In the material pretreatment link of industrial production, from limestone crushing in cement plants to resource utilization of construction waste and raw material processing in chemical plants, a kind of equipment that realizes material crushing by high-speed impact has always occupied a core position—it is the
hammer crusher. For practitioners in industries such as mining, building materials and electric power, a deep understanding of the core information of hammer crushers is crucial for optimizing production processes and accurate selection. Focusing on the core question “What is a hammer crusher”, this article will provide a comprehensive and detailed analysis from definition, working principle, type classification to selection points, offering practical technical references for you.
To use a
hammer crusher well, it is first necessary to clarify its core concept and applicable scope. Only by knowing clearly what it “can do” and “is suitable for doing” can mismatching problems be avoided in actual production.
A
hammer crusher (also known as a hammer mill) is a crushing equipment that crushes lumpy or granular materials into smaller particle sizes through the
repeated impact of high-speed rotating hammers. Its core working logic revolves around “impact crushing”, converting the kinetic energy of the hammer into the crushing energy of materials to meet the processing needs from coarse crushing to fine crushing.
Not all materials are suitable for processing with hammer crushers, and there are clear requirements for the hardness and humidity of materials:
- Hardness Requirement: It is only applicable to medium-hard and brittle materials, and the compressive strength of materials must be controlled within 150MPa. If the material hardness is too high (such as basalt and granite), it will cause excessive wear of the hammer, which not only increases maintenance costs but also reduces crushing efficiency.
- Humidity Requirement: The moisture content of materials should be ≤15%. If the humidity is too high, materials are likely to adhere to the inner wall of the crushing chamber or the screen bars, causing blockage and even leading to equipment shutdown for cleaning in severe cases.
With the advantages of efficient and convenient crushing, hammer crushers are widely used in various industrial fields, with specific scenarios as follows:
- Cement Industry: Used for crushing cement raw materials such as limestone, clay and gypsum, providing materials with qualified particle sizes for subsequent raw meal grinding and clinker calcination.
- Chemical Industry: Processing fertilizer raw materials (such as phosphate rock) and chemical intermediate ores to meet the refined requirements of material particle sizes for chemical reactions.
- Electric Power Industry: Crushing fuels such as coal and gangue, grinding lumpy fuels into uniform particles to improve combustion efficiency and reduce energy waste.
- Construction Waste Treatment: Crushing construction waste such as concrete blocks, bricks and waste stone materials to realize resource recycling and produce recycled aggregates that can be reused in building material production.
- Mining Industry: Used for tailings treatment in small and medium-sized mines and fine crushing of non-metallic minerals (such as talc and calcite), reducing the difficulty of subsequent processing.
The working process of a hammer crusher seems simple, but it is actually a coherent process of “power transmission – impact crushing – cyclic refinement”. Understanding its principle can help users better judge equipment failures and optimize operating parameters.
Before analyzing the principle, it is necessary to clarify the key components of the hammer crusher, which jointly support the crushing process:
- Rotor: The power core of the equipment, composed of a main shaft and discs, serving as a carrier for fixing hammers and realizing high-speed rotation driven by an electric motor.
- Hammer: The executive component of the crushing action, mostly made of high manganese steel or alloy steel. The number and shape of hammers can be adjusted according to material characteristics.
- Crushing Chamber: A closed space for material crushing. The inner wall is usually equipped with wall plates or impact plates to rebound materials and realize secondary crushing.
- Feed Inlet / Discharge Outlet: Responsible for the input of materials and the output of materials with qualified particle sizes respectively. Some equipment is equipped with screen bars at the discharge outlet to control the particle size of finished products.
The working process of a hammer crusher can be divided into 5 key steps, which are closely linked to ensure the crushing effect:
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Step 1: High-Speed Rotation of Hammers (Power Startup)
The electric motor drives the rotor to rotate through a coupling, and the rotation speed of the rotor can usually reach 500-1500r/min. The hammers fixed on the rotor discs move synchronously with the rotor, forming strong centrifugal force and impact force to reserve kinetic energy for subsequent crushing.
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Step 2: Materials Entering the Crushing Chamber (Feeding Link)
The materials to be crushed enter the crushing chamber evenly from the feed inlet through a conveyor belt or a feed hopper. At this time, the materials are in a free-falling state and will directly come into contact with the high-speed rotating hammers, and the crushing process officially starts.
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Step 3: Impact Crushing by Hammers (Core Link)
The high-speed moving hammers collide violently with the materials, and the impact force exceeds the compressive strength of the materials in an instant, causing the materials to be crushed and split into smaller particles. The higher the rotation speed and the greater the weight of the hammers, the stronger the impact force and the higher the crushing efficiency.
