PRESS FOR DIRECT EXTRUSION OF METAL PRODUCTS

Abstract

A press for the direct extrusion (100) of billets comprises a shear (6) for cutting the bottom precisely along a plane orthogonal to the extrusion axis (X) which is carried by the columns (9′, 9″) by means of sliding guides (13′, 13″), so as to allow the shear (6) to slide and to position in different points along the extrusion axis (X) in different steps of the extrusion operation to carry out the cutting operation and to position in quiescent position during which the easy replacement of the container (3) may also be carried out.

Description

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention refers to a press for the direct extrusion of metal section bars, obtained from the extrusion of billets, provided with shear for cutting the bottom.

2. State of the Art

Direct extrusion presses essentially comprise a main cylinder which serves the task of providing the push or force required to deform a billet. Billets are the starting product on which the process of extrusion is carried out, and may consist of metals or alloys, such as aluminium, copper, brass, steel, etc. The cross-sections thereof may differ in diameter.

It is known that the push which is to be exerted by the main cylinder in direct extrusion presses is adapted to the type of metal to be extruded and to the diameter of the billet. Presses currently on the market develop extrusion forces which vary between 600 and 15,000 tons, while the diameters of the billets which are extruded in such presses may fall between a range of 152 mm (6″) and 600 mm (24″).

All metals have their own minimum specific working pressure, which is to be supplied by the press, below which extrusion becomes impossible. For example, aluminium has a specific pressure between 50 and 80 kg/mm², according to the force of the press and the cross-section of the billet. The maximum extrusion speeds achievable also differ based on the metal to be extruded: for example, aluminium may be extruded with die crossing speeds between 0 and 30 mm/sec, copper and brass with speeds between 0 and 65 mm/sec, steel with speeds between 0 and 400 mm/sec.

Essential elements forming extrusion presses are a main cylinder which, through a pressing stem, pressurizes the billet inside a container and then causes it to cross the hole of a die. A shear is provided at the end of the extrusion of the billet, with the task of cutting the last stretch of billet, called “bottom”, which remained upstream of the die because the billet impurities are conveyed therein. Thus, the bottom remains attached to the die itself and is removed and caused to fall by means of the action of a shear with a top-downwards cutting movement orthogonal to the billet axis.

Documents JP8033917 and JP8010831 disclose solutions for fixing the shear to the press in which the shear is firmly anchored to the reaction crosspiece of the press by means of a frame arranged overhangingly above the die pack. The structure for anchoring the shear with the reaction crosspiece of the press is therefore staggered by a given distance with respect to the cutting cross-section, which, during shearing, causes a bending moment on the anchoring structure given by the product of the cutting force multiplied by the distance from the surface of the crosspiece to which the anchoring structure is fixed.

This bending moment, which is generated during the cutting of the bottom, is released onto the press structure through the anchoring structure of the shear, thus compromising the flatness of the cut. A curved-oblique cut is generated, corresponding to a tilted surface crosswise to the longitudinal axis of the billet due to the deviation of the blade from the ideal trajectory, which corresponds to a plane orthogonal to the billet axis, thus progressively moving the blade edge away from the surface of the die as the blade sinks into the body of the bottom. At the end of the cutting operation, there is material protruding on the lower edge of the die due to the tilted cutting surface with respect to the die plane. Accordingly, at the successive approach of the container against the die, such a residual protruding material prevents an effective gripping between the container and the die, thus leaving a gap through which the material partly escapes from the successive billet to be extruded, thus causing a waste of material and the need to manage such escapes during the activity of the press.

Another problem with the shears described in the above-mentioned documents JP8033917 and JP8010831, concerns the impediment caused by the volume of the shear during the replacement of the container. During such an operation, the container is removed from the pressing stem in axial direction and is then extracted from the top of the press in direction crosswise to the axial direction. During the course of such an extraction, the shear structure is therefore a hindrance to the movement of the container, thus forcing longer travels for the container to be provided to have increased free space on the side of the main cylinder and to thus allow the extraction of the container from the top.

Document U.S. Pat. No. 3,220,237 describes an extrusion press provided with a shear mounted on two longitudinal columns of the press along which the shear may carry out a very limited sliding amplitude, within millimeters, in order to calibrate the position of the cutting plane of the shear knife. Sliding is only manually controlled by means of tightening a nut about a threaded rod, an operation which is insufficient to free up the area above the plane where contact occurs between the die and the container, thus an increased length of the columns is to be provided to allow the extraction of the container from the press. The sliding of the shear is only possible outside the working cycle of the press, for example during maintenance operations, while it is not possible to carry it out during the working cycle.

SUMMARY OF THE INVENTION

The object of the invention is to provide a press equipped with a shear for the direct extrusion of metal products which overcomes the above-mentioned problems and improves the cutting quality of the bottom, thus generating precise and planar cutting surfaces, thus ensuring complete cleaning of the die surface from the bottom, so as to prevent residues of extruded material on the die.

