The Loading Zone Challenge
Where material falls onto a conveyor belt is the highest-stress point in the system. A 300mm rock falling 2 meters delivers a significant impact force to the belt. The belt support at this point determines whether that impact is absorbed gradually or transmitted as a sharp blow that damages the belt carcass.
There are two main approaches to supporting the belt at loading zones: impact idlers (rollers with rubber rings) and impact cradles (continuous support bars). They work differently and suit different applications.
Impact Idlers (Impact Roller Sets)
Standard troughed idler sets use steel tube rollers. At loading zones, impact idlers replace these with rollers fitted with thick rubber rings along their length. The rubber rings compress under impact and absorb energy, reducing the peak load transmitted to the belt.
How they work: As material lands on the belt, the belt deflects slightly into the rubber rings. The rubber compresses and springs back, absorbing impact energy. The belt is still supported by discrete rollers with gaps between them.
Advantages: - Standard installation β fit into the same frames as normal idlers - Low rolling resistance β belt runs efficiently over rubber-ringed rollers - Easy to replace individual rollers when worn - Good for moderate impact loads - Works well for material that needs to flow/settle after landing
Limitations: - Belt sags between rollers β the gaps allow belt deflection - Under very heavy impact, the belt can bottom out between rollers, causing carcass stress - Not suitable for very high drop heights with large lump material - Rollers can seize if not properly sealed in dusty environments
Impact Cradle (Belt Support Cradle)
An impact cradle replaces rollers entirely with a continuous row of UHMWPE (ultra-high molecular weight polyethylene) or rubber-topped bars that provide continuous support across the full width of the belt at the loading point.
How they work: The belt rests on the continuous surface of the cradle bars. Material impact is distributed across a larger area and absorbed by the bar material and any underlying rubber cushioning layer. There are no gaps in support.
Advantages: - Continuous support β no gaps for belt to deflect into - Better suited to very high impact loading (large lump, high drop height) - Reduces belt carcass stress compared to rollers under extreme impact - Can be designed with rubber cushion layer beneath UHMWPE bars for additional absorption - Helps seal the skirt board system β continuous support makes skirt sealing easier
Limitations: - Higher belt friction β belt slides over UHMWPE surface rather than rolling over rollers - Higher belt tension and drive power required - UHMWPE bars wear over time and need replacement - Not suitable for very long loading zones (friction accumulates) - Higher initial cost than impact idlers
Side-by-Side Comparison
| Property | Impact Idlers | Impact Cradle |
|---|---|---|
| Support type | Discrete rollers with gaps | Continuous surface |
| Impact absorption | Moderate β rubber ring compression | Good β full surface distribution |
| Rolling resistance | Low | Higher β sliding friction |
| Suitable for high drop height (3m+) | Marginal | Yes |
| Suitable for large lump ore (300mm+) | Moderate | Better |
| Wear components | Rubber rings, bearings | UHMWPE bars |
| Replacement difficulty | Easy β standard roller replacement | Moderate β bar sets |
| Drive power impact | Minimal | Moderate increase |
| Belt tension impact | Minimal | Increases locally |
| Cost | Lower | Higher |
How to Choose
Use impact idlers for: - Moderate impact loading β drop heights under 2m, material size under 200mm - Long loading zones where friction from a cradle would be impractical - Applications where drive power is already at capacity - Retrofit situations where changing from standard idlers to cradle would require structural modifications
Use impact cradles for: - High drop heights (2m+) with significant lump material - Primary crusher discharge belts where belt carcass damage is a recurring problem - Loading zones where you're experiencing repeated belt damage at the impact point - New installations where the loading point is designed from scratch
Combination approach: Some installations use a cradle at the point of initial impact and impact idlers for the remainder of the loading zone. This addresses the worst impact point while keeping overall friction manageable.
Frequently Asked Questions
We keep damaging our belt at the crusher discharge. Which should we use? If you're seeing repeated longitudinal cuts or carcass damage at the loading point, impact cradle is likely the more effective solution. Impact idlers reduce impact but still allow localized belt deflection between rollers. A cradle eliminates the gap. Also check your drop height and whether impact bars (liners) are installed in the feed chute above the belt.
How long do UHMWPE cradle bars last? This varies significantly by material abrasiveness and belt speed. In coal applications, 6β18 months is typical. In hard rock mining, 3β6 months. UHMWPE is very abrasion-resistant but it does wear in highly abrasive applications.
Can I retrofit a cradle into an existing conveyor? Usually yes, if the loading zone structure has adequate space. The main consideration is whether existing drive power is sufficient to handle the increased friction. A belt tension calculation should be done before retrofitting a cradle.
Contact Elephant Rubber
We supply both impact roller sets and impact cradle systems. Contact us with your loading zone dimensions, drop height, material size, and current belt damage pattern for a recommendation.