US20160236388A1 - Injection molded elongated objects - Google Patents
Injection molded elongated objects Download PDFInfo
- Publication number
- US20160236388A1 US20160236388A1 US15/135,064 US201615135064A US2016236388A1 US 20160236388 A1 US20160236388 A1 US 20160236388A1 US 201615135064 A US201615135064 A US 201615135064A US 2016236388 A1 US2016236388 A1 US 2016236388A1
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- US
- United States
- Prior art keywords
- sidewall
- endwall
- mold
- plastic
- core
- 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.)
- Abandoned
Links
- 238000002347 injection Methods 0.000 title claims abstract description 14
- 239000007924 injection Substances 0.000 title claims abstract description 14
- 229920000139 polyethylene terephthalate Polymers 0.000 claims description 3
- 239000005020 polyethylene terephthalate Substances 0.000 claims description 3
- 239000002991 molded plastic Substances 0.000 claims description 2
- -1 polyethylene terephthalate Polymers 0.000 claims description 2
- 239000004033 plastic Substances 0.000 description 25
- 229920003023 plastic Polymers 0.000 description 25
- 238000000034 method Methods 0.000 description 18
- 239000012530 fluid Substances 0.000 description 12
- 238000000465 moulding Methods 0.000 description 12
- 238000001746 injection moulding Methods 0.000 description 8
- 239000011800 void material Substances 0.000 description 5
- 230000007704 transition Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000013011 mating Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 239000000806 elastomer Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
Images
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
- 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
- B29C45/36—Moulds having means for locating or centering cores
-
- 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
- B29C45/0025—Preventing defects on the moulded article, e.g. weld lines, shrinkage marks
-
- 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
- B29C45/27—Sprue channels ; Runner channels or runner nozzles
- B29C45/28—Closure devices therefor
-
- 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
- B29C45/76—Measuring, controlling or regulating
- B29C45/762—Measuring, controlling or regulating the sequence of operations of an injection cycle
-
- 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
- B29C45/36—Moulds having means for locating or centering cores
- B29C2045/363—Moulds having means for locating or centering cores using a movable core or core part
-
- 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
- B29C45/36—Moulds having means for locating or centering cores
- B29C2045/366—Moulds having means for locating or centering cores using retractable pins
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2101/00—Use of unspecified macromolecular compounds as moulding material
Definitions
- This invention relates generally to injection molding and more particularly to apparatus and methods for injection molding elongated objects having a high aspect ratio.
- injection molding is a well-known process in which plastic is melted, then forced into the cavity of a mold and then allowed to solidify, resulting in finished parts.
- the temperatures and pressures used in the molding process are significant.
- the fluid plastic may be injected a pressure of about 207 mPa (30,000 lbf/in 2 ) and a temperature between 260 to 316° C. (500 to 600° F.).
- FIGS. 1 and 2 illustrate an exemplary part 1 which has been injection molded and therefore has a structure which may be described as unitary or monolithic.
- the part 1 has a generally cylindrical sidewall 2 closed off at one end by an endwall 3 .
- the ratio of the overall length “L” of the part 1 to the thickness “t” of the sidewall 2 is quite high, for example the ratio may be on the order of 100 .
- a mold cavity for making such elongated parts typically includes a cylindrical cavity with a long cylindrical core disposed coaxially therein.
- plastic for example polyethylene terephthalate or “PET”
- PET polyethylene terephthalate
- Core shift results in a lower-quality part, increases the chance of total rejects (e.g. because of voids in the part), and can result in damaging contact between the core and the cavity.
- an injection molded part having a monolithic structure including a sidewall with a closed perimeter, an endwall closing off one end of the sidewall, and a boss extending axially inward from an interior surface of the endwall.
- FIG. 1 is a side view of a part made using the apparatus and method of the present invention
- FIG. 2 is an end view of the part of FIG. 1 ;
- FIG. 3 is a schematic, partially cross-sectioned diagram of a molding apparatus constructed according to an aspect of the present invention
- FIG. 4 is an enlarged view of a portion of FIG. 3 ;
- FIG. 5 is an enlarged cross-sectional view of a portion of a mold assembly shown in FIG. 3 , in a first position;
- FIG. 6 is an enlarged cross-sectional view of a portion of a mold assembly shown in FIG. 3 , in a second position;
- FIG. 7 is an enlarged, cross-sectional view of a portion of the part of FIG. 1 .
