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MT/T 668-2019: Steel cord fire resistant conveyor belting for coalmine
MT/T 668-2019
MT
COAL INDUSTRY STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 83.140.99; 53.040.20; 13.220.40
G 42
Replacing MT 668-2008
Steel cord fire resistant conveyor belting for coalmine
ISSUED ON. NOVEMBER 28, 2019
IMPLEMENTED ON. JUNE 01, 2020
Issued by. State Administration of Coal Mine Safety
Table of Contents
Foreword... 3
1 Scope... 6
2 Normative references... 6
3 Product categories, models, specifications... 7
4 Technical requirements... 9
5 Test methods... 16
6 Inspection rules... 20
7 Marking, packaging, storage, transportation... 23
Appendix A (Normative) Method for determination of bonding strength of covering
layer... 24
Appendix B (Normative) Determination method of bonding fatigue resistance of
dynamic steel wire core... 27
Appendix C (Normative) Determination method of rubber permeability... 29
Appendix D (Normative) Method for determination of dynamic durability of wire rope
joints... 31
Appendix E (Normative) Dimensions and technical requirements of fire resistant belt
joints... 36
Steel cord fire resistant conveyor belting for coalmine
1 Scope
This standard specifies the product classification, model, specifications, technical
requirements, test methods, inspection rules, marking, packaging, storage,
transportation of steel cord fire resistant conveyor beltings for coal mines (hereinafter
referred to as "fire resistant belts").
This standard applies to steel cord fire resistant conveyor beltings used in coal mines.
2 Normative references
The following documents are essential to the application of this document. For the dated
documents, only the versions with the dates indicated are applicable to this document;
for the undated documents, only the latest version (including all the amendments) is
applicable to this standard.
GB/T 528-2009 Rubber, vulcanized or thermoplastic - Determination of tensile
stress-strain properties
GB/T 3512 Rubber, vulcanized or thermoplastic - Accelerated ageing and heat
resistance tests - Air-oven method
GB/T 5752 Conveyor belts - Marking
GB/T 5753 Steel cord conveyor belts - Methods for the determination of total
thickness and cover thickness
GB/T 5754.2 Steel cord conveyor belts - Longitudinal traction test - Part 2.
Measurement of tensile strength
GB/T 5755 Steel cord conveyor belts - Cord-to-coating bond test - Initial test and
after thermal treatment
GB/T 7983 Conveyor belts - Transverse flexibility (troughability) - Test method
GB/T 9770-2013 Steel cord conveyor belts for general use
GB/T 9867 Rubber, vulcanized or thermoplastic - Determination of abrasion
resistance using a rotating cylindrical drum device
GB/T 12753 Steel wire ropes for conveyer belts
between the supplier and the buyer. If there is no agreement through negotiation, it shall
be governed by the provisions of Table 3 in GB/T 9770-2013.
4 Technical requirements
4.1 Appearance quality
4.1.1 The fire resistant belt shall not have edge waves.
4.1.2 When the depth of the exposed scar on the fire resistant belt is greater than 1 mm,
it shall be repaired (if the depth is not greater than 1 mm, it will not be repaired).
4.1.3 The total area of blisters and delamination on the fire-retardant belt's covering
layer shall not exceed 1600 cm2 per 100 m2; they shall be repaired and in good condition.
4.1.4 The cumulative length of the edge rubber sponges or torn off edge tape on both
sides of the fire resistant belt shall not exceed 8% of the belt length, which shall be
repaired and in good condition.
4.1.5 For every 100 m of fire resistant belt, no more than 5 places with a depth greater
than 1 mm shall be pressed with edge glue; they shall be repaired (those with a depth
not greater than 1 mm will not be repaired).
4.1.6 There shall be no exposed steel wire rope on the fire resistant belt.
4.2 Dimensions
4.2.1 Width deviation
The width limit deviation of the fire resistant belt shall comply with the provisions of
Table 1.
4.2.2 Covering layer thickness
The thickness of the covering layer of the fire resistant belt shall comply with the
requirements in Table 2.
joint tensile strength of the fire resistant belt shall not be less than 80% of the
longitudinal rated tensile strength of the belt.
4.11.4 For fire resistant belts of models above ST/S7500 (not included), the static joint
tensile strength of the fire resistant belt shall not be less than 75% of the longitudinal
rated tensile strength of the belt.