Another object of the invention is to ensure a clean gripping surface, between die and container, without any flashes so as to prevent discontinuity through which the billet, which is then extruded, may escape thus causing a loss of material and the formation of further flashes.

Another, no less important object of the invention is the one of providing an extrusion press which is compact while ensuring easy maintenance operations.

These and other problems which will be apparent by reading the following description, according to a first aspect of the invention, are resolved by means of a press for extrusion of a metal product, in particular a billet, in which an extrusion axis is defined and which, according to claim 1 comprises: a main cylinder arranged at a first end of the press with respect to the extrusion axis and comprising a piston, a movable crosspiece, mounted on the piston of said main cylinder, a pressing stem coaxial to and actuated by the main cylinder piston, a container having a through hole therein coaxial to the axis and configured to contain the billet during an extrusion operation, a reaction crosspiece, arranged at a second end of the press in relation to the extrusion axis, having a through hole coaxial to the axis to allow the passage of the metal product after the extrusion operation, having an extrusion die, with a hole coaxial to the axis and a pressing ring, arranged between the die and the reaction crosspiece and coaxial to the axis, at least three longitudinal columns parallel to the extrusion axis, which connect the main cylinder to the reaction crosspiece, configured to transmit the reaction forces generated in the extrusion operation, a shear configured to cut the metal product along a cutting plane crosswise to the extrusion axis, adapted to be arranged coplanar to the cutting plane orthogonal to the extrusion axis, coupled directly to two fixing columns of the at least three longitudinal columns, with a kinematic sliding coupling parallel to the extrusion axis, which allows the shear to position in different axial positions along the extrusion axis, characterized in that when the shear is in a position proximal to the reaction crosspiece, it is not intersected by the cutting plane crosswise to the axis (X).

Due to the features of the invention claimed, rather than being restrained to the reaction crosspiece, the shear is mounted on the longitudinal columns and more precisely, on the cases of the columns, in a preferred embodiment.

After the extrusion of all billets, when the bottom is cut, the shear is vertically aligned at the surface of the die and, since the cut extends along the axis of the shear, no bending moments are generated, but there is only a vertical reaction to the cut which is released onto the columns of the press which are very rigid and do not undergo significant deformations following the cutting operation. Thereby, a precise and rectilinear cut may be carried out along the entire traverse, thus preventing curved-oblique cuts to be made and therefore residual material from remaining on the contact surface between the die and the container.

Advantageously, the structure which restrains the shear to the columns may be equipped with sliding blocks due to which longitudinal movement can be carried out along the columns themselves by means of suitable sliding guides and controlled for example by means of hydraulic or pneumatic cylinders or rack cylinders. Due to such a coupling mode, the shear may be arranged in different axial positions along the columns also during the course of extrusion.

Moreover, as the shear may be moved parallel to the axis of the columns of the press, and as an approach space for the shear is provided close to the reaction crosspiece, the shear can avoid being a hindrance during the operation for changing the container: indeed, it is possible to retract it within the volume space of the die thus freeing up the space in front of the end plane of the die, thus making a larger space available to carry out the extraction of the container from the top since the shear is no longer a hindrance. This further allows the columns to be shortened by a quantity equal to the thickness of the protuberance of the shear structure with respect to the die.

The solution of the invention allows both movement outside of the working cycle, in which the shear is moved to allow the extraction of the container for maintenance, and during the working cycle, in which the shear is moved from the cutting line during the extrusion step to make room for the container and the related crosspiece.

A further advantage of the invention consists in the possibility of automatically controlling the axial sliding of the shear during the working cycle, but without excluding the possibility of also automating the movement during maintenance.

Thereby, a direct extrusion press may be provided with columns, and accordingly the entire structure, which are shorter in length with respect to known presses, thus ensuring increased rigidity of the press and improved quality of the extrusion product.

According to another aspect of the invention, the problems mentioned are resolved by means of an extrusion process carried out by the above press and in accordance with claim 8.

Due to the press of the invention, the following advantages are thus obtained:

• • increased overall rigidity of the press structure, which positively affects the end quality of the extruded product;
  • increased productivity due to the decreased possibility of the escape of material and the formation of flashes, which involve stopping the machine;
  • decreased weights and volumes of the press structure;
  • decreased manufacturing costs of the press structure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a diagrammatic side view of the extrusion press in accordance with the invention;

FIG. 2 shows a sectional view on a plane orthogonal to the direction of the axis of the press of the invention;

FIG. 3 shows a sectional view on an axial plane of the press of the invention, in a first working position;

FIG. 4 shows a sectional view on an axial plane of the press of the invention, in a second working position;

FIG. 5 shows a sectional view on an axial plane of the press of the invention, in a second working position;