- FIGS. 3 and 4 illustrate an injection molding apparatus 10 constructed according to an aspect of the present invention which is useful for molding plastic parts in general, and especially elongated parts as shown in FIG. 1 .
- the basic components of the injection molding apparatus 10 include a plastic supply 12 , a molder/extruder 14 , a mold assembly 16 , and a controller 18 .
- the plastic supply 12 comprises apparatus of a known type such as a hopper, tank, etc. suitable for storing and dispensing plastic in the form of small solid pellets.
- the molder/extruder 14 is a known type of device operable to receive the plastic from the plastic supply 12 , melt it to an appropriate temperature so that it forms a viscous fluid, and inject the fluid into the mold assembly 16 at suitable temperatures and pressures.
- the fluid plastic may be injected at about 207 mPa (30,000 lbf/in 2 ) and between 260 to 316° C. (500 to 600° F.).
- the mold assembly 16 includes a cavity which receives the fluid plastic. After injection, the plastic cools and solidifies in the cavity, which is then opened to eject the finished part.
- One or more actuators 20 are coupled to the mold assembly 16 and are used to open and close various portions of the mold assembly 16 during the molding procedure.
- the specific type of actuator is not critical and may be electrical, pneumatic, or hydraulic, for example.
- the controller 18 comprises apparatus effective to control one or more aspects of the operation of the injection molding apparatus 10 . It may be implemented as a general-purpose electronic computer, as one or more application-specific electronic processors, or as one or more discrete mechanical or electrical components or modules.
- the controller 18 is depicted with single-line connections indicating control and/or sensing paths to the plastic supply 12 , molder/extruder 14 , and actuators 20 , 44 , 76 .
- the mold assembly 16 is modular in nature, being built up from several plates 22 A- 22 F.
- Each plate 22 A- 22 F has a pair of parallel, spaced-apart mating faces. The mating faces of adjacent plates 22 A- 22 F abut each other when the assembly is closed.
- Each plate 22 A- 22 F incorporates one or more functional components of the mold assembly 16 .
- the individual plates 22 A- 22 F can be coupled to each other or to static structure in any combination.
- single plates 22 A- 22 F or groups of plates 22 A- 22 F may be mounted to the actuators 20 , so as to be selectively moveable along a main axis “A”.
- groups of the plates 22 A- 22 F may be pushed together or pulled apart along the main axis A to effect opening and closing of the mold assembly 16 . It is noted that the principles of the present invention are equally applicable to other mold configurations which are not modular in nature.
- the mold assembly 16 has a front end 24 and an rear end 26 . Movement of a component towards the front end 24 may be described as “forward” motion and movement towards the rear end 26 may be described as “aft” motion. These directional terms are used herein solely for the purpose of convenience in description and do not imply that any particular orientation of the components described is required.
- the first two plates 22 A, 22 B carry a valve assembly 28 and a valve block 30 .
- the valve assembly 28 includes a valve nozzle 32 with a frustoconical nozzle end 34 and a cylindrical valve gate pin 36 .
- the valve block 30 includes a chamber 38 that receives the valve nozzle 32 .
- One end of the chamber 38 is closed off by a conical endwall 40 that matches the shape of the nozzle end 34 .
- the nozzle end 34 is spaced a short distance from the endwall 40 .
- An injection orifice 42 sized to receive the valve gate pin 36 extends through the center of the endwall 40 .
- the valve assembly 28 also includes an actuator 44 operable to selectively move the valve gate pin 36 so that it is in contact with the injection orifice 42 or retracted away from the orifice 42 . in the retracted position, a fluid flowpath is open between an interior channel 39 of the valve nozzle 32 and the injection orifice 42 . In operation the molder/extruder 14 described above supplies the pressurized fluid plastic to the interior channel 39 of the nozzle 32 .
- the next plate 22 C carries a mold block 46 which has an internal block cavity 48 .
- the block cavity 48 is shaped and sized to define a portion of the outer surface contours of the part 1 .
- the left end of the block cavity 48 mates with a domed end cavity 50 in the valve block 30 .
- Collectively the block cavity 48 and the end cavity 50 constitute a mold structure and cooperatively define a complete mold cavity. This end cavity 50 communicates with the injection orifice 42 .
