CA2038288A1 - Distributing material in blow mold head - Google Patents
Distributing material in blow mold headInfo
- Publication number
- CA2038288A1 CA2038288A1 CA 2038288 CA2038288A CA2038288A1 CA 2038288 A1 CA2038288 A1 CA 2038288A1 CA 2038288 CA2038288 CA 2038288 CA 2038288 A CA2038288 A CA 2038288A CA 2038288 A1 CA2038288 A1 CA 2038288A1
- Authority
- CA
- Canada
- Prior art keywords
- mandrel
- mandrels
- flow
- chamber
- casing
- 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
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- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A blow head for blow molding thermoplastic products includes a casing and a concentric assembly of mandrels aligned with a predetermined flow axis. The mandrels and casing cooperate to define distinct concentric flow channels. A former shapes molten thermoplastic materials discharged from the flow channels into a single tube with a selected cross-sectional thickness.
Spiral grooves are formed in external surfaces of the mandrels to distribute material more evenly around an associated flow channel. Each mandrel has a circumferential chamber for receiving thermoplastic material under pressure and supplying the material to upstream ends of the flow channel and grooves associated with the mandrel. Material inlets inject the materials under pressureinto each chamber in a direction transverse to the axis. The inlets are constituted by passage sections formed in the casing and the mandrels that align simultaneously to constitute the inlets. A heart-shaped flow divider in each chamber immediately confronts and divides the flow from the associated inlet into substantially equal flows in circumferentially opposing directions around the chamber. Thermoplastic materials are distributed more evenly in the flow channels so that the tube and final product formed from the tube have greater uniformity.
A blow head for blow molding thermoplastic products includes a casing and a concentric assembly of mandrels aligned with a predetermined flow axis. The mandrels and casing cooperate to define distinct concentric flow channels. A former shapes molten thermoplastic materials discharged from the flow channels into a single tube with a selected cross-sectional thickness.
Spiral grooves are formed in external surfaces of the mandrels to distribute material more evenly around an associated flow channel. Each mandrel has a circumferential chamber for receiving thermoplastic material under pressure and supplying the material to upstream ends of the flow channel and grooves associated with the mandrel. Material inlets inject the materials under pressureinto each chamber in a direction transverse to the axis. The inlets are constituted by passage sections formed in the casing and the mandrels that align simultaneously to constitute the inlets. A heart-shaped flow divider in each chamber immediately confronts and divides the flow from the associated inlet into substantially equal flows in circumferentially opposing directions around the chamber. Thermoplastic materials are distributed more evenly in the flow channels so that the tube and final product formed from the tube have greater uniformity.
Description
2~38288 DTSTRTBUTING MATERTAL IN BLOW MOLD HEAD
FIELD OF THE INVENTION
The invention relates to blow molding of thermoplastic materials, and more particularly, to features of a blow mold head that encourage5 discharge of a uniform tubular thermoplastic material for subsequent expansion into a desired shape.
BACKGROUND OF THE INVENTION
Existing blow mold heads typically have a mandrel or multiple mandrels that define one or more flow channels ~or producing a tube or 10 concentric tubes of thermoplastic material. A former shapes and discharges the single tube or alternatively forms ehe multiple concent~ic tubes into a single tube with a particular cross-section. Even distribution of molten therrnoplastic material around each flow channel is important to ensuring product uniformity and avoiding warpage and fracturing on product setting. To that end, each flow 15 channel will normally be associated with a supply chamber. Molten thermoplastic material is injected under pressure axially into a particular region of the chamber (in the general direction of the flow channel) and distributed around the upstream end of the associated flow channel. Spiral grooves are sometimes formed in the exterior of a mandrel to receive material from the 20 supply chamber and enhance distribution throughout the associated flow channel. However, axial injection tends not to produce an optimal distribution of material around the chamber and ultimately in the flow channel.
The present invention introduces inter ~_ methods and ~ -apparatus for injecting thermoplastic materials transversely into a blow head and 25 dividing such flows so as to produce a more even distribution of material throughout flow channels. It also addresses the problem of providing such transverse injection for multiple concentric mandrels.
20382~8 SUMMARY OF TI~E INVENTTON
In one aspect, the invention pro~ides a blow head for use in blow molding thermoplastic material. The blow head has an axis and a hollow casing with a circurnferential sidewall surrounding the axis. A mandrel is S mounted within the casing in general alignment with the axis. An exterior surface portion of the mandrel cooperates with the casing sidewall to define a Mow channel with upstream and downstream ends. A multiplicity of spiral grooves are formed in the exterior surface portion. Each groove has a downstream end terminating within the flow channel and an upstream end. A
10 circumferential recess is formed in the mandrel upstream of the flow channel and of the spiral grooves. The recess cooperates with the casing sidewall to de~me a chamber into which open the upstream ends of the flow channel and the grooves. A material inlet extends through the casing sidewall and discharges a flow of thermoplastic material into the chamber in a direction transverse to the15 axis. A flow divider attached to the mandrel and positioned within the recessconfronts the flow of thermoplastic material discharged from the inlet. The flow divider is shaped to divide the flow of thermoplastic material into substantially equal flows in circumferentially opposing directions around the ;~chamber. A former downstream of the flow channel forms thermoplastic 20 material discharged from the downstream end of the flow channel into a tube with a preselected cross-section. This can be expanded according to conventional blow molding techniques to produce a required product.
In another aspect, the invention provides a comparable blow head, but comprising a plurality of hollow mandrels including at least an 25 innermost mandrel and an outermost mandrel. The mandrels are dimensioned and shaped to seat within one another in a predetermined concentric ~; arrangement. Each mandrel has a circumferential sidewall surrounding the axis of the blow head and an external surface portion defined by its circumferential . .
` 20~8288 sidewall. Each mandrel is associated with a flow channel external to the mandrel. The exterior surface portion of the outermost mandrel cooperates with the circumferential sidewall of the casing associated with the blow head to define its associated external flow channel. The exterior surface portion of each 5 inner mandrel cooperates with the circumferential sidewall of an immediately outer mandrel to define its associated external flow channel. The exterior surface portion of each mandrel comprises a multiplicity of spiral grooves, eachgroove comprising an upstream end and comprising a downstream end terminating within the external flow channel associated with the mandrel. Each 10 mandrel has a circumferential recess upstream of its associated external flowchamlel and of its spiral grooves. The recess associated with the outermost mandrel cooperates with the sidewall of the casing to define a chamber, and the recess of each inner mandrel cooperates with the sidewall of an immediately outer mandrel to define a similar chamber. The ups~eam ends of the external 15 flow channel and spiral grooves associated with each mandrel opening into the chamber associated with the mandrel.
