EP0281515B1 - Cooling device for a press for the extrusion of light metals - Google Patents

Abstract

To increase the extrusion speed for extrusion of light-weight metal such as aluminum, without incurring hot short cracks, or fissures, and retaining high-quality smooth surface of the extruded material, the region of the extrusion chamber immediately ahead of the extrusion die (3) is cooled by placing a cooling ring (12, 12') between the bore (9) of the extrusion cylinder in which the ram piston (13) operates. The cooling ring may be a unitary structure, or a multi-part structure, in which an independent inner ring is located within a cooling ring (12). For mechanical strength, a prestressing outer ring (20) is shrink-fitted around the cooling ring. The outer ring is retained, for example by screws (24), on the cylinder (2) within which the extrusion chamber (9, 10) is located. The cooling fluid may be water, a vaporizable liquid, or a gas, and is separated from the billet (1) within the extrusion chamber.

Description

The invention relates to a device for cooling a light metal extrusion press, wherein at least one cooling ring is provided in the forming zone area in the direction of movement in front of the pressing die, in which a coolant circulates closed for dissipating the forming heat, with lines for the supply and discharge of the Coolant are connected.

When extruding light metals, very high forces are exerted on the material to be pressed, so that a preheated press bolt can be reduced to the extruded profile or profiles determined by a die. The temperatures of the press billet and the material to be pressed, pressure, degree of deformation, extrusion speed, surface quality and metallurgical properties of the extruded profile are mutually dependent. The situation is relatively complex because the parameters mutually influence each other when changes are made. When the material is formed, internal deformation and frictional heat is generated in addition to that of the press stud heated to the extrusion temperature.

Extruded light metal extruded profiles are particularly critical with regard to the pressing temperature and extrusion speed because hot short cracking easily occurs.

A flawless, smooth surface of the extruded strand is particularly disturbed if a critical temperature is exceeded in the material to be pressed, at which the eutectic components present as residues become liquid and as a result lead to a rough strand surface.

These problems have previously limited the possible extrusion speed, although the extrusion presses would generally allow a higher press speed.

So far, attempts have been made to solve the problem of hot cracks in the extruded strand by accepting a relatively low pressing speed.

From FR-A-980781 a cooling device for light metal extrusion presses is known, in which a cooling channel is arranged in a so-called antechamber upstream of the die, which follows the contour of the particular profile shape to be produced. With this arrangement, the area immediately in front of the die and the end face of the die are cooled. In the case of different extruded profiles, this requires an adaptation of the cooling channels of the cooling ring. For the numerous different profile shapes to be produced on extrusion presses, there is a great deal of effort, since practically for each extruded profile a separate cooling ring with channels that are adapted to the profile shape has to be produced, which has to be carried out with every tool change must be changed.

With the majority of multi-hole matrices, the effort increases disproportionately. Experience has also shown that it will be very difficult to achieve the exact same cooling effect for each strand, which is absolutely necessary for the emerging profiles to run in sync.

So-called chamber, bridge and cross mandrel (= spider) tools are used for the production of hollow profiles. The proposed solution cannot be used for these types of tools.

In practice, the matrices are stressed to the limit of their resilience. Due to the non-uniform cooling, additional stresses of thermal origin arise in the die, which in many cases lead to breakage or at least to a reduced service life of the tools.

EP-A-01210 256 relates to a process for continuous casting in which the material to be formed is cooled in front of the die. For this purpose there is a plate with a cooling channel open towards the face of the die.

In addition, it is known to cool the die itself, but this greatly increases the manufacturing costs of the die and limits the cooling intensity because of the risk of the die cracking.

Furthermore, it is known to provide a step-by-step reduction in the cross section between the pressing bolt and the extruded profile and to cool the intermediate stages. This results in additional, expensive expenses for the tools and is practically only suitable for single-hole extrusion tools.

From US-A-3 112 828 an internally cooled single-hole extrusion die is known, in which the die itself is provided with a cooling channel surrounding the central die opening. The cooling takes place only in the die itself, i.e. after the main forming of the material. A separate cooling system must be incorporated into each die, which significantly increases the cost of die production. The internal cooling also leads to a cross-sectional limitation and weakening of the die, which is highly stressed due to the temperature gradient in the inside of the die.

A similar solution for multi-hole dies is shown in DE-A-2 240 391. The cooling system, the shape of which is determined by the profile shape to be produced, is located here in the pre-dies and in the main die. Here too there is the disadvantage that the cooling system has to be incorporated into the dies and adapted to the respective extruded profile shape. In addition, the die is weakened and susceptible to cracking due to the temperature gradient. In addition, the main purpose of this cooling device is to regulate the exit speed of the individual strands in order to obtain strands that are as long as possible.

According to DE-C-2 211 645, cooling is carried out at the end of the die. This type of construction is particularly suitable for the use of liquid nitrogen as a cooling medium, which escapes in gas form and is directed onto the strand. The shape and effect of the cooling system depends on the profile shape to be produced.

