Grizzly Screen and Scalper Motor: Screening and Feeding Before the Crusher

A grizzly screen is the heavy-duty scalper that stands just in front of the primary crusher and separates soil and small pieces that need no crushing from blasted quarry rock by passing them through widely spaced thick bars (grizzly bars); the electric motor shakes this bar deck either through belts, through cardan shafts or directly as a vibration motor. On separate grizzly screens the market shows 11–37 kW on single-motor models and 7.5–37 kW per shaft on twin-motor models; on large grizzly feeders that combine feeding and scalping, a single motor reaches 132 kW [1][2][3][5].

This page covers what scalping gives the crusher, the difference between a feeder with grizzly and a separate scalping screen, the number of motors and the DRG equivalents. Other motors of the primary line are on the Stone Crushing Plant Motors page; current prices of standard motors are in the Buy Electric Motors Online store.

What does a grizzly screen do and why does it stand before the primary crusher?

A large part of blasted rock is already smaller than the crusher opening, and it contains unwanted fines such as clay and soil. If this material enters the crusher it wastes crusher capacity, causes wear on jaws or blow bars and, when wet, packs the crushing chamber. The grizzly screen removes it before the crusher: the fraction passing the bar gap goes on a bypass conveyor to a separate stockpile or directly to the next stage, while the large rock drops into the crusher.

One manufacturer states that a separate grizzly screen placed right after the primary feeder gives more effective scalping than a feeder with a built-in grizzly; stroke and speed stay constant while feed rate is adjusted through the feeder [1]. The operating limits given by the same manufacturer: separation 60–250 mm, stroke 5–16 mm, mechanism speed 700–980 rpm, acceleration up to 5 g [1]. Grizzly bars are arranged in steps; as the rock drops from one step to the next it turns over and the fines separate better.

Feeder with grizzly or separate scalping screen?

Scalping in front of a crusher is done in two ways, and the motor arrangement differs between them.

Feeder with grizzly: A grizzly section is added at the discharge end of a vibrating feeder pan. Feeding and scalping in one machine saves space. One manufacturer's feeders with grizzly run on two vibrators at 2 × 8–11.9 kW, and those with a separate grizzly screen section on four vibrators at 4 × 9.8–10.2 kW; vibrator frequency is set from the panel [6]. On such feeders the vibrators are usually vibration motors bolted to the box; they cannot be replaced by a standard IEC motor. DRG's 0.12–15 kW vibration motor range is on the Vibration Motors page; since vibration motors are not sold in the store, ask for a quotation for the right model and current price via contact or WhatsApp. For the concept see what vibration motors are.

Separate grizzly screen: An independent screening machine placed after the feeder. In one range there are two parallel shafts, each turned by its own motor through a cardan shaft without gears; the two shafts self-synchronise and the box makes a linear stroke. The motors are IEC standard, IP55, B3 foot-mounted [1]. The same manufacturer's circular-motion range runs on a single motor with V-belts and sheaves [1]. Another maker uses a single motor with V-belts [2], and a third lists a single 1500 rpm motor [3].

How many kW for a grizzly screen motor? Single and twin motor

A) Motor power seen in models on the market

In this machine group, motor options of about 7.5–132 kW per motor are seen depending on the manufacturer's model and feed capacity [1][5]. On separate grizzly screens a single motor is 11–37 kW; on twin-motor types it is 7.5–37 kW per shaft, 15–74 kW in total [1][2][3]. The main factor is box size and the rock load it carries: in one maker's range, as width rises from 1220 mm to 2420 mm, power per shaft climbs from 7.5 kW to 30 kW [1]. Feed capacity (t/h), maximum lump size and drop height select the box size; a large box means a large motor. On feeders with grizzly and mining grizzly feeders power is higher, because it also covers moving the rock forward as well as scalping [4][5]. The values here are for one machine; total primary line power is calculated separately with the crusher and conveyors.

B) Matching motors in the DRG range

The 7.5–37 kW motors of separate grizzly screens and the 45–132 kW single motors of grizzly feeders fall within the DRG cast iron range (0.55–355 kW). Non-overlapping parts: since one manufacturer specifies 750, 1000 or 1500 rpm depending on screen size [1], large cardan-driven models requiring 750 rpm are outside the DRG range; the vibration motors of vibrator-type grizzly feeders are not standard motors either and are handled by quotation.

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Example: motors on a twin-motor grizzly screen and the effect of scalping

A quarry places a two-shaft 2120×3900 mm grizzly screen with 2 × 18.5 kW motors (per shaft) in front of its primary jaw crusher [1]. With a gearless cardan drive the mechanism turns at motor speed, and the manufacturer's mechanism range is 700–980 rpm [1]; assume a 1000 rpm motor for this size. The match is DRG-200L1-6: 18.5 kW, 980 rpm, 35.9 A at 400 V, rated torque 180.3 Nm.

• Total power of the two motors is 37 kW, total current 2 × 35.9 = 71.8 A; each motor is protected by its own overload relay and contactor.
• Starting torque ratio is 2.0: each motor gives about 360.6 Nm at start. If the heavy box starts loaded this torque becomes decisive; the screen should start empty.
• The force of the unbalanced weight rises with the square of speed. Fitting a 980 rpm motor to a mechanism designed for 750 rpm multiplies the force by about (980 / 750)² ≈ 1.71; springs, bearings and box are not designed for that load. Motor speed is therefore chosen only from the screen's nameplate.

