CA1036763A - Pipe die - Google Patents
Pipe dieInfo
- Publication number
- CA1036763A CA1036763A CA220,524A CA220524A CA1036763A CA 1036763 A CA1036763 A CA 1036763A CA 220524 A CA220524 A CA 220524A CA 1036763 A CA1036763 A CA 1036763A
- Authority
- CA
- Canada
- Prior art keywords
- die
- extrusion
- extrudate
- extrusion path
- path
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/25—Component parts, details or accessories; Auxiliary operations
- B29C48/30—Extrusion nozzles or dies
- B29C48/32—Extrusion nozzles or dies with annular openings, e.g. for forming tubular articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
- B29C48/03—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor characterised by the shape of the extruded material at extrusion
- B29C48/09—Articles with cross-sections having partially or fully enclosed cavities, e.g. pipes or channels
Abstract
ABSTRACT OF THE DISCLOSURE
A die suitable for the extrusion of pipes comprising an outer die body, an inner core, an extrusion path interme-diate said outer die body and inner core, said extrusion path including lower and upper reservoirs, a restricted choke section in the extrusion path intermediate said lower and upper reservoirs, and a helical chamber of diminishing inte-rior dimensions in the flow direction of an extrudate.
A die suitable for the extrusion of pipes comprising an outer die body, an inner core, an extrusion path interme-diate said outer die body and inner core, said extrusion path including lower and upper reservoirs, a restricted choke section in the extrusion path intermediate said lower and upper reservoirs, and a helical chamber of diminishing inte-rior dimensions in the flow direction of an extrudate.
Description
~036763 This invention relates to extrusion dies and more particularly, relates to extrusion dies suitable for the extrusion of pipes of an extrudable material and an improved method for extruding said pipes.
Generally, extrusion dies employed in the prior ¦ art include a die body, a central core, and an extrusion ¦ pàth intermediate the body portion and the central core.
The material is fed to the die wherein it follows the extru-sion path and is extruded at an annular orifice. The material forming the pipe may be any suitable extrudable plastic màterial; generally, suitable thermoplastic materials are well known to those skilled in the art.
` Prior art dies suitable for the extrusion of thermoplastic pipes have generally been of a spider design.
i In a spider design, the die includes a`plurality of members or spiders holding the central core concentric to the main land portion of the die, thus defining an annular extrusion path. When extruding the thermoplastic material through the die, the molten material is "split" by these spiders as it passes along an extrusion path between the central core and the main body portion. The splitting of the extrudate has caused problems due to the "memory" of the thermoplastic material whereby there is created what is known in the art as "weld lines n which remain present in the extruded pipe ` betraying the presence of the spiders. These weld lines represent lines of relative weakness and frequently, the j extruded pipe will suffer from a loss of burst strength along these weld lines.
The problem caused by the presence of the weld lines in the extruded pipe becomes more serious the thicker the wall of the extruded pipe is. For example, Canadian Standard Association specifications for 1~ inch polyethylene ~ .
- 1- ~ , pipe call for a wall thickness of .190 inch I .009 with a minimum pressure rate of 160 pounds per square inch.
To date, in order to produce pipe falling within the above specifications, an extrusion die must be operated at a relatively low output. For example, in the above given case of 1~ inch polyethylene pipe, the industry considers an extrusion output of 200 to 300 pounds per hour to be an optimum figure. Heretofore, any attempt to increase output has resulted in excessive back pressure since the extrusion dies employed are relatively small and thus have a high spe-cific resistance or K value. At a faster output, the high back pressure will cause variation in the wall thickness leading to unacceptable products.
A In all conventional die designs, the flow of ; thermoplastic material through the extrusion path must be divided at one or more points as it passes around the various mechanical components which support the center core or so-called mandrel within the die body. This division of the melt flow has heretofore required low extrusion output rates in order to adequately control the weld lines. Thus, the ; extrusion of thermoplastic pipes has called for a "trade-off"
between the quality of the plpe being produced and the rate of output.