FIG. 6 shows a view from above of the press of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The direct extrusion press of the invention, globally indicated with reference 100 defining the extrusion axis X, comprises a main cylinder 1, a pressing stem 2 which extends the main cylinder piston 1 and is about the same in diameter as billet 7, before the extrusion operation. The pressing stem 2 serves the purpose of transmitting the extrusion pressure generated by the main cylinder 1 onto the billet to cause it to pass inside the axial hole 3′ of container 3. The diameter of this hole 3′ is substantially equal to billet 7 before extrusion so that it does not place resistance to the passage of the billet when it is pushed by the pressing stem 2 against die 4. Arranged at the end of the pressing stem 2 is a pressing block 2′ which serves to seal hole 3′ of the container and prevent metal leakage from the inlet.

Container 3 serves the purpose of laterally containing billet 7 during the extrusion process, and of totally guiding the metal flow inside die 4. Container 3 is kept heated with heating temperatures which depend on the metal to be processed, for example for aluminium it is kept at temperatures of about 450° C.

Die 4 consists of a threader with a machined middle hole shaped like the cross-section of the linear product to be obtained at the end of extrusion. The cross-section of the surface of the shape of the middle hole of die 4 is smaller than the area of the cross-section of billet 7 before extrusion. The flow of the metal mass crosses die 4 under the pushing force exerted by the main cylinder 1 on the rear end of billet 7 thus taking the shape of the cross-section wanted, and lengthening and forming bars also more than 100 m long. Due to the principle of the conservation of mass, the end bar will have the same weight as the billet introduced into the container less the bottom, while its length will be defined according to the area of its end crosswise cross-section with respect to the initial one of billet 7.

The structure of the extrusion press 100 comprises a reaction crosspiece 5 on which a pressing ring 10 is mounted coaxially to the extrusion axis, which serve the purpose of countering the force of the main cylinder 1 exerted on the billet, thus transmitting it to the columns 9′, 9″ of the structure, and also to the columns 9ⁱⁱⁱ and 9^iv not shown in FIG. 1. There is a hole 8 in the middle of the reaction crosspiece 5 and of the pressing ring 10 which allows the escape of the section bar generated in die 4 towards the area of further processing provided on the production line. The longitudinal columns 9′, 9″, 9ⁱⁱⁱ and 9^iv are preferably four in number and comprise the pre-tensioned tie rods 16′, 16″, 16ⁱⁱⁱ, 16^iv closed within respective cases 17′, 17″, 17ⁱⁱⁱ, 17^iv which also serve as spacers between the two crosspieces 5 and 15 of the extrusion press 100. Head 5 is thereby rigidly connected to the support of the main cylinder 1.

In an alternative embodiment of the press of the invention, not shown in the figures, it is possible to provide only three columns for connecting the main cylinder 1 and the reaction crosspiece 5, being possible for example to replace two columns resting on the floor with a single column forming the resting base of the press.

In a first variant of the invention, the structure of shear 6 is restrained to the cases 17′ and 17ⁱⁱⁱ of at least two of the columns, for example of the two upper columns 9′ and 9ⁱⁱⁱ, by means of restraints which during the cutting operation, only allow it to develop a reaction which is vertical to the cut, which is released onto the columns of the press; due to such restraints, the shear is precisely fixed on the vertical of the cutting plane and is in perfectly orthogonal position to axis X; thereby, the cut obtained is perfectly linear and has no material residuals.

A second variant of the invention provides that shear 6 is restrained for example to cases 17′ and 17ⁱⁱⁱ of the upper columns 9′ the 9ⁱⁱⁱ by means of a kinematic coupling which allows it to slide longitudinally along the columns 9′ and 9ⁱⁱⁱ, but keeps it stable in a middle position between the two cases 17′ and 17ⁱⁱⁱ in direction parallel and crosswise to axis X, thus allowing the execution of the cutting movement along the direction of arrow Z. This is obtained by means of the sliding blocks 18′ and 18″ integral to the shear structure which slide within two longitudinal guides 13′, 13″ parallel to the extrusion axis X, integral with a respective column 9′, 9″. Due to such a sliding kinematic connection, blade 12 of the shear may be positioned precisely on the vertical of the cutting plane and in position perfectly orthogonal to axis X, thus also minimizing in this case the bending moment which acts on the structure of shear 6 during the cutting, which values are much lower than the ones generated with shear configurations of the state of the art.

It is also possible to use a different sliding kinematic coupling, equivalent to the one of the sliding blocks which slide within guides, a person skilled in the art being capable of making such a coupling according to the design loads of the shear.

A movement system is provided (not shown in the figures) for sliding shear 6 along the guides 13, for example made by means of a hydraulic or pneumatic cylinder or through a rack, controlled in a completely automated manner. This coupling of shear 6 allows it to be positioned in different axial positions along the columns also during extrusion.

