US3509616A - Methods for rolling metal powder - Google Patents

Description

.May 5, 1970 E. GEHRING 3,509,616

METHODS FOR ROLLING METAL POWDER Filed Sept. 50, 1966 United States Patent 3,509,616 METHODS FOR ROLLING METAL POWDER Eckard Gehring, Dusseldorf, Germany, assignor to Schloemann Aktiengesellschaft, Dusseldorf, Germany, a corporation of Germany Continuation-impart of application Ser. No. 362,864, Apr. 27, 1964. This application Sept. 30, 1966, Ser. No. 583,290 Claims priority, application Germany, May 3, 1963, Sch 33,230 Int. Cl. B22f 3/24 US. Cl. 29-420 2 Claims ABSTRACT OF THE DISCLOSURE A method of rolling discrete metal particles, of a diameter greater than one millimeter, into strips, by heating the particles to a temperature above their recrystallization temperature but below their melting point, and then allowing them to fall into the roll gap between a pair of rolls having their axes substantially in the same horizontal plane, from such a height that their speed on reaching the roll gap is at least as great as the peripheral speed of the rotating rolls.

This invention is a continuation-in-part of my Patent No. 3,309,735, dated Mar. 21, 1967.

In rolling metal particles, such as metal powder or metal granules, into strips or the like, the rolling speed, that is to say, the peripheral speed of the rolls, which is also the speed at which the rolled product leaves the rolls, cannot be increased indefinitely at will. This is attributable, at least in part, to the fact that the stock located within the gripping range of the rolls, in order to overcome its inertia has to be accelerated up to the rolling speed by frictional forces.

By the gripping range of the rolls is meant the space between the roll peripheries within which the rolls exert compression upon the particles. This compression ceases at the plane containing the axes of the rolls, after starting at a plane parallel thereto, the position of which is determined by the angle of friction between the roll peripheries and the particles. The gripping angle is the angle subtended at the axis of each roll by the part of the ro l periphery bounded by the two abovementioned planes. These necessary frictional forces stand in a functional ratio to the inertia forces of the metal particles. The greater the peripheral speed of the rolls, and therefore the greater the rolling speed, the higher must be the accelerating forces acting upon the stock that is being rolled, in order to bring the initially stationary stock up to the ultimate rolling speed.

In the case of pairs of rolls the axes of which lie in the same horizontal plane, there act upon the stock, as accelerating forces, not only the acceleration due to gravity but also the friction between the roll surfaces and the stock. The acceleration of the stock produced by friction is limited by the distance through which this acceleration acts. This acceleration distance is determined by the gripping angle of the rolls, and for a given gripping angle the accelerating distance can only be lengthened by increasing the diameter of the rolls. On technical grounds, however, and also on grounds of economy, an attempt is made to keep the dimensions of the rolls, as regards periphery or diameter, as small as possible. The limitation, associated therewith, of the frictional accelerating distance for the stock, constitutes at the same time a measure of the maximum rolling speed.

At the same time, however, the rolling speed is also dependent upon the width of the roll gap. The wider the roll gap, the larger must be the gripping region in which 3,509,616 Patented May 5, 1970 the deformation of the metal particles or granules, for a given compaction or consolidation, takes place. The increase in the size of the deformation region or gripping range of the rolls involves however at the same time a further shortening of the acceleration distances for the metal granules, and, independently thereof, a reduction in the speed of rolling.

The object of the present invention is to render pos sible, with a constant roll diameter and a given roll gap, an increase in the rolling speed.

A further object of the invention is to obtain a rolled product of high density.

Yet another aim of the invention is to produce as thick as possible a rolled product, without reducing its compactness or density.

The invention accordingly consists in a method of rolling a strip from metal particles of more than one-tenth of a millimeter in diameter in every direction, wherein, a roll gap, formed by two rolls located substantially horizontally side by side, is first of all filled to a greater or less extent with the metal particles, and then, with the rolls revolving, further particles, at a temperature above the recrystallization temperature of the metal, but below its melting point, are continuously supplied to the roll gap in quantities per unit of time which corresponds to the quantities of metal issuing from the roll gap per unit of time, so that the gripping-range space of the rolls remains only just about filled, the particles being allowed to fall from such a height that they impinge upon the particles already located in the gripping-range space at a speed which is at least as great as the peripheral speed of the rolls. The invention furthermore relates to a closing device which causes the hot metal particles to fall on to the grippingrange space in the desired quantities.

Since the metal particles impinge upon the grippingrange space with a speed which is at least as great as the peripheral speed of the rolls, the rolls are not required to accelerate the stock supplied to them, so that the factor based thereon, as regards the upper limit of the rolling speed, no longer applies. The rolling speed can therefore be considerably increased, as compared with the conventional method, in which the incoming stock acted upon the stock already in the gripping-range merely by its own weight. For the effective maintenance of the kinetic energy of the stock during the rolling operation, the quantity of feed is preferably so selected that the space enclosed by the gripping angles of the pair of rolls remains filled without heaping.

The falling stock, in consequence of its retardation in the region of the gripping angles of the rolls, exerts a pressure upon the stock already located between the rolls. This increase of pressure on the inlet side of the rolls results in an increase of the gripping angle, so that with a given roll diameter, strips of greater thickness can be rolled.

The means for supplying the stock to the rolls with the requisite quantity and speed preferably comprise a conveyor belt charged from a receiving hopper and running at a variable speed, the rolls being arranged horizontally side by side, and the belt feeding the stock to the roll gap, through a definite height of fall, correspondingly to the required feeding speed.

