Extrusion machine and method of extrusion

Abstract

This invention relates to an extrusion machine and to a method of extrusion using the machine. The invention relates in particular to the extrusion of metals such as aluminium and copper. The extrusion machine comprises an extrusion wheel and a die chamber. The extrusion wheel has a single groove adapted to accommodate two rods of feedstock material. The die chamber has a single port through which the two rods of feedstock material can pass in use.

Description

FIELD OF THE INVENTION

[0001] This invention relates to an extrusion machine and to a method of extrusion using the extrusion machine. The invention relates in particular to the extrusion of metals such as aluminium and copper and the following description relates primarily to those materials. The invention is nevertheless suitable for the extrusion of other materials.BACKGROUND TO THE INVENTION

[0002] Extrusion is a well-known and widely-used method of making products and components, particularly products which are desired to be made in continuous (or significant) lengths.

[0003] A traditional extrusion machine has a heating cylinder or container into which an ingot or billet of feedstock material is inserted and heated. One end of the container is open and the other end of the container is generally closed but has a die with one or more openings. A ram is introduced into the open end of the container behind the billet which forces the feedstock material through the die opening(s) to form a length of product having a consistent cross-sectional size and shape determined by the die.

[0004] A new extrusion machine and method of extrusion was developed in the 1980s and is described in EP 0 125 788. Instead of using an ingot or billet, the machine uses an elongate rod of feedstock material. Also, the container is replaced by an extrusion wheel and die chamber. The periphery of the extrusion wheel has a groove, the width of which is smaller than the cross-section (diameter) of the rod of feedstock material. A coining roll is used to force the rod of feedstock material into the groove. The rod of feedstock material is carried by the extrusion wheel from the coining roll to an opening or port of the die chamber. The die chamber has a projecting abutment immediately behind the port which extends into the groove and which forces the rod of feedstock material to leave the extrusion wheel and pass through the port. As the extrusion wheel rotates it forces the rod through the port of the die chamber from where the feedstock material is extruded through the die. The rod of feedstock material therefore acts similarly to the ram of a traditional extrusion machine with the extrusion wheel providing the force to drive the rod into and through the die chamber.

[0005] A coating of the feedstock material is applied to the groove of the extrusion wheel and the coining roll forces the rod of feedstock material into the groove with sufficient force to create a temporary bond with the coating so that the force generated by the extrusion wheel can be transferred effectively to the rod.

[0006] The rod of feedstock material is therefore forced to deform somewhat as it is forced into the groove by the coining roll. It is subsequently forced to bend around the extrusion wheel, and is further forced to deform as it engages the abutment and passes through the port of the die chamber. All of these actions generate heat in the rod of feedstock material. In some applications sufficient heat is generated to allow the rod of feedstock material to be extruded without requiring additional heat, but in other applications the die chamber is heated so that the feedstock material reaches a sufficient temperature to be extruded.

[0007] It will be understood that the abutment causes the rod of feedstock material to leave the extrusion wheel immediately adjacent to the port of the die chamber and the extrusion wheel lies as close as possible to the port and to the abutment. Nevertheless, a small clearance gap necessarily exists between the rotating extrusion wheel and the stationary die chamber in order to prevent damage to one or both of these components. As the rod of feedstock material passes from the groove to the port it crosses the clearance gap and the extrusion pressure will typically force the rod of feedstock material to deform to substantially fill the clearance gap. Some of the feedstock material will subsequently be squeezed off the rod in the form of thin strips of feedstock material as the rod passes through the port, which material is often called flash.

[0008] The rod of feedstock material is transported in the groove of the extrusion wheel for less than one complete rotation of the extrusion wheel (and in practical applications around a quarter of a rotation). A scraper blade is located in the other part of the rotation (between the abutment and the coining roll). The scraper blade has a similar shape to the groove and projects into the groove. As the extrusion wheel rotates past the stationary scraper blade flash is removed from the surface of the extrusion wheel. The scraper blade is a necessary component for preventing flash being fed by the extrusion wheel back to the die chamber. When the feedstock material is aluminium or copper, the flash will typically contain oxides as well as other contaminants; if the flash enters the die chamber it will be extruded as part of the product, usually forming blisters and / or marks upon the surface of the extruded product.

