CA1323971C - Coolant introduction in blow molding - Google Patents
Coolant introduction in blow moldingInfo
- Publication number
- CA1323971C CA1323971C CA000587801A CA587801A CA1323971C CA 1323971 C CA1323971 C CA 1323971C CA 000587801 A CA000587801 A CA 000587801A CA 587801 A CA587801 A CA 587801A CA 1323971 C CA1323971 C CA 1323971C
- Authority
- CA
- Canada
- Prior art keywords
- article
- cooling
- cooling medium
- wall
- nozzle
- 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 - Fee Related
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
- B05B1/14—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with multiple outlet openings; with strainers in or outside the outlet opening
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B13/00—Machines or plants for applying liquids or other fluent materials to surfaces of objects or other work by spraying, not covered by groups B05B1/00 - B05B11/00
- B05B13/06—Machines or plants for applying liquids or other fluent materials to surfaces of objects or other work by spraying, not covered by groups B05B1/00 - B05B11/00 specially designed for treating the inside of hollow bodies
- B05B13/0627—Arrangements of nozzles or spray heads specially adapted for treating the inside of hollow bodies
-
- 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
- B29C49/00—Blow-moulding, i.e. blowing a preform or parison to a desired shape within a mould; Apparatus therefor
- B29C49/42—Component parts, details or accessories; Auxiliary operations
- B29C49/64—Heating or cooling preforms, parisons or blown articles
- B29C49/66—Cooling by refrigerant introduced into the blown article
Landscapes
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
Abstract of the Disclosure A more efficient cooling of a blow molded thermoplastic article can be achieved by directing sprays of cooling medium against those specific zones of the wall of the article which require a more rapid cooling while avoiding directing the sprays at areas requiring a less rapid cooling. This cooling procedure is achieved using a spray head having a plurality of individual spray nozzles which direct sprays specifically against the areas requiring more rapid cooling.
Description
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:1 TITLE OF INVENTION
COOL~NT IN R DUCTION IN BLOW MOLDING
FIRLD OF INVENTION
The present invention relates to the blow molding of thermoplastic articles to form a variety of blow molded products, and in particular to the cooling of such articles during their manufacture.
BACKGROUND TO THE INVENTION
In the conventional production of blown plastic forms or articles, an extruded tube (parison) of thermoplastic material which is at a temperature above its melting point, is enclosed in an appropriately-15 shaped mold and pressurized air is used to expand the parison against the wall of the mold to assume the contour of the mold.
Following completion of the blowing cycle, the temperature of the molded article is decreased by 20 cooling to a level below the melting point of the thermoplastic material at which the formed plastic article retains its shape. The length of time required to effect the cooling often takes up a large proportion of the total time required to complete the molding 25 cycle.
The heat is removed from the blown molded article by a variety of procedures, including through the cooled mold walls and through the use of blowing air as a heat transfer medium. To improve the effectiveness of the 30 heat removal portion of the cycle, refrigerants, usually liquid nitrogen, have been introduced into the plastic form, after it has been blown to the shape of the mold.
The conventional manner of introduction of the refrigerant into the formed article is by injection of a j~ 35 refrigerated gas or liquid refrigerant through the blow Z pin which is used to introduce the blowing air d ~ ng J
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the blowing step or through a small tuhe contained within the blow pin.
The cooling medium either is introduced admixed with air or is separately in~ected in an undirected manner into the blown article. In all blown articles, there are regions which are thicker than others and henee require more cooling time than the thinner portions. The thicker portions thereby become the limiting factor controlling cooling time.
It has been previously suggested in U.S. Patent No.
3,488,801 to achieve a more uniform cooling of the blow molded artiele by employing a needle having an angled end which enables cooling fluid to be direeted towards a eertain locus of the hot thermoplastic material. The needle may be moved during the cooling operation to direet the cooling fluid towards a plurality of different loci on the interior of the parison by rotating and/or lonyitudinally moving the needle. In this prior art operation, therefore, while differential eooling may be achieved by directing eoolant at specific loeations, it is possible to apply additional coolant to only one location at one time.
SUMMARY OF INVENTION
In accordance with the present invention, a novel method of injection of refrigerant into the mold for cooling a parison is provided which directs cooling medium towards the portions of the article which require a greater degree of cooling and away from those portions of the blown article where crystallinity and/or stiffness are more critical. The combination of these two effects results in an accelerated cooling of the thieker portions oP the article whieh are limiting the eyele time while retaining a high degree of erystallinity, density and/or stiffness in those regions of the product where the property is an advantage in the finished product.
