GB/T 17469-2024 English PDF (GBT17469-2024)

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GB/T 17469-2024: Characteristics evaluation of brake linings for automobile - Small sample bench test method
GB/T 17469-2024
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 43.040.40
CCS Q 69
GB/T 17469-2024
Replacing GB/T 17469-2012
Characteristics evaluation of brake linings for automobile -
Small sample bench test method
ISSUED ON: SEPTEMBER 29, 2024
IMPLEMENTED ON: APRIL 01, 2025
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 5
4 Test equipment ... 5
5 Test preparation ... 8
6 Test procedure ... 10
7 Result processing ... 11
8 Friction coefficient classification and friction coefficient level marking ... 12
9 Test report ... 13
Annex A (informative) Test data record table and data curve graph... 14
Annex B (informative) Product test result report format ... 16
Characteristics evaluation of brake linings for automobile -
Small sample bench test method
1 Scope
This document specifies the test equipment, test preparation, test procedure, result
processing, friction coefficient classification and friction coefficient grade marking, and
test report for the small sample bench test method for friction performance evaluation
of brake linings for automobile.
This document applies to automotive disc brake linings and automotive drum brake
linings (hereinafter referred to as “linings”).
This document does not apply to parking brake linings.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 5620 Road vehicles - Vocabulary and definition for braking of automotive
vehicles and their trailers
3 Terms and definitions
For the purpose of this document, the terms and definitions defined in GB/T 5620 apply.
4 Test equipment
4.1 Test machine
The schematic diagram of small sample bench test machine for friction materials is
shown in Figure 1. The test machine shall have the following functions:
a) measure the temperature of the brake drum;
b) heat the brake drum;
c) control the heating rate of the brake drum;
5.1.1 Randomly select 5 linings from each batch of products. Prepare a test piece from
each lining.
5.1.2 The test piece shall be cut from the middle part of the lining, and the distance from
the sampling position to the periphery of the lining shall be roughly equal.
5.1.3 The length and width of the test piece is (25.4 ± 0.2) mm × (25.4 ± 0.2) mm; the
test friction surface is arc-shaped, and the radius of the arc shall match the brake drum;
the back is flat, and the thickest thickness (or the test piece plus the silencer) is (6.0 ±
0.5) mm. When the thickness of the test piece is insufficient, it is supplemented by
bonding. The test friction surface of the test piece shall be the friction surface of the
lining.
5.1.4 For test pieces that have been ground, at least 0.3 mm shall be ground off from
the friction surface, but not more than 0.5 mm. For unground test pieces (taken directly
from the mold), 1.0 mm ~ 1.2 mm shall be ground off from the friction surface so that
the resin impregnation layer on the lining surface can be completely removed.
5.1.5 The test friction surface of the prepared test pieces shall not be touched by hand,
and foreign impurities shall be avoided.
5.2 Processing of brake drum surface
5.2.1 When using a new or re-ground brake drum, before the first test, remove all wear
marks with 320 sandpaper or emery cloth, then polish with 320 sandpaper, and remove
dust on the brake drum with clean dry air or soft cloth. Finally, use the reference test
piece to run continuously at a speed of 417 r/min, a load of 440 N, and a temperature
below 93 ℃ until the friction coefficient stabilizes.
5.2.2 Before each test, the surface of the brake drum shall be polished with 320
sandpaper or emery cloth, and then polished with 320 sandpaper. Remove dust on the
brake drum with clean dry air or soft cloth.
5.3 Running-in of test pieces
Under the conditions of brake drum speed of 312 r/min, load of 440 N, and maximum
temperature of 93℃, the test piece is run-in for not less than 20 min. If the contact area
of the test piece is still less than 95 % after running-in for 20 min, the test piece is
abandoned and re-prepared.
5.4 Measurement of initial thickness and mass
Take out a run-in test piece, take three points (outside, center, inside) on the center line
parallel to the axis of the test piece and the brake drum to measure the thickness (to the
nearest 0.1 mm) and record it. At the same time, weigh the mass of the test piece (to the
nearest 1 mg) and record it. Then install the test piece on the test machine and run it
continuously for 5 min under the conditions of load 222 N and speed 208 r/min. The
brake drum is stationary, and the load is unloaded. At this time, the initial spacing
between the test piece and the brake drum shall be 0.3 mm ~ 0.4 mm; if it does not meet
the requirements, the loading apparatus needs to be adjusted.
5.5 Measurement of initial wear
When the brake drum is stationary, the temperature is 88 ℃ ~ 99 ℃, and the load is
667 N, measure the height of the top of the test piece fixture (to the nearest 0.1 mm)
and record it.
6 Test procedure
6.1 First baseline
At a brake drum speed of 417r/min, load (load 667 N) the test piece for 10 s and unload
for 20 s, for a total of 20 times. The test starts from the brake drum temperature of 82 ℃
~ 93 ℃, and the cooling air is used to maintain the brake drum temperature at 82 ℃ ~
104 ℃ during each loading. The cooling air is turned off for the 20th loading.
6.2 First decay
Turn off the heating and air cooling, and let the brake drum rotate at 417 r/min to cool
naturally. When the brake drum temperature drops to 82 ℃, load the test piece and turn
on the heater at the same time. Continuously drag-wear at a speed of 417 r/min and a
loading force of 667 N. When the temperature reaches 288 ℃ or the drag-wear time
reaches 10 min, whichever of the two conditions is met first, the test is completed.
Starting from 93 ℃, record the friction force and friction coefficient every 28 ℃, and
record the time, friction force and friction coefficient to reach 288 ℃.
6.3 First recovery
After the first decay (6.2) is completed, turn off the heater and turn on the cooling air.
At a test speed of 417 r/min, during the process of brake drum temperature dropping
from 288 ℃ to 93 ℃, load (load 667 N) the test piece for 10 s at 260 ℃, 204 ℃, 149 ℃
and 93 ℃, and record the friction force and friction coefficient at each loading.
6.4 Second wear measurement
Perform wear measurement according to 5.5.
6.5 Wear test
At a brake drum speed of 417 r/min, load (load 667 N) the test piece for 20 s and
unloaded for 10 s, for a total of 100 times. The test starts from the brake drum
temperature of 193 ℃ ~ 204 ℃, and the brake drum temperature shall be kept between
193 ℃ ~ 216 ℃, which can be achieved by using a heater or air cooling.
6.6 Third wear measurement
After the wear test (6.5) is completed, when it cools to 88 ℃ ~ 99 ℃, perform wear
measurement again according to 5.5.
6.7 Second decay
After the third wear measurement (6.6) is completed, turn off the heater and cooling air
immediately, and let the brake drum r...