A plurality of material inlets are each associated with a different mandrel and shaped to discharge a flow of thermoplastic material into the chamber associated with the mandrel in a direction transverse to the axis. The 20 material inlet associated with the outermost mandrel includes a passage section extending through the sidewall of the casing. The material inlet associated witheach inner mandrel comprises alignable passage sections formed in and extending through the casing sidewall and each mandrel surrounding the -mandrel. The passage sections of the material inlets are formed in 25 predetermined locations and orientations such that the passage sections alignsimultaneously to form the passagPs of the material inlets when the plurality ofmandrels are arranged in the predetermined concentric arrangement.
Accordingly, despite the presence of multiple concentric mandrels, each , . . . . . , . . , ,, ............ ~ .. . . ,, ~. . . .
....... . .. .. ~ , :. . .~ .: . : - ... .
20~82~8 mandrel can receive thermoplastic material by injection transverse to the axis of the blow head.
Each mandrel comprises a flow divider. The flow divider is positioned within the recess of the mandrel to confront the flow of thermoplastic material discharged from the material inlet associated with the mandrel. Each flow divider is shaped to divide the incoming flow of thermoplastic material into substantially equal flows in circurnferentially opposing d~rections around the chamber associated with the mandrel. A former downstream of the flow channels forms thermoplastic materials discharged from the downstream ends of the flow channels into a single tube with a preselected cross-section.
Other aspects of the invention including methods and features associated with a blow head will be apparent from a description below of a preferred embodiment and will be more specifically defined in the appended claims.
DESCRTPF~ON QEI~ DRA~NGS
The invention will be better understood with reference to drawings in which:
fig. 1 is a cross-sectional view of a blow head in a vertical plane containing the general axis of the blow head;
fig. 2 is an enlarged fragmented elevational view illustrating a chamber and flow divider associated with an intermediate mandrel of the blow head;
fig. 3 is a fragmented elevational view in partial cross-section showing further detail of the intermediate mandrel, including the flow divider and portions of the supply chamber associated with the outer mandrel.
DESCRIPI~Q~ OF PRE~ RRED EMBODIMNTS
Reference is made to fig. 1 which illustrates a blow head 10 for 2Q~8288 use in blow molding thennoplastic material. The blow head 10 has a central axis 12 which is generally aligned with the direction of material flow. An arrowD indicates a downstream direction of material flow. An arrow U indicates an upstream direction of material flow. This particular embodiment of a blow head 5 10 is intended to produce a three-layered tube 14 (layering not illustrated) that might consist of inner and outer layers of virgin thermoplastic material and an intermediate layer of recycled plastic. A typical application for the blow head 10 might be production of plastic bottles.
The general construction of the blow head 10 will be described 10 with reference to fig. 1. A hollow caslng 16 comprises an upstream end structure 18. It also comprises a circumferential sidewall 20 surrounding the axis 12 and defined by a downstream end plate 22 and a generally cylindrical section 24. An assembly of hollow mandrels, including an innermost mandrel 26, an interrnediate mandrel 28, and an outermost mandrel 30, is located within 15 the casing sidewall 20 in general alignment with the axis 12. The mandrels 26, 28, 30 are formed with complementary interlocking internal shoulders (not numbered) that permit the mandrels 26, 28, 30 to be bolted to the upstream end structure 18 to form a unitary assembly in a predeterrnined concentric relationship, all of which will be readily apparent from fig. 1. A former 32 is 20 oriented in general alignment with the axis 12 downstream of the mandrel assembly. The former 32 shapes thermoplastic material discharged downstream of the mandrels 26, 28, 30 into the tube 14 ultimately discharged from the blow head 10. The former 32 comprises an outer former portion 34 which is bolted to the downstream end plate 22 of the casing 16 over an aperture formed in the 25 end plate 22, and a hollow inner former portion 36 ~readed onto a hollow support rod 38 extending through the interior of the innermost mandrel 26. The rod 38 can be displaced axially by a hydraulic cylinder 40 to adjust the cross-sectional thickness of the tube 14. A central passage 42 through the rod ,.... . . . . .. . . .
38 communicates with an air supply chamber 44 in the upstream end structure 18. This permits air under pressure to be applied to the interior of the tube 14(through the rod 38 and inner former portion 36) downstream of the former 32.
The air under pressure is used in a conventional manner to expand the tube 14 5 against a mold (not illustrated) to produce a product (not illustrated) of a particular shape.
The casing 16 and mandrel assembly cooperate lo define three flow channels. In general terms, each mandrel has a circumferential sidewall surrounding the axis 12. An external surface portion of that sidewall cooperates10 with an outer structure to define a flow channel associated with the mandrel and external to the mandrel itself.
More specifically, the exterior surface portion 46 of the outermost mandrel 30 cooperates with the circumferential sidewall 20 of the casing 16 to define an outermost flow channel 48 associated with the outermost mandrel 30. The exterior surface portion 50 of the intermediate mandrel 28 cooperates with a circumferential sidewall 52 of the outermost mandrel 30 to define an intermediate flow channel 54. The exterior surface portion 56 of the innermost mandrel 26 cooperates with the circumferen~ial sidewall 58 of the intermediate mandrel 28 to define an innermost flow channel 60. Each of the 20 flow channels will ultimately produce a substantially tubular flow of thermoplastic material.
The exterior surface portion of each mandrel is formed with a multiplicity of spiral grooves. The grooves associated with the intermediate mandrel 28 are typical and are identified collectively by the reference numeral 25 62. These are best illustrated in the views of figs. 2 and 3. The various grooves 62 are oriented in parallel relationship ar.d are substantially identical.
Each groove has an upstream end (such as the upstream end 66) that terminates smoofriyattheexteriorrufaceporiin5Uoftheintermediatemandrel28 ~: ' . . .. .,, . .. , . .... ~ . , ~ . . :
within the intermediate flow channel 54. Each groove has an enlarged downstream end (such as the downstream end 68) that is open-ended. The depth of each groove decreases substantially continuously from its downstream end to its upstream end. This arrangement forces thermoplastic material supplied under pressure to the upstream ends of the grooves 62 to blend smoothly into flows otherwise occurring in the intermediate flow channel 54.