- the next plate 22 D carries an ejector 52 which has a generally frustoconical shape with an end face 54 that mates against an aft face 56 of the mold block 46 .
- the end face 54 has a hole 58 formed therein which is slightly smaller in diameter than the block cavity 48 , and a conical bore 60 that communicates with the hole 58 .
- the next plate 22 E carries a core element 62 .
- the core element 62 includes a cylindrical main body 64 , a conical transition section 66 , and a cylindrical core 68 .
- the transition section 66 is sized and shaped to mate with the conical bore 60 of the ejector 52 when the mold assembly 16 is closed.
- the transition section 66 is also shaped and sized to close off the aft end of the block cavity 48 when the mold assembly 16 is closed.
- the core 68 is shaped and sized to define the interior surface contours of the part 1 . When the mold assembly 16 is closed, the core 68 is positioned coaxially within the block cavity 48 but not touching it, the space between the two components defining a mold envelope 70 that is filled with fluid plastic during molding process.
- the mold envelope 70 is bounded by an inner sidewall, an inner endwall disposed at one end of the inner sidewall, an outer sidewall spaced apart from the inner sidewall, and an outer endwall spaced apart from the inner endwall.
- the sidewalls each have a closed perimeter, and can take on any shape such as circular, elliptical, or polygonal.
- the outer sidewall is defined by the block cavity 48
- the inner sidewall and the inner endwall are defined by the core 68
- the outer endwall is defined by the end cavity 50 in the valve block 30 ; however different arrangements are possible.
- the end cavity 50 could be eliminated and the core 68 simply spaced away from the valve block 30 to define the outer and inner endwalls.
- a central bore 72 extends through the core element 62 , and a locking pin 74 is received in the central bore 72 , mounted so that it can move back and forth parallel to the main axis A.
- the aft end of the locking pin 74 is coupled to an actuator 76 carried in the last plate 22 F.
- the actuator 76 is operable to selectively extend or retract the locking pin 74 .
- FIG. 5 illustrates the spatial relationship of the valve block 30 , valve nozzle 32 , core 68 , and locking pin 74 in more detail.
- the flat end face 77 of the core 68 includes a generally frustoconical void 78 that receives the tip 80 of the locking pin 74 .
- the tip 80 of the locking pin 74 is chamfered and includes one or more shallow slots 82 formed around its periphery.
- FIG. 5 shows the locking pin 74 in its extended position. In this position, the tip 80 is registered in the injection orifice 42 of the valve block 30 , and functions to prevent any relative lateral movement of the core 68 inside the block cavity 48 .
- the shallow slots 82 communicate with the interior channel 39 and the block cavity 48 , and provide a flow path for fluid plastic.
- the mold assembly 16 is closed with the valve block 30 abutting the mold block 46 and defining the mold envelope 70 as shown in FIG. 5 .
- the locking pin 74 is extended into the injection orifice 42 of the valve block 30 , and the valve gate pin 36 is in an open position.
- plastic in a fluid state is forced past the valve gate pin 36 , through the slots 82 in the locking pin tip 80 , and begins to flow into the mold envelope 70 .
- the plastic enters the frustoconical void 78 in the core 68 , where it surrounds the locking pin 74 and begins to solidify. This has the effect of rigidly locking the relative lateral position of the locking pin 74 to the core 68 , and the combination of those two elements to the valve block 30 . This prevents lateral shifting of the core 68 relative to the block cavity 48 .
- the locking pin 74 is retracted as shown in FIG. 6 , creating a flow path into the frustoconical void 78 .
- the valve gate pin 36 is extended rearward, extruding a small volume of plastic into the opening left by the locking pin 74 . Once this volume of plastic solidifies, it closes off the endwall 3 of the part 1 . This entire process is rapid, for example it may take less than one second.
- the mold assembly 16 is opened, exposing the part 1 , and the part 1 is ejected from the block cavity 48 by moving the ejector 52 forward. The mold assembly 16 is then re-closed, ready to form another product.
- the steps of the injection process may be controlled by various means.
- a discrete electronic or mechanical timer (shown schematically at 84 in FIG. 3 ) may be started when the mold shot is initiated by the controller 18 .
- the timer 84 counts a predetermined time and then signals the locking pin 74 and valve gate pin 36 to begin their movement.
- a timer could be incorporated into the software or hardware of the controller 18 itself.
