artLcle surrounds the core 8a. If the second part of the article is tn be provided with an undercut, the second core 8a is replaced with a core which is an-alogous to or identical wi~h the first core. The actuating unit 24 then moves the components of tha second core in the same or sim-ilar way as will be describPd in connection with the actuating unit 124 and the first core.
The manner in which an article including the portions 4, 5 and 6 is formed in the mold cavity 31, and the manner in which the article is thereupon treated and separated from the first core 10~45i9 including the components 3 and 7, is shown in FIGS. 3, 4 and 5. As stated above, FIG. 3 shows the mold in closed position in which the left-hand end portion 18 of the tubular component 7 of the composite first core abuts against an external shoulder 9 of the cylindrical main component 3. A collar 7a at the right-hand end of the tubular component 7 is engaged by an internal shoulder 10 of the sleeve 8 with a force which suffices to insure that the end portion 18 remains in abutment with the shoulder 9. The outer diameter of the end portion 18 equals the outer diameter of an enlarged portion 3a of the main component, and the portions 3a, 18 determine the inner diameter of the outer portion 4 of the article which is formed in the mold cavity 31. The inner diameter of the undercut intermediate portion 5 of the article is determined by the outer diameter of a ring-shaped larger portion or projection 13 of the tubular component 7, and the inner diameter of the outer portion 6 is determined by an intermediate portion 7b of the component 7. It will be noted that the radius of the projection 13 exceeds the radius of the portion 7b or 18 to an extent which is greater than the wall thickness of the article in the mold cavity 31; in fact, the difference between the radius of projection 13 and the radii of portions 7b, 18 may be several times the wall thickness of an article.
The mold section 101 has been omitted in FIGS, 3 to 5 for the sake of clarity. The mold section 1 has a substantially semi-circular wedge-like locking member 12 which extends into a circum-ferential groove 11 of the sleeve 8 to maintain the sleeve in the position of FIG. 3. The locking member 12 is optional; it can be omitted if the motion transmitting member 15 of the actuating unit 124 is capable of holding the sleeve 8 in the end position of FIG.
3 without any axial movement in a direction away from the enlarged portion 3a of the component 3. The right-hand end portion 19 of Lhe main component 3 constitutes a collar which serves to guide the sleeve ~ during axiaL movement with respect to the first core and mold sections 1, 101. The sleeve 8 includes a removable portion or insert 14 which is secured thereto by one or more radially ex-tending pins 14a and whose internal surface determines the outer diameters of the portions 5, 6 of an article in the mold cavity 31.
The outer diameter of the portion 4 is determined by the adjacent internal surfaces of the mold sections 1 and 101. The right-hand end face 16 of the insert 14 can be moved against an external shoul-der 17 of the tubular component 7 to mOve the latter in a direction away from the shoulder ~ (compare FIGS. 4 and 5). The main compon-ent 3 of the first core of the improved mold can be moved axially in a direction to the right, as viewed in FIGS. 3, 4 and 5, when its collar 19 is engaged by an internal shoulder 21 of the sleeve ~ and the sleeve contlnues to move in a direction to the right (up-wardly, as viewed in FIG. 1 or 2).
The insert 14 contains a heating device 22, preferably an electric resistance heater, which surrounds the portiDns 5 and 6 of the article in the mold cavity 31 and serves to insure that these portions (or at least the portion 6) will remain sufficiently elas-tic to allow for extraction of the projection 13 from the interior of the article, i.e., to allow the projection 13 to forcibly expand the outer portion 6 during movement of such projection from the po-sition of FIG. 4 to the position of FIG. 5.
The reference character 20 denotes a cylindrical median portion of the component 3 which is surrounded by the tubular com-ponent 7 and extends from the enlarged portion 3a to the collar 19.
The plane in which the mold sections 1 and 101 abut against each -other when the mold is closed preferably includes the axis 2.
The portions 4, 5 and 6 may constitute only a small part -.
1~)74519 of an article (e.g., a fitting) which is obtained in response to injection and subsequent hardening of plasticized synthetic plastic material in the mold cavity 3L. The major part of such article can be formed on the second core 8a in that portion of the cavity 31 which is located to the left of FIGS. 3 to 5. The exact configura-tion of such major part of the article is immaterial for the pur-poses of the present invention; all that counts is to design and operate the improved mold in such a way that the article can be pro-vided with an undercut portion 5 which is flanked by two outer por-tions having smaller inside or inner diameters than the inside orinner diameter of the undercut portion S and that the provision of such undercut intermediate portion takes place at the time the art-icle is formed, i.e., as a direct result of injection of plasticiz-ed material into the closed mold without resorting to a core having a radially movable projection which is retracted after the material of the article sets in order to allow for movement of the finished article axially of the first core and/or vice versa. As a rule, the undercut portion 5 will serve to receive an annular sealing ele-ment (not shown), such as a packing or a gasket, depending upon whether or not the part which is surrounded by the portions 4, 5 and 6 moves relative to the article.
If the external surface of the undercut intermediate por-tion 5 of the article is not cylindrical, e.g., if such surface slopes t~ward the axis 2 in a direction to the right, as viewed in FIG. 3, the insert 14 of the sleeve 8 surrounds that portion of such external surface which is located to the right of the maximum-diameter portion. This is desirable because the insert 14 should be movable between the positions shown in FIGS. 3 and 4.
