JP2002518178A - Improvements in or related to the manufacture of extrusion dies - Google Patents

Abstract

The extrusion die has a zero bearing die cavity (12) shaped to correspond to the required cross-sectional shape of the extrusion. To control the flow of extruded material through the cavity, a preforming chamber (17) is provided that communicates with the die cavity but has a larger area. The depth and width of the preform chamber will vary in different areas, and the size of each area will be related to the size and location of the corresponding area of the die cavity (12). In use, the extruded material subsequently passes at different speeds through different areas of the preforming chamber such that it passes through all areas of the die cavity at a substantially uniform speed. The depth of the preform chamber is not greater than about 5 mm and can have any small depth up to less than about 0.5 mm. Regardless of the very small depth, the preforming chamber allows precise speed control of the extruded material and at the same time maintains a high extrusion speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an extrusion die used to produce elongated shapes of metals such as aluminum, plastics and the like. In an extrusion die, it is desirable that all portions of the extruded material pass through the die at substantially the same speed. Otherwise, the extruded shape will deform.

[0002]

[Prior art]

As is well known, the speed of material extruded through a die in an extrusion die is determined by the width of the die cavity in any particular area of the die cavity, the position of the area relative to the center of the die, the die in that area. It depends on the bearing length of the cavity, ie its length in the extrusion direction.

[0003] The width and location of each area of the die cavity is determined primarily by the particular shape being extruded, and usually the different dimensions of the die cavity are such that the speed of the extruded material is as uniform as possible throughout the die cavity. There is a need to control speed by adjusting the bearing length in the area. In this way, to achieve equal speed, the narrow part of the die cavity requires a shorter bearing length than the wide part of the cavity.

[0004] The required change in bearing length is usually at the back of the die, that is, the surface far from the entrance of material extruded through the exit cavity relative to the overall shape of the die (die cavity plus multifaceted clearance). Achieved by forming. Thus, the depth of this exit cavity is varied to adjust the effective bearing length of the die cavity itself. Various methods for producing such extrusion dies are disclosed, for example, in GB 2143445 and GB 2184371.

[0005] The required bearing length is usually achieved by trial and error methods based on the knowledge of an experienced die designer or by using a computer program to calculate the bearing length from the shape and location of the die cavity. . However, these methods have drawbacks and are subject to International Specification No. WO 97/0291
No. 0 discloses an extrusion die shape such that these disadvantages are reduced or overcome.

[0006] According to the disclosure in WO 97/02910, a preforming chamber having a shape generally similar to the die cavity but having a larger cross-sectional area is provided in front of the die cavity (ie upstream with respect to the extrusion direction). Wherein the area of the preform chamber communicates with the corresponding area of the die cavity. The flow of extruded material through the die is controlled by managing the length of the preform chamber rather than the length of the die cavity. That is, each area of the preforming chamber is such that material extruded through the area of the preforming chamber in use is such that the material is moved at a substantially uniform rate through the entire area of the die cavity. Given the bearing length corresponding to the dimensions and position.

[0007] Such an arrangement is such that the entire area of the die cavity has a substantially uniform bearing length, since all speed control is provided by adjusting the bearing lengths in different sections of the preforming chamber. Enable. In particular, the disclosed configuration allows the entire area of the die cavity to have a substantially zero bearing length.

A substantially zero bearing length die cavity has a negatively tapered die hole through the die plate, ie, the wall of the die hole expands from the front to the back of the die plate. It is formed by providing such a die hole. A zero bearing length die is disclosed in EP 0186340 and as described therein,
A negative taper angle of at least 0.8 ° is desirable so that the frictional stress between the die wall and the flow of material therethrough is negligible. It is believed that a negative taper angle of 1.5 ° is more reliable.

[0009] It is recognized that it is not really possible to have a truly zero bearing length die cavity due to the small radius present at the intersection of the negatively tapered die cavity and the front surface of the die plate. Can be EP 0186340 relates to an arrangement in which the radius of this curvature is not greater than 0.22 meters. However, for the purposes of this specification, the radius of curvature at the upstream end of the die cavity (which may be greater or less than 0.2 millimeters) as the die cavity increases in width as it extends from the front of the die plate. Regardless, the die cavity is deemed to have zero bearing length.

As is known from EP 0186340, conventional zero bearing length die designs do not allow for modification of the hole shape to speed up or slow down the passage of material. If the extrusion of the shape required by a conventional zero bearing length die could not be achieved, the die could not be modified. However, WO 97
The method of / 02910 allows for control of the speed of the metal upstream of the die, thus allowing the use of a zero bearing length die for virtually all types of cross sections.