- the part 1 is unitary or monolithic molded plastic and has a closed perimeter sidewall 2 , which can take on any shape such as circular, elliptical, or polygonal.
- the sidewall 2 is generally cylindrical.
- the sidewall 2 is closed off at one end by an endwall 3 .
- the ratio of the overall length “L” of the part 1 to the thickness “t” of the sidewall 2 is quite high, for example the ratio may be on the order of 100 .
- a boss 90 extends axially from an interior surface 92 surface of the endwall 3 .
- the boss 90 is annular, with a closed perimeter wall 94 and one open end.
- the outer surface 96 of the perimeter wall 94 matches the shape of the frustoconical void 78 described above.
- the inner surface 98 of the perimeter wall matches the chamfered shape of the tip 80 of the locking pin 74 .
- the shape of the boss 90 is defined by fluid plastic flowing into the space between the void 78 and the locking pin 74 during the molding process, as described above. The presence of the boss facilitates the use of the molding method described above, which results in the sidewall 2 having a highly uniform thickness around its periphery.
- the method and apparatus described above provides a means for molding plastic parts. It is especially useful for producing elongated parts with good quality and good yields while protecting the molding equipment from damages. These principles may be applied to molding all kinds of plastic parts as well as the molding of other materials where support of a core within a mold is necessary or desirable, such as elastomers and low-melting-point metals.
Abstract
An injection molded part includes a monolithic structure including a sidewall with a closed perimeter, an endwall closing off one end of the sidewall, and a boss extending axially inward from an interior surface of the endwall.
Description
- This invention relates generally to injection molding and more particularly to apparatus and methods for injection molding elongated objects having a high aspect ratio.
- injection molding is a well-known process in which plastic is melted, then forced into the cavity of a mold and then allowed to solidify, resulting in finished parts. The temperatures and pressures used in the molding process are significant. For example, the fluid plastic may be injected a pressure of about 207 mPa (30,000 lbf/in2) and a temperature between 260 to 316° C. (500 to 600° F.).
- Some part geometries are challenging to produce through injection molding. For example,
FIGS. 1 and 2 illustrate anexemplary part 1 which has been injection molded and therefore has a structure which may be described as unitary or monolithic. Thepart 1 has a generallycylindrical sidewall 2 closed off at one end by anendwall 3. The ratio of the overall length “L” of thepart 1 to the thickness “t” of thesidewall 2 is quite high, for example the ratio may be on the order of 100. - A mold cavity for making such elongated parts typically includes a cylindrical cavity with a long cylindrical core disposed coaxially therein. When plastic (for example polyethylene terephthalate or “PET”) is injected, it tends to flow into the space between the two mold components asymmetrically. This causes unavoidable lateral shift of the core. Core shift results in a lower-quality part, increases the chance of total rejects (e.g. because of voids in the part), and can result in damaging contact between the core and the cavity.
- Accordingly, there is a need for reliably produced injection molded elongated parts.
- This need is addressed by the present invention, which according to one aspect provides a an injection molded part having a monolithic structure including a sidewall with a closed perimeter, an endwall closing off one end of the sidewall, and a boss extending axially inward from an interior surface of the endwall.