4.12 Dynamic joint durability
There is no damage to the fire resistant belt joint after 10000 cycles.
4.13 Surface resistance properties
The arithmetic average surface resistance of the two surfaces on the fire resistant belt
and the lower surface shall not be greater than 3.0 × 108 Ω.
4.14 Fire resistant properties
4.14.1 Roller friction performance
When the fire resistant belt is subjected to the roller friction test, flaming or flameless
combustion shall not occur in any part of the fire resistant belt; the surface temperature
of the roller shall not exceed 325 °C.
4.14.2 Blowtorch combustion performance
The fire resistant belt shall comply with the following requirements, after the alcohol
blowtorch combustion test.
a) For specimens with complete coverage, the arithmetic mean of the flaming
burning time and the arithmetic mean of the flameless burning time of the
specimen shall not be greater than 3.0 s, where the single value of flaming burning
time and flameless burning time of each specimen shall not be greater than 10.0
s;
b) For the test piece with the covering layer peeled off, the arithmetic mean value of
the flaming burning time and the arithmetic mean value of the flameless burning
time of the test piece shall not be greater than 5.0 s, where the single value of
flaming burning time and the flameless burning time of each test piece shall not
be greater than 15.0 s.
4.14.3 Propane tunnel combustion performance
If the fire resistant belt meets either of the following two requirements, the conveyor
belt is deemed to be qualified. The requirements are as follows.
a) The undamaged length of each specimen shall not be less than 600 mm;
b) The undamaged length shall not be less than 50 mm; the maximum average
temperature rise shall not be greater than 140 °C; the length of the belt loss shall
not be greater than 1250 mm.
A conveyor belt's propane tunnel burning test is deemed to have failed, when the test is
terminated prematurely, due to endangerment to people and equipment during the
burning process.
5 Test methods
5.1 Sample collection
Take samples, 24 h after the product is manufactured.
5.2 Appearance quality
Use visual inspection and measuring tools for inspection.
5.3 Dimensional measurements
5.3.1 Width measurement
Use a steel belt measure or steel ruler, which has a minimum resolution of not less than
1 mm, for measurement. Make 3 measurements in total. The longitudinal interval of
each measurement shall not be less than 0.5 m. Take the median value as the
measurement result.
5.3.2 Measurement of covering layer thickness
Follow the provisions of GB/T 5753.
5.3.3 Measurement of tear-resistant layer configuration
Follow the provisions of HG/T 3646.
5.4 Longitudinal tensile strength test
Follow the provisions of GB/T 5754.2.
5.5 Adhesion strength test
5.5.1 The bonding strength of the steel wire rope shall be carried out in accordance with
the provisions of GB/T 5755.The measurement of the total thickness of the belt and the
thickness of the upper and lower covering layers shall be carried out, in accordance
with the provisions of GB/T 5753.The difference between the total thickness of the belt
and the thickness of the upper and lower covering layers is the diameter of steel wire
rope d.
5.5.2 The measurement of the bonding strength of the covering layer shall be carried
out, in accordance with the provisions of Appendix A.
5.6 Performance test of steel wire rope in fire resistant belt
5.6.1 The diameter of the wire rope shall be in accordance with the provisions of GB/T
12753.
5.6.2 The distance between steel wire ropes shall be measured in accordance with the
provisions of GB/T 9770.
5.6.3 The number of wire ropes shall be determined by visual inspection.
5.6.4 The determination of the eccentricity value of the wire rope shall be carried out
in accordance with the provisions of GB/T 9770.
5.7 Covering layer performance test
5.7.1 The tensile properties of the covering layer shall be in accordance with the
provisions of GB/T 528-2008.The specimen shall be cut using a type 2 [narrow parallel
section width (4.0 ± 0.1) mm] dumbbell-shaped cutter.
5.7.2 The aging resistance of the covering layer shall be in accordance with the
provisions of GB/T 3512.
5.7.3 The wear resistance of the covering layer shall be in accordance with the
provisions of GB/T 9867.
5.8 Bonding fatigue resistance test of dynamic wire rope
Follow the provisions of Appendix B.
5.9 Tear resistance test
Follow the provisions of HG/T 3646.
5.10 Troughing performance test
Follow the provisions of GB/T 7983.