[0009] EP 0 398 747 discloses a so-called "twin groove extrusion wheel" which is a development of the new machine and method described above. The extrusion wheel has two grooves so that two rods of feedstock material can be transported together to the die chamber. Using two rods of feedstock material has significant benefits, including increasing the rate of production of extruded products, facilitating the production of larger cross-section hollow extruded products, and achieving the required flow balance for the production of certain hollow extruded products. It will be understood, however, that two rods of feedstock material will typically produce twice as much flash which must be removed by the scraper blade or blades.

[0010] Some practical applications of a twin groove extrusion wheel utilise a die chamber with two ports, one port for each rod of feedstock material, in an arrangement often called "twin groove and twin port". Other practical applications utilise a die chamber with only a single port for both of the rods, often called "twin groove single port". This latter arrangement is typically used to increase the rate of production of extruded product but has the disadvantage that at least some of the flash generated between the two grooves will easily enter the port of the die chamber, often resulting in a poor surface finish of the extruded product, particularly for larger extruded products.SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide an extrusion machine having a twin groove and single port arrangement which reduces or avoids the problems with the known tooling of this type.

[0012] According to the invention there is provided an extrusion machine comprising an extrusion wheel and a die chamber, the extrusion wheel having a single groove adapted to accommodate two rods of feedstock material, the die chamber having a single port through which the two rods of feedstock material can pass in use.

[0013] Preferably, the groove is adapted to accommodate the two rods of feedstock material in a side-by-side configuration. Accordingly, the width of the groove is based upon twice the width of the rods.

[0014] Preferably, the cross-sectional shape of the two rods is circular (or substantially circular) before insertion into the groove. Desirably, the diameters of the two rods of feedstock material are identical. Preferably, the width of the single groove is less than twice the diameter. It will therefore be understood that the two rods are deformed somewhat as they are forced into the single groove. It is arranged that the deformation is sufficient to create a temporary bond between the rods of feedstock material and the surface of the single groove as in the known extrusion machines.

[0015] Preferably, the groove has a raised rib, desirably located centrally of the groove. The raised rib effectively divides the bottom of the groove into a first part to accommodate a first rod of feedstock material and a second part to accommodate a second rod of feedstock material. Such a groove has the general form of a "W" and can be described as a W-groove.

[0016] Desirably, the bottom of the first part of the W-groove and the bottom of the second part of the W-groove are of part-circular form with a radius of curvature slightly smaller than the radius of the rods of feedstock material. In preferred embodiments with a raised rib each rod of feedstock material is thereby forced by the coining roll into a "well" which closely matches the shape of the periphery of the rod. This better enables the required temporary bond to be created with the coating of the groove.

[0017] Preferably, the extrusion machine has a coining roll adapted to force the rods of feedstock material into the single groove. Desirably, there is only a single coining wheel. Accordingly, both of the rods of feedstock material are introduced into the single groove at the same location.

[0018] Desirably, the depth of the single groove is slightly greater than the diameter of the rods. This is similar to the known twin groove tooling, it being recognised as beneficial that the coining roll project into the single groove by a small distance in order to ensure that the rods are properly bonded to the extrusion wheel.

[0019] Desirably, the extrusion machine has an abutment adjacent to the port adapted to force the rods of feedstock material out of the single groove. Preferably, the die chamber has a housing and the abutment is a part of the housing. There is preferably a single abutment and the abutment preferably projects into the single groove.

[0020] Preferably, a single scraper blade is provided having a shape closely to match the single groove of the extrusion wheel.

[0021] A first benefit of the present invention is that no flash is created in the region between the rods of feedstock material as the rods pass through the single port, so that less flash is created than with the known twin groove and twin port tooling. In some applications it is expected that the amount of flash created can be around 50% less than with the known twin groove and twin port arrangements (flash being created at the two side edges of the single port as opposed to the four side edges of the twin ports).

