GB2117282A

GB2117282A - Method and apparatus for the plating of strip by rolling

Info

Publication number: GB2117282A
Application number: GB08308593A
Authority: GB
Inventors: Heinrich Rennebaum
Original assignee: Sundwiger Eisenhuette Maschinenfabrik Grah and Co; Sundwiger Eisenhuette Maschinenfabrik GmbH and Co
Current assignee: Sundwiger Eisenhuette Maschinenfabrik Grah and Co; Sundwiger Eisenhuette Maschinenfabrik GmbH and Co
Priority date: 1982-03-31
Filing date: 1983-03-29
Publication date: 1983-10-12
Also published as: FR2524359A1; GB8308593D0; JPS58212884A; DE3211943A1

Abstract

Strips of two materials such as stainless steel 1 and aluminium 10 are conducted over heated rollers 2, 3, 4 directly forwardly of the roll gap 5, 6 whereby they are rapidly heated over a short distance to the desired diffusion-bonding temperature and while being heated up the strips are brought together, there being no need to guide the strips through a protective gas atmosphere. In the roll gap 5, 6 besides diffusion bonding, a thickness reduction takes place, which is however limited in such a way as to eliminate the need for subsequent heat treatment of the compound material at a sufficiently high temperature for recrystallisation of the component material having the higher fusion temperature which is not possible due to the presence of the other material having the lower fusion temperature. <IMAGE>

Description

SPECIFICATION Method and apparatus for the plating of strip by rolling The invention relates to a method of strip plating by rolling pre-heated strips of different metallic materials, in particular of materials whereof one material has a fusion temperature which is lower than the recrystallisation temperature of the other material.

According to a known method of this kind aluminium strip and stainless steel strip are heated to about 5000C in a non-oxidising atmosphere prior to rolling. As a result of such pre-heating of the strip to temperatures far above the diffusion temperature, which latter is at about 4000C, a substantially stronger thickness reduction may be obtained in the roll gap for the aluminium strip than for the steel strip; for a total reduction of the compound material by 30 to 40% the steel strip will be reduced in thickness only by 2 to 7%. This differential degree of deformation between aluminium and steel strip may be increased further by still greater increases in temperature and by the application of a rolling lubricant.Rolling at such widely differing deformation rates in the two component materials is applied exclusively for the purpose of reducing the cross section of the compound material. Metal diffusion between the two strips in the roll gap is counteracted by the fact that the strips are chilled when coming into contact with the cooled rolling dies. It is only after leaving the roll gap that the strips are heat treated at diffusion temperature in order to obtain the desired diffusion bond.

Such a process is costly because it necessitates the treatment of the strip being applied under a protective gas atmosphere this is described in German AS 1 621 320. It is an object of the present invention to provide a method of stripplating by rolling, and suitable apparatus for the execution of this method, which without major expense and outlay, allows the production of firmly bonded compound strip material which retains its deformability, notably in respect of deep-drawing deformation, for the intended future application.

According to the invention there is provided a method of plating by rolling preheated strips of different metallic materials, in particular materials of which one has a fusion temperature which is below the recrystallisation temperature of the other material, characterised in that the strips are heated to approximately diffusion temperature directly forwardly of the roll gap and diffusion bonding occurs in or behind the roll gap and that the thickness reduction of the material having the higher fusion temperature is limited to a degree which eliminates the need for application of subsequent heat treatment to the compound material for the purpose of recrystallation of the material having the higher fusion temperature.

In a practical embodiment of the invention the material which has the higher fusion point is reduced in the roll gap by more than 10% of its original thickness. This kind of reduction is possible owing to the relatively low diffusion temperature because at this temperature the mechanical strength or hardness characteristics of the two materials are not yet too far apart to result substantially in a thickness reduction of only that material which has the lower fusion point. The strips can be heated up very quickly to diffusion temperature with the aid of heated rollers over which they are looped. Preferably the material is heated up in successive stages by being looped over several heated rollers.

In order to protect above all the more easily oxidising strip from oxidation on being heated, the strips should be brought together prior to or during heat application.

According to a further aspect of the invention there is provided apparatus for plating strip by rolling, comprising a rolling mill and a throughflow heater station arranged forwardly of said rolling mill, characterised in that the through-flow heater station comprises a plurality of heated rollers looped by the strips which are to be combined and arranged directly in front of the roll gap.

Due to the fact that the strips are heated directly forwardly of the roll gap and are mutually combined, or brought together at the same time, there cannot occur such strong oxidation at the interface of the strips as would impair the mutual diffusion bonding of the strips. In view of the fact that the material having the lower fusion temperature - for example in a combination of aluminium and stainless steel, aluminium is very strongly reduced in thickness the oxidated layer breaks up so that sufficiently large non-oxidated regions can make contact and diffuse. It is also within the scope of the method that the two strips need not be simultaneously heated prior to being combined. With strips of very different thickness it is sufficient to pre-heat the thicker material, nor is it necessary that the diffusion process should be concluded in the roll gap.It is sufficient if diffusion is initiated in the roll gap so that the two strips stick together. The diffusion bonding process may then be finished by further heat application behind the roll gap.

This limitation in respect of thickness reduction assures that the material having the higher fusion temperature, for example steel, remains deepdrawable without needing subsequent heat treatment for re-crystallisation. By contrast, in the presence of excessively strong thickness reduction it would be necessary to restore deep-drawability of the material by application of a subsequent heat treatment at a temperature higher than the fusion temperature of the material having the lesser fusion temperature.. Under such high heat application however the material having the lesser fusion temperature would flow off thus destroying the compound material. The limit of projected maximum reduction will depend on the intended application of the compound material and on the components of the compound material.

Thus the invention therefore provides on the one hand for maintaining the material having the higher fusion point deep-drawable for maximum thickness reduction (no heat treatment required for the purpose of re-crystallisation) and on the other hand for guaranteeing the diffusion bonding of the two components in the compound material.

The invention is hereinafter more particularly described with reference to the accompanying drawings which illustrate an embodiment of the invention by way of example and in which: Figure 1 is a schematic side elevation of a plating mill, constructed in accordance with the invention and Figure 2 is a schematic side view of a modified plating mill constructed in accordance with the invention.

Stainless steel strip 1, fed from a dispenser reel, not shown, is conducted over three successively arranged electrically heated rollers 2, 3, 4 which are arranged directly in front of the roll gap in a rolling mill comprising the die rolls 5, 6 and the backing rolls 7, 8. Aluminium strip 10 is fed from a reel 9 at a point between the first heated roller 2 and the second heated roller 3. The rollers 2, 3, 4 are heated in such a manner that the strips are heated up stepwise to a diffusion temperature of about 4000C. At the point where the strips 1, 10 are brought together the steel strip 1 has already been heated up to a first, low temperature. The aluminium strip 10 however begins to be heated only at roller 3, that is to say, where the two strips 1, 10 come together.Since from then onwards the two strips 1, 10 are closely superposed the oxidation process cannot progress any further in the course of further heat application to reach diffusion temperature. With the heated rollers 2 to 4 looped by the strips 1, 10 is it possible to come very close to the roll gap and due to the intimate contact between roller surface and strip to ensure rapid heating up of the strips, 1, 10. Thickness reduction at the roll gap will be adjusted in accordance with ultimate intended application or use of the compound material in such a way as to avoid undue hardening of the steel strip 1 which could preclude further treatment or processing, for example deep drawing.

The embodiment of the invention shown in Figure 2 differs from that of Figure 1 only in that the aluminium strip 10 is heated at a comparatively still later point by means of a heated roller 11 and only at this point brought together with the other strip 1. Such an arrangement may be useful where it is desirable to compensate the lower velocity of the more strongly reduced aluminium strip 10 relative to the velocity of steel strip 1.

For a second material consisting of aluminium strip and stainless steel strip the material is heated up by stages corresponding to the arrangement of Figure 1 the steel strip 1 being heated on the first roller 2 to about 1 000C, the second roller 3 heating steel strip 1 and aluminium strip 10 to about 3000C and the third heated roller 4 heating steel strip 1 and aluminium strip 10 to about 4000 C. Due to the intimate contact of strips 1, 10 and heater rollers 2, 4 along the loop path, and also to the good thermal conductivity of the strip materials and the contact-dwelling times at the individual rollers of a little less than one second per roller for a strip feed speed of 6 to 30 m/min the desired stepwise heating up process can be applied without problems in the immediate vicinity of the roll gap without having to provide a protective gas atmosphere. The very closeness to the roll gap does not allow any significant amount of cooling of the strip; at any rate the imparted heat is enough to produce the diffusion bonding process in the roll gap. In so far as the temperature of the strips on entering into the roll gap is slightly lower than the required diffusion bonding temperature the deformation heat will be enough to raise this temperature up to the diffusion bonding temperature level.

Claims

1. A method of plating by rolling preheated strips of different metallic materials, in particular materials of which one has a fusion temperature which is below the re-crystallisation temperature of the other material, characterised in that the strips are heated to approximately diffusion temperature directly forwardly of the roll gap and diffusion bonding occurs in or behind the roll gap and that the thickness reduction of the material having the higher fusion temperature is limited to a degree which eliminates the need for application of subsequent heat treatment to the compound material for the purpose of re-crystallisation of the material having the higher fusion temperature.

2. A method according to claim 1. wherein the material having the high fusion temperature is reduced in thickness by more than 10% in the roll gap.

3. A method according to claim 1 or 2, wherein for the purpose of preheating, the strips are conducted over heated rollers.

4. A method according to any of claims 1 to 3 wherein the preheating of each strip takes place from the back side thereof.

5. A method according to any of claims 1 to 4, wherein the strips are brought together prior to or during the heating up process.

6. Apparatus for plating strip by rolling, comprising a rolling mill and a through-flow heater station arranged forwardly of said rolling mill, characterised in that the through-flow heater station comprises a plurality of heated rollers looped by the strips which are to be combined and arranged directly in front of the roll gap.

7. Apparatus according to claim 6, wherein the rollers which succeed one another in the direction of feed of the strips are adapted to be heated to stepwise increasing temperatures.

8. A method of plating by rolling preheated strips of different metallic materials substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

9. Apparatus for plating strip by rolling substantially as hereinbefore described with reference to and as shown in the accompanying drawings.