According to one aspect of the present invention, there is provided an improved die wherein a higher output may be achieved while minimizing the problem of weld line ; weaknesses.
In one embodiment, there is provided a die suit-able for the extrusion of pipes comprising an outer die body, an inner core, an extrusion path intermediate said outer die body and inner core, said extrusion path including lower and upper reservoirs, a restricted choke section in the extrusion lQ36763 path intermediate said lower and upper reservoirs, and a helical chamber of diminishing interior dimensions in the flow direction of an extrudate.
In a further embodiment, in a method suitable for the extrusion of an extrudable material and including the step of extruding the material through a die lip, there is the improvement wherein the method includes the step of passing an extrudate through arcuate portions of an extrusion path, and subsequently passing the extrudate through a straight portion of the extrusion path.
Generally, the improved die includes a pair of body portions which may be called an upper body portion and a lower body portion. In this respect, the upper body por-tion is situated at the end at which the thermoplastic material is extruded through the die orifice to form the pipe while the lower body portion is adapted to receive the molten thermoplastic material from a source thereof. In construction of the die according to the present invention, conventional materials well known to those skilled in the art and presently employed in the manufacture of dies may be used.
The lower body portion of the die is "bottom fed"
from a source of thermoplastic material through a plurality of "fan-shaped" channels. In other words, a feeding conduit is employed which feeds the extrudate through a plurality of radially extending channels which are defined by diverg-ing walls. The fan-shaped channels are adapted to reduce the shear of the thermoplastic material when employing a high output rate as will be discussed in greater detail hereinafter. The walls defining the fan-shaped channels may have means associated therewith for connecting the lower body portion to the remaining components of the extrusion 10367~3 apparatus - for example, cooperative systems such as threaded bolts adapted to fit within the lower body portion may be employed. The fan-shaped channels may be formed as an integral part of the lower body portion or alternatively, they may be formed in conjunction with a suitable base plate I as will be discussed in greater detail hereinafter.
¦ The fan-shaped channels through which the material passes communicate with a lower annular reservoir. This annular reservoir, as will be seen from the drawings dis-cussed hereinbelow, may be formed completely within the lower body portion or alternatively~ may be formed as in the case of the fan-shaped channels in association with a base plate. Associated with the lower annular reservoir is an upper annular reservoir contained within the lower body por-tion; the two annular reservoirs are connected by a restricted passageway or choke section. The choke section, as the name implies chokes the melt flow to wipe out any memory retained ` ` therein.
In communication with the upper annular reservoir is a spiral chamber. The chamber is contained within the lower body portion and comprises a chamber spiralling about the central axis of the die. Preferably, this spiral cham-ber has wall portions of an arcuate configuratio~ and has a reducing dimension in the direction of flow of the thermo-plastic material.
The upper body portion, according to the novel die of the present invention, provides an annular extrudate channel in communication with the aforementioned spiral chamber of the lower body portion. The extrusion channel has a "wavy" configuration whereby the length of the travel of the extrudate therethrough is substantially longer than would be the case if the channels were of the normal 10367~3 "straight" configuration. By so doing, the upper body por-tion may be of a reduced overall length and still supply sufficient back pressure within the die. This enables an increased die gap to be used.
I The upper body portion may be connected to the ¦ lower body portion by any suitable means; such means may I include cooperating means such as threaded screws~ clips~! etc.
Conventional features of dies may be incorporated I 10 with the novel die of the present invention such as, for ! example, heater bands about the exterior. Also, the upper I and lower body portions will contain provision for the sup-j ply and outlet of a cooling fluid interiorly of the extru-sion channel.
Having thus generally described the invention, ~ reference will be made to the accompanying drawings illus-`~ trating an embodiment thereof, and in which:
j FIGURE 1 is a side elevational view of a conven-tional die;
FIGURE 2 is a side elevational view of one embodi-ment of the die according to the present invention;
FIGURE 3 is an end view of the die of Figure 2;
FIGURE 4 is a cross-sectional view of the die of Figure 2 taken along the lines 4-4 thereof; and FIGURE 5 is a cross-sectional view taken along the lines 5-5 of Figure 4.
