Patent Description:
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 <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 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 <NUM> inches or more, a tube having an outer diameter of less than about <NUM> 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. <CIT> discloses an extruder assembly for extrusion of tetrafluoroethylene polymer tubes. <CIT> discloses a tube extrusion mold used for molding glass or plastic material. <CIT> discloses a self-centering extrusion die for extruding tubular products. <CIT> discloses a core-free wire and cable extrusion head mold. <CIT> discloses an extrusion die, including an extrusion die body and a forming mandrel.

According to an aspect of the invention, an extrusion device is provided as defined in claim <NUM>.

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.

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.

<FIG> illustrates a partial cross-section of an extrusion device in accordance with embodiments of the present disclosure. The extrusion device <NUM> as shown includes a die bushing <NUM> and die pin <NUM>. The die pin <NUM> extends through a barrel <NUM> and is centrally positioned in bore <NUM> of the barrel <NUM>. The extrusion device <NUM> further includes a collar <NUM> positioned over the die bushing <NUM> and barrel <NUM> and attached to a face plate <NUM> to maintain the relative position of the die bushing <NUM> and barrel <NUM> and to provide support thereto.

Referring now to <FIG>, an enlarged partial cross-sectional view of the extrusion die of <FIG> is shown. Die bushing <NUM> is shown with a channel <NUM> that extends through the die bushing <NUM> and terminates in an opening <NUM>. The opening <NUM> is generally circular with a diameter D1 in the range of, for example, but without limitation, about <NUM> inches to about <NUM> inches, or in the range of about <NUM> inches to about <NUM> inches, or even in the range of about <NUM> inches to about <NUM> inches. The die bushing <NUM> includes a first section <NUM> having a generally cylindrical shape and a length L<NUM>, along a longitudinal axis <NUM> of the die bushing <NUM>, known conventionally as the "land length" of the die. The length L<NUM> of the first section <NUM> may be in the range of, for example, but without limitation, about <NUM> inches to about <NUM> inches, or in the range of about <NUM> inches to about <NUM> inches. The die bushing <NUM> further includes a second section <NUM> having a generally frusto-conical shape with a surface that forms an angle θ1 with the longitudinal axis <NUM>. The angle θ1 may be between about <NUM> degrees and about <NUM> degrees, or between about <NUM> degrees and about <NUM> degrees, or even between about <NUM> degrees and about <NUM> degrees.

As shown in <FIG>, the die pin <NUM> extends through the channel <NUM> and is centrally positioned therein, the distal section <NUM> of the die pin <NUM> extending through the first section <NUM> and terminating at the opening <NUM> of the die bushing <NUM> (i.e., the distal face <NUM> of the die pin <NUM> is approximately parallel to and coincident with the distal face <NUM> of the die bushing <NUM>). Optionally, the distal end of the die pin <NUM> can be offset from the opening <NUM> by a short length in either direction (i.e., stopping proximal of the opening <NUM> or extending through the opening <NUM>). The die pin <NUM> is generally cylindrical in shape and includes distal section <NUM> with a diameter D2 less than a diameter D3 of a proximal section <NUM>. The diameter D2 of the distal section <NUM> may be in the range of, for example, but without limitation, about <NUM> inches to about <NUM> inches, or in the range of about <NUM> inches to about <NUM> inches, or even in the range of about <NUM> inches to about <NUM> inches. A transition region <NUM> transitions the die pin <NUM> from the proximal section <NUM> to the distal section <NUM>, the transition region <NUM> forming an angle with respect to a longitudinal axis of the die pin <NUM> of between about <NUM> degree to about <NUM> degrees, or between about <NUM> degrees and about <NUM> degrees, or even between about <NUM> degrees and about <NUM> degrees.

Referring again to <FIG>, the die bushing <NUM> further includes a die pin support feature <NUM> extending between the die pin <NUM> and the die bushing <NUM>. As shown, the die pin support feature <NUM> is disposed in the first section <NUM> of the die bushing <NUM>. The die pin support feature <NUM> retains the position of the die pin <NUM> within the channel <NUM> to prevent shifting of the die pin <NUM>, which in turn ensures a uniform wall thickness of the extruded parison. As will be explained in more detail below, in describing the die pin support feature <NUM> as extending between the die pin <NUM> and the die bushing <NUM>, it is not meant to limit embodiments of the present disclosure to a particular configuration. For example, the die pin support feature <NUM> may extend from a first end that is attached to the die bushing <NUM> to a second end that is attached to the die pin <NUM>. According to embodiments of the present disclosure, and as will be described in greater detail below, the die pin support feature <NUM> may be integrally formed on a surface of the die bushing <NUM> and extend into the channel in the direction of the die pin <NUM>. Alternatively, and as will be described in greater detail below, the die pin support feature <NUM> may be integrally formed on a surface of the die pin <NUM> and extend into the channel <NUM> in the direction of the die bushing <NUM>.