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The present invention also provides a novel apparatus for introducing and directlng the flow of refrigerating medium to those loca~ions within the blown article where the effect of the refrigerant is most 5 beneficial and away from those locations where rapid cooling may be detrimental by employing a novel injection nozzle.
Accordingly, in one aspect, the present invention provides an improvement in a method of blow molding an 10 article of thermoplastic material by blowing the article in a mold of the desired shape with the article haviny a non-uniform wall thlckness and cooling the blown article by introducing a cooliny medium to the interior of the article to a temperature whereat the article is self-15 sustaining and can be removed from the mold.
The improv~ment of the present invention is wherein the cooling medium is introduced to the interior of the article in such a manner as to effect a directed cooling to thicker areas of the wall of the article and 20 a less rapid cooling to thinner areas of the wall of the article, so as to decrease the overall cooling time.
In another aspect, the present invention provides a novel nozzle for injection of refrigerant into a blow-molded article, comprising a body having a rounded head 25 and an internal bone exkending to the rounded head. A
V-shaped groove is formed in the outer surface of the rounded head and extends over the crown thereof. A
plurality of passageways connect the groove to the internal bone to permit refriyerant fluid in the bone to 30 pass out of the nozzle in a plurality of fan shaped ~ sprays having a pattern corresponding to the location Z and number o~ the plurality of passageways.
BRIEF DESCRIPTION OF DRAWINGS
Figures lA and lB are side and end views 35 respectively of a system commonly-employed for i' ' ~ ' : '. .: : ~' i ,. . ~ ' ' , `,. . ~ : :, :,' , ~ : - :
" 1323~71 introducing cooling medium to a blow-molded article during cooling;
Figures 2A and 2B are side and end views respectively of a system for the introdu~tion of cooling medium to a blow-molded article constructed in accordance with one embodiment of this invention; and Figure 3 is a close-up sectional view of one embodiment of nozzle used in the cooling medium of Figures 2A and 2B.
DESCRIPTION OF PREFERRED EMBO~IMENT
Referring to the drawings, Figure 1 illustrates a typical prior art procedure ~or introducing coolant to a blow molded article 10 through a central pipe 12 concentric with the blowing air pipe 14. The pattern 16 of the cooling medium is that of a broad cone, the dimensions of which are defined by well-known fluid-gas relationships.
Depending upon the design of the particular article, certain portions of the article represent a limitation to decreasing the cooling time. In Figures 1 and 2 respectively, these regions have been designated Al and A2. The broad cone 16 of cooling medium is largely directed to non-critical areas of the article 10, such as the sidewalls B1, and those portions of the article which should be cooled at a slower rate receive, as a result of their large area, a relatively large fraction of the total cooling. This inefficient use of coolant cannot be readily overcome by the device shown in U~S. Patent No. 3,488,801, in that the angled end of the injection pipe 12 succeeds only in changing the angle at which the broad cone 16 is directed within the article 10 and does not materially result in a more efficient use of refrigerant.
Referring now to Figures 2 and 3, in accordance with one embodiment of the invention, there is provided a novel coolant spray head 20 connected to the coolant ,. ~' , , ~ ~ , .~ : :
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inlet line 12. The spray head 20 is of generally cylindrical shape and has a rounded head 22 and an internal bone 24 communicating with the inlet line 12.
The rounded head 22 has a V-shaped groove 26 ~ormed in the surface thereof extending over the crown of the head. These passageways 28, 30 and 32 extend through the head 24 and establish communication with the bone 24 to permit refrigerant to enter the article 10 and act as nozzle. The V-shape of the groove 26 ensures thak the refrigerant is in a planar fan spray pattern and also softens the direct blow from the passageways and directs some coolant to areas B1. The passageways 28, 30 and 32 provide specific spray patterns 34, 36 and 38 respectively directed towards the portions A2 of the article 10, which require more rapid cooling in view of their thickness and, at the same time, the flow of coolant towards the other regions, sidewalls including B2, is diminished. Each of the passageways 28, 30 and 32 may be dimensioned to direct only a specific amount of coolant therethrough, thereby further improving the efficiency.
The actual design of spray head 20 and the number and form of the passageways associated therewith varies and is customized for the particular hlow molded product that it is desired to cool, and the construction of the same can be readily carried out by a person skilled in the art, knowing the principles of the present invention, as described above. The coolant medium may be any desired material, preferably carbon dioxide or nitrogen.
