A roller conveyor is the right pick when the unit is rigid-bottomed, flat-based, and the line runs horizontal or on a shallow decline — pick a belt or vibratory alternative when the load is a soft pouch, an open-top bin, or a steep incline is required.
Selection collapses into four spec gates you lock before brand: load per roller (kg/roller), total distributed load (kg/m), roller diameter and axle size, and drive method (gravity, line-shaft, belt-driven, motorized pulley/DR, or chain-driven MDR). Get those four right and the rest is frame finish, sensors, and controls.
Step 1: Classify the Load and Unit Before You Touch a Catalog
Carton, tote, pallet, and drum each impose a different minimum roller specification — a corrugated case on 30 mm rollers is fine for parcel hubs, while a full EUR pallet (1200×800 mm, 600–1000 kg) needs 76–89 mm steel rollers with 6000-series bearings and frame rated for at least 1500 kg/m distributed [S2].
Capture four numbers up front: unit length × width × weight, bottom contact shape (flat, ribbed, runnered, full-edge), and the worst-case dynamic load during accumulation. A 25 kg carton on 50 mm pitched rollers at 75 mm spacing gives three rollers under the footprint; design point is roughly 8–10 kg/roller, not the 25 kg unit weight. Skip this calculation and you oversize the rollers and the price doubles for no operational gain.
Step 2: Roller Diameter, Spacing and Material — the Mechanical Core
Roller diameter is set by the longest unsupported span on the bottom of the unit — rule of thumb used by integrators is roller pitch ≤ 1/3 of the load length for cartons, ≤ 1/2 for full-pallet loads on heavy frames [S1].
Common diameters and where they actually apply:
- 30–40 mm steel or PVC: light parcel, 0–50 kg/m, manual picking stations, gravity lanes for totes.
- 50 mm steel with 6202/6203 bearings: 50–150 kg/m, the workhorse for carton conveyors in 3PL and e-com.
- 60–76 mm heavy-wall steel: 150–400 kg/m, pallet transfer, drum handling, drum/tyre lines.
- 89 mm taper or straight: 400+ kg/m, full-pallet accumulation, AS/RS infeed/outfeed where the tapered roller bearing at the end frame takes the impact load.
Tube material is a cost vs environment decision: galvanized mild steel for general dry goods, zinc-plated for indoor ambient, stainless 304/316 for food/pharma washdown, PVC or HDPE sleeves where the line carries soft-sided or painted parts. Roller length should equal the widest unit plus 50–75 mm clearance per side, not the frame width.
Step 3: Drive Method — Gravity, Line-Shaft, Belt-Driven, MDR
Drive method is chosen from throughput, accumulation behaviour, and noise budget, not from a brand preference — gravity is free to run but demands a 3–5° decline and zero back-pressure; powered options buy throughput and bidirectional control. [S1]
The four powered options line up against four criteria:
- Line-shaft O-ring drive: low-cost, 25–60 m typical runs, easy field service, but loud above 50 m and cannot run at low speed with a heavy unit. Best for 3PL carton lines under 30 cartons/min.
- Belt-driven (flat belt or V-belt under the roller): quiet, handles 50–200 m runs, can accumulate with zero-pressure, but the belt itself becomes a wear part every 18–36 months in 24/7 lines.
- Motorized pulley / drum motor (DR): sealed, hygienic, ideal for food-grade, but limited torque below 1.5 kW and expensive to repair in the field.
- MDR (motorized drive roller) with 24/48 V brushless DC gear motors: each roller is a node on a polymer chain of controls, zero-pressure accumulation is native, and the line reconfigures by PLC logic instead of mechanical change. The roller chain of MDRs in a zone is fed by a single 24 VDC bus; failure of one card stops one zone, not the line.
For accumulation zones, specify zero-pressure or low-pressure (sluggish) accumulation explicitly — they are not the same and a low-pressure zone under variable carton weight will crush lightweight units.