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Step 4: Secondary / Multiple Impacts on Materials (Refinement Link)
After the initial crushing, the materials will be thrown to the wall plates or impact plates of the crushing chamber under the action of inertia, and then collide with the hammers again after rebounding. This process will be repeated until the material particle size meets the preset requirements, avoiding the situation of “uncrushed coarse particles”.
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Step 5: Discharge of Qualified Materials (Discharge Link)
Materials that meet the particle size requirements will be discharged from the crushing chamber through the screen bars (or gaps) at the discharge outlet, and enter the subsequent conveying, screening or storage links; the unqualified coarse particles remain in the crushing chamber and continue to be impacted by the hammers until they meet the standards.
Hammer crushers are not a “single type of equipment” but a large family of equipment. According to structural characteristics such as number of rotors, rotation direction, hammer layout and application scenarios, they can be divided into various types, and different types have significant differences in applicable scenarios and performance.
The rotor is the core power component of the hammer crusher, and its number directly determines the crushing capacity and output of the equipment.
- Structural Features: It contains only one rotor, with a simple structure, low manufacturing cost, no need to disassemble complex double-rotor linkage components during maintenance, and low operating threshold.
- Working Principle: The single rotor rotates at high speed, and the hammers impact materials in one direction. Crushing is completed through “one impact + one rebound”, which is suitable for medium and low output requirements.
- Applicable Scenarios: Small and medium-sized production lines, such as small sand and gravel plants and chemical laboratory raw material crushing, processing medium-soft materials (limestone, coal, etc.) with an hourly output usually ranging from 50 to 300 tons.
- Structural Features: It contains two parallel rotors, driven by independent electric motors to rotate in opposite directions; the machine shell is equipped with an arched grate (composed of bow-shaped screen bars) to accurately control the particle size of the discharged materials.
- Core Advantages: Strong crushing capacity, with a crushing ratio of up to 40 (about 10-20 for ordinary single-rotor ones), and the output is equivalent to two single-rotor equipment of the same specification, with more uniform particle size of finished products.
- Applicable Scenarios: Large and medium-sized production lines, such as large cement plants and construction waste treatment plants, processing large-sized materials (with a feed particle size of more than 1000mm) with an hourly output of more than 1000 tons.
Whether the rotor can rotate in both directions determines the continuous working capacity of the equipment and the service life of the hammers.
- Structural Features: The rotor can only rotate in one direction, and the gap between the hammer and the impact plate is fixed and cannot be adjusted; it is mostly a single-rotor multi-row design, and the discs on the main shaft are fixed by pressing discs and lock nuts to prevent axial movement.
- Working Limitations: After one end of the hammer is worn, it is necessary to stop the machine to change the direction of the hammer or replace it with a new one, which affects the continuous production efficiency.
- Applicable Scenarios: Scenarios where materials have low hardness and low wear resistance requirements, such as coal and gangue crushing, suitable for small factories with low requirements on production continuity.
- Structural Features: The rotor can rotate in both directions, the vertical center line of the equipment is symmetrical, and the feed inlet is set in the middle; both ends of the hammer can be used alternately without frequent shutdown for replacement.
- Core Advantages: The service life of the hammer is more than twice that of the non-reversible type, and by adjusting the rotation direction of the rotor, it can adapt to the crushing needs of different materials; however, the equipped screen bars are prone to blockage when dealing with materials with excessively high humidity (>15%).
- Applicable Scenarios: Scenarios requiring continuous production and materials with strong wear resistance, such as medium-sized ore processing plants and sand and gravel production lines, processing materials such as limestone and gypsum.
- Structural Features: A multi-row hammer design is adopted on the rotor, and the crushing area is 30%-50% larger than that of the single-row type. The discharge port is specially designed to reduce the residence time of materials in the crushing chamber.
- Performance Advantages: High crushing efficiency and good uniformity of the particle size of finished products, avoiding the situation of “mixed large and small particles”.
- Applicable Scenarios: Industries with high requirements on the particle size of finished products, such as the cement industry (for producing cement raw meal) and the chemical industry (for crushing fertilizer raw materials), to ensure the consistency of materials in subsequent processing links.
The heavy hammer crusher is a special type designed for the needs of “high output and integrated coarse and medium crushing”, which can realize “one-time crushing forming” and reduce crushing links.
- Large hammer weight: The weight of a single hammer usually exceeds 20kg, and the crushing force is more than 50% stronger than that of ordinary hammer crushers.
- High output: The maximum hourly output can reach 3000 tons, far exceeding that of ordinary single-rotor equipment.
- Limited applicable materials: Only suitable for medium-soft materials such as limestone, gangue and construction waste. It is strictly forbidden to crush ultra-hard materials such as pebbles and basalt (to avoid excessive wear of hammers).
For materials with excessively high humidity (>15%) and easy adhesion (such as wet coal, clay, and sludge-mixed ore), ordinary hammer crushers are prone to blockage, so a special type for sticky and wet materials has been developed.
