Difference And Application Between S.I.R and EPDM Of Cold Shrink Joints

As we all know, cold shrink relies on the incredible elastic memory of advanced polymers and its spring of forming a seal without the need for torches or heat guns. The two commonly used raw materials in this domain are S.I.R(Silicone Rubber) and EPDM(Ethylene Propylene Diene Monomer).

Production Process

EPDM(Ethylene Propylene Diene Monomer)'s production follows a more traditional rubber processing route. EPDM is a copolymer of Ethylene and Propylene, with a small amount of a third monomer. The ethylene and propylene provide flexibility and chemical stability, while the diene introduces unsaturation in the polymer chain, which is crucial for vulcanization. EPDM polymer is mixed with a suite of additives in a large mixer. Then, EPDM compound is extruded and then vulcanized.

S.I.R(Silicone Rubber) is an element borrowed from sand which inorganic backbone is the source of its unique properties. The base silicone polymer is a relatively weak gum. To become a useful engineering material, it is compounded with reinforcing fillers, most famously fumed silica. This is the same substance that makes the thixotropic texture of ketchup possible, and in silicone, it adds tremendous tensile strength and tear resistance. Other additives include heat stabilizers and pigments.The compounded silicone is then shaped, often by extrusion, into its final "pre-expanded" tube form. To create the elastic memory, it undergoes vulcanization. This is typically a two-part process involving a platinum.

Performance

Silicone rubber can operate continuously at temperatures of 180°C to 200°C and withstand short-term spikes even higher. However, EPDM typically has a maximum continuous operating temperature of around 130°C to 150°C. Silicone is exceptionally resistant to UV radiation and ozone, meaning it won't crack or degrade from sunlight exposure for decades. In fact, EPDM also boasts excellent weather resistance. But some formulations of EPDM can be susceptible to UV degradation over very long periods so that it often mitigated by adding carbon black. Silicone remains remarkably flexible and elastic at extremely low temperatures (down to -50°C and beyond). It does not become brittle. However, EPDM can stiffen significantly in sub-zero conditions, making installation difficult and risking improper sealing if not handled correctly. Silicone is highly resistant to moisture, oxidation, and many common chemicals.EPDM offers good resistance to water, steam, and mild acids and alkalis. However, EPDM is vulnerable to attack by oils, solvents, and petroleum-based fluids.Mechanical strength is where EPDM often shines. Traditional EPDM compounds tend to have higher abrasion resistance and tear strength than standard silicone rubbers. This makes EPDM joints more resistant to mechanical damage during backfilling or in rocky trenches.

Application Scenarios

Choose S.I.R When:

Its superior hydrophobicity recovery and tracking resistance are critical in salt-laden air or industrial areas where conductive pollution can lead to surface leakage currents and eventual flashovers.

Excellent dielectric strength and tracking resistance allow for more compact joint designs, which is vital in crowded substations or for higher voltage ratings. Ideal for locations that experience both scorching heat and freezing cold, or for cables that experience significant load-related temperature cycles. Its stability is unmatched.

Near electrical equipment that generates ozone (like switchgear), S.I.R.'s complete immunity is a significant advantage.

Choose EPDM When:

Its high tensile strength, abrasion resistance, and excellent water resistance make it the premier choice for joints buried directly in the ground, where backfill and rocks could pose a physical threat.

For most standard outdoor applications which on poles, in conduits, or in trenches. EPDM provides a perfect balance of weather resistance, electrical properties, and mechanical durability at a competitive cost.

In mining, industrial plants, or anywhere the joint may be subject to vibration, accidental impact, or abrasion, EPDM's tougher nature provides an extra layer of security.

Crucial Precautions

In fact, cold shrink joints have a finite shelf life because the rubber is held in a state of constant stress. What’s more, always check the manufacturer's expiration date and do not use expired products. In addtion, cable must be scrupulously clean, dry, and free of any contaminants, sharp edges, or burrs. Use the specified cleaning wipes and abrasives to prepare the semiconductor and insulation surfaces. A single tiny metal burr can act as a focal point for electrical stress, leading to eventual failure. Once you begin pulling the core, do not stop. The joint will begin to shrink immediately. A slow, steady, and continuous pull is essential to ensure the joint shrinks evenly and concentrically around the cable, without twisting or leaving gaps. Ensure the joint kit is rated for the specific cable voltage, diameter and construction (e.g., tape shield, wire shield). Otherwise, using an undersized or incorrectly rated kit is a recipe for failure.