Feed presentation is the condition material is in when it reaches a sensor-based sorter: how fast it is arriving, how deep it is piled, how far across the belt it is spread, and whether individual pieces are separated from each other. Published throughput numbers for optical sorters assume good feed presentation. If your plant does not deliver it, you are not running the machine you bought — and the fix is upstream, on the conveyor.
The Sorter Is Probably Not Your Bottleneck
When a sort line underperforms, the reflex is to spec a better sorter. The optical and AI sorting on the market now is genuinely good. That is not the argument. The argument is what those throughput numbers assume: material arriving singulated, evenly metered, spread at a steady depth across the belt.
What often arrives instead is slugs. A surge from the feeder, a bare patch, another surge. The machine sees a pile and guesses.
You bought recovery rate. You are running feed presentation.
Before you spec the next machine, go stand at the belt feeding the one you already own and watch it for ten minutes. If the material comes in waves, the sorter is not your ceiling. The conveyor in front of it is.
What a Sorter's Throughput Rating Assumes
A sensor-based sorter classifies material piece by piece. Near-infrared units light the stream and read which wavelengths each material reflects back; camera and AI systems read color, shape, and texture. Either way the machine maps what is on the belt, then fires a bank of precisely timed air jets at the discharge to knock the targets off their trajectory.
Three things have to be true for that to work:
- The sensor has to see each item. Overlapping or stacked pieces hide each other, and what the sensor cannot see it cannot classify.
- The controller has to know where each item will be a fraction of a second later. That is a prediction based on belt speed. If the item tumbles, or a pile shifts on the way to the discharge, the prediction is wrong and the jet fires at empty air.
- The jet has to move that item alone. Every valve that fires into a clump takes the neighbors with it.
Industry guidance on preparing material for sensor-based sorting is blunt about the requirement: the goal is to get material down to a single layer so the separation device has a chance to succeed. That single-layer condition is what the rated throughput was measured under. Feed the same machine a pile and the sensor sees a pile.
Feed Presentation, Broken Into Parts
Feed presentation sounds vague until you split it into variables you can actually change. Each one is set by a machine upstream of the sorter.
| Feed variable | What good looks like | What controls it |
|---|---|---|
| Feed rate | Steady tons per hour, no waves, no dry spots | Storage bin, feeder, and a metered feed conveyor with variable speed |
| Burden depth | Thin, approaching a single layer | Belt width and belt speed for the tonnage being run |
| Lateral spread | Material across the full belt width, not roped down the center | Chute and hood geometry, feeder pan width, spreaders |
| Singulation | Pieces separated from each other, not touching or stacked | A speed step up from the feed belt to the acceleration belt |
| Stability at speed | Items riding flat, not floating, tumbling, or drifting sideways | Belt speed limits, drop height, a wind tunnel over the acceleration belt |
| Size range | Oversize and fines already removed | Screens ahead of the sorter |
Feed Rate: Surge Control Belongs at the Bin
A bucket loader dumping onto a floor hopper is a surge machine. Nothing downstream can average that out by itself, which is why plants that run well put a storage-and-metering step between the loader and the line. A live floor bin absorbs the dump and discharges at a controlled rate instead of all at once. A vibratory feeder under the bin evens the flow out further, walking material forward in short strokes at a rate set by the drive.
From there the infeed conveyor sets the pace for the whole line. Remcon builds these with variable speed drive as an option, plus an automated feed control that monitors how much material is on the belt and varies belt speed from a low of 20 percent of normal up to 200 percent of normal to flatten out surges and dry spots. The same logic applies to the sort line feed conveyor ahead of a manual pick station: a steady belt is what makes the labor worth paying for.
Burden Depth: Width and Speed, Not Wishes
Burden depth is the thickness of the material layer riding on the belt. For a given tonnage, burden depth, belt width, and belt speed move together — the same tons per hour spread over a wider belt, or over a faster belt, ride thinner. There is no way to hold tonnage constant, leave width and speed alone, and get a thinner layer.
That arithmetic is why a sorter dropped onto an existing narrow feed belt so often disappoints. The machine is rated for a near-single-layer presentation, and that belt cannot produce one at the tonnage you want to run. The same limit applies to the people on a quality control line: nothing buried gets identified, whether the thing looking at it is a camera or a person.
Incline matters here too. A steep feed section meters better than a shallow one, because gravity works against the pile and doles it out. That is the reasoning behind a dual-angle incline, which starts steep to help with metering and then flattens to prevent rollback. Our guide to maximum conveyor incline angle covers where those limits sit.
Lateral Spread: Use the Whole Belt
A wide belt with a rope of material down the middle is a narrow belt you paid extra for. Material lands where the chute puts it, so chute and hood geometry are part of the sorter spec whether or not anyone quoted them that way. A vibratory feeder or a disc spreader dropping material across the full width of the acceleration conveyor is the standard fix, and it is a smaller project than reworking the sorter itself.
The Speed-Ratio Principle
Here is the mechanism behind an acceleration belt. Put two conveyors in series and run the second one faster than the first. As each item transfers, it accelerates away from the item behind it. The center-to-center spacing between pieces grows in proportion to the ratio of the two belt speeds — run the second belt twice as fast and the spacing roughly doubles.
That is the whole trick. The acceleration conveyor does not sort anything. It takes a dense, slow, touching stream and stretches it into a fast, thin, gapped one, because gaps are what the sensor and the valve bank need.
There is a ceiling on how fast you can run a bare belt. Trade guidance on preparing material for sensor-based sorting puts the limit around 550 to 600 feet per minute, the speed at which light sheet paper and film start to fly up and drift. The answer is a wind tunnel over the acceleration conveyor, moving air along the belt at the same speed as the belt so light items stay down. With one fitted, that same guidance puts acceleration conveyor speeds at 800 to 1,000 feet per minute.
Why Slugs Cost You Twice
A surge does not just cause misses. It causes wrong ejections. Buried target material rides through into the residue, and the jets that do fire into a clump throw good material out with the bad. Both errors land in the same place: a recirculation load, or a downgraded bale, or both.
Then it moves downstream. Whatever the optical misses shows up at the quality control sorting conveyor, where people catch it by hand at whatever speed the surge dictated. A sort line paced by slugs alternates between overwhelmed and idle, which is the worst way to buy labor.
Mechanical separators suffer the same way. A disc screen fed in surges loses its cut, because a slug buries the discs and everything rides over the top, unders included. Screening is presentation work too, and a machine fed badly makes the next machine's feed worse.
Ten Minutes at the Belt
Before anyone writes a capital request, go watch the feed conveyor with a stopwatch. You are looking for six things:
- Waves. Time the peaks. A rhythm rather than a stream means the metering upstream is the problem.
- Bare belt. Dry spots between surges are throughput you already paid for and did not use.
- Depth. Can you see belt between pieces, or is it two and three items deep in the heavy patches?
- Edges. Is the outer six inches of a wide belt carrying anything at all?
- Tumbling. Items that roll or flip on the way to the discharge break the position prediction.
- The residue. Sample the reject stream. Good material coming out in clusters rather than singles means the jets are firing into clumps.
If the answers point upstream, a new sorter buys you nothing except a faster way to guess.
Fixing It Is a Conveyor Problem
Feed presentation is built out of ordinary equipment specified deliberately: the right belt width for the tonnage, the right speed, a drive that holds a set rate under load, chute geometry that lands material across the full width, and enough metering upstream that the belt sees a stream instead of a dump.
Remcon has built heavy-duty recycling equipment since 1977 and builds every conveyor to order — belt widths from 12 to 72 inches, with variable frequency drive optional and automated feed control available on infeed conveyors. We also select and integrate equipment we do not build, such as disc screens, vibratory screens, and vibratory feeders, plus the support structures, transition chutes, and platforms that connect them. Everything is quoted per job, because the right width and speed depend on your tonnage and your building, not a catalog page.
If you are already out for quotes on a sorter, ask the vendor what feed presentation their throughput number assumes, then ask whether your existing conveyor can produce it. Our guide to buying a conveyor covers the rest of the questions worth asking.
Optical Sorter Feed Presentation FAQ
Why is my optical sorter underperforming its rated throughput?
Most often because of how material is presented to it, not because of the machine. Sensor-based sorters are rated assuming material arrives at a steady rate, spread across the belt in close to a single layer, with pieces separated from each other. If material arrives in surges and piles, the sensor cannot see buried items and the air jets fire into clumps. The fix is on the conveyor and metering equipment upstream.
What is singulation in recycling, and why does it matter?
Singulation means separating a dense mass flow of material into individual pieces with gaps between them, rather than a touching or stacked stream. It matters because an optical sorter classifies material piece by piece and aims its air jets at individual targets. Without gaps, the sensor sees overlapping items and each burst of air moves whatever is nearby, so good material leaves with the reject and target material rides through.
What is burden depth on a conveyor?
Burden depth is the thickness of the material layer riding on the belt. For a given tonnage, it is set by belt width and belt speed: the same tons per hour spread across a wider belt, or carried on a faster belt, ride thinner. Sensor-based sorters and screens both work better at low burden depth, which is why feed belts ahead of them are often wider and faster than the conveyors that feed them.
How does an acceleration conveyor spread material out?
By running faster than the belt that feeds it. When an item transfers from a slower belt to a faster one, it accelerates away from the item behind it, so the spacing between pieces grows in proportion to the ratio of the two belt speeds. Placing conveyors in series at different speeds is the standard way to turn a dense stream into a thin, gapped one ahead of a sorter.
How fast does the conveyor feeding an optical sorter run?
Faster than most plant conveyors. Trade guidance on preparing material for sensor-based sorting puts the bare-belt limit around 550 to 600 feet per minute, the speed at which light sheet paper and film start to fly up and drift. A wind tunnel over the acceleration conveyor, blowing air along the belt at belt speed, holds those items down and lets the belt run at 800 to 1,000 feet per minute.
Should I upgrade the sorter or fix the feed conveyor first?
Watch the existing feed belt before deciding. If material arrives in waves, with bare patches between surges and pieces piled two or three deep, the sorter is not the limiting factor and a new one will inherit the same problem. Metering equipment, belt width, belt speed, and chute geometry set the ceiling the sorter works under, and changing them is normally a smaller project than replacing the sorter.