Repair of Cracking (“Tortoise Shell” Cracks) in Jack Shock-Absorbing Rubber Blocks
Cracking, often described as “tortoise shell” cracking, is a common degradation phenomenon in jack shock-absorbing rubber blocks after prolonged service. Such cracks reduce elasticity, damping performance, and load-bearing reliability. While severely aged rubber blocks should be replaced, minor surface cracking can be repaired to extend service life under certain conditions.
1. Assessment Before Repair
Before attempting any repair, the severity of cracking must be evaluated.
Superficial surface cracks without deep penetration or structural deformation may be repairable.
Deep cracks, extensive hardening, loss of elasticity, or permanent deformation indicate advanced aging and require replacement rather than repair.
Proper assessment ensures that repaired blocks can still operate safely.
2. Surface Cleaning and Preparation
Effective repair depends on thorough surface preparation.
Remove dirt, oil, and loose rubber particles using a mild solvent compatible with rubber.
Dry the surface completely to ensure proper adhesion of repair materials.
Lightly abrade the cracked area to improve mechanical bonding and remove oxidized rubber layers.
3. Crack Filling and Sealing
For shallow cracks, flexible rubber repair compounds or elastomeric sealants can be applied.
The repair material should have similar elasticity and hardness to the original rubber.
Fill cracks gradually to avoid trapping air and ensure uniform bonding.
Smooth the surface to reduce stress concentration during subsequent loading.
4. Adhesive and Curing Process
Use rubber-compatible adhesives or vulcanizing agents designed for elastomer repair.
Follow manufacturer-recommended curing temperature and time.
Avoid loading the rubber block during curing to prevent crack reopening or bond failure.
5. Protective Surface Treatment
After repair, apply a protective coating or rubber conditioner to slow further aging.
Anti-ozone or UV-resistant coatings help reduce environmental degradation.
Periodic application can significantly delay crack propagation.
6. Operational and Preventive Measures
Avoid overloading and prolonged static compression.
Store rubber blocks in cool, dry environments away from direct sunlight and ozone sources.
Inspect repaired areas regularly and replace the block if cracks reappear or deepen.
Conclusion
Repair of tortoise shell cracking in jack shock-absorbing rubber blocks is feasible only for minor surface cracks and requires careful assessment, proper surface preparation, elastic repair materials, and controlled curing. However, repair is a temporary measure, and severely aged or structurally compromised rubber blocks should be replaced to ensure lifting safety.
References
Gent, A. N. Engineering with Rubber: How to Design Rubber Components. Hanser Publishers, 2012.
ASTM D573 – Standard Test Method for Rubber—Deterioration in an Air Oven.
ISO 1431-1 – Rubber, Vulcanized or Thermoplastic — Resistance to Ozone Cracking.
Lake, G. J. “Fatigue and Fracture of Elastomers.” Rubber Chemistry and Technology, 2000.
