Conveyor and Material Handling Frames
A conveyor frame is a long, repetitive, relatively light structure where almost nothing is difficult except the one thing that matters: keeping features in line over a distance where a small angular error becomes a large linear one.
It is also usually bought in quantity and shipped in sections, which changes the fabrication economics completely compared with a one off frame.
What this application demands
- Alignment over lengthDrive and idler bores, bearing mounts and rail seats have to line up along a structure several metres long. The error budget is fixed while the distance grows, so the same tolerance is far harder at 6 m than at 600 mm.
- Repeatability across a batchTwenty frames that each differ slightly are twenty installation problems. This is where a proper fixture pays for itself, and it is why you should state the annual quantity even when ordering one.
- Bolt pattern positionFrames bolt to each other and to floor steel. Positional tolerance on hole patterns, with a material condition modifier where it suits, gives the shop the bonus tolerance it needs without loosening what matters.
- Shipping splitsA 20 m conveyor does not travel in one piece. Where it splits, how the splice is aligned on site and whether the splice faces are machined are design decisions, not site decisions.
- Finish that survives the plantFood, washdown, outdoor and abrasive environments each drive a different answer, from painted carbon steel through galvanising to stainless. The environment decides, and it is often the only thing that pushes this part out of mild steel.
What goes wrong
In roughly the order we see it on drawings.
Tolerancing the whole length tightly
Overall length of a welded frame is a fabrication dimension. Putting a machining tolerance on it forces the shop to machine both ends of a long part or quietly ignore the note.
No fixture on a repeat order
The first frame is tacked on the table and comes out fine. The second is built by a different crew and comes out slightly different. Say the quantity up front.
Splice faces left as welded
Two as-welded faces bolted together on site do not sit flat. If the splice has to align, the faces get machined.
Continuous welds everywhere
Long lightly loaded joints are exactly where intermittent welds belong. A quarter of the weld metal and far less distortion, if the loading and the code allow it.
What to put on the drawing
Every line here removes an assumption a shop would otherwise price as risk. Risk is always priced against you.
The full package is on the RFQ checklist, which is printable and remembers your ticks in your own browser.
- Quantity now and expected programme quantity, so the fixture decision is made properly.
- Straightness and twist over the full length, stated as an ISO 13920 form class.
- Positional tolerance on bolt patterns and bearing mounts, referenced to machined datums.
- Where the frame splits for shipping, and whether splice faces are machined.
- Intermittent welds specified wherever the loading permits them.
- Environment and coating system, including washdown or food contact requirements.
Questions on this part type
How straight can a long welded frame be made?
Straightness on a welded structure is normally held to a general fabrication class such as ISO 13920, where the permitted deviation grows with length. Tighter than that means machining a reference surface or straightening after welding, both of which are cost lines. State what the application actually needs.
Should conveyor frames be galvanised or painted?
The environment decides. Indoor dry plant is usually painted. Outdoor or washdown pushes towards galvanising or stainless. If the frame also has machined features, galvanising changes the process order because the part moves in the zinc bath.
Is stainless worth it for food handling?
Where washdown chemistry or contact rules require it, yes, and it brings its own requirements. Stainless moves roughly one and a half times as much as carbon steel for the same weld, closed sections need back purging, and the welds need pickling and passivation or they rust at the joint.
Go deeper
- Why Your Frame Came Out Bowed, and What a Shop Does About ItThe six causes of weld distortion in large weldments and the controls fabricators use: joint design, weld sequence, heat input, fixturing, prebending and balanced welding.
- Fit-Up Decides the Weldment, Not the WeldingWhy fit-up and fixturing set the outcome of a large weldment, what modular and dedicated fixtures cost, and what a buyer should say about tacking and root gaps.
- What Changes When a Welded Frame Is Stainless Instead of Carbon SteelDistortion, sensitisation, back purging, pickling and passivation on 304L and 316L weldments, and what each adds to the cost of a stainless fabricated frame.
- Coating a Weldment Without Ruining the Faces You Just MachinedMasking, coating sequence and the distortion risk of hot dip galvanising on machined weldments, plus what to specify so machined faces arrive usable.
Have a drawing for one of these?
We read it and match it with up to 3 shops that weld, stress relieve and machine parts like it in house. Free for buyers, reply within 24 business hours.