5.11 Rubber permeability test
Follow the provisions of Appendix C.
5.12 Tensile strength test of static joint
The number of samples is 3 pieces. The sample size shall meet the requirements of
Figure 4.The width b shall be (250 ± 30) mm. The tensile speed of the holder is (100 ±
10) mm/min. The static joint's tensile strength is calculated according to formula (1).
f) Inspection conclusion;
g) Inspector.
6.2 Exit-factory inspection
6.2.1 The product shall be inspected by the quality inspection department of the
manufacturer. 1000 m is considered a batch (less than 1000 m is also considered a batch,
in which the post-aging test of the covering layer is conducted once a quarter), which
shall be inspected once. Only after it passes the inspection and the certificate of
conformity is issued can it leave the factory.
6.2.2 See Table 9 for exit-factory inspection items.
6.3 Type inspection
6.3.1 Type inspection shall be carried out under any of the following circumstances.
a) Type finalization of trial production of new products or old products after trans-
plant production;
b) After formal production, there are major changes in structure, materials, processes
that may affect product performance;
c) When the production is resumed after suspension for two years;
d) When the exit-factory inspection results are inconsistent with the last type
inspection results;
e) When relevant national supervisory agencies, etc. propose type inspection
requirements.
6.3.2 Samples for type inspection shall be selected from products that have passed exit-
factory inspection, with a sampling base of 100 m and a total sample length of 10 m
(excluding joint performance test specimens).
6.3.3 Type inspection items are as shown in Table 9.
Appendix A
(Normative)
Method for determination of bonding strength of covering layer
A.1 Determination of bonding strength between covering layer and adhesive layer
A.1.1 Test piece preparation
A.1.1.1 The test piece is a rectangular strip, which has a thickness of the full thickness
of the strip and a width of at least 25 mm. It shall contain two steel wire ropes (the wire
ropes are arranged symmetrically) and have a length of at least 500 mm (along the
direction of the wire ropes).
A.1.1.2 The number of test pieces is 3.Cut and prepare the test pieces from the sample
belt, according to the following method.
Cut the specimen parallel to the axis of the belt, at a distance of at least 50 mm from
the edge of the belt. At one end of the test piece, peel off one side of the covering layer
in full width close to the edge of the wire rope for a length of 50 mm (this shall ensure
that the test piece is firmly clamped in the holder of the testing machine). Use the same
method to peel off the other side of the covering from the other end of the test piece.
A.1.2 Instruments and equipment
A.1.2.1 Tensile testing machine. It has an accuracy of 1% and a device for automatically
recording the peeling force.
A.1.2.2 Holder. It shall be able to ensure that the test piece is well fixed, does not slip
during the test, the moving speed can be controlled at (100 ± 10) mm/min.
A.1.3 Measurement steps
A.1.3.1 The cut specimens shall be placed in such environment, which has a
temperature of (23 ± 2) °C and a relative humidity of 45%RH ~ 75%RH for at least 2
hours. The test shall also be conducted in this environment.
A.1.3.2 Fix the specimen in the holder of the tensile testing machine. Use one chuck to
clamp the peeled covering layer; use another chuck to clamp the wire rope and
surrounding covering layer. The automatic graphing instrument records peeling off
force, which is required to peel the covering layer for 100 mm, when the holder is
separated at a constant speed of (100 ± 10) mm/min. The unpeeled part of the specimen
may not be fixed.
A.1.3.3 The average peel force and bonding strength are determined according to
A.1.4.1 and A.1.4.2, respectively.
A.1.3.4 If the test piece breaks, record the maximum stress value of the two test pieces,
which is determined by the automatic graphing instrument.
A.1.4 Determination of average peeling force and bonding strength
A.1.4.1 Determination of the average peeling force. The initial force recorded
automatically can be ignored. Take the automatically recorded curve with the effective
peeling length of the covering layer not less than 75 mm, to determine the peeling force.
A.1.4.2 The bonding strength is the ratio of the peeling force to the width of the
specimen, in Newtons per millimeter (N/mm).
A.1.5 Result expression
The average peeling force between the upper and lower covering layers and bonding
layers of each specimen shall be recorded separately; the average bonding strength of
the three specimens shall be calculated.
A.2 Bonding strength within covering layer containing fabric layer
A.2.1 Test piece p...