The spray head 20 is threadedly mounted to the inlet-outlet pipe 40 in communication with the inlet line 12 extending through the pip8 40. The spray head is located in the desired central position by a locking nut 42.
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An outlet passage 44 for spent cooling medium is provided communicating with the interior of article 10 through openings 46.
EX~MPLE
5 gallon (20 l) high density polyethylene jerry cans each weighing 3.25 lbs were extruded using a single cavity mold and subsequently cooled using conventional cooling equipmenk (as seen in Figure 1) and also using a multipost nozzle as illustrated in Figures 2 and 3. The cycle time for production of such jerry cans by the two procedures was determined and the results appear in the following Table:
TABLE
Procedure Coolant Cycle Time (secsi) Conventional Air 57 Conventional Nitrogen 46.7 Invention Nitrogen 29 As can be seen from the data presented in the above Table, by using the multipost nozzle, a considerable decrease in cycle time of 26.5% was achieved.
SUMMARY OF DISCLOSURE
In summary of this disclosure, the present 1 25 invention provides a novel method of effecting cooling ¦ of blown plastic articles by directing coolant in ~i specific locations corresponding to those requiring a greater cooling rate using-nozzle of unique .I construction, thereby decreasing the overall cooling i 30 time for the article. Modifications are possible within the scope o~ this invention.
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:1 TITLE OF INVENTION
COOL~NT IN R DUCTION IN BLOW MOLDING
FIRLD OF INVENTION
The present invention relates to the blow molding of thermoplastic articles to form a variety of blow molded products, and in particular to the cooling of such articles during their manufacture.
BACKGROUND TO THE INVENTION
In the conventional production of blown plastic forms or articles, an extruded tube (parison) of thermoplastic material which is at a temperature above its melting point, is enclosed in an appropriately-15 shaped mold and pressurized air is used to expand the parison against the wall of the mold to assume the contour of the mold.
Following completion of the blowing cycle, the temperature of the molded article is decreased by 20 cooling to a level below the melting point of the thermoplastic material at which the formed plastic article retains its shape. The length of time required to effect the cooling often takes up a large proportion of the total time required to complete the molding 25 cycle.
The heat is removed from the blown molded article by a variety of procedures, including through the cooled mold walls and through the use of blowing air as a heat transfer medium. To improve the effectiveness of the 30 heat removal portion of the cycle, refrigerants, usually liquid nitrogen, have been introduced into the plastic form, after it has been blown to the shape of the mold.
The conventional manner of introduction of the refrigerant into the formed article is by injection of a j~ 35 refrigerated gas or liquid refrigerant through the blow Z pin which is used to introduce the blowing air d ~ ng J
.,. .. . - . .. . .
~32~97~
the blowing step or through a small tuhe contained within the blow pin.
The cooling medium either is introduced admixed with air or is separately in~ected in an undirected manner into the blown article. In all blown articles, there are regions which are thicker than others and henee require more cooling time than the thinner portions. The thicker portions thereby become the limiting factor controlling cooling time.
It has been previously suggested in U.S. Patent No.
3,488,801 to achieve a more uniform cooling of the blow molded artiele by employing a needle having an angled end which enables cooling fluid to be direeted towards a eertain locus of the hot thermoplastic material. The needle may be moved during the cooling operation to direet the cooling fluid towards a plurality of different loci on the interior of the parison by rotating and/or lonyitudinally moving the needle. In this prior art operation, therefore, while differential eooling may be achieved by directing eoolant at specific loeations, it is possible to apply additional coolant to only one location at one time.
SUMMARY OF INVENTION
In accordance with the present invention, a novel method of injection of refrigerant into the mold for cooling a parison is provided which directs cooling medium towards the portions of the article which require a greater degree of cooling and away from those portions of the blown article where crystallinity and/or stiffness are more critical. The combination of these two effects results in an accelerated cooling of the thieker portions oP the article whieh are limiting the eyele time while retaining a high degree of erystallinity, density and/or stiffness in those regions of the product where the property is an advantage in the finished product.
. i, .
:
1323~7~
The present invention also provides a novel apparatus for introducing and directlng the flow of refrigerating medium to those loca~ions within the blown article where the effect of the refrigerant is most 5 beneficial and away from those locations where rapid cooling may be detrimental by employing a novel injection nozzle.