The effect of scalping on the crusher shows in a simple calculation: with 600 t/h of quarry rock fed and 20% assumed finer than the bar gap, 600 × 0.2 = 120 t/h bypasses the crusher and 480 t/h goes in. Not carrying those 120 tonnes frees crusher capacity; the effect on its motor power is read from the crusher manufacturer's table.

Motor selection checklist, mounting and start sequence

• Machine type: separate grizzly screen or feeder with grizzly, vibrator or belt drive?
• Number of motors (1, 2 or 4) and the nameplate of each; on cardan types the motor base dimensions.
• Box width and length, number of steps, bar gap.
• On belt types, pulley diameters; on cardan types, cardan flange and shaft end.
• Truck tipping point: drop height of the rock and largest block size.
• Panel interlocks: in what order do screen, feeder and crusher start and stop?

On cardan-driven grizzly screens the motors are B3 foot-mounted on a fixed base outside the vibrating box; vibration is absorbed in the cardan shaft [1]. On belt types the motor is also foot-mounted, and pulley alignment and belt tension are checked regularly. The exact mounting type comes from the machine manufacturer's drawing. In a primary line the start sequence usually runs from the end to the beginning: conveyors first, then crusher, then grizzly screen, feeder last; stopping is the reverse. This way the screen never stops with rock on it or starts loaded. The 400/690 V winding of DRG motors from 4 kW allows star-delta starting on 400 V. Panel work must be done by a qualified electrician.

DRG motors that fit grizzly screens

DRG Motor is a manufacturer, supplier and seller of electric motors. The three-phase induction motors we make span 0.25–11 kW in aluminium frames and 0.55–355 kW in cast iron frames; 1000/1500/3000 rpm; 230/400 V or 400/690 V windings; B3, B5, B14 and B35 mounting stated with the order. Cast iron frames suit the dusty, impact-loaded area in front of the primary. Example models for belt- and cardan-driven grizzly screens:

DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the delivery date (warranty certificate). For vibrator-type grizzly feeders, quotations are prepared from the Vibration Motors range.

Motors in this power range:

• DRG-160M-6 – 7.5 kW – 970 rpm – 160M cast iron
• DRG-160L-6 – 11 kW – 970 rpm – 160L cast iron
• DRG-200L2-6 – 22 kW – 980 rpm – 200L cast iron
• DRG-160M-4 – 11 kW – 1465 rpm – 160M cast iron
• DRG-250M-4 – 55 kW – 1485 rpm – 250M cast iron
• DRG-280S-4 – 75 kW – 1486 rpm – 280S cast iron

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Grizzly screen motor: frequently asked questions

Are a grizzly screen and a vibrating feeder the same machine?

No. A vibrating feeder carries rock to the crusher; a grizzly screen only scalps. A feeder with grizzly combines both in one body.

Why must the two motors of a grizzly screen run together?

On two-shaft types each shaft turns with one motor and the box moves linearly because both shafts turn together. If only one motor runs, the motion is lost and the box is strained; the panel must interlock both motors.

What speed should a grizzly screen motor have?

Depending on screen size, the manufacturer specifies 750, 1000 or 1500 rpm motors. Keep the speed on the existing nameplate; 750 rpm motors are not in the DRG range.

Does the motor struggle when grizzly bars clog?

If wet clay closes the bar gap, load on the box rises and separation stops. Check bar gap and inclination with the manufacturer; a larger motor is not the answer.

Send us the grizzly screen model, number of motors, old motor nameplates and drive type (belt, cardan, vibrator), and we will choose the right motor together. Contact: +90 (542) 666 11 11, [email protected], our contact page. All standard motors are in the Buy Electric Motors Online store.

Sources

1. Sandvik – SG & SG-H Grizzly Screens, technical specification – SG: two shafts, one motor per shaft, cardan drive without gears; IEC, IP55, B3, 750/1000/1500 rpm; 2 × 7.5 … 2 × 37 kW; mechanism 700–980 rpm. SG-H: single motor, V-belts, 18.5–22 kW.
2. Weir Minerals – Screening brochure (Trio THDS scalping screens) – THDS scalping screens with V-belt drive; 1575×4280 mm 22 kW, 1850×4675 mm and 2156×4780 mm 37 kW; 800–1,200 mm feed.
3. MEKA (MBF Group) – Grizzly screens MGS – MGS1230 11 kW, MGS1430 15 kW, MGS1640 18.5 kW; 1500 rpm; 2 decks.
4. Metso – Opti-Flo range: VG scalpers (Toromont Cat kopyası) – VG primary scalpers with MV vibrators, electric or hydraulic drive; 15–30 kW for 500–1,200 t/h, VG860 55 kW with 2 × MV3 for 1,500 t/h.
5. FLSmidth – Vibrating Grizzly Feeder, product datasheet – combines feeding and scalping; unbalance exciter driven by one motor via V-belt; 45 / 75 / 132 kW; 1.2–3.6 m width.
6. MEKA – MF Series Feeders (katalog) – vibrating grizzly feeders 2 × 8 … 2 × 11.9 kW (1000 rpm), feeders with grizzly screen 4 × 9.8 and 4 × 10.2 kW; vibrator frequency adjustable from the panel.