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INTERNATIONAL ISO
STANDARD 6691

Second edition
2000-05-15

Thermoplastic polymers for plain

bearings — Classification and designation
Polymères thermoplastiques pour paliers lisses — Classification et
désignation

Reference number
ISO 6691:2000(E)

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ISO 6691:2000(E)

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ISO 6691:2000(E)

Contents Page

Foreword.....................................................................................................................................................................iv
1 Scope ..............................................................................................................................................................1
2 Normative references ....................................................................................................................................1
3 Classification and designation system .......................................................................................................2
4 Designation examples...................................................................................................................................9
5 Ordering information...................................................................................................................................10
Annex A (informative) Properties and applications of the most common unfilled thermoplastic
polymers .......................................................................................................................................................11
Annex B (informative) Fundamental application procedures ...............................................................................17
Bibliography ..............................................................................................................................................................23

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ISO 6691:2000(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 3.

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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

International Standard ISO 6691 was prepared by Technical Committee ISO/TC 123, Plain bearings,
Subcommittee SC 2, Materials and lubricants, their properties, characteristics, test methods and testing conditions.

This second edition cancels and replaces the first edition (ISO 6691:1989), of which has been technically revised.

Annexes A and B of this International Standard are for information only.

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INTERNATIONAL STANDARD ISO 6691:2000(E)

Thermoplastic polymers for plain bearings — Classification and

designation

1 Scope
This International Standard specifies a classification and designation system for a selection of the most common
unfilled thermoplastic polymers for plain bearings.

The unfilled thermoplastic polymers are classified on the basis of appropriate levels of distinctive properties,
additives and information about their application for plain bearings. The designation system does not include all
properties; thermoplastic polymers having the same designation cannot therefore be interchanged in all cases.

It also provides an outline of the properties and applications of the most common unfilled thermoplastic polymers as
well as listing some of the fundamental parameters that influence the selection of thermoplastic polymers for use
for plain bearings.

NOTE In the further course of the work it is intended to prepare standards on "thermosetting polymers" and "mixed
polymers" for plain bearings.

2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.

ISO 307, Plastics — Polyamides — Determination of viscosity number.

ISO 527-1, Plastics — Determination of tensile properties — Part 1: General principles.

ISO 527-2, Plastics — Determination of tensile properties — Part 2: Test conditions for moulding and extrusion
plastics.

ISO 527-3, Plastics — Determination of tensile properties — Part 3: Test conditions for films and sheets.

ISO 527-4, Plastics — Determination of tensile properties — Part 4: Test conditions for isotropic and orthotropic
fibre-reinforced plastic composites.

ISO 527-5, Plastics — Determination of tensile properties — Part 5: Test conditions for unidirectional
fibre-reinforced plastic composites.

ISO 1133, Plastics — Determination of the melt mass-flow rate (MFR) and the melt volume-flow rate (MVR) of
thermoplastics.

ISO 1183, Plastics — Methods for determining the density and relative density of non-cellular plastics.

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ISO 6691:2000(E)

ISO 1628-5, Plastics — Determination of the viscosity of polymers in dilute solution using capillary viscometers —
Part 5: Thermoplastic polyester (TP) homopolymers and copolymers.

ISO 1872-2, Plastics — Polyethylene (PE) moulding and extrusion materials — Part 2: Preparation of test
specimens and determination of properties.

ISO 1874-2, Plastics — Polyamide (PA) moulding and extrusion materials — Part 2: Preparation of test specimens
and determination of properties.

ISO 7148-2, Plain bearings — Testing of the tribological behaviour of bearing materials — Part 2: Testing of
polymer-based bearing materials.

3 Classification and designation system

3.1 General

The classification and designation are based on a block system consisting of a "description block" and "identity
block". The "identity block" comprises an "International Standard number block" and an "individual item block". For
unambiguous coding of all thermoplastic polymers, the "individual item block" is subdivided into five data blocks.

Designation
Identity block
Description International Individual item block
block Standard Data Data Data Data Data
number block block block block block block
1 2 3 4 5

The "individual item block" starts with a dash. The data blocks are separated by commas.

