A log conveyor is a continuous belt conveyor used in mining and timber operations to move bulk material — run-of-mine ore, coal, waste rock, or whole logs — along a fixed trajectory between extraction and processing points. It is essential in underground coal mines, where drift conveyors haul cut coal kilometres to the surface stockpile. A driven head pulley pulls a rubber belt over troughed idlers while material rides on the loaded carry side and the empty belt returns underneath. The result is steady, high-tonnage flow with far lower energy and labour cost than truck or rail haulage at the mine.
Inside the Log Conveyer
A log conveyor moves bulk solids by friction between a driven head pulley and a continuous rubber belt. The belt sits in a trough formed by 3-roll or 5-roll idler sets — typically 20°, 35°, or 45° troughing angle — so the cross-section of material on the belt is roughly trapezoidal. Material loads onto the carry side at a feed chute, rides at belt speed (typically 2.5 to 5.5 m/s for ROM ore handling), and discharges over the head pulley into the next chute or stockpile. The empty belt returns under the structure on flat return idlers. A gravity or screw take-up keeps tension in a working window — usually 1.5 to 2 times the slack-side tension needed to drive the belt without slip.
The design lives or dies on three numbers: belt speed, troughed cross-section area, and the surcharge angle of the material (the angle the load naturally piles above the trough line, usually 20° for damp ore, 25° for dry crushed coal). Multiply cross-section area by belt speed by bulk density and you get tonnes per hour. Get the troughing angle wrong and capacity drops by 15-20%; get the take-up tension wrong and the belt either slips on the head pulley under full load or chews up its splices from over-tensioning.
Failure modes are predictable. Belt mistracking — usually from a worn idler bearing on one side, or material build-up on the head pulley — wears the belt edge against the structure within hours. Excessive belt sag between idlers (above 3% of idler spacing) spills fines and accelerates idler wear because the belt slaps each roll on entry. Splice failures show up first as belt thump on the head pulley; if you notice that sound, shut down before the splice opens at full tension.
Key Components
- Head pulley (drive pulley): The driven pulley at the discharge end that transmits motor torque to the belt through friction. Lagged with rubber or ceramic to lift coefficient of friction from 0.25 (bare steel) to 0.35-0.45 (rubber lag) or 0.5+ (ceramic lag). Diameter sized to belt class — typically 630 mm to 1600 mm for ST-rated steel cord belts.
- Tail pulley: The non-driven pulley at the loading end where the belt reverses direction. Often fitted with a rubber lagging and a V-return scraper to keep fines off the belt's back side. Diameter is usually one size below the head pulley.
- Troughed carry idlers: Three- or five-roll sets that shape the belt into a trough. Standard troughing angles are 20°, 35°, and 45°. Spacing is typically 1.0 to 1.5 m on the carry side. Bearing life rated to 60,000 hours at design load — a worn idler shows as a hot bearing housing or audible rumble.
- Return idlers: Flat or V-return rolls supporting the empty belt underside. Spacing is 2 to 3 m — wider than carry side because the empty belt carries no load. V-return idlers (10° angle) help self-centre the belt on long runs.
- Take-up unit: Maintains belt tension as the belt stretches and the splices bed in. Gravity take-ups use a counterweight (typical mass 2-10 tonnes depending on belt class); screw take-ups use a threaded rod for short conveyors under 60 m. Travel must accommodate belt stretch — usually 1.5% of total belt length.
- Conveyor belt: The flexible carrying medium. Fabric belts (EP-class) handle up to ST-1000 ratings; steel cord belts (ST-class) go from ST-630 to ST-7800 N/mm for overland conveyors. Cover thickness typically 6 mm top / 3 mm bottom for ROM ore handling, with abrasion-resistant grades for sharp-edged crushed rock.
- Skirtboard and feed chute: Contains material at the loading point and centres it on the belt. Skirt rubber must clear the belt by 3-5 mm at the leading edge — too tight and the rubber drags and burns the belt cover; too loose and fines escape and pile up under the conveyor.
- Belt scraper (cleaner): Removes carryback material from the belt after the head pulley. A primary scraper sits against the head pulley face; a secondary scraper sits a metre downstream on the return run. Carryback is the leading cause of belt mistracking on the return side.
Who Uses the Log Conveyer
Log conveyors anchor bulk material handling across mining, processing, and primary industry. Anywhere you need to move thousands of tonnes per hour over distances measured in hundreds or thousands of metres, a belt conveyor beats trucks on cost, energy, and labour. They scale from short 20 m stacker conveyors at a quarry to 20 km overland conveyors crossing terrain that no haul truck could economically cover.
- Underground coal mining: The drift conveyor at Prosper-Haniel colliery in Germany hauled run-of-mine coal from the longwall face up a 6 km drift to the surface plant at roughly 2,000 t/h on an ST-2500 steel cord belt before closure in 2018.
- Iron ore export: Rio Tinto's overland conveyor systems at the Cape Lambert port facility in the Pilbara feed shiploaders at sustained rates above 11,000 t/h using twin troughed belt lines.
