CA1272362A - Turbulent flow gate for the injection molding of tubular parts, including parisons suitable for blow molding - Google Patents
Turbulent flow gate for the injection molding of tubular parts, including parisons suitable for blow moldingInfo
- Publication number
- CA1272362A CA1272362A CA000545694A CA545694A CA1272362A CA 1272362 A CA1272362 A CA 1272362A CA 000545694 A CA000545694 A CA 000545694A CA 545694 A CA545694 A CA 545694A CA 1272362 A CA1272362 A CA 1272362A
- Authority
- CA
- Canada
- Prior art keywords
- passage
- gate
- annular
- mixing chamber
- plastic material
- 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
Landscapes
- Blow-Moulding Or Thermoforming Of Plastics Or The Like (AREA)
Abstract
Abstract of the Disclosure Injection molding apparatus is disclosed in which weld lines are removed from a part, such as a parison, which weld lines are caused by the interruption or split-ting of the flow of plastic material around core support pins or the like by the provision of an annular mixing chamber which opens into the plastic material flow pas-sage. The plastic material is caused to move radially into the mixing chamber where it is spread by reason of the increasing volume encountered, accompanied by a rever-sal of flow radially inwardly into an annular injection gate. The movement of plastic material within the chamber and the resultant increase in temperature by reason of shear, eliminates the weld lines which have been formed in the material by reason of the splitting of flow around the pins.
Description
~723~:
PQE~ 020 P2 -1-TURBULENT FLOW GATE FOR THE
INJECTIOM MOLDING OF TUBULAR PARTS, I~CLUDING PARISONS SUITABLE FOR F~LOW MOLDING
_ Back~round of the_Invention It has long been recognized that obstructions upstream of a gate, in the molding of tubular parts, such as parisons, about a core or pin, can result in flow lines in the part. In the case of a parison, the flow lines are carried to the blown part. Such flow lines are caused by the parting of the plastic material, such as a polymer, as it flows around an obstruction, such as a core-support pin, positioned upstream of the orifice or gate. At the least~ flow lines result in poor appearance of the blown piece. However, such lines can severely impair the strength of a finished part. Strength impairment is par-ticularly critical in the forming of parisons from thermo-plastic polymers which have high melt viscosities and which, when parted, do not readily flow or mix together, or rejoin, in a laminar state. While the finished part may present only a slight marring when physically examined, with many such polymer materials it has been found that the finished part is also severely weakened along these lines and can lead to premature failure. Such premature failure is particularly critical in blown auto motive bellows and boots which are subject to mechanical as well as environmental stresses.
The problem is particularly acute in the manufac-ture of boots and bellows and the like from parisons which are formed about cores, where the latter are supported by conventional radially extendiny core support pins at the inlet end of the mold. There accordingly exists a need PQB 02~ P~ -2-for apparatus and method for the remixing of such polymer material on the downstream side of such core support pins to eliminate such weld lines and lines of iMperfection or weakness in the completed part.
Sum~y of the Invention This invention relates to the molding o~ tubular parts and more particularly to the molding of parisons ~or use in the blow molding of finished parts, such as boots and bellows for automo~ive applications and the like.
More particularly, the invention relates ~o the elimina-tion of weld line problems caused by upstream obstructions in the polymer passageway, such as core support pins.
It is believed that the sensitivity of certain polymers to reform or reweld after having been separated by flow around a core pin or the like is due at least in parS to the chilling or surface cooling of the polymer, such that it does not readily reweld downstream of the pin. As an example, while the polymer may be injected at 450 F, the metal making up the mold and mold parts may be substantially cooler, such as 340, thus providing a chil-ling effect to the surface of the material where it has been parted.
It has been found that the material may be remixed to eliminate the weld line or line of disconti-nuity by causing the material to undergo shear, such as by causing the material to be folded back upon itself. The added turbulence and resulting heat dissipates the rela-tive chill at the contact line, and permits the remixing of the polymer across the line boundaries, thereby reweld-ing the material as a homogeneous massD
More particularly, the invention is adapted to .. . . . .
,.~ . , ' , , - : ' , ' ' ~23~
the manufacture of parisons, to eliminate weld lines which are caused by the interruption or splitting of the flow of the plastic melt, between the injector and the gate open-ing into the parison cavity, by reason of one or more interposed core support pins which extend through the polymer passageway leading to the gate, upstream of the gate. A generally radiall~ formed remixing chamber com-municates at its inner circumference with the gate and with a generally radially outwardly directed flow passage downstream of the core support pins. The plastic material flows outwardly into the chamber into an expanding volu~e, where the flow is reversed accompanied by radially inward flow through into a contracting volume leading to the gate. The resulting shear has a tendency to increase the temperature of the polymer, and the resulting mixing by reason of the flow of the plastic first radially outwardly into the mixing chamber and then radially inwardly to the gate, effectively remixes the material across the weld lines so that the material entering the parison cavity through the gate is circumferentially homogeneous.