Referring to Figure 1, there is illustrated therein a "conventional" die as used in the prior art for the extru-sion of pipe and which is generally designated by reference numeral 10; die 10 comprises body portion 12 surrounding a concentric core 14.
103676;~
Intermediate body 12 and core 14 is an annular extrusion path 16 into which a molten or at least semi-molten ¦ thermoplastic material is fed. It will be noted from Figure ¦ 1 that after the polymer has been fed to extrusion path 16, there is provided a chamber having a portion 18 of increasing dimensions followed by a portion 20 of decreasing dimensions.
! After passing through portions 18 and 20, the thermoplastic material is extruded through an annular orifice 22 to form the pipQ. A conduit 24 is provided interiorly of the die for feeding a gaseous material to the pipe as it is being formed.
Referring to Figure 2, there is illustrated the ~ improved die of the present invention which is designated ¦ generally by reference numeral 30. Die 30 includes an upper body portion 32 and a lower body portion 34 secured to a bottom plate 36 with anchor bolts 38. Located interiorly of upper portion 32 and lower outer portion 34 are upper and lower cores or land portions 40 and 42 respectively. As will be noted from Figure 2, there are also provided a plurality of anchor bolts 44 mounting portion 32 to portion 34.
Located circumferentially of die device 30 are a plurality of spaced apart adjustment bolts designated generally by refer-`~ ence numeral 46.
Within bottom plate 36 a die bore entry 46 communi-` cates with a plurality of fan-shaped channels designated generally by reference numeral 48. As may be seen from Figure 5, a plurality of raised land portions 47 provide an i interior space between lower body portion 34 and base plate 36 into a plurality of channels 48 which are "diverging" or of increasing dimension as they radiate out from die bore entry 46. As aforementioned, anchor bolts 38 extend through raised land portions 47.
~03676;~
Extending in an annular manner within lower body portion 34 is a lower annular chambèr 50. Lower chamber 50 in turn, leads to an upper chamber 54 via a restricted passageway 52 In the embodiment illustrated, the side walls of outer body portion 34 may converge in an angle of 30 degrees to form passageway 52 which is one-half inch long and has an internal diameter of .120 inches. Upper chamber 54 is formed by a diverging wall also having an angle of 30 degrees in the illustrated embodiment.
10Also within the lower body portion and communi-cating with upper chamber 54 is a spiral chamber generally designated by reference numeral 56. Spiral chamber 56 con-verges inwardly towards core 42 and may have, for example, ; portions having arcs of one-half inch radius. It will be noted that the spiral chamber becomes smaller or converges in the direction of movement of the polymer melt.
Formed intermediate of upper core 40 and upper outer body portion 32 is melt path 58 as illustrated in Figure 2. Path 58, as may be seen, has arcuate or wavy portions whereby the length of the path the thermoplastic material follows is substantially longer than would be the case if it were straight. The final portion 60 of path 58 is a substantially straight portion and opens to die gap 62.
As may be seen from Figures 2 and 3, a further conduit 66 extends through bottom plate 36, bottom core 42 and upper core 40, which conduit is adapted to receive a supply of gaseous material such as air.
According to the method of the present invention, an extrudable thermoplastic material of which the pipe is to be formed is fed to die bore entry 46. Such materials include, for example, polyethylene, polypropylene, etc.
In this respect, the thermoplastic material is fed in a ~36763 molten or at least semi-molten state and the temperature thereof will depend on those factors known to those skilled in the art.
After being fed through die bore entry 46, the thermoplastic material is distributed to a bottom chamber 50 through fan-shaped conduits 48. Due to the bottom feed through the fan-shaped conduits, a substantial portion of the "memory" of the molten thermoplastic material is removed.
From bottom chamber 50, the polymeric material is fed to upper chamber 54 through section 52 which acts as a choke to wipe out any memory still left in the polymer flow after passing through fan-shaped conduits 48.
