Hammer Crusher Motor: Motor Selection for Limestone and Soft Rock

A hammer crusher is an impact crusher in which free-swinging hammers hung on discs along a shaft strike the stone and break it, and the broken material leaves through a grate underneath; the electric motor turns this hammer rotor at high speed through V-belts or a coupling and supplies all of the crushing energy. It is used on medium-hard and soft rock such as limestone, gypsum, marl and clay. In models on the market, motor power starts at 5.5 kW on small single-rotor machines and reaches 2,500 kW on the giant single-stage crushers of cement plants [1][3][4].

Below: the crusher's place in the line, the drive layout, reading power from a capacity table and the DRG equivalents. All plant motor groups are on the Stone Crushing Plant Motors page, and current prices for suitable motors are on Buy Electric Motors Online.

What is a hammer crusher and where is it used in a crushing line?

The heart of the machine is the rotor: a shaft, discs mounted on the shaft and hammers fitted on pins between the discs. As the rotor turns, the hammers swing outward under centrifugal force, hit the falling stone and throw it against the breaker plates of the housing. Crushing continues on the grate beneath the hammers: small pieces pass through the gaps between the bars, oversize pieces are struck again. The grate gap therefore sets the top size of the product.

In aggregate plants the hammer crusher usually works in the secondary or fine crushing stage; one manufacturer catalogue describes the machine for fine crushing of medium-hard to soft material [1]. In the cement industry, large single-rotor types reduce quarry limestone boulders to mill feed in a single pass, so they act as the primary crusher [3]. Suitable materials:

• Limestone and dolomite (aggregate and cement raw material),
• Gypsum, clay and marl (cement and ceramic raw material),
• Coal and lignite (power plants and cement fuel preparation) [2].

One manufacturer requires the feed to have a compressive strength below 150 MPa and moisture below 15% [4]. Abrasive rock such as basalt and granite usually goes to jaw and cone crushers.

What sets the hammer crusher apart from other crushers and from the hammer mill?

Our separate article on the hammer mill motor covers small high-speed machines that turn products such as feed and spices into fine powder. The hammer crusher is a stone-crushing machine with a heavy rotor that handles quarry rock and has grate gaps of several tens of millimetres.

How does the motor turn the hammer rotor?

On single-rotor aggregate types the motor usually sits on a slide rail beside the machine and turns the rotor through V-belts. The pulley ratio converts motor speed into the rotor speed required by the hammer tip speed; speed changes are made only with the machine manufacturer's approval, because tip speed directly changes the product and hammer wear. On some types the motor is coupled directly to the rotor shaft.

On twin-rotor types the two rotors turn in opposite directions and each rotor has its own motor; in one manufacturer's range the smallest model has 2 × 132–160 kW and the largest 2 × 1,400 kW [2]. On large cement-type machines the inlet rollers are driven by a separate motor as well [3]; this auxiliary motor must not be confused with the main motor.

At start-up the motor faces a heavy rotor. Hammers and discs create a large inertia, so the machine always starts empty and feed is opened only after the rotor reaches full speed. In star-delta starting, the torque on the star step is one third of the direct-on-line torque; with a full hopper this torque may not be enough to turn the rotor. The general background is in our article on high torque in crushing plant motors; panel settings must be made by a qualified electrician.

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How many kW should a hammer crusher motor be?

A) Motor power seen in models on the market

In this machine group, motor options of about 5.5–2,500 kW are seen depending on the manufacturer's model and capacity [4][3]. Even within one model, power is not a single number: manufacturers give installed power as a range, because the required product fineness (grate gap), hourly tonnage, rock hardness and moisture all change it. As the grate narrows, material stays longer inside the rotor and a larger motor is needed for the same tonnage; as tonnage rises, power rises too. On a twin-rotor machine the stated value is per rotor; do not read the sum of two motors as single-motor power. The total installed power of the plant is calculated separately together with feeders, screens and conveyors.

B) Matching motors in the DRG range

The part of the range above that overlaps the DRG range is 4- and 6-pole motors (1500 and 1000 rpm) between 5.5 and 355 kW. This covers small and medium single-rotor aggregate crushers and the rotor motors of twin-rotor types up to 355 kW per rotor. Models supplied with 8-pole (750 rpm) motors [4], twin-rotor types above 355 kW per rotor and 500–2,500 kW cement primary crushers [3] are outside the DRG range. Using a 1000 rpm motor in place of a 750 rpm motor requires a change of pulley ratio; that decision belongs to the crusher manufacturer alone.

How is motor power read from a capacity table? Example

For a hammer crusher, reading the manufacturer's capacity table is more reliable than a power calculation with the Bond work index. Example: a limestone plant wants 80 tonnes of product per hour and is considering maker A's Ø1000 mm rotor model. The table gives 50–100 t/h capacity and 90–132 kW installed power for this model [1].

• 80 t/h lies at 60% of the capacity range: (80 − 50) / (100 − 50) = 0.6.
• Simple linear reading at the same ratio in the power range: 90 + 0.6 × (132 − 90) ≈ 115 kW.
• 115 kW is not a standard rating; the next lower 110 kW is marginal, so the next higher 132 kW is chosen.

This reading is only a first estimate; the manufacturer clearly notes that values vary with the material [1]. The final power comes from the manufacturer, based on a rock sample and the grate gap. If 4-pole is chosen, the match is DRG-315M-4: 132 kW, 1488 rpm, 224 A at 400 V, rated torque 847.2 Nm. With a starting torque ratio of 2.0, direct-on-line start gives about 1,694 Nm and the star step about one third of that, roughly 565 Nm; that is only 0.67 times rated torque, so the rotor accelerates comfortably on star only when empty. With a starting current ratio of 7.0, about 1,568 A is drawn direct-on-line and about 523 A on star; the transformer and panel must be checked against these currents.

Data needed for motor selection, speed and mounting

Prepare the following information when asking for a hammer crusher motor:

• Machine nameplate or catalogue: rotor diameter and width, single or twin rotor.
• Old motor nameplate: kW, speed, IEC frame, voltage, foot or flange mounted.
• Drive: for belts, motor pulley diameter and number of grooves; for couplings, coupling hub and shaft size.
• Rotor speed or hammer tip speed (from the machine manufacturer).
• Starting: direct, star-delta, soft starter or inverter; number of starts per hour.
• Material: rock type, moisture, clay content (risk of grate clogging).

On speed the rule is simple: motor speed is part of the machine design. If the table says 6-pole, buy a 1000 rpm motor; if it says 4-pole, a 1500 rpm motor; poles are not changed without recalculating the pulleys. You can check the pulley relationship with the pulley-belt calculator. On belt-driven machines a B3 foot-mounted motor on a tensioning slide rail is common; the exact type comes from the machine manufacturer's drawing. DRG motors from 4 kW up are wound for 400/690 V and are suitable for star-delta starting on a 400 V supply.

DRG motors that fit hammer crushers

DRG Motor is a manufacturer, supplier and seller of electric motors. Our range covers 0.25–11 kW in aluminium frames and 0.55–355 kW in cast iron frames; 1000, 1500 and 3000 rpm; 3-phase, 230/400 V or 400/690 V; mounting B3, B5, B14 and B35 (with an order note). For the dusty, vibrating environment of a crusher house, cast iron frames are preferred on hammer crushers. Example models for medium and large single-rotor crushers and for the rotor motors of twin-rotor types:

DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the delivery date (warranty certificate). The general steps of the quotation process for crusher motors are in our article on crusher motor price and quotation.

Motors in this power range:

• DRG-280S-6 – 45 kW – 985 rpm – 280S cast iron
• DRG-315S-4 – 110 kW – 1488 rpm – 315S cast iron
• DRG-315M-4 – 132 kW – 1488 rpm – 315M cast iron
• DRG-315L1-4 – 160 kW – 1488 rpm – 315L cast iron
• DRG-315L2-4 – 200 kW – 1490 rpm – 315L cast iron
• DRG-355L-4 – 315 kW – 1490 rpm – 355L cast iron

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Hammer crusher motor: frequently asked questions

Are a hammer crusher and an impact crusher the same machine?

No. Both strike with a rotor; in a hammer crusher the hammers swing and a grate below limits the product, in an impact crusher the blow bars are fixed and there is no grate.

What speed should a hammer crusher motor have?

It depends on the machine design. Belt-driven types use 1000 or 1500 rpm motors with a pulley ratio; some models are supplied with 750 rpm motors, and that speed is not in the DRG range.

Why does the motor trip on overload when the grate clogs?

When wet clay or marl closes the grate, material builds up inside the rotor and load torque rises. Raising the overload setting is not the answer; clean the grate and check the feed moisture.

Should the two motors of a twin-rotor hammer crusher be identical?

Yes, each rotor carries its own motor and the two are usually the same power and speed. When replacing, check the nameplate data of both together.

Send us the crusher catalogue, the old motor's nameplate and the panel starting method, and we will confirm the right DRG model together. Phone +90 (542) 666 11 11, e-mail [email protected], contact page. All models and current prices: Buy Electric Motors Online.

Sources

1. MEKA – Hammer Crushers (katalog sayfası) – rotor Ø1000×1400 mm 50–100 t/h, 90–132 kW; Ø1200×1400 mm 100–170 t/h, 132–160 kW installed power.
2. HAZEMAG – Hammer Crusher HDS, technical data – twin-rotor range; smallest model 2 × 132–160 kW, largest 2 × 1,400 kW; limestone, marl, clay, gypsum, coal.
3. Fuller Technologies – EV Hammer Impact Crusher (broşür) – reduces quarry boulders to mill feed in one stage; 2,200 t/h with grate; motors typically 500–2,500 kW; inlet rollers on a separate motor.
4. Zhengzhou ZK – Hammer Crusher PCH, specifications – 400×200 mm rotor 8–12 t/h 5.5 kW (6-pole); 800×800 mm 75–105 t/h 45 kW (8-pole); feed compressive strength <150 MPa, moisture <15%.