It is accordingly an important object of this invention to provide for the remixing of plastic material leadiny to an extrusion gate, in the manufacture of a parison.
Another object of the invention is the provision of injection apparatus and method in which a generally radially directed remixing chamber is positioned inwardly of an annular gate to a parison cavity.
Another object of the invention is the provision of molding apparatus in which weld seams otherwise caused by the division of flow of a polymer material to a cavity ~27;~36~
are eliminated by remixing.
A still further object of the invention is the remixing of plastic material which has been flow divided, in a generally radially arranged cavity, for delivery of such remixed material to a parison cavity through a gate free of weld lines or lines or weaknesses.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.
Brief Description of the Drawings Fig. 1 is a fragmentary sectional view through a die head for the injection molding of parisons, incorpora-ting a mixing chamber in accordance with this invention;
and Fig. 2 is a transverse section looking generally along the line 2--2 of Fig. 1.
Description of the Preferred Embodiment Referring to Fig. 1, a center fed or mold die head is illustrated generally at 10, as supporting a core
PQE~ 020 P2 -1-TURBULENT FLOW GATE FOR THE
INJECTIOM MOLDING OF TUBULAR PARTS, I~CLUDING PARISONS SUITABLE FOR F~LOW MOLDING
_ Back~round of the_Invention It has long been recognized that obstructions upstream of a gate, in the molding of tubular parts, such as parisons, about a core or pin, can result in flow lines in the part. In the case of a parison, the flow lines are carried to the blown part. Such flow lines are caused by the parting of the plastic material, such as a polymer, as it flows around an obstruction, such as a core-support pin, positioned upstream of the orifice or gate. At the least~ flow lines result in poor appearance of the blown piece. However, such lines can severely impair the strength of a finished part. Strength impairment is par-ticularly critical in the forming of parisons from thermo-plastic polymers which have high melt viscosities and which, when parted, do not readily flow or mix together, or rejoin, in a laminar state. While the finished part may present only a slight marring when physically examined, with many such polymer materials it has been found that the finished part is also severely weakened along these lines and can lead to premature failure. Such premature failure is particularly critical in blown auto motive bellows and boots which are subject to mechanical as well as environmental stresses.
The problem is particularly acute in the manufac-ture of boots and bellows and the like from parisons which are formed about cores, where the latter are supported by conventional radially extendiny core support pins at the inlet end of the mold. There accordingly exists a need PQB 02~ P~ -2-for apparatus and method for the remixing of such polymer material on the downstream side of such core support pins to eliminate such weld lines and lines of iMperfection or weakness in the completed part.
Sum~y of the Invention This invention relates to the molding o~ tubular parts and more particularly to the molding of parisons ~or use in the blow molding of finished parts, such as boots and bellows for automo~ive applications and the like.
More particularly, the invention relates ~o the elimina-tion of weld line problems caused by upstream obstructions in the polymer passageway, such as core support pins.
It is believed that the sensitivity of certain polymers to reform or reweld after having been separated by flow around a core pin or the like is due at least in parS to the chilling or surface cooling of the polymer, such that it does not readily reweld downstream of the pin. As an example, while the polymer may be injected at 450 F, the metal making up the mold and mold parts may be substantially cooler, such as 340, thus providing a chil-ling effect to the surface of the material where it has been parted.
It has been found that the material may be remixed to eliminate the weld line or line of disconti-nuity by causing the material to undergo shear, such as by causing the material to be folded back upon itself. The added turbulence and resulting heat dissipates the rela-tive chill at the contact line, and permits the remixing of the polymer across the line boundaries, thereby reweld-ing the material as a homogeneous massD
More particularly, the invention is adapted to .. . . . .