From DE-C-429 376 it is known to cool a die rigidly connected to the press pin receiver and projecting into the press space outside of the press space.

US-A-4 462 234 shows a two-stage die that is cooled outside the press room. Such a cooling device is practically only suitable for single-hole matrices. The cooling device is also not independent of the die.

The object to be achieved by the invention is to provide an effective cooling device in a light metal extrusion press, which can be produced with simple means, is independent of the die and thus of the extrusion profile forms to be produced, and the cooling is effective in the area of the largest material forming.

The device according to the invention with which this object is achieved is characterized in that the cooling ring, which consists of one or more coaxial rings and is independent of the pressing die, has a bore of the same diameter as the receiving bore of the pressing bolt, and a plurality of rings which are distributed in the ring surface in the axial direction and run to bore the There are radially distanced pairs of pressbore receptacles, which are connected at their area facing away from the die-side mouth by a radial bore which is closed to the outside, and the cooling ring is surrounded radially on the outside by at least one shrunk-on pressure ring which is rigidly connected to the pressbolt pickup.

This is based on the knowledge that when the press material is formed from a large original press stud diameter to a substantially smaller cross-section of the extruded profiles, additional heat is generated during material forming due to internal friction, which has a major influence on the formation of the "hot crack". According to the invention, this heat is dissipated in the area in which it arises - namely directly from the pressing chamber, that is to say in front of the die and not first in the die itself or behind the die. It is therefore more effective to carry out the cooling, if possible, at the point at which the greatest material deformation and thus the greatest temperature increase take place.

The practical implementation of this knowledge, however, creates problems in that the temperature differences in the components affected by the cooling result in a risk of cracking. This risk of cracking is successfully counteracted by the cooling ring formation and the shrunk-on pressure ring. In addition, the ring-like structure of the cooling system results in largely symmetrical cooling. In addition, the cooling channels can be created relatively easily by straight-line bores - thus avoiding winding cooling channel shapes.

Since the cooling device is a component that is independent of the die, no additional cooling channels or other changes need to be provided on the exchangeable dies themselves, which simplifies their manufacture and permits the further use of existing dies. The cooling ring does not have to be changed for different profile shapes. In addition, the highly stressed die is not affected by temperature jumps charged. The largest possible extrusion diameter is not affected by the cooling device. In addition, the same cooling device can be used for different types of profiles, such as solid or hollow profiles, single or multi-hole matrices and for pipes with cooled or uncooled mandrel. The design of the cooling elements around the die-side end of the press pin receiver bore allows the cooling medium to be brought close to the material to be cooled in the forming zone and thus to achieve a rapidly reacting and effective cooling of this forming zone. By removing the friction and forming heat directly from the forming zone, a higher inlet temperature of the press bolt can be used.

Fig. 1

einen Längsschnitt durch eine Strangpresse für Leichtmetalle im Bereich der Umformzone mit Kühlvorrichtung

Fig. 2

einen Schnitt durch die nach der Matrize austretenden Profilstränge nach der Linie II-II in Fig.1.

Fig. 3

einen Längsschnitt durch eine Ausführungsvariante.

Two exemplary embodiments of the device according to the invention are shown in the drawing and are described in more detail below. It shows:

Fig. 1

a longitudinal section through an extrusion press for light metals in the area of the forming zone with cooling device

Fig. 2

a section through the exiting profile strands along the line II-II in Fig.1.

Fig. 3

a longitudinal section through an embodiment.

The material to be pressed in the form of a light metal bolt is inserted in the heated, but not liquid state into the bore 9 of a press bolt receiver 2 of an extrusion press. A press die 3 contains single or multiple openings 4, corresponding to the cross-sectional shape of extruded profiles 5 to be produced in a one-step operation closed circulates. "Closed circulation" is to be understood to mean that the cooling medium does not come into contact with the goods to be cooled, but is supplied via a feed line and is led away from the cooling ring via a return line. This cooling ring 12 sits coaxially on a one-piece inner ring 8. The cylindrical bore 10 of this inner ring 8 is the axial continuation of the diameter of the pressing pin receiver bore 9 and thus corresponds to the diameter of the punch 13. In the cooling ring 12 are all over Annular ring-shaped and evenly distributed several, in the axial direction extending pairs of holes 14, 15, the mutual distance on their inner pitch circle 15-50 mm, depending on the diameter of the bore 9. Each pair of holes 14, 15 is close to the inside of the cooling ring 12 its end facing away from the die each flow-connected through a radial bore 16. These radial bores 16 are each closed at their outer ends by a plug 17. This results in a circulation for the cooling medium inside the cooling ring 12, the cooling medium not coming into direct contact with the material to be pressed 1. On the end face 6 of the cooling ring 12 adjacent to the die 3, the pairs of holes 14, 15 are each connected to a feed line or return line, which are each in an annular housing 18. In the annular housing there are two concentric annular chambers 27, 28 with different diameters on the end face 6 of the cooling ring 12, with all of the openings of the bores 14 lying radially outside and the other all openings of the bores 15 being radially further into the other lie inside, flow into. 18 connecting nipples 29 are provided in the annular housing for connecting pipe or hose lines. In the feed or return line 26, a controllable throttle valve V is preferably installed, with which the flow and thus the cooling capacity can be continuously adapted to the requirements so that the temperature of the pressed material 1 in the forming zone can be kept at its optimal temperature level, for example using of a temperature sensor. If, for reasons of space, the preferred arrangement of the supply and discharge of the cooling medium at the die-side end of the cooling ring is not possible for existing presses, the lines for supply and discharge of the cooling medium can also be designed as radial bores on the pressing pin receiver side.