Upper chamber 54 feeds the material through spiral chamber 56 which will compress the molten thermoplastic flow and at the same time, the spiral wall surface churns the outer surface of the flow melt. I
From spiral chambers 56, the thermoplastic material follows feed path 58 within the top outer body portion 32.
As may be seen from Figure 2, path 58 has arcuate portions therein wherein the thermoplastic material being extruded is forced to travel a greater distance through the conduit than would be the case if conduit 58 were substantially straight as is known in the prior art. It will be noted that portion 60 of conduit 58 is straight to provide a uniform surface finish for the extruded product.
Referring again to Figure 2, there is designated generally by reference numeral 64 heater bands which may be employed in conjunction with the extrusion die of the present invention in the manner well known to those skilled in the art.
In operation, by having the wavy land, the drag on the stream of molten thermoplastic material is increased and :10367~;~
the wavy land design also creates shear at the wall. The final straight portion 60 will iron out the stream of molten polymeric material.
¦ As aforementioned, the spiral bores are fan-shaped hence overheating will not occur at high output. After the ¦ molten polymer leaves the bottom reservoir and passes through the choke, the compression section will work to give shear at the wall.
It will be obvious that many changes and modifica-tions may be made to the above-described embodiments without departing from the spirit and scope of the invention. Thus, for example, the die has been illustrated as comprising upper and lower body portions 32 and 34 respectively. Alternatively, a single body portion could be provided; the two body portions allow the use of interchangeable top portion whereby, with the same lower body portion, pipes of different sizes could be extruded. Furthermore, some of the embodiments above-described may be used in dies suitable for purposes other than the extr~sion of pipes.
_ g_
Generally, extrusion dies employed in the prior ¦ art include a die body, a central core, and an extrusion ¦ pàth intermediate the body portion and the central core.
The material is fed to the die wherein it follows the extru-sion path and is extruded at an annular orifice. The material forming the pipe may be any suitable extrudable plastic màterial; generally, suitable thermoplastic materials are well known to those skilled in the art.
` Prior art dies suitable for the extrusion of thermoplastic pipes have generally been of a spider design.
i In a spider design, the die includes a`plurality of members or spiders holding the central core concentric to the main land portion of the die, thus defining an annular extrusion path. When extruding the thermoplastic material through the die, the molten material is "split" by these spiders as it passes along an extrusion path between the central core and the main body portion. The splitting of the extrudate has caused problems due to the "memory" of the thermoplastic material whereby there is created what is known in the art as "weld lines n which remain present in the extruded pipe ` betraying the presence of the spiders. These weld lines represent lines of relative weakness and frequently, the j extruded pipe will suffer from a loss of burst strength along these weld lines.
The problem caused by the presence of the weld lines in the extruded pipe becomes more serious the thicker the wall of the extruded pipe is. For example, Canadian Standard Association specifications for 1~ inch polyethylene ~ .
- 1- ~ , pipe call for a wall thickness of .190 inch I .009 with a minimum pressure rate of 160 pounds per square inch.
To date, in order to produce pipe falling within the above specifications, an extrusion die must be operated at a relatively low output. For example, in the above given case of 1~ inch polyethylene pipe, the industry considers an extrusion output of 200 to 300 pounds per hour to be an optimum figure. Heretofore, any attempt to increase output has resulted in excessive back pressure since the extrusion dies employed are relatively small and thus have a high spe-cific resistance or K value. At a faster output, the high back pressure will cause variation in the wall thickness leading to unacceptable products.
A In all conventional die designs, the flow of ; thermoplastic material through the extrusion path must be divided at one or more points as it passes around the various mechanical components which support the center core or so-called mandrel within the die body. This division of the melt flow has heretofore required low extrusion output rates in order to adequately control the weld lines. Thus, the ; extrusion of thermoplastic pipes has called for a "trade-off"
between the quality of the plpe being produced and the rate of output.
According to one aspect of the present invention, there is provided an improved die wherein a higher output may be achieved while minimizing the problem of weld line ; weaknesses.
