ISO/DIS 25408-2:2026(en)

ISO/ TC 17/SC 17

Secretariat: SAC

Date: 2025-12-12

Testing method for bead wire – Part 2: Adhesion test

© ISO 2026

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Contents

Foreword Ⅳ

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle 1

5 Apparatus & tools 1

5.1 Tensile Testing Machine 1

5.2 Vulcanization press 1

5.3 Mould 1

5.4 Block holder 2

5.5 Rubber pad remover & pressure roll 3

5.6 Solvent 3

5.7 Rubber cutter 4

5.8 Consumable 4

5.8.1 rubber compound 4

5.8.2 Mould release lubricant: 4

6 Procedure 4

6.1 Preparation for rubber compound 4

6.2 Preparation for vulcanization mould 4

6.3 Sample preparation 5

6.4 Preparation of the rubber block 5

6.4.1 Hot moulding method 5

6.4.2 Prebuilding mould method 6

6.5 Cleaning process 7

6.6 Pull out test 7

7 Calculation and report of Pull-out force 8

8 Precision & variance 8

9 Rubber Coverage Rate (RCR) 8

10 Calculation and report of Rubber Coverage Rate (RCR) 9

Foreword

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Testing method for bead wire – Part 2: Adhesion test

This document specifies the test method for strength of adhesion of Bead wire (round & shaped) to vulcanized rubber compounds.

The method applies to, but is not limited to, wire made from brass, bronze, or zinc coated steel wire.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements 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 16650, Bead wire

For the purposes of this document, the terms and definitions given in ISO 16650 apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

Specimens of bead wire vulcanized into a block of rubber and force necessary to pull Bead wires linearly out of the rubber is measured. The used clamp or block holder shall be equipped with a circle hole to guarantee the homogenous stress. If required, the visual evaluation of rubber coverage is also determined.

a) CRE (Constant-Rate-of-Extension) tensile testing machine capacity that the measured force required to fracture the wire shall be within force measurement range. Device equipped with a load and extension recorder, digital read-out, automated data logger or computer controlled tensile test machine.

b) Cross-head speed: maximum speed must be ≥ 150 mm/min. (≠ test speed)

c) Machine accuracy Class 0,5 = Load weighing accuracy: +/- 0,5 %

d) Load cell capacity depends on the type and characteristics of the wire.

a) Vulcanization press type electrical or steam heat and large enough to take the mould dimensions and capable of a minimum pressure of 3,5 MPa over the total area of the mould plate used.

b) Dimension of the press platens: Minimum 400 mm x 400 mm.

c) Temperature capacity: Maximum 200 °C.

d) For a standard 1 cavity mould (50 mm embed) a pressure of 70 kN to 100 kN is to apply.

e) Heating for the top and the bottom platens shall be of sufficient capacity for maintaining the mould components at the specific temperatures required for the rubber compound being used.

f) The heat up power of the press must be min 10 °C/min or better 20 °C/min.

g) Temperature resolution: 0,5 °C.

h) Temperature in the rubber must controlled within ±2 °C during vulcanization.

a) Mould is designed for a 13 mm thick block of rubber, 200 mm long, and 50 mm wide, with 15 wire slots across the width of the mould spaced 12,5 mm apart at the middle of the mould thickness, and with top and bottom plates for the mould.

b) Moulds with embed lengths of 12,5 mm or 15 mm or 20 mm or 25 mm are also possible according to requester requirements.

c) The 15 wire slots have a typical ‘Y’ shape groove for Bead wire adhesion testing.

d) The ‘Y’ shape slot width can be according to wire thickness. Standard slot widths are 1,15 mm & 2,1 mm & 3,1 mm. Standard depth of ‘Y’ shape slots is 7,5 mm.

Figure 1 — Vulcanization Mould

The block holder grip shall be a special holder made for the vulcanized block sample. The opposite grip may be any type of clamp of sufficient capacity to handle the specimen and designed to prevent its slippage in the grip area.

Figure 2 — Block holder

Rubber pad remover or manual mould ejector is recommended for safely and quickly removing of rubber block out of the hot mould without extreme bending of the ongoing adhesion pad.

a) The use of solvent on rubber surface or Bead wire surface can influence the adhesion process.

b) Cleaning or even touching rubber surface and Bead wire surface is not allowed.

c) Only if the requester really requires cleaning the rubber surface or the Bead wire surface is it allowed.

d) The re-freshening action must take place at least 10 minutes prior to the pad assembly.

e) A suitable solvent has been found to be lead-free gasoline (normal heptane’s), with a distillation range from 40 to 141 °C and a maximum recovery of 97 %, available from most solvent suppliers.

a) A rubber cutter is needed. It shall be able to cut rubber with a thickness of 7 mm with acceptable precision to achieve correct rubber sheath dimensions.

b) A big paper cutter or clicker dies with exact target dimensions are to be used.

a) The rubber compound can be provided in sheath form, 7 mm thick on a non-hygroscopic backing, such as a plasticizer free plastic material, or may be provided un-milled in a form requiring milling immediately prior to use.

b) The rubber compound is provided by the customer, along with information regarding storage conditions and shelf - life. If the customer has no special requirements, the storage conditions and shelf - life shall be implemented in accordance with the following requirements:

① The rubber compound shall be stored in the laboratory environment with a temperature of (23 ± 5) °C and a humidity of ( 40-55 ) % RH. It shall be protected from light. The shelf life is 3 months;

② Or store the rubber compound in a refrigerator at (5 ± 5) °C. The shelf life is 6 months. If the rubber compound is stored in a freezer at (5 ± 5) °C, it shall be taken out of the freezer 24 hours in advance before use.

Mould release lubricant can be applied to an empty mould to limited residue rubber parts on the mould after vulcanization and to ease test block removal. Mould release spray cannot be applied just before mould build-up process. Best is to apply mould release spray before a time-out period of at least 2 hours before next vulcanization and let the spray be evaporated during that time.

a) Set the roller temperature of lab rubber re-miller at maximum 50 ± 5 °C. Temperature of compounds after re-milling shall be not higher than 70 °C.

b) The spacing of the mixing rolls is determined by the original rubber thickness. Adjust the roller space according to the target thickness of the rubber. Take out the rubber from the rollers.

c) The target thickness of rubber compound shall be (7,5 + 0,5) mm or overlap two pieces of rubber sheets together to 7,5 + 0,5 mm.

d) Cover the compound with polythene film to avoid the contamination on rubber surface, which will affect adhesion property.

There are multiple sizes of cavities (embed length) for vulcanization mould: 50 mm & 25 mm & 20 mm etc., select the vulcanization mould according to requester requirement.

Note: This document recommends using a vulcanization mould with a 50 mm cavity (embed length)

a) For bead wire specimens, select 4 different samples numbered 1, 2, 3, 4. Cut each sample into at least 3 specimens, each with a minimum length of 180 mm. For example, cut sample 1 into specimens 1 - 1, 1 - 2, 1 - 3; cut sample 2 into specimens 2 - 1, 2 - 2, 2 - 3, and so on

b) When handling specimens, embedded area shall not be touched to avoid contamination of sample surface.

c) Reference material is recommended, which monitor stability of vulcanization process. Reference material shall have stable & known adhesion performance. Cut 3 pieces of the reference material (RM1, RM2, RM3) and put them at position 1, 8, 15.

a) The hot moulding method is the best practice in Bead wire vulcanization process because this method reduces the heat impact variation thanks to the use of pre-heated mould.

b) Position the vulcanization mould in the centre of the platens. Close the top and bottom platens with low contact pressure to preheat the vulcanization mould till target temperature has been meet then waiting for at least 30 minutes.

c) Cut rubber sheets according to the dimension of the vulcanization mould.

Figure 3 — Rubber block

d) Collect test samples & standard samples without touching wire surface at the area where adhesion process will occur. Best practice is to have all samples already in correct sequence as they will be loaded into the hot mould. Take these samples and rubber sheets to the vulcanization press.

e) When pre-heat process is finished, take out the hot mould and place it on a wooden surface to avoid extreme heat loss.

f) Take out the top plate and put it into the hot press.

g) Remove the plastic foil of the bottom rubber sheet and put it into the hot mould without touching the rubber side that will be in contact with the bead wire samples.

h) Load the hot mould with all bead wire samples and standard or reference samples in correct sequence. Add the top rubber sheath and remove plastic foils on top of the samples after the rubber sheath is loaded into the mould.

Figure 4 — Sample sequence or sample distribution

i) Perform this loading action within 3 minutes to prevent too high heat loss.

j) Set curing pressure curing temperature and curing time according requester’s info. Start the vulcanization process.

k) When vulcanization process is finished, open the press platens and remove the rubber pad from the hot mould using a rubber pad remover (see 5.5)

l) The length of the residual compound extruded from the embedded length shall be equal length on both side of the mould and the target length of the rubber flow is 25 mm +/-10 mm.

m) Put the hot rubber pad on a metal table surface to reduce cool down period to room temperature.

n) The cleaning process can be found in Chapter 6.5.

a) In the pre-building mould method, a cold pre-build mould is used. The rubber and test samples and standard & reference samples are assembled in a pre-build mould at room temperature. Then the assembled rubber pad is put into the pre-heated mould from the vulcanization press.

b) Mould pre-heat process: Position the vulcanization mould in the centre of the platens. Close the top and bottom platens with low contact pressure to preheat the vulcanization mould till-target temperature has been meet then waiting for at least 30 minutes.

c) Cut rubber according to the dimension of the vulcanization mould.

d) Place the bottom piece of rubber in the cavity of the pre-build mould after removing both sides of polythene film of rubber.

Figure 5 — Rubber block in pre-builder mould

e) Place all specimens in individual slots of pre-build mould with approximately equal length, the minimum length for lower part is 25 mm. The 4 test samples and the standard samples each with 3 repetitions, need to be distributed over the complete rubber block. This position sequence is to apply for all vulcanizations.

4 samples with each 3 repetitions= 12 wire slots

1 standard with 3 repetitions = 3 wire slots

Total wire slots = 15

Figure 6 — Sample sequence or sample distribution

f) Remove the polythene film of both sides of the top piece of rubber and place it in the cavity. Unprotected rubber side that it is in contact with the test samples shall not be touched. Press firmly with pressure roll (see 5.1.5) and make the mark on the rubber block to identify sample information.

g) Take the rubber block out of the pre-build mould without extreme bending of the rubber block, keep it at room temperature maximum 4 hours. When the wire rubber stickiness is low there is a real risk that wires are changing position during this removing action.

h) When pre-heat process is finished, take the preheated mould out of the press and put it on a wooden table surface to avoid extreme heat loss. Remove the top plate of the mould. Place the assembled rubber block into the hot mould and cover again with the top plate. Position the vulcanization mould to the centre of the press. Complete this process within 2 minutes.

i) Set curing pressure & curing temperature and curing time according to requester info. Close the press platens and start the vulcanization process. If no requester pressure requirement is known, then apply pressure of 70 kN to 100 kN for a 1 cavity mould.

j) When vulcanization process is finished, open the press platens, and remove the rubber pad from the hot mould with the using of a rubber pad remover see 5.5.

k) Put the hot rubber pad on a metal table surface to reduce cool-down period to room temperature.

l) The cleaning process can be found in Chapter 6.5.

a) Waiting time limits for holding the cured rubber pad between vulcanizing and cleaning & testing is according to requester requirements. If no customer minimum and maximum requirements are known, the waiting time before cleaning & testing actions must not be less than 16 h and advisable max 48 h. Too long waiting time can change the adhesion performance.

b) Cut off specimens of lower part of block till there is less than 1 mm of remaining bead wire. Trim rubber flow at the upper side of block. Do not damage the specimens or cut into the body of the test block.

Note: Check if all specimens are in the middle of width of the rubber block.

Figure 7 — Cleaning of rubber block

a) Set pull out rate between 50 mm/min and 150 mm/min or according to customer.

b) First, install the block holder at the position of the bottom clamp of the tensile machine. Then, bring the trimmed rubber block into the block holder and ensure that each specimen is positioned at the centre of the 12,5 mm diameter hole of the block holder. Finally, adjust the bottom plate of the block holder so that the block has the minimum deformation during testing.

c) Rubber block is located at the lower block holder, adjust the height of the upper grip then clamp specimen in the upper grip in a perfect perpendicular position. Make sure clamped specimen is in the center of circle of the block holder.

d) Start the tensile test machine to pull out the specimen one by one from the rubber block, record the maximum force to the nearest 1 N.

Pull-out force for sample 1#: The average of pull-out force for three specimens 1-1, 1-2, 1-3;

Pull-out force for sample 2#: The average of pull-out force for three specimens 2-1, 2-2, 2-3;

Pull-out force for sample 3#: The average of pull-out force for three specimens 3-1, 3-2, 3-3;

Pull-out force for sample 4#: The average of pull-out force for three specimens 4-1, 4-2, 4-3;

The result of reference material is only for internal monitoring, no need to report.

a) The variance of the test method is expressed in %CV.

b) The coefficient of variation (CV) is defined as the ratio of standard deviation-sigma to the mean.

c) Coefficient of variation = (StDev/Avg)*100

Table 1 — Maximum acceptable CV% of BW POF

d) CV% is calculated of 9 BW labs with a total of 27 lab analysts performing BW adhesion POF test with n=9 on 5 different BW constructions. Outliers were eliminated.

e) The CV% evaluation shall only be done based on data coming from controlled cross checks or MSA studies. Test samples shall be as stable as possible and be randomized before use. Test rubber compound shall be as homogeneous as possible.

a) Evaluate the rubber coverage of the pulled specimen:

b) The complete embedment length needs to be evaluated during wire rotation over 360° turn.

— The real shiny areas are judged to be 0 % RCR.

— The clear rubber covered areas are judge as 100 % RCR.

— The grey areas are the area in between the shiny areas and the clear rubber areas, the grey areas are judged to be as 50 % RCR.

c) To have an acceptable detailed view for evaluating the BW RCR one need to use a magnification of minimum 8x and apply extra LED light to be able to see differences between the black wire surface and the black rubber residue (grey areas).

d) Record the rubber coverage to the nearest 10 %.

Table 2 — Evaluation criteria of rubber coverage

Rubber coverage for sample 1#: The average of rubber coverage for three specimens 1-1, 1-2, 1-3;

Rubber coverage for sample 2#: The average of rubber coverage for three specimens 2-1, 2-2, 2-3;

Rubber coverage for sample 3#: The average of rubber coverage for three specimens 3-1, 3-2, 3-3;

Rubber coverage for sample 4#: The average of rubber coverage for three specimens 4-1, 4-2, 4-3;

The result of reference material is only for internal monitoring, no need to report.

Calculate and report the Average Rubber Coverage Rate(RCR) of the 3 specimens per spool to the nearest 1 %.

Second report method:

Table 3 — Report of RCR