The sleeve 8 can contain or carry one or more temperature measuring devices (not shown) which monitor the temperature o~ the - : . ,, :. ~ .
16)7 4519 insert 14 and regulate the heating action of the device 22 so that the t:emperature o~ the insert 14 and of portions 5 and 6 o~ the article in the mold cavity 31 invariably remains within an optimum range which is best suited to insure that at least the outer portion 6 (but preferably the portions 5 and 6) will remain sufficiently elastic to allow for temporary radial expansion during e~traction of the projection 13 as well as that such expansion is followed by contraction o~ the portion 5 and/or 6 so that the inner diameter of the portion 5 will again exceed the inner diameters of portions
The outer diameter of the portion 4 is determined by the adjacent internal surfaces of the mold sections 1 and 101. The right-hand end face 16 of the insert 14 can be moved against an external shoul-der 17 of the tubular component 7 to mOve the latter in a direction away from the shoulder ~ (compare FIGS. 4 and 5). The main compon-ent 3 of the first core of the improved mold can be moved axially in a direction to the right, as viewed in FIGS. 3, 4 and 5, when its collar 19 is engaged by an internal shoulder 21 of the sleeve ~ and the sleeve contlnues to move in a direction to the right (up-wardly, as viewed in FIG. 1 or 2).
The insert 14 contains a heating device 22, preferably an electric resistance heater, which surrounds the portiDns 5 and 6 of the article in the mold cavity 31 and serves to insure that these portions (or at least the portion 6) will remain sufficiently elas-tic to allow for extraction of the projection 13 from the interior of the article, i.e., to allow the projection 13 to forcibly expand the outer portion 6 during movement of such projection from the po-sition of FIG. 4 to the position of FIG. 5.
The reference character 20 denotes a cylindrical median portion of the component 3 which is surrounded by the tubular com-ponent 7 and extends from the enlarged portion 3a to the collar 19.
The plane in which the mold sections 1 and 101 abut against each -other when the mold is closed preferably includes the axis 2.
The portions 4, 5 and 6 may constitute only a small part -.
1~)74519 of an article (e.g., a fitting) which is obtained in response to injection and subsequent hardening of plasticized synthetic plastic material in the mold cavity 3L. The major part of such article can be formed on the second core 8a in that portion of the cavity 31 which is located to the left of FIGS. 3 to 5. The exact configura-tion of such major part of the article is immaterial for the pur-poses of the present invention; all that counts is to design and operate the improved mold in such a way that the article can be pro-vided with an undercut portion 5 which is flanked by two outer por-tions having smaller inside or inner diameters than the inside orinner diameter of the undercut portion S and that the provision of such undercut intermediate portion takes place at the time the art-icle is formed, i.e., as a direct result of injection of plasticiz-ed material into the closed mold without resorting to a core having a radially movable projection which is retracted after the material of the article sets in order to allow for movement of the finished article axially of the first core and/or vice versa. As a rule, the undercut portion 5 will serve to receive an annular sealing ele-ment (not shown), such as a packing or a gasket, depending upon whether or not the part which is surrounded by the portions 4, 5 and 6 moves relative to the article.
If the external surface of the undercut intermediate por-tion 5 of the article is not cylindrical, e.g., if such surface slopes t~ward the axis 2 in a direction to the right, as viewed in FIG. 3, the insert 14 of the sleeve 8 surrounds that portion of such external surface which is located to the right of the maximum-diameter portion. This is desirable because the insert 14 should be movable between the positions shown in FIGS. 3 and 4.
The sleeve 8 can contain or carry one or more temperature measuring devices (not shown) which monitor the temperature o~ the - : . ,, :. ~ .
16)7 4519 insert 14 and regulate the heating action of the device 22 so that the t:emperature o~ the insert 14 and of portions 5 and 6 o~ the article in the mold cavity 31 invariably remains within an optimum range which is best suited to insure that at least the outer portion 6 (but preferably the portions 5 and 6) will remain sufficiently elastic to allow for temporary radial expansion during e~traction of the projection 13 as well as that such expansion is followed by contraction o~ the portion 5 and/or 6 so that the inner diameter of the portion 5 will again exceed the inner diameters of portions
4 and 6. If desired, the heating device 22 can be replaced with a heating device 122 (shown in FIG. 5 by broken lines) which is in-stalled in the projection 13. Alternatively, the improved mold may comprise two heating devices, one in the insert 14 (which latter can be said to form part of the sleeve 8) and one in the projaction 13.
The aforementioned temperature measuring or monitoring means can be used to regulate the heating action of the davice 22, of the device 122 or of the devices 22, 122 in a fully automatic way, or it may include a pointer whose position is read by an at-tendant so that the attendant can manually adjust the heating ac-tion when the monitored temperature deviates from an optimum tem-perature or temperature range. Monitoring devices which can be used in or in combination with the mold of the present invention are known in the art.