- The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
-
FIG. 1 is a side view of a part made using the apparatus and method of the present invention; -
FIG. 2 is an end view of the part ofFIG. 1 ; -
FIG. 3 is a schematic, partially cross-sectioned diagram of a molding apparatus constructed according to an aspect of the present invention; -
FIG. 4 is an enlarged view of a portion ofFIG. 3 ; -
FIG. 5 is an enlarged cross-sectional view of a portion of a mold assembly shown inFIG. 3 , in a first position; -
FIG. 6 is an enlarged cross-sectional view of a portion of a mold assembly shown inFIG. 3 , in a second position; and -
FIG. 7 is an enlarged, cross-sectional view of a portion of the part ofFIG. 1 . - Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
FIGS. 3 and 4 illustrate aninjection molding apparatus 10 constructed according to an aspect of the present invention which is useful for molding plastic parts in general, and especially elongated parts as shown inFIG. 1 . The basic components of theinjection molding apparatus 10 include aplastic supply 12, a molder/extruder 14, amold assembly 16, and acontroller 18. - The
plastic supply 12 comprises apparatus of a known type such as a hopper, tank, etc. suitable for storing and dispensing plastic in the form of small solid pellets. - The molder/
extruder 14 is a known type of device operable to receive the plastic from theplastic supply 12, melt it to an appropriate temperature so that it forms a viscous fluid, and inject the fluid into themold assembly 16 at suitable temperatures and pressures. For example, the fluid plastic may be injected at about 207 mPa (30,000 lbf/in2) and between 260 to 316° C. (500 to 600° F.). - The
mold assembly 16 includes a cavity which receives the fluid plastic. After injection, the plastic cools and solidifies in the cavity, which is then opened to eject the finished part. One ormore actuators 20 are coupled to themold assembly 16 and are used to open and close various portions of themold assembly 16 during the molding procedure. The specific type of actuator is not critical and may be electrical, pneumatic, or hydraulic, for example. - The
controller 18 comprises apparatus effective to control one or more aspects of the operation of theinjection molding apparatus 10. It may be implemented as a general-purpose electronic computer, as one or more application-specific electronic processors, or as one or more discrete mechanical or electrical components or modules. Thecontroller 18 is depicted with single-line connections indicating control and/or sensing paths to theplastic supply 12, molder/extruder 14, andactuators - Referring to
FIGS. 3, 4, and 5 , themold assembly 16 will now be described in more detail. In the illustrated example, themold assembly 16 is modular in nature, being built up fromseveral plates 22A-22F. Eachplate 22A-22F has a pair of parallel, spaced-apart mating faces. The mating faces ofadjacent plates 22A-22F abut each other when the assembly is closed. Eachplate 22A-22F incorporates one or more functional components of themold assembly 16. Theindividual plates 22A-22F can be coupled to each other or to static structure in any combination. Furthermore,single plates 22A-22F or groups ofplates 22A-22F may be mounted to theactuators 20, so as to be selectively moveable along a main axis “A”. Stated another way, groups of theplates 22A-22F may be pushed together or pulled apart along the main axis A to effect opening and closing of themold assembly 16. It is noted that the principles of the present invention are equally applicable to other mold configurations which are not modular in nature. - The
mold assembly 16 has afront end 24 and anrear end 26. Movement of a component towards thefront end 24 may be described as “forward” motion and movement towards therear end 26 may be described as “aft” motion. These directional terms are used herein solely for the purpose of convenience in description and do not imply that any particular orientation of the components described is required. - Considering
FIG. 3 from left to right along the main axis A, the first twoplates valve assembly 28 and avalve block 30. Thevalve assembly 28 includes avalve nozzle 32 with afrustoconical nozzle end 34 and a cylindricalvalve gate pin 36. Thevalve block 30 includes achamber 38 that receives thevalve nozzle 32. One end of thechamber 38 is closed off by aconical endwall 40 that matches the shape of thenozzle end 34. Thenozzle end 34 is spaced a short distance from theendwall 40. Aninjection orifice 42 sized to receive thevalve gate pin 36 extends through the center of theendwall 40. Thevalve assembly 28 also includes anactuator 44 operable to selectively move thevalve gate pin 36 so that it is in contact with theinjection orifice 42 or retracted away from theorifice 42. in the retracted position, a fluid flowpath is open between aninterior channel 39 of thevalve nozzle 32 and theinjection orifice 42. In operation the molder/extruder 14 described above supplies the pressurized fluid plastic to theinterior channel 39 of thenozzle 32. - The
next plate 22C carries amold block 46 which has aninternal block cavity 48. Theblock cavity 48 is shaped and sized to define a portion of the outer surface contours of thepart 1. In the specific example illustrated, the left end of theblock cavity 48 mates with adomed end cavity 50 in thevalve block 30. Collectively theblock cavity 48 and theend cavity 50 constitute a mold structure and cooperatively define a complete mold cavity. Thisend cavity 50 communicates with theinjection orifice 42. - The