In one embodiment, there is provided a die suit-able for the extrusion of pipes comprising an outer die body, an inner core, an extrusion path intermediate said outer die body and inner core, said extrusion path including lower and upper reservoirs, a restricted choke section in the extrusion lQ36763 path intermediate said lower and upper reservoirs, and a helical chamber of diminishing interior dimensions in the flow direction of an extrudate.
In a further embodiment, in a method suitable for the extrusion of an extrudable material and including the step of extruding the material through a die lip, there is the improvement wherein the method includes the step of passing an extrudate through arcuate portions of an extrusion path, and subsequently passing the extrudate through a straight portion of the extrusion path.
Generally, the improved die includes a pair of body portions which may be called an upper body portion and a lower body portion. In this respect, the upper body por-tion is situated at the end at which the thermoplastic material is extruded through the die orifice to form the pipe while the lower body portion is adapted to receive the molten thermoplastic material from a source thereof. In construction of the die according to the present invention, conventional materials well known to those skilled in the art and presently employed in the manufacture of dies may be used.
The lower body portion of the die is "bottom fed"
from a source of thermoplastic material through a plurality of "fan-shaped" channels. In other words, a feeding conduit is employed which feeds the extrudate through a plurality of radially extending channels which are defined by diverg-ing walls. The fan-shaped channels are adapted to reduce the shear of the thermoplastic material when employing a high output rate as will be discussed in greater detail hereinafter. The walls defining the fan-shaped channels may have means associated therewith for connecting the lower body portion to the remaining components of the extrusion 10367~3 apparatus - for example, cooperative systems such as threaded bolts adapted to fit within the lower body portion may be employed. The fan-shaped channels may be formed as an integral part of the lower body portion or alternatively, they may be formed in conjunction with a suitable base plate I as will be discussed in greater detail hereinafter.
¦ The fan-shaped channels through which the material passes communicate with a lower annular reservoir. This annular reservoir, as will be seen from the drawings dis-cussed hereinbelow, may be formed completely within the lower body portion or alternatively~ may be formed as in the case of the fan-shaped channels in association with a base plate. Associated with the lower annular reservoir is an upper annular reservoir contained within the lower body por-tion; the two annular reservoirs are connected by a restricted passageway or choke section. The choke section, as the name implies chokes the melt flow to wipe out any memory retained ` ` therein.
In communication with the upper annular reservoir is a spiral chamber. The chamber is contained within the lower body portion and comprises a chamber spiralling about the central axis of the die. Preferably, this spiral cham-ber has wall portions of an arcuate configuratio~ and has a reducing dimension in the direction of flow of the thermo-plastic material.
The upper body portion, according to the novel die of the present invention, provides an annular extrudate channel in communication with the aforementioned spiral chamber of the lower body portion. The extrusion channel has a "wavy" configuration whereby the length of the travel of the extrudate therethrough is substantially longer than would be the case if the channels were of the normal 10367~3 "straight" configuration. By so doing, the upper body por-tion may be of a reduced overall length and still supply sufficient back pressure within the die. This enables an increased die gap to be used.
I The upper body portion may be connected to the ¦ lower body portion by any suitable means; such means may I include cooperating means such as threaded screws~ clips~! etc.
Conventional features of dies may be incorporated I 10 with the novel die of the present invention such as, for ! example, heater bands about the exterior. Also, the upper I and lower body portions will contain provision for the sup-j ply and outlet of a cooling fluid interiorly of the extru-sion channel.
Having thus generally described the invention, ~ reference will be made to the accompanying drawings illus-`~ trating an embodiment thereof, and in which:
j FIGURE 1 is a side elevational view of a conven-tional die;
FIGURE 2 is a side elevational view of one embodi-ment of the die according to the present invention;
FIGURE 3 is an end view of the die of Figure 2;
FIGURE 4 is a cross-sectional view of the die of Figure 2 taken along the lines 4-4 thereof; and FIGURE 5 is a cross-sectional view taken along the lines 5-5 of Figure 4.
