1. Skeleton oil seal (standard part): Metal skeleton (fixed support) + rubber lip + self-tightening spring; the spring makes the lip grip the shaft and form an oil film seal, used in drum bearing housings and reducer output shafts.

Idler combination seal (non-standard): Labyrinth seal (nylon/plastic non-contact the first barrier against dust and water) + rubber lip seal (contact type.

The second barrier); the two are assembled as a set inside the idler bearing housing, the mainstream design for maintenance-free idlers.

Materials

1. NBR (nitrile butadiene rubber, most commonly used): Resistant to grease and abrasion, 40–120°C; for mining, sand and gravel, and coal.

Not resistant to strong acids, alkalis, or high temperatures.

FKM fluororubber: High-temperature resistance and acid/alkali corrosion resistance; for clinker and high-temperature chemical service, at high cost.

HNBR (hydrogenated nitrile butadiene rubber): Better wear and heat resistance than NBR; used in heavy-duty, harsh mining applications.

Labyrinth housing: PA nylon, modified PP.

Metal skeleton: cold-rolled steel sheet.

Spring: Stainless steel, to stop corrosion and loss of elasticity.

Classification

1. By structural form1) Skeleton oil seal (single lip/double lip).

Single lip: Seals lubricant only.

Double lip: Main lip seals the oil and the secondary lip excludes dust; used in drum bearing housings, couplings, and reducer shaft ends.2) Idler labyrinth lip seal combination.

Single-stage labyrinth: For normal dry conditions. Multiple labyrinth + double-lip rubber seal: For coal mines, ports, and washed materials.

Strong water- and dust-exclusion capability; the mainstream idler configuration.3) Taconite seal: Dedicated to heavy-duty drum bearing housings.

Multiple labyrinth + oil seal design, greaseable, for high-dust mining environments. By Mode.

Contact oil seal: The lip fits tightly against the shaft, giving good dust and water exclusion, but it wears; skeleton oil seals and rubber lip seals.

Non-contact labyrinth seal: Frictionless and long-lived but it cannot be used alone and must be combined with a contact oil seal to block coarse dust particles and muddy water.

Scenarios

1. Idler rollers: All use a labyrinth + rubber lip seal combination; NBR for ordinary sand and gravel, FKM for chemical corrosion.

Idlers are grease-filled at the factory and are mostly maintenance-free. Drive/bend drum bearing housings: Double-lip skeleton oil seals, with Taconite seals in harsh conditions, and periodic greasing.

Reducers, fluid couplings, and couplings: Standard skeleton oil seals, to stop gear oil leakage.

By environment: NBR is sufficient for dry dust; water, water spray, and slurry require a multi-labyrinth + double-lip oil seal.

FKM for high-temperature clinker and chemical service. Problems and Failures

1. Lip wear and spring corrosion or breakage: Dust particles enter the lip and scratch the shaft surface.

The spring loses its grip, causing oil leakage and dust/water ingress, and the bearing quickly corrodes and seizes.

The idler stops rotating altogether and wears out the belt. Rubber aging and cracking: High temperature sunlight.

And media corrosion cause the rubber to harden and crack leading to complete seal failure. The labyrinth cavity is blocked by coal powder and sludge: The labyrinth gaps fill with material and lose their pressure-relief and mud-blocking function.

So muddy water is forced directly into the bearing cavity; this occurs frequently in damp mining areas.

Assembly issues: Burrs or sharp edges on the shaft scratch the oil seal lip during assembly; the oil seal is fitted off-center or with poor coaxiality, causing rapid localized overload wear on the lip.

Grease problems: Excessive grease expands when heated creating high internal pressure that pushes the oil seal lip open.

Causing oil leakage and dust ingress. Key points for operation and maintenance: Oil seals are wear-prone parts.

A damaged idler seal normally means replacing the whole idler whereas drum and reducer skeleton oil seals can be replaced individually.

Multi-labyrinth combination seals are preferred in wet, splashing conditions.