Drive belts: choice and service
V-belt or flat belt for a conveyor drive: selection criteria, correct tension, service life and maintenance practice.
A drive belt transmits rotary motion from the motor to a conveyor working unit. It is an inexpensive part, but it often decides whether the line stops mid-shift. This article breaks down how to choose between a V-belt and a flat belt, how to tension the drive correctly and what gives a real service life.
Why a drive needs a belt
A belt drive has several advantages over a direct motor-to-unit connection. It smooths jerks and damps torsional vibration, protects the motor when a unit jams by slipping, lets the motor and the actuator be spaced apart, and makes it easy to change the gear ratio by selecting pulleys. On food conveyors a belt drive also eases washing: the motor is moved out of the wet zone, which extends its life and simplifies the protection class.
The belt in a drive also acts as a “fuse”: on overload it slips before the costlier gearbox is destroyed. It is a deliberate weak link, cheap and quick to replace.
V-belt or flat belt
The two main drive belt types solve different tasks. A V-belt runs in the wedge groove of a pulley, transmits a high torque on a compact drive through the wedging effect in the groove and holds load well. A flat belt runs on smooth pulleys, gives higher efficiency and lower noise, and suits high speeds better.
V-belts are standardised by cross-section: classic profiles Z, A, B, C, D and narrow SPZ, SPA, SPB, SPC. For the same dimensions, narrow profiles transmit 1.5–2 times more torque, so on new conveyor drives we usually choose them. The angular profile of a V-belt is standardised at 40°, and the pulley groove must match it exactly, otherwise the belt sits on the groove bottom and slips.
| Parameter | V-belt | Flat belt |
|---|---|---|
| Transmitted torque | high | medium |
| Drive efficiency | 92–95% | 96–98% |
| Noise level | moderate | low |
| Speed | up to 30 m/s | up to 60 m/s |
| Minimum pulley diameter | from 63 mm (SPZ) | small diameters allowed |
| Operating temperature range | −30…+80 °C | −20…+70 °C |
| Sensitivity to pulley misalignment | high | very high |
| Typical application | conveyor drives, reducers | fans, high-speed units |
For most conveyor drives we choose a V-belt: it forgives slight misalignment and transmits the required torque on a compact drive.
Correct belt tension
Tension is the key operating parameter. A slack belt slips, heats up, wears fast and loses torque: slipping of just 1–2% already noticeably heats the belt and shortens its life. An over-tensioned belt overloads the bearings of the motor and the unit, shortening their life many times over. Correct tension is checked by deflection: when the middle of the free span is pressed with a force about equal to its weight, the belt should deflect by about 16 mm per metre of centre distance.
On multi-belt drives, tension is conveniently checked with a frequency meter: the natural vibration frequency of the free span is measured after a light tap, and it should fall within the range the belt maker specifies for the given cross-section and length. This is more accurate than “by feel” and gives a repeatable result from one mechanic to another.
Engineer’s tip. The biggest belt wear comes not from load but from pulley misalignment. Before adjusting tension, always check alignment: lay a straightedge against the faces of both pulleys — they should lie in one plane. A misalignment of a couple of millimetres shortens belt life by a factor of 2–3.
Common causes of premature wear
In practice a drive belt fails before its term due to several recurring causes:
- skew or misalignment of pulleys;
- incorrect tension — slack or excessive;
- oil or cleaning agents reaching the belt;
- worn pulleys with a stripped groove profile;
- drive overload above the design torque.
Eliminating these causes extends belt life many times over at no extra cost.
Servicing the belt drive
We include the belt drive in the scheduled maintenance routine. Once a month — a visual inspection for cracks, delamination and a glazed surface, plus a tension check. Once a quarter — a check of pulley alignment and groove profile condition. A new belt stretches slightly in the first hours of operation, so 24–48 hours after replacement the tension is checked again.
Belts in a multi-belt drive must be replaced as a set: a new belt next to a worn one takes a disproportionate share of the load and fails quickly.
Diagnostics by external signs
A belt’s condition can be assessed visually without dismantling the drive. Cracks on the inner surface across the belt are a sign of thermal ageing and over-tensioning. Glazed shiny side faces are a trace of prolonged slipping in the groove. Delamination and fraying along the edge are a consequence of misalignment or a worn pulley groove. A cut, “rounded-off” bottom corner of the belt means the pulley groove is worn and the belt sits on the bottom.
Separately, we inspect the pulleys themselves: a worn groove with sharp edges cuts a new belt within weeks. If the groove profile is worn, replacing one belt will not help — the pulley must be changed.
Service life
With correct tension, aligned pulleys and a clean drive, a V-belt runs 12–24 months of continuous operation. Saving on belt quality is dubious: the price difference is small, while line downtime from a snapped belt costs incomparably more. So we always keep a spare belt set in the customer’s stock. In a multi-belt drive, belts should be taken from one batch and as a set matched by actual length — this evens out the load distribution. For more on servicing units, see the articles tagged maintenance.
Conclusion
A drive belt is an inexpensive but critical conveyor part. The right type choice, accurate tension and aligned pulleys give a reliable drive and a service life of 1–2 years. Need advice on your conveyor drive or scheduled maintenance? Get in touch — we’ll select the belt drive and set up the drive.