Alternatively, the grooves 62 may have a uniform depth and may incline progressively further away from the axis 12 from their downstream ends to their upstream ends. The configuration of spiral grooves for such purposes is known in the art and will not be described further.
Each of the mandrels 26, 28, 30 has a circumferential recess upstream of the associated external flow channel and its spiral grooves. The function and shape of the recess 70 of the intermediate mandrel 28 is typical. It -is specifically identified only in the views of figs. 2 and 3. The recess 70 cooperates with the sidew~ll 52 of the outerrnost mandrel 30 to define a chamber 72 for receiving thermoplastic material under pressure. That chamber 72 distributes the received materials to the intermediate flow channel 54 and toeach of the grooves 62 associated with the intermediate mandrel 28. More specifically, the interrnediate mandrel 28 comprises first and second axially opposing surface portions 74, 76 that bound its recess 70. The first surface portion 74, which is discontinuous, has been indicated in edge view with a dashed horizontal in fig. 3. It should be noted that the upstream end of the intermediate flow channel 54 and the enlarged upstream ends of the grooves 62 of the intermediate mandrel 28 intersect that first surface portion 74 and consequently open into the chamber 72 to receive material. Similar chambers 78, 80 are defimed by recesses associated with the other two mandrels 26, 30 and bear similar relationships to the external flow path and grooves associated ' :.' ' ~:
. ,' ,, , . . . ~ . . ~ ., ,, , . - . . . . . -20~8288 with thcir respective mandrels. The recess associated with the innermost mandrel 26 cooperates with the sidewall 58 of the intermediate mandrel 28 to define the chamber 78 while the recess associated with the outermost mandrel 30 cooperates with the sidewall 20 of the casing 16 to de~me the chamber 80.
Three material inlets 82, 84, 86 are provided to receive thermoplastic material under pressure. Each inlet discharges matexial into a chamber associated with a different one of the mandrels 26, 28,30 in a direction transverse to the blow head axis 12. The material inlet 84 associated with the intermediate mandrel 28 includes a passage section 88 extending through the sidewall 20 of the casing 16 and an aligned passage section 90 extending through the outexmost mandrel 30. The material inlet 86 associated with the outermost mandrel 30 comprises a single passage section 92 extending through the sidewall 20 of the casing 16. The material inlet 82 associated wi~h the innennost mandrel 26 has a passage comprising three passage sections 94, 96,98 fo~ned respectively in the casing 16, the outermost mandrel 30, and the interrnediate mandrel 28, that align to communicate with the chamber 78 associated with the innermost mandrel 26. The various passage sections are radially oriented and circumferentially positioned in the mandrels 26,28,30 such that they align simultaneously to constitute the material inlets 82, 84,86 when the mandrel assembly is in the predetermined concentric arrangement shown in fig. 1. The mandrels 26, 28,30 may simply be rotated relative to one another, prior to bolting to the upstream end structure 18, to achieve the particular concentric arran~ement necessary to align the various passage sections. Accordingly, in this particular aspect of the invention, it is possible to supply materials simultaneously by transverse injection into the chambers associated with each of a multiplicity of concentric mandrels.
Each of the mandrels 26, 28,30 is associated with a flow divider. The flow divider 100 associated with the intermediate mandrel 28 is - :'- : , :
2~38~88 typical and is most apparent in figs. 2 and 3. It is positioned within the recess 70 associated with the intelmediate mandrel 28 to confront the flow of thermoplastic material discharged from the material inlet 84. It divides the flow of the thermoplastic material into substantially equal flows in c~rcumferentially S opposing directions (as indicated by arrows in fig. 3) around the chamber 72 of the mandrel. The flow divider 100 is substantially heart-shaped with a crux 102 and a tip 104, the tip 104 being positioned axially upstream from the crux -102. The particular shape has been determined empirically to optimize distribution of materials to both the flow channel and the various grooves 10 associated with a mandrel. An alternative shape that also produces an effective flow divider is semi-circular with the "flat end" positioned upstream, the peripheral edges of such a divider, of course, being smoothed. Thermoplastic flows are not particularly predictable and no comprehensive explanation can be offered for the effect observed. However, any divider shaped to encourage 15 substantially equal and opposite flows about such a chamber will enhance ultimate distribution of materials. Flow dividers 106, 108 associated with the innermost and outermost mandrels are identified in fig. 1.
The shape of the chamber 72 associated with the intermediate mandrel 28 should be noted. The first surface portion 74 bounding the 20 associated recess is substantially planar and perpendicular to the axis 12. The second surface portion 76 is substantially planar, but inclined relative to the axis ,`
12 as apparent in fig. 2. This causes the chamber 72 to have a maximum axial length proximate to the associated inlet 84 and a minimum axial length radially opposite from the inlet 84. Tapering the axial dimensions of chamber 72 in 25 such a manner has been found particularly important to processing of nylon and polyvinylchloride. These materials tend otherw;se to remain resident in a portion of the chamber 72 and become subject to burning (the blow head being heated in a conventional manner). The arrangement is believed to prevent g . . . . . . . . . . . ............. . ....... .. . . . . .
~ ' .' , , . ., ,. . ', , . ' , :, : , ~; . : . i ' ' :
:: - :. , . ,, , . ~ :.. - . .. . ,. -pooling in portions of the chamber 72 radially opposite the material inlet 84 and axially opposite the upstream ends of the grooves. With other matenals, such tapering of the chamber is not necessary to eliminate burning, but very significantly enhances distribution of the materials circumferentially about theflow channels, producing a more uni~orrn final product. The chambers 78, 80 associated with the other mandrels 26, 30 are similarly configured.
Annular notches may be formçd in the mandrels upstream of the spiral grooves to provide a measure of pooling and smoothing of flows.
Notches 110, 112 have been provided in the intermediate and outermost mandrels 28, 30, but have not been used in connection with the innermost mandrel 26. Use of such notches is well known and will not be described further.
