Crusher discharge conveyors are ordinary belt conveyors everywhere except one stretch. Past the load zone they carry rock the way any troughed belt does. Inside it they take the crusher's full drop energy, in one place, every few seconds of the shift. That is where the belt gets cut, the frames bend, the bearings die, and the spillage pile forms. Three things decide whether it holds up: what supports the belt where the rock lands, how far the skirtboard runs before the load settles, and how much drop energy the chute takes out first.
Load Zone Design: Impact Idlers, Beds, and Cradles
Three families of support get used under a drop point. They are not interchangeable, and a load zone that keeps failing is usually one of them doing the next one's work. The duty ranges below are the component makers' own guidance.
| Support | Typical duty | What it costs you |
|---|---|---|
| Impact idlers: rubber cushion-disc rolls, set closer than the carrying idlers | 3 to 4 inch minus material dropping 6 to 8 feet | Support at discrete points, so the belt still rises and falls under the seal |
| Impact beds: rubber-cored bars with a UHMW face, nothing rotating | 5 to 6 inch material dropping 8 to 10 feet | Sliding drag, so the drive needs headroom; bars sit under the skirt and are slow to change |
| Impact cradles: heavier support on replaceable wear pads | Loads past what a bed is sized for | More up front, bought back in faster pad changes |
Most load zones use more than one: continuous support directly under the drop, closely spaced idlers after it.
Idler Spacing Under the Skirting
Belt sag between supports goes with the square of the spacing: halve the spacing and sag falls to about a quarter. Common practice under a skirtboard is a foot directly beneath the drop and two feet through the rest of it. CEMA's design sag limits of 3, 2, and 1.5 percent are set by trough angle and by how much of the load is full-size lumps rather than fines, and sag depends on tension and spacing together, so a tighter limit means more tension, closer sets, or both.
The reason is the seal, not the belt. Widely spaced sets give the belt a bumpy path, so the gap between skirt rubber and belt opens and closes as each set passes. Fines blow out as it opens; material works in as it closes and cuts a groove down the cover.
Skirtboard Sizing, and Why the Stock One Is Short
Skirtboard length is set by belt speed, not by the size of the chute opening: the skirt has to run past the point where the load has settled. The rule of thumb is two feet of skirtboard per 100 feet per minute of belt speed, three feet per 100 fpm where enclosure airflow is heavy, plus about 25 percent to let dust settle. At 400 feet per minute that is eight to twelve feet before the margin, and a load zone built to the size of the chute is a fraction of it, which is why the spillage pile sits just past the end of the skirt.
Width has its own rules. CEMA recommends about two thirds of belt width, or half for free-flowing material, a ratio that runs tight on narrow belts and generous on wide ones. What does not scale is the free belt edge outside the skirt: at least 115 mm, about four and a half inches, each side regardless of belt width. That edge is what the seal clamps to.
The Chute Does Half the Work
Free-fall distance sets the impact system, not the height of the crusher. Every foot of fall the chute takes out is energy that never arrives. Ledges or steps break one long drop into short ones. A rock box lets material build a shelf of itself, so falling rock lands on rock instead of plate. And the discharge should turn the stream into the direction of belt travel at near belt speed: material fed across the belt or against it scours the top cover and shoves the load off center.
Material does not always leave a crusher under gravity alone: a jaw fractures rock at the discharge, so fragments arrive with energy of their own. Size to the real lumps, not the crusher's rated product. Liner grade matters too: AR400 runs roughly 360 to 440 Brinell and balances toughness against wear, AR500 is harder and less forgiving. Which grade goes where is in stainless vs abrasion-resistant steel. Where a surge hopper sits between the crusher and the belt instead of a straight chute, that is on the bins, bunkers, and hoppers page.
Do not load on the transition
Between the tail pulley and the first full troughing set the belt is still changing shape. Loading there is a standing entry on lists of conveyor design mistakes: the belt is not in its final profile, the edges are not where a skirt seal expects them, and it cannot be sealed. Put the drop downstream of the transition: the rule of thumb is a transition of about two and a half to three times the belt width, with loading starting after the first full trough idler. That is a layout call, made before the chute and the support steel are drawn.
One Shop for the Chute and the Conveyor
Drop energy is decided upstream of the belt. Whoever draws the chute controls how much of it survives; whoever specs the impact system pays for whatever does. Split those between two vendors and neither can trade against the other: the chute gets drawn for flow, and the conveyor gets impact protection sized for the worst case somebody described in an email. Take the fall out in the chute and the support underneath can often be lighter: less drag and fewer wear parts.
Remcon designs, fabricates, and installs the conveyor and the chute work that feeds it, and integrates third-party equipment where the line calls for it. Nothing is catalog stock: trough angle, idler class, and spacing are sized to the application and quoted per job. Belt widths run 12 to 72 inches across the line, a long conveyor ships in bolted sections rather than one piece, and the troughing idler conveyor page has the full spec table. Remcon has used Dodge Torque Arm II shaft-mounted reducers since 1990; these reducers have been used almost exclusively in the sand, rock, gravel, and mining industries for many years, and are well proven. Everything ships and installs nationwide from Airway Heights, WA, with Remcon's own crews. Where the whole run is the job rather than one machine, see turn-key conveyor systems.