<FIG> shows an extrusion device <NUM> having a single die pin support feature <NUM>; however, it should be appreciated that extrusion devices <NUM> in accordance with embodiments of the present disclosure may include any number of die pin support features <NUM>. <FIG> show exemplary extrusion devices <NUM> each having different configurations and different numbers of die pin support features <NUM>. <FIG> shows an extrusion device <NUM> that includes a single die pin support feature 60a. <FIG> shows an extrusion device <NUM> that includes two die pin support features 60a, 60b separated by about <NUM> degrees of the circumference of the die pin <NUM>. <FIG> shows an extrusion device <NUM> that includes three die pin support features 60a, 60b, 60c separated by about <NUM> degrees of the circumference of the die pin <NUM>. <FIG> shows an extrusion device <NUM> that includes four die pin support features separated by about <NUM> degrees of the circumference of the die pin <NUM>. <FIG> shows an extrusion device <NUM> that includes five die pin support features separated by about <NUM> degrees of the circumference of the die pin <NUM>. <FIG> shows an extrusion device <NUM> that includes six die pin support features separated by about <NUM> degrees of the circumference of the die pin <NUM>. The configurations and the number of die pin support features <NUM> shown in <FIG> are meant to be exemplary and non-exhaustive illustrations of embodiments according to the present disclosure. It should be appreciated that extrusion devices <NUM> as described herein may include any number of die pin support features <NUM> in any configuration so long as the melt is permitted to flow through channel <NUM> to opening <NUM>. Furthermore, it should be appreciated that while the figures illustrate several exemplary shapes, the die pin support features <NUM> may have any shape that retain the position of the die pin within the channel <NUM> while also permitting flow of the melt through channel <NUM> to opening <NUM>.

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 <FIG>, the extrusion device <NUM> is shown as having a discrete die pin support feature <NUM>; however, it should be appreciated that extrusion devices <NUM> in accordance with embodiments of the present disclosure may include continuous die pin support features <NUM>. As used herein, the term "discrete feature" is used to refer to a die pin support feature <NUM> having a length LF along the longitudinal axis <NUM> that is less than about half the length L<NUM> of the first section <NUM> of the die bushing <NUM>. As used herein, the term "continuous feature" is used to refer to a die pin support feature <NUM> having a length LF along the longitudinal axis <NUM> that is greater than about <NUM>% of the length L<NUM> of the first section <NUM> of the die bushing <NUM>. <FIG> illustrates an exemplary extrusion die having four die pin support features 60a-60d. <FIG> and <FIG> illustrate alternative configurations of the extrusion die shown in <FIG> in accordance with embodiments of the present disclosure. <FIG> illustrates a cross-sectional view of the extrusion die of <FIG> taken along line A-A. Die pin support features 60a, 60c are shown in <FIG> as being discrete die pin support features. <FIG> illustrates an alternative cross-sectional view of the extrusion die of <FIG> taken along line A-A. Die pin support features 60a, 60c are shown in <FIG> as being continuous die pin support features. It should be appreciated that discrete die pin support features and continuous die pin support features are not mutually exclusive and embodiments of the present disclosure may include extrusions dies having at least one discrete die pin support feature and at least one continuous die pin support feature. Additionally, embodiments of the present disclosure may include more than one discrete die pin support feature <NUM> positioned at different locations along the length L<NUM> of the first section <NUM> of the die bushing <NUM>.

Referring again to <FIG> and <FIG>, the die pin support features 60a, 60c may not extend along the entire length of the die bushing <NUM> to the opening <NUM>. Stated another way, the extrusion die may include a gap <NUM> between the die pin support <NUM> and the opening <NUM> of the die bushing <NUM> where the gap <NUM> has a length LD along the longitudinal axis <NUM>. The length LD of the gap <NUM> may be, for example, less than about <NUM>% of the length L<NUM> of the die bushing <NUM>, or less than about <NUM>% of the length L<NUM> of the die bushing <NUM>, or even less than about <NUM>% of the length L<NUM> of the die bushing <NUM>.