How the blow head 10 is used to produce molded product will be readily apparent to those skilled in the art. The blow head 10 will normally b,e oriented with its axis 12 vertical and the forrner 32 facing downwardly. Thehydraulic cylinder 40 will be operated to adjust the position of the inner former portion 36 and consequently the thickness of the tube 14 discharged from the former 32. Material is delivered under pressure to the three inlets 82, 84, 86 and three tubular concentric streams are discharged downstream of the mandrels 26, 28, 30. The former 32 combines the flows to produce a single tube 14 with a sandwich-type construction. As mentioned above, a mold will be located about the tube 14, and air under pressure will be delivered to the interior of the tube 14 through the central rod 38 and inner forrner portion 36 to expand the tube 14 within the internal cavity of the mold. The finished product can then beremoved. Details o~ this process will be apparent to those skilled in the art The general object of the invention in such blow molding operations is to encourage even distribution of flows circumferentially in the '' ' ', ~ : ' .
..
~low channels and consequently to discharge a tube of vel~ uniform wall thickness. The spiral grooves encourage even flows in a well-known manner.
The injection of raw material transverse to the axis 12 of the blow head 10, rather than conYentional axial injection, and use of flow dividers immediately 5 confronting the injeceed flows, ensures more even delivery of materials to theupstream ends of both the spiral grooves and the flow channels. This itself significantly enhances the uniforrnity of the tube 14 ultimately discharged fromthe former 32. The tapering of the axial dimensions of the chamber further encourages even supply of material to the grooves and flow path. Use of flow 10 dividers in the preferred heart-shape with upstream location of their tips appears to enhance the uniformity of the tube 14 further.
It will be appreciated that a particular embodiment oi the invention has been described and that modifications may be made therein without departing from the spirit of the invention or necessarily departing from the scope of the appended claims. ~ , i --- - . . . . . . . . . . .
:, .~ : . , . ~ . , r; ' , ~ ; i , '
FIELD OF THE INVENTION
The invention relates to blow molding of thermoplastic materials, and more particularly, to features of a blow mold head that encourage5 discharge of a uniform tubular thermoplastic material for subsequent expansion into a desired shape.
BACKGROUND OF THE INVENTION
Existing blow mold heads typically have a mandrel or multiple mandrels that define one or more flow channels ~or producing a tube or 10 concentric tubes of thermoplastic material. A former shapes and discharges the single tube or alternatively forms ehe multiple concent~ic tubes into a single tube with a particular cross-section. Even distribution of molten therrnoplastic material around each flow channel is important to ensuring product uniformity and avoiding warpage and fracturing on product setting. To that end, each flow 15 channel will normally be associated with a supply chamber. Molten thermoplastic material is injected under pressure axially into a particular region of the chamber (in the general direction of the flow channel) and distributed around the upstream end of the associated flow channel. Spiral grooves are sometimes formed in the exterior of a mandrel to receive material from the 20 supply chamber and enhance distribution throughout the associated flow channel. However, axial injection tends not to produce an optimal distribution of material around the chamber and ultimately in the flow channel.
The present invention introduces inter ~_ methods and ~ -apparatus for injecting thermoplastic materials transversely into a blow head and 25 dividing such flows so as to produce a more even distribution of material throughout flow channels. It also addresses the problem of providing such transverse injection for multiple concentric mandrels.
20382~8 SUMMARY OF TI~E INVENTTON
In one aspect, the invention pro~ides a blow head for use in blow molding thermoplastic material. The blow head has an axis and a hollow casing with a circurnferential sidewall surrounding the axis. A mandrel is S mounted within the casing in general alignment with the axis. An exterior surface portion of the mandrel cooperates with the casing sidewall to define a Mow channel with upstream and downstream ends. A multiplicity of spiral grooves are formed in the exterior surface portion. Each groove has a downstream end terminating within the flow channel and an upstream end. A
10 circumferential recess is formed in the mandrel upstream of the flow channel and of the spiral grooves. The recess cooperates with the casing sidewall to de~me a chamber into which open the upstream ends of the flow channel and the grooves. A material inlet extends through the casing sidewall and discharges a flow of thermoplastic material into the chamber in a direction transverse to the15 axis. A flow divider attached to the mandrel and positioned within the recessconfronts the flow of thermoplastic material discharged from the inlet. The flow divider is shaped to divide the flow of thermoplastic material into substantially equal flows in circumferentially opposing directions around the ;~chamber. A former downstream of the flow channel forms thermoplastic 20 material discharged from the downstream end of the flow channel into a tube with a preselected cross-section. This can be expanded according to conventional blow molding techniques to produce a required product.
In another aspect, the invention provides a comparable blow head, but comprising a plurality of hollow mandrels including at least an 25 innermost mandrel and an outermost mandrel. The mandrels are dimensioned and shaped to seat within one another in a predetermined concentric ~; arrangement. Each mandrel has a circumferential sidewall surrounding the axis of the blow head and an external surface portion defined by its circumferential . .
` 20~8288 sidewall. Each mandrel is associated with a flow channel external to the mandrel. The exterior surface portion of the outermost mandrel cooperates with the circumferential sidewall of the casing associated with the blow head to define its associated external flow channel. The exterior surface portion of each 5 inner mandrel cooperates with the circumferential sidewall of an immediately outer mandrel to define its associated external flow channel. The exterior surface portion of each mandrel comprises a multiplicity of spiral grooves, eachgroove comprising an upstream end and comprising a downstream end terminating within the external flow channel associated with the mandrel. Each 10 mandrel has a circumferential recess upstream of its associated external flowchamlel and of its spiral grooves. The recess associated with the outermost mandrel cooperates with the sidewall of the casing to define a chamber, and the recess of each inner mandrel cooperates with the sidewall of an immediately outer mandrel to define a similar chamber. The ups~eam ends of the external 15 flow channel and spiral grooves associated with each mandrel opening into the chamber associated with the mandrel.
A plurality of material inlets are each associated with a different mandrel and shaped to discharge a flow of thermoplastic material into the chamber associated with the mandrel in a direction transverse to the axis. The 20 material inlet associated with the outermost mandrel includes a passage section extending through the sidewall of the casing. The material inlet associated witheach inner mandrel comprises alignable passage sections formed in and extending through the casing sidewall and each mandrel surrounding the -mandrel. The passage sections of the material inlets are formed in 25 predetermined locations and orientations such that the passage sections alignsimultaneously to form the passagPs of the material inlets when the plurality ofmandrels are arranged in the predetermined concentric arrangement.
Accordingly, despite the presence of multiple concentric mandrels, each , . . . . . , . . , ,, ............ ~ .. . . ,, ~. . . .