Referring to Figure 1, there is illustrated therein a "conventional" die as used in the prior art for the extru-sion of pipe and which is generally designated by reference numeral 10; die 10 comprises body portion 12 surrounding a concentric core 14.
103676;~
Intermediate body 12 and core 14 is an annular extrusion path 16 into which a molten or at least semi-molten ¦ thermoplastic material is fed. It will be noted from Figure ¦ 1 that after the polymer has been fed to extrusion path 16, there is provided a chamber having a portion 18 of increasing dimensions followed by a portion 20 of decreasing dimensions.
! After passing through portions 18 and 20, the thermoplastic material is extruded through an annular orifice 22 to form the pipQ. A conduit 24 is provided interiorly of the die for feeding a gaseous material to the pipe as it is being formed.
Referring to Figure 2, there is illustrated the ~ improved die of the present invention which is designated ¦ generally by reference numeral 30. Die 30 includes an upper body portion 32 and a lower body portion 34 secured to a bottom plate 36 with anchor bolts 38. Located interiorly of upper portion 32 and lower outer portion 34 are upper and lower cores or land portions 40 and 42 respectively. As will be noted from Figure 2, there are also provided a plurality of anchor bolts 44 mounting portion 32 to portion 34.
Located circumferentially of die device 30 are a plurality of spaced apart adjustment bolts designated generally by refer-`~ ence numeral 46.
Within bottom plate 36 a die bore entry 46 communi-` cates with a plurality of fan-shaped channels designated generally by reference numeral 48. As may be seen from Figure 5, a plurality of raised land portions 47 provide an i interior space between lower body portion 34 and base plate 36 into a plurality of channels 48 which are "diverging" or of increasing dimension as they radiate out from die bore entry 46. As aforementioned, anchor bolts 38 extend through raised land portions 47.
~03676;~
Extending in an annular manner within lower body portion 34 is a lower annular chambèr 50. Lower chamber 50 in turn, leads to an upper chamber 54 via a restricted passageway 52 In the embodiment illustrated, the side walls of outer body portion 34 may converge in an angle of 30 degrees to form passageway 52 which is one-half inch long and has an internal diameter of .120 inches. Upper chamber 54 is formed by a diverging wall also having an angle of 30 degrees in the illustrated embodiment.
10Also within the lower body portion and communi-cating with upper chamber 54 is a spiral chamber generally designated by reference numeral 56. Spiral chamber 56 con-verges inwardly towards core 42 and may have, for example, ; portions having arcs of one-half inch radius. It will be noted that the spiral chamber becomes smaller or converges in the direction of movement of the polymer melt.
Formed intermediate of upper core 40 and upper outer body portion 32 is melt path 58 as illustrated in Figure 2. Path 58, as may be seen, has arcuate or wavy portions whereby the length of the path the thermoplastic material follows is substantially longer than would be the case if it were straight. The final portion 60 of path 58 is a substantially straight portion and opens to die gap 62.
As may be seen from Figures 2 and 3, a further conduit 66 extends through bottom plate 36, bottom core 42 and upper core 40, which conduit is adapted to receive a supply of gaseous material such as air.
According to the method of the present invention, an extrudable thermoplastic material of which the pipe is to be formed is fed to die bore entry 46. Such materials include, for example, polyethylene, polypropylene, etc.
In this respect, the thermoplastic material is fed in a ~36763 molten or at least semi-molten state and the temperature thereof will depend on those factors known to those skilled in the art.
After being fed through die bore entry 46, the thermoplastic material is distributed to a bottom chamber 50 through fan-shaped conduits 48. Due to the bottom feed through the fan-shaped conduits, a substantial portion of the "memory" of the molten thermoplastic material is removed.
From bottom chamber 50, the polymeric material is fed to upper chamber 54 through section 52 which acts as a choke to wipe out any memory still left in the polymer flow after passing through fan-shaped conduits 48.
