Limestone vertical roller mill Introduction

A limestone vertical roller mill is a specialized equipment used for grinding and processing limestone. Limestone is a mineral mainly composed of calcite, which is rich in resources and widely used in building materials, metallurgy, chemical industry and construction industry. in the cement industry. It is mainly used as raw material for satin-fired cement clinker. After mixing limestone and cement, it can improve the lightness and hardness of concrete, bricks and other building materials. Limestone vertical roller mill is widely used in the cement production line, after it is being grinding, it will be sent to the raw material silo and with other additives it will enter the rotary kiln undergo the calcination process to produce clinker. Limestone vertical roller mill is also suitable for grinding a variety of material such as clinker, coal, blast furnace slag, steel slag, furnace slag, manganese slag, metallurgical slag, limestone, dolomite, calcite, gypsum, pozzolan, clays, silica sand, non-metallic minerals, and other raw materials. The limestone vertical roller mill operates by rotating a grinding table that is driven by the gearbox and motor. The material to be ground is fed into the mill from the top and is ground between the rotating grinding table and the grinding rollers.

Limestone vertical roller mill structure

The main components of the limestone vertical roller mill include the grinding table, grinding rollers, grinding roller shaft, grinding roller wheel hub, grinding roller tyre, rocker arms, separator, transmission system, base frame. 

Grinding Table: The grinding table is a rotating part of the limestone vertical roller mill responsible for grinding materials. It is mounted on a gearbox-driven spindle and can be tilted to control the product fineness and optimize the grinding process. The detailed structure of the grinding table includes guide ring, air ring, retaining ring, liner, disc body, scraper.

Grinding Rollers: Grinding roller is the main part for crushing and grinding materials. The grinding roller is composed of cast steel roller sleeve, forging shaft and wear-resistant surfacing bushing. The grinding roller is installed on the rocker arm of the limestone vertical roller mill, under the action of external force, it is pressed tightly on the material of the grinding table, as the grinding table rotates the material is crushed. The grinding roller is equipped with a limit device to ensure that it does not directly contact the grinding table during operation

Grinding Rollers shaft: A forged shaft could refer to various components such as the main shaft that supports the grinding rollers or other critical shafts within the mill's structure. These components need to withstand significant mechanical loads and stresses, and using forged shafts can ensure the necessary strength and durability. The term "forged shaft" refers to a shaft that has been manufactured using a forging process, this process enhances the mechanical properties of the metal, such as strength, durability, and resistance to impact and fatigue.

Grinding Rollers wheel hub: The grinding roller wheel hub is a metal casting part that is mounted on the outside of the grinding roller shaft. The wheel hub refers to the central part of the grinding roller that connects it to the driving mechanism of the mill. The wheel hub is designed to transmit the rotational motion and force from the mill's drive system to the grinding roller, allowing it to rotate and exert pressure on the material.

Grinding roller tyre: The grinding roller tire of a vertical roller mill is a crucial component that directly contacts the material being ground during the milling process. It's also commonly referred to as the grinding roller or roller shell. This component is made up of a cylindrical shell or tire-like structure that rotates around a central shaft. The grinding roller tire is typically equipped with segments or studs that aid in grinding and pulverizing the material as the mill's table or bowl rotates.

Rocker Arms: The function of the rocker arm device of the limestone vertical roller mill is to transmit the pressure provided by the hydraulic cylinder to the grinding roller, so that it can be transformed into the grinding force act on the material bed. The rocker arm device is mainly composed of upper rocker arm, lower rocker arm, rocker arm shaft, bearing and bearing housing and other components. The upper rocker arm is used to install the grinding roller, the lower rocker arm is connected to the hydraulic system, and the two rocker arms are connected as a whole through shafts, taper sleeves and taper pins.

Classifier: Powder classifier (also known as coarse powder separator) of the limestone vertical roller mill plays a vital role in the selection of powder during grinding. The ground material is carried by the high-speed rotating airflow in the mill and enters the powder classifier through the stationary blades. The material is screened under the high-speed rotation of the cage rotor, and the screened fine particle material is taken out by the exhaust gas and enters the cyclone. The coarse particle material falls into the grinding disc through the lower cone tube for re-grinding.

Middle shell: The middle casing of the limestone vertical roller mill is a welded structural part, which supports the weight of the entire separator. There are 4 inspection doors on the middle casing for roll overhaul. The door is designed with a sealing sheath that is in close contact with the grinding roller to Prevent air leakage. The inner wall of the middle shell is laid with a wear-resistant lining to protect the inner shell.

Base Frame: The support base of the limestone vertical roller mill is generally four peripheral support pedestal and a central support base, and the support base and the installation foundation are connected and fixed by anchor bolts. All the limestone vertical roller mills of Tongli will be pre-assembled and leveling calibrated before leaving the factory to ensure that the equipment can be installed smoothly on site.

Transmission device: The transmission device of the limestone vertical roller mill is composed of a planetary gear reducer, a motor and a coupling in the middle of 4 supporting beams. The planetary gear reducer is a reduction device with a vertical output shaft, and the output end is connected to the grinding table with a flange. The vertical downward force is supported by the hydraulic thrust bearing on the top of the reducer during operation.

PLC control system: A PLC is a digital computer-based system that is designed to control various industrial processes automatically. In the context of a vertical roller mill, a PLC is used to monitor and control parameters such as temperature, rotation speed, air flow, fuel flow, and other critical variables that affect the performance of the kiln and the quality of the products being processed. Tongli vertical roller mill is controlled with PLC control system which is capavle of monitoring temperature, vibration, filling rate, output rate. Tongli vertical roller mill also equipped with CO, O2 real-time gas analyzer to ensure save production.

Design principles of limestone vertical roller mill

Working principle: The raw material is lifted by the bucket elevator and then pass through the iron remover to remove the other object, after that the raw material is fed into the limestone vertical roller mill through a star airlock valve, once the material drops down form the top of the limestone vertical roller mill landed at the center of the grinding table, through centrifugal force, the raw material will be thrown to the edge of the grinding table.

A hydropneumatics spring tension cylinder pulls on the rocker arm and exert a vertical force on the grinding roller and the grinding table, as the grinding table rotates cause the material to be crushed under the compressive force and the shear force. Fine particle will be taken to the classifier by a upstream, coarse particle will return to the grinding table for regrinding, also there is a exit chute on the edge of the grinding table for iron to exit in case it is not removed by the iron remover in the previous step. Foreign object and bulks of raw material exit from the chute will be sent to the bucket elevator and pass through the iron remover again. This raw material vertical roller mill system also integrates drying, it has a portal that can utilize the waste gas from the rotary kiln, or if no heat source it also can connect to the hot air generator through this portal.

Advanced design: As one of the leading vertical roller mill manufacturers, Tongli limestone vertical roller mills are advanced in design, integrating the functions of crushing, drying, grinding, classifying, conveying. Adapt to fluctuating raw material qualities, adapt to different product qualities.

High grinding efficiency: The stand-alone production capacity of the limestone vertical roller mill is large, low energy consumption compared with ball mills, the energy consumption is usually 40%-50% lower than the ball mill;

Dust-free operation: The limestone vertical roller mill system adopts a fully enclosed system, and the whole system operates under negative pressure without dust spillage, which can meet the requirements of clean production

Customized deisgn: Tongli’s limestone vertical roller mill has two types of grinding rollers, one is cone-shaped and the other is tire-shaped. According to different materials and different technological processes, we customized the equipment that meet your specific need.

Adaptability: Tongli limestone vertical roller mill can process kaolin, barite, fluorite, talc, water slag, lime calcium powder, wollastonite, gypsum, limestone, phosphate rock, marble, potassium feldspar, quartz sand, bentonite, Manganese ore and other materials with a hardness below 7 on the Mohs scale.

Compact layout: the occupation area is only 50% of that of a ball mill and It can be arranged outside, no workshop needed. Due to this reason, it can effectively reduce construction costs and helping enterprises reduce initial investment costs.

Pre-assembling: the base frame is pre-assembled in our workshop and marked with number so that when it comes to installation on site, it is a lot of easier, the owner can put it together like Lego.

