BS AU 222:1988 download free.Method of evaluating surface and material flaws of disc brake pads after testing.
0 Introduction
Disc brake pads may show damage after being subjected to vehicle or laboratory tests. BS AU 222 has the purpose of specifying a method of describing some of this damage.
1 Scope and field of application
BS AU 222 identifies the types of flaws of surface and material after testing of disc brake pads, and specifies the method of measuring these flaws and of setting out the results.
BS AU 222 applies to disc brake pads intended for fitting to the brakes of road vehicles.
2 Identification of defects
The presence of a flaw is decided only if it is detectable with the naked eye.
Flaws to be considered are of four types:
Type I — Cracks (see Figure 1)
Type II — Edge flaking (see Figure 2)
Type III — Blistering and pitting (see Figure 3)
Type IV — Material separation from the support
or material lamina separation (see Figure 4)
3 Measuring equipment
Transparent millimetric grid of sufficient area to cover the whole area on which defects are to be measured (see Figure 5).
4 Measurement method
4.1 Preliminary measurements
4.1.1 On the lining, prior to testing, measure and record:
a) the lining height measured on the lining median line, H, in millimetres (see Figure 1), or, for non-symmetrical shapes, the maximum height:
b) the friction surface area, A(,, in square millimetres.
4.1.2 Determine a reference point A, located at the middle of height H (see Figure 5).
4.2 Measurement of flaws
4.2.1 Flaws of type I (see Figure 1)
Measure the length, 1, of each crack.
Position the millimetric grid on point A, as
illustrated in Figure 5.
Count the cracks within the 10 mm X 10 mm area which has the greatest density of cracks. All cracks partially crossing the area are to be included.
4.2.2 Flaws of types II and III (see Figure 2 and Figure 3)
Place the millimetric grid on the work surface.
Determine the area of each flaw with the naked eye.
NOTE For simplicity, edge flaking can be characterized
by a x b (see Figure 2).
4.2.3 Flaws of type IV (see Figure 4) Measure the length, L.
5 Expression of results
5.1 Cracks (type I)
5.1.1 Calculate, as a percentage of the lining height H, and record:
a) length of the longest crack; b) sum of all crack lengths.
5.1.2 Record the greatest number of cracks observed per 100 mm2.
5.2 Edge flaking (type II), blistering and pitting (type III)
Add all these flaws (types II and III). Calculate the total as a percentage of the surface area A, and record:
a) area of the biggest flaw; b) sum of all flaw areas.
5.3 Material separation from support and material lamina separation (type IV)
Calculate, as a percentage of the lining height, H, and record:
a) longest separation length; b) sum of all separation lengths.