The operation:
When the mold is to be closed, the un:it 25 moves the mold section 1 and the actuating units 24, 124 toward the platen 28, r and the nozzle 26b injects plasticized synthetic plastic material (e.g., a thermoplastic substance) into the cavity 31. When the ma-terial in the cavity 31 becomes self-supporting, the mDld section 1~74S~t 1 is moved away rom the mold section 101 (the moLd section 1 th~n assumes the position shown in FI&S. 4 and 5) whereby the mold sec-tion 1 withdraws the locking member 12 from the groove 11 and thus enables the motion transmitting member 15 of the actuating unit 124 to move the sleeve 8 from the position of FIG. 3 to the position of FIG. 4. The rightward movement of the sleeve 8 is terminated when the end face 16 of the insert 14 moves into abutment with the external shoulder 17 of the tubular component 7. The external sur-faces of the portions 4, 5 and 6 of the article in the mold cavity 3L are then exposed because the insert 14 has been moved axially of the main component 3 and away from the shoulder 9 and the mold section 1 has been moved radially of and away from the axis 2 and also away from the mold section 101.
The cooling of the portion 4 of the article in the mold cavity 31 is more pronounced than that of the portions 5 and 6 (this is due to the provision of heating device 22, heating device 1~2 or heating devices 22 and 122). The arrangement may be such that the heating device or devices are connected with an energy source subsequent to injection of plasticized material or prior to or during such injection, i.e., the heating means can prevent ex-cessive cooling of injected material or the heating means reheats the material of the portions 5 and 6 subsequent to completion of the injecting step. All that counts is to insure that the material of the portions 5 and 6 remains in or is brought into a state in which the portions 5 and 6 can undergo elastic expansion to permit for extraction of the projection 13 from the article (in a direc-tion toward and through the outer portion 6). If the injected plasticlzed material is polyvinyl chloride, the heating element 22 can be set to maintain the insert 14 at a temperature of 70-130C.
in the course of the injecting step. Such heating of the insert _ 14 -L4 does not prevent any and all cooling of the portions 5 and 6 (and it also ~ails to pr~vent a reorientation of molecules of in-jected material in accordance with the nature of the mold cavity;
however, it has been found that the aforementioned temperature range is no~ally sufficient to insure that the material of the article does not harden to such an extent (or sets) that the portions 5 and 6 would be incapable of undergoing temporary elastic expansion dur-ing withdrawal o~ the projection 13.
In order to withdraw the projection 13 from the undercut intermediate portion 5 of the article~ the motion transmitting mem-ber 15 of the actuating unit 124 moves the sleeve beyond the posi-tion of FIG. 4 whereby the end face L6 of the insert 14 (which is rigid with the sleeve 8) entrains the tubular component 7 of the first core in a direction to the right so that the projection 13 expands the tapering part of the intermediate portion 5 as well as the outer portion 6. The elasticity of the portions 5 and 6 is suf-ficient to insure that these portions contract upon extraction of the projection 13 whereby the internal surface of the outer portion 6 preferably comes into abutment with the external surface of the end portion 18 of the tubular component 7 to prevent excessive con-traction of such outer portion. The tubular component 7 thereupon remains in the position of FIG. 5 untiL the material of the article sets sufficientLy to warrant complete separation of the article from the first core, e.g., by moving the internal shoulder 21 of the sleeve 8 into abutment with the coLlar 19 and by causin~ the actuating unit 124 to move the sleeve 8 beyond the position shown in FIG. 5. The actuating unit 24 withdraws the second core 8a prior to, simultaneously with or subsequent to separation of portions 4,
The aforementioned temperature measuring or monitoring means can be used to regulate the heating action of the davice 22, of the device 122 or of the devices 22, 122 in a fully automatic way, or it may include a pointer whose position is read by an at-tendant so that the attendant can manually adjust the heating ac-tion when the monitored temperature deviates from an optimum tem-perature or temperature range. Monitoring devices which can be used in or in combination with the mold of the present invention are known in the art.
The operation:
When the mold is to be closed, the un:it 25 moves the mold section 1 and the actuating units 24, 124 toward the platen 28, r and the nozzle 26b injects plasticized synthetic plastic material (e.g., a thermoplastic substance) into the cavity 31. When the ma-terial in the cavity 31 becomes self-supporting, the mDld section 1~74S~t 1 is moved away rom the mold section 101 (the moLd section 1 th~n assumes the position shown in FI&S. 4 and 5) whereby the mold sec-tion 1 withdraws the locking member 12 from the groove 11 and thus enables the motion transmitting member 15 of the actuating unit 124 to move the sleeve 8 from the position of FIG. 3 to the position of FIG. 4. The rightward movement of the sleeve 8 is terminated when the end face 16 of the insert 14 moves into abutment with the external shoulder 17 of the tubular component 7. The external sur-faces of the portions 4, 5 and 6 of the article in the mold cavity 3L are then exposed because the insert 14 has been moved axially of the main component 3 and away from the shoulder 9 and the mold section 1 has been moved radially of and away from the axis 2 and also away from the mold section 101.
