How to Select Gravity Rollers for a Roller Conveyor
What Decides Gravity Roller Strength
Gravity roller strength depends on the product's bottom material and the impact force during loading. A hard, rigid bottom spreads weight over fewer rollers, while a flexible bottom like a sack or carton deforms and contacts more rollers. Impact from forklifts, hoists, or manual drop loading increases the effective load beyond static weight.
Load per Roller for a Hard Bottomed Product
When the product bottom is hard and does not deform, such as steel or rigid plastic, only two rollers are in real contact at any time. The load per roller is the product weight divided by two. Sizing based on average load across the lane will underestimate required roller strength.
Load per Roller for a Flexible Bottomed Product
When the product bottom is flexible, it sags between rollers and contacts multiple rollers. The load per roller is the product weight divided by the number of rollers in contact minus one. Use the actual number of rollers under the product, not the total in the lane.
Applying the Impact Coefficient
Multiply the calculated load per roller by a coefficient N based on how the product is loaded. Use N = 1 for no impact, 1.5 for slow hand loading, 1.5 to 2 for forklift loading, 2 to 3 for hoist or crane loading, and 3 for loading from a person's shoulder.
Impact Spread Over Several Rollers or Only One
If impact is distributed over four or more rollers, the impact load on one roller is the load per roller times N. If impact lands on a single roller, the load on that roller is the full product weight times N. This single roller case is critical for end cap strength and must be checked when products are dropped onto a defined point.
Double Track Conveyors
A double track roller conveyor increases the number of supporting rollers, allowing it to carry 1.5 to 1.8 times the normal weight. This configuration is typically used when conveying products on pallets.
The Final Check
The roller's strength must be greater than or equal to the maximum load per roller multiplied by the impact coefficient N. Once this value is known, specify the roller by tube outside diameter, tube wall thickness, shaft diameter, and matching end cap or bearing.
Questions on This Topic
How many rollers should be under the product at all times?
Enough to support the load based on the product's bottom material and contact pattern. For flexible bottoms, count only the rollers actually in contact with the product.
What coefficient should I use for forklift loading?
Use 1.5 to 2 for loading by forklift. Use 2 to 3 when a hoist or crane places the load.
Does a double track conveyor really carry more?
Yes, a double track roller conveyor can carry 1.5 to 1.8 times the normal weight due to increased supporting rollers, typically used with palletized products.
What do I need to know before ordering replacement rollers?
You need the tube outside diameter, tube wall thickness, shaft diameter, and the calculated load per roller including the impact coefficient N.
Do plastic end caps carry as much as metal ones?
Metal end cap housings are used for higher calculated loads or impact, while plastic housings are used for lower loads and quieter operation.
Apply This to Your Own Line
Send your dimensions and load figures and the matching catalogue models come back with a price.