GB2146554A

GB2146554A - An aluminium brake component provided with a wearing surface

Info

Publication number: GB2146554A
Application number: GB08423561A
Authority: GB
Inventors: Lars-Erik Larsson; Lars Mats Goran Dahlen; Per Holsen; Anders Erik Wickberg; Lennart Birger Valent Johnsson
Original assignee: Volvo AB
Current assignee: Volvo AB
Priority date: 1983-09-21
Filing date: 1984-09-18
Publication date: 1985-04-24
Also published as: FR2552182B1; SE8305097L; IT8448884A0; IT8448884A1; IT1179439B; GB8423561D0; NO843701L; JPS6089558A; DE3434403A1; FR2552182A1; SE8305097D0; GB2146554B

Abstract

A method for producing a brake component of the kind forming part of a brake system in which a brake lining is pressed against said brake component which is made of an aluminium-based alloy and which is provided with a wear-resistant layer or surface. The brake component is produced by permitting an aluminium-based melt to solidify under pressure in a molten metal press mould, and providing the solidified or solidifying aluminium-based component with a wear-resistant layer. This layer comprises a chromium-carbon-iron-alloy containing 10-30%, preferably 15-20% by weight chromium, and preferably 2-4% by weight carbon. The layer has a thickness of 0.3-1.0 mm and is preferably applied by means of a plasma spraying process.

Description

SPECIFICATION An aluminium brake-component provided with a wearing surface The present invention relates to a method for manufacturing a novel kind of brake component for friction brakes, in which the braking surface or wearing surface comprises a coating applied to an aluminium based member which carries the braking surface or wearing surface and against which a brake lining can be caused to bear. The invention applies in particular to braking surfaces in disk and drum brakes.

The invention is described in the following with reference to automobile disk brakes, although it generally relates to a method for producing an improved brake component having a friction brake surface against which a brake lining can be brought to bear. At present, disk brakes are normally manufactured from cast-iron, nodular-iron or steel. This results firstly in a brake of relatively large mass which rotates unsprung, secondly a brake which tends to corrode rather readily and heavily, and thirdly a brake of relatively low resistance to wear, which shortens the useful life of the brake and increases the wear on the brake lining.

In addition, these iron alloys are of relatively low thermal conductivity, which results in temperature differences and difficulties in achieving effective cooling. When the disk brakes of an automobile are applied heavily and frequently, the brake temperature can rise to 700"C, and even higher in the friction or wearing surface, which can lead to serious difficulties in maintaining the efficiency of the brakes and in effectively cooling the same.

A solution to these problems has long been sought. For example, there is described to this end in Swedish Patent Application 7809374-7 a braking surface which comprises a layer of cermet applied thermally to an aluminium-based metal component. The ceramic component of the cermet layer comprises metal oxides of, for 2 example, the metals aluminium, titanium, zirconium or chromium.

Problems are encountered, however, in effectively binding the cermet layer to the aluminium-based component. Furthermore no brake disks of this kind are yet to be found on the market. In an older German Patent Specification, Serial Number 825 032, there is proposed a lightmetal brake or clutch disk which can be provided with an outer layer of steel. This brake design is not to be found on the market either. In a patent addition, Serial Number 843 634, to the aforesaid German Specification, it is mentioned that this outer layer may comprise chromium steel, vanadium steel, manganese steel, or like materials.

In accordance with the invention there is provided a method for manufacturing brake components of the kind which form part of a braking system in which the brake linings are pressed against a brake component made of an aluminiumbased alloy and provided with a wear resistant surface, wherein a melt of said aluminium based alloy is allowed to solidify under pressure in a molten metal pressure mould, and wherein said brake component is provided with a wear-resistant sur face comprising a chromium-carbon-iron-alloy con taining 10-30% by weight, preferably 15-20% by weight chromium, and 2-4% carbon.

In the application of disk-type brake components, conventional brake linings are pressed against the wear-resistant surface on the aluminium brake component. The energy, which is hereby converted to thermal energy, is conducted through the alu minium, to colder regions. Because aluminium has good thermal conductivity, the heat is transferred rapidly to all areas of the aluminium-based brake component. In the case of a brake disk, this can be either flushed with cooling air, or provided with channels through which a coolant can be passed.

The disk can also form an integral part of the wheel for which it is intended. For example, the whole of the wheel rim can be cast in one piece and serve as 3 a cooling means. It will be understood that the wheel can also be provided with cooling fins and like elements, for optimal cooling of the brake disk.

The aluminium alloy used suitably has a high melting range, and the presence of the alloying elements should not cause the thermal conductivity of the aluminium alloy to be poorer than that of pure aluminium. The feature of good thermal conductivity must be combined with that of high temperature stability. The appropriate selection of a suitable alloy possessing these properties lies well within the expertise of one of normal skill in this art. Suitable alloys are AA 2618, AA 2014 and AA 5056, which can be imparted the desired combination of properties by subjecting them to squeezeforming or squeeze-casting processes.