[0022] A second benefit is that the size of the region between the extrusion wheel and the port of the die chamber can be reduced by approximately 30-40% over the known twin groove and twin port tooling. This in turn is expected to reduce the load on the extrusion wheel and extend the tooling life.

[0023] A third benefit is that the provision of a single groove for two rods of feedstock material enables the width of the extrusion wheel and coining wheel to be reduced, thereby reducing the tooling cost.

[0024] In a development of the present invention, an extrusion wheel can be adapted to accommodate four rods of feedstock material, the four rods being forced into two grooves, each groove cooperating with a single port. The use of four rods of feedstock material can further increase the production rate of extruded product.

[0025] The invention also provides a method of extrusion using the extrusion machine as defined, in which two rods of feedstock material are forced into a single groove by the coining roll, parts of the two rods interengaging in the single groove, and in which the two rods of feedstock material are forced out of the single groove by an abutment and pass together through a single port of the die chamber.BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig.1shows the an extrusion machine according to the present invention; Fig.2shows an enlarged cross-sectional view along the line A-A of Fig.1; Fig.3shows an enlarged cross-sectional view along the line B-B of Fig.1; Fig.4shows an enlarged cross-sectional view along the line C-C of Fig.1; and Fig.5shows a part of the die chamber of the extrusion machine of Fig.1. DETAILED DESCRIPTION

[0027] Fig.1 shows an extrusion machine of the present invention.

[0028] Two rods 10 of feedstock material are created and fed side-by-side to the extrusion machine. Only one rod 10 can be seen in Fig.1 as the other rod is hidden behind the rod 10. The rods 10 are initially circular in cross-section and have the same diameter. As the rods 10 pass between an extrusion wheel 12 and a coining roll 14 they are pressed (together) into a groove 16 in the periphery of the extrusion wheel 12.

[0029] In known fashion, the groove 16 has a coating 18 of feedstock material, i.e. the same material as the rods 10. This coating 18, together with the deformation of the rods 10 as they are forced into the groove 16 by the coining roll 14, creates an effective bond between the extrusion wheel 12 and the rods 10. In particular, the rods 10 bond with the extrusion wheel 12 sufficiently to remain in the groove 16 as they are forced to bend around the rotating extrusion wheel 12.

[0030] As the extrusion wheel 12 rotates the rods 10 of feedstock material are carried to a stationary die chamber 20. The die chamber 20 has an abutment 22 and a port 24 which is immediately adjacent to the abutment. As shown in Fig.3, the abutment 22 projects into the groove 16. As the rods 10 of feedstock material engage the abutment 22 they are forced out of the groove 16 and through the port 24 of the die chamber 20. As the extrusion wheel 12 continues to rotate, more feedstock material is forced into the die chamber 20 and is subsequently forced through a die 26, the feedstock material forming an extruded product 28 with a size and shape determined by the die.

[0031] As seen in Figs. 2-4, the groove 16 with its coating 18 is of somewhat complex form with a general W-shape. The groove 16 and abutment 22 have the same profile, but the dimensions of the groove 16 and coating 18 upstream of the abutment 22 are slightly larger than the dimensions of the abutment 22.

[0032] The shape of the groove 16 is described in more detail with reference to Fig.4. The width W of the groove 16 (with its coating 18) is slightly smaller than twice the diameter of the rods 10 of feedstock material. A raised rib 30 is located centrally at the bottom of the groove 16. The raised rib 30 divides the bottom of the groove 16 into two parts, one part for each of the rods 10 as is shown in Fig.2. The surface of each part of the bottom of the groove 16 is part-circular with a radius of curvature R. The radius of curvature R is slightly smaller than the radius of the rods 10 of feedstock material. Also, the separation S between the centres of curvature of the surface of each part of the bottom of the groove 16 is slightly smaller than twice the radius of the rods 10 of feedstock material. These relative dimensions ensure that the rods 10 of feedstock material must be deformed as they are forced into the groove 16 by the coining roll 14.