What Remcon Has Built for Rock
One machine, and better you read it here than work it out later. Remcon has fabricated a heavy-duty troughing idler conveyor for a silver mine. The photographs on the troughing idler conveyor page show it loaded for transport in our yard. That is the record, and we are not going to inflate it. A wall of aggregate references is not something we have.
What we do have is the shop. Remcon comes at this work from the recycling industry, equipment that handles materials that are rough on machines, such as whole and broken glass and tin and aluminum cans, and we have built machinery for mining, construction, and manufacturing alongside our recycling and solid waste lines since 1977. Broken glass is abrasive and it cuts. Rock is abrasive, it cuts, and it arrives in lumps from a height. The overlap is real and it is not total. What carries over without an asterisk is the drawing: the chute, the skirtboard, and the support under the drop get sized the same way whatever lands on the belt, and the people who draw them are the people who weld them and bolt them down on your site. The rest of the aggregate line is on the quarry and aggregate conveyors page.
What We Need to Quote It
A load zone gets quoted off the drop, not off a model number. Six things:
- The crusher: what type it is, and what it is fed.
- The largest lump that actually comes out of it, rather than the rated product size.
- The free-fall distance from the crusher discharge to the belt, and what sits in between.
- Belt width and belt speed, if there is already a conveyor under there.
- Whether this is a new conveyor, a new load zone under an existing one, or chute work.
- Indoors or out, and whether dust has to stay contained.
Send that and we can draw it. Without the lump size and the drop, any impact recommendation is a guess dressed up as a spec.
Upgrade Triggers You Can Diagnose Yourself
The machine tells you when the load zone is undersized:
- Idlers replaced on a schedule at one station. Ordinary life everywhere else points at the load zone, not the idlers.
- Bent frames, failed rolls, premature bearing failure. Impact energy past what a frame absorbs, and the point where a bed or cradle is the fix.
- Denting or cupping in the belt under the drop. Support too far apart, or too hard.
- A groove down the length of the belt at the skirt line. Material trapped between skirt rubber and a sagging belt. Closer support, not a tighter skirt.
- Spillage back the day after cleanup, in the same spot. If the pile sits past the end of the skirtboard, the skirt is short and the load is still settling. Dust escaping there says the same.
Any of them is worth a call before ordering another belt: a new belt into an unchanged load zone is a repeat purchase. Remcon repairs and rebuilds equipment as well as building it new, including machines other shops built.
Crusher Discharge & Load Zone FAQ
What is a crusher discharge conveyor?
A belt conveyor built to take material straight from a crusher. What separates it from a general-purpose conveyor is the load zone: material arrives in lumps, from a height, sometimes with energy the crusher gave it rather than gravity. So it gets continuous or closely spaced impact support where the rock lands, a skirted enclosure long enough for the load to settle, and chute work sized to cut the free-fall distance.
Impact idlers or an impact bed under a crusher?
It depends on how hard the material lands. Component selection guidance puts impact idlers at roughly three- to four-inch-minus material dropping six to eight feet, beds at five- to six-inch material dropping eight to ten feet, and cradles above that. Your own load zone is the other input: bent frames, failed rolls, and premature bearing failures mean the frames are absorbing more than they were built for. A bed adds sliding drag, so check the drive has headroom.
How long should the skirtboard on a crusher discharge conveyor be?
Long enough that the load has settled before the belt leaves it, which makes it a function of belt speed rather than chute size. The rule of thumb is two feet of skirtboard per 100 feet per minute of belt speed, three feet per 100 fpm where enclosure airflow is heavy, plus about 25 percent to let dust settle. At 400 feet per minute that is eight to twelve feet before the margin, and skirtboards built to the size of the chute opening fall well short.
Can Remcon rebuild the load zone on a conveyor we already have?
Yes. Remcon repairs and rebuilds equipment as well as building it new, including machines other shops built. On an existing conveyor the work is usually the chute, the skirtboard, and the support under the drop, sometimes with the idler spacing changed through the skirted length. Tell us the belt width and speed, the free-fall distance from the crusher, and the largest lump, and we will say whether the fix is a rebuild or a new machine. If a rebuild does the job, we will tell you that.
Has Remcon built conveyors for crushed rock before?
Yes. A heavy-duty troughing idler conveyor fabricated for a silver mine, photographed on our troughing idler conveyor page. Sand conveyors, a drag chain belt for a contractor who services mines, and a magnetite separation job are also in the book. Remcon comes at this work from the recycling industry, equipment that handles materials that are rough on machines, such as whole and broken glass and tin and aluminum cans, and we have built machinery for mining, construction, and manufacturing alongside our recycling and solid waste lines since 1977. If a long list of aggregate references is a requirement, we are not the right shop.
Can Remcon build the chute and hopper as well as the conveyor?
Yes, and the chute and the conveyor are worth buying from one shop. Drop energy is decided in the chute, and the impact system underneath pays for whatever the chute lets through. Remcon fabricates chutes, hoppers, and hoods along with the conveyor, so fall distance, discharge direction, skirtboard length, and idler spacing get settled on one drawing. Built to order, then shipped and installed nationwide from Airway Heights, Washington, with Remcon's own crews.