,.~ . , ' , , - : ' , ' ' ~23~
the manufacture of parisons, to eliminate weld lines which are caused by the interruption or splitting of the flow of the plastic melt, between the injector and the gate open-ing into the parison cavity, by reason of one or more interposed core support pins which extend through the polymer passageway leading to the gate, upstream of the gate. A generally radiall~ formed remixing chamber com-municates at its inner circumference with the gate and with a generally radially outwardly directed flow passage downstream of the core support pins. The plastic material flows outwardly into the chamber into an expanding volu~e, where the flow is reversed accompanied by radially inward flow through into a contracting volume leading to the gate. The resulting shear has a tendency to increase the temperature of the polymer, and the resulting mixing by reason of the flow of the plastic first radially outwardly into the mixing chamber and then radially inwardly to the gate, effectively remixes the material across the weld lines so that the material entering the parison cavity through the gate is circumferentially homogeneous.
It is accordingly an important object of this invention to provide for the remixing of plastic material leadiny to an extrusion gate, in the manufacture of a parison.
Another object of the invention is the provision of injection apparatus and method in which a generally radially directed remixing chamber is positioned inwardly of an annular gate to a parison cavity.
Another object of the invention is the provision of molding apparatus in which weld seams otherwise caused by the division of flow of a polymer material to a cavity ~27;~36~
are eliminated by remixing.
A still further object of the invention is the remixing of plastic material which has been flow divided, in a generally radially arranged cavity, for delivery of such remixed material to a parison cavity through a gate free of weld lines or lines or weaknesses.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.
Brief Description of the Drawings Fig. 1 is a fragmentary sectional view through a die head for the injection molding of parisons, incorpora-ting a mixing chamber in accordance with this invention;
and Fig. 2 is a transverse section looking generally along the line 2--2 of Fig. 1.
Description of the Preferred Embodiment Referring to Fig. 1, a center fed or mold die head is illustrated generally at 10, as supporting a core
2~ pin 12, which core pin extends axially from the head 10 into the interior of a mold 15, for the extrusion or injection forming of a parison 20. The die head 10 is formed with a central melt passageway 22, which passageway is divided by the rear conical portion 24 of the core pin 12 into a circumferentially annular diverging passageway section 25 and to a cylindrical annular passageway section 26.
The core pin 12 itself is conventionally sup-ported within the mold 15 on generally radially extending core support pins 30. The core support pins 30, which maybe four in number, are shown in Fig. 2 as supporting the .
. ~ :
core pin generally centrally of the passageway 26 and centrally of the mold cavity 3? defined between the body of the core pin 12 and the mold 15. It will be understood that the central or inlet passage 22 is fed by a polymer resin or me.lt through a suitable adapter from a plastic inject~ion machine, to form the parison 20. Center-fed molds of the kind shown are in common use s:ince they have the advantage of providing a rather uniform distribution of the plastic melt around the core. However, the flow of polymer material is caused to be divided as it flows around the core support pins 30 and to the downstream side of the pins as defined by the passageway section 26.
The invention provides apparatus which causes the remixing of the polymer material downstream of the core pins 30 to eliminate the weld line which would otherwise be formed in the polymer material, as previously noted.
Por this purpose a generally radially-extending mixing chamber 40 is formed in the head 10 between the passageway 26 and an axially tapered gate 42 leading in~o.the mold 15. The chamber 40 is connected to the passageway portion 36 through a radially out-turned section 45, which directs the polymer material radially outwardly into the cavity 40. As shown in Fig. 1, the mixing chamber defined by the cavity 40 i5 annular and is generally rectangular in cross section, and communicates with the polymer at an inlet region 47 at the outer end of the radial section 4S and communicates with the gate 42 at an outlet portion 48 axially spaced from the inlet port or region 47.
It will be noted that the mixing chamber 40 has a
The core pin 12 itself is conventionally sup-ported within the mold 15 on generally radially extending core support pins 30. The core support pins 30, which maybe four in number, are shown in Fig. 2 as supporting the .
. ~ :
core pin generally centrally of the passageway 26 and centrally of the mold cavity 3? defined between the body of the core pin 12 and the mold 15. It will be understood that the central or inlet passage 22 is fed by a polymer resin or me.lt through a suitable adapter from a plastic inject~ion machine, to form the parison 20. Center-fed molds of the kind shown are in common use s:ince they have the advantage of providing a rather uniform distribution of the plastic melt around the core. However, the flow of polymer material is caused to be divided as it flows around the core support pins 30 and to the downstream side of the pins as defined by the passageway section 26.
The invention provides apparatus which causes the remixing of the polymer material downstream of the core pins 30 to eliminate the weld line which would otherwise be formed in the polymer material, as previously noted.
