WO2012003540A2

WO2012003540A2 - Extruding machine

Info

Publication number: WO2012003540A2
Application number: PCT/AU2011/000853
Authority: WO
Inventors: Glen Titmuss
Original assignee: Gt Ex-Press Pty Ltd
Priority date: 2010-07-06
Filing date: 2011-07-06
Publication date: 2012-01-12
Also published as: WO2012003540A3

Abstract

Disclosed herein is an extruding machine (10). The extruding machine (10) comprises a frame defined by upper and lower pairs of tie rods (12), between which extend a main cylinder platen (14), a front platen (16), and a crosshead container fixture (18), all of which are axially adjustably mounted on the tie rods (12). The extruding machine (10) comprises a hollow cylindrical container (20), which is mounted to the frame via the crosshead container fixture (18). The container (20) defines a press chamber (22) having a longitudinal axis (24) and has a first open end (26) and an opposite second open end (28) communicating with the press chamber (22). The second end (28) of the container is adapted to receive a die (30), which is held in a die holder (32). The die holder (32) is axially slidably mounted to the frame via a slide assembly (34) that extends from the front platen (16).

Description

"Extruding machine"

Cross-Reference to Related Applications

The present application claims priority from Australian Provisional Patent Application No. 2010902999, the entire content of which is incorporated herein by reference.

Field

The present disclosure relates to an extrusion machine and to a method of extrusion. The extrusion machine and extrusion method have been developed primarily for use in extruding aluminium alloys and will be described hereinafter with reference to this application. However, it will be appreciated that the broad concepts enunciated in the present disclosure may also be applied to the extrusion of other metal alloys, such as magnesium, titanium, lead, tin, zinc, copper, steel and their alloys, extrudable plastics, or other extrudable materials, or indeed may find application in other fields, such as in the extrusion of food or pharmaceutical products. Background

Known extrusion techniques include direct (or "conventional") extrusion, indirect extrusion, and so-called "continuous" extrusion.

Conventional direct and indirect extrusion

Direct extrusion involves loading a pre-heated metal billet of predetermined length into one end of a container and then applying a pressing load through a stem fixed to a hydraulic ram to cause extrusion of the metal through an orifice in a die that is fixed in position at the other end of the container. When the loaded billet is nearly consumed, the pressing is stopped and a remaining portion of billet is sheared off from the entry to the die. This sheared off material typically contains an accumulation of billet skin, an accumulation of oxidised remnants of previous billets from the container, and potential contaminants, such as lubricants used to avoid welding between the stem and billet. The stem must be withdrawn from the container whilst a new billet is loaded. The new billet is then "upset" to fill the container, the system is depressurised to evacuate entrapped air between billet, container and die, and extrusion recommences. This non-extruding billet reloading cycle takes around 16 to 20s in efficient extruding perations. After extrusion has recommenced, a die mark or "stop mark" manifests itself around the entire cross section of the extruded profile. This is a result of changed state of deflection of the die bearing at rest compared to under load, which marks the extruded section. The extruded material is then cooled and stretched before being cut to customer lengths. For aesthetic reasons, these lengths cannot contain the "stop mark". Therefore, careful billet length planning is required for every die shape and customer order to obtain the required number of lengths and to minimise waste cut-offs. Theoretically, recoveries of 89 to 93% of billet starting weight are possible with extrusion of common aluminium alloys. In reality, well managed extruding operations achieve recoveries between 80 to 85%. A major factor affecting lower recovery is that product density (referred to as section mass per metre) is often quite variable during the starting billets of any extrusion run on a given die, resulting in either missed customer lengths, due to the extruded length being too short, or excessive waste, as a result of extruded length being too long. Other factors affecting the extruded length include billet diameter tolerance, billet cut length tolerances or shearing tolerances, and the precision of extruded length measurements on the extrusion press, since the section mass per metre value calculated from this data is used for billet length planning the next time the die is extruded.