[0033] It will be understood that the raised central rib 30 comprises a continuation of the part-circular surfaces and lies between the rods 10 as they are forced into the groove 16. The top end of the raised rib 30 (and its coating 18) has a radius of curvature r which is very small so that the rib 30 is relatively sharp. Fig.2 shows that the rods 10 have been deformed somewhat by their engagement with the coining roll 14 and with each other and in practice the radius of curvature r of the raised rib 30 is sufficiently small, and the deformation of the rods 10 by the coining roll 14 is sufficiently great, that no gaps remain between rods 10 and the raised rib 30, whereby the deformed rods 10 will substantially fill the bottom of the groove 16.

[0034] The depth D of the groove 16 is slightly greater than the diameter of the rods 10 of feedstock material. Accordingly, the coining roll 14 projects into the groove 16 as shown in Fig.2. The coining roll 14 presses the two rods 10 of feedstock material into the groove 16 at the same location and at the same time.

[0035] The die chamber 20 is shown in Fig.5. The die chamber has a single port 24 through which both rods 10 of feedstock material pass, together. Immediately behind the port 24 (in the direction of rotation of the extrusion wheel 30) is the abutment 22, which is a part of the housing providing the die chamber 20.

[0036] Downstream of the abutment 22, the profile of the coating 18 in the groove 16 of the extrusion wheel 12 matches the profile of the abutment 22.

[0037] Fig.1 shows the scraper blade 36 which projects into the groove 16 and which removes flash from the groove 16 as the extrusion wheel 12 rotates past the scraper blade. It will be understood that the scraper blade removes the material (flash) which has been squeezed between the die chamber 20 and the extrusion wheel 12, the removed material 38 being shown in Fig.1. It will be understood that significantly less flash will be created by the present extrusion machine than with the known twin groove and twin port arrangement since with the present machine the facing portions of the two rods 10 of feedstock material are not required to move past a wall of the port at which flash would be produced.

Examples

Embodiment Construction

[0026]The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

Fig.1shows the an extrusion machine according to the present invention; Fig.2shows an enlarged cross-sectional view along the line A-A of Fig.1; Fig.3shows an enlarged cross-sectional view along the line B-B of Fig.1; Fig.4shows an enlarged cross-sectional view along the line C-C of Fig.1; and Fig.5shows a part of the die chamber of the extrusion machine of Fig.1.

DETAILED DESCRIPTION

[0027]Fig.1 shows an extrusion machine of the present invention.

[0028]Two rods 10 of feedstock material are created and fed side-by-side to the extrusion machine. Only one rod 10 can be seen in Fig.1 as the other rod is hidden behind the rod 10. The rods 10 are initially circular in cross-section and have the same diameter. As the rods 10 pass between an extrusion wheel 12 and a coining roll 14 they are pressed (together) into a groove 16 in the periphery of the extrusion w...

FIELD OF THE INVENTION

[0001] This invention relates to an extrusion machine and to a method of extrusion using the extrusion machine. The invention relates in particular to the extrusion of metals such as aluminium and copper and the following description relates primarily to those materials. The invention is nevertheless suitable for the extrusion of other materials.BACKGROUND TO THE INVENTION

[0002] Extrusion is a well-known and widely-used method of making products and components, particularly products which are desired to be made in continuous (or significant) lengths.

[0003] A traditional extrusion machine has a heating cylinder or container into which an ingot or billet of feedstock material is inserted and heated. One end of the container is open and the other end of the container is generally closed but has a die with one or more openings. A ram is introduced into the open end of the container behind the billet which forces the feedstock material through the die opening(s) to form a length of product having a consistent cross-sectional size and shape determined by the die.

