Roller conveyor specification often starts with a catalogue table and ends with a product that tips between rollers. The two calculations below prevent most of those problems, and they take less time than correcting a installed line.
Key takeaways
- Surface speed depends on roller diameter and RPM, not on motor RPM alone.
- Roller pitch should be no more than two-thirds of the shortest product length, and tighter for unstable loads.
- Load per roller is not the same as total load divided by roller count; the product footprint matters.
- Gravity sections and powered sections need different checks.
Surface speed: the only speed that matters
The product moves at the roller surface speed. If the roller diameter is 50 mm and the roller turns at 60 RPM, the surface speed is:
v = π × D × n / 60, where D is in metres and n is RPM. For D = 0.05 m and n = 60, v = 3.14 × 0.05 × 60 / 60 = 0.157 m/s, or about 9.4 m/min.
A gear motor may be rated at 1,400 RPM, but the output shaft speed after the gearbox is what turns the roller. Check the ratio, not the motor nameplate. With a drum motor, the RPM is fixed by the drum and cannot be changed without a VFD or a different drum.
| Roller diameter | Roller RPM | Surface speed | Typical application |
|---|---|---|---|
| 38 mm | 80 | 9.5 m/min | Small cartons, light totes |
| 50 mm | 60 | 9.4 m/min | General carton transport |
| 50 mm | 100 | 15.7 m/min | Higher-rate packing lines |
| 60 mm | 50 | 9.4 m/min | Heavier totes, pallet modules |
| 89 mm | 35 | 9.8 m/min | Pallet conveying, heavy loads |
Roller pitch: stability before strength
The product must always be supported by at least three rollers. With two rollers, the product can rock; with one, it will tip. For a product of length L, the maximum pitch is L/2 in theory. In practice, use two-thirds of L to leave a margin for product overhang, soft packaging and acceleration.
A 300 mm carton therefore needs a pitch of 200 mm or less. A 1,200 mm pallet can use a 400 mm pitch, but pallet conveyors usually use a 75–100 mm pitch for strength and to support the pallet boards evenly. The pitch is set by the weakest load, not the average one.
Load per roller and load per metre
Total load divided by roller count is misleading. A rigid pallet spreads its weight over many rollers; a small carton concentrates it on three. Calculate the load per roller from the product footprint: the number of rollers under the product is the footprint length divided by pitch, rounded up, plus one.
For a 20 kg carton, 400 mm long, on a 150 mm pitch, the roller count under the product is 400/150 + 1 = 3.7, so four rollers. The static load per roller is 5 kg. Apply a dynamic factor of 1.5 for starting and stopping, and the design load is 7.5 kg per roller. That is well within a standard 50 mm roller rated at 60–80 kg, which is why light cartons rarely govern the roller choice; the frame and the drive do.
Gravity or powered?
A gravity roller conveyor needs a slope of about 2–4% for cartons with good rolling resistance, and more for heavy or dirty loads. The product must also have a flat, rigid base. Bags, soft packs and products with uneven bottoms do not convey reliably on gravity rollers.
A powered line is required when the slope is unacceptable, when the product must stop and accumulate, or when the route includes inclines, curves or transfers. Powered roller lines usually run at 8–20 m/min; faster speeds increase noise and wear without improving throughput on a line with stations.
Curves, transfers and gaps
A curve reduces the effective roller pitch on the inside radius. If the curve radius is small, the inner ends of the rollers are closer together than the outer ends, and a long product may jam. Check the product diagonal against the curve width and the roller arrangement. For tight curves, a tapered roller or a transfer ball section is often necessary.
At a transfer or merge, the gap between the end of one conveyor and the start of the next should be no more than one-third of the product length. Larger gaps cause the product to nose-dive, especially if it is front-heavy.
Frequently asked questions
Can I change the speed of an existing roller conveyor?
Yes, within limits. A VFD can reduce the speed of a gear motor drive, but torque falls at low speed. Increasing speed usually requires a different gear ratio or a larger drum motor, and the bearings and rollers must be rated for the higher RPM.
What is the minimum roller diameter for a 50 kg load?
It depends on the roller construction and bearing type, not only the diameter. A 50 mm roller with a 12 mm shaft and sealed ball bearings can carry 60–80 kg per roller in light duty. Confirm the manufacturer's load rating at the actual speed and duty cycle.
Do I need a brake on an incline?
Yes. A brake motor or a mechanical backstop is required on any incline where the load could run away when power is removed. The brake must be rated for the holding torque of a fully loaded conveyor, not the running torque.
Send us the product drawing, weight and required rate through the contact page, and we will return a roller diameter, pitch and drive recommendation with the layout. More detail on drive options is in our powered roller conveyor section.