The operation of shear 6 on the extrusion press 100 is carried out in the following way. During the extrusion of billet 7, the position of shear 6 is the quiescent one shown in FIG. 3. Once the extrusion of billet 7 is completed, container 3 and the pressing stem 2 retract with respect to die 4, i.e. they move to the left with reference to the view of FIG. 1 or to the right with reference to FIG. 3, thus moving along axis X. At the same time, shear 6 is caused to slide in direction of arrow X′ until it reaches the working position, as shown in FIG. 4, vertically above the top surface of die 4 and then, with a vertical movement in the direction of arrow Z, perfectly orthogonal to the extrusion axis X, it cuts the last stretch of billet, or “bottom”, as shown in FIG. 5, thus leaving a cutting surface which is perfectly coplanar to the top surface of die 4.

Since the structure of shear 6 is fixed to the cases 17′, 17ⁱⁱⁱ of the columns in an area immediately above the bottom to be cut, the cutting operation occurs without any significant bending moments on the structure of shear 6, thus ensuring a completely planar and precise cut which does not leave material surpluses protruding from the surface of the die because it is perfectly flush with the top surface of die 4 and therefore it allows a perfect contact surface of the container on the die at each billet extrusion cycle after the bottom cut.

With particular reference to FIG. 3, die 4 is restrained to the reaction crosspiece 5 so as to leave a sufficient approach space above die 4 in axial direction to house shear 6 without it protruding past the cutting plane and therefore without it being intersected by the cutting plane when it is in a position proximal to the reaction crosspiece 5 which corresponds to the quiescent position.

Due to this configuration of the press structure of the invention, the guides 13 are designed with a limited length which simply allows shear 6 to go from the working position shown in FIG. 5, when the press is in extrusion activity and shear 6 cuts the bottom, to the quiescent position shown in FIG. 3, when shear 6 is in inactive position above die 4 and it is easier to replace container 3 in this position since all the vertical volume band of shear 6 between die 4 and container 3 remains free, unlike known solutions of the state of the art. Therefore, this allows the length of the columns 9′, 9″, 9ⁱⁱⁱ, 9^iv and of the cases 17′, 17″, 17ⁱⁱⁱ, 17^iv to be designed smaller with respect to other configurations of extrusion presses of the state of the art, thus increasing the overall rigidity of the entire press structure.

Claims

1. A press for a direct extrusion of a metal product, in particular a billet, wherein an extrusion axis X is defined, comprising a main cylinder arranged at a first end of the press with respect to the extrusion axis X and comprising a piston,a movable crosspiece, mounted on the main cylinder piston,a pressing stem, coaxial to and actuated by the main cylinder piston,a container having a through hole therein, coaxial to the extrusion axis X and configured for containing the metal product during an extrusion operation,a reaction crosspiece, arranged at a second end of the press in relation to the extrusion axis X, having a through hole coaxial to the extrusion axis X for allowing the passage of the metal product after the extrusion operation, having an extrusion die, with a hole coaxial to the extrusion axis X, and a pressing ring arranged between the extrusion die and the reaction crosspiece and coaxial to the extrusion axis X,at least three longitudinal columns parallel to the extrusion axis, which connect the main cylinder to the reaction crosspiece, configured for transmitting reaction forces generated in the extrusion operation,a shear configured for cutting the metal product along a cutting plane crosswise to the extrusion axis X, adapted to be positioned coplanar to the cutting plane orthogonal to the extrusion axis X,

2. An extrusion press according to claim 1, wherein there are provided coupling means defining a the kinematic sliding coupling comprising linear sliding guides fixed to said two fixing longitudinal columns and sliding blocks fixed integrally with the shear and adapted to slide within the linear sliding guides.

3. An extrusion press according to claim 1 or 2, wherein the at least three longitudinal columns each comprise a respective pre-tensioned tie rod contained within respective cases, which serve as spacers between the movable crosspiece and the reaction crosspiece.

4. An extrusion press according to claim 3, wherein the linear sliding guides are fixed onto the cases of said two fixing longitudinal columns.

5. An extrusion press according to claim 1, wherein said two fixing longitudinal columns are two upper columns.

6. An extrusion press according to claim 1, wherein said two fixing longitudinal columns are two lower columns.

7. An extrusion process carried out by the press according to claim 1, comprising the steps of: a) pushing the metal product through the extrusion die so as to take a shape of a predetermined end metal product, during which the shear is in a quiescent position, distal from the extrusion die andb) cutting an end stretch of the metal product during which the shear is in a working position, coplanar to the cutting plane orthogonal to the extrusion axis X and proximal to the extrusion die.

8. An extrusion process according to claim 7, wherein during step a) the shear is in the quiescent position at an axial position along the extrusion axis X different and away from the cutting plane.