Coukd you show us some pictures?

Hi smoshylife,

Good question — the masking element on a reel-to-reel wheel is one of those details that quietly decides your mask-line quality. Here is the engineering logic we use when selecting masking media for plating service; it applies to belts just as it does to masking tapes:

1. Chemical compatibility — but scope it to the whole line, not just the gold bath. Gold baths themselves are mild toward most elastomers (as Ted noted, even PE/PP/PVC survive them). The steps that usually attack masking materials are the alkaline cleaners and acid dips/activators upstream. FKM (Viton-type) has excellent acid and solvent resistance but is comparatively stiff and honestly overkill for a gold line. Fluorosilicone keeps silicone’s softness while adding oil/solvent resistance, but its resistance to strong alkalis is actually poorer than FKM — so check your cleaner pH before choosing on chemistry alone.

2. Conformability is usually the real decider. On a wheel, the belt must make continuous, even contact with the part under light pressure. A softer material (silicone in the ~40-60 Shore A range) conforms to minor surface irregularities and gives a tighter mask line; a harder belt lets plating solution wick under the edge, and you get “bleed” or halo plating around the masked zone. If I had to pick one balance point for a gold line, softness wins.

3. Clean release. Whatever masks the part must release without tearing or leaving residue on the contact — the same criterion we apply to masking tapes (the bond must survive the bath, then let go cleanly). PTFE films are the champions of release because of their low surface energy, which is why PTFE-based masking dominates aggressive processes like anodizing or hard chrome in acid/alkali. Our YJY-CR chemical-resistant PTFE masking tape, for example, is specified exactly for acid/alkali plating and anodizing masking with residue-free removal. On a contoured wheel, though, film conformability is lower than an elastomer belt — so match the form to the geometry.

4. Fatigue and thermal life. A reel-to-reel belt flexes continuously, so check fatigue/abrasion resistance and the continuous service temperature (silicone ~200 C, FKM ~200-250 C, PTFE ~260 C) against your dryer/cure steps.

Practical takeaway for your gold line: start with a soft silicone or fluorosilicone belt (~40-60 Shore A) for sealing, verify compatibility specifically against the alkaline cleaner and acid dips, and inspect the mask line under magnification on trial strips. Reserve FKM for lines with aggressive solvents, and PTFE-based masking for aggressive acid/alkali chemistries like anodizing.

Happy to go deeper on the selection criteria if you can share the chemistry sequence (no photos needed).

— Zhang Sheng