The Belt That Tore at the Loading Point: Impact Energy, Not Tension
A belt conveyor carrying 1 kg metal parts. The parts dropped 300 mm onto the belt at the loading point. After two weeks, the belt had a 50 mm tear at the loading zone. The belt wasn’t over-tensioned. The parts were landing on it too hard. This is the impact energy calculation that determines the bed under the belt.
The impact energy
A 1 kg part dropping 300 mm hits the belt with:
E = m · g · h = 1 × 9.8 × 0.3 = 2.94 J
That doesn’t sound like much. But the impact is concentrated on a small area (the part hits the belt over about 500 mm²). The pressure is E / A = 2.94 / 500 = 0.006 J/mm². The belt’s fabric reinforcement flexes under this impact. Over thousands of cycles, the fatigue cracks propagate. The belt tears.
What’s under the belt matters
A belt running on a flat steel pan has no give. The part hits the belt, the belt hits the steel, and the energy goes into both. A belt running on impact idlers (free-rotating rollers at the loading point) has some give — the idlers absorb the impact. A belt running on a deck with impact bars (thick rubber strips under the belt) absorbs the energy through the rubber’s compression.
| Bed under belt at loading | Impact absorption | Best for |
|---|---|---|
| Flat steel pan | None (rigid) | Light parts, low drop height |
| Steel slider bed | None (still rigid) | Not for impact loading |
| Impact idlers (rollers) | Medium (free rotation) | Medium loads, moderate drop |
| Impact bars (rubber-ceramic) | High (rubber compresses) | Heavy impact, high drop |
| Impact bed (suspended) | Very high (springs + rubber) | Ore, bulk material, large drop |
What we changed
The original belt ran on a flat steel pan. We replaced the pan at the loading point (300 mm section) with impact bars: 10 mm thick rubber strips bonded to a steel backing, spaced every 100 mm. The rubber compresses 5 mm under the part’s impact. The energy is absorbed by the rubber, not the belt. The belt stopped tearing.
We also reduced the drop height. The parts used to drop from 300 mm. We added a chute that guides them down to 100 mm. The impact energy dropped from 2.94 J to 0.98 J. Combined with the impact bars, the belt now lasts its full rated life (5+ years).
The drop height rule
For a 1 kg part, keep the drop under 150 mm. For a 5 kg part, keep it under 50 mm. Use chutes, rollers, or guided paths to reduce the free-fall. The energy scales with height — cutting the drop in half cuts the energy in half.
E = m · g · h
If you can’t reduce the drop (parts come from an upstream machine at a fixed height), use impact bars. They absorb the energy that the belt can’t.
The belt construction
For impact loading, specify a belt with a thick bottom cover (2+ mm) and a polyester or nylon fabric carcass. The bottom cover takes the impact. The fabric carcass resists tearing. A light-duty belt (1 mm cover, cotton carcass) tears easily under impact. A heavy-duty belt (3 mm cover, polyester) handles it.
The impact rule: A belt that tears at the loading point isn’t over-tensioned. It’s absorbing impact energy it shouldn’t. Reduce the drop height with a chute. Add impact bars under the belt at the loading zone. Specify a heavy-duty belt. The belt that tore in two weeks was a light-duty belt on a rigid bed, catching 1 kg parts from 300 mm.