....... . .. .. ~ , :. . .~ .: . : - ... .
20~82~8 mandrel can receive thermoplastic material by injection transverse to the axis of the blow head.
Each mandrel comprises a flow divider. The flow divider is positioned within the recess of the mandrel to confront the flow of thermoplastic material discharged from the material inlet associated with the mandrel. Each flow divider is shaped to divide the incoming flow of thermoplastic material into substantially equal flows in circurnferentially opposing d~rections around the chamber associated with the mandrel. A former downstream of the flow channels forms thermoplastic materials discharged from the downstream ends of the flow channels into a single tube with a preselected cross-section.
Other aspects of the invention including methods and features associated with a blow head will be apparent from a description below of a preferred embodiment and will be more specifically defined in the appended claims.
DESCRTPF~ON QEI~ DRA~NGS
The invention will be better understood with reference to drawings in which:
fig. 1 is a cross-sectional view of a blow head in a vertical plane containing the general axis of the blow head;
fig. 2 is an enlarged fragmented elevational view illustrating a chamber and flow divider associated with an intermediate mandrel of the blow head;
fig. 3 is a fragmented elevational view in partial cross-section showing further detail of the intermediate mandrel, including the flow divider and portions of the supply chamber associated with the outer mandrel.
DESCRIPI~Q~ OF PRE~ RRED EMBODIMNTS
Reference is made to fig. 1 which illustrates a blow head 10 for 2Q~8288 use in blow molding thennoplastic material. The blow head 10 has a central axis 12 which is generally aligned with the direction of material flow. An arrowD indicates a downstream direction of material flow. An arrow U indicates an upstream direction of material flow. This particular embodiment of a blow head 5 10 is intended to produce a three-layered tube 14 (layering not illustrated) that might consist of inner and outer layers of virgin thermoplastic material and an intermediate layer of recycled plastic. A typical application for the blow head 10 might be production of plastic bottles.
The general construction of the blow head 10 will be described 10 with reference to fig. 1. A hollow caslng 16 comprises an upstream end structure 18. It also comprises a circumferential sidewall 20 surrounding the axis 12 and defined by a downstream end plate 22 and a generally cylindrical section 24. An assembly of hollow mandrels, including an innermost mandrel 26, an interrnediate mandrel 28, and an outermost mandrel 30, is located within 15 the casing sidewall 20 in general alignment with the axis 12. The mandrels 26, 28, 30 are formed with complementary interlocking internal shoulders (not numbered) that permit the mandrels 26, 28, 30 to be bolted to the upstream end structure 18 to form a unitary assembly in a predeterrnined concentric relationship, all of which will be readily apparent from fig. 1. A former 32 is 20 oriented in general alignment with the axis 12 downstream of the mandrel assembly. The former 32 shapes thermoplastic material discharged downstream of the mandrels 26, 28, 30 into the tube 14 ultimately discharged from the blow head 10. The former 32 comprises an outer former portion 34 which is bolted to the downstream end plate 22 of the casing 16 over an aperture formed in the 25 end plate 22, and a hollow inner former portion 36 ~readed onto a hollow support rod 38 extending through the interior of the innermost mandrel 26. The rod 38 can be displaced axially by a hydraulic cylinder 40 to adjust the cross-sectional thickness of the tube 14. A central passage 42 through the rod ,.... . . . . .. . . .
38 communicates with an air supply chamber 44 in the upstream end structure 18. This permits air under pressure to be applied to the interior of the tube 14(through the rod 38 and inner former portion 36) downstream of the former 32.
The air under pressure is used in a conventional manner to expand the tube 14 5 against a mold (not illustrated) to produce a product (not illustrated) of a particular shape.
The casing 16 and mandrel assembly cooperate lo define three flow channels. In general terms, each mandrel has a circumferential sidewall surrounding the axis 12. An external surface portion of that sidewall cooperates10 with an outer structure to define a flow channel associated with the mandrel and external to the mandrel itself.
More specifically, the exterior surface portion 46 of the outermost mandrel 30 cooperates with the circumferential sidewall 20 of the casing 16 to define an outermost flow channel 48 associated with the outermost mandrel 30. The exterior surface portion 50 of the intermediate mandrel 28 cooperates with a circumferential sidewall 52 of the outermost mandrel 30 to define an intermediate flow channel 54. The exterior surface portion 56 of the innermost mandrel 26 cooperates with the circumferen~ial sidewall 58 of the intermediate mandrel 28 to define an innermost flow channel 60. Each of the 20 flow channels will ultimately produce a substantially tubular flow of thermoplastic material.
The exterior surface portion of each mandrel is formed with a multiplicity of spiral grooves. The grooves associated with the intermediate mandrel 28 are typical and are identified collectively by the reference numeral 25 62. These are best illustrated in the views of figs. 2 and 3. The various grooves 62 are oriented in parallel relationship ar.d are substantially identical.
Each groove has an upstream end (such as the upstream end 66) that terminates smoofriyattheexteriorrufaceporiin5Uoftheintermediatemandrel28 ~: ' . . .. .,, . .. , . .... ~ . , ~ . . :
within the intermediate flow channel 54. Each groove has an enlarged downstream end (such as the downstream end 68) that is open-ended. The depth of each groove decreases substantially continuously from its downstream end to its upstream end. This arrangement forces thermoplastic material supplied under pressure to the upstream ends of the grooves 62 to blend smoothly into flows otherwise occurring in the intermediate flow channel 54.
Alternatively, the grooves 62 may have a uniform depth and may incline progressively further away from the axis 12 from their downstream ends to their upstream ends. The configuration of spiral grooves for such purposes is known in the art and will not be described further.
