mineral processing industries
mineral processing industries or mills :
Milling, sometimes also known as the fine grinding, pulverising or the comminution, is the process of reducing materials to a powder of fine or fine size. It is distinct from crushing or granulation, that involves size reduction to rock, pebble or grain size. Milling is used to produce a variety of materials which either have end uses themselves or are raw materials or additives used in the manufacture of other products.
A wide range of mills has been developed for particular applications. Some types of mills may be used to grind a large variety of materials whereas others are used for certain specific grinding requirements. The brief aims to present factors to consider when choosing a particular grinding applications and to give an overview of the equipment which is available.
Material grinding is quite often an integral part of the industrial process, whether carried out on large or small scale and in some cases the grinding mill may be the single most costly item for t production operation. Installing grinding mill which is suitable for the purpose would be one of the main requirements for cost-effective and trouble-free material processing if a grinding stage is involved.
Material Characteristics :
When a material is to be milled there are certain characteristics which have to be taken into the account. These include following
• Softening and melting temperature
• Structure (e.g. close grained or cellular)
• Specific gravity
• Free moisture content
• Chemical stability
Types of mills :
In this brief we can categorise mills in 3 groups:
1. Low-speed tumbling mills
2. Roller mills
3. Very fine grinding mills, which include the following types of mill:
• High speed pulveriser or hammer mill
• The vibrating mill
• Pin mill
• Turbo mill
• Fluid energy mill
• Stirred media mill
There is also a section which looks at traditional mills used in developing countries and other forms of size reduction other than milling:
• Attrition mills e.g. stone milling
• Cutting machines
• Cryogenic communication
Rod Mills :
The rod mill is another tumbling mill but having a large percentage of its volume (30 – 40%) loaded with the steel rods.Rods are placed axially in the mill and are loose and free to move within mill. Internal lining of the drum has a series of lifters which raise the rods and drop them at predetermined point. Mineral is fed in at one end with a maximum size of about the 25mm. Rods crush the rock and as the charge passes through the mill it is reduced in size to approximately from 2mm to 0.1mm.. The mill may be fed from one end with the product removed from the other end or the alternatively, mill may be fed from both ends with the discharge at centre. Process may be wet or dry but is more commonly carried out wet. Maximum rod length is about from 6 -7 metres, there is a risk of the rods bowing. The drum diameter is limited to 0.6 / 0.7 times the length of the mill.
Q1: How to reduce cost of the mineral processing industries ?
Ans: Operating Costs Reduces by :
• Mechanism designed to give the maximum bubble particle contact for the improved coarse and fine particle recovery.
• Impellers and the diffusers are supplied in high abrasionresistant elastomers or the molded polyurethane.
• Impeller profile is designed to minimizethe the absorbed power.
Q2: What is mineral processing industries?
Ans: Hammer mills :
These are high-speed mills operating at speeds of between 2000 and 6000 rpm A set of ‘hammers’ rotate about a central axis in vertical or a horizontal plane. Hmmers can either be fixed or may swing freely, in that case mill is termed swing-hammer mill. The whole system is enclosed in a housing and the outlet for the product is usually via a screen which sieves the product and allows only the required size of particle to pass.
Q3: Write the typical installation of mineral processing industries?
Ans: Typical installations:
The Mill Scale treatment in the Continuous Casting, Hot Rolling and Scarfing. For the industrial dewatering applications settling areas
from 8 m2 – 200 m2
Flow Rates up to 1 500 m3/h.
Q4: explain Roller Mills:
Ans: Roller Mills :
There are two distinct type of roller mill. The first is a series of rollers which rotate around a central axis within a drum. The reduction takes place between the rollers and the drum. The second is where there are a series of fixed rollers and a rotating table. The milling takes place between the rollers and the table. This type of mill is used for dry grinding only and accepts relatively soft minerals. Small machines can have a throughput of only a few tens of kg per hour whereas larger machines are capable of handling up to 40 or 50 tons per hour and it occasionally more. Feed size varies according to machine. Machines are often fitted with screens for the closed circuit grinding.The Product size may be controlled by changing screens.
Q5:What is tube press?
Ans: The Tube Press is a membