Hammer mill: design and operating principle
The intensity of many processes depends on the area of the processed material surface; in this case as the surface area increases by means of the lumps size decrease, the process rate increases, and the finished product output and quality increase also.
The solid material lump size decrease is called crushing or grinding; crushing is often understood to mean decrease of large lumps size only. The process of comminution of small pieces is often referred to as grinding.
Grinding is applied to ore fuel, raw material (mine rock, ores), semi-finished and finished products.
Grinding is commonly referred to as coarse if the cross dimension of the pieces being processed is 1000 to 200 mm, medium and intermediate – within 250 to 50 mm, small-sized –within 50 to 20 mm, and fine (grinding) – within 25 to 3 mm and less. Grinding can be dry or wet; in the latter case some water is added to the source material.
Much mechanical power is consumed during crushing and grinding, and so it is important to select the comminution method correctly. The intermediate material grinding is commonly carried out using centrifugal impact mills in which grinding is performed by means of impacts and cracking. Such mills are equipped with special impact devices (hammers, blocks, fingers, etc.) which rotate at high speed in the enclosure. The centrifugal impact mills are used to grind viscous and brittle materials.
Hammer mills are the most common units of such type. Such mills are used for preliminary and final fine grinding of the material the moisture content of which does not exceed 15 %.
Fine material grinding in the hammer mills is carried out not only as a result of hammer blows, but also because of mutual friction of particles against each other and against the mill walls under the action of an air flow created by the hammers.
Diameter of the disc with hammers is hammer mills is 1500 mm, the rotation frequency varies from 500 to 800 rpm for large and 1000 to 2500 rpm for small hammer mills.
The grinding degree in hammer mills is usually 10 to 15 when interim grinding is used and 30 to 40 in case of fine grinding.
Hammer mill grinder
A hammer mill grinder consists of a drum cylinder (casing) with a frame, a rotor, classifier, support and thrust bearings, pin flexible coupling, and an electric motor.
The material intended for grinding is loaded tangentially into the mill.
Fine grinding (secondary grinding) is achieved by the repeated impact of beaters on the entered raw material. The material is pressed against the body armor of the grinding unit. That is how the feed material gets pulverized inside of the hammer tangential mill. Also, the material is grinded inside of the grinder while migrating in the clearance between the body armor of the hammer tangential mill and its rotor.
The grinded material gets unloaded from the grinding chamber into a separator where oversized lumps are separated and, thereafter, return back into the grinder until the desired product comes out.
The grinded and dried material is unloaded from the grinder with a dust-air flow into the dust-laying system.
Hammer tangential mills
Hammer tangential mills are designed for fine grinding with simultaneous drying of medium hardness and soft materials (coal grinding and drying, gypsum grinding and drying, dolomite paste grinding and drying, talc grinding and drying, shell stone grinding and drying, kaolin grinding and drying, etc.).
A hammer tangential mill consists of a drum casing with a frame, rotor, classifier, support and combined support and thrust bearings, pin flexible coupling, and an electric motor.
The raw material for grinding is loaded into the hammer tangential mill tangentially.
Fine grinding is achieved by the repeated impact of beaters on the entered raw material. The material gets pressed against the body armor of this fine grinder and gets pulverized. Also, the material gets grinded inside of the hammer tangential mill while floating inside of the clearance between the body armor of the grinding unit and the rotating rotor of the grinding unit.
The Samara Strommashina plant manufactures separator hammer mills designed for fine grinding and simultaneous drying of medium-strength materials and soft materials (gypsum, dolomite powder, talcum, shell stone, kaolin, etc.).
A distinctive feature of the mill is intensive forced ventilation combined with increased circumferential rotor speed which ensures high grinding quality and good drying.
Specialists of our plant are always available to provide all necessary services for selection, designing and installation of hammer mills.