Each of the mandrels 26, 28, 30 has a circumferential recess upstream of the associated external flow channel and its spiral grooves. The function and shape of the recess 70 of the intermediate mandrel 28 is typical. It -is specifically identified only in the views of figs. 2 and 3. The recess 70 cooperates with the sidew~ll 52 of the outerrnost mandrel 30 to define a chamber 72 for receiving thermoplastic material under pressure. That chamber 72 distributes the received materials to the intermediate flow channel 54 and toeach of the grooves 62 associated with the intermediate mandrel 28. More specifically, the interrnediate mandrel 28 comprises first and second axially opposing surface portions 74, 76 that bound its recess 70. The first surface portion 74, which is discontinuous, has been indicated in edge view with a dashed horizontal in fig. 3. It should be noted that the upstream end of the intermediate flow channel 54 and the enlarged upstream ends of the grooves 62 of the intermediate mandrel 28 intersect that first surface portion 74 and consequently open into the chamber 72 to receive material. Similar chambers 78, 80 are defimed by recesses associated with the other two mandrels 26, 30 and bear similar relationships to the external flow path and grooves associated ' :.' ' ~:
. ,' ,, , . . . ~ . . ~ ., ,, , . - . . . . . -20~8288 with thcir respective mandrels. The recess associated with the innermost mandrel 26 cooperates with the sidewall 58 of the intermediate mandrel 28 to define the chamber 78 while the recess associated with the outermost mandrel 30 cooperates with the sidewall 20 of the casing 16 to de~me the chamber 80.
Three material inlets 82, 84, 86 are provided to receive thermoplastic material under pressure. Each inlet discharges matexial into a chamber associated with a different one of the mandrels 26, 28,30 in a direction transverse to the blow head axis 12. The material inlet 84 associated with the intermediate mandrel 28 includes a passage section 88 extending through the sidewall 20 of the casing 16 and an aligned passage section 90 extending through the outexmost mandrel 30. The material inlet 86 associated with the outermost mandrel 30 comprises a single passage section 92 extending through the sidewall 20 of the casing 16. The material inlet 82 associated wi~h the innennost mandrel 26 has a passage comprising three passage sections 94, 96,98 fo~ned respectively in the casing 16, the outermost mandrel 30, and the interrnediate mandrel 28, that align to communicate with the chamber 78 associated with the innermost mandrel 26. The various passage sections are radially oriented and circumferentially positioned in the mandrels 26,28,30 such that they align simultaneously to constitute the material inlets 82, 84,86 when the mandrel assembly is in the predetermined concentric arrangement shown in fig. 1. The mandrels 26, 28,30 may simply be rotated relative to one another, prior to bolting to the upstream end structure 18, to achieve the particular concentric arran~ement necessary to align the various passage sections. Accordingly, in this particular aspect of the invention, it is possible to supply materials simultaneously by transverse injection into the chambers associated with each of a multiplicity of concentric mandrels.
Each of the mandrels 26, 28,30 is associated with a flow divider. The flow divider 100 associated with the intermediate mandrel 28 is - :'- : , :
2~38~88 typical and is most apparent in figs. 2 and 3. It is positioned within the recess 70 associated with the intelmediate mandrel 28 to confront the flow of thermoplastic material discharged from the material inlet 84. It divides the flow of the thermoplastic material into substantially equal flows in c~rcumferentially S opposing directions (as indicated by arrows in fig. 3) around the chamber 72 of the mandrel. The flow divider 100 is substantially heart-shaped with a crux 102 and a tip 104, the tip 104 being positioned axially upstream from the crux -102. The particular shape has been determined empirically to optimize distribution of materials to both the flow channel and the various grooves 10 associated with a mandrel. An alternative shape that also produces an effective flow divider is semi-circular with the "flat end" positioned upstream, the peripheral edges of such a divider, of course, being smoothed. Thermoplastic flows are not particularly predictable and no comprehensive explanation can be offered for the effect observed. However, any divider shaped to encourage 15 substantially equal and opposite flows about such a chamber will enhance ultimate distribution of materials. Flow dividers 106, 108 associated with the innermost and outermost mandrels are identified in fig. 1.
The shape of the chamber 72 associated with the intermediate mandrel 28 should be noted. The first surface portion 74 bounding the 20 associated recess is substantially planar and perpendicular to the axis 12. The second surface portion 76 is substantially planar, but inclined relative to the axis ,`
12 as apparent in fig. 2. This causes the chamber 72 to have a maximum axial length proximate to the associated inlet 84 and a minimum axial length radially opposite from the inlet 84. Tapering the axial dimensions of chamber 72 in 25 such a manner has been found particularly important to processing of nylon and polyvinylchloride. These materials tend otherw;se to remain resident in a portion of the chamber 72 and become subject to burning (the blow head being heated in a conventional manner). The arrangement is believed to prevent g . . . . . . . . . . . ............. . ....... .. . . . . .
~ ' .' , , . ., ,. . ', , . ' , :, : , ~; . : . i ' ' :
:: - :. , . ,, , . ~ :.. - . .. . ,. -pooling in portions of the chamber 72 radially opposite the material inlet 84 and axially opposite the upstream ends of the grooves. With other matenals, such tapering of the chamber is not necessary to eliminate burning, but very significantly enhances distribution of the materials circumferentially about theflow channels, producing a more uni~orrn final product. The chambers 78, 80 associated with the other mandrels 26, 30 are similarly configured.
Annular notches may be formçd in the mandrels upstream of the spiral grooves to provide a measure of pooling and smoothing of flows.
Notches 110, 112 have been provided in the intermediate and outermost mandrels 28, 30, but have not been used in connection with the innermost mandrel 26. Use of such notches is well known and will not be described further.
How the blow head 10 is used to produce molded product will be readily apparent to those skilled in the art. The blow head 10 will normally b,e oriented with its axis 12 vertical and the forrner 32 facing downwardly. Thehydraulic cylinder 40 will be operated to adjust the position of the inner former portion 36 and consequently the thickness of the tube 14 discharged from the former 32. Material is delivered under pressure to the three inlets 82, 84, 86 and three tubular concentric streams are discharged downstream of the mandrels 26, 28, 30. The former 32 combines the flows to produce a single tube 14 with a sandwich-type construction. As mentioned above, a mold will be located about the tube 14, and air under pressure will be delivered to the interior of the tube 14 through the central rod 38 and inner forrner portion 36 to expand the tube 14 within the internal cavity of the mold. The finished product can then beremoved. Details o~ this process will be apparent to those skilled in the art The general object of the invention in such blow molding operations is to encourage even distribution of flows circumferentially in the '' ' ', ~ : ' .
..
~low channels and consequently to discharge a tube of vel~ uniform wall thickness. The spiral grooves encourage even flows in a well-known manner.
The injection of raw material transverse to the axis 12 of the blow head 10, rather than conYentional axial injection, and use of flow dividers immediately 5 confronting the injeceed flows, ensures more even delivery of materials to theupstream ends of both the spiral grooves and the flow channels. This itself significantly enhances the uniforrnity of the tube 14 ultimately discharged fromthe former 32. The tapering of the axial dimensions of the chamber further encourages even supply of material to the grooves and flow path. Use of flow 10 dividers in the preferred heart-shape with upstream location of their tips appears to enhance the uniformity of the tube 14 further.