[0004] A new extrusion machine and method of extrusion was developed in the 1980s and is described in EP 0 125 788. Instead of using an ingot or billet, the machine uses an elongate rod of feedstock material. Also, the container is replaced by an extrusion wheel and die chamber. The periphery of the extrusion wheel has a groove, the width of which is smaller than the cross-section (diameter) of the rod of feedstock material. A coining roll is used to force the rod of feedstock material into the groove. The rod of feedstock material is carried by the extrusion wheel from the coining roll to an opening or port of the die chamber. The die chamber has a projecting abutment immediately behind the port which extends into the groove and which forces the rod of feedstock material to leave the extrusion wheel and pass through the port. As the extrusion wheel rotates it forces the rod through the port of the die chamber from where the feedstock material is extruded through the die. The rod of feedstock material therefore acts similarly to the ram of a traditional extrusion machine with the extrusion wheel providing the force to drive the rod into and through the die chamber.

[0005] A coating of the feedstock material is applied to the groove of the extrusion wheel and the coining roll forces the rod of feedstock material into the groove with sufficient force to create a temporary bond with the coating so that the force generated by the extrusion wheel can be transferred effectively to the rod.

[0006] The rod of feedstock material is therefore forced to deform somewhat as it is forced into the groove by the coining roll. It is subsequently forced to bend around the extrusion wheel, and is further forced to deform as it engages the abutment and passes through the port of the die chamber. All of these actions generate heat in the rod of feedstock material. In some applications sufficient heat is generated to allow the rod of feedstock material to be extruded without requiring additional heat, but in other applications the die chamber is heated so that the feedstock material reaches a sufficient temperature to be extruded.

[0007] It will be understood that the abutment causes the rod of feedstock material to leave the extrusion wheel immediately adjacent to the port of the die chamber and the extrusion wheel lies as close as possible to the port and to the abutment. Nevertheless, a small clearance gap necessarily exists between the rotating extrusion wheel and the stationary die chamber in order to prevent damage to one or both of these components. As the rod of feedstock material passes from the groove to the port it crosses the clearance gap and the extrusion pressure will typically force the rod of feedstock material to deform to substantially fill the clearance gap. Some of the feedstock material will subsequently be squeezed off the rod in the form of thin strips of feedstock material as the rod passes through the port, which material is often called flash.

[0008] The rod of feedstock material is transported in the groove of the extrusion wheel for less than one complete rotation of the extrusion wheel (and in practical applications around a quarter of a rotation). A scraper blade is located in the other part of the rotation (between the abutment and the coining roll). The scraper blade has a similar shape to the groove and projects into the groove. As the extrusion wheel rotates past the stationary scraper blade flash is removed from the surface of the extrusion wheel. The scraper blade is a necessary component for preventing flash being fed by the extrusion wheel back to the die chamber. When the feedstock material is aluminium or copper, the flash will typically contain oxides as well as other contaminants; if the flash enters the die chamber it will be extruded as part of the product, usually forming blisters and / or marks upon the surface of the extruded product.

[0009] EP 0 398 747 discloses a so-called "twin groove extrusion wheel" which is a development of the new machine and method described above. The extrusion wheel has two grooves so that two rods of feedstock material can be transported together to the die chamber. Using two rods of feedstock material has significant benefits, including increasing the rate of production of extruded products, facilitating the production of larger cross-section hollow extruded products, and achieving the required flow balance for the production of certain hollow extruded products. It will be understood, however, that two rods of feedstock material will typically produce twice as much flash which must be removed by the scraper blade or blades.

[0010] Some practical applications of a twin groove extrusion wheel utilise a die chamber with two ports, one port for each rod of feedstock material, in an arrangement often called "twin groove and twin port". Other practical applications utilise a die chamber with only a single port for both of the rods, often called "twin groove single port". This latter arrangement is typically used to increase the rate of production of extruded product but has the disadvantage that at least some of the flash generated between the two grooves will easily enter the port of the die chamber, often resulting in a poor surface finish of the extruded product, particularly for larger extruded products.SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide an extrusion machine having a twin groove and single port arrangement which reduces or avoids the problems with the known tooling of this type.