- Anti-Blocking Design:
- A track-type rotating impact plate is installed in front of the rotor, driven by a separate electric motor, which can prevent materials from accumulating at the feed inlet, and the hammer can automatically remove the adhesive materials on the impact plate.
- A vertical closed chain belt (with horizontal scrapers) is arranged behind the rotor. When the chain belt rotates, it can scrape off the adhesive materials on the wall of the shell and discharge the accumulated materials.
- Applicable Scenarios: Wet coal crushing in coal washing plants, clay ore processing, and crushing of sludge-ore mixed materials in sewage treatment plants.
Selection is the “first step” and also the most critical step in the application of hammer crushers. If the selection is wrong, it will not only lead to low production efficiency but also increase equipment maintenance costs. The following provides practical selection methods from 4 core dimensions.
Material characteristics are the basis for selection, and 3 indicators need to be focused on:
- Hardness: For medium-soft materials with compressive strength ≤150MPa (such as limestone and coal), ordinary single-rotor/double-rotor hammer crushers can be selected; if they are sticky and wet materials, the “special type for sticky and wet materials” should be directly selected; for ultra-hard materials (such as basalt), hammer crushers are strictly prohibited, and jaw crushers or cone crushers are recommended instead.
- Humidity: For materials with moisture content ≤15%, ordinary models can be selected; for materials with moisture content >15%, the “special type for sticky and wet materials” must be selected to avoid blockage.
- Feed Particle Size: For materials with a feed particle size ≤750mm, small and medium-sized models such as PCZ1512 can be selected; for materials with a feed particle size >1000mm, large heavy hammer crushers such as PCZ1820 need to be selected to ensure “one-time crushing forming”.
Production capacity should be combined with the “actual demand + reserved space” of the production line:
- Calculate Actual Demand: First, clarify the hourly output of the production line (for example, a small sand and gravel plant needs 200 tons per hour, and a large plant needs 1000 tons per hour).
- Reserve Production Capacity Space: When selecting a model, a model with a production capacity slightly higher than the actual demand should be selected (for example, if the demand is 200 tons per hour, PCZ1512 with a capacity of 250-320 tons per hour can be selected) to avoid accelerated wear and frequent failures caused by full-load operation of the equipment.
Motor power directly affects the crushing force and efficiency, and the principle of “matching power with production capacity” should be followed:
- Small single-rotor hammer crushers (with an hourly output of 50-100 tons): The supporting motor power is usually 30-55kW.
- Medium-sized double-rotor/heavy hammer crushers (with an hourly output of 300-500 tons): The supporting motor power is 110-220kW.
- Large heavy hammer crushers (with an hourly output of more than 1000 tons): The supporting motor power needs to be more than 315kW.
- Note: Avoid “a small horse pulling a big cart” (insufficient power leading to incomplete crushing) or “a big horse pulling a small cart” (excessive power increasing energy consumption).
There are 3 discharge methods for hammer crushers, which need to be selected according to the subsequent treatment process:
- Gravity Discharge: Materials are discharged by their own gravity, with a simple structure and low cost. It is suitable for small single-rotor equipment (such as laboratory use), and manual or simple conveyor belt transfer is required afterward.
- Negative Pressure Suction Discharge: The finished products are sucked out through a negative pressure device, which can reduce the humidity of the finished products (facilitating storage), improve the crushing efficiency by 10%-15%, and reduce dust pollution. It is suitable for medium-sized equipment (such as in the chemical and cement industries).
- Mechanical Conveying Discharge: The finished products are directly conveyed to the next link through a conveyor belt. It is suitable for large-sized equipment (such as double-rotor and heavy hammer crushers) to realize continuous production and adapt to high-output scenarios.
With the advantages of “simple structure, high crushing efficiency and wide application range”,
hammer crushers have become the “main force” in the field of industrial crushing. Whether it is the raw material pretreatment in cement production or the resource utilization of construction waste, they can provide support for enterprises to reduce costs and improve efficiency.
For selection, the core suggestion is to “
not blindly pursue large models and not ignore material characteristics“: If you are a small and medium-sized sand and gravel plant processing medium-soft materials such as limestone, the PCZ1512 heavy hammer crusher is a cost-effective choice; if you are a large cement plant that needs to process large-sized materials and has high output requirements, a double-rotor hammer crusher or a PCZ1820 heavy hammer crusher is more suitable; if you process sticky and wet materials such as wet coal and clay, directly select the “special type for sticky and wet materials” to avoid subsequent blockage troubles.
Finally, it is recommended to fully communicate with the equipment manufacturer before selection, provide detailed parameters such as the hardness, humidity and output of the materials, and obtain a customized selection plan to ensure that the equipment is accurately matched with the production needs.