Many known direct extrusion press operations have automated stretching and cutting equipment to reduce labour costs. However, such equipment relies on actual extruded lengths matching planned lengths for every billet. In practice, a compromise is employed where either scrap allowances are increased_, and/or the operations are run part-manually (i.e. only semi-automatically).

In direct extrusion operations, in order to maximise recovery, in-line hot billet shears or hot saws are required to achieve desired billet length. A sophisticated feedback system is also required to calculate section running weight and plan for the next extrusion run, which could require a different extruded length.

Heavy mass per meter extruded sections have a lower recovery because they impose a maximum upper limit on billet length (constrained by container length and press capacity) and scrap allowances for "stretcher crush" and "stop mark" are essentially fixed lengths and therefore represent a higher proportion of billet start weight.

Another disadvantage of current extrusion processes, is their being stop-start, which results in thermal cycling within dies. The changes in temperature associated with the thermal cycling cause movement in the die, particularly in shapes incorporating channels, which result in undesirable shape variations from the start of the billet to when temperatures increase again towards the end of the billet.

Conventional continuous extrusion

In a conventional continuous extrusion process, a solid feedstock, such as an aluminium rod or other solid or powdered material, is fed in an unheated state into a circumferential groove on a rotating wheel. A portion of the circumference of the wheel, typically about one-quarter of the length thereof, is maintained in close contact with a fixed heavy metal block known as an extrusion shoe. At the end of the contacting portion, a blocking abutment enters the groove and obstructs the path of the feedstock, preventing it from being carried further along the groove in the rotating wheel. As the extrusion material is pushed against the blocking abutment by the frictional force exerted by the continuously rotating wheel, sufficient force is produced to extrude the material through a die retained at the end of a chamber in the shoe adjacent to the blocking abutment. With this process, there are significant limitations on the complexity of extruded shapes that can be produced, which are well documented. This limitation is understood to result from:

i) the feedstock being forced to make a substantially right angle turn at the abutment before flowing through the die, which substantially prevents a uniform flow pattern of metal entering a complex die shape; and

") significant restrictions in the size or cross sectional area of the feedstock, which is limited to a diameter of approximately 50mm. Accordingly, an expansion chamber is required on any extruded shape with circumscribing larger than 50mm, which in practice represents the majority of extruded shapes in most commercial extrusion plants. Moreover, expansion chambers create further flow complications when extruding.

Known continuous extrusion processes are particularly susceptible to a number defects associated with the flow and intrusion of feedstock skin into the extruded product cross section, which can result in de-lamination and poor extruded product integrity. Again, this is caused by the relationship between the feedstock and the abutment, which requires the feedstock to perform a 90 degree turn before flowing through the die.

In known continuous extrusion processes, the feedstock is heated only by friction to facilitate flow of the feedstock during extrusion through the die. That is, the feedstock is not pre-heated prior to entry into the wheel. The frictional heating imposes stresses on the feedstock, with the feedstock being subjected very significant cold working stresses which, when the feedstock material heats up, result in different and non-uniform grain structures compared to a similar profile extruded by direct or indirect extrusion. In United States Patent 5167138, which discloses a continuous extrusion process, the authors themselves acknowledge the non-uniformity of the grain structure of extruded product, although they attribute the cause to purely temperature related reasons. The authors of the Ί 38 patent also acknowledge that the inconsistent grain size results in structural deficiencies in the extruded product.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary

Throughout this specification the word "comprise", or variations such as

"comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

In a first aspect, the present disclosure provides an extruding machine comprising:

a hollow cylindrical container defining a press chamber having a longitudinal axis, the container having a first open end and an opposite second open end communicating with the press chamber, the second end of the container being adapted to receive a die;

a main piston assembly mounted for connection relative to the container, the main cylinder assembly comprising a main piston axially slidably engageable with the press chamber via the first open end of the container, the main piston, in use, being adapted to engage and compress a billet of extrudable material in the press chamber against the die;

a retainer mounted for connection relative to the container, the retainer being selectively engageable with the billet to retain the billet in position upon disengagement of the main piston from the billet and withdrawal of the main piston from the press chamber, the retainer being adapted to apply sufficient restraining force to the billet to hold the billet in position during extrusion of the extrudable material.

