Roll Crusher Motor: Motor Selection for Single and Double Roll Crushers

A roll crusher breaks rock by squeezing it between two rolls turning towards each other, or between a single toothed roll and a fixed breaker plate; on double-roll types each roll is turned by its own electric motor. That is why roll crusher motor power is stated "per roll": models on the market show motors from about 5.5 kW up to 250 kW per roll, and the total of a two-roll machine is twice that [5][3]. It is chosen for coal, clay, marl and soft limestone when the product must contain few fines.

For other motor groups see Stone Crushing Plant Motors; for prices of suitable motors see Buy Electric Motors Online.

What is a roll crusher, and for which materials and stages is it used?

In a double roll crusher the two rolls turn in opposite directions; rock is drawn between them and crushed as it passes the gap. One roll runs in fixed bearings, the other is movable to set the crushing gap and compensate for wear; one manufacturer states that this adjustment can be mechanical, hydraulic or electromechanical and that overload protection is always integrated [3]. The roll surface is smooth, profiled or toothed; a toothed surface grips sticky clay.

The same manufacturer describes the double roll crusher for both primary and secondary crushing, with feed size up to about 1,500 mm, product size 15–300 mm and a reduction ratio up to 1:5 [3]. Smaller smooth-roll types work in fine crushing: another manufacturer's range gives target grain sizes down to 2 mm and a 10:1 reduction ratio [1]. Typical uses:

• Coal and lignite preparation: power plant and cement fuel lines,
• Clay and marl crushing in brick, tile and ceramic plants,
• Medium-hard and brittle materials such as limestone, coke, sinter and cullet [3].

What is the difference between single-roll and double-roll crushers?

In a single roll crusher a toothed roll turns against a curved breaker plate (anvil); material is split and sheared between the roll teeth and the plate. In a double roll crusher crushing takes place between two moving surfaces. For the motor the difference is this: on a double-roll machine each roll usually has its own motor; on a single-roll machine the one roll is driven either by one motor or by one motor at each end.

Compared with jaw, cone, hammer and impact crushers, the roll crusher produces few fines thanks to low roll speed and gap control.

How does the motor turn the rolls? Belts, gearbox and flywheel

Rolls turn slowly. One single roll crusher maker gives a roll speed of 15–60 rpm [4], while the motor turns at 1000 or 1500 rpm. A speed-reduction stage is therefore always present between motor and roll. Three layouts given by manufacturers:

• Motor + coupling + gears + V-belts: in one double-roll range each roll is driven in counter-rotation by its own motor, coupling and gears via V-belts [3].
• Motor + flexible coupling + gearbox + chain: in one single-roll, double-drive range there is one drive group at each end; the flexible coupling absorbs shocks and misalignment [4].
• V-belts + large flywheel + gear-pinion: on another single-roll type the inertia of the flywheel supports the motor while breaking large lumps, so relatively low motor power is enough [6].

In a geared layout the motor delivers high speed and low torque, while the roll shaft sees low speed and high torque; the general relationship is explained in our article on the role of a gearbox in an electric motor. On a two-motor machine where the motors are not mechanically linked, each carries its own load; if one roll jams, only its motor is overloaded. Each motor therefore needs its own overload protection, and the panel should be interlocked so that if one motor stops the other stops too. One manufacturer supplies its motor as inverter-ready [1].

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How many kW for a roll crusher motor? Power per motor and total

A) Motor power seen on roll crushers on the market

In this machine group, motor options of about 5.5–250 kW per roll are seen depending on the manufacturer's model and capacity [5][3]; on a two-motor machine the total is twice that, about 11–500 kW. Even on the same machine, power changes with the required product size: in one maker's table the 06-08 type crushes 170 t/h at P90 = 50 mm, 65 t/h at 10 mm and 10 t/h at 1 mm with a motor band of 11–15 kW [2]. So as the product gets finer, the tonnage passing with the same motor power falls; getting the same tonnage at a fine product needs a larger machine and motor. Feeder and conveyor motors are not part of this table.

B) Matching motors in the DRG range

The whole 5.5–250 kW per roll range lies inside DRG's 0.55–355 kW cast iron range; 1000 rpm (6-pole) and 1500 rpm (4-pole) options are chosen according to belt and gearbox ratio. If a non-standard nameplate value such as 37.5 kW is seen, the next standard rating (45 kW) is considered; this change must be confirmed with the manufacturer. Very large mining-scale roll crushers above 355 kW per roll and drives that require 750 rpm motors are outside the DRG range.