Upper chamber 54 feeds the material through spiral chamber 56 which will compress the molten thermoplastic flow and at the same time, the spiral wall surface churns the outer surface of the flow melt. I
From spiral chambers 56, the thermoplastic material follows feed path 58 within the top outer body portion 32.
As may be seen from Figure 2, path 58 has arcuate portions therein wherein the thermoplastic material being extruded is forced to travel a greater distance through the conduit than would be the case if conduit 58 were substantially straight as is known in the prior art. It will be noted that portion 60 of conduit 58 is straight to provide a uniform surface finish for the extruded product.
Referring again to Figure 2, there is designated generally by reference numeral 64 heater bands which may be employed in conjunction with the extrusion die of the present invention in the manner well known to those skilled in the art.
In operation, by having the wavy land, the drag on the stream of molten thermoplastic material is increased and :10367~;~
the wavy land design also creates shear at the wall. The final straight portion 60 will iron out the stream of molten polymeric material.
¦ As aforementioned, the spiral bores are fan-shaped hence overheating will not occur at high output. After the ¦ molten polymer leaves the bottom reservoir and passes through the choke, the compression section will work to give shear at the wall.
It will be obvious that many changes and modifica-tions may be made to the above-described embodiments without departing from the spirit and scope of the invention. Thus, for example, the die has been illustrated as comprising upper and lower body portions 32 and 34 respectively. Alternatively, a single body portion could be provided; the two body portions allow the use of interchangeable top portion whereby, with the same lower body portion, pipes of different sizes could be extruded. Furthermore, some of the embodiments above-described may be used in dies suitable for purposes other than the extr~sion of pipes.
_ g_
Claims (11)
1. A die suitable for the extrusion of pipes comprising an outer die body, an inner core, an extrusion path interme-diate said outer die body and inner core, said extrusion path including lower and upper reservoirs, a restricted choke section in the extrusion path intermediate said lower and upper reservoirs, and a helical chamber of diminishing interior dimensions in the flow direction of an extrudate.
2. The die of claim 1 including an upper die body and a lower die body.
3. The die of claim 1, further characterized by including bottom feed means, and a plurality of fan-shaped diverging channels communicating with said lower reservoir.
4. The die of claim 3, including a bottom plate, said fan-shaped diverging channels being formed in association with said bottom plate and said die body.
5. The die of claim 1, 2 or 3, further comprising a centrally located conduit interiorly of said inner core.
6. The die of claim 1, 2 or 3, wherein said extrusion path has at least one arcuate portion prior to a die lip.
7. The die of claim 1, 2 or 3, further including means for supplying heat to said die.
8. In an extrusion die suitable for the extrusion of pipes of a plastic material and having an extrusion path through which an extrudate is extruded, the improvement wherein said extrusion path includes a lower reservoir, an upper reservoir, a restricted choke section providing communication between said lower and upper reservoirs, and a helical chamber of diminishing interior dimen-sions in the flow direction of the extrudate communicating with said upper reservoir.
9. The die of claim 1 or 8 wherein said extrusion path terminates in a die lip, the extrusion path further including a plurality of arcuate portions extending from said helical chamber and terminating in a straight portion at the die lip.
10. The die of claim 8 including means for feeding the extrudate to said lower reservoir, said means comprising a plurality of diverging channels radiating from a die bore entry.
11. In a method of manufacture of plastic pipes wherein a plastic extrudate is extruded through a die, the improvement comprising the step of extruding the extrudate through the die of claim 1 or 8.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA220,524A CA1036763A (en) | 1975-02-20 | 1975-02-20 | Pipe die |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA220,524A CA1036763A (en) | 1975-02-20 | 1975-02-20 | Pipe die |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1036763A true CA1036763A (en) | 1978-08-22 |
Family
ID=4102336
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA220,524A Expired CA1036763A (en) | 1975-02-20 | 1975-02-20 | Pipe die |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1036763A (en) |
-
1975
- 1975-02-20 CA CA220,524A patent/CA1036763A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
Effective date: 19950822 |
|
| MKEX | Expiry |
Effective date: 19950822 |