A die holder for holding the die may be axially slidably mounted relative to the container to engage and compress the die against the restrained billet during withdrawal of the main piston.

The retainer may comprise a gate that is slidably engageable in a transverse slot extending through the container between an open configuration and a closed configuration. The gate may have an opening therein of complimentary shape to a transverse cross-sectional shape of the container, such that, in the open configuration, the gate opening aligns with the press chamber and, in the closed configuration, the gate opening is transversely offset from the press chamber. During movement from the open configuration to the closed configuration, the gate may be adapted to shear off a portion of the billet. Upon loading of a new billet in the press chamber and re- · engagement of the main piston, the gate may be adapted to slide back to its open configuration and reinstate the sheared off portion of the billet.

The main piston may be adapted for transverse movement out of alignment with the press chamber. A pusher may align with the press chamber, when the main piston is out of alignment with the press chamber, and may extend between a retracted configuration and an extended configuration to push a billet into the press chamber.

A controller may be provided for monitoring consumption of a loaded billet and maintaining a substantially constant rate of axial movement of a rear end of the loaded billet relative to the die. The controller may maintain this constant rate by controlling relative axial movement of the main piston and die when the retainer is disengaged from the loaded billet, and by controlling relative axial movement of the die and retainer when the retainer is engaged with the loaded billet.

In a second aspect, the present disclosure provides an extrusion method comprising:

loading a first billet of extrudable material into a press chamber having a longitudinal axis;

applying a compressive force to the first billet to extrude the material through a die at one end of the chamber;

maintaining the compressive force at a level to achieve substantially constant extrusion whilst loading a second billet of the extrudable material into the press chamber;

applying a compressive force to the second billet to extrude the material of the second billet and residual material from the first billet through the die.

The application of compressive force to the first billet may comprise applying a compressive force in a first direction along the longitudinal axis. The maintenance of the compressive force at a level to achieve a substantially constant extrusion speed whilst loading the second billet may comprise applying a compressive force in an opposite second direction along the longitudinal axis. The application of a compressive force to the second billet may comprise applying a compressive force in the first direction. Brief Description of the Drawings

An embodiment of the subject extruding machine will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic plan view of an embodiment of an extruding machine in accordance with the present disclosure;

Fig. 2 is an end elevational view of the gate of the extruding machine of Fig. 1 ; and

Figs. 3a to 3s show, in schematic plan view, an operating sequence of the extruding machine of Fig. 1. Detailed Description

Referring to the drawings, there is shown an extruding machine 10. The extruding machine 10 comprises a frame defined by upper and lower pairs of tie rods 12, between which extend a main cylinder platen 14, a front platen 16, and a crosshead container fixture 18, all of which are axially adjustably mounted on the tie rods 12. The extruding machine 10 comprises a hollow cylindrical container 20, which is mounted to the frame via the crosshead container fixture 18. The container 20 defines a press chamber 22 having a longitudinal axis 24 and has a first open end 26 and an opposite second open end 28 communicating with the press chamber 22. The second end 28 of the container is adapted to receive a die 30, which is held in a die holder 32. The die holder 32 is axially slidabiy mounted to the frame via a slide assembly 34 that extends from the front platen 16.

A main cylinder assembly 36 is mounted to the frame, and thereby is mounted relative to the container 20, via the main cylinder platen 14. The main cylinder assembly 36 comprises a hydraulic cylinder 38, in this embodiment shown as double- acting, which actuates a main piston 40 that is axially slidabiy engageable with the press chamber 22 via the first open end 26 of the container 20. In use, the main piston 40 is adapted to engage and compress a billet 42 of extrudable material in the press chamber 22 against the die 30 to form an extrusion 43 on a downstream side of the die.