Por this purpose a generally radially-extending mixing chamber 40 is formed in the head 10 between the passageway 26 and an axially tapered gate 42 leading in~o.the mold 15. The chamber 40 is connected to the passageway portion 36 through a radially out-turned section 45, which directs the polymer material radially outwardly into the cavity 40. As shown in Fig. 1, the mixing chamber defined by the cavity 40 i5 annular and is generally rectangular in cross section, and communicates with the polymer at an inlet region 47 at the outer end of the radial section 4S and communicates with the gate 42 at an outlet portion 48 axially spaced from the inlet port or region 47.
It will be noted that the mixing chamber 40 has a
3~ volume which is at least twice the volume of the flow channel defined by the passageway section 26 downstream of '' ' . ' ' :.. ' ` :
~2~3~
P~B 020 P2 -6-the impediments or pins 30. Further, it defines an ofset which at least equals the radial dimensions of the channel portions 25 and 26, and in effect provides a region of expanding volume as the plastic material enters through the entrance region 47 and flows radially outwardly to the outer wall 50. The direction of movement o:E the material is reversed within the chamber 4~ as the material proceeds to the outlet region 48 and to the gate ~2 for in~ection into the mold cavity 3Z to form the parison 20. The ~ expanding volume of the chamber 40 in the radially outward direction, and the corresponding contracting volume occu-pied by the polymer material as i~s direction of flow reverses and moves radially inwardly effectively remixes the ma~erial across the weld lines or lines of parting, caused by the core pins 30. Further, the move~ent within the chamber 40 induces frictional heat into the material by reason of the shear on the material which overcomes the resistance of the material to reweld and reform across the shear lines otherwise caused by the chilling at the pins 30. When the material exits the chamber 40 through the region 48 and gate ~2, it has been thoroughly remixed and no weld lines are visible thereafter.
While the method herein described, and the form of apparatus for carrying this method into effect, con-stitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.
What is claimed is:
, .
.
: .
~2~3~
P~B 020 P2 -6-the impediments or pins 30. Further, it defines an ofset which at least equals the radial dimensions of the channel portions 25 and 26, and in effect provides a region of expanding volume as the plastic material enters through the entrance region 47 and flows radially outwardly to the outer wall 50. The direction of movement o:E the material is reversed within the chamber 4~ as the material proceeds to the outlet region 48 and to the gate ~2 for in~ection into the mold cavity 3Z to form the parison 20. The ~ expanding volume of the chamber 40 in the radially outward direction, and the corresponding contracting volume occu-pied by the polymer material as i~s direction of flow reverses and moves radially inwardly effectively remixes the ma~erial across the weld lines or lines of parting, caused by the core pins 30. Further, the move~ent within the chamber 40 induces frictional heat into the material by reason of the shear on the material which overcomes the resistance of the material to reweld and reform across the shear lines otherwise caused by the chilling at the pins 30. When the material exits the chamber 40 through the region 48 and gate ~2, it has been thoroughly remixed and no weld lines are visible thereafter.
While the method herein described, and the form of apparatus for carrying this method into effect, con-stitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.
What is claimed is:
, .
.
: .
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Injection apparatus for forming a molded part such as a parison free of weld lines in a mold cavity about a core by injection of plastic material into said cavity through an annular gate surrounding said core from an annular lead-in passage, and in which said core is supported on one or more core pins, which core pins extend through the annular lead-in passage and cause a parting of the plastic material flowing through said passage to said gate, the improvement comprising:
means in said injection apparatus between said passage and said gate defining an annular mixing chamber opening into said passage at a radially inner portion of said chamber, said mixing chamber communicating with said gate at a radially inner portion thereof axially spaced from said annular passageway, said mixing chamber having a volume which is at least twice the volume defined by said annular lead-in passage downstream of said core pins, providing for a volumetric expansion and dwell of plastic material entering therein from said passage accompanied by reversal of direction of movement of said material creating shear in said material and the remixing of said material across the weld lines formed by said core support pins.
means in said injection apparatus between said passage and said gate defining an annular mixing chamber opening into said passage at a radially inner portion of said chamber, said mixing chamber communicating with said gate at a radially inner portion thereof axially spaced from said annular passageway, said mixing chamber having a volume which is at least twice the volume defined by said annular lead-in passage downstream of said core pins, providing for a volumetric expansion and dwell of plastic material entering therein from said passage accompanied by reversal of direction of movement of said material creating shear in said material and the remixing of said material across the weld lines formed by said core support pins.
2. The injection apparatus of claim 1 in which said mixing chamber is generally rectangular in cross-section and in which said annular passage leads radially into said mixing chamber and in which said gate leads axially from said chamber adjacent an inner radius thereof.