[0012] According to the invention there is provided an extrusion machine comprising an extrusion wheel and a die chamber, the extrusion wheel having a single groove adapted to accommodate two rods of feedstock material, the die chamber having a single port through which the two rods of feedstock material can pass in use.

[0013] Preferably, the groove is adapted to accommodate the two rods of feedstock material in a side-by-side configuration. Accordingly, the width of the groove is based upon twice the width of the rods.

[0014] Preferably, the cross-sectional shape of the two rods is circular (or substantially circular) before insertion into the groove. Desirably, the diameters of the two rods of feedstock material are identical. Preferably, the width of the single groove is less than twice the diameter. It will therefore be understood that the two rods are deformed somewhat as they are forced into the single groove. It is arranged that the deformation is sufficient to create a temporary bond between the rods of feedstock material and the surface of the single groove as in the known extrusion machines.

[0015] Preferably, the groove has a raised rib, desirably located centrally of the groove. The raised rib effectively divides the bottom of the groove into a first part to accommodate a first rod of feedstock material and a second part to accommodate a second rod of feedstock material. Such a groove has the general form of a "W" and can be described as a W-groove.

[0016] Desirably, the bottom of the first part of the W-groove and the bottom of the second part of the W-groove are of part-circular form with a radius of curvature slightly smaller than the radius of the rods of feedstock material. In preferred embodiments with a raised rib each rod of feedstock material is thereby forced by the coining roll into a "well" which closely matches the shape of the periphery of the rod. This better enables the required temporary bond to be created with the coating of the groove.

[0017] Preferably, the extrusion machine has a coining roll adapted to force the rods of feedstock material into the single groove. Desirably, there is only a single coining wheel. Accordingly, both of the rods of feedstock material are introduced into the single groove at the same location.

[0018] Desirably, the depth of the single groove is slightly greater than the diameter of the rods. This is similar to the known twin groove tooling, it being recognised as beneficial that the coining roll project into the single groove by a small distance in order to ensure that the rods are properly bonded to the extrusion wheel.

[0019] Desirably, the extrusion machine has an abutment adjacent to the port adapted to force the rods of feedstock material out of the single groove. Preferably, the die chamber has a housing and the abutment is a part of the housing. There is preferably a single abutment and the abutment preferably projects into the single groove.

[0020] Preferably, a single scraper blade is provided having a shape closely to match the single groove of the extrusion wheel.

[0021] A first benefit of the present invention is that no flash is created in the region between the rods of feedstock material as the rods pass through the single port, so that less flash is created than with the known twin groove and twin port tooling. In some applications it is expected that the amount of flash created can be around 50% less than with the known twin groove and twin port arrangements (flash being created at the two side edges of the single port as opposed to the four side edges of the twin ports).

[0022] A second benefit is that the size of the region between the extrusion wheel and the port of the die chamber can be reduced by approximately 30-40% over the known twin groove and twin port tooling. This in turn is expected to reduce the load on the extrusion wheel and extend the tooling life.

[0023] A third benefit is that the provision of a single groove for two rods of feedstock material enables the width of the extrusion wheel and coining wheel to be reduced, thereby reducing the tooling cost.

[0024] In a development of the present invention, an extrusion wheel can be adapted to accommodate four rods of feedstock material, the four rods being forced into two grooves, each groove cooperating with a single port. The use of four rods of feedstock material can further increase the production rate of extruded product.

[0025] The invention also provides a method of extrusion using the extrusion machine as defined, in which two rods of feedstock material are forced into a single groove by the coining roll, parts of the two rods interengaging in the single groove, and in which the two rods of feedstock material are forced out of the single groove by an abutment and pass together through a single port of the die chamber.BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Fig.1shows the an extrusion machine according to the present invention; Fig.2shows an enlarged cross-sectional view along the line A-A of Fig.1; Fig.3shows an enlarged cross-sectional view along the line B-B of Fig.1; Fig.4shows an enlarged cross-sectional view along the line C-C of Fig.1; and Fig.5shows a part of the die chamber of the extrusion machine of Fig.1. DETAILED DESCRIPTION

[0027] Fig.1 shows an extrusion machine of the present invention.