Accordingly, in one aspect, the present invention provides an improvement in a method of blow molding an 10 article of thermoplastic material by blowing the article in a mold of the desired shape with the article haviny a non-uniform wall thlckness and cooling the blown article by introducing a cooliny medium to the interior of the article to a temperature whereat the article is self-15 sustaining and can be removed from the mold.
The improv~ment of the present invention is wherein the cooling medium is introduced to the interior of the article in such a manner as to effect a directed cooling to thicker areas of the wall of the article and 20 a less rapid cooling to thinner areas of the wall of the article, so as to decrease the overall cooling time.
In another aspect, the present invention provides a novel nozzle for injection of refrigerant into a blow-molded article, comprising a body having a rounded head 25 and an internal bone exkending to the rounded head. A
V-shaped groove is formed in the outer surface of the rounded head and extends over the crown thereof. A
plurality of passageways connect the groove to the internal bone to permit refriyerant fluid in the bone to 30 pass out of the nozzle in a plurality of fan shaped ~ sprays having a pattern corresponding to the location Z and number o~ the plurality of passageways.
BRIEF DESCRIPTION OF DRAWINGS
Figures lA and lB are side and end views 35 respectively of a system commonly-employed for i' ' ~ ' : '. .: : ~' i ,. . ~ ' ' , `,. . ~ : :, :,' , ~ : - :
" 1323~71 introducing cooling medium to a blow-molded article during cooling;
Figures 2A and 2B are side and end views respectively of a system for the introdu~tion of cooling medium to a blow-molded article constructed in accordance with one embodiment of this invention; and Figure 3 is a close-up sectional view of one embodiment of nozzle used in the cooling medium of Figures 2A and 2B.
DESCRIPTION OF PREFERRED EMBO~IMENT
Referring to the drawings, Figure 1 illustrates a typical prior art procedure ~or introducing coolant to a blow molded article 10 through a central pipe 12 concentric with the blowing air pipe 14. The pattern 16 of the cooling medium is that of a broad cone, the dimensions of which are defined by well-known fluid-gas relationships.
Depending upon the design of the particular article, certain portions of the article represent a limitation to decreasing the cooling time. In Figures 1 and 2 respectively, these regions have been designated Al and A2. The broad cone 16 of cooling medium is largely directed to non-critical areas of the article 10, such as the sidewalls B1, and those portions of the article which should be cooled at a slower rate receive, as a result of their large area, a relatively large fraction of the total cooling. This inefficient use of coolant cannot be readily overcome by the device shown in U~S. Patent No. 3,488,801, in that the angled end of the injection pipe 12 succeeds only in changing the angle at which the broad cone 16 is directed within the article 10 and does not materially result in a more efficient use of refrigerant.
Referring now to Figures 2 and 3, in accordance with one embodiment of the invention, there is provided a novel coolant spray head 20 connected to the coolant ,. ~' , , ~ ~ , .~ : :
: .
~ ~ 3~3~
inlet line 12. The spray head 20 is of generally cylindrical shape and has a rounded head 22 and an internal bone 24 communicating with the inlet line 12.
The rounded head 22 has a V-shaped groove 26 ~ormed in the surface thereof extending over the crown of the head. These passageways 28, 30 and 32 extend through the head 24 and establish communication with the bone 24 to permit refrigerant to enter the article 10 and act as nozzle. The V-shape of the groove 26 ensures thak the refrigerant is in a planar fan spray pattern and also softens the direct blow from the passageways and directs some coolant to areas B1. The passageways 28, 30 and 32 provide specific spray patterns 34, 36 and 38 respectively directed towards the portions A2 of the article 10, which require more rapid cooling in view of their thickness and, at the same time, the flow of coolant towards the other regions, sidewalls including B2, is diminished. Each of the passageways 28, 30 and 32 may be dimensioned to direct only a specific amount of coolant therethrough, thereby further improving the efficiency.
The actual design of spray head 20 and the number and form of the passageways associated therewith varies and is customized for the particular hlow molded product that it is desired to cool, and the construction of the same can be readily carried out by a person skilled in the art, knowing the principles of the present invention, as described above. The coolant medium may be any desired material, preferably carbon dioxide or nitrogen.
The spray head 20 is threadedly mounted to the inlet-outlet pipe 40 in communication with the inlet line 12 extending through the pip8 40. The spray head is located in the desired central position by a locking nut 42.
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: ~ , :
.