Step 4: Frame, Supports, and the Spacing That Holds the Line
Frame cross-section is selected from the heaviest load and the longest unsupported span between supports — 100×40×3 mm rectangular tube handles most carton lines, 120×60×4 mm or formed channel handles pallet conveyor up to 1500 kg/m, and anything beyond needs an engineered beam calculation, not a catalog guess [S2].
Support centres on gravity lines are typically 1500–2000 mm for 50 mm rollers, 1200 mm for 76–89 mm heavy rollers; powered lines tighten to 1000–1500 mm because the drive reaction adds fatigue cycles. Floor-to-roller-top height for an ergonomic pick station is 700–900 mm; for pallet conveyor feeding an AS/RS, match the crane fork height window to within ±10 mm — see the AS/RS system price and cost guide for the upstream-downstream interface bands that drive that match.
Legs should be height-adjustable (jacking bolt or sleeve on M16 base) — fixed-height frames fail the first time the floor is out of level by 8 mm, and that is a common condition in older brownfield sites.
Step 5: Controls, Sensors and the Options That Move the Real Cost
Photo-eye zoning (retro-reflective or diffuse), zero-pressure accumulation logic, and VFD-controlled speed are the three control layers that change a conveyor from a piece of structure into a working module — and the controls cost is typically 30–45% of the line price, not the 10% most buyers assume [S1].
Specify the I/O count and fieldbus before brand: 24 VDC PNP sensors on a 4–8 zone MDR line is the default; PROFINET, EtherNet/IP, or IO-Link on the MDR cards is now standard on all major lines. If the upstream unit is a belt conveyor selection with its own VFD, hand-off logic should be defined at the sensor level, not the PLC level — otherwise the gap timing drifts and you get carrier jams at the merge.
Useful options to spec explicitly rather than leave to vendor default: brake rollers on declines over 3°, side guides adjustable in 25 mm increments, skirt rails on incline sections, and emergency pull-cords on any run over 6 m that a person can reach into.
Step 6: Sourcing, Standards, and the Levers You Can Pull
Roller conveyor lead time in 2026 runs 4–8 weeks for standard galvanized carton line, 10–14 weeks for heavy pallet conveyor with MDR, and 16–24 weeks for stainless food-grade; price spread between Asia-sourced and EU/US-sourced is typically 30–45% on heavy pallet conveyor, but Asia-sourced frames using non-equivalent steel certifications are a common failure point on inspection. [S2]
Standards to anchor a spec: CEMA (Conveyor Equipment Manufacturers Association) for unit handling conveyors in North America, ISO 5048 / ISO 5049 for the calculation of belt and idler/roller conveyors, EN 619 for continuous handling equipment safety in the EU, and OSHA 1910.219 for guarding and lockout. Bearing life is normally L10 of 20,000–40,000 hours; the roller bearing grade is the single biggest determinant of service interval.
Request three documents with every quote: roller cut-sheet with bearing type and seal, frame steel certificate (grade and country of origin), and a control wiring diagram with zone-by-zone I/O list. Quotes without the third item are the ones that surprise at site acceptance.
When a Roller Conveyor Is the Wrong Choice
A roller conveyor is not the right pick when the unit has a soft, deformable, or convex bottom (open bag, polybag, unstable roll), when the required incline exceeds ~5° without special tapered rollers, when sanitary washdown with chlorinated foam is needed (use stainless belt or tabletop chain instead), or when the line must index precision-stop a heavy pallet without drift — a chain conveyor or crossed roller guide-backed transfer is more accurate. [S3]
For accumulating totes in a tight loop, an overhead power-and-free line (see overhead conveyor price & cost guide 2026) is often cheaper per metre of enclosed track than a floor-mounted MDR loop and frees floor space.
Lock the four spec gates (load per roller, total kg/m, diameter/pitch, drive method), set the frame and sensor list, and only then request firm quotes from two or three vendors with the same RFQ package — quotes on different specs are not comparable, and the cheapest one is rarely the one that runs the longest.