The cooling medium can be water, but other liquids, vapors or gases can also be used.

The die rests on the face against the cooling ring 12 and the inner ring 8. The axial length of the cooling ring 12 is preferably 0.25-2 times the diameter of the press pin bore 9. Furthermore, the wall thickness of the ring 8 is less than half the wall thickness of the cooling ring 12. In order to obtain a rapidly reacting cooling effect, the wall thickness is Ring 8 preferably less than 1/4 of the diameter of the press pin bore 9. The radially innermost, approximately horizontal axes of the cooling bores 15 are arranged on a ring, the diameter of which is less than 1 1/2 times, preferably less than 1 1/4 times of the diameter of the press pin receiver bore 9.

A radially outer shrunk-on pressure ring 20 surrounds the cooling ring 12 on the outside. It is fastened with screws 24 to the end face 32 of the press pin receiver 2. For reasons of strength, it is also possible to provide a plurality of pressure rings 20 lying coaxially one above the other, which are shrunk onto one another. The cooling ring 12 is also shrunk onto the inner ring 8. For the transmission of axial forces, the inner ring 8 and the cooling ring 12 and the pressure ring 20 are each provided with ring shoulders 11 and 22, respectively. Instead of ring shoulders, the rings 8, 12, 20 could also be conical on their interlocking parts.

In Fig. 3, an embodiment is shown in which the cooling ring 12ʹ is formed with the omission of the inner ring 8 directly as the same diameter coaxial limitation of the die-near press pin bore 9. At least one pressure ring 20 is shrunk onto the contact ring 12 auf in a coaxial arrangement. Otherwise, the same reference numerals correspond to the same parts and the same functions as in the exemplary embodiment according to FIGS. 1 and 2.

It is also possible for the inner ring 8 and / or the cooling ring 12, 12 'to be conical over part of its length in the region on the die side, but the entry-side end of the bore 10 being of the same diameter as the press bolt bore 9.

The forming and frictional heat can thus be dissipated directly from the main forming zone in front of the press die 3 by cooling in order to keep the temperature of the pressed material 1 at an optimal level. This enables a sudden increase in the pressing speed.

• American Society for Testing and Materials Philadelphia (ASTM),
• Aluminium Association Washington DC 20006.
  

Typical examples of results achieved are listed below. The definition of the light metal alloy ASTM is contained in the following standards:

• American Society for Testing and Materials Philadelphia (ASTM),
• Aluminum Association Washington DC 20006.
  

Claims (5)

1. Apparatus for cooling a press for the extrusion of light metals, in the region of the deformation zones, in the direction of movement in front of the press die (3), at least one cooling ring (8, 12, 12') being provided, in which a coolant for dissipating the deformation heat circulates in a closed circuit, pipes (26, 28) for the supply and discharge of the coolant being connected to the cooling ring, characterised in that the cooling ring (8, 12, 12') consisting of one or a plurality of coaxial rings and which is independent of the press die (3) has a bore (10) of the same diameter as the receiving bore (9) of the press bolt (13) and a plurality of pairs of axial bores (14, 15) are provided, which are distributed in the form of a ring in the annular surface, extend in the axial direction and are spaced apart radially with respect to the bore (9) of the press bolt receiver, which pairs of axial bores (14, 15) are connected on their region remote from the opening adjacent the die by a radial bore (16) respectively closed towards the outside and the cooling ring is surrounded radially on the outside by at least one shrunk-on thrust ring (20), which is rigidly connected to the press bolt receiver (2).
2. Apparatus according to Claim 1, characterised in that the radially innermost cooling channels (15) in the cooling ring (12, 12') are arranged respectively on a ring, whereof the diameter is less than 1 1/2 times, preferably less than 1 1/4 times the diameter of the cylindrical press bolt receiver bore (9).
3. Apparatus according to Claims 1 or 2, characterised in that the supply and discharge of the coolant takes place through two concentric ring conduits (27, 28) at the end of the cooling ring adjacent the die, into which conduits the bores (14, 15) open.
4. Apparatus according to one of Claims 1 to 3, characterised in that located in the supply or return line (26, 28) for the coolant is a controllable throttle valve (V).
5. Apparatus according to one of Claims 1 to 4, characterised in that the axial length of the cooling ring (12, 12') is shorter than twice the diameter of the cylindrical press bolt bore (9).

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