GB2025274A - Brake Shoes and Their Manufacture - Google Patents

Abstract

The invention relates to brake shoes for internal shoe drum brakes and to a method of manufacture of such shoes. The brake shoe comprises an arcuated web 121 lying in a radial plane relative to the axis of rotation of the braking surface and a pair of integral oppositely extending axial flanges 118 forming a surface normal to the web. The flanges 118 are formed by circumferential splitting and axial bending of a circumferential margin of the material of the web. The method of manufacture relates to a method that includes the step of edgewise splitting sheet steel strip to form two flanges and then bending the flanges outwards to form a 'T' section strip. The strip can be formed to its arcuate shape, before or after, the edgewise splitting operation. <IMAGE>

Description

SPECIFICATION Brake Shoes This invention relates to brake shoes for but not exclusively for vehicle internal shoe drum brakes.

Internal drum brake shoe assemblies typically have a friction lining secured on a shoe consisting of an arcuate web which lies in a radial plane relative to the axis of rotation of the drum, and a platform secured normal to the web to form a section. One method of manufacture of the above shoe is to blank the shaped arcuate web out of sheet steel and weld a length of steel strip around the outer radial edge of the arcuate blank.

This blanking of arcuate components out of sheet steel is wasteful of material since the shapes of webs will not completely nestle together. Furthermore the assembly of the platform and web is an operation which it is desirable to eliminate.

The object of the present invention is to provide a one piece brake shoe and a method of manufacture thereof.

According to this invention there is provided a brake shoe comprising an arcuate web lying in a radial plane relative to the axis of rotation of the braking surface, and a pair of integral oppositely extending axial circumferential flanges forming a surface normal to the web and formed by circumferential splitting and axial bending of a circumferential margin of the material of the web.

Conveniently the shoe is for an internal shoe drum brake and the axial flanges are formed by splitting the radially outer circumferential margin.

Also according to this invention there is provided a method of making brake shoes including the steps of edgewise splitting of sheet steel strip material to form two flanges, and then oppositely bending the flanges outwards to extend perpendicularly to the strip to form 'T' section strip, the 'T' section strip forming a brake shoe member of which the webs are provided by the unsplit strip and the friction lining platform by the flanges.

The 'T' section strip can be formed continuous by edgewise splitting of the strip which is then bent to shape prior to cutting, or alternatively the strips can be formed into an arcuate shape and then edgewise split to form the 'T' section.

The invention will be described by way of example and with reference to the accompanying drawings in which: Fig. 1 shows a schematic method according to this invention of the manufacture of a brake shoe from continuous sheet steel strip; Figs. 2, 3 and 4 are sections through the strip at 11--11, Ill-Ill, and IV-IV respectively; Fig. 5 shows a number of turns of a close packed helical coil, of the type utilised for making the shoes from arcuate sheet steel; Fig. 6 shows a portion of one coil of the helix clamped by its radially inner margin (radially with respect to the coil); Fig. 7 shows the coil in Fig. 6 being split edgewise to form two flanges; and Fig. 8 shows an unfinished brake shoe cut from the split continuous helix.

With reference to Figs. 1 to 4 of the drawings, sheet steel strip 11 having a cross-section as shown in Fig. 2 is fed by a pair of vertical rollers 1 2 into a slitting disc 1 3 which edgewise splits one edge of the strip 11. The sheet steel strip 11 is continuously split by the disc 13 and the split strip is then flared by a flaring tool 14 to spread two flanges 1 8 on the split edge into a 'Y'-shape section as shown in Fig. 3.

The strip is then fed into a pair of horizontal rollers 1 5 that iron out the 'Y'-shaped crosssection strip into a 'T'-shaped section strip as shown in Fig. 4. The 'T' sectioned strip is passed through another set of rollers 1 6 which arc the strip. The arcuate 'T' sectioned strip is then cut to length by a cutter 19, to provide arcuate shaped lengths of 'T' sectioned material, as shown in Fig.

8, which are then trimmed to their final shape to provide a finished brake shoe.

The unsplit portions 21 of the strip 11 provides the web of the brake shoe and the two flanges 18 provide the friction lining platform.

As an alternative the formed 'T' section strip can be cut to length prior to forming into arcuate members, and the arcuate members can be formed by pressing the 'T' section material to shape.