The cooling of the portion 4 of the article in the mold cavity 31 is more pronounced than that of the portions 5 and 6 (this is due to the provision of heating device 22, heating device 1~2 or heating devices 22 and 122). The arrangement may be such that the heating device or devices are connected with an energy source subsequent to injection of plasticized material or prior to or during such injection, i.e., the heating means can prevent ex-cessive cooling of injected material or the heating means reheats the material of the portions 5 and 6 subsequent to completion of the injecting step. All that counts is to insure that the material of the portions 5 and 6 remains in or is brought into a state in which the portions 5 and 6 can undergo elastic expansion to permit for extraction of the projection 13 from the article (in a direc-tion toward and through the outer portion 6). If the injected plasticlzed material is polyvinyl chloride, the heating element 22 can be set to maintain the insert 14 at a temperature of 70-130C.
in the course of the injecting step. Such heating of the insert _ 14 -L4 does not prevent any and all cooling of the portions 5 and 6 (and it also ~ails to pr~vent a reorientation of molecules of in-jected material in accordance with the nature of the mold cavity;
however, it has been found that the aforementioned temperature range is no~ally sufficient to insure that the material of the article does not harden to such an extent (or sets) that the portions 5 and 6 would be incapable of undergoing temporary elastic expansion dur-ing withdrawal o~ the projection 13.
In order to withdraw the projection 13 from the undercut intermediate portion 5 of the article~ the motion transmitting mem-ber 15 of the actuating unit 124 moves the sleeve beyond the posi-tion of FIG. 4 whereby the end face L6 of the insert 14 (which is rigid with the sleeve 8) entrains the tubular component 7 of the first core in a direction to the right so that the projection 13 expands the tapering part of the intermediate portion 5 as well as the outer portion 6. The elasticity of the portions 5 and 6 is suf-ficient to insure that these portions contract upon extraction of the projection 13 whereby the internal surface of the outer portion 6 preferably comes into abutment with the external surface of the end portion 18 of the tubular component 7 to prevent excessive con-traction of such outer portion. The tubular component 7 thereupon remains in the position of FIG. 5 untiL the material of the article sets sufficientLy to warrant complete separation of the article from the first core, e.g., by moving the internal shoulder 21 of the sleeve 8 into abutment with the coLlar 19 and by causin~ the actuating unit 124 to move the sleeve 8 beyond the position shown in FIG. 5. The actuating unit 24 withdraws the second core 8a prior to, simultaneously with or subsequent to separation of portions 4,
5 and 6 from the first core. The machine 23 is then ready to start the next cycle which begins as soon as the mold cLoses. Such clos-i~4Sl9 ing includes a mOVement of components 3 and 7 of the first core back to ~he positions shown in FIG. 3 (whereby the internal shoul-der 10 of the sleeve 8 urges the end portion 18 of the tubular com-ponent 7 against the shoulder 9 of the main component 3) and subse-quent movement of the mold section 1 toward the moLd section 101 so that the locking member 12 can enter the groove 11 of the sleeve 8 and the unit 25 can cLamp the sections 1 and 10L to each other. Al-so, the actuating unit 24 returns the second core 8a to the position shown in FIG. 2.
In order to reduce the length of interval~ which are need-ed for the completion of a cycle, the injection molding machine 23 may COmpriSe means for promoting the setting of plastic material of an article, especiaLly subsequent to withdrawal of the projection 13. This can be achieved by providing the mold sections 1 and 101 with ports (see the ports lb in the mold section 1 of FIG. 4) which direct compressed air or another fluid coolant against the external surface of the article on the main component 3 of the first core.
It is further possible to facilitate the withdrawal of projection 13 from the interior of the article by establishing a layer Dr film of a preferably gaseous fluid between the core and the internal surfaces of the portions 4, 5 and 6 (or at least be-tween the first core and the portions 5 and 6). This can be achiev-ed by providing the portion 20 of the main component 3 and/or the end portion 18 and projaction 13 of the tubular component 7 o the first core with ports which dischaxge fluid against the internal surface of the article. One such port is shown in FIG. 5, as at 118.
My invention is based on the recognition that the major-ity of synthetic plastic materials which are presently used for the making of pipe fittings or the like (especially synthetic thermo-I . , plastic materials) exhibit a pronounced elasticity immediately upon completi~n of the injecting step in an injection molding or an an-alogous machine, that such elas~icity can be enhanced and/or main-tained by appropriate treatment (especially heating) to insure that the annular portions 5 and 6 of an article in the mold cavity 31 can expand during forcible extraction of the larger portion or pro-jection 13 of the tubular component 7, and tha~ such annular por-tions thereupon contract a~tomatically to reassume or to at least closely approach their desired shape (espe~ially the inner diameters as determined by the outer diameters of projection 13 and smaller portion 7b of the tubular component 7). All that is necessary is to maintain at least the outer portion 6 (but preferably also the undercut intermediate portion 5) within a temperature range which depends on the nature and/or composition of selected synthetic plas-tic material and w~ich, in the case of polyvinyl chloride, is norm-ally that temperature which is achieved by heating the insert L4 of the sleeve 8 to a temperature of 70-130C, preferably 80-90C. The conditioning of articles in the mold cavity 31 prior tn and during extraction of the projection 13 can be enhanced by localized cool-ing of articles in addition to aforementioned heating by the device22 and/or 122, e.g., by cooling with air streams which issue from the ports lb and/or 118. The feature that the undercut intermediate portion 5 of an article in the mold cavity is finished simultaneous-ly with the making of the article (i.e., without necessitating re-sort to a secondary treatment, such as removal of material by one or more to~Ls and/or a blowing operation) contr:Lbutes to a much high-er output of the machine and reduces the initial cost of the arti-cles. Moreover, the dimensions of each and every article of a long series of articles are invariably identical since the circumstances under which the undercut intermediate portions 5 of successive art-~ 0'74519 icles are formed remain unchanged during each cycle o~ the injection molding machine.