[0011]

[Problems to be solved by the invention]

Heretofore, in carrying out the disclosure of WO 97/02910, the preform chamber has been used to have a bearing length in the zone of at least 6-12 millimeters. It was thought that it was necessary to have a bearing length of at least such dimensions for effective control of the speed of the extruded material. However, the present invention provides a practical solution by controlling the effective speed of the extruded material by significantly reducing the preform chamber bearing length to dimensions once thought to be too small for effective speed control. Is based on the surprising finding that it can be enhanced.

[0012] The dimensions of the preform chamber concerned here are defined by the depth of the chamber in the extrusion direction, rather than the bearing length of the chamber. This is because during extrusion,
This is because in many cases the extruded material only touches a part of the depth of the preforming chamber next to the chamber entrance. Thus, the effective bearing length of the preform chamber may actually be less than the physical depth of the preform chamber. The true effective bearing length is therefore difficult to measure, but it appears that the dominant in determining the velocity of the extruded material is the physical depth of the preform chamber. At present, the effective bearing length is simply related to the physical depth of the preforming chamber, or from the entrance of the die cavity itself to the entrance of the preforming chamber, regardless of the effective bearing length in the preforming chamber. It is not clear if the distance is dominant.

Therefore, according to the present invention, a die cavity having a shape corresponding to the required cross-sectional shape of the extrusion, and a region having an area larger than the region of the die cavity communicating with the corresponding region of the die cavity are provided. The dimensions of each area of the preforming chamber are such that in use the material extruded through said area of the preforming chamber subsequently passes through the corresponding area of the die cavity at a substantially uniform velocity. Related to the size and position of the corresponding area of the die cavity, so that they can be moved at such speeds, at least some of said areas of the preforming chamber each have a depth in the extrusion direction not more than 5 mm. It is characterized by having.

The depth of said section of the preforming chamber may be less than 2.5 millimeters, preferably less than 1 millimeter. In an embodiment of the present invention, the depth is 0.5 millimeter or less.

[0015] At least some, and preferably all, of the corresponding areas of the die cavity have substantially equal bearing lengths. The invention is particularly applicable to extrusion dies in which some or preferably all of said areas of the die cavity have substantially zero bearing length.

By using the pre-forming chamber of the present invention, the material is substantially rapidly followed by two, one
One is extruded through the preforming chamber and another through the die cavity itself. Surprisingly, it has been found that such a small depth of the preforming chamber is still sufficient to control the velocity of the extruded material and to provide a uniform velocity flow through the die cavity. In fact, it has been found that in many cases the control by these very small depths of the preformation chamber is in fact greater than the control by a higher depth preformation chamber. Furthermore, the reduced depth of the preforming chamber means that the overall speed of the extruded material can be significantly increased while providing the necessary control over the speed through different parts of the die. Thus, the production rate of the extrusion die according to the present invention is particularly high when used with a zero bearing length die cavity, or when compared to a conventional die without a preforming chamber, or at a depth greater than the depth according to the present invention. It can be significantly increased when compared to a die having a preforming chamber.

Also, due to the reduced bearing length of the preforming chamber, the dies of the present invention can be used at lower pressures, and thus at lower temperatures, if necessary, than prior art dies. Generally speaking, the rate of physical degradation of an extrusion die depends on the extrusion pressure at which it is used, and the heat resulting from that pressure. Thus, the die according to the invention degrades more slowly and can be used longer than prior art dies.

It has also been found that the present invention allows for faster extrusion due to lower temperatures. The extrusion speed of prior art dies is limited by the temperature of the extrusion. It is also conceivable that the extrusion surface finish is improved by extrusion at lower temperatures.

By using a very small depth of the preforming chamber according to the present invention, the flow velocity of the extruded material through the die cavity is not as strict as in prior art configurations relative to the location of the area of the die cavity with respect to the center of the die. I also knew there was no This means that the location and orientation of some die cavities is less critical, which allows more cavities to be provided on one die. For example, in a prior art extrusion die having four cavities to extrude four shapes, to ensure that all unfolded portions are at substantially equal distance from the die center, It was necessary to deploy the developed part of the die as far as possible in the radial direction of the die. This required orientation limits the number of shapes that can be placed within the die area. However, in accordance with the present invention, where the distance from the die center is less critical, the developed feature can be separated from the die center, which allows more features to be provided within the die area. This again increases the productivity of the die. Also, because a reasonable number of shapes are contained in one die, more different types of shapes are provided within the radius of a single die, and manufacturers have to use different sized to produce different shapes. Where a press may be required, only a single size press is required for shapes within a certain range.