3. The injection apparatus of claim 1 in which said lead-in passage directs plastic material radially into said chamber.
4. Injection apparatus for forming a parison free of weld lines in a mold cavity about a core by injection of plastic material into said cavity through an annular gate surrounding said core from a lead-in passage, and in which said core is supported on one or more pins, which pins extend through the lead-in passage and cause a parting of the plastic material flowing through said passage to said gate, the improvement comprising:
means in said injection apparatus between said passage and said gate defining an annular mixing chamber opening into said passage at a radially inner portion of said chamber, said mixing chamber communicating with said gate at a radially inner portion thereof axially spaced from said annular passageway, said mixing chamber providing for a radial outflow of plastic material entering therein from said passage accompanied by reversal of direction of flow of said material to said gate creating shear in said material and the remixing of said material across the weld lines formed by said core support pins.
means in said injection apparatus between said passage and said gate defining an annular mixing chamber opening into said passage at a radially inner portion of said chamber, said mixing chamber communicating with said gate at a radially inner portion thereof axially spaced from said annular passageway, said mixing chamber providing for a radial outflow of plastic material entering therein from said passage accompanied by reversal of direction of flow of said material to said gate creating shear in said material and the remixing of said material across the weld lines formed by said core support pins.
5. In an apparatus for the delivery of plastic material to a die, in which a die head body is formed with an annular flow passage leading to a gate , and at least one flow dividing impediment is positioned upstream of said gate in said flow passage, the improvement for eliminating the weld line which is otherwise formed by said impediment, comprising:
means in said body adjacent said gate forming an annular mixing chamber extending generally radially outwardly of said passage, said mixing chamber communicating with said gate at a radially inner portion of said passage, said annular passage being configured to direct plastic material radially outwardly into said chamber, said mixing chamber providing for the radial outflow of plastic material entering therein from said passageway accompanied by reversal of direction of flow of said material to said gate creating shear in said material and remixing of said material across the weld line formed by said flow-dividing impediment.
means in said body adjacent said gate forming an annular mixing chamber extending generally radially outwardly of said passage, said mixing chamber communicating with said gate at a radially inner portion of said passage, said annular passage being configured to direct plastic material radially outwardly into said chamber, said mixing chamber providing for the radial outflow of plastic material entering therein from said passageway accompanied by reversal of direction of flow of said material to said gate creating shear in said material and remixing of said material across the weld line formed by said flow-dividing impediment.
6. The apparatus of claim 5 in which said mixing chamber has a volume at least twice the volume defined by said annular passage downstream of said flow dividing impediment.
7. In the delivery of molten plastic material to a mold in the manufacture of parisons for the blow molding of tubular plastic products in which the plastic material is delivered to the mold through a passageway, and in which the material is parted by an impediment in the passageway, the method of mixing said material downstream of said impediment to eliminate the weld line otherwise formed in the products by the impediment, comprising the steps of causing said material downstream of said impediment and prior to delivery thereof to said mold to move in a direction generally radially outwardly into an annular mixing chamber which has increasing internal volume with increasing radial dimensions, causing said material to reverse direction in said chamber and flow radially inwardly upon itself while within said chamber to a constricted exit region at a radially inner portion of said chamber, whereby the movement of said material into an increasing volume followed by radial inflow upon itself induces frictional heat and causes remixing of said material across the weld line formed by the flow-dividing impediment.
8. The method of claim 7 in which said material is caused to move into a chamber which has at least twice the volume defined by the passageway immediaely downstream of said impediment.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000545694A CA1272362A (en) | 1987-08-31 | 1987-08-31 | Turbulent flow gate for the injection molding of tubular parts, including parisons suitable for blow molding |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000545694A CA1272362A (en) | 1987-08-31 | 1987-08-31 | Turbulent flow gate for the injection molding of tubular parts, including parisons suitable for blow molding |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1272362A true CA1272362A (en) | 1990-08-07 |
Family
ID=4136364
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000545694A Expired - Fee Related CA1272362A (en) | 1987-08-31 | 1987-08-31 | Turbulent flow gate for the injection molding of tubular parts, including parisons suitable for blow molding |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1272362A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3000576B1 (en) | 2014-09-26 | 2018-05-09 | Michel Thorsten | Mould with roughness at the weldlinewall |
-
1987
- 1987-08-31 CA CA000545694A patent/CA1272362A/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3000576B1 (en) | 2014-09-26 | 2018-05-09 | Michel Thorsten | Mould with roughness at the weldlinewall |
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| Date | Code | Title | Description |
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| MKLA | Lapsed |