Abnormal Hardness in Jack Shock-Absorbing Rubber Blocks: Causes and Solutions
Jack shock-absorbing rubber blocks are designed to absorb impact, reduce vibration, and provide stable load distribution. Abnormal hardness, either too high or too low, can compromise performance, reduce safety, and accelerate wear. Understanding the causes of abnormal hardness and implementing corrective measures is crucial for reliable operation.
1. Material Aging and Environmental Exposure
Over time, exposure to heat, ultraviolet radiation, ozone, or aggressive chemicals can alter the rubber’s molecular structure. Oxidative aging often increases hardness, making the rubber stiff and less elastic. Conversely, prolonged exposure to oils or solvents can soften the rubber, reducing hardness and load-bearing capacity.
2. Improper Material Selection
Using a rubber compound unsuitable for the operating conditions often leads to abnormal hardness. For example, natural rubber may harden in high-temperature or outdoor applications, while softer rubbers may swell or lose stiffness when exposed to oils or chemicals.
3. Manufacturing and Vulcanization Issues
Incorrect vulcanization temperature, time, or pressure can result in under- or over-curing. Under-cured rubber is too soft, exhibits high compression set, and deforms easily. Over-cured rubber becomes excessively hard and brittle, increasing the risk of cracking under load. Inconsistent filler dispersion or uneven compounding can also cause local hardness variations.
4. Mechanical Overload and Stress Concentration
Repeated overloading or localized stress can densify the rubber matrix in certain areas, leading to localized hardening. Over time, this affects uniform load distribution and increases the likelihood of cracks or deformation in softer regions.
5. Preventive Measures and Corrective Actions
Material Selection: Choose rubber compounds suitable for the operating environment, such as NBR for oil resistance, EPDM for outdoor applications, and polyurethane for high-load resistance.
Process Control: Ensure proper vulcanization parameters and quality control during manufacturing.
Environmental Protection: Minimize exposure to excessive heat, UV, ozone, and harmful chemicals. Protective coatings or storage in controlled environments can help.
Load Management: Avoid overloading and uneven load application during use.
Inspection and Replacement: Regularly check rubber hardness and replace blocks showing abnormal stiffness or softness to maintain performance.
Conclusion
Abnormal hardness in jack shock-absorbing rubber blocks results from material aging, improper compound selection, manufacturing defects, and mechanical overload. By selecting appropriate materials, optimizing manufacturing processes, protecting against environmental degradation, and controlling operating loads, the hardness can be maintained within the desired range, ensuring safe and effective jack performance.
References
Gent, A. N. Engineering with Rubber: How to Design Rubber Components. Hanser Publishers, 2012.
ASTM D2240 – Standard Test Method for Rubber Property—Durometer Hardness.
Lake, G. J. “Fatigue and Fracture of Elastomers.” Rubber Chemistry and Technology, 2000.
ISO 7619-1 – Rubber, Vulcanized or Thermoplastic — Determination of Indentation Hardness.