The very small preforming chamber depth does not cause distortion of the extruded shape that can occur with a conventional extrusion die or an extrusion die having a preforming chamber with a depth greater than the depth proposed by the present invention. It turned out that there was a tendency. For example, in prior art dies, one side wall of the extruded section is inclined relative to the other side wall,
It was widely observed that the web connecting the two was curved.

It has also been found that the short preform chamber depth of the present invention has greater tolerance for extrusion rates in different parts of the die cavity. The depth of the small preform chamber of the present invention is controlled to make the velocities of the different areas of the die cavity uniform, but to avoid shape distortion, such velocities are similar to prior art configurations. Need not be uniform. As is well known, changes in extrusion speed at different portions of the die cavity are indicated by deformation of the leading surface or "nose" where the extruded material exits the die cavity. If the speed is uniform throughout the die cavity, the leading surface of the extruded material will be planar. According to the present invention, the deformation of the leading surface with the distortion of the extruded shape according to the prior art arrangement is such that the extrusion die comprises a very small depth preforming chamber for controlling the flow velocity according to the present invention. It was found that such a deformation did not accompany.

According to an embodiment of the present invention, controlling the speed of an area of the preform chamber comprises determining the length of the preform chamber and then adjusting the chamber depth to give the desired result. Or by determining the depth of the preforming chamber and then adjusting the width and / or length of each section of the chamber to give the desired result.
In the latter, all areas of the preform chamber are therefore of the same depth. Alternatively, the flow velocity through a particular area is controlled by adjusting the width, length and / or depth of that area.

One advantage of the present invention is that prior art dies, especially when using zero bearing lengths, require less pre-forming than the manual processing required to modify the shape of the actual die cavity. The chamber is easily formed to the desired dimensions by precision mechanical processing. This allows the shape of the die to be accurately repeated and, if necessary, desired by the die without the need to manually modify the die, which previously had to be performed by a skilled and experienced operator. Extrusion molding can be performed. For example, a zero bearing length die does not require "squaring" by hand. Without the present invention, it would be necessary to ensure that the sides of the die cavity were parallel and perpendicular to the front of the die.

According to the invention, the preforming chamber and the front side of the die can also be polished by mechanical treatment.

The extrusion die may include one or more additional preforming chambers in communication with the first preforming chamber. The area of the forming chamber increases with distance from the die cavity, and the additional preforming chamber or chamber also has a depth of no more than about 5 millimeters in the extrusion direction.

As with the first preforming chamber, the depth of the additional preforming chamber or chamber may be less than 2.5 millimeters, preferably less than 1 millimeter. In embodiments of the present invention, the depth of the additional preform or chamber is about 0.5 millimeters or less.

At least one or each area of the preforming chamber is arranged substantially symmetrically with respect to a corresponding area of the die cavity.

Alternatively, at least one area of the preforming chamber is arranged asymmetrically with respect to a corresponding area of the die cavity. For example, the width of the asymmetric area of the preforming chamber can be greater on one side of the die cavity than on the opposite side of the die cavity. Alternatively / further, the depth of said area of the preforming chamber may be greater on one side of the die cavity than on the opposite side of the die cavity.

[0029] The width of said area of the preforming chamber can vary along each side of the die cavity, the width of the preforming chamber along one side of the die cavity to the width of the opposite side of the die cavity. Corresponding changes can be made in opposite ways. In this case, the overall width of said section of the preforming chamber is constant or varies depending on the width of the die cavity.

The depth of said area of the preforming chamber can also vary along each side of the die cavity,
The depth of the preforming chamber can vary oppositely along one side of the die cavity, corresponding to a depth opposite the die cavity.

[0031] At least a portion of the bottom surface of the preforming chamber (where the entrance to the die cavity itself is formed) is formed of extruded material across the bottom surface as material passes from the preforming chamber into the die cavity. Primed or polished to enhance flow. The sidewalls of the preform chamber are also primed or polished.

Preferably, the die cavity and preform chamber or chamber are integrally formed in a single piece. Such a configuration maintains the overall strength of the extrusion die. WO
In the prior art arrangement according to 97/02910, the preforming chamber can be formed in a separate plate screwed or otherwise fixed to the plate in which the die cavity itself is formed. However, the present invention requires that the plate on which the preform chamber is formed be extremely thin, so that it tends to bend or buckle when screwed or otherwise secured to the die cavity plate. .

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION

The following is a more detailed description of embodiments of the invention, by way of example and with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, the extrusion die has a circular body 10 with a number of cavities 11 shaped to the shape to be extruded. In this case, three die cavities are provided (but any reasonable number of cavities can be provided on a single die as is well known). The extruded material, such as plastic or aluminum or other metal, passes through the die in the direction indicated by arrow 15.