In accordance with presently knGwn molding techniques, molded articles are expelled from the cavity or separated from the core after the material of the articles has been allowed to set.
This is considered necessary in view of the generaLly accepted be-lief that a pronounced deformation of an article whose material is still hot will result in permanent deformation. Therefore, certain presentLy known injection molding machines for the production of hollow articles having undercut tubular portions employ a cylindri-cal core of constant diameter and a collapsible ring which surrounds the core and is received in the undercut portion of the article.
When the material of the article has been allowed to set, the core is withdrawn from the article and from the collapsible ring, and the ring is thereupon collapsed so that it can be readily withdrawn from the undercut portion. The mold of the just described conven-tional machine does not have an outer housing so that the wall thick-ness is li~ely to vary ~and normally varies) from article to article.
~lso, the removal of collapsible ring is a time-consuming operation which contributes to the cost of articles.
The method of the present invention takes advantage of the aforediscussed peculiarity (thermal restoration) of synthetic plastic materials, i.e., the portions (5 and 6) which are expanded radially outwardly in response to movement of the projection 13 from the position of FIG. 4 to the position of FIG. 5 exhibit a pronounced tendency to reassume the shape shown in FIGS. 3 and 4 with the result that the portions 5 and 6 contract as soon as the projection 13 has been withdrawn. As stated above, the temperature of portions 5 and 6 during extraction of the projection 13 from the article should be selected with a v;ew to avoid any interference . : , 16)74519 with such orientation of molecules which takes place when the plas-ticized material is injected into the mold cavity 31. This insures that the portions 5 and 6 contract as soon as the extraction of the projection 13 is completed. In other words, whereas the so-called thermal restoration is undesirable in accordance with certain pres-ently known techniques of making tubular articles with undercut por-tions, such characteristic of plastic material is used in accordance with the present method to insure the making of undercut tubular articles by resorting to relatively simpLe and inexpensive molds which need not employ collapsible rings or other complex devices for the making of undercuts.
Other presently preferred materials which can be utilized for the making of undercut holLow articles in the improved machine include high- and low-density polyethylene, polypropylene, poly-styrene and acrylonitrile-butadiene~styrene copolymers. The pres-ently preferred temperature range during temporary expansion of articles which consist of the above-enumerated materials is between 70 and 130C.
FIG. 6 shows a portion of a mold wherein all such parts which are identical with or clearly analogous to corrPsponding parts of the mold of FIGS. 3 to 5 are denoted by similar reference char-acters. The main difference between the two molds i9 that the mold of FIG. 6 does not have a heating means in or on the insert 14 of the sleeve 8. The moLd Qf FIG. 6 is shown in closed position corre-sponding to that of F~G. 3. The nature of material which forms the article in the mold cavity is assumed to be such that the elasticity of portions 5 and 6 suffices (without resorting to a heating device in or on the insert 14) to insure that the projection 13 can be withdrawn from the article and that these portions contract as soon as the projection 13 reaches a position corresponding to t~a~ shown - lg -107~Sl9 in FIG. 5.
The improved mold is susceptible of many additional mod-ifications. For example, the housing of the mold may consist of more than three sections and the tubular component 7 of the first core may also consist of two or more sections which are movable relative to each other in a given sequence so as to withdraw the projection 13 from the undercut intermediate portion 5 before the material of the article sets but subsequent to exposure of the under-cut portion 5 and outer portion 6. Furthermore, the configuration of the outer surfaces of all three annular portions 4, 5 and 6 of an article in the mold cavity 31 can be determined by the mold sec-tions 1 and 101 alone. In such molds, the motion transmitting means of the actuating unit 124 (or an analogous actuating unit) can be coupled directly to the tubular component 7 of the first core.
It will be readily appreciated that fittings (e.g., el-bows) and/or the like constitute but a few examples of articles which can be produced in accordance with the method and by resort-ing to the apparatus of the present invention. The improved method can be resorted to for the production of a large variety of arti-cles, especially articLes wherein the inner diameter of the under-cut portion greatly exceeds the inner diameters of the adjoining outer portions, including articles of circular, oval or polygonal cross-sectional outline as well as articles which are closed at ~ne end, e.g., plastic containers which are provided with undercut por-tions constituting aerating channels or the like. If the undercut portion of a container is immediately adjacent to one end wall (e.g., the bottom wall), such end wall constitutes an equivalent of the portion 4 of the article shown in FIG. 3, and the inner diameter of such end wall is zero.
It is further clear that the method and apparatus can be ~ - 20 -; -1~74519 used for the production of fittings or other types of hollow arti-cles each of which has two or mOre undercut portions.
