Conveyor System Aluminium Profile Extrusion Frame 45×60 mm for Belt and Roller Lines

A conveyor is a fatigue structure

Every revolution of a roller, every pass of a belt splice and every product transfer puts a load cycle into the frame. A line running 16 hours a day at 30 m/min with a 500 mm roller pitch sees about 57,000 roller rotations per hour, and each one loads and unloads the side rail. Over a year that is tens of millions of cycles. No static frame experiences anything like it.

Aluminium does not have an endurance limit the way steel does — its fatigue strength keeps falling as the cycle count rises rather than flattening out. For 6063-T5 extrusion the practical design stress for a high-cycle application is a small fraction of the yield strength, and the consequence is that the frame has to be sized so the alternating stress is low. In practice that means sizing on deflection, because a frame stiff enough to hold its shape is automatically well below the fatigue stress.

Size the side rail on deflection, not on stress

The side rail has to hold the pulley centres and the roller pitch within tolerance, because belt tracking is controlled by the relationship between the two pulleys. A useful working limit is a deflection of about 1 mm per metre of span, which is span divided by 1000. Working backwards from that limit gives the second moment of area the rail needs, and that number is the design. The table below assumes a combined belt, roller and product load of 0.5 N/mm, which is roughly 50 kg per metre of conveyor.

Two things follow from that table. First, a belt conveyor needs a support leg roughly every 1.5 m — the span, not the section, is what decides whether the rail is stiff enough. Second, the 60 mm dimension has to be vertical. Laid flat the same rail uses only its 21 cm4 figure and the achievable span drops by about a third. Getting the orientation wrong is the single most expensive mistake on a conveyor frame, because it is invisible until the belt starts tracking badly.

The bolt is not the weak link — the slot is

This is the point that decides how a conveyor frame should be jointed, and it is routinely missed. An M8 grade 8.8 bolt has a tensile capacity of the order of 15 kN. But an M8 hammer-head T-slot nut in an 8 mm groove of a 40 series profile pulls out of the slot at around 1.5 to 2.2 kN per nut in a standard section. The bolt is seven times stronger than the slot it is anchored in.

So the capacity of a T-slot joint is set by the slot, and the tightening torque ceiling is correspondingly low — about 15 N m for an M8 nut in a 40 or 45 series slot, and about 30 N m for an M10 nut in a 50 series slot. Over-torquing does not make the joint stronger; it deforms the slot lip and makes it weaker.

The practical rule for a conveyor frame is therefore: wherever a member is loaded in tension — a leg hanging under a rail, a pulley mount, a drive reaction — do not rely on the slot alone. Use an end-face connection into the profile’s core bore, a joining plate, or an anchor connector, all of which transfer the load into the section rather than into the slot lip. Keep the slot connections for members in shear and for brackets, and use more of them than the load strictly needs. The joining plates and anchor connectors ranges cover both cases.

Keeping a bolted frame tight on a running line

1. Torque to the slot ceiling, not to the bolt rating An M8 bolt can take far more torque than the slot can. Use the nut’s ceiling — about 15 N m for M8 in a 40 or 45 series slot — and use a torque wrench rather than feel.
2. Use the largest washer face the slot allows A formed flange or a hardened washer spreads the clamping load over more of the slot lip, which is what the joint is actually limited by.
3. Use anti-torsion nuts where the load is one-sided A nut that can rotate in the slot will rotate under vibration. A serrated or ribbed nut body locks against the slot wall and holds its position.
4. Re-torque after the first 100 hours, then again at 500 Most preload loss happens in the first weeks of running. A scheduled re-torque catches it before it becomes a tracking problem.
5. Check the frame for squareness, not just for tightness A conveyor frame can be perfectly tight and still be out of square. Measure the diagonals of each bay at commissioning and record them so you have a baseline to compare against.

Frequently asked questions