As shown in FIG. 1, the die cavity itself is designated by the reference numeral 12. This example is a zero bearing length die cavity. That is, the side wall 13 of the cavity extends from the entrance edge 14 of the cavity and expands. The formation of the material passing through the die in the direction of the arrow 15 is thus performed exclusively by the inlet rim 14 and there is no frictional engagement between the extruded material and the expanding side wall 13.

As previously described, the edge 14 inevitably has a small radius of curvature, which may have a smaller or larger radius of curvature, for example 0.25. Extremely small, such as millimeters. As is well known, for a given cavity width, increasing the bearing length slows the extruded material as it passes through that cavity, and the use of zero bearing length thus allows for the maximum possible flow velocity. I do.

Although the present invention is particularly applicable to zero bearing length dies, the present invention can also provide advantages to dies having positive bearing lengths.

Near the edge 14 of the die cavity, the sidewalls 13 are angled at a very small angle (eg, 1.5 °) to provide adequate strength and support to the edge 14 forming the extruded material. However, further downstream, the cavity is wider at a larger angle, as shown at 16, to allow free passage of the extruded material.

According to WO 97/02910, a preforming chamber 17 is formed in the front of the die at the entrance of the cavity 12. The preform chamber 17 has a shape generally similar to the die cavity 12, as shown in FIG. 2, but has a larger area. The preforming chamber 17 extends symmetrically on each side of the die cavity 12. Die cavity 1 with zero bearing length
The material extruded through 2 is therefore first passed to the preforming chamber 17 and
According to 7/02910, the velocity of the extruded material is such that the extruded material subsequently passes through the entire area of the die cavity 12 at a substantially uniform velocity.
It can be controlled by selecting the appropriate dimensions of the preform chamber 17. According to the invention, the depth P of the preforming chamber 17 is much smaller than previously thought necessary, and a typical example of dimensions is shown.

In the configuration of FIG. 2, the width of each section of the preform chamber 17 is substantially larger than the width of the corresponding area of the die cavity 12 by a percentage page, and the extrusion through different sections of the preform chamber 17 is performed. The speed of the molding material is controlled by varying the depth P1 of the preform chamber 17 in different areas such that the extruded material passes through the entire area of the die cavity 12 at a substantially uniform speed. On the other hand, the speed of the extruded material can be changed by changing the area of the preforming chamber 17. Increasing the depth P1 of the preforming chamber 17 slows down the extruded material, while increasing the width of the preforming chamber 17 increases the speed. In some cases, both the depth and width of the preform chamber 17 can vary together in different areas of the chamber, but it is preferable to fix one parameter and vary the other to effect the adjustment.

It has heretofore been considered that the preforming chamber 17 must have a considerable depth in order to obtain a sufficiently precise control of the speed of the extruded material. Typically, in prior art configurations, the depth P1 of the preform chamber was in the 6-15 millimeter zone. However, in accordance with the present invention, effective and accurate speed control requires a much smaller depth of the preform chamber, for example, a few millimeters not exceeding 5 millimeters.
It was found that it can be realized by about 1/0.

As can be seen from FIG. 2, the die cavities need not be positioned so that the corresponding areas of the different cavities are at substantially equal distances from the die center. As previously explained, according to the present invention, the use of a very shallow preforming chamber makes the flow velocity less sensitive with respect to the location of each area of the die cavity with respect to the die center.

The letters AD in FIG. 2 indicate the depth of the preforming chamber 17 in different areas of each die cavity. The depth of each area depends on the shape and size of the die cavity in each area,
And to allow for the location of that area relative to the die center axis. As is well known, the flow velocity through an extrusion die decreases with distance from the central axis.

In the die of FIG. 2, the depth P 1 of the preforming chamber 17 in the indicated area can typically be as follows:

A = 0.7 mm B = 1.0 mm C = 1.3 mm D = 2.3 mm In the configuration of FIG. 2, the die shape has two elongated arms that extend mainly at an angle to each other. ing. Where the depth of the preforming chamber 17 is different at both ends of one arm, the depth typically increases continuously from one end of the arm to the other, so that the side walls of the preforming chamber change gradually. Or it is decreasing.

It can be seen that precise control of the speed of the extruded material is achieved with the use of the very shallow preform chamber described above. At the same time, the small depth of the preforming chamber has only a small overall effect on the speed of the extruded material so that a high material throughput and thus a high production rate can be maintained.

FIGS. 3, 4, and 5 show other types of typical designs of extrusion dies.