Example: choosing power per motor from a capacity table

A brick plant wants to crush a limestone additive at 90 tonnes per hour to a P90 = 10 mm product and uses maker B's table [2]:

• The 06-10 type crushes 80 t/h at 10 mm: not enough. The 06-12 type crushes 100 t/h at 10 mm: suitable. Its motor band is 18–30 kW per roll.
• The required 90 t/h is 90% of the machine's 100 t/h capacity; since the machine will run close to its limit, the top of the band, 30 kW per roll, is chosen. Total installed power is 2 × 30 = 60 kW.
• For a 6-pole choice the match is DRG-225M-6: 30 kW, 980 rpm, 56.2 A at 400 V, rated torque 292.3 Nm. The two motors draw about 112.4 A in total, but each motor is protected by its own overload relay.
• Assuming a roll speed of 60 rpm, the overall reduction ratio is 980 / 60 ≈ 16.3; ignoring losses, the roll shaft sees about 292.3 × 16.3 ≈ 4,770 Nm. You can compute the ratio with your own values in the gearbox output speed and torque calculator.
• With a starting torque ratio of 2.0 the motor delivers about 584.6 Nm at start. This value is decisive when starting with rock jammed between the rolls; the machine should start empty or the jam should be cleared first.

Pre-order data list, roll speed and connection

When asking for a roll crusher motor, send the following together:

• Single or double roll; roll diameter and width; how many motors.
• Nameplate of each motor: kW, speed, frame, voltage, mounting type. If the two motors differ, list both.
• Drive train: belt and pulley diameters, gearbox ratio or chain sprockets, flywheel or not.
• Roll speed and surface type (smooth, profiled, toothed).
• Material and moisture: sticky clay or frozen coal raises starting torque.
• Starting and interlocking: do both motors start together, does one stop when the other stops, is there an inverter.

Speed depends on the drive ratio: if the gearbox and pulleys were designed for 1000 rpm, a 1500 rpm motor raises roll speed by about 50% and changes product and capacity. Keep the old motor's speed when replacing. A belt drive may need a B3 foot-mounted motor on a tensioning rail; a drive flanged to a gearbox may need a B5 or B35 motor; the exact type comes from the machine manufacturer's drawing. Since DRG windings are 400/690 V from 4 kW, these motors can be started in star-delta on 400 V; starting the two motors with a short delay rather than simultaneously lowers the current peak on the supply.

DRG motors that fit roll crushers

DRG Motor is a manufacturer, supplier and seller of electric motors. Product range: cast iron 0.55–355 kW, aluminium 0.25–11 kW, three-phase, 1000/1500/3000 rpm, 230/400 V or 400/690 V windings; B3, B5, B14, B35 mounting stated in the order note. On a double-roll machine two identical motors are ordered. Example models per roll:

DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the delivery date (warranty certificate). For a general overview of motors in a crushing line, see our article electric motors for stone crushing plants.

Motors in this power range:

• DRG-180L-6 – 15 kW – 978 rpm – 180L cast iron
• DRG-200L1-6 – 18.5 kW – 980 rpm – 200L cast iron
• DRG-225M-6 – 30 kW – 980 rpm – 225M cast iron
• DRG-250M-6 – 37 kW – 985 rpm – 250M cast iron
• DRG-280M-6 – 55 kW – 985 rpm – 280M cast iron
• DRG-315M-6 – 90 kW – 988 rpm – 315M cast iron

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Roll crusher motor: frequently asked questions

Does a double roll crusher have two motors?

On most models yes: each roll turns with its own motor and the "2 × kW" value in the catalogue is power per roll. On some types both rolls are driven together from one motor through gears; check the nameplate.

What speed should a roll crusher motor have?

Rolls turn at low speeds such as 15–60 rpm; the motor runs at 1000 or 1500 rpm and belts, a gearbox or a chain make up the difference. Keep the old motor's speed.

Can a roll crusher run if one motor fails?

It should not. The roll still turning carries the whole load and overheats; the panel should stop the other motor when one stops.

Why does the motor struggle when crushing clay?

Wet clay sticks to the roll surface and narrows the gap; load torque rises. Check the scrapers and the adjustable roll, and do not raise the overload setting.

Send us the roll crusher catalogue, the nameplates of both motors and the drive ratio, and we will confirm the right DRG model together. Phone +90 (542) 666 11 11, e-mail [email protected], contact page. Store models: Buy Electric Motors Online.

Sources

1. Merz Aufbereitungstechnik – Roller Crusher WBG (föy) – roll Ø350–1000 mm, ≤150 t/h, power input 7–55 kW; motor 400 V 50 Hz IP55, inverter-ready.
2. CPC Crushing Processing – Roll Crusher SR 11 (föy) – double-roll types 06-08 … 08-24; t/h for P90 50/10/1 mm; 2 × 11–15 … 2 × 45–75 kW per roll.
3. AUBEMA – Double Roll Crusher (broşür) – each roll driven separately by motor, coupling, gears and V-belts in counter-rotation; one loose roll; up to 2,500 m³/h, up to 2 × 250 kW.
4. Magaldi – Heavy-duty single roll crusher – single roll, double drive: 2 × (motor + coupling + gearbox + chain); 15–60 rpm; 2 × 7.5–18.5 … 2 × 37.5–55 kW.
5. HXJQ – Roll Crusher 2PG, technical data – 2PG double-roll series; Ø400×250 mm 3–10 t/h 5.5 × 2 kW … Ø1500×600 mm 30–110 t/h 110 × 2 kW.
6. McLanahan – Single Roll Crushers – single roll crusher driven by V-belts, a large flywheel and gear-pinion set; flywheel inertia allows relatively low motor power.