Data blocks 1 to 5 include the following information:

data block 1: material symbol (see 3.2)

data block 2: intended application or method of processing (see 3.3)

data block 3: distinctive properties (see 3.4)

data block 4: type and content of fillers or reinforcing materials (see 3.5)

data block 5: information about tribological properties for plain bearings (see 3.6)

The meaning of the letters and digits is different for each data block (see 3.2 to 3.6).

Data block 2 comprises up to 4 positions. If at least one of positions 2 to 4 is used, but no information is given in
position 1, then the letter "X" shall be placed in position 1. The letters in positions 2 to 4 shall be arranged in
alphabetical order.

If a data block is not used, this shall be indicated by consecutive data block separators, i.e. two commas (,,).

Designation examples are given in clause 4.

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ISO 6691:2000(E)

3.2 Data block 1

The chemical nature of the thermoplastic polymer is designated by its symbol in accordance with ISO 1043-1.

Table 1 — Symbols for the chemical structure of the materials

Thermoplastic polymers
Name and chemical structure
Group/Name Symbol
Polyamide PA 6 Polyamide 6; homopolymer based on
-caprolactam
PA 6 cast Polyamide 6, cast; homopolymer based on
-caprolactam
PA 66 Polyamide 66; homopolycondensate based on
hexamethylenediamine and adipic acid
PA 12 Polyamide 12; homopolymer based on -laurinlactam or
-aminododecanoic acid
PA 12 cast Polyamide 12, cast; homopolymer based on -laurinlactam or
-aminododecanoic acid
PA 46 Polyamide 46; a co-condensate based on 1,4-diaminabutane and
adipic acid
Polyoxymethylene POM Polyacetal (homopolymer)
Polyacetal (copolymer)
Polyalkyleneterephthalate PET Polyethylene terephthalate
PBT Polybutylene terephthalate
Polyethylene PE-UHMW Polyethylene with ultra high molecular weight
PE-HD High density polyethylene
Polyfluorocarbon PTFE Polytetrafluoroethylene
Polyimide PI Polyimides from polyaddition reactions are available as thermo-
setting plastics. Polyimides from polycondensation reactions are
available as thermoplastics and thermosetting plastics, as well as
copolymers of the imide group. Some thermoplastic polyimides are
"apparent thermosetting plastics" because their thermoplastic range
lies above the decomposition temperature. Because of their
intermediate position, polyimides and imide copolymers are only
treated marginally in this International Standard.
Polyetheretherketone PEEK Polyaryletherketone
Polyvinylidene fluoride PVDF Homopolymer based on difluorodichloroethane
Polyphenylene sulfide PPS Polyphenylene sulfide, linearly structured phenyl ring and sulfur
atoms (tribologically modified material)
Poly(amide-imide) PAI Poly(amide-imide) reacted by polycondensation is a hard/tough,
amorphous thermoplastic. After postcuring the PAI parts cannot be
used for re-processing ("pseudo-thermoset plastics").

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ISO 6691:2000(E)

3.3 Data block 2

Position 1 gives the code for the intended application (see Table 2).

Table 2 — Data block 2 — Position 1

Code Intended application

E Extrusion
G General use
M Injection moulding
Q Compression moulding
R Rotational moulding
X No indication

Up to three important properties and/or additives can be indicated in positions 2 to 4 (see Table 3).

Table 3 — Data block 2 — Positions 2 to 4

Code Intended application

A Processing stabilized
F Special burning characteristics
H Heat ageing stabilized
L Light and weather stabilized
R Release agent
S Slip agent, lubricated

3.4 Data block 3

3.4.1 General

The levels of distinctive properties are coded by letters and numbers.

The properties used for the designation are different for every thermoplastic polymer.

Owing to manufacturing tolerances, single property values can lie on, or to either side of, two intervals. It is up to
the manufacturer to state which interval will designate the thermoplastic polymer.

3.4.2 Polyamides

Polyamides are designated in data block 3 by their viscosity number, represented by two digits (see Table 4) in
accordance with ISO 1874-1 and, separated by a dash, their modulus of elasticity represented by three digits (see
Table 5).

In the last position, rapid-setting products may be indicated with the letter N.

The viscosity number shall be determined in accordance with ISO 307 using the solvents given in Table 4. The
modulus of elasticity shall be determined in the dry state in accordance with ISO 527-1, ISO 527-2, ISO 527-3,
ISO 527-4 and ISO 527-5, under the conditions specified in ISO 1874-2.