next plate 22D carries anejector 52 which has a generally frustoconical shape with anend face 54 that mates against anaft face 56 of themold block 46. Theend face 54 has ahole 58 formed therein which is slightly smaller in diameter than theblock cavity 48, and aconical bore 60 that communicates with thehole 58. - The
next plate 22E carries a core element 62. The core element 62 includes a cylindricalmain body 64, aconical transition section 66, and acylindrical core 68. Thetransition section 66 is sized and shaped to mate with the conical bore 60 of theejector 52 when themold assembly 16 is closed. Thetransition section 66 is also shaped and sized to close off the aft end of theblock cavity 48 when themold assembly 16 is closed. Thecore 68 is shaped and sized to define the interior surface contours of thepart 1. When themold assembly 16 is closed, thecore 68 is positioned coaxially within theblock cavity 48 but not touching it, the space between the two components defining amold envelope 70 that is filled with fluid plastic during molding process. - Generally stated, the
mold envelope 70 is bounded by an inner sidewall, an inner endwall disposed at one end of the inner sidewall, an outer sidewall spaced apart from the inner sidewall, and an outer endwall spaced apart from the inner endwall. The sidewalls each have a closed perimeter, and can take on any shape such as circular, elliptical, or polygonal. In the specific example illustrated, the outer sidewall is defined by theblock cavity 48, the inner sidewall and the inner endwall are defined by thecore 68, and the outer endwall is defined by theend cavity 50 in thevalve block 30; however different arrangements are possible. For example, theend cavity 50 could be eliminated and the core 68 simply spaced away from thevalve block 30 to define the outer and inner endwalls. - A
central bore 72 extends through the core element 62, and alocking pin 74 is received in thecentral bore 72, mounted so that it can move back and forth parallel to the main axis A. The aft end of the lockingpin 74 is coupled to anactuator 76 carried in thelast plate 22F. Theactuator 76 is operable to selectively extend or retract the lockingpin 74. -
FIG. 5 illustrates the spatial relationship of thevalve block 30,valve nozzle 32,core 68, and lockingpin 74 in more detail. Theflat end face 77 of thecore 68 includes a generallyfrustoconical void 78 that receives thetip 80 of the lockingpin 74. Thetip 80 of the lockingpin 74 is chamfered and includes one or moreshallow slots 82 formed around its periphery.FIG. 5 shows the lockingpin 74 in its extended position. In this position, thetip 80 is registered in theinjection orifice 42 of thevalve block 30, and functions to prevent any relative lateral movement of thecore 68 inside theblock cavity 48. Theshallow slots 82 communicate with theinterior channel 39 and theblock cavity 48, and provide a flow path for fluid plastic. - The molding operation will now be described in sequence. Initially, the
mold assembly 16 is closed with thevalve block 30 abutting themold block 46 and defining themold envelope 70 as shown inFIG. 5 . The lockingpin 74 is extended into theinjection orifice 42 of thevalve block 30, and thevalve gate pin 36 is in an open position. - During the actual mold “shot”, plastic in a fluid state is forced past the
valve gate pin 36, through theslots 82 in thelocking pin tip 80, and begins to flow into themold envelope 70. At the very beginning of this process the plastic enters thefrustoconical void 78 in thecore 68, where it surrounds the lockingpin 74 and begins to solidify. This has the effect of rigidly locking the relative lateral position of the lockingpin 74 to thecore 68, and the combination of those two elements to thevalve block 30. This prevents lateral shifting of the core 68 relative to theblock cavity 48. - Subsequently, fluid plastic flows around the end of the
core 68 and into themold envelope 70. During this process the plastic may flow asymmetrically down the elongated sides, resulting in significant lateral pressure on thecore 68. However, the stabilization provided by the lockingpin 74 prevents deflection of thecore 68. Stated another way, the part wall thickness “t1” on one side of the core 68 remains substantially equal to the part wall thickness “t2” on the opposite side. - As the
mold envelope 70 nears complete filling, the lockingpin 74 is retracted as shown inFIG. 6 , creating a flow path into thefrustoconical void 78. Simultaneously, thevalve gate pin 36 is extended rearward, extruding a small volume of plastic into the opening left by the lockingpin 74. Once this volume of plastic solidifies, it closes off theendwall 3 of thepart 1. This entire process is rapid, for example it may take less than one second. Subsequently, themold assembly 16 is opened, exposing thepart 1, and thepart 1 is ejected from theblock cavity 48 by moving theejector 52 forward. Themold assembly 16 is then re-closed, ready to form another product. - The steps of the injection process may be controlled by various means. For example, a discrete electronic or mechanical timer (shown schematically at 84 in