- Copper concentrator feed: The SAG mill feed conveyor at Codelco's Chuquicamata operation in Chile delivers crushed ore to the grinding circuit at design rates of 12,000 t/h on a 2.4 m wide belt.
- Cross-border overland haulage: The Bou Craa phosphate conveyor in Western Sahara — 98 km end-to-end and the longest belt conveyor system in the world — moves rock phosphate to the Atlantic coast at El Aaiún at around 2,000 t/h.
- Forestry and pulp logs: Whole-log infeed conveyors at Canfor's sawmills in British Columbia stage debarked stems toward the primary breakdown saw using heavy chain-and-flight log haul rather than rubber belt — a true log conveyor variant under the same name.
- Aggregate quarry stockpiling: Radial stacker conveyors at Lafarge limestone quarries build conical stockpiles up to 25 m high using 1.0 m belts running at 2.5 m/s with a luffing boom.
The Formula Behind the Log Conveyer
The CEMA capacity formula tells you how many tonnes per hour your belt will actually deliver. The numbers shift hard across the operating range. At the low end of typical belt speeds (1.5 m/s on a 1.0 m belt, 35° trough, ROM ore at 1.6 t/m³) you'll see roughly 600 t/h — fine for a small quarry but undersized for a mine plant. At nominal mining speed (3.5 m/s) the same belt does 1,400 t/h. Push to 5.5 m/s on the same geometry and you theoretically hit 2,200 t/h, but in practice you start spilling fines at the loading point and the belt cover wears out in 12-18 months instead of 4-5 years. The sweet spot for ROM ore handling is 3 to 4.5 m/s — fast enough to move tonnage, slow enough that the surcharge angle holds and the cover lasts.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Q | Conveyor capacity (mass flow rate) | t/h | ton/h |
| A | Cross-sectional area of material on the belt (function of belt width, troughing angle, and surcharge angle) | m² | ft² |
| v | Belt speed | m/s | ft/min |
| ρ | Bulk density of conveyed material | t/m³ | lb/ft³ |
Worked Example: Log Conveyer in a potash mine main drift conveyor
Nutrien's Cory potash mine near Saskatoon is sizing the main drift conveyor that hauls run-of-mine sylvinite from the underground crusher up to the surface mill. The belt is 1.2 m wide, runs on 35° troughed idlers, and the material has a surcharge angle of 20° and bulk density of 1.35 t/m³. The engineering team needs to confirm the conveyor will deliver the design rate of 1,500 t/h at a sensible belt speed.
Given
- B = 1.2 m (belt width)
- trough angle = 35 °
- surcharge angle = 20 °
- ρ = 1.35 t/m³
- Qtarget = 1500 t/h
Solution
Step 1 — calculate the cross-sectional area of material on the belt. For a 1.2 m belt at 35° troughing with 20° surcharge, the CEMA tables give A ≈ 0.165 m². This is the trapezoidal cross-section of material the belt actually carries.
Step 2 — at nominal belt speed of 3.5 m/s (the sweet spot for ROM ore handling), compute the capacity:
That comfortably exceeds the 1,500 t/h target, which means the engineering team has design margin — they can run the belt slower to extend cover life and reduce dust generation at transfer points.
Step 3 — at the low end of the typical operating range, 2.0 m/s (a conservative speed favoured for short underground conveyors with frequent stops):
This still meets target with thin margin. At this speed the belt is quiet, dust is minimal, and cover life pushes past 6 years — but you have nothing in reserve if upstream feed surges.
Step 4 — at the high end, 5.0 m/s (aggressive overland practice):
You'd never run this fast for 1,500 t/h target — the belt would be running 25% loaded, which causes load instability, side-to-side material shift, and accelerated mistracking. High belt speed only pays off when you're actually loading the belt to capacity.
Result
At nominal 3. 5 m/s the conveyor delivers 2,807 t/h — nearly double the 1,500 t/h target, so the design choice becomes which belt speed gives the best lifecycle cost. At 2.0 m/s you hit 1,604 t/h with quiet operation and long cover life; at 5.0 m/s you'd theoretically hit 4,010 t/h but at a fraction of belt utilisation and with much higher wear. The right design point is around 2.2 to 2.5 m/s, giving 1,750-2,000 t/h and a clean 15-20% capacity reserve. If your measured throughput comes in below predicted, check three things first: (1) actual surcharge angle — wet sylvinite slumps to 12-15° instead of the assumed 20°, dropping cross-section area by 18%; (2) belt loading offset — material centred 50 mm off-centre at the feed chute reduces effective trough fill on one side; (3) belt slip on the head pulley under load — visible as belt creep against the lagging, usually traced to take-up tension set 20-30% below the calculated T2 slack-side requirement.