It will be appreciated that a particular embodiment oi the invention has been described and that modifications may be made therein without departing from the spirit of the invention or necessarily departing from the scope of the appended claims. ~ , i --- - . . . . . . . . . . .
:, .~ : . , . ~ . , r; ' , ~ ; i , '
Claims (11)
1. A blow head for use in blow molding thermoplastic material, comprising:
an axis;
a hollow casing comprising a circumferential sidewall that surrounds the axis;
a mandrel mounted within the casing in general alignment with the axis and having an exterior surface portion, the exterior surface portion cooperating with the sidewall of the casing to define between them a flow channel having an upstream end and a downstream end;
a multiplicity of spiral grooves formed in the exterior surface portion of the mandrel, each of the multiplicity of spiral grooves having a downstream end terminating within the flow channel and an upstream end;
a circumferential recess formed in the mandrel upstream of the flow channel and of the multiplicity of spiral grooves, the recess cooperating with the sidewall of the casing to define a chamber, the upstream ends of the flow channel and of each of the multiplicity of spiral grooves opening into the chamber;
a material inlet for receiving thermoplastic material under pressure, the material inlet extending through the sidewall of the casing and being shaped to discharge a flow of thermoplastic material into the chamber in a direction transverse to the axis;
a flow divider attached to the mandrel and positioned within the recess to confront the flow of thermoplastic material discharged from the material inlet, the flow divider being shaped to divide the flow of thermoplastic material into substantially equal flows in circumferentially opposing directions around the chamber; and, a former mounted to the casing in general alignment with the axis downstream of the flow channel for forming thermoplastic material discharged from the downstream end of the flow channel into a tube with a preselected cross-section.
an axis;
a hollow casing comprising a circumferential sidewall that surrounds the axis;
a mandrel mounted within the casing in general alignment with the axis and having an exterior surface portion, the exterior surface portion cooperating with the sidewall of the casing to define between them a flow channel having an upstream end and a downstream end;
a multiplicity of spiral grooves formed in the exterior surface portion of the mandrel, each of the multiplicity of spiral grooves having a downstream end terminating within the flow channel and an upstream end;
a circumferential recess formed in the mandrel upstream of the flow channel and of the multiplicity of spiral grooves, the recess cooperating with the sidewall of the casing to define a chamber, the upstream ends of the flow channel and of each of the multiplicity of spiral grooves opening into the chamber;
a material inlet for receiving thermoplastic material under pressure, the material inlet extending through the sidewall of the casing and being shaped to discharge a flow of thermoplastic material into the chamber in a direction transverse to the axis;
a flow divider attached to the mandrel and positioned within the recess to confront the flow of thermoplastic material discharged from the material inlet, the flow divider being shaped to divide the flow of thermoplastic material into substantially equal flows in circumferentially opposing directions around the chamber; and, a former mounted to the casing in general alignment with the axis downstream of the flow channel for forming thermoplastic material discharged from the downstream end of the flow channel into a tube with a preselected cross-section.
2. The blow head of claim 1 in which the mandrel comprises first and second axially opposing surface portions bounding the recess, the first surface portion being substantially planar and perpendicular to the axis, the first surface portion being intersected by the flow channel and the rear end portion of each of the multiplicity of spiral grooves, the second surface portion being substantially planar and inclined relative to the axis such that the chamber has a maximum axial length proximate to the inlet and a minimum axial length radially opposite from the inlet.
3. The blow head of claim 2 in which the flow divider is substantially heart-shaped with a crux and a tip, the tip being positioned axially upstream from the crux.
4. The blow head of claim 1 in which the mandrel comprises a pair of axially opposing surface portions bounding the recess, the pair of surface portions being oriented relative to one another and shaped such that the chamberhas a maximum axial length proximate to the inlet and a minimum axial length radially opposite from the inlet.
5. The blow head of claim 1 in which the flow divider is substantially heart-shaped with a crux and a tip, the tip being positioned axially upstream from the crux.
6. The blow head of claim 1 comprising means defining a passage extending through the interior of the mandrel and extending through the former for delivering air under pressure into the interior of the tube downstream of the former.
7. A blow head for use in blow molding thermoplastic material, comprising:
an axis;
a plurality of hollow mandrels dimensioned and shaped to seat within one another in a predetermined concentric arrangement, each of the plurality of mandrels comprising a circumferential sidewall surrounding the axisand comprising an external surface portion defined by its circumferential sidewall, the plurality of mandrels including at least an innermost mandrel and an outermost mandrel;
a hollow casing comprising a circumferential sidewall that surrounds the axis, the plurality of hollow mandrels being mounted in the predetermined concentric relationship within the casing in general alignment with the axis;
each of the plurality of mandrels being associated with a flow channel external to the mandrel and having an upstream end and a downstream end, the exterior surface portion of the outermost mandrel cooperating with the circumferential sidewall of the casing to define the flow channel associated with the outermost mandrel, the exterior surface portion of each of the plurality of mandrels within the outermost mandrel cooperating with the circumferential sidewall of an immediately outer one of the plurality of mandrels to define the flow channel associated with the mandrel;
each of the plurality of mandrels being associated with a multiplicity of spiral grooves formed in its exterior surface portion, each of the multiplicity of spiral grooves comprising an upstream end and composing a downstream end terminating within the flow channel associated with the mandrel with which the multiplicity of grooves is associated;
each of the plurality of mandrels being associated with a circumferential recess formed in the mandrel upstream of the associated flow channel and of the multiplicity of spiral grooves associated with the mandrel, the recess associated with the outermost mandrel cooperating with the sidewall of the casing to define a chamber associated with the outermost mandrel, the recess associated with each of the plurality of mandrels that is located within the outermost mandrel cooperating with the sidewall of the immediately outer mandrel to define a chamber associated with the associated mandrel;
the upstream ends of the external flow channel and of each of the multiplicity of spiral grooves associated with each of the multiplicity of mandrels opening into the chamber associated with the associated mandrel;
a plurality of material inlets for receiving thermoplastic material under pressure, each of the material inlets being associated with a different one of the plurality of mandrels and being shaped to discharge a flow of thermoplastic material into the chamber associated with the different one of themandrels in a direction transverse to the axis, the material inlet associated with the outermost mandrel including a passage section extending through the sidewall of the casing, the material inlet associated with each of the plurality of mandrels that is within the outermost mandrel comprising alignable passage sections formed in and extending through the casing and each of the plurality ofmandrels that surrounds the mandrel, the passage sections of the plurality of material inlets being formed in predetermined locations and orientations such that the plurality of material inlets are simultaneously formed when the plurality of mandrels are arranged in the predetermined concentric arrangement;
a plurality of flow dividers, each of the flow dividers being associated with a different one of the plurality of mandrels, each of the flow dividers being positioned within the recess of the associated mandrel to confront the flow of thermoplastic material discharged from the material inlet associatedwith the associated mandrel, each of the flow dividers being shaped to divide the flow of thermoplastic material confronted by the flow divider into substantially equal flows in circumferentially opposing directions around the chamber of the associated mandrel; and, a former mounted to the casing in general alignment with the axis downstream of the flow channels for forming thermoplastic materials discharged from the downstream ends of the flow channels into a single tube with a preselected cross-section.