- 20a -
In order to reduce the length of interval~ which are need-ed for the completion of a cycle, the injection molding machine 23 may COmpriSe means for promoting the setting of plastic material of an article, especiaLly subsequent to withdrawal of the projection 13. This can be achieved by providing the mold sections 1 and 101 with ports (see the ports lb in the mold section 1 of FIG. 4) which direct compressed air or another fluid coolant against the external surface of the article on the main component 3 of the first core.
It is further possible to facilitate the withdrawal of projection 13 from the interior of the article by establishing a layer Dr film of a preferably gaseous fluid between the core and the internal surfaces of the portions 4, 5 and 6 (or at least be-tween the first core and the portions 5 and 6). This can be achiev-ed by providing the portion 20 of the main component 3 and/or the end portion 18 and projaction 13 of the tubular component 7 o the first core with ports which dischaxge fluid against the internal surface of the article. One such port is shown in FIG. 5, as at 118.
My invention is based on the recognition that the major-ity of synthetic plastic materials which are presently used for the making of pipe fittings or the like (especially synthetic thermo-I . , plastic materials) exhibit a pronounced elasticity immediately upon completi~n of the injecting step in an injection molding or an an-alogous machine, that such elas~icity can be enhanced and/or main-tained by appropriate treatment (especially heating) to insure that the annular portions 5 and 6 of an article in the mold cavity 31 can expand during forcible extraction of the larger portion or pro-jection 13 of the tubular component 7, and tha~ such annular por-tions thereupon contract a~tomatically to reassume or to at least closely approach their desired shape (espe~ially the inner diameters as determined by the outer diameters of projection 13 and smaller portion 7b of the tubular component 7). All that is necessary is to maintain at least the outer portion 6 (but preferably also the undercut intermediate portion 5) within a temperature range which depends on the nature and/or composition of selected synthetic plas-tic material and w~ich, in the case of polyvinyl chloride, is norm-ally that temperature which is achieved by heating the insert L4 of the sleeve 8 to a temperature of 70-130C, preferably 80-90C. The conditioning of articles in the mold cavity 31 prior tn and during extraction of the projection 13 can be enhanced by localized cool-ing of articles in addition to aforementioned heating by the device22 and/or 122, e.g., by cooling with air streams which issue from the ports lb and/or 118. The feature that the undercut intermediate portion 5 of an article in the mold cavity is finished simultaneous-ly with the making of the article (i.e., without necessitating re-sort to a secondary treatment, such as removal of material by one or more to~Ls and/or a blowing operation) contr:Lbutes to a much high-er output of the machine and reduces the initial cost of the arti-cles. Moreover, the dimensions of each and every article of a long series of articles are invariably identical since the circumstances under which the undercut intermediate portions 5 of successive art-~ 0'74519 icles are formed remain unchanged during each cycle o~ the injection molding machine.
In accordance with presently knGwn molding techniques, molded articles are expelled from the cavity or separated from the core after the material of the articles has been allowed to set.
This is considered necessary in view of the generaLly accepted be-lief that a pronounced deformation of an article whose material is still hot will result in permanent deformation. Therefore, certain presentLy known injection molding machines for the production of hollow articles having undercut tubular portions employ a cylindri-cal core of constant diameter and a collapsible ring which surrounds the core and is received in the undercut portion of the article.
When the material of the article has been allowed to set, the core is withdrawn from the article and from the collapsible ring, and the ring is thereupon collapsed so that it can be readily withdrawn from the undercut portion. The mold of the just described conven-tional machine does not have an outer housing so that the wall thick-ness is li~ely to vary ~and normally varies) from article to article.
~lso, the removal of collapsible ring is a time-consuming operation which contributes to the cost of articles.
The method of the present invention takes advantage of the aforediscussed peculiarity (thermal restoration) of synthetic plastic materials, i.e., the portions (5 and 6) which are expanded radially outwardly in response to movement of the projection 13 from the position of FIG. 4 to the position of FIG. 5 exhibit a pronounced tendency to reassume the shape shown in FIGS. 3 and 4 with the result that the portions 5 and 6 contract as soon as the projection 13 has been withdrawn. As stated above, the temperature of portions 5 and 6 during extraction of the projection 13 from the article should be selected with a v;ew to avoid any interference . : , 16)74519 with such orientation of molecules which takes place when the plas-ticized material is injected into the mold cavity 31. This insures that the portions 5 and 6 contract as soon as the extraction of the projection 13 is completed. In other words, whereas the so-called thermal restoration is undesirable in accordance with certain pres-ently known techniques of making tubular articles with undercut por-tions, such characteristic of plastic material is used in accordance with the present method to insure the making of undercut tubular articles by resorting to relatively simpLe and inexpensive molds which need not employ collapsible rings or other complex devices for the making of undercuts.
Other presently preferred materials which can be utilized for the making of undercut holLow articles in the improved machine include high- and low-density polyethylene, polypropylene, poly-styrene and acrylonitrile-butadiene~styrene copolymers. The pres-ently preferred temperature range during temporary expansion of articles which consist of the above-enumerated materials is between 70 and 130C.
