How does rubber harden soften and have elasticity？

Quick Answer: Can Hardened Rubber Be Restored?

Sometimes, a temporary change in flexibility can be reversed when it is caused by a reversible physical effect. However, rubber that has deteriorated through heat aging, oxidation, chemical attack or permanent deformation cannot be assumed to recover its original sealing performance.

For industrial O-rings, oil seals and hydraulic seals, do not use boiling water, household oils, acids or microwave heating as general restoration methods. Identify the material, exposure conditions and failure symptoms first. Replace a seal when its integrity or ability to seal reliably cannot be established.

1. Why Does Rubber Harden, Soften or Lose Elasticity?

The elastic properties of rubber result from the properties of the polymer chains contained in the elastomeric formulation. Factors such as the chemical composition, cross-linking arrangement, presence of fillers and additives, as well as the environment in which the material is used, affect the way the material deforms.

Just having high hardness does not mean that the seal works. There could be seals that have equal values of hardness but differ in their compression recovery properties, resistance to chemicals and damage. Hence, an effective evaluation takes into account both visual and performance factors.

Heat and oxidative aging

Unfavorable thermal treatment may change the nature of the polymer network. This may be an increase in hardness, decrease in elongation, cracking of the surface, and permanent deformation depending on the type of rubber and conditions of operation. High temperature may also hasten the degradation due to an incompatible liquid.

The corresponding temperature threshold will depend on the particular compound and medium in which it operates. Generic temperature advice cannot take place of manufacturer's data.

Fluid incompatibility and swelling

Swelling, softening, or changes in dimensions can take place when a rubber compound absorbs incompatible fluids, while the fluid may leach out some components from the formulation resulting in shrinking or hardening of the material. Chemical reactions may adversely affect the material even without any dimensional changes.

All lubricating oils, cleaning solvents, process fluids, and their additives must be taken into account when investigating a failed seal. This is explained in the Parker O-Ring Handbook.

Compression set and loss of elastic recovery

The seal which is compressed needs to have sufficient surface contact. If the seal doesn't have the capability to return to its shape after deformation, it will fail to provide adequate sealing ability. Such a process is usually measured using a compression set test.

Permanent deformation occurs due to compression, high temperatures, material constraints, or aging. It is not enough just to make the deformed seal soft again.

Technical reference: ISO 815-1:2019 specifies methods for determining the compression set of vulcanized or thermoplastic rubber under defined test conditions.

2. How to Identify Common Rubber Aging Symptoms

Examine the seal after you have gone through the proper disassembly and maintenance procedures provided by the equipment manufacturer. Note the area where the damage occurred, the medium of operation, and any history of temperature or changes in cleaning practices. Please see below for some preliminary indications of possible causes.

The symptoms may coincide. It is possible that there will be softening caused by fluid uptake and also a loss in the mechanical properties of the material at the same time. Inspection will aid in pinpointing the problem, although further testing may be necessary in certain cases.

3. What Should You Do When a Rubber Seal Changes?

The correct answer lies in whether the observed change is reversible, whether the seal is still operating within its designated limits, and whether the results are acceptable. The target for an industrial seal is to ensure proper sealing performance, not mere softness.

Why common household restoration methods are unsuitable

The boiling water, microwaving, vinegar, and the use of uncontrolled heat for treating rubber are not advisable as methods of repairing rubber seals in industry.

The immersion of the rubber seal in vegetable oil or mineral oil is also not an option for repairing seals. The oil that will swell one rubber compound might react differently to another compound of rubber. It is also important to remember that just because there has been some change in the dimensions or the texture of the rubber does not mean that it is compatible with the oil being used.

Commercial rubber conditioners cannot be assumed to be appropriate for use in O-ring seals and other hydraulic seals unless otherwise specified by the manufacturer.

When should a rubber seal be replaced?

The option of replacement is better when the seal is cracked, cut, permanently distorted past its maximum limits, and not dimensionally stable or cannot keep a dependable seal. Replacement is recommended when the material has been subjected to an inappropriate substance or when the condition of the material cannot be confirmed.

Prior to installing a new seal, find out the reason behind the failure of the old seal. Identify the material, dimensions, groove condition, pressure, temperature, and compatibility with fluid. Otherwise, you may end up with the same problem with the new seal.

4. How to Reduce Premature Rubber Seal Degradation

Premature deterioration is prevented through choosing an appropriate material and controlling the conditions under which the material works. Avoiding unnecessary wear can be achieved by maintenance personnel and OEM purchasers who evaluate the following parameters.

Match the compound to the application

Selection of materials must consider the specific liquid, operating temperature, pressure, motion, lifetime expectancy, and any mechanical considerations that are required. NBR, FKM, EPDM, and silicone each have unique properties and no one material can be used in all environments. Verify the specific compound and not just the generic polymer name.

Control installation and operating conditions

Inspect grooves and mating surfaces for scratches, burrs, contamination and other defects. Use an installation procedure and lubricant compatible with the seal material. Excessive compression, improper stretching, unsuitable clearances and excessive friction can all contribute to premature damage.

Store seals appropriately

Follow the material supplier's storage instructions. In general, elastomer seals should be protected from unnecessary heat, direct sunlight, ozone sources, contamination and damaging deformation. Packaging, stock rotation and material identification also help prevent avoidable deterioration before installation.

Use appropriate testing for critical applications

Where the aging process or heat resistance of the rubber is an issue, it is preferable to have defined test methods than unregulated restoration processes. ISO 188:2023 deals with accelerated aging and heat resistance tests on vulcanized or thermoplastic rubbers. Testing is used for specific characteristics under defined conditions and does not necessarily mean the rubber is suited for all applications.

From the point of view of industrial purchasers, recording the specification of the rubber compound, its dimensions, and operating conditions becomes relatively straightforward.

Choosing a Suitable Replacement Seal

The right replacement depends on more than the original seal's dimensions. Material compatibility, operating conditions, profile design and installation requirements should all be checked before a new component is approved.

Explore our O-rings, hydraulic seals and custom rubber gaskets and seals to review relevant product categories. Confirm the required material and specifications against your actual application before selecting a replacement.

Frequently Asked Questions

Answers to common questions about rubber aging, elasticity and industrial seal maintenance.

Conclusion

Various reasons can lead to rubber hardening, softening, and a loss of elasticity, therefore, there is not one way of restoring all seals. First steps involve identification of the material used and assessment of the conditions under which it was in use and whether it was able to fulfill its purpose.

Industrial O-rings, oil seals, and hydraulic seals would benefit from being replaced and the reason for their early deterioration corrected rather than undergoing an uncertain restoration process.