an axis;
a plurality of hollow mandrels dimensioned and shaped to seat within one another in a predetermined concentric arrangement, each of the plurality of mandrels comprising a circumferential sidewall surrounding the axisand comprising an external surface portion defined by its circumferential sidewall, the plurality of mandrels including at least an innermost mandrel and an outermost mandrel;
a hollow casing comprising a circumferential sidewall that surrounds the axis, the plurality of hollow mandrels being mounted in the predetermined concentric relationship within the casing in general alignment with the axis;
each of the plurality of mandrels being associated with a flow channel external to the mandrel and having an upstream end and a downstream end, the exterior surface portion of the outermost mandrel cooperating with the circumferential sidewall of the casing to define the flow channel associated with the outermost mandrel, the exterior surface portion of each of the plurality of mandrels within the outermost mandrel cooperating with the circumferential sidewall of an immediately outer one of the plurality of mandrels to define the flow channel associated with the mandrel;
each of the plurality of mandrels being associated with a multiplicity of spiral grooves formed in its exterior surface portion, each of the multiplicity of spiral grooves comprising an upstream end and composing a downstream end terminating within the flow channel associated with the mandrel with which the multiplicity of grooves is associated;
each of the plurality of mandrels being associated with a circumferential recess formed in the mandrel upstream of the associated flow channel and of the multiplicity of spiral grooves associated with the mandrel, the recess associated with the outermost mandrel cooperating with the sidewall of the casing to define a chamber associated with the outermost mandrel, the recess associated with each of the plurality of mandrels that is located within the outermost mandrel cooperating with the sidewall of the immediately outer mandrel to define a chamber associated with the associated mandrel;
the upstream ends of the external flow channel and of each of the multiplicity of spiral grooves associated with each of the multiplicity of mandrels opening into the chamber associated with the associated mandrel;
a plurality of material inlets for receiving thermoplastic material under pressure, each of the material inlets being associated with a different one of the plurality of mandrels and being shaped to discharge a flow of thermoplastic material into the chamber associated with the different one of themandrels in a direction transverse to the axis, the material inlet associated with the outermost mandrel including a passage section extending through the sidewall of the casing, the material inlet associated with each of the plurality of mandrels that is within the outermost mandrel comprising alignable passage sections formed in and extending through the casing and each of the plurality ofmandrels that surrounds the mandrel, the passage sections of the plurality of material inlets being formed in predetermined locations and orientations such that the plurality of material inlets are simultaneously formed when the plurality of mandrels are arranged in the predetermined concentric arrangement;
a plurality of flow dividers, each of the flow dividers being associated with a different one of the plurality of mandrels, each of the flow dividers being positioned within the recess of the associated mandrel to confront the flow of thermoplastic material discharged from the material inlet associatedwith the associated mandrel, each of the flow dividers being shaped to divide the flow of thermoplastic material confronted by the flow divider into substantially equal flows in circumferentially opposing directions around the chamber of the associated mandrel; and, a former mounted to the casing in general alignment with the axis downstream of the flow channels for forming thermoplastic materials discharged from the downstream ends of the flow channels into a single tube with a preselected cross-section.
8. The blow head of claim 7 in which each of the plurality of mandrels comprises first and second axially opposing surface portions bounding the recess associated with the mandrel, the first surface portion beingsubstantially planar and perpendicular to the axis, the first surface portion being intersected by the external flow channel associated with the mandrel and the rear end portion of each of the multiplicity of spiral grooves associated with the mandrel, the second surface portion being substantially planar and inclined relative to the axis such that the chamber associated with the mandrel has a maximum axial length proximate to the inlet associated with the mandrel and a minimum axial length radially opposite from the inlet associated with the mandrel.
9. The blow head of claim 8 in which the flow divider associated with each of the mandrels is substantially heart shaped with a crux and a tip, the tip being positioned axially upstream from the crux.
10. The blow head of claim 7 in which each of the plurality of mandrels comprises a pair of axially opposing surface portions bounding the recess associated with the mandrel, the pair of surface portions being oriented relative to one another and shaped such that the chamber associated with the mandrel has a maximum axial length proximate to the inlet associated with the mandrel and a minimum axial length radially opposite from the inlet associated with the mandrel.
11. The blow head of claim 1 comprising means defining a passage extending through the innermost mandrel and the former for delivering air under pressure into the interior of the tube downstream of the former.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2038288 CA2038288A1 (en) | 1991-03-14 | 1991-03-14 | Distributing material in blow mold head |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2038288 CA2038288A1 (en) | 1991-03-14 | 1991-03-14 | Distributing material in blow mold head |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2038288A1 true CA2038288A1 (en) | 1992-09-15 |
Family
ID=4147189
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2038288 Abandoned CA2038288A1 (en) | 1991-03-14 | 1991-03-14 | Distributing material in blow mold head |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2038288A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6305922B1 (en) * | 1991-11-14 | 2001-10-23 | Davis-Standard Corporation | Spiral fed multi-layer tubular die |
-
1991
- 1991-03-14 CA CA 2038288 patent/CA2038288A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6305922B1 (en) * | 1991-11-14 | 2001-10-23 | Davis-Standard Corporation | Spiral fed multi-layer tubular die |
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