ISO 4928:2006

INTERNATIONAL ISO
STANDARD 4928
Third edition
2006-07-15

Road vehicles — Elastomeric cups and
seals for cylinders for hydraulic braking
systems using a non-petroleum base
hydraulic brake fluid (Service
temperature 120 °C max.)
Véhicules routiers — Coupelles et joints en caoutchouc pour cylindres
de dispositifs de freinage hydrauliques utilisant un liquide de frein à
base non pétrolière (Température maximale d'utilisation 120 °C)



Reference number
ISO 4928:2006(E)
©
ISO 2006

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ISO 4928:2006(E)
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©  ISO 2006
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ISO 4928:2006(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 General requirements. 2
4.1 Workmanship and finish . 2
4.2 Marking . 2
4.3 Packaging . 2
4.4 Sampling. 2
5 Test requirements. 2
5.1 Resistance to fluid at elevated temperature . 2
5.2 Precipitation . 2
5.3 Wheel cylinder seals heat pressure stroking . 2
5.4 Master cylinder seals heat pressure stroking . 3
5.5 Low-temperature performance. 4
5.6 Oven ageing . 4
5.7 Corrosion. 4
5.8 Storage corrosion test. 5
6 Test procedures . 5
6.1 Resistance to fluid at elevated temperature — Dimensional test. 5
6.2 Precipitation test. 7
6.3 Wheel cylinder seals heat pressure stroking . 8
6.4 Master cylinder seals heat pressure stroking . 9
6.5 Low-temperature performance. 11
6.6 Oven ageing . 12
6.7 Hardness determination. 12
6.8 Corrosion test . 13
6.9 Storage corrosion test. 14

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ISO 4928:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 40421 was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 2, Braking
and systems equipment.
This third edition cancels and replaces the second edition (ISO 4928:1980), which has been technically
revised.

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INTERNATIONAL STANDARD ISO 4928:2006(E)

Road vehicles — Elastomeric cups and seals for cylinders for
hydraulic braking systems using a non-petroleum base
hydraulic brake fluid (Service temperature 120 °C max.)
1 Scope
This International Standard specifies performance tests of brake cups and seals for hydraulic braking systems
for road vehicles; it does not include requirements relating to chemical composition, tensile strength and
elongation of the rubber compound. Disc brake seals are not covered by this International Standard.
This International Standard is applicable to moulded seals (cups or double-lipped type gland seals), 60 mm in
diameter and smaller, compounded from high temperature-resistant rubber, for use in hydraulic actuating
cylinders using road vehicle non-petroleum base hydraulic brake fluid conforming to the requirements of
ISO 4925.
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.
ISO 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and
100 IRHD)
ISO 188:1998, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests
ISO 1250, Mineral solvents for paints — White spirits and related hydrocarbon solvents
ISO 4925, Road vehicles — Specification of non-petroleum-base brake fluids for hydraulic systems
ISO 4926, Road vehicles — Hydraulic braking systems — Non-petroleum base reference fluids
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
sloughing
release of carbon black on the surface of the rubber
3.2
scoring
formation of grooves in the rubber parallel to the direction of travel of the piston or seal
3.3
scuffing
visible erosion of the outer surface of the rubber
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ISO 4928:2006(E)
4 General requirements
4.1 Workmanship and finish
Seals shall be free from blisters, pin-holes, cracks, protuberances, embedded foreign material or other
physical defects which can be detected by thorough inspection, and shall conform to the dimensions specified
on the drawings.
4.2 Marking
The identification mark of the manufacturer and other details as specified on drawings shall be moulded into
each seal. Each seal in conformity with this International Standard may also have the following mark:
“ISO 4928”.
4.3 Packaging
Seals shall be packaged to meet requirements specified by the purchaser.
4.4 Sampling
The minimum lot on which complete specification tests shall be conducted for quality control testing, or the
frequency of any specific type test used to control production, shall be agreed upon by the manufacturer and
the purchaser.
5 Test requirements
5.1 Resistance to fluid at elevated temperature
After being subjected to the test for resistance to compatibility fluid at elevated temperature as prescribed in
6.1, the seals shall conform to the requirements specified in Table 1, and shall show no excessive
disintegration as evidenced by blisters or sloughing.
Table 1 — Requirements for fluid resistance at elevated temperature (120 °C)
Characteristics Permitted change
Volume From 0,0 % to + 20,0 %
Outside diameter, lip From 0,0 % to + 5,75 %
Outside diameter, base From 0,0 % to + 5,75 %
Hardness From − 15 IRHD to 0 IRHD
5.2 Precipitation
Not more than 0,3 % sediment by volume shall be formed in the centrifuge tube after the seals have been
tested as specified in 6.2.
5.3 Wheel cylinder seals heat pressure stroking
5.3.1 General
Wheel cylinder seals, when tested by the procedure specified in 6.3, shall meet the performance requirements
specified in 5.3.2 to 5.3.6.
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ISO 4928:2006(E)
5.3.2 Lip diameter change
The minimum lip diameter of wheel cylinder seals after the stroking test shall be greater than the wheel
cylinder bore by the minimum dimensions specified in Table 2.
Table 2 — Lip diameter change of wheel cylinder seals
Dimensions in millimetres
Diameter of wheel cylinder bore Minimum excess over bore
u 19,05 0,40
> 19,05; u 25,4 0,50
> 25,4; u 38,1 0,65
> 38,1; u 60 0,75
5.3.3 Leakage
No constant dampness past the seals or fluid discoloration of the filter paper on two or more inspections shall
occur.
5.3.4 Corrosion
Pistons and cylinder bore shall not show corrosion as evidenced by pitting to an extent discernible to the
naked eye, but staining or discoloration shall be permitted.
5.3.5 Change in hardness
Rubber seals shall not decrease in hardness by more than 15 IRHD when tested in accordance with the
procedure as specified in 6.7.
5.3.6 Condition of test seals
Wheel cylinder seals shall not show excessive deterioration such as scoring, scuffing, blistering, cracking,
chipping (heel abrasion) or change in shape from original appearance.
5.4 Master cylinder seals heat pressure stroking
5.4.1 General
Master cylinder seals, when tested by the procedure specified in 6.4, shall meet the performance
requirements specified in 5.4.2 to 5.4.6.
5.4.2 Lip diameter change
The minimum lip diameter of master cylinder seals after the stroking test shall be greater than the master
cylinder bore by the minimum dimensions specified in Table 3.
Table 3 — Lip diameter change of master cylinder seals
Dimensions in millimetres
Diameter of master cylinder bore Minimum excess over bore
u 19,05 0,30
> 19,05; u 25,4 0,40
> 25,4; u 38,1 0,50
> 38,1; u 60 0,65
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ISO 4928:2006(E)
5.4.3 Leakage
The same requirement as specified for wheel cylinder seals shall be applied (see 5.3.3).
5.4.4 Corrosion
The same requirement as specified for wheel cylinder seals shall be applied (see 5.3.4).
5.4.5 Change in hardness
The same requirement as specified for wheel cylinder seals shall be applied (see 5.3.5).
5.4.6 Condition of test seals
The same requirement as specified for wheel cylinder seals shall be applied (see 5.3.6).
5.5 Low-temperature performance
5.5.1 Leakage
No leakage of fluid shall occur when seals are tested according to the procedure specified in 6.5.1.
5.5.2 Bend test
The seal shall not crack and shall return to approximately its original shape within 1 min when tested
according to the procedure specified in 6.5.2.
5.6 Oven ageing
5.6.1 General
Seals, when tested according to the procedure specified in 6.6, shall meet the requirements specified in 5.6.2
and 5.6.3.
5.6.2 Change in hardness
The change in hardness shall be within the limits of ± 5 IRHD.
5.6.3 Condition of test seals
The seal shall show no evidence of deterioration, or change in shape from original appearance.
5.7 Corrosion
5.7.1 General
Seals, when tested according to the procedure specified in 6.8, shall meet the requirements specified in 5.7.2
and 5.7.3.
5.7.2 Corrosion of metal strips