In FIG. 3, the letters E, F, G indicate areas of the preforming chamber of different depths, and these depths can typically be as follows:

E = 0.6 mm F = 1.3 mm G = 1.5 mm In FIG. 3, as shown at 17 a, the width of the preforming chamber is determined by the area of each die cavity where the cavity is particularly small. Then it is increased. This increase in the width of the preform chamber increases the velocity of the extruded material passing through the preform chamber, and thus compensates for the substantial reduction in velocity that occurs in particularly small areas of the die cavity.

For the more complex shaped extrusion die of FIG. 4, the indicated area depth of the preforming chamber can be as follows.

H = 0 J = 0.5 mm K = 0.7 mm L = 0.8 mm M = 0.9 mm N = 1 mm O = 1.2 mm P = 1.3 mm Q = 1.5 mm R = 1.7 mm For the more complex shaped extrusion die of FIG. 5, the indicated area depth of the preforming chamber can be as follows.

S = 1.0 mm T = 1.3 mm U = 1.5 mm V = 2.0 mm W = 2.5 mm In FIGS. 4 and 5 no additional preformation chamber 18 is shown, but if necessary Can be provided.

FIG. 6 shows a schematic cross section of a die for extruding a hollow shape, for example of rectangular or circular cross section. In a known manner, the die is
Having a male portion 19 surrounded by a substantially annular die cavity 21 therebetween. In a known manner, the material to be extruded flows around the male part 19 and through the cavity 21 between it and the female part 20.

According to the invention, the preforming chamber is formed in front of the male and female parts of the die. The preform chamber is generally similar in shape to the cavity 21, but has a larger area. It is hollow 21
Can extend symmetrically (although an asymmetric configuration is also possible, as described herein) with respect to each side. The portions of the male and female preform chambers preferably have equal depth.

The male part 19 and the female part 20 can each be formed to have zero bearing edges. However, there may be slight axial movement of the male portion 19 relative to the female portion 20 during use of the die. Therefore, to compensate for this, the zero bearing edge of the male part 19 is preferably pre-positioned slightly upstream of the zero bearing edge of the female part, and the bearing edge is aligned by the axial displacement of the male part during extrusion. To do it. While such an arrangement is preferred, FIG. 7 shows another possible arrangement for axial displacement of the male part during extrusion.

FIG. 7 shows the alternative shape of the die cavity in enlarged cross section. In the female part 20 of the die, the bearing length of the die cavity is again zero. That is, the side wall 22 of the cavity is inclined outwardly so as to be apart from the entrance edge 23 of the cavity. The shaping of the outer surface of the hollow cross section results in the edge 2 only as it passes through the die cavity in the direction of arrow 24.
3, there is no frictional engagement between the extruded material and the inclined surface 22. As in the previous configuration, the edge 23 has a very small radius of curvature.

In this case, however, the male part 19 does not have a zero bearing edge to allow for a slight axial movement between the male part 19 and the female part 20, but the female part has a zero bearing. It has a small axial bearing surface 25 extending on either side of the rim 23. This surface 25 has a bearing length of, for example, about 1.0 millimeter. Similarly, the side wall 26 of the cavity downstream of the opening is sloped such that the inner and outer side walls 26, 22 of the cavity widen so that they extend downstream.

As before, a preformed chamber is formed in the front of the male and female parts of the die (the female part is indicated by 27 and the male part is indicated by 28). The preforming chambers 27, 28 extend symmetrically to the enlarged side of the cavity 21, but the male part-side cavity part 28 is smaller in depth than the female part 27, where the male bearing surface 25 is visible. Have.

Typically, according to the present invention, the depth of the preformed chamber portion 27 can be 1.5 millimeters and the depth of the portion 28 can be 1.0 millimeter. If the hollow shape to be extruded is generally rectangular, or other cross-sectional shape with corners, the depth of the preform chamber at each corner is generally less than the depth along the sides of the cross-sectional shape, and typically It can be about 5 millimeters.

The present invention provides a preforming chamber having a depth no greater than 5 millimeters. In some configurations described above, the depth of the preform chamber is in the 0.5 to 2.5 millimeter zone. For the extrusion of harder aluminum alloys, such as those used in the production of aluminum ladder rungs, it has been found that a preformed chamber depth at the upper end of the zone according to the invention is preferred. For example, given that a preforming chamber depth of 0.8-1.8 millimeters would provide good results in extrusion of an aluminum alloy,
For harder alloys, a preform chamber depth of about twice this zone (ie, 1.6-3.6 millimeters) will cause the stresses encountered in use (the hollow extruded ladder rungs to be attached to the ladder spar) (Stress such as swaging sometimes applied to the end portion).