One embodiment of apparatus for carrying out the method according to the invention, for feeding the stock to be rolled into the gripping range of the rolls, is illustrated by way of example in the accompanying drawings, in which:

FIGURE 1 shows a side view, partly in section on the line II in FIGURE 2; and

FIGURE 2 is a plan view of the left-hand part of the same embodiment, in section on the line IIII in FIGURE 1.

In these drawings, heated particles 4 from a receiving hopper 3 are supplied to the rolls 1 by means of a conveyor belt 2. The distance of the container 3 above the conveyor belt 2 can be altered, as hereinafter described, in order to vary the depth of the layer of particles upon the conveyor belt. The stock, in the form of granules or metal powder, is supplied to the conveyor belt in accurately dosed quantities, and falls, after leaving the conveyor belt 2, into the gripping-range 5 of the rolls 1, which are arranged in a horizontal plane. The height of the conveyor belt 2 above the rolls 1 is so adjusted that the metal powder, after falling through the height b under the action of gravity, acquires a speed at least as great as the peripheral speed or speed of rolling of the rolls. The conveyor belt 2 and the container 3 can be jointly adjustable in height, as hereinafter described, so that the distance b can be varied as required.

The speed of running of the conveyor belt 2 is variable, so that the quantity of stock can be accurately dosed. The stock supplied should not become heaped up in the gripping-region of the rolls substantially above the height a in order that the kinetic energy of the falling stock may remain fully effective within the gripping-range of the rolls. The quantity of stock supplied is therefore to be adapted to the absorption capacity of the rolls. The height a of the line 6 above the level of the horizontal plane containing the axes of the rolls is in its turn determined by the gripping angle 7, the magnitude of which depends upon the nature of the surface of the rolls and of the particles.

The conveyor belt 2 runs upon belt pulleys 8 and 9, at least one of which can be positively driven in a manner known in itself. The belt pulleys 8 and 9 are rotatable about shafts 10 and llrespectively. The ends of the shaft 10 are suspended by ropes 12, which pass round rope pulleys 14, and which each carry a counterpoise at its end.

The two rope pulleys 14 are mounted fast upon a shaft 18, the ends of which are rotatably mounted upon two stationary bearings 20. The shaft 18 is driven by a motor 24 at one end, through a continuously variable changespeed gear 22. The shaft 11 is suspended by its ends from two ropes 13, each of which passes round a rope pulley and carries at its end a counterpoise 17.

By raising or lowering the weights 16 and/or 17, the height of the discharge point of the conveyor belt 2 above the gripping-range space 5 can be altered, the distance of the conveyor belt 2 from the reception hopper 3 also being changed at the same time. If such a change of distance is not required, or if it is desired to vary this distance independently of the upward or downward movement of the conveyor belt 2, the height of the hopper 3, which hangs from a rope 26, can be adjusted. The rope 26 passes once or twice round a rope pulley 28, and is secured by its end to this rope pulley. The rope pulley 28 is rotatable upon a stationary pivot 36, and can be braked by the action of a weight 30, which is mounted upon a brake lever 32, which is rockable about a stationary fulcrum 34. When the weight 30 is slightly lifted, the height of the hopper 3 can be adjusted.

The method adopted in carrying out the invention may be illustrated by the following example: the particles employed were of pure aluminium (American designation 1050) containing 99.5% Al, 0.22% Fe and 0.07% Si. They were of fairly uniform size, giving a screen analysis of 54% over 8 mm. and 46% between 4 mm. and 8 mm.

These granules were heated in an oven to a temperature of 450 C., and were then fed, by a conveyor belt running at a speed of 0.3 meter per second, to a rolling mill having a roll diameter of 300 mm., the rolling speed amounting to 80 meters per minute. In this 'mill the granules were welded into a strip.

When such granules were directly fed in the usual way to the rolling mill from a hopper mounted upon the mill and filled to a depth of about 200 mm., a strip having a thickness of not more than 2.2 mm. could be produced.

When however, according to the present invention, the granules were charged into the roll gap by falling freely from a height of two meters, and rolled at the roll speed indicated, strips up to 2.8 mm. in thickness were produced.

Tests of the strip made according to the present invention showed a tensile strength b of 9.6 kp./mm. with an elongation of 35% on fracture. After a heat treatment of 20 minutes at 500 C. the tensile strength [2 was 7.4 kpL/mmfi, and the elongation at fracture These values correspond to those of conventionally produced strip.

I claim:

1. A method of rolling a strip from discrete metal particles of a diameter of more than one-tenth of a millimeter, comprising the steps of: arranging a pair of rollingmill rolls side by side with their axes in substantially the same horizontal plane, heating the particles to be rolled to a temperature above the recrystallization temperature of the metal but below its melting point, filling the gripping-range space of the roll gap between the rolls with the particles to be rolled, rotating the rolls, and at the same time continuously supplying to the roll gap a further quantity of the metal particles per unit of time corresponding to the quantity of metal strip issuing from the roll gap per unit of time, the particles so supplied being allowed to fall freely from a height of at least two meters onto the particles already in the gripping-range space the height being such their speed of free fall is at least as great as the peripheral speed of the rolls.

2. A method of rolling a strip of metal from metal particles as claimed in claim 1, comprising the step of carrying the particles from a hopper on a horizontally moving conveyor belt, and allowing the particles to fall from the conveyor belt at a point above the roll gap.

References Cited UNITED STATES PATENTS 3,270,409 9/1966 Grant 29-4205 PAUL M. COHEN, Primary Examiner U.S. C1. X.R, 29--420.5

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