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.
Which Crusher, and Which Stage of the Circuit
"Crusher discharge conveyor" covers several different belts. Which crusher sits above it, and which stage of the circuit it serves, changes the lump, the fines, the tonnage and the way material arrives, and all four land on the load zone.
Primary, secondary, tertiary
Pit run crosses a grizzly or a scalping screen, goes through a primary crusher, then on to secondary and tertiary crushing and the sizing screens. Top size falls at every stage and the fines fraction rises, and the belt under each stage inherits a different problem.
The belt under a primary sees the biggest lump the plant will ever produce, arriving with the fewest fines to cushion it. That is where the lump-to-belt-width ratio and the impact support get decided, and where chute work earns most of its keep. Further down the circuit the stream is smaller, better graded and carries more fines, and the problems change with it: sealing at the skirt, dust, and cover wear rather than impact. Same page of design rules, different lines underlined.
Size to the lump, not to the setting
A closed side setting is a nominal, not a maximum. Published design guidance puts the working lump at two to three times the nominal or specified figure, because settings get opened up and screens get run harder whenever somebody needs more production out of the same plant. On a discharge belt that matters twice over: the real lump sets belt width, and the real lump plus the free fall sets whether the load zone gets impact idlers, an impact bed, or a cradle. Both decisions run off a number the crusher's data sheet does not carry, and on a jaw the free-fall arithmetic understates it further, for the reason given in the chute section above.
Open circuit and closed circuit
In an open circuit, material passes through the crusher once and leaves. In a closed circuit, a screen separates finished product and routes the oversize back to the crusher for another pass, which is how a tight gradation gets held.
The belt to watch in a closed circuit is the return run, and undersizing it is a quiet way to cap a whole stage. Everything inside the loop, the crusher, the screening surface, and the elevating and conveying capacity, handles the fresh feed plus the circulating load. 911 Metallurgist makes exactly that point: the circulating load does not just bear on the capacity of the stage, it determines the screening surface and the elevating capacity the circuit needs. It also works the arithmetic. Thirty percent oversize in the crusher product at ninety percent screen efficiency comes out at a circulating load a little over fifty percent, which means the machinery inside that loop is moving about one and a half times the fresh feed. Size the return conveyor against that, not against what leaves the plant as product.
Surge between the stages
Every one of those stages stops sometimes, and a circuit with no storage in it stops with them. A surge bin, a surge hopper, or a surge pile with a reclaim feeder under it lets one end pause while the other keeps running, and it is also what keeps a stopped belt from being restarted loaded under a packed chute. Remcon fabricates the bins, bunkers and hoppers and the feeder underneath that meters material back out, along with the conveyors themselves.
What is not Remcon's scope here
Not the crusher, not the sizing screen, not the plant chassis. On a wheel-mounted portable plant or a track-mounted mobile plant, the belt under the crusher ships as part of that machine, from the plant's manufacturer. What Remcon builds is the fixed steel: the under-crusher conveyor on a stationary plant, the closed-circuit return run, the belt off each screen deck, the transfers between them, the chute, skirtboard and load zone on all of it, and the surge and access steel around it. The whole boundary, overland conveyors and stacking equipment included, is set out on the quarry and aggregate conveyors page.
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.
The Other End of the Belt: Handing Off to a Stacking Conveyor
Everything above is about what lands on the belt. On a portable or modular plant, the belt has a second problem at the far end, because the crusher discharge conveyor is frequently the machine that feeds the stockpiling end directly. One belt, two pieces of geometry: rock arriving from a height at the tail, and a handoff into another machine at the head.
The head end rule is the load zone rule running backwards. At the tail you want the chute to take fall out and turn the stream into the direction of belt travel at close to belt speed. At the head you are the chute: the stream should leave your conveyor going the way the receiving belt runs, at close to its speed, landing centered inside its opening, with as little free fall as the elevations allow. Every foot of drop you design out at the handoff is cover wear and dust that never happens, and it is the same arithmetic as the chute at the crusher, spent one machine further down the line.
Where the receiving machine is a radial stacking conveyor, that machine pivots at its feed end and sweeps its head through an arc, so the feed point itself stays put. The transfer is fixed and can be engineered properly. What moves is the boom and the wheels, and the discharge conveyor, its legs, and its footings have to stand clear of that arc and of the pile it builds. Remcon fabricates the fixed conveyor, the head chute, and the support steel. The stacking conveyor is not one of the machines Remcon builds. It is a separate machine, from its own manufacturer, with its own published dimensions, and the fixed run gets built to them.
Three things worth settling before the drawing:
- Discharge height against feed height. The elevation the receiving point sits at, and how far it moves across the machine's working range, sets the head height of the conveyor feeding it. This is the number that gets discovered late and fixed expensively.
- What happens when the far end stops. A stopped stockpiling run leaves a crusher discharge belt with nowhere to put material, which is a plugged chute and a loaded belt on restart. Interlocks are half the answer. Storage between the two is the other half: see bins, bunkers, and hoppers.
- Whether the plant moves. If the crusher relocates around the pit, the conveyor between it and the stockpiling end has to be built to come apart and go back together. Long runs already ship in bolted sections, and Remcon relocates and reconfigures conveyor systems it did not originally build as well as ones it did.
None of that is exotic. It is the same drawing discipline as the load zone, applied at the opposite end of the same belt, and it fails for the same reason: two vendors, two scopes, and an interface neither owned. Remcon draws the chute, the load zone, the belt, and the discharge into the next machine as one set, then ships and installs nationwide from Airway Heights, Washington, with its own crews. What a radial stacking conveyor changes about the pile is on the quarry and aggregate conveyors page.
Guarding and Cleanup Access at the Load Zone
The load zone is the one stretch of a belt that people walk to on purpose. Spillage gets shoveled there. Skirt rubber gets adjusted there. Impact bars and idler sets get changed there. It is also the stretch with the most moving steel close to a walking surface, because the tail pulley, the take-up and often the drive all sit at that end. On a mine site, that combination is what the standards below are written about.
The standard that applies is Part 56, not OSHA
A surface quarry or a sand and gravel pit is a mine, inspected under 30 CFR Part 56, and three of its standards land straight on a load zone. 56.14107 requires guarding on gears, sprockets, chains and the drive, head, tail and takeup pulleys, along with the shafts and couplings around them, and exempts moving parts at least seven feet from walking or working surfaces. 56.14109 requires an unguarded conveyor next to a travelway to carry either an emergency stop device a falling person can readily reach, or a railing that keeps them off it. 56.14112 requires the guards themselves to withstand vibration, shock and wear, not create a hazard by their use, and stay in place while the machine is running. The fuller treatment, access steel and handrails included, is on the quarry and aggregate conveyors page.
Draw the cleanup in, or pay for it every shift
- Reach to the skirt clamp. Skirt rubber is adjusted and replaced on a schedule, and both sides need a working surface to do it from. Where the only access is across the belt, the adjustment stops happening and the groove down the cover starts.
- Somewhere for the spillage to go. A load zone raised clear with an open drop under it is a loader job now and again. The same load zone boxed in by legs and cross-bracing at floor level is a shovel job every shift. That is settled by where the support steel goes, and the support steel is settled on the drawing.
- Room to pull an impact bar. Bars sit under the skirt, and changing one means clearing the skirt and sliding the bar out lengthways. Either the clearance for that exists or the change becomes a shutdown.
- Guards that hinge. A guard taken off to reach a grease fitting is a guard that stays off. Hinge the panel, keep the fasteners captive, and run the grease line out to where a gun can reach it without tools. None of that costs anything in the shop.
- Where the pull cord and its switches sit. A cord needs brackets, corner pulleys, and a switch positioned on the side the walking surface is on, close enough that somebody going down actually reaches it.
Guarding is a fabrication decision, and an early one
Everything on that list is steel, and all of it is cheaper drawn than retrofitted. Retrofit guarding gets built around a machine that is already in the way, which is how a plant ends up with panels that foul the take-up travel and a railing that blocks the one route to the tail pulley. It is the same failure as a load zone specified for a gentler drop than it gets: not a bad part, an interface nobody drew.
Remcon fabricates the guarding on the machines it builds, along with the platforms, catwalks, stairways, ladders, handrails and toeboards around them, and installs them with its own crews. Remcon does not certify your site and does not sell a compliance package. The standard is the site's and the steel is ours, so the one thing needed at quote time is which standard applies. On a recycling plant that access steel gets drawn to OSHA. On a pit it gets drawn to Part 56, and the difference is real enough to be worth a sentence on the quote request.
What Remcon Has Built for Rock
Four jobs, 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. Also in the job book: sand conveyors built in 2012, a drag chain belt built in 2025 for a contractor who services mines, and a magnetite separation job in 2011. 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.
Our crusher discharge belt feeds a stockpiling conveyor. Can Remcon build it?
Yes, and both ends of that belt get designed at once. The tail end is the load zone: impact support under the drop, skirtboard long enough for the load to settle, and chute work that cuts the free fall from the crusher. The head end is a transfer into the next machine: discharge height built to the receiving machine's feed height, the stream leaving in the direction the receiving belt runs at close to its speed, and a head chute that lands the material centered in the opening. Tell us the crusher, the largest real lump, the drop, and the receiving machine's published dimensions.
What should happen at the handoff if the stockpiling end stops?
Two things, and neither is optional on a plant that runs unattended stretches. Interlocks stop upstream equipment when the downstream machine stops, so the discharge chute does not pack and the belt does not restart loaded. Storage between the crusher and the stockpiling end absorbs the rest, so a short stop at the pile does not shut the crusher down. Remcon fabricates the surge hoppers and bins and the feeder conveyor underneath them along with the conveyors themselves.
Can the conveyor be built to move when the crusher moves?
Yes. Long conveyors already ship from Airway Heights in bolted sections so they can be trucked and assembled on site, and the same joints let a run come apart and go back together when the plant relocates around the pit. Say at quote time that the plant moves, because it changes the frame, the joints, and the support design rather than being something to work out later. Remcon also relocates and reconfigures installed conveyor systems, including ones other shops built.
Do I size the discharge belt to the crusher setting or to the lumps we actually see?
The lumps you actually see. A closed side setting is a nominal. Published design guidance says to work to two or three times it, because settings get opened up and screens get run harder whenever somebody needs more production from the same plant. On a discharge belt that lump does two jobs: with belt width it sets the lump-to-width ratio, and with the free-fall distance it sets whether the load zone gets impact idlers, an impact bed, or a cradle. Send the top size that comes over the belt, the free fall from the crusher discharge, and the width and speed of whatever conveyor is under there now.
Is the belt under a cone different from the belt under a jaw?
The support under the drop is set by the lump and the free fall, not by the badge on the crusher, so the method is the same and the numbers are not. What changes is the stage. The belt under a primary sees the biggest lump the plant will ever make with the fewest fines to cushion it, so impact support and chute work dominate. Belts further down the circuit carry a smaller, better-graded stream with more fines in it, where the problems are skirt sealing, dust and cover wear rather than impact. A jaw adds one thing on top: it fractures rock at the discharge, so fragments arrive with energy of their own and the free-fall arithmetic alone understates what lands.
Should the closed-circuit return conveyor be sized to plant output?
No, and that is a common way to cap a crushing stage without meaning to. In closed circuit a screen separates finished product and routes oversize back to the crusher, so everything inside the loop, the crusher, the screening surface and the conveying capacity, handles the fresh feed plus the circulating load. 911 Metallurgist works the case: thirty percent oversize in the crusher product at ninety percent screen efficiency is a circulating load a little over fifty percent, meaning the machinery in that loop is moving about one and a half times the original feed. Size the return run against the circulating load, not against what leaves the plant as product.
Our crusher is on tracks. Can you build the conveyor under it?
Not the one on the chassis. That belt is part of the plant and comes from the plant's manufacturer, and Remcon builds neither the plant nor the conveyor bolted to it. What Remcon builds is the fixed steel from there on: the run that takes the plant's discharge, the transfer into it, the surge bin and the feeder underneath, and the chute, skirtboard and load zone at the drop. A fixed run can still be built to come apart: the bolted joints that get it onto a truck are the same ones that let it be taken down and re-erected when the pit moves. That is a different answer from a portable plant, and the two are worth keeping separate on a quote request.