In the configuration described above with respect to FIGS. 1-7, the preforming chamber (eg, FIG. 1,
Each area of the two preforming chambers 17) is arranged symmetrically with respect to the corresponding area of the die cavity. That is, the width and bearing depth of the preforming chamber are substantially equal to those of the opposite side of the die cavity. However, according to another important aspect of the invention, the manner in which the material to be extruded flows through the die cavity is such that the area of the preforming chamber is asymmetric with respect to the corresponding area of the die cavity, e.g. Is further controlled by having different widths and / or depths on opposite sides. This asymmetry effect exerts a lateral force or bias on the extruded material as it passes through the die cavity, thereby affecting the shape and / or direction of the extruded material.

FIG. 8 illustrates a die configuration in which such an arrangement would be advantageous. In FIG. 8, the die cavity 30 has an inwardly bent flange portion 3 from its opposite end.
3 has a central hollow box cross section 31 with protruding spaced parallel branches 32.

When extruding shapes from a die of this type, it is a common problem that the extruded branches formed by the die cavity area 32 expand instead of becoming parallel.
In conventional dies, it has been difficult to correct such expansion strain by adjusting the bearing length of the die cavity itself using conventional die correction procedures. Thus, the shape of the die cavity is such that the area 32 in the die cavity converges slightly and the tendency of the corresponding part of the extrusion to spread out offsets this convergence and the two branches of the finished extruded shape are parallel. It is often necessary to compensate for and remove such distortions by modifying. In practice, however, it is difficult to match the required convergence in the area of the die cavity with the expansion that occurs during extrusion so that they exactly cancel each other. Thus, shaping the die cavity is a trial-and-error process that is likely to be a time and material investment, and it is practically impossible to obtain an extruded shape with exactly parallel branches.

In accordance with this aspect of the invention, the controlled lateral bias as the material is extruded is such that the lateral distortion of the extrusion is compensated for, such as the expansion of extruded branches. In a manner, a preforming chamber can be arranged to feed the material. This lateral deflection is achieved by making the preform chamber asymmetric with respect to the die cavity. One such configuration is shown in FIGS. 8 and 92, where the preform chamber 34 has a greater width on one side of the die cavity area 32 than on the other side, the two different widths each being 34A and 34B. The larger width 34A on one side of the die cavity 32 of the preforming chamber imparts a lateral bias to the extruded material, as schematically illustrated by arrow 35 in FIG. The effect of this is to "push" the extruded branches toward each other so as to offset the tendency of the extruded branches to expand as the extruded material passes through the die cavity area 32. .

Some similar effects can be achieved by forming the preforming chamber at a different bearing depth on the opposite side of the die cavity as shown in FIG. In this case, the depth of the side wall 36A of the preforming chamber 36 is the same as the depth of the side wall 36B opposite to the preforming chamber.
Greater than the bearing depth. The greater bearing depth of the side wall 36A also causes the material to be extruded through the die cavity 37 in the lateral direction, as schematically illustrated by arrow 38.
Pressing "(thus offsetting the tendency of the extruded branches to spread) to provide a lateral bias.

In the configuration of FIG. 9, the bearing depth on the two sides of the preforming chamber is the same, and in the configuration of FIG. 10, the width of the preforming chamber 36 is the same on each side of the bearing cavity. This facilitates modification of the preforming chamber to achieve the desired effect, as only one dimension needs to be changed in each case. However, the invention can also include configurations in which both the width and the bearing depth of the preform chamber vary on the opposite side of the die cavity.

Since the offset of the distortion tendency of the extrusion is controlled exclusively by the dimensions of the preforming chamber, making small adjustments to offset the distortion is much more than with the prior art methods described above. Easy. Thus, if extrusion distortion occurs in a symmetrically formed preforming chamber, simply increase the width of the preforming chamber on one side of the die cavity to a degree that offsets the distortion, or The bearing depth of the preforming chamber opposite the die cavity may be reduced.

The configuration of the flow control described with respect to FIGS. 8-10 is particularly applicable to the extrusion of the first aspect of the invention, in which the bearing depth of the preforming chamber is significantly less than in such cases. Although applicable to molding dies, the flow control of the extruded material is similar for extrusion dies with a larger preforming chamber bearing depth as in the prior art, as evidenced by the disclosure of WO 97/02910. So affect.