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ISO 6691:2000(E)

Table 4 — Viscosity number for polyamides

Viscosity number, ml/g
Polyamide Code Solvent
Sulfuric acid 96 % (m/m) m-cresol
> u > u
09 — 90
10 90 110
12 110 130
PA 6 14 130 160
PA 6 cast 18 160 200 —
PA 66 22 200 240
27 240 290
32 290 340
34 340 —
11 — 110
12 110 130
PA 12 14 130 150
PA 12 cast 16 — 150 170
18 170 200
22 200 240
24 240 —

Table 5 — Modulus of elasticity

Modulus of elasticity
Code N/mm2
> u
001 50 150
002 150 250
003 250 350
004 350 450
005 450 600
007 600 800
010 800 1 500
020 1 500 2 500
030 2 500 3 500
040 3 500 4 500
050 4 500 5 500
060 5 500 6 500
070 6 500 7 500
080 7 500 8 500
090 8 500 9 500
100 9 500 10 500
110 10 500 11 500
120 11 500 13 000
140 13 000 15 000
160 15 000 17 000
190 17 000 20 000
220 20 000 23 000
250 23 000 —

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ISO 6691:2000(E)

3.4.3 Polyethylenes

Polyethylenes are designated by their density represented by two digits (see Table 6) in accordance with
ISO 1872-1 and, separated by a dash, their melt flow rate (MFR) represented by one letter and three digits (see
Table 7).

The density of the base material shall be determined in accordance with ISO 1183 under the conditions specified in
ISO 1872-2.

The melt flow rate shall be determined in accordance with ISO 1133 at 190 °C with a load of 2,16 kg (symbol D).
For thermoplastic polymers with a melt flow rate < 0,1 g/10 min, a test under a load of 5 kg (symbol T) is
recommended. If the melt flow rate is still < 0,1 g/10 min, the test should then be carried out under a load of 21,6 kg
(symbol G).

The symbols D, T and G shall precede the code for melt flow rate given in Table 7.

Table 6 — Density

Density a
Code g/cm3
> u
15 — 0,917
20 0,917 0,922
25 0,922 0,927
30 0,927 0,932
35 0,932 0,937
40 0,937 0,942
45 0,942 0,947
50 0,947 0,952
55 0,952 0,957
60 0,957 0,962
65 0,962 —
a Density ranges for uncoloured and unfilled polyethylene materials.

Table 7 — Melt flow rate (MFR)

Melt flow rate
Code
g/10 min
> u
000 — 0,1
001 0,1 0,2
003 0,2 0,4
006 0,4 0,8
012 0,8 1,5
022 1,5 3
045 3 6
090 6 12
200 12 25
400 25 50
700 50 100

3.4.4 Polyalkyleneterephthalates

The distinctive property of polyalkyleneterephthalates is the viscosity number according to ISO 7792-1, determined
in accordance with ISO 1628-5, and designated by two digits (see Table 8).

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ISO 6691:2000(E)

Table 8 — Viscosity number for polyalkyleneterephthalate

Polyalkylene- Viscosity number, ml/g

Code
terephthalate > u
06 — 60
07 60 70
08 70 80
PET 09 80 90
10 90 100
11 100 120
13 120 140
15 140 —
08 — 90
10 90 110
PBT 12 110 130
14 130 150
16 150 170
18 170 —

3.4.5 Other polymers

The coding for the distinctive properties of polyoxymethylene, polytetrafluoroethylene, poly(amide-imide) and
polyimide will be included in a future edition of this International Standard.

3.5 Data block 4

The fillers and reinforcing materials, as well as additives specific for the application in plain bearings, are coded as
follows:

position 1: types of fillers and reinforcing materials, coded by a letter (see Table 9)

position 2: physical forms of fillers and reinforcing materials, coded by a letter (see Table 10)

positions 3 and 4: mass content of fillers and reinforcing materials, coded by two digits (see Table 11)

positions 5 and 6: fillers in position 1, coded by two letters (see Table 12)

Table 9 — Types of fillers and reinforcing materials (position 1)

Code Type
C Carbon
G Glass
K Chalk
S Synthetic organic material
T Talcum
X No indication

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