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Part 1: Structure of Vertical Roller Mill (VRM)
Crusher shell: Covers the internal parts of the crusher and creates a crushing cavity. The crusher shell is composed of a cylindrical part and a conical part. The upper part of the crusher shell is fitted with a separator motor and an exhaust pipe that brings the crushed product to the sump (cyclone) to recover the crushed product.
Grinding table: With a Y-shaped cross section, the grinding table surface is lined by pads forming a disc shape. The pads are made of wear-resistant alloy and are fixed to the mill table by bolts. The grinding table is supported by a hydraulic support. The load from the grinding table is transmitted to the bearing through an oil film supplied by a high-pressure pump.
Rollers: Consists of three rollers. Each roller has a hydraulic system for lifting and lowering, creating its own crushing pressure. The rollers are lined with a tire-shaped wear-resistant liner. The roller rim can reverse position when worn too much thus greatly increasing the service life. Crusher plates and roller tires are subject to natural wear and tear. When reaching a certain limit these parts need to be soldered or replaced.
Gearbox and motor:
The grinding table is rotated by an electric motor that drives through the gear box. The reducer is a vertical mechanism consisting of a drive gear and a transmission gear. The reducer has a solid structure that can withstand the load of the crushing forces acting on it. The reducer is fitted with a vibration measuring device to monitor vibration and protect the crusher.
Feeding part: It has the effect of evenly supplying crushed materials to the grinding table, because the pressure inside the crushing chamber is negative pressure, so the feeding part is to ensure airtight, limiting fake gas entering the crusher. . The mill feeder consists of a rotary valve and a two-way valve to prevent adhesion and jamming of the material. The blades of the rotary valve are covered with an elastic and wear-resistant rubber.
Barrier and injector ring: The grinding table is surrounded by a barrier and injector ring. The barrier around the grinding table has the effect of spreading the material evenly into a layer of a certain thickness. The air injection ring has the effect of dividing the air. Distribute air flow around the edge of the grinding table to roll the crushed material spilling from the barrier onto the separator.
Separator: The separator is flanged to the upper part of the mill housing. Dissociation includes the system of moving and static wings. Below the separator is arranged a conical hopper to recover raw materials that have not yet ensured the required fineness. The fineness of the product can be adjusted by varying the speed of the separator and the gas flow through the mill.
External return system: The material particles spilling out of the grinding table and falling through the air injection ring are collected by the vanes out through the counterbalance valve into the bucket to upgrade the feed back to the crusher.
Part 2: Working principle
Raw materials after quantification are transported to the crusher by conveyor through two-way valve and rotary valve system. On the feeding conveyor is arranged magnetic and non-magnetic metal separation system. The backflow of the mill is also passed through a non-magnetic metal separation system before returning to the grinding table. The material is fed into the center of the grinding table.
The grinding table is driven by the motor through the gear box. Thanks to the rotation of the grinding table, under the action of centrifugal force the material is evenly spread and enters the crushing zone between the rollers (crushing rollers). Due to the friction and pressure of the roller on the grinding table, the material is crushed and finely ground.
The hot air flow to dry the material fed into the mill is taken after the cooling tower or the auxiliary combustion chamber, through the inlet duct divided into two branches. The air flow through the mill can be adjusted through the valve opening of the fan.
The material after being crushed will move in the direction towards the air injection ring. The drying air flow blows through the air injection ring pushing the mixture with the wrapped material to separate. The raw material particles hit the wings of the separator lose kinetic energy, fall to the recovery cone, return to the grinding chamber, the smaller material particles reach the required fineness size according to the gas flow and are transported to the settling tanks. cyclon) and is recovered mostly here, the rest goes to the bag filter and is recovered at the dust filter.
Please watch the video below to learn the operation process of a vertical coal crusher: