Potting compound for connectors and cable exits
Connectors and cable exits are the most critical points in an assembly, both mechanically and in terms of sealing. Potting provides three functions here: strain relief, sealing, and kink protection. The crucial factor is almost always adhesion to the cable jacket.
To the point
Use a flexible silicone sealant – the cable moves, a rigid sealant will tear at the joint. Ensure good adhesion to the sheath (often with a primer), a tight IP seal, and effective strain relief.
The crux of the matter: adhesion to the cable jacket
Cable sheaths are made of PVC, PUR, PE, or TPE – materials to which silicone adheres very differently. Without adhesion, however, there is no tight, tensile-resistant seal: the potting compound deteriorates, and moisture creeps along the interface into the housing. Three ways lead to the goal:
- Primer/adhesion promoter on a cleaned, degreased surface, e.g. BLUESIL Primer PM 820, Primaire PM 811 or adhesion promoter V-2 Primer.
- Self-adhesive (primerless) encapsulants such as DOWSIL EL-2888, which adhere to many substrates without a primer and save a work step.
- Surface pretreatment – low-energy plastics such as PE and PP absolutely require primers or physical pretreatment (plasma, flame treatment, pickling).
| cable sheath | Liability | Recommendation |
|---|---|---|
| PUR, PA | good to average | Clean, primer if necessary |
| PVC, TPE | medium | Primer recommended |
| PE, PP | bad | Primer + Plasma/Flame treatment |
The other requirements
Strain relief and kink protection
Tension and bending forces act at the cable joint. A flexible material with high elongation distributes these forces and prevents tearing at the joint; a rigid mass fails there first because the changes in stiffness are concentrated at the clamping point.
Sealing
For protection classes according to IEC 60529 (IP67/IP68), the potting compound must tightly enclose the housing and cable transition – this is only possible with sufficient adhesion. A visually clean but poorly adhering potting compound only gives the false impression of a tight seal.
Movement and vibration
Moving connections and vibration require a permanently elastic, damping material that can withstand alternating loads over many cycles without fatigue.
Material selection and products
Flexible, pourable silicones such as SILISIL RTV PP-Flex 12, MF-Flex 20 , or PC-Flex 20 are the typical choice, combined with the appropriate primer. Where a particularly tough, abrasion-resistant coating is required, polyurethane can be a suitable option – see epoxy, silicone, or PU.
processing
Clean and degrease the casing, apply primer and allow to dry completely, then mix thoroughly, degas, and pour (step-by-step instructionsto avoid mistakes). Calculate the fill quantity using the potting and mold making calculator.
Frequently Asked Questions
Which primer for PUR cables? PUR often adheres well on its own; a silicone primer like PM 820 increases reliability. For PE/PP, there's no way around using a primer plus pretreatment.
When to work without a primer? If you want to save a step and the substrate is suitable – it's best to test a self-adhering encapsulant like DOWSIL EL-2888 in a preliminary trial.
Does IP68 protection hold up permanently? Only if the adhesion to the jacket and housing is permanent. That's why cleaning and priming are not optional.
Consultation and samples
Tell us about the connector type, cable jacket material, and protection rating – we'll recommend potting compound and primer and provide a sample. Contact us or write to info@silitech.ch.
