Metal deforming – By extruding through orifice – Work supplying
Patent
1996-02-12
1998-09-08
Larson, Lowell A.
Metal deforming
By extruding through orifice
Work supplying
72257, 723422, 723426, B21C 3300
Patent
active
058029052
DESCRIPTION:
BRIEF SUMMARY
During metal extrusion processes, the blocks heated to extrusion temperature are taken from a container and extruded through a die; for insertion to take place the outer diameter of the blocks must be slightly smaller than the inner diameter of the container. After the block has initially been upset so that it fills the inner diameter of the container, it is extruded through the die to produce an extruded product. The heat released by the forming work flows away into the remainder of the block, the die and its holder, and the container. Additionally, during direct extrusion the block slides or shears along the wall of the container in a manner dependent on the prevailing tribological conditions, heat thereby being produced in the region near the surface of the block. A proportion of this heat also remains in the block for extrusion. Hence during the course of extrusion the block and the forming region become increasingly hotter and consequently the structure of the extruded product has different mechanical properties both radially and over the extruded length. In order to eliminate this phenomenon, an isothermal extrusion process is sought by varying the extrusion speed over the length of the block, or by applying an axial temperature gradient to the block before the beginning of the extrusion process, the end of the block near the die being hotter than the end near the ram.
Pusher-type induction heating means are used to produce a temperature gradient which can be reproduced during the extrusion cycle, the means being known from DE-B 1 014 678, the block firstly being heated therein to a uniform lower temperature in a first furnace or part of a furnace, and then being further heated in a second furnace or part of a furnace by induction in a regionally differing manner so that the block has a higher temperature at one end. Use of an induction-heating installation allows production of a temperature gradient which can be better reproduced, the installation being provided with a plurality of--generally four or more--induction coils which can be adjusted and controlled separately. Because of its complicated structure the installation is costly and entails considerable additional investment on the part of the authority operating the extrusion installation.
However, application of an axial temperature gradient by regionally differing induction heating is not sufficient for optimising the extrusion speed under isothermal extrusion conditions. In addition to application of an axial temperature gradient, this requires application of a reproducible radial temperature gradient, more particularly one having a temperature which decreases from the inside outwards, when using direct extrusion. This cannot be achieved by induction heating.
The object of the invention is to use a suitable temperature influence on the block for extrusion in order to apply a temperature profile thereto, with which profile the extrusion process, i.e. isothermal extrusion at maximum extrusion speed, can be optimised whilst taking into account all influencing quantities.
In accordance with the invention, the temperature influencing takes place in that the metal blocks for extrusion are heated to an extrusion temperature suitable for the metal, the blocks are stored at this temperature and undergo chilling in a manner synchronised with the extrusion cycle, the chilling being divided into control zones, control in the zones taking place by influence on the amount and/or temperature of coolant and/or the duration of cooling in such a way as to provide the block both axially and radially with a temperature distribution ensuring isothermal extrusion at optimal extrusion speed whilst taking into account the heat conductivity of the metal, the heat flow to the remainder of the block, the block container and the extrusion tools (ram and die) and heating of the block brought about by forming heat and (if present, i.e. during direct extrusion) friction of the block inside the container.
Application of the temperature gradient in the axial direction from
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Biswas Amit Kumar
Steinmetz Alfred
Venaas Ivar
Hydro Aluminium a.s. Karmoy
Larson Lowell A.
SMS Hasenclever GmbH
Tolan Ed
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