Most conveyor specifications assume a carton: flat-based, rigid, stable, roughly rectangular. Plenty of product is not like that, and the moment it is not, the conveyor stops being a catalogue decision.
This page covers the product shapes that cause trouble on a conveyor, what makes each one difficult, and the techniques used to handle them. If your product rolls, topples, sags or nests, this is the territory you are in.
Why shape decides the conveyor
A conveyor moves product by friction between the product and the carrying surface, and it keeps the product where it is by relying on the product staying put. Both assumptions break down as soon as the base is small relative to the height, curved rather than flat, or soft rather than rigid.
What follows is not usually a different conveyor. It is the same conveyor with something added that constrains the product — a guide, a hold-down, a shaped chain, or a carrier the product travels in rather than on.
The shapes that cause trouble
Round and cylindrical
Bottles, cans, tins, jars and tubes all share the same problem: a curved surface that wants to roll, and often a small contact patch. Standing upright they are stable enough on a flat chain until the conveyor accelerates, decelerates or turns. Lying down they roll off unless something stops them.
Cylindrical product is also awkward to accumulate, because items in contact transmit force to each other and a queue can push itself out of line.
Tall and narrow
Anything with a high centre of gravity relative to its base will topple before it slides. The critical moments are starting, stopping and any change of direction, which is why tall product is often the constraint on how fast a line can index or how tight a bend can be.
Stacks and nested items
Stacked tins, nested trays and lidded containers behave as one item only while the stack holds. Any acceleration that shifts the top of a stack relative to the bottom starts to separate it. Stacks generally need supporting on more than one face, not just carried from below.
Soft or flexible bases
Sacks, pouches, bags and part-filled containers sag between anything they are not fully supported by. On rollers they drop into the gaps; on chain they can deform enough to catch. These usually need a continuous flat surface or a carrier.
Very small or very light
Small items fall between rollers and are blown around by air movement. Light items lack the weight to generate reliable friction, so they slip rather than travel with the surface. Both tend to end up in a carrier rather than being conveyed directly.
How awkward product gets handled
Guides and side rails
The first and simplest answer. Rails either side of the chain keep product on line through bends and stop it wandering under acceleration. Adjustable guides matter where a line runs more than one product size, because a rail set for the widest item does nothing for the narrowest.
Hold-downs and brushes
Where product needs pressing against the carrying surface rather than merely resting on it, a brush or a sprung hold-down does the job. Brushes suit items that must not be marked, and they accommodate variation in product height in a way a rigid hold-down cannot. This is a common approach for conveying tins and similar items on an incline or vertically, where friction alone will not hold them.
Shaped and profiled chains
Instead of a flat carrying surface, the chain itself can be profiled to cradle the product. A v-shaped chain holds cylindrical items or stacks between two angled faces, which stops rolling and keeps a stack aligned without needing guides tight to the product.
Side-grip
For products that cannot rest on anything at the required angle, two chains grip the item from either side and carry it between them. This is what makes vertical conveying possible for items that would otherwise fall — vertical slat conveyors use side-grip and friction chain configurations for exactly this reason.
Pucks, trays and carriers
Where the product genuinely cannot be conveyed, the answer is to convey something else. The item travels in a puck, tray or carrier that presents a flat rigid base to the conveyor, and the line handles the carrier. It adds the cost of the carriers and the need to return them, and it solves problems nothing else will.
This is standard practice for unstable, small or soft product, and it also gives downstream automation a consistent shape to work with regardless of what is inside.
Where it usually goes wrong
- Specifying for the nominal product. Lines rarely run one item. The awkward variant is the one that decides the design, not the average one.
- Underestimating acceleration. Product that is stable at constant speed can topple at a start or stop. Indexing magnifies this, because every cycle is an acceleration and a stop.
- Ignoring accumulation forces. Product standing in a queue pushes on the item in front. Round and stacked items are particularly prone to riding up or twisting under that load — see accumulation.
- Fixed guides on a variable line. Guides set for one product size become an obstruction for another.
- Leaving it to commissioning. Handling problems discovered when the line is being commissioned are the most expensive kind, because everything else is already built around them.
Common questions
How do you convey round products without them rolling?
Upright on a flat chain with side guides for most bottles and cans. Where they have to lie down, travel on an incline, or move vertically, a profiled or v-shaped chain cradles them, and a brush or hold-down presses them against the carrying surface.
What can be done with tall, unstable products?
Reduce what acts on them or hold them. Gentler acceleration, wider bends and slower indexing all reduce the force; guides, side-grip or a carrier hold the product. Which applies depends on how fast the line has to run.
Can bags and pouches be conveyed?
On a continuous flat surface, yes. On rollers, generally not — a soft base sags into the gaps. Where a line has to handle both bags and rigid items, a carrier is usually the answer.
Are pucks and carriers worth the cost?
They add carrier cost and a return loop, so they are not a first choice. They become the right answer when the product cannot be handled directly, or when giving downstream equipment one consistent shape is worth more than the carriers cost.
How do I know a design will work before building it?
Test the uncertain part. Where handling a particular product is the risk in a project, that is precisely what proof of concept development is for — proving the method on the actual product before the rest of the system is committed to.
Does this affect which conveyor type I need?
Often, yes. Rigid carrying surfaces with profiled chain suit awkward shapes better than a plain belt, which is one of the reasons slat systems are common on bottling and packaging lines.
If your product is the difficult part
Handling method is decided during conveyor system design, and where nobody is confident it will work, we prove it before building it.
We are based in Finglas, Dublin 11 and work with manufacturers across Ireland. Tell us what the product is — shape, weight, how stable it is — and we will tell you how it needs handling.