FIG. 3 ) may be started when the mold shot is initiated by thecontroller 18. Thetimer 84 counts a predetermined time and then signals the lockingpin 74 andvalve gate pin 36 to begin their movement. Alternatively, a timer could be incorporated into the software or hardware of thecontroller 18 itself. - An example of a resulting
part 1 is shown inFIGS. 1, 2, and 7 . As noted above, thepart 1 is unitary or monolithic molded plastic and has a closedperimeter sidewall 2, which can take on any shape such as circular, elliptical, or polygonal. In the specific example illustrated, thesidewall 2 is generally cylindrical. Thesidewall 2 is closed off at one end by anendwall 3. The ratio of the overall length “L” of thepart 1 to the thickness “t” of thesidewall 2 is quite high, for example the ratio may be on the order of 100. Aboss 90 extends axially from aninterior surface 92 surface of theendwall 3. Theboss 90 is annular, with aclosed perimeter wall 94 and one open end. Theouter surface 96 of theperimeter wall 94 matches the shape of thefrustoconical void 78 described above. Theinner surface 98 of the perimeter wall matches the chamfered shape of thetip 80 of the lockingpin 74. The shape of theboss 90 is defined by fluid plastic flowing into the space between the void 78 and the lockingpin 74 during the molding process, as described above. The presence of the boss facilitates the use of the molding method described above, which results in thesidewall 2 having a highly uniform thickness around its periphery. - The method and apparatus described above provides a means for molding plastic parts. It is especially useful for producing elongated parts with good quality and good yields while protecting the molding equipment from damages. These principles may be applied to molding all kinds of plastic parts as well as the molding of other materials where support of a core within a mold is necessary or desirable, such as elastomers and low-melting-point metals.
- The foregoing has described a method and apparatus for injection molding. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
- Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
- The invention is not restricted to the details of the foregoing embodiment(s). The invention extends any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying potential points of novelty, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
Claims (7)
1. An injection molded part comprising: a monolithic structure including a sidewall with a closed perimeter, an endwall closing off one end of the sidewall, and a boss extending axially inward from an interior surface of the endwall.
2. The part of claim 1 wherein the boss has a perimeter wall with a frustoconical outer surface.
3. The part of claim 2 wherein the perimeter wall of the boss has a tapered inner surface.
4. The part of claim 1 wherein the monolithic structure comprises molded plastic.
5. The part of claim 1 wherein an overall length of the part is about 100 times greater than a thickness of the sidewall.
6. The part of claim 1 wherein the monolithic structure comprises polyethylene terephthalate.
7. The part of claim 1 wherein the sidewall is cylindrical.
Priority Applications (1)
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US15/135,064 US20160236388A1 (en) | 2014-10-16 | 2016-04-21 | Injection molded elongated objects |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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US14/516,038 US9162383B1 (en) | 2014-10-16 | 2014-10-16 | Method and apparatus for injection molding elongated objects |
US14/861,238 US9339960B2 (en) | 2014-10-16 | 2015-09-22 | Apparatus for injection molding elongated objects |
US15/135,064 US20160236388A1 (en) | 2014-10-16 | 2016-04-21 | Injection molded elongated objects |
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US14/861,238 Division US9339960B2 (en) | 2014-10-16 | 2015-09-22 | Apparatus for injection molding elongated objects |
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US20160236388A1 true US20160236388A1 (en) | 2016-08-18 |
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US14/516,038 Expired - Fee Related US9162383B1 (en) | 2014-10-16 | 2014-10-16 | Method and apparatus for injection molding elongated objects |
US14/861,238 Active US9339960B2 (en) | 2014-10-16 | 2015-09-22 | Apparatus for injection molding elongated objects |
US15/135,064 Abandoned US20160236388A1 (en) | 2014-10-16 | 2016-04-21 | Injection molded elongated objects |
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US14/516,038 Expired - Fee Related US9162383B1 (en) | 2014-10-16 | 2014-10-16 | Method and apparatus for injection molding elongated objects |
US14/861,238 Active US9339960B2 (en) | 2014-10-16 | 2015-09-22 | Apparatus for injection molding elongated objects |
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US7955071B1 (en) * | 2009-11-30 | 2011-06-07 | Dme Company Llc | Apparatus for injection molding |
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-
2015
- 2015-09-22 US US14/861,238 patent/US9339960B2/en active Active
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US9162383B1 (en) | 2015-10-20 |
US20160107355A1 (en) | 2016-04-21 |
US9339960B2 (en) | 2016-05-17 |
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