A retainer, in the form of a gate 44, is slidabiy mounted in a transverse slot 46 extending through the container 20. As shown in Fig. 2, the gate 44 has an opening 48 therein that corresponds with a transverse cross-sectional shape of the container 20. In an open configuration, the gate opening 48 aligns with the press chamber 22, such that a loaded billet 42 can be compressed, through the gate opening 48, against the die 30. In a closed configuration, the gate opening 48 is transversely offset from the press chamber 22, such that gate body engages a butt end of the loaded billet 42. It will be appreciated that with the gate 44 in the closed configuration, engagement of the gate body with the butt end of the loaded billet 42 applies sufficient restraining force to retain the loaded billet 42 in position whilst extrusion continues and whilst the main piston 40 is withdrawn from the press chamber 22 and a new billet 42' is loaded in the container 20. With the gate 44 closed, four hydraulic cylinders 50 axially slidably move the die holder 32 on the slide assembly 34 to engage and compress the die 30 against the restrained billet 42 and continue extrusion during withdrawal of the main piston 40, loading of the new billet 42', re-engagement of the main piston 40, and re-opening of the gate 44.

During movement of the gate 44 from the open configuration to the closed configuration, the gate 44 is adapted to shear off a portion 42a of the billet 42. Upon loading of the new billet 42' in the press chamber 22 and re-engagement of the main piston 40, the gate 44 is adapted to slide back to its open configuration and reinstate the sheared off portion 42a of the billet 42. A double-acting hydraulic cylinder 52 is provided to move the gate 44 between its open and closed configurations.

The main piston 40 is also adapted for transverse movement out of alignment with the press chamber 22 in order to facilitate loading of the new billet 42' in the container 20. When the main piston 40 is out of alignment, a pusher 54 aligns with the press chamber 22 and moves from a retracted configuration to an extended configuration to push the new billet 42' into the press chamber 22. The pusher 54 is then retracted and moved out of alignment with the press chamber 22 and the main piston 40 is re-aligned with the press chamber 22. A transversely oriented hydraulic cylinder 56 is provided to move the main piston 40 and pusher 54 into and out of alignment with the press chamber 22.

A controller (not shown) is provided for monitoring consumption of the loaded billet 42 and maintaining a substantially constant rate of axial movement of a rear end of the loaded billet 42 relative to the die 30. The controller maintains this constant rate by controlling relative axial movement of the main piston 40 and die 30, via a hydraulic system comprising the main hydraulic cylinder 38, cylinders 50 and a counterbalance valve circuit or similar load control, when the gate 44 is in its open configuration and disengaged from the loaded billet 42, and by controlling relative axial movement of the die 30 and gate 44, via the four of hydraulic cylinders 50, when the gate 44 is in its closed configuration and engaged with the loaded billet 42. The controller also controls movement of the gate 44 from its open to its closed configuration, via the hydraulic cylinder 52, when it is sensed that the main piston 40 has compressed the loaded billet 42 to a point where the head of the main piston 40 is adjacent the gate 44. The controller also controls withdrawal of the main piston 40, via the main cylinder 38, along with transverse movement of the main piston 40 and pusher 54, via the transversely oriented hydraulic cylinder 56. Also, the controller controls extension and retraction of the pusher 54, via a pusher cylinder 58. Upon loading of a new billet 42', the controller controls engagement of the main piston 40 with the newly loaded billet 42', which the main piston 40 compresses against a rear of the gate 44. With the new billet 42' compressed against the rear of the gate 44, the controller controls movement of the gate 44 from its closed to its open configuration. It will be appreciated that during this entire process, in order to obtain a substantially constant extrusion speed, the speed of movement of the piston 40 and die holder 32 must be carefully synchronised in relation to each other to obtain a substantially constant compressive force at the interface between the front face of the billet 42 and the die.