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An outlet passage 44 for spent cooling medium is provided communicating with the interior of article 10 through openings 46.
EX~MPLE
5 gallon (20 l) high density polyethylene jerry cans each weighing 3.25 lbs were extruded using a single cavity mold and subsequently cooled using conventional cooling equipmenk (as seen in Figure 1) and also using a multipost nozzle as illustrated in Figures 2 and 3. The cycle time for production of such jerry cans by the two procedures was determined and the results appear in the following Table:
TABLE
Procedure Coolant Cycle Time (secsi) Conventional Air 57 Conventional Nitrogen 46.7 Invention Nitrogen 29 As can be seen from the data presented in the above Table, by using the multipost nozzle, a considerable decrease in cycle time of 26.5% was achieved.
SUMMARY OF DISCLOSURE
In summary of this disclosure, the present 1 25 invention provides a novel method of effecting cooling ¦ of blown plastic articles by directing coolant in ~i specific locations corresponding to those requiring a greater cooling rate using-nozzle of unique .I construction, thereby decreasing the overall cooling i 30 time for the article. Modifications are possible within the scope o~ this invention.
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Claims (8)
1. In a method of blow molding an article of thermoplastic material by blowing the article in a mold of the desired shape, said article having a non-uniform wall thickness, and cooling said blown article by introducing a cooling medium to the interior of said article to a temperature whereat said article is self-sustaining and can be removed from said mold, the improvement wherein said cooling medium is introduced to said interior in such a manner as to effect directed cooling to thicker areas of the wall of said article and a less rapid cooling to thinner areas of the wall of said article, whereby the overall cooling time is decreased.
2. The method of claim 1 wherein said cooling medium is introduced to said interior in a plurality of individual jets of cooling medium directed one against each of said thicker areas of said wall.
3. The method of claim 2 wherein said individual jets are of respective volumes corresponding to the desired cooling rate in each of said thicker areas of said wall.
4. The method of claim 3 wherein said individual jets form fan sprays which infringe upon the thicker areas of the wall.
5. The method of claim 1 wherein said cooling medium is carbon dioxide.
6. The method of claim 1 wherein said cooling medium is nitrogen.
7. A nozzle for injection of refrigerant into a blow-molded article, comprising:
elongate cylindrical body means having a hemispherically-rounded head at a downstream end thereof in the intended direction of flow refrigerant therethrough and an eleonate internal bore extending from an upstream end of said body means in the intended direction of flow of refrigerant therethrough to said hemispherically-rounded head, a V-shaped groove formed in the outer surface of said hemispherically-rounded head having a uniform depth and a uniform width along its entire length and extending over the entire crown of said hemispherically rounded head, and a plurality of passageways each connecting the base of said groove to said internal bore to permit refrigerant fluid in said bore to pass out of said nozzle in a plurality of fan-shaped sprays having a pattern corresponding to the location and number of said plurality of passageways.
elongate cylindrical body means having a hemispherically-rounded head at a downstream end thereof in the intended direction of flow refrigerant therethrough and an eleonate internal bore extending from an upstream end of said body means in the intended direction of flow of refrigerant therethrough to said hemispherically-rounded head, a V-shaped groove formed in the outer surface of said hemispherically-rounded head having a uniform depth and a uniform width along its entire length and extending over the entire crown of said hemispherically rounded head, and a plurality of passageways each connecting the base of said groove to said internal bore to permit refrigerant fluid in said bore to pass out of said nozzle in a plurality of fan-shaped sprays having a pattern corresponding to the location and number of said plurality of passageways.
8. The nozzle of claim 7 wherein said elongate cylindrical body means has a screw-threaded outer surface for mounting said nozzle in nozzle holding means.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000587801A CA1323971C (en) | 1989-01-09 | 1989-01-09 | Coolant introduction in blow molding |
| US07/549,121 US5052626A (en) | 1989-01-09 | 1990-07-06 | Coolant introduction in blow molding |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000587801A CA1323971C (en) | 1989-01-09 | 1989-01-09 | Coolant introduction in blow molding |
| US29549489A | 1989-01-11 | 1989-01-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1323971C true CA1323971C (en) | 1993-11-09 |
Family
ID=25672367
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000587801A Expired - Fee Related CA1323971C (en) | 1989-01-09 | 1989-01-09 | Coolant introduction in blow molding |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1323971C (en) |
-
1989
- 1989-01-09 CA CA000587801A patent/CA1323971C/en not_active Expired - Fee Related
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |