Two labs test the same rubber compound and may report tensile strength results differently. This happens in the absence of a standard that regulates the results as per industry norms, irrespective of the region where products are manufactured. Most of the time the real reason is how the test pieces were prepared.
This is where ISO 23529 comes into the picture for the rubber industry with a recognized set of rules. In this article, we will go through what rubber testing means, what the standard covers & how the procedure runs in practice. If you work in a QC lab or on a rubber shop floor, you will find useful information before conducting rubber testing.
What Is Rubber Testing & Why Is It Important?
Rubber testing is the measurement of how a rubber material behaves under force, heat, aging or chemical exposure. It is common in industries that manufacture tires, seals, tubes, belts, footwear and other rubber products.
There are various products with different characteristics. For instance, rubber seals have to remain flexible for a longer time, while the conveyor belts need durability to withstand different loads over time. Tires should not wear out on different types of pavement. Testing gives manufacturers an idea about how the materials behave.
Some tests performed in the rubber industry include tensile strength, elongation, hardness, tear resistance, compression set & heat aging. Each gives you a number you can compare against a spec. But a number is only worth something if another lab can repeat the test and land close to it. Rubber makes that hard. It’s soft, it stretches, it recovers slowly & it responds to temperature and humidity more than most people expect. A sample left near a sunny window for two days is a different sample from one kept in a closed cabinet.
What is ISO 23529?
ISO 23529 is an international standard for preparing and conditioning rubber test pieces before physical testing. It covers the general procedures for handling samples so they are ready for testing under suitable and controlled conditions.
The full title of ISO 23529 standard is Rubber: General procedures for preparing and conditioning test pieces for physical test methods. The current published edition listed by ISO is ISO 23529:2016. It covers sample preparation, measurement, marking, storage, conditioning and preferred test conditions.
This International Standard was developed for the preparation and conditioning of rubber test pieces for physical tests (ISO 23529). Does not test the rubber. Ensures all tests begin at the same location.
If the rules for preparation are not agreed upon, results obtained from different laboratories, on different days or on different shifts in the same plant cannot be compared adequately. The most expensive tester on the market can have the best test data, yet it can be data no one believes. In plain terms, this standard protects your results before the machine even switches on.
It deals with lab temperature and humidity, the time between curing and testing, how samples are stored, how they are cut and measured, and how long they’re conditioned. Each item removes one small source of error. Small errors pile up quickly with rubber, so that matters.
ISO 23529 PDF Download
For detailed requirements, download ISO 23529 PDF document rather than relying only on a summary. The standard contains the procedures and conditions needed for proper preparation & conditioning of rubber test pieces.
ISO 23529 Scope & Purpose
ISO 23529 scope covers general procedures for preparing and conditioning test pieces used in physical tests on vulcanized and thermoplastic rubber. The purpose is simple: make results repeatable and comparable no matter where the testing happens.
It applies to pieces molded in the lab and also to pieces cut from finished products. That second case gets messy. A cut from a molded part may have uneven thickness, a surface skin or internal stress, and the standard gives guidance on handling those situations.
Purpose of ISO 23529: The aim stretches beyond good paperwork. A customer from one country & a vendor from another get into a dispute over a shipment of seals. If both parties utilize the same preparation guidelines, the dispute gets quicker because they can believe the figures.
The standard ensures the following things are under control and in line with industry norms:
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Temperature and humidity around the test piece
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Time between vulcanization and testing
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Storage conditions before testing
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Dimensions and surface finish of the sample
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Conditioning time before the test starts
ISO 23529 Testing Procedure for Rubber
The ISO 23529 testing process involves the vulcanization phase, ensuring that rubber samples are stored & cut correctly. It is important to test rubber in a controlled environment, as measurements may differ depending on the testing method being used.
Prepare the test pieces
Choose the appropriate die or cutter for your particular test whether you are running a molded sheet or working from a slab or finished product. Always use a sharp blade. If the blade is dull, it will not only make small cuts but also rip easily from these small cuts. If there is an area that needs to be buffed, move at a slow speed, as rubber gets heated up by fast movement.
Observe the time interval after vulcanization
Rubber keeps changing after it leaves the mold, so the standard asks for at least 16 hours before testing. There’s a ceiling too. Four weeks for non-product tests, and generally three months for product tests. If you’re comparing samples, try to test them all after a similar interval.
Store the samples correctly
Dark place, steady temperature, away from heat, ozone, oils and solvents. A closed cabinet does the job. Don’t pile things on top of the samples.
Measure the dimensions
Take thickness and width at a few points along the piece, using the gauge and contact pressure the standard specifies. Rubber is soft, so a gauge pressing too hard squeezes it and shows a thinner value than the real one. It’s an easy mistake to make and a hard one to spot afterwards.
Conditioning of pieces
Put them in the standard laboratory atmosphere before testing. The usual temperatures are 23°C or 27°C within a narrow tolerance, and humidity control comes in when the material is moisture sensitive. Three hours is a common minimum. Some tests ask for more.
Test in the same condition
Run the test where the pieces were conditioned. If a sample goes out to a warm corridor and comes back, it’s already a different sample.
Record the details
Curing date, storage time, temperature, humidity, and how the pieces were cut. Boring work, but when two batches disagree a month from now, this record is the first thing anyone will ask for.
Conclusion
ISO 23529 is an international standard for rubber manufacturers that helps to promote good practice and safe working. It is important in the context of every rubber testing laboratory, as it ensures that each sample is prepared and tested in the same manner, leading to uniformity of results from one lab to the next. Don't fault equipment first if the results seem suspect in your lab. First, consider the re-treatment and conditioning of your specimens again.
Good preparation also needs good equipment. Testronix Instruments makes testing instruments for rubber, plastics and packaging, built to support consistent, standard-compliant testing in everyday lab conditions. If you’re setting up a new rubber testing lab or upgrading an old one, their team is worth a conversation.
If you want higher-quality, more trustworthy rubber test results, get in touch with Testronix Instruments today and consult about testing solutions that fit your lab.