An operating sequence of the extrusion machine 10 is shown in Figs. 3a to 3s, where:

- Fig. 3a shows the initial loading of a billet 42;

- Fig. 3b shows the billet 42 being upset against the die 30 and extrusion commencing;

- Fig. 3c shows extrusion continuing with further application of compression to the billet 42 via the main piston 40;

- Figs. 3d shows the extrusion process continuing, but at this point, the main piston 40 starts to decelerate whilst the die 30 and die holder 32 start to accelerate in a direction towards the gate 44;

- Fig. 3e shows a point in the extrusion process where the main piston 40 has progressed to a stop at a point adjacent the gate 44 whilst the die 30 has now accelerated to reach nominal speed;

- Fig. 3f shows the gate 44 moving to its closed configuration and shearing off a portion of the billet 42, whilst extrusion continues via billet compression due to axial movement of the die holder 32 toward the gate 44 and piston 40 remains hydraulically locked in position;

- Fig. 3g to 3k show the main piston being withdrawn and a new billet 42' being loaded, whilst extrusion continues via billet compression due to axial movement of the die holder 32 toward the gate 44;

- Fig. 31 shows the new billet being compressed against the rear of the gate, whilst extrusion continues via billet compression due to axial movement of the die holder 32 toward the gate 44; - Fig. 3m and 3n show the gate 44 returning to its open configuration, whilst extrusion continues via billet compression due to axial movement of the die holder 32 toward the gate 44, with the main piston 40 remaining hydraulically locked in position until the gate 44 has fully opened; and

- Figs. 3o shows a transition wherein axial movement of the die holder 32 towards the gate 44 decelerates at the same time as the main piston 40 starts to accelerate toward the gate 44. This transition ends when the main piston 40 reaches its nominal speed and the die holder 32 ceases axial movement.

- Figures 3p to 3s show the die returning to its forwardmost position, whilst extrusion continues due to compression of the new billet 42' via the main piston 40.

The speeds of the main piston 40 and the die 30 are adjusted during the extrusion process to maintain a substantially constant compressive force at the interface between the die 30 and the front face of the loaded billet 42, 42' to achieve a substantially constant speed of extruded metal exiting the die. For example, the main piston 40 moves faster during the sequences shown in Figs. 3p to 3s than it does at other times in order to adjust for the die 30 returning to its forwardmost position.

It will be appreciated that the illustrated extruding machine 10 extrudes without the emitting extrusion stopping, and thereby without rendering a die "stop mark" until the desired length of extrusion is obtained. The elimination of stop marks provides improved material recovery rates, easier planning, and planning "on the run". The illustrated extrusion machine 10 is also able to provide a range of extruded cross- sectional shape complexities typically required in commercial extrusion operations. Grain structure uniformity and structural integrity of product extruded with the illustrated extrusion machine 10 is consistent with that of product obtained from known commercial direct extrusion operations. The" illustrated extrusion machine 10 also facilitates improved productivity, since there is no down-time during billet loading. The elimination of stoppages for billet loading also reduces thermal cycling and reduces extruded section shape variability that can occur from front to back of an extruded billet run due to this phenomena in sensitive shapes. The illustrated machine 10 also provides better material recovery, due to variable extruded section mass at the beginning of a run not influencing the attainment of the target run-out lengths. The illustrated machine 10 is also suited to smaller laboratory style presses for conducting more authentic testing of die material and alloys, etc, at reduced cost. Conventional laboratory style presses do not provide representative thermal cycling of full-size presses due to the smaller scale of press and billet resulting in the extrusion contact time per billet being very short (at a given ram speed in mm/s), with the dead cycle by comparison being much longer, so that tooling has less time to heat during extrusion but relatively longer to cool and a lower thermal mass to hold heat. The illustrated machine 10 results in a net saving in energy usage due to greater yield of saleable extrusion per kilogram of starting billet mass. The greater yield reduces the level of recycling scrap and thereby reduces energy usage and greenhouse emissions. Even with aluminium requiring the lowest recycling energy input of all metals, the cut-off value for this process is only 1% yield improvement. Accordingly, any greater yield improvement above 1% obtained from the illustrated machine 10 results in a net energy and emissions saving. The cut-off point will be even lower for other extrudable and recyclable materials.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the embodiment described above and shown in the drawings without departing from the broad general scope of the present disclosure. The illustrated embodiment is, therefore, to be considered in all respects as illustrative and not restrictive. Examples of possible variations and/or modifications include, but are not limited to:

• the double-acting piston 40 may be replaced with a ram that is retracted via side cylinders;

• the double-acting hydraulic cylinder 52 may be replaced with two single-acting cylinders disposed at opposite ends of the gate 44 for moving the gate 44 between its closed and open configurations;

• the cylinder assembly driving the gate 44 may have a rod that is not physically connected to the gate 44 but which is brought into contact with the gate 44 to push the gate 44 to one side. There may be an identical cylinder assembly on the other side of the container to push the gate 44 back in the opposite direction when required. In this way, heat transfer to the rod and cylinder assembly is reduced;

• the cylinder assemblies driving the die holder 32 may take other forms, such as a large single hollow piston cylinder assembly mounted onto the front platen 16;

• the die holder 32 may be driven by an alternative press structure, referred to as a pullback press, where the tie rods are cylinder rods in cylinders also mounted adjacent to the main cylinder 36 in the main cylinder platen 14; at their other end, the cylinder rods may be fixed to the front platen 16, or to a crosshead, and the die holder 32 may be mounted on the front platen or the crosshead; and the front platen 16 may be mounted on slides and movable along the press axis driven by the pullback rod cylinder assemblies; and/or

he process by which a new billet is loaded into the container being achieved by means other than using pusher 54 driven by cylinder 58, such as by motor driven rollers incorporated into the billet tray or a cable driven puller attached to a slide mounted into the billet tray

Claims

CLAIMS:

1. An extruding machine comprising:

2. An extruding machine according to claim 1 , wherein a die holder for holding the die is axially slidably mounted relative to the container to engage and compress the die against the restrained billet during withdrawal of the main piston.

3. An extruding machine according to claim 1 or claim 2, wherein the retainer, comprises a gate that is slidably engageable in a transverse slot extending through the container between an open configuration and a closed configuration.

4. An extruding machine according to claim 3, wherein the gate comprises an opening therein of complimentary shape to a transverse cross-sectional shape of the container, such that, in the open configuration, the gate opening aligns with the press chamber and, in the closed configuration, the gate opening is transversely offset from the press chamber.

5. An extruding machine according to claim 3 or claim 4, wherein during movement from the open configuration to the closed configuration, the gate is adapted to shear off a portion of the billet.

6. An extruding machine according to claim 5, wherein upon loading of a new billet in the press chamber and re-engagement of the main piston, the gate is adapted to slide back to its open configuration and reinstate the sheared off portion of the billet.

7. An extruding machine according to any one of the preceding claims, wherein the main piston is adapted for transverse movement out of alignment with the press chamber.

8. An extruding machine according to any one of the preceding claims, comprising a controller for monitoring consumption of a loaded billet and maintaining a substantially constant rate of axial movement of a rear end of the loaded billet relative to the die.

9. An extruding machine according to claim 8, wherein the controller maintains this constant rate by controlling relative axial movement of the main piston and die when the retainer is disengaged from the loaded billet, and by controlling relative axial movement of the die and retainer when the retainer is engaged with the loaded billet.

10. An extrusion method comprising:

. maintaining the compressive force at a level to achieve a substantially constant extrusion speed whilst loading a second billet of the extrudable material into the press chamber;

11. A method according to claim 10, wherein the application of compressive force to the first billet comprises applying a compressive force in a first direction along the longitudinal axis.

12. A method according to claim 11, wherein the maintenance of the compressive force at a level to achieve a substantially constant extrusion speed whilst loading the second, billet may comprise applying a compressive force in an opposite second direction along the longitudinal axis.

13. A method according to claim 11 or claim 12, wherein the application of a compressive force to the second billet may comprise applying a compressive force in the first direction.