In the configuration of FIGS. 8-10, the effect of the asymmetric preform chamber is to impart a net bias to the extruded material to offset material distortion as it passes through the die cavity. However, in the modified configuration shown in FIG. 11, the preforming chamber is asymmetric such that the net bias does not act on the extruded material so as to offset the effects of the asymmetric shape of the different sections of the preforming chamber. Made in. Thus, as shown in FIG. 11, the width of the preform chamber 39 on one side of the die cavity 40 varies between a small width area 39A and a large width area 39B. The width of the preform chamber along one side of the die cavity varies inversely with the width of the opposite side, such that each smaller width area is opposite the larger width area. As a result, some sections of the preform chamber tend to bias the extruded material laterally in one direction, while other sections tend to bias the extruded material in the opposite direction. The sum of the deviations in each direction is designed so that the net lateral deviations do not affect the extruded material. However, the opposing lateral biasing forces "grab" the extruded material as it passes through the die cavity, which changes its shape as the extruded material is extruded from the die cavity 40. It was found that the distortion of the extruded material was suppressed so as to more accurately correspond to the shape. In the configuration of FIG. 11, the opposing lateral biasing force is provided by adjusting the width of the preform chamber 39, but similar effects are exerted on different areas of the preform chamber as described with respect to FIG. 10. This is achieved by having different bearing depths.

As can be seen from FIG. 11, the width of the preform chamber varies along each side of the die cavity, but the overall width of the chamber varies with the width of the die cavity 40 but remains substantially constant. Will be maintained.

In any configuration according to the present invention, one or more additional preforming chambers having a greater width may be provided upstream of the preforming chamber, as shown at 18 in FIG. Further, the preforming chamber or chamber also affects the velocity of the extruded material passing through the die cavity, and the depth of the main preforming chamber 17 where one or more additional preforming chambers are provided. P1 and the additional preform chamber depth P2 can be reduced. However, in other configurations, the additional chamber, such as chamber 18, has a width that does not significantly affect the extruded material passing through preform chamber 17 and die cavity 12.

In any configuration of the invention, the extruded material flows inwardly on the bottom wall of each preform chamber as it approaches the edge of the die cavity. Thus, preferably, the bottom wall of the preform chamber is primed and polished to reduce resistance to flow. The bottom wall of the preform chamber is also primed and polished.

Preferably, the bottom wall is polished to a mirror finish, and the side walls and the bottom wall of the preform chamber are shaped and polished, such as by a nitridation method typically used for mirror finishing of the die cavity itself. Is mirror-finished.

The additional preforming chamber, if provided, is initially formed by a planing process, followed by grinding the bottom wall of the preforming chamber and sanding. It is important that the bottom wall is ground and polished to such an extent that it completely removes the planing marks remaining on the bottom wall. Where such planing traces extend to the edges of the die cavity, they are microscopically toothed around the edges of the die cavity (where small grooves formed by the planing process are Extending laterally to the edge of the cavity). Such a toothed shape produces undesirable marks on the surface of the extrusion, and polishing the bottom wall of the preform chamber has the effect of smoothing the edges of the die cavity itself.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view through a part of an extrusion die according to the present invention.

FIG. 2 is a schematic front view of different shapes of an extrusion die according to the present invention.

FIG. 3 is a schematic front view of different shapes of an extrusion die according to the present invention.

FIG. 4 is a schematic front view of different shapes of an extrusion die according to the present invention.

FIG. 5 is a schematic front view of different shapes of an extrusion die according to the present invention.

FIG. 6 is a schematic sectional view passing through a part of a die for extruding a hollow portion.

FIG. 7 is an enlarged view of a part of the die shown in FIG. 6;

FIG. 8 is a schematic front view of yet another form of an extrusion die according to the present invention.

FIG. 9 is a schematic sectional view taken along line 9-9 in FIG. 8;

FIG. 10 is a schematic sectional view of a modification of the die of FIGS. 8 and 9;

FIG. 11 is a schematic front view of a further form of an extrusion die according to the present invention.

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Claims (29)

