The Belt That Tore at the Loading Point
We loaded boxes onto a belt conveyor from a chute. The boxes dropped 300 mm onto the belt. After a week, the belt tore at the loading point — the box’s corner hit the belt edge-on. The problem: no impact bed. The boxes dropped onto the belt (which was supported by thin rollers). The impact bent the belt (and the rollers). The box’s corner cut the belt. We added an impact bed (a slider bed of UHMW strips, article 116, with rubber cushions) under the loading point. The box landed on the bed (solid, cushioned). The belt didn’t bend. No more tears. The mistake was dropping heavy boxes onto a roller conveyor without an impact bed.
Conveyor impact bed cushions the loading point. This article covers the design.
Where the Impact Happens
The belt conveyor’s loading point (where the product drops onto the belt) takes the impact. A box (or a part) falls onto the belt. The belt is supported by rollers (spaced every 300–500 mm). Between the rollers, the belt sags. The impact bends the belt (and the rollers). For heavy or fast-dropping product, the belt tears (or the rollers break).
The Impact Bed
An impact bed (also called a impact cradle) replaces the rollers under the loading point with a solid (cushioned) surface. It’s a frame with UHMW strips (article 116) on top (the belt slides on them) and rubber cushions underneath (absorbs the impact). The product lands on a solid bed (no sag), and the cushions absorb the energy.
Step 1: When to Use an Impact Bed
Use an impact bed when:
- The product drops onto the belt: Over 100 mm drop height.
- The product is heavy: Over 5 kg (or a dense part).
- The product has sharp edges: A corner that can cut the belt.
For light boxes (0.5 kg, dropped from 50 mm), the standard rollers are fine. For heavy parts (10 kg, dropped from 300 mm), use an impact bed.
The impact bed rule: At the loading point (where product drops on), replace the rollers with an impact bed (UHMW strips on rubber cushions). The belt that tore had boxes dropping on rollers. The impact bed absorbs the drop. For a 10 kg box dropping 300 mm, the impact energy is high — rollers can’t take it.
Step 2: Bed Length
The impact bed covers the loading zone (where the product lands and settles). A standard bed is 600–1000 mm long (covers the first few rollers). The product lands, settles, then runs on the regular rollers (after the bed).
Step 3: UHMW Slider Surface (Article 116)
The bed’s top is UHMW strips (article 116) — low friction, wear-resistant. The belt slides on the UHMW (not on metal). For a long belt, the UHMW wears (replace when thin). For a low-throughput conveyor, the UHMW lasts years.
Step 4: Impact Energy
The impact energy (to size the bed’s cushions) is:
E = m × g × h
Where m is the product mass (kg), g is 9.81, and h is the drop height (m). For m = 10 kg, h = 0.3 m: E = 10 × 9.81 × 0.3 = 29.4 J. That’s the energy the bed (and belt) absorbs. The bed’s rubber cushions are rated for impact energy (pick a bed rated for the energy). For higher energy (a 50 kg casting dropping 0.5 m = 245 J), use a heavy-duty impact bed (with thick rubber).
Step 5: Skirt Board
At the loading point, add a skirt board (a rubber curtain on each side). It contains the product (stops it from bouncing off the belt). The skirt is soft (rubber) so it doesn’t cut the belt. For a dusty product, the skirt also contains the dust.
| Loading Condition | Support |
|---|---|
| Light (0.5 kg, 50 mm drop) | Standard rollers |
| Medium (5 kg, 100 mm drop) | Closely spaced rollers |
| Heavy (10 kg, 300 mm drop) | Impact bed (UHMW + rubber) |
| Very heavy (50 kg, 500 mm) | Heavy-duty impact bed (thick rubber) |
An Impact Bed Checklist
- How heavy is the product? (kg?)
- What is the drop height? (mm?)
- Calculate E = m × g × h?
- Is it over 10 J? (Use an impact bed?)
- Is the bed 600–1000 mm long? (Loading zone?)
- Is the top UHMW strips? (Low friction?)
- Are the rubber cushions rated for the energy?
- Is there a skirt board? (Contains the product?)
- Does the belt run smoothly on the bed? (No rubbing?)
- Is the UHMW wear checked? (Replace when thin?)
The Bottom Line
Conveyor impact bed cushions heavy loading. The belt that tore had 10 kg boxes dropping on rollers. Calculate E = m·g·h. For heavy/dropping product, replace the rollers with an impact bed (UHMW strips on rubber cushions). Add a skirt board. The belt that lasted wasn’t the strongest one — it had an impact bed at the loading point.