The wear-resistant surface or layer is applied to the brake component by means of a method suitable here for. One preferred method is the plasmaspraying method, which enables the layer-forming metal to be sprayed directly onto the base metal, such as to obtain a good bond between the base metal and the surface-forming metal. The particle size of the powderous alloy used in plasma-spraying also affects the strength of the bond obtained between the aforesaid metals. A particle size of 20 200/1*m has been found suitable in this connection, and provides an exceedingly strong bond, without requiring the use of a particular binding layer between the base metal and the wearing surface.Although other methods can be applied for applying a layer of the metal alloy to the base metal, it is often necessary when applying such methods to use a layer of binding agent between the metal alloy and the base metal, in order to obtain a sufficiently strong bond. The wearing surface may also be formed by applying the metal alloy to the base metal in a finely divided form. In this method discrete droplets of molten alloy are applied to the squeeze-formed aluminium-based brake component, to form a layer thereon, and the layer is 4 then densified with the aid of pellet-blasting techniques.In another preferred method, the moltenmetal pressure mould, or squeeze-forming mould, is provided on inner surfaces thereof with a layer of a wear resistant chromium-carbon-iron alloy to a thickness of 0.3-1.0 mm, and the pressure-moulding operation is effected in the presence of both these layers, so that these layers are found on the pressed component. This method obviates the need for subsequent treatment of the manufactured component. An extremely good bond can also be obtained between the wear-resistant layer and the aluminium-based component, as a result of the squeeze-forming process. This bond can be further strengthened by scoring or roughening the wear-resistant chromium-carbon-iron-alloy layer, or by providing said layer with other surface-adhesion means on the ultimate boundary surface between the base metal and the wear resistant metal.The selection of an appropriate method for applying the aforesaid layer and the possible need of a binder layer lies well within the expertise of one of normal skill in this art. Still a further method is one in which the wearing layer or surface is cast in situ with the aluminium-based brake component.

When applying the plasma spray method, there is used a powderous spray of such composition that the resultant wear-resistant layer contains 1030% chromium and 2-4% carbon, with the remainder comprising iron and incidental impurities.

Thus, it is necessary to take into account the fact that a certain amount of carbon and chromium will be burned-off during the plasma spraying process.

Chromium dissolved in the iron is desirable since this increases the resistance of the brake component to wear. The magnitude of this wear-resistance is dependent upon the formation of chromium carbides, and consequently the ratio of chromium to carbon is significant. Consequently, the alloy used has a much higher carbon content than conventional chromium steel.

The wear-resistant layer should have a thickness of 0.3-1.0 mm, preferably 0.3-0.5 mm, in order for a satisfactory result to be achieved. The upper limit of this range is not critical, and merely indicates an optimum with respect to the higher costs incurred by greater layer thicknesses. The lower limit represents a thickness which allows the brake member to be used over a considerable length of time without decreasing its resistance to wear, and which enables the commercial use of automobiles over a useful-life period which is comparable with that of conventional brake disks.

It is also important that the layer or surface applied to the brake component is not excessively porous, since a porous layer has a lower thermal conductivity, is more likely to corrode and is less resistant to wear.

Claims

1. A method for producing a brake component of the kind which forms part of a brake system in which a brake lining is pressed against a wear-resistant surface on said brake component, comprising solidifying an aluminium-based melt under pressure in a molten metal pressure mould to form said brake component, and providing said thus formed brake component with a wear resistant surface comprising a chromium-carbon-iron alloy containing 10-30%, preferably 15-20% by weight chromium and 2-4% by weight carbon.

2. A method according to Claim 1, wherein the wear-resistant surface is applied to said brake member by a plasma spraying process.

3. A method according to Claim 1, wherein the wear-resistant surface is applied to said brake component by finely dividing the molten aluminium-base metal and applying said finely-divided metal to said component in droplet form to form a surface thereon, and wherein the wear-resistant surface is bonded to the brake component with the aid of pellet-blasting techniques.

4. A method according to Claim 1, wherein the wear-resistant surface is applied to the brake component by placing sheets of chromium-carbon-ironalloy in a molten-metal press mould on both sides of the solidifying melt.

5. A method according to Claim 1, wherein the wear-resistant surface is formed to a thickness of 0.3-0.1 mm.

6. A brake member produced in accordance with any one of Claims 1-5, characterized in that it comprises a molten metal pressed base material and a wear resistant surface adhered thereto, said surface having a thickness of 0.3-1.0 mm and comprising a chromium carbon-iron-alloy containing 10-30% by weight, preferably 15-20% by weight chromium, and 2-4% by weight carbon.

7. A method for producing a brake component substantially as hereinbefore described.

8. A brake member substantially as hereinbefore described.