With reference to Figs. 5 to 8 of the drawing, a continuous helix, a section of which is shown in Fig. 5, is formed from flat sheet steel strip which is wound edgewise into a helical coil which is compressed axially to produce a close wound helix of substantially no pitch excepting the thickness of the material, and having substantially the desired diameter of the brake shoe to be formed. Such a process is described in depth in British Patent 1 280 331.

The helical tube formed from the strip is then rotated and one end of the strip is stretched away from the tube, possibly by the use of wedges, so that the continuous helical turn 111 can be cut into desired arcuate lengths.

The cut arcuate lengths of strip are then clamped between a pair of jaws 112 which grips the radially inner circumferential margin 121 (radially with respect to the arc) of the arcuate length as shown in Fig. 2. The jaws 112 are fitted to a lathe machine (not shown) and rotate about an axis CL which passes through the rotational centre of the arcuate sheet.

As shown in Fig. 7, a cutting and flaring tool 114 is brought into contact with the rotating radially outer edge 124 of the arcuate sheet. The tool 114 is pressed radially inwards to edgewise split the radially outer circumferential margin of the arcuate sheet into two flanges 11 8 of substantially equal thickness. The two flanges 118 are also flared apart at the same time, and are bent outwards by a subsequent operation so as to extend in axially opposite directions and form a platform running the length of the inner margin 121 and being normal thereto. Thus a 'T' section arcuate member has been manufactured as is shown in Fig. 8 and this is subsequently machined into the brake shoe.

The above process has several advantages in that the two integral flanges 1 18 are each substantially half the thickness of the inner margin web 121 and thus is a very desirable feature in brake shoe design. Furthermore since the shoes formed from helically wound strip which is then chopped to length, very little waste occurs.

An alternative procedure would be for the helical coil to be continuously wound off from one end of the coil and fed through a supporting jig where the splitting and parting tool 114 forms the flanges 1 18. The desired arcuate lengths are then cut in preparation for forming a brake shoe.

Whilst the process has been described for a method using helically wound strips it will be appreciated that annular rings of sheet metal, possibly formed by the same process, can be edgewise split in the same manner, and the shoes subsequently cut from the resultant shallow cylinder. This second process however, will produce more waste material since two shoes would occupy a total arc of about 2600 and thus 1000 of the annulus would be wasted.

Further it should also be appreciated that arcuate oversize webs can be blanked out of sheet material and the webs can then be edgewise split to form the platform. Whilst this will not reduce the waste caused by the shapes of the webs not nestling together it will eliminate the assembly step in the manufacture of the shoe.

Claims (11)

Claims

1. A brake shoe comprising an arcuate web lying in a radial plane relative to the axis of rotation of the braking surface, and a pair of integral oppositely extending axial circumferential flanges forming a surface normal to the web and formed by circumferential splitting and axial bending of a circumferential margin of the material of the web.

2. A brake shoe as claimed in Claim 1, wherein the brake shoe is a shoe for an internal shoe drum brake and the axial flanges are formed by splitting the radially outer circumferential margin.

3. A brake shoe substantially as described herein and with reference to the accompanying drawings.

4. A method of making brake shoes including the steps of edgewise splitting of sheet steel strip material to form two flanges, and then oppositively bending the flanges outwards to extend perpendicularly to the strip to form 'T' section strip, the 'T' section strip forming a brake shoe member of which the webs are provided by the unsplit strip and the friction lining platform by the flanges.

5. A method as claimed in Claim 4, wherein the 'T' section strip is formed from continuous splitting of sheet steel strip and the 'T'-section strip subsequently bent into an arcuate shape prior to cutting to the desired length for the brake shoe.

6. A method as claimed in Claim 4, wherein the sheet steel strip is arcuate sheet material and the flanges are bent to extend axially relative to the axis of rotation of the arc to form a platform normal to the arcuate sheet.

7. A method as claimed in Claim 6, wherein the outer circumferential margin of the arcuate sheet material is split edgewise.

8. A method as claimed in Claim 6 or 7, wherein the arcuate sheet material is constituted by a portion of a helical coil of metal strip which is wound edgewise into the coil.

9. A method as claimed in Claim 8, wherein the coil is passed continuously through a means of edgewise splitting the circumferential margin thereof, and the arcuated 'T'-section members are cut to the desired length from the continuous coil.

10. A method as claimed in Claim 8, wherein one end of the coil is continuously wound off from the coil and is then cut into the desired arcuate lengths which are then edgewise split.

11. A method of manufacture of a brake shoe substantially as described herein.