[Claims] 1. A die cavity having a shape corresponding to the cross-sectional shape of a required extruded product, and a region communicating with a corresponding region of the die cavity and having a larger area than the region of the die cavity. Wherein the dimensions of each area of the preforming chamber are such that in use the extruded material passing through said area of the preforming chamber subsequently passes through the corresponding area of the die cavity at a substantially uniform velocity. An extrusion die that is related to the size and location of a corresponding area of the die cavity so that it can be moved at a predetermined speed such that at least some of said areas of the preform chamber are about 5 millimeters in the extrusion direction. An extrusion die characterized by having a depth that is no greater. 2. The extrusion die of claim 1, wherein the depth of said area of said preform chamber is less than about 2.5 millimeters. 3. The extrusion die according to claim 1, wherein the depth of the section of the preforming chamber is less than about 1 millimeter. 4. The extrusion die according to claim 1, wherein the depth of the section of the preform chamber is less than about 0.5 millimeter. 5. The extrusion die according to claim 1, wherein at least some of the corresponding areas of the die cavity have a substantially constant bearing length. . 6. An extrusion die according to claim 1, wherein all the corresponding areas of the die cavity have a substantially constant bearing length. 7. The extrusion die according to claim 5, wherein the corresponding area of the die cavity has a substantially zero bearing length. 8. The method according to claim 1, further comprising one or more additional preforming chambers in communication with the first said preforming chamber, wherein the area of the preforming chambers increases with distance from the die cavity. An extrusion die according to any one of claims 1 to 7, characterized in that: 9. The extrusion die of claim 8, wherein the additional preform chamber or chamber has a depth in the direction of extrusion that is no greater than about 5 millimeters. 10. The extrusion die according to claim 8, wherein the additional preforming chamber or chamber has a depth in the direction of extrusion that is no greater than about 2.5 millimeters. 11. The extrusion die according to claim 8, wherein the additional preform chamber or chamber has a depth in the direction of extrusion that is no greater than about 0.5 millimeters. 12. The method according to claim 1, wherein at least one area of the preforming chamber is arranged substantially symmetrically with respect to a corresponding area of the die cavity. Extrusion die. 13. The extrusion die according to claim 1, wherein at least one area of the preforming chamber is arranged asymmetrically with respect to a corresponding area of the die cavity. . 14. The extrusion die according to claim 13, wherein the width of the asymmetric section of the preforming chamber is greater on one side of the die cavity than on the opposite side of the die cavity. 15. The extrusion die according to claim 13, wherein the depth of the area of the preforming chamber is greater on one side of the die cavity than on the opposite side of the die cavity. 16. The width of the section of the preforming chamber varies along each side of the die cavity, and the width of the preforming chamber along one side of the die cavity extends along the opposite side of the die cavity. The extrusion die according to any one of claims 13 to 15, wherein the width of the die is inversely proportional to the width of the die. 17. The extrusion die according to claim 16, wherein the entire width of the area of the preforming chamber is substantially constant. 18. The extrusion die according to claim 16, wherein the total width of the section of the preforming chamber varies according to the width of the die cavity. 19. The depth of the section of the preform chamber varies along each side of the die cavity, and the depth of the preform chamber along one side of the die cavity is opposite the die cavity. The extrusion die according to any one of claims 13 to 18, wherein said die is inversely proportional to the depth along the axis. 20. At least a portion of the bottom wall of the preforming chamber having an inlet to the die cavity itself is formed by extrusion across the bottom wall as extruded material passes from the preforming chamber to the die cavity. 20. The extrusion die according to any of claims 1 to 19, wherein the die is primed and / or polished to enhance the flow of the molding material. 21. The extrusion die according to claim 1, wherein a side wall of the preforming chamber is undercoated or polished or both. 22. The extrusion die according to claim 1, wherein the die cavity and the preforming chamber or chamber are integrally formed in a single part. 23. The control of the speed in the preformation chamber area is performed by fixing the width and length of each area of the preformation chamber and adjusting the chamber depth in different areas. An extrusion die according to any one of claims 1 to 22. 24. The method according to claim 1, wherein the control of the speed in the area of the preforming chamber is performed by fixing the depth of the preforming chamber and adjusting the width of the chamber in different areas.
23. The extrusion die according to any one of to 22. 25. The method according to claim 1, wherein the control of the speed in the area of the preforming chamber is effected by adjusting the width, length and depth of the chamber in different areas and any combination thereof. The extrusion molding die according to any one of the above. 26. A method of making an extrusion die having a die cavity having a shape corresponding to the required cross-sectional shape of the extruded product, the method comprising communicating with a corresponding area of the die cavity; Providing a preforming chamber having areas each having a larger area than the area of the cavity, wherein the preforming chamber, in use, has an asymmetric arrangement of the preforming chamber in the extruded material passing through the preforming chamber. Characterized by being asymmetric with respect to the die cavity so as to counteract lateral distortion of the extruded material passing through the die cavity by exerting a lateral biasing force resulting from the die. Production method. 27. The preforming chamber is made asymmetric with respect to the die cavity by forming the preforming chamber to have a greater width on one side of the die cavity than on the opposite side of the die cavity. 27. The method of manufacturing an extrusion die according to claim 26, wherein: 28. The preform chamber is made asymmetric with respect to the die cavity by forming the preform chamber to have a greater depth on one side of the die cavity than on the opposite side of the die cavity. 27. The method of manufacturing an extrusion die according to claim 26, wherein: 29. The extruded material is passed through the preforming chamber and the die cavity, and attention is paid to the lateral distortion of the extruded material as it passes through the die cavity, and the extruded material is extruded so as to cancel the distortion. 29. The method according to claim 26, further comprising the step of modifying the symmetry of the preforming chamber by applying a net lateral biasing force to the molding material.
The method for producing an extrusion die according to any one of the above.