Separator Balance test: All the separator needs to pass the balance test before assemble, we have a balance test machine that test the vibrate and concentricity when the cage rotor rotates, Tongli make sure all the separator is running smooth.

Gas sealing system: Tongli limestone vertical roller mill is equipped with a high-speed centrifugal blower to send high-speed air into the seal of the roller bearing to form a gas seal to prevent dust from entering the roller bearing. By doing this we can greatly improve the bearing service life.

Water spray system: The limestone vertical roller mill of Tongli is equipped with a water spray system, one is to reduce the outlet temperature of the mill, and the other is to speed up the accumulation of the material layer on the grinding table.

Lubrication system: Tongli limestone vertical roller mill is equipped with a forced lubrication device to ensure the service life of bearings and key components during operation.

PLC control system: Real-time monitoring of the limestone vertical roller mill with operating parameters. Highly automatic, features remote control and touch screen control, Siemens control system.

Easy Maintenance: Swing-out feature allows the maintenance of the grinding roller to be easy and fast. Grinding roller can be rolled out of the machine by hydraulic device, and the replacement of the roller sleeve liner and the maintenance of the mill is very convenient; No need to arrange material layer on the grinding table before starting the machine, Tongli limestone vertical roller mill can be started without load.

Specifications of limestone vertical roller mill

Note: *The diameter is middle diameter of the grinding table.

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Industry knowledge extension

What is the difference between ball mill and vertical roller mill?

Both ball mills and vertical roller mills plays a vital role in the cement grinding plant. Ball mills are versatile and cost-effective, suitable for various materials and simple to maintain. On the other hand, vertical roller mills offer superior energy efficiency and particle size control, making them ideal for cement and ore grinding applications. The choice between the two depends on specific requirements, budget constraints, and technical expertise.

What is the relationship between vertical roller mill and rotary kiln?

In the cement production line, the vertical roller mill is widely used. The vertical roller mill can be used not only as the grinding equipment for raw materials, but also as the grinding equipment for finished cement clinker. When the raw material is broken into small pieces by the crushers, it enters the vertical roller mill. The ground limestone powder and other additives enter the clinker rotary kiln for calcination to produce clinker, and the calcined clinker enters the vertical roller mill or ball mill for final grinding.

What is the application of limestone?

Limestone powder, also known as calcium carbonate powder, is a versatile material with various applications across different industries due to its unique properties.

Concrete Production: Limestone powder is often used as a partial replacement for cement in concrete. It contributes to improved workability, durability, and sulfate resistance. It can also reduce the heat of hydration and enhance long-term strength.

Mortar and Plaster: Limestone powder is used in mortar and plaster formulations to improve workability, adhesion, and setting time.

Tile Adhesives: It is added to tile adhesives to enhance their bonding strength and workability.

Stabilization of Soil: Limestone powder can be added to soil to stabilize it, improve load-bearing capacity, and reduce soil erosion.

Soil Amendment: Limestone powder is used as a soil conditioner to adjust pH levels in acidic soils. It improves soil structure, enhances nutrient availability, and promotes healthy plant growth.

Flue Gas Desulfurization (FGD): Limestone powder is used in FGD systems to remove sulfur dioxide (SO2) from flue gases generated by industrial processes and power plants. It reacts with SO2 to produce calcium sulfate, which can be further processed into gypsum.

Iron and Steel Production: Limestone powder is used as a flux in iron and steel production to remove impurities and facilitate the melting process.

Glass Manufacturing: It is used in glass manufacturing to control the melting temperature and improve the optical properties of glass.

Filler in Paints: Limestone powder is used as a filler in paints and coatings to improve opacity, gloss, and impact resistance.

Filler in Plastics and Rubber: Limestone powder can be used as a filler in plastics and rubber products to enhance strength, stiffness, and dimensional stability.

PH Adjustment: Limestone powder is used in water treatment to adjust pH levels and neutralize acidic water.

Calcium Supplement: Limestone powder is added to animal feed as a calcium supplement for livestock and poultry. It helps improve bone health and eggshell quality.

Filling Agent: Limestone powder is used as a filler in the paper and pulp industry to improve paper properties, such as brightness and opacity.