FIG. 6 shows a portion of a mold wherein all such parts which are identical with or clearly analogous to corrPsponding parts of the mold of FIGS. 3 to 5 are denoted by similar reference char-acters. The main difference between the two molds i9 that the mold of FIG. 6 does not have a heating means in or on the insert 14 of the sleeve 8. The moLd Qf FIG. 6 is shown in closed position corre-sponding to that of F~G. 3. The nature of material which forms the article in the mold cavity is assumed to be such that the elasticity of portions 5 and 6 suffices (without resorting to a heating device in or on the insert 14) to insure that the projection 13 can be withdrawn from the article and that these portions contract as soon as the projection 13 reaches a position corresponding to t~a~ shown - lg -107~Sl9 in FIG. 5.
The improved mold is susceptible of many additional mod-ifications. For example, the housing of the mold may consist of more than three sections and the tubular component 7 of the first core may also consist of two or more sections which are movable relative to each other in a given sequence so as to withdraw the projection 13 from the undercut intermediate portion 5 before the material of the article sets but subsequent to exposure of the under-cut portion 5 and outer portion 6. Furthermore, the configuration of the outer surfaces of all three annular portions 4, 5 and 6 of an article in the mold cavity 31 can be determined by the mold sec-tions 1 and 101 alone. In such molds, the motion transmitting means of the actuating unit 124 (or an analogous actuating unit) can be coupled directly to the tubular component 7 of the first core.
It will be readily appreciated that fittings (e.g., el-bows) and/or the like constitute but a few examples of articles which can be produced in accordance with the method and by resort-ing to the apparatus of the present invention. The improved method can be resorted to for the production of a large variety of arti-cles, especially articLes wherein the inner diameter of the under-cut portion greatly exceeds the inner diameters of the adjoining outer portions, including articles of circular, oval or polygonal cross-sectional outline as well as articles which are closed at ~ne end, e.g., plastic containers which are provided with undercut por-tions constituting aerating channels or the like. If the undercut portion of a container is immediately adjacent to one end wall (e.g., the bottom wall), such end wall constitutes an equivalent of the portion 4 of the article shown in FIG. 3, and the inner diameter of such end wall is zero.
It is further clear that the method and apparatus can be ~ - 20 -; -1~74519 used for the production of fittings or other types of hollow arti-cles each of which has two or mOre undercut portions.
- 20a -
Claims (23)
1. A method of making a tubular pipe fitting of the type having a longitudinally extending axis and a predetermined wall thickness throughout and wherein two circumferentially extending outer annular portions having first inner diameters flank a circumferentially extending intermediate annular portion having a larger second inner diameter and defining a circumferentially extending annular groove for reception of a sealing element, the difference between the radii of said outer annular portions and the radius of said intermediate annular portion being at least equal to said thickness, comprising the steps of introducing plasticized synthetic plastic material into a mold whose cavity has a configuration matching that of the fitting, the mold being shiftable between an open position to facilitate removal of the fitting and a closed position to form the cavity and facilitate formation of the fitting, the mold cavity being defined by a core having a first core part for cooperating in forming one of the outer annular portions and a second core part for cooperating in forming the other of the outer annular portions together with the intermediate annular portion, the core parts being axially shiftable relative to one another between a first position in which the core parts cooperate in forming the mold cavity and second position in which the second core part is adapted to be stripped from the intermediate annular portion of the fitting, the mold cavity also being defined by a first outer mold part radially shiftable between a first position in which it cooperates in forming part of the cavity for one of the outer annular portions and part of the intermediate annular portion and second radial position away from the fitting to permit stripping of the core, the mold cavity also being defined by a second outer mold part shiftable axially between a first axial position in which it cooperates in forming part of the cavity for the other of the outer annular portions and the remainder of the intermediate annular portion and a second axial position away from the fitting to permit stripping of the core, the mold cavity around the core including a larger portion with an outer diameter corresponding to said second inner diameter and two smaller portions flanking said larger portion and having outer diameters corresponding to said first diameters whereby the introduced material is converted into said fitting;
exposing the exterior of the fitting by shifting the first and second outer mold parts to their respective second positions, at least in the region of said intermediate portion and one of said outer portions; maintaining the exposed outer portion of the fitting in a state in which it can undergo elastic deformation; and moving the fitting and the second core part relative to each other in a direction to force the larger portion of the core through said exposed outer portion of the fitting whereby such outer portion expands during the passage of said larger portion therethrough and thereupon contracts so that its inner diameter is again less than the inner diameter of said intermediate portion.
exposing the exterior of the fitting by shifting the first and second outer mold parts to their respective second positions, at least in the region of said intermediate portion and one of said outer portions; maintaining the exposed outer portion of the fitting in a state in which it can undergo elastic deformation; and moving the fitting and the second core part relative to each other in a direction to force the larger portion of the core through said exposed outer portion of the fitting whereby such outer portion expands during the passage of said larger portion therethrough and thereupon contracts so that its inner diameter is again less than the inner diameter of said intermediate portion.
2. A method as defined in claim 1, wherein said introducing step includes injecting said plastic material into the cavity.
3. A method as defined in claim 1, wherein said plasticized material is a thermoplastic substance and said maintaining step includes maintaining the temperature of said exposed outer portion within a predetermined range.