The seals shall not cause corrosion exceeding the limits shown in Table 4. The metal strips outside of the
area where the strips are in contact shall be neither pitted nor roughened to the extent discernible to the
naked eye, but staining or discoloration is permitted.
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ISO 4928:2006(E)
Table 4 — Permissible change in mass of corrosion test strips
Permissible change in mass
Test strips
2
mg/cm of surface
Tinned iron ± 0,2
Steel ± 0,2
Aluminium ± 0,1
Cast iron ± 0,2
Brass ± 0,4
Copper ± 0,4
Zinc ± 0,4
5.7.3 Fluid-water mixture characteristics
The fluid-water mixture at the end of the test shall show no jellying at 23 °C ± 5 °C. No crystalline type
deposits shall form and adhere to either the glass wall or the surface of metal strips. The fluid-water mixture
shall contain no more than 0,2 % sediment by volume.
5.8 Storage corrosion test
After twelve cycles in the humidity cabinet when operated according to the procedure specified 6.9, there shall
be no evidence of corrosion adhering to or penetrating the wall of the cylinder bore that was in contact with the
test seal.
Slight discoloration (staining) or any corrosion or spots away from the contact surface of the test seals may be
permissible.
6 Test procedures
6.1 Resistance to fluid at elevated temperature — Dimensional test
6.1.1 Apparatus and material
6.1.1.1 Micrometer, shadowgraph or other suitable apparatus, to measure accurately to 0,02 mm.
6.1.1.2 Glass container, of capacity approximately 250 ml and diameter 50 mm, which can be tightly
sealed.
6.1.1.3 Chemical balance, capable of weighing to 1 mg.
6.1.1.4 Oven, uniformly heated dry air type, conforming to the requirements for Method B of
ISO 188:1998.
6.1.1.5 Two glass-stoppered weighing bottles, of adequate mouth size to hold the seals under test.
6.1.1.6 Isopropyl or ethyl alcohol, of 95 % (by volume) reagent grade for washing purpose.
6.1.2 Test specimens
Two seals shall be used for testing at 120 °C.
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ISO 4928:2006(E)
6.1.3 Procedure
Rinse the cups in the alcohol (6.1.1.6) and wipe dry with a clean, lint-free cloth to remove dirt and packing
debris. Do not leave the seals in the alcohol for more than 30 s.
Measure the lip and base diameters to the nearest 0,02 mm, taking the average of two readings at right
angles to one another. Take care when measuring the diameters before and after ageing that the
measurements are made in the same manner and at the same locations.
Determine and record the initial hardness of the test seals. (See 6.7 and Figure 3.)
Determine the volume of each seal in the following manner: weigh the seals in air (m ) to the nearest 0,001 g
1
and then weigh the seals immersed in distilled water at room temperature (m ). Quickly dip each specimen in
2
alcohol and then blot dry with filter paper free of lint and foreign material.
Immerse two seals completely in 75 ml ± 1 ml of compatibility reference fluid as defined in ISO 4926, in the
glass container (6.1.1.2) and seal the container to prevent vapour loss. Place the container in the oven
(6.1.1.4) set at 120 °C ± 2 °C for a period of 70 h ± 2 h. At the end of the heating period, remove the container
from the oven and allow the seals to cool in the container at 23 °C ± 5 °C for 60 min to 90 min. At the end of
the cooling period, remove the seals from the container and rinse in the alcohol and wipe dry with a clean,
lint-free cloth. Do not allow the seals to remain in the alcohol for more than 30 s.
After removal from the alcohol and drying, place each seal in a separate, tarred, stoppered weighing bottle
(6.1.1.5) and weigh (m ). Remove each seal from its weighing bottle and weigh immersed in distilled water
3
(m ) to determine water displacement after hot fluid immersion. Make all weighings to the nearest 0,001 g.
4
Determine the final volume, dimensions and hardness of each seal within 60 min of rinsing in the alcohol.
6.1.4 Expression of results
6.1.4.1 Volume change
Volume change ∆V shall be reported as a percentage of the original volume. The change in volume is given
by the equation:
mm−−m−m
() ( )
34 1 2
∆V = ×100
mm−
()
12
where
m is the initial mass in air, in grams;
1
m is the initial apparent mass in water, in grams;
2
m is the mass in air after immersion in test fluid, in grams;
3
m is the apparent mass in water after immersion test fluid, in grams.
4
6.1.4.2 Dimensional changes
The original measurements of the lip and base diameters shall be subtracted from measurements taken after
the test and the difference reported in millimetres and as percentages of the original diameters.
6.1.4.3 Hardness
Change in hardness shall be determined and recorded.
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ISO 4928:2006(E)
6.1.4.4 Disintegration
The seals shall be examined for disintegration as evidenced by blisters or sloughing.
6.2 Precipitation test
6.2.1 Apparatus
6.2.1.1 Glass containers, of capacity approximately 250 ml and diameter 50 mm, which can be tightly
sealed.
6.2.1.2 Cone-shaped centrifuge tube, of capacity 100 ml.
6.2.1.3 Oven, uniformly heated dry air type, conforming to the requirements for Method B of
ISO 188:1998.
6.2.2 Test specimen
From two or more seals to be tested, obtain a sample of mass 4,0 g ± 0,5 g. Since sizes of seals vary, small
pieces may be cut from the seal to reach the specified mass. Use the minimum number of pieces to obtain a
mass of 4,0 g ± 0,5 g.
6.2.3 Procedure
To determine the precipitation compatibility characteristics of the test seals, place the sample (6.2.2) in one of
the specified glass containers (6.2.1.1) containing 75 ml of compatibility fluid of ISO 4926. Seal the container
to prevent vapour loss and place in the oven (6.2.1.3) at 120 °C ± 2 °C for 70 h ± 2 h.
As an optional test, a blank test may be run on the brake fluid prior to the real test and any sediment from the
blank test may be subtracted from the sediment amount obtained from the real test.
At the end of the heating period, remove the container from the oven and allow to cool at room temperature
for 24 h, after which remove the seals.
Agitate thoroughly the contents of the jar and transfer the fluid and suspended particles to a cone-shaped
centrifuge tube (6.2.1.2) of 100 ml capacity and determine the sediment as follows.
a) Measure a 10 ml sample of the fluid and suspended particles to be tested, into each of two clean, dry
centrifuge tubes at room temperature. Fill each tube to the 100 ml mark with the naphtha (see cautio
...