When to Use a Log Conveyer and When Not To
Belt conveyors are not the only way to move bulk solids out of a mine or quarry. The right choice depends on tonnage, distance, terrain, and what the material is doing to your equipment. Compare on the dimensions that actually drive the decision.
| Property | Log (belt) conveyor | Haul truck fleet | Rail haulage |
|---|---|---|---|
| Throughput capacity | 500-12,000 t/h continuous | Typically 200-1,500 t/h fleet effective rate | 1,000-10,000 t/h batched |
| Economic distance | 50 m to 100 km (overland) | 0.5-15 km practical limit | 5 km to unlimited |
| Energy cost per tonne-km | 0.05-0.15 kWh/t·km | 0.4-0.8 kWh/t·km diesel equivalent | 0.08-0.20 kWh/t·km |
| Capital cost | High up-front, low per added tonne | Low up-front, scales linearly with fleet | Very high up-front (track + locomotives) |
| Maintenance interval | Idler replacement every 30,000-60,000 hours, belt 5-15 years | Tyre replacement every 4,000-8,000 hours, engine overhaul 15,000 h | Track maintenance ongoing, locomotive overhaul 20,000 hours |
| Terrain tolerance | Up to 18° incline (smooth belt), 30° (cleated) | Up to 10% grade sustained | Limited to ~2% grade for heavy haul |
| Labour intensity | 1 operator monitors km of conveyor | 1 operator per truck | 1 crew per train |
| Application fit | Continuous high-tonnage flow over fixed route | Flexible routing, expanding pit geometry | Long-haul to port or smelter |
Frequently Asked Questions About Log Conveyer
Loaded mistracking with empty-belt running true is almost always a load-centring problem at the feed chute, not an idler problem. When the belt runs empty, the troughed idlers self-centre it through their geometry. Add 1,500 t/h of material biased 50-100 mm to one side and the centroid of belt-plus-load shifts off the conveyor centreline, and the belt drifts toward the loaded side until it scrapes structure.
Check the chute liner wear pattern first — if one side is worn smooth and the other side has built-up fines, the feed is biased. The fix is usually adjusting the chute internal deflector or adding a centring skirt extension. Self-aligning idlers further downstream will fight the symptom but won't fix the cause.
The deciding factor is required tension class, which scales with conveyor length, lift, and tonnage. As a rule of thumb, EP belts cover up to about ST-1000 equivalent — practical for conveyors under 500 m with moderate lifts. Beyond that, steel cord wins on stretch behaviour: a 2 km EP belt will stretch 0.5-1.5% under load, eating up most of your take-up travel; the same length in ST stretches 0.1-0.2%.
Steel cord also splices stronger (90-95% rated tension vs 70-80% for EP) which matters on long overland conveyors where a splice failure means days of downtime. The price premium for ST is roughly 1.8-2.5x EP per metre, but the extra capital pays back in service life on any conveyor over 800 m.
Three causes account for almost every case of excess power draw. First, idler rolling resistance — if idlers are seized, contaminated, or the bearing grease has gone hard from cold weather, the rolling friction coefficient climbs from a design value of 0.020 to 0.035-0.040. On a long conveyor with thousands of idlers, this alone adds 25-40% to the running power.
Second, material build-up on return rolls. Carryback that bypasses the belt scrapers builds up on return idlers, shifting them off-axis and adding drag. Third, take-up tension set too high. Operators often crank up tension to chase a mistracking problem; every extra tonne of belt tension above design adds proportional friction at every pulley wrap. Walk the conveyor and feel idler bearing housings — anything noticeably hotter than ambient is robbing your motor.
The 35° trough is the default for almost all mining and quarry applications because it gives 90-95% of the capacity of a 45° trough with significantly lower belt edge stress. A 45° trough forces the belt to flex sharper at the idler junctions, which fatigues the carcass and shortens belt life by 15-25% on long conveyors.
Use 20° troughs only for short conveyors carrying light bulk density material, or where the belt also has to track over a tripper or stacker that needs a flatter profile. Use 45° only when capacity is the absolute constraint and you can accept the shorter belt life — typical on space-constrained underground feeders.
If take-up is genuinely at spec and the belt still slips, the issue is the friction coefficient at the head pulley wrap, not the tension. Bare steel lagging gives roughly μ = 0.25 dry, dropping to 0.10-0.15 wet — easily exceeded by drive demand on a heavy conveyor. The cure is rubber lagging (μ ≈ 0.35) or ceramic lagging (μ ≈ 0.5).
Check whether the lagging has worn smooth or polished — a glazed rubber lag behaves like bare steel. Also look at the wrap angle. A snub pulley arrangement that increases wrap from 180° to 210-220° dramatically improves drivable tension, often more cheaply than upgrading lagging.
The counterweight must supply enough slack-side tension (T2) to drive the belt without slip at full load, plus accommodate belt stretch over the conveyor's life. Working rule: T2 = T1 / (e^(μθ)) where T1 is the tight-side tension at the head pulley, μ is the lagging friction coefficient, and θ is the wrap angle in radians. The counterweight mass equals 2 × T2 (because the take-up pulley sees tension on both strands).
For belt stretch, allow 1.5% of total belt length as travel for EP belts, 0.3% for ST belts. If the counterweight bottoms out during normal operation, the belt has stretched past design — time to shorten and re-splice rather than add weight, because excess counterweight mass increases all running tensions and accelerates wear at every component on the conveyor.
References & Further Reading
- Wikipedia contributors. Conveyor belt. Wikipedia
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