[0028] Two rods 10 of feedstock material are created and fed side-by-side to the extrusion machine. Only one rod 10 can be seen in Fig.1 as the other rod is hidden behind the rod 10. The rods 10 are initially circular in cross-section and have the same diameter. As the rods 10 pass between an extrusion wheel 12 and a coining roll 14 they are pressed (together) into a groove 16 in the periphery of the extrusion wheel 12.

[0029] In known fashion, the groove 16 has a coating 18 of feedstock material, i.e. the same material as the rods 10. This coating 18, together with the deformation of the rods 10 as they are forced into the groove 16 by the coining roll 14, creates an effective bond between the extrusion wheel 12 and the rods 10. In particular, the rods 10 bond with the extrusion wheel 12 sufficiently to remain in the groove 16 as they are forced to bend around the rotating extrusion wheel 12.

[0030] As the extrusion wheel 12 rotates the rods 10 of feedstock material are carried to a stationary die chamber 20. The die chamber 20 has an abutment 22 and a port 24 which is immediately adjacent to the abutment. As shown in Fig.3, the abutment 22 projects into the groove 16. As the rods 10 of feedstock material engage the abutment 22 they are forced out of the groove 16 and through the port 24 of the die chamber 20. As the extrusion wheel 12 continues to rotate, more feedstock material is forced into the die chamber 20 and is subsequently forced through a die 26, the feedstock material forming an extruded product 28 with a size and shape determined by the die.

[0031] As seen in Figs. 2-4, the groove 16 with its coating 18 is of somewhat complex form with a general W-shape. The groove 16 and abutment 22 have the same profile, but the dimensions of the groove 16 and coating 18 upstream of the abutment 22 are slightly larger than the dimensions of the abutment 22.

[0032] The shape of the groove 16 is described in more detail with reference to Fig.4. The width W of the groove 16 (with its coating 18) is slightly smaller than twice the diameter of the rods 10 of feedstock material. A raised rib 30 is located centrally at the bottom of the groove 16. The raised rib 30 divides the bottom of the groove 16 into two parts, one part for each of the rods 10 as is shown in Fig.2. The surface of each part of the bottom of the groove 16 is part-circular with a radius of curvature R. The radius of curvature R is slightly smaller than the radius of the rods 10 of feedstock material. Also, the separation S between the centres of curvature of the surface of each part of the bottom of the groove 16 is slightly smaller than twice the radius of the rods 10 of feedstock material. These relative dimensions ensure that the rods 10 of feedstock material must be deformed as they are forced into the groove 16 by the coining roll 14.

[0033] It will be understood that the raised central rib 30 comprises a continuation of the part-circular surfaces and lies between the rods 10 as they are forced into the groove 16. The top end of the raised rib 30 (and its coating 18) has a radius of curvature r which is very small so that the rib 30 is relatively sharp. Fig.2 shows that the rods 10 have been deformed somewhat by their engagement with the coining roll 14 and with each other and in practice the radius of curvature r of the raised rib 30 is sufficiently small, and the deformation of the rods 10 by the coining roll 14 is sufficiently great, that no gaps remain between rods 10 and the raised rib 30, whereby the deformed rods 10 will substantially fill the bottom of the groove 16.

[0034] The depth D of the groove 16 is slightly greater than the diameter of the rods 10 of feedstock material. Accordingly, the coining roll 14 projects into the groove 16 as shown in Fig.2. The coining roll 14 presses the two rods 10 of feedstock material into the groove 16 at the same location and at the same time.

[0035] The die chamber 20 is shown in Fig.5. The die chamber has a single port 24 through which both rods 10 of feedstock material pass, together. Immediately behind the port 24 (in the direction of rotation of the extrusion wheel 30) is the abutment 22, which is a part of the housing providing the die chamber 20.

