The present disclosure generally relates to extrusion devices having an extrusion die and more particularly to extrusion dies for forming tubular articles.
In conventional extrusion processes, molten polymer materials are extruded through an extruder die for forming extrusions of various shapes and/or configurations. For example, in the extrusion of polymer tubes, a molten polymeric material typically is extruded through an extrusion head that includes a die bushing and a die pin so that a hollow, tubular extrusion is formed. In general, a tubular extrusion is formed by feeding polymeric material into an extruder where it is subjected to high temperatures to create a molten substrate known as a melt. The melt proceeds through an extrusion head, at the end of which the melt passes through a die. The die contains the circular cross-sectional profile shape to be extruded. The melt hardens as it exits the die in the desired cross-sectional form. The hardened material forms a tube that can grow to arbitrary length as additional melt is extruded and can be further processed to into any desired shape or configuration.
The ultimate shape of the extrusion is determined by a melt flow passage in the die between a die bushing which surrounds a die pin or mandrel. For circular pipe, the die pin is circular in cross-section and an opening in the die bushing which surrounds the die pin is circular. In addition to controlling the shape of the die opening, the location of the die pin in the die bushing controls the wall thickness of the tube.
Although certain specific embodiments shown and described herein are directed to tubular shapes have substantially circular cross-sections, it is contemplated that other shapes may be used in one or more embodiments. Thus, the term “tubular,” as used herein, may refer to hollow structures of various cross-sectional shapes, including circular, oval, triangular, square, rectangular, and other shapes. For example, the cross-sectional shape a tubular body may have one or more sides with straight and/or curved portions, including simple or complex curves, or curves of different or varying curvatures. Straight portions of a tubular body may be connected by one or more vertices, and the tubular body may have a cross-section with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or greater number of sides, surfaces, or facets.
In conventional extrusion dies, the shape of the die opening between the die pin and die bushing is adjusted by laterally shifting the die bushing relative to the die pin. In certain extrusion dies, this is accomplished by manually loosening and tightening several radial bolts that engage the die bushing around the circumference of the bushing. In other extrusion dies, the die pin may alternatively, or additionally, be adjustable relative to the die bushing. Manual adjustment of the die bushing or the die pin to control the thickness of the tube is a difficult, imprecise, and time-consuming process. This is in part due to the extrusion end of the die being located closely adjacent to a blow molding machine where, during operation, molds are rapidly moved toward and away from the die head which causes the die to be exposed to high temperature conditions. Additionally, the actual movement of the die bushing and the die pin in response to tightening or loosening of the bolts is not assured because of stick slip due to the tightness with which the bushing and/or the pin is held in place by a clamp nut.
Adjustment of the bushing and/or the pin may require an entire system to be shut down in order to permit tightening and loosening of the bolts. There is considerable down time and lost production during such adjustments. Further, it is often unclear if the tightening and loosening of the bolts does in fact locate the bushing and/or the pin in the desired position. Often the actual position of the bushing and pin can only be determined by re-starting the entire system, forming tubes with the bushing and/or pin in their new positions and then checking the wall thickness of the resulting tubes to determine whether the intended adjustment has been achieved. Frequently, it is necessary to shut down the system additional times to make further adjustments to achieve a desired positioning of the bushing and/or the pin. Alternatively, adjustment of the bushing and/or the pin in certain systems may be performed without shutting down the entire system. However, such “live adjustment” results in material waste while the system continues to operate during bushing and/or the pin adjustment.
In applications where precise and uniform tubing wall thickness is desired, the distance between the die bushing and the die pin must be maintained throughout the extrusion process. Uniform tubing wall thickness is maintained by keeping the die pin located axially or concentrically in the die bushing. However, the pin is often shifted as a result of the extrusion process such that the pin becomes located to one side of the bushing and the tubes formed after such shifting are thinner on one side than on an opposite side. As such, conventional extrusion dies cannot provide a continuous process.
The deficiencies of conventional extrusion dies described above are exacerbated by reductions in target dimensions of the formed tube. For example, as compared to plastic piping having an outer diameter of about 3.0 inches or more, a tube having an outer diameter of less than about 0.05 inches is formed using a die having a bushing with a significantly smaller outer diameter. Additionally, the smaller tube is formed using a die pin having a smaller outer diameter. The smaller bushing and pin are more likely to deform under the high processing temperatures of extrusion process, which in turn increases the likelihood of the die pin because misaligned. Also, the smaller bushing and pin are more flexible and more likely to bend and/or break under forces exerted during the extrusion process.
According to embodiments of the present disclosure, an extrusion device is provided. The extrusion device includes an extrusion die having a die bushing comprising a channel extending to an opening of the die bushing, a die pin positioned in the channel, and at least one die pin support feature extending between the die pin and the die bushing.
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.
The disclosure will be understood more clearly from the following description and from the accompanying figures, given purely by way of non-limiting example, in which:
Reference will now be made in detail to the present embodiment(s), an example(s) of which is/are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.
The singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. The endpoints of all ranges reciting the same characteristic are independently combinable and inclusive of the recited endpoint. All references are incorporated herein by reference.
As used herein. “have,” “having,” “include.” “including,” “comprise,” “comprising” or the like are used in their open ended sense, and generally mean “including, but not limited to.”
All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure.
The present disclosure is described below, at first generally, then in detail on the basis of several exemplary embodiments. The features shown in combination with one another in the individual exemplary embodiments do not all have to be realized. In particular, individual features may also be omitted or combined in some other way with other features shown of the same exemplary embodiment or else of other exemplary embodiments.