According to embodiments of the present disclosure, extrusion devices <NUM> may include discrete die pin support features <NUM> having a shape that, in combination with at least one other discrete die pin support feature <NUM>, form a plurality of holes <NUM> around the die pin <NUM>. <FIG> illustrates one such example where the extrusion die includes eight die pin support features 60a-<NUM> having curved surfaces which, in combination, form the boundaries of eight holes 62a-<NUM>. In the example shown in <FIG>, the die pin support features 60a-<NUM> include two curved surfaces on opposite sides of the die pin support features. One of the curved surfaces of one of the die pin support features 60a-<NUM> may be positioned to interact with one of the curved surfaces of another of the plurality of die pin support features 60a-<NUM> to form the boundaries of a hole 62a-<NUM>. While the die pin support features 60a-<NUM> as shown in <FIG> are described and labeled as being separate components in the present disclosure, it should be appreciated that the die pin support features 60a-<NUM> may be portions of an integrally formed component which includes a plurality of holes 62a-<NUM>. Furthermore, while the extrusion die of <FIG> is shown as having eight die pin support features 60a-<NUM> interacting to form eight 62a-<NUM>, embodiments of the present disclosure are not so limited and may include any number of die pin support features <NUM>. As further shown in <FIG>, the die pin <NUM> may include a die pin channel extending the length of the die pin <NUM>. In the extrusion die shown in <FIG>, the die pin channel may provide a path through which air
pressure can escape from the die which may advantageously prevent collapse of the parison as the melt exits from opening <NUM>.

As previously described, the die pin support feature <NUM> may be integrally formed on a surface of the die bushing <NUM> and extend into the channel in the direction of the die pin <NUM>. The die pin support feature(s) <NUM> may be formed on the surface of the die bushing <NUM> through, for example, direct machining, mechanically bonding, or 3D printing. Referring again to <FIG>, an extrusion die having four die pin support features 60a, 60b, 60c. 60d extending from the surface of the die bushing <NUM> and into the channel <NUM> in the direction of the die pin <NUM>. The extrusion die of <FIG> is shown as having a clearance fit between the die pin support features 60a, 60b and 60c and the die pin <NUM>; however, it should be appreciated that the extrusion die may include an interference fit between the die pin support features 60a, 60b and 60c and the die pin <NUM>. As used herein, the term "clearance fit" refers to a fit type where a first component can be axially inserted into and removed from a recess of a second component, but the first component cannot generally be moved in a transverse direction perpendicular to the axial direction when disposed in the recess. Stated another way, a clearance fit exists where the outer diameter of the first component and the inner diameter of the second component are sufficiently similar to permit one of the components to be fittingly received in the other component. In contrast, as used herein, the term "interference fit" refers to a fit between two parts that are maintained by frictional forces as opposed to by some other fastening arrangement (e.g., an adhesive or a fastener).

As previously described, the die pin support feature <NUM> may be integrally formed on a surface of the die pin <NUM> and extend into the channel <NUM> in the direction of the die bushing <NUM>. The die pin support feature(s) <NUM> may be formed on the surface of the die pin <NUM> through, for example, direct machining, mechanically assembly, or by drawing/die forming. <FIG> shows an example of a die pin <NUM> having three die pin support features 60a, 60b and 60c extending from the surface of the die and into the channel <NUM> in the direction of the die bushing <NUM>. <FIG> illustrates a cross-sectional view of the extrusion die of <FIG> taken along line B-B. <FIG> show a clearance fit between the die pin support features 60a, 60b and 60c and the die bushing <NUM>; however, it should be appreciated that embodiments of the present disclosure may include an interference fit between the die pin support features 60a, 60b and 60c and the die bushing <NUM>.

Claim 1:
An extrusion device comprising:
an extrusion die comprising:
a die bushing (<NUM>) comprising a channel extending to an opening of the die bushing;
a die pin (<NUM>) positioned in the channel; and
a plurality of die pin support features (60a-<NUM>) extending between the die pin and the die bushing having curved surfaces, wherein a curved surface of one of the plurality of die pin support features (60a-<NUM>) interacts with a curved surface of another of the plurality of die pin support features (60a-<NUM>) to form the boundaries of a hole (62a-<NUM>).