[0036] Downstream of the abutment 22, the profile of the coating 18 in the groove 16 of the extrusion wheel 12 matches the profile of the abutment 22.

[0037] Fig.1 shows the scraper blade 36 which projects into the groove 16 and which removes flash from the groove 16 as the extrusion wheel 12 rotates past the scraper blade. It will be understood that the scraper blade removes the material (flash) which has been squeezed between the die chamber 20 and the extrusion wheel 12, the removed material 38 being shown in Fig.1. It will be understood that significantly less flash will be created by the present extrusion machine than with the known twin groove and twin port arrangement since with the present machine the facing portions of the two rods 10 of feedstock material are not required to move past a wall of the port at which flash would be produced.

Examples

Embodiment Construction

[0026]The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

Fig.1shows the an extrusion machine according to the present invention; Fig.2shows an enlarged cross-sectional view along the line A-A of Fig.1; Fig.3shows an enlarged cross-sectional view along the line B-B of Fig.1; Fig.4shows an enlarged cross-sectional view along the line C-C of Fig.1; and Fig.5shows a part of the die chamber of the extrusion machine of Fig.1.

DETAILED DESCRIPTION

[0027]Fig.1 shows an extrusion machine of the present invention.

[0028]Two rods 10 of feedstock material are created and fed side-by-side to the extrusion machine. Only one rod 10 can be seen in Fig.1 as the other rod is hidden behind the rod 10. The rods 10 are initially circular in cross-section and have the same diameter. As the rods 10 pass between an extrusion wheel 12 and a coining roll 14 they are pressed (together) into a groove 16 in the periphery of the extrusion w...

Claims

1. Extrusion machine comprising an extrusion wheel and a die chamber, the extrusion wheel having a single groove adapted to accommodate two rods of feedstock material, the die chamber having a single port through which the two rods of feedstock material can pass in use.

2. The extrusion machine according to claim 1 in which the single groove is adapted to accommodate the two rods of feedstock material in a side-by-side configuration, and in which the single groove has a width which is less than the combined width of the two rods.

3. The extrusion machine according to claim 1 or claim 2 in which the single groove is configured to accommodate two rods of feedstock material which have a substantially circular cross-section before insertion into the single groove.

4. The extrusion machine according to claim 3 in which the single groove is configured to accommodate two rods of feedstock material which have substantially identical diameters, and in which the width of the single groove is less than twice the diameter of the two rods.

5. The extrusion machine according to any one of claims 1-4 in which the single groove has a raised rib.

6. The extrusion machine according to claim 5 in which the raised rib is located centrally in the single groove.

7. The extrusion machine according to claim 5 or claim 6 in which the single groove has a bottom part, the bottom part comprising a first bottom part and a second bottom part which are separated by the raised rib.

8. The extrusion machine according to claim 7 in which the first bottom part and the second bottom part are both of part-circular form.

9. The extrusion machine according to claim 8 in which the single groove is configured to accommodate two rods of feedstock material having an identical and circular cross-section with a cross-sectional radius which is larger than the radius of curvature of the part-circular form of the first bottom part and the second bottom part.

10. The extrusion machine according to any one of claims 1-9 in which the single groove has a depth and is configured to accommodate two rods of feedstock material having a cross-sectional dimension which is smaller than the depth.

11. The extrusion machine according to any one of claims 1-10 having a coining roll configured to force the two rods of feedstock material into the single groove.

12. The extrusion machine according to any one of claims 1-11 having an abutment located adjacent to the single port, and in which the abutment projects into the single groove.

13. The extrusion machine according to claim 12 in which the die chamber has a housing and the abutment is a part of the die chamber housing.

14. The extrusion machine according to any one of claims 1-13 having a scraper blade with a cross-sectional shape closely matching the cross-sectional shape of the single groove.

15. A method of extrusion using the extrusion machine according to any one of claims 1-14, in which two rods of feedstock material are forced into a single groove, parts of the two rods interengaging in the single groove, and in which the two rods of feedstock material are forced out of the single groove and pass together through the single port of the die chamber.

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