Embodiments of the present disclosure relate to extrusion devices having an extrusion die. The extrusion die includes a die pin extending through, and centrally positioned in, a channel of the extrusion die. The extrusion die also includes at least one die pin support feature that is configured to retain the position of the die pin within the channel and to prevent shifting of the die pin. The die pin support feature facilitates consistent melt flow out of the extrusion die and minimizes variations in wall thickness of the extruded parison. This consistency eliminates the need to adjust the die and/or die pin and thereafter test the wall thickness of the extruded parison by trial and error. This in turn reduces downtime, loss of production and material waste associated with extrusion dies that do not include die pin support features as described herein. The die pin support feature also provides support to the die pin, which further reduces the likelihood that the die pin will become deformed and/or misaligned due to the extrusion process conditions, and also reduces the likelihood that the die pin may become damaged and require replacement.
Referring now to
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According to one or more embodiments herein, the arrangement of the die pin and die pin support feature(s) within the bushing may help to achieve improve concentricity in the extruded shape. As used herein, “concentricity” refers to the alignment of the geometric center of a shape circumscribed by the inner surface of the tubular body with the geometric center of a shape circumscribed by the outer surface of the tubular body. An extruded shape having a high degree of concentricity will have these centers nearly or substantially aligned, while an extruded shape having a low degree of concentricity will have these centers separated and not substantially aligned.
Referring again to
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According to embodiments of the present disclosure, extrusion devices 10 may include discrete die pin support features 60 having a shape that, in combination with at least one other discrete die pin support feature 60, form a plurality of holes 62 around the die pin 30.
As previously described, the die pin support feature 60 may be integrally formed on a surface of the die bushing 20 and extend into the channel in the direction of the die pin 30. The die pin support feature(s) 60 may be formed on the surface of the die bushing 20 through, for example, direct machining, mechanically bonding, or 3D printing. Referring again to
As previously described, the die pin support feature 60 may be integrally formed on a surface of the die pin 30 and extend into the channel 22 in the direction of the die bushing 20. The die pin support feature(s) 60 may be formed on the surface of the die pin 30 through, for example, direct machining, mechanically assembly, or by drawing/die forming.
Aspects of various embodiments of this disclosure are provided below.
Aspect 1 pertains to an extrusion device including an extrusion die comprising: a die bushing comprising a channel extending to an opening of the die bushing; a die pin positioned in the channel; and at least one die pin support feature extending between the die pin and the die bushing.
Aspect 2 pertains to the extrusion device of Aspect 1, wherein the at least one die pin support feature includes a first end attached to the die bushing and a second end attached to the die pin.
Aspect 3 pertains to the extrusion device of Aspect 1, wherein the at least one die pin support feature is integrally formed on a surface of the die bushing.
Aspect 4 pertain to the extrusion device of Aspect 1, wherein the at least one die pin support feature is integrally formed on a surface of the die pin.
Aspect 5 pertains to the extrusion device of Aspect 1 comprising at least one discrete die pin support feature.
Aspect 6 pertains to the extrusion device of Aspect 1 comprising a plurality of discrete die pin support features.
Aspect 7 pertains to the extrusion device of Aspect 1 comprising at least one continuous die pin support feature.
Aspect 8 pertains to the extrusion device of Aspect 1 comprising at least one discrete die pin support feature and at least one continuous die pin support feature.
Aspect 9 pertains to the extrusion device of Aspect 1 comprising a clearance fit between the at least one die pin support feature and the die pin.
Aspect 10 pertains to the extrusion device of Aspect 1 comprising an interference fit between the at least one die pin support feature and the die pin.
Aspect 11 pertains to the extrusion device of Aspect 1 comprising a clearance fit between the at least one die pin support feature and the die bushing.
Aspect 12 pertains to the extrusion device of Aspect 1 comprising an interference fit between the at least one die pin support feature and the die bushing.
Aspect 13 pertains to the extrusion device of any of the preceding Aspects comprising a plurality of die pin support features.
Aspect 14 pertains to the extrusion device of Aspect 1 comprising a plurality of die pin support features having curved surfaces, wherein a curved surface of one of the plurality of die pin support features interacts with a curved surface of another of the plurality of die pin support features to form the boundaries a hole.
Aspect 15 pertains to the extrusion device of Aspect 1, wherein the at least one die pin support feature comprises a spiral groove member.
Aspect 16 pertains to the extrusion device of Aspect 1, wherein the die bushing comprises a first section having a cylindrical shape and a length L1, and wherein the die bushing comprises a second section having a frusto-conical shape.
Aspect 17 pertains to the extrusion device of Aspect 16, wherein the at least one die pin support feature has a length LF, the at least one die pin support feature being disposed in the first section of the die bushing.
Aspect 18 pertains to the extrusion device of Aspect 17, wherein LF is less than about 50% of L1.
Aspect 19 pertains to the extrusion device of Aspect 18, wherein LF is greater than about 50% of L1.
Aspect 20 pertains to the extrusion device of Aspect 17, wherein the first section of the die bushing further comprises a gap having a length LD extending from the opening of the die bushing to the at least one die pin support feature.
Aspect 21 pertains to the extrusion device of Aspect 20, wherein LD is less than about 25% of L1.
While the present disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the present disclosure.
This application claims the benefit of priority under 35 U.S.C § 120 of U.S. Provisional Application Ser. No. 62/693,700 filed on Jul. 3, 2018, the content of which is relied upon and incorporated herein by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/US2019/039232 | 6/26/2019 | WO | 00 |
Number | Date | Country | |
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62693700 | Jul 2018 | US |