SEALING DEVICE FOR THE PLUNGER OF AN EXTRUDER

Abstract: A device on an extruder for the evacuation of air, consisting of a cylinder (1) with a die mounted at one end, the outlet, and a piston (2) designed to move from a position outside the other end, the inlet, to a position inside the cylinder. At the inlet, a separate sealing device (11) is mounted which accompanies the piston when it is retracted from the cylinder. The sealing device consists of a casing (4) with sealing rings (8, 9) mounted on the piston/piston rod (2, 3).

Description: SEALING DEVICE FOR THE PLUNGER OF AN EXTRUDER The present invention relates to a sealing device for an extruder for the evacuation of air, the extruder consisting of a cylinder with a die and a reciprocating piston. In the production of longitudinal metal sections by the traditional method, a shaping machine of the above type is used. A metal billet with a circular cross-section, is pre-heated and placed in the cylinder. Then the piston presses the billet through the die with great force. The extrusions thus formed take on different shapes depending on the shape of the hole in the die. Work is being done to develop methods of producing metal sections based on the use of particulate material such as metal powder or needles. However, when one uses particulate material to make a bolt or metal extrusion, there are increased problems with air pockets and moist and this detracts from the quality of the extrudate. EP Patent Application No. 0397423 describes a method and equipment for producing metal objects by consolidation of particulate material, using an extruder with a solution for the evacuation of gas. A piston is used with a wedge, where the gas is sucked out past the wedge and through a bore in the piston. This solution gives an end product which is very close to optimum - i.e. which to all intents and purposes is without deleterious impurities and pores, and which has an almost impermeable surface which prevents absorption of humidity and gas during later use. However, there is one disadvantage in the equipment described by the above-mentioned Norwegian patent application - that it does not achieve a satisfactory seal between the piston and the cylinder, and this in turn means that air is drawn into the cylinder during the extraction operation when a strong vacuum is used. Also known is an extruder where air is extracted from the extruder cylinder by means of a venting plate which is pressed against a venting ring mounted on the cylinder. The venting plate can be moved by means of piston/cylinder mechanisms. This solution is complicated and costly. In addition, it requires a great deal of space and would obstruct the movements of anyone operating it. With the present invention a sealing device has been obtained for an extruder which provides an almost complete seal, and which, combined with the use of an efficient vacuum pump, can provide pressures lower than 10 "3 atm. The pressure can be further reduced by using a molecular or diffusion pump. With this invention a sealing mechanism has been obtained for an extruder which is characterized in that a separate sealing mechanism has been installed at the inlet, which sealing mechanism accompanies the piston when it is retracted from the cylinder, as defined in Claim 1. The subordinated Claims 2-5 define advantageous features of the invention. The invention will now be described in more detail by means of an example and references to the attached drawing, which shows part of an extruder, in partial cross-section. It consists of a cylinder 1, a piston 2, and a sealing device 11. The die of the extruder, the equipment for feeding the particulate material and the hydraulic arrangement for moving the piston are not shown in the drawing and will not be discussed in any more detail here. The cylinder 1 is provided with a diagonally-placed radial hole or bore 6 running from the feed end and opening into the cylinder. The bore is furnished with a threaded steel pipe (not shown) which is in turn connected with a vacuum pump (not shown either) . To obtain a seal between the cylinder 1 and the piston rod 3, a sealing device 11 is installed outside the piston rod 3 and the piston 2. See Claim 1. This consists of a casing 4, mainly of aluminium, furnished with an inside seal 8 against the piston rod 3, and a V-ring 9 in heat-resistant material as a seal against the end of the cylinder 1. On the front of the casing against the cylinder a series of permanent magnets 7 is attached. The permanent magnets keep the casing centred, i.e. in position in relation to the cylinder until a vacuum arises in the cylinder in connection with the extraction operation, which helps to press the casing against the wall around the cylinder opening. In addition, the permanent magnets - or rather the force they exert - will help to make the piston, during its return movement, wedge in an inside cone 11 (sealing device and inside cone not shown in the figure) on the casing 4 and will withdraw it to the starting position. To improve the seal and reduce wear on the sealing ring 8, a lubrication arrangement (not shown) is provided for the casing, which ensures that lubrication oil is supplied to the area at the sealing ring. In addition, to prevent loss of magnetic force at temperatures over 200°C, a water-cooled steel ring 3 is provided on the cylinder (at 10) , against which the magnets impact. The evacuation device works as follows: As long as the piston rod 3 with the piston 2 is outside the cylinder 1, the casing 4 with the magnets 7 will be wedged firmly to the piston 2. After the cylinder has been charged with a billet or particulate material, the piston rod 3 with the piston 2 is inserted in the cylinder 1. The casing will be "held" in position by the magnets as shown in the drawing and the air/gas can now be evacuated from the cylinder through the vent bore 6. As the air is evacuated a tighter seal is obtained between the cylinder/casing and piston/casing respectively through the sealing rings 8 and 9, and the casing will, as mentioned above, be pressed against the cylinder. Trials have shown that a 100% seal is achieved for a pressure of 10 "3 atm. At the end of the evacuation operation the piston with piston rod moves on into the cylinder until the extrusion cycle has been completed. The evacuation mechanism as described in accordance with this invention was in principle developed for use in connection with the evacuation of air/gas when extruding particulate material. However, the mechanism, as defined in the claims, can also be used to evacuate air when extruding billets. It can further be used in connection with an extruder to evacuate gas through the piston as mentioned in the EP patent application referred to initially in the specification.

Claims: Patent claims 1. Extruder for the evacuation of air, where the extruder consists of a cylinder (1) with a die at one end, the outlet, and a piston (2) designed to be moved from a position outside the other end, the inlet, to a position in the cylinder, c h a r a c t e r i z e d i n t h a t a separate sealing device (11) is provided at the inlet and which is withdrawn with the piston when it is retracted from the cylinder. 2. A device in accordance with Claim 1, c h a r a c t e r i z e d i n t h a t the sealing device consists of a casing (4) with sealing rings (8, 9) mounted on the piston/piston rod (2, 3). 3. A device in accordance with Claims 1 and 2 , c h a r a c t e r i z e d i n t h a t the casing (4) is provided with permanent magnets (7) attaching it to the cylinder (1) . 4. A device in accordance with Claim 3 c h a r a c t e r i z e d i n t h a t the cylinder (1) is provided with a water-cooled steel ring (4) against which the magnets impact. 5. A device in accordance with the above Claims 1-4 , c h a r a c t e r i z e d i n t h a t the cylinder (1) is furnished with a bore (6) for the evacuation of air, extending diagonally in a radial direction from the inlet end of the cylinder and opening into the inside of the cylinder.

Inventors: AURAN LARS, SOERHEIM OLE JOHAN, VIK KAI MAGNE, AURAN, LARS, SOERHEIM, OLE, JOHAN, VIK, KAI, MAGNE
Applicants: NORSK HYDRO AS, NORSK HYDRO A.S
Application year: 1992
Main classification: B21C23
IPC codes: B21C23, B21C27