4. A method as defined in claim 1, further comprising the first additional step of causing the material of the entire fitting to set and the second additional step of thereupon completely withdrawing the core from the fitting.
5. A method as defined in claim 4, further comprising the step of internally supporting at least said latter outer portion of the fitting in the course of said first additional step.
6. A method as defined in claim 1, wherein said maintaining step includes maintaining said exposed outer portion of the fitting at a first temperature and maintaining the other outer portion of the fitting at a second temperature which is lower than said first temperature.
7. A method as defined in claim 1, further comprising the step of establishing a layer of gaseous fluid between said core and at least a portion of the surrounding fitting in the course of said moving step.
8. A method as defined in claim 7, wherein said gaseous fluid is compressed air.
9. In an apparatus for the production of tubular articles of the type wherein two outer annular portions having first inner diameter flank an undercut intermediate annular portion having a larger second inner diameter, particularly in an injection molding machine for thermoplastic synthetic plastic materials, a combination comprising a mold having an open-and-shut housing and a core including components movable relative to each other, said core being spacedly surrounded by and defining with said housing an annular cavity having a configuration matching the configuration of said articles, said core including a larger portion with an outer diameter corresponding to said second inner diameter and two smaller portions flanking said larger portion and having outer diameters corresponding to said first inner diameters; means for introducing into said cavity a charge of plasticized synthetic plastic material which fills said cavity and is thus converted into an article of said type; means for maintaining at least one outer portion of the article on said core in a state in which said one outer portion can undergo elastic deformation in open position of said housing; and means for moving said core and the article thereon relative to each other in a direction to force said larger portion through said one outer portion whereby said one outer portion expands and thereupon contracts so that its inner diameter is again less than said second inner diameter.
10. A combination as defined in claim 9, wherein said core comprises a first component including said larger portion and one of said smaller portions and a second component including at least a part of the other of said smaller portions, one of said components being movable axially of the other of said components and of the article which surrounds said core.
11. A combination as defined in claim 10, wherein said one component is said first component, said first component constituting a tube which is slidable on said second component and said larger portion constituting an external ring-shaped projection of said first component.
12. A combination as defined in claim 9, wherein said housing comprises a section which spacedly surrounds said larger portion of the core and the smaller portion of the core for said one outer portion of the article in the closed position of said housing, said section being movable axially of said core between first and second positions in which the intermediate portion and said one outer portion of the article on said core are respectively concealed and exposed.
13. A combination as defined in claim 12, wherein said section of said housing is a sleeve which is coaxial with said core.
14. A combination as defined in claim 13, further comprising actuating means for moving said sleeve between said first and second positions and beyond said second position, said means for moving said core and the article thereon relative to each other being movable with said sleeve and moving said larger portion through said one outer portion of the article on said core in response to movement of said sleeve beyond said second position.
15. A combination as defined in claim 9, wherein said core comprises a further portion which is received in said one outer portion of the article upon completion of movement of said larger portion of said core through said one outer portion of the article.
16. A combination as defined in claim 15, wherein said further portion forms part of one of said smaller portions.
17. A combination as defined in claim 15, wherein said core comprises a first component including said larger portion, the other of said smaller portions, and said further portion, and a second component which is surrounded by said first component and includes another part of said one smaller portion.
18. A combination as defined in claim 9, wherein said maintaining means comprises a heating device in said housing.
19. A combination as defined in claim 9, wherein said maintaining means comprises a heating device in said core.
20. A combination as defined in claim 9, wherein said core has at least one port for introduction of a layer of fluid between said core and the article thereon.
21. A combination as defined in claim 20, wherein said fluid is a compressed gas.
22. A combination as defined in claim 9, wherein said housing has means for discharging a fluid coolant against the exterior of the article on said core.
23. A combination as defined in claim 9, wherein said housing includes three sections including first and second sections movable toward and away from each other radially of said core and a third section movable in the axial direction of said core.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT587875A AT356369B (en) | 1975-07-29 | 1975-07-29 | INJECTION MOLD FOR MAKING FITTINGS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1074519A true CA1074519A (en) | 1980-04-01 |
Family
ID=3580532
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA258,002A Expired CA1074519A (en) | 1975-07-29 | 1976-07-28 | Method and apparatus for producing undercut tubular synthetic plastic articles |
Country Status (4)
| Country | Link |
|---|---|
| AT (1) | AT356369B (en) |
| CA (1) | CA1074519A (en) |
| YU (1) | YU186776A (en) |
| ZA (1) | ZA764530B (en) |
-
1975
- 1975-07-29 AT AT587875A patent/AT356369B/en not_active IP Right Cessation
-
1976
- 1976-07-28 ZA ZA764530A patent/ZA764530B/en unknown
- 1976-07-28 YU YU01867/76A patent/YU186776A/en unknown
- 1976-07-28 CA CA258,002A patent/CA1074519A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| ATA587875A (en) | 1977-07-15 |
| YU186776A (en) | 1983-12-31 |
| ZA764530B (en) | 1977-08-31 |
| AT356369B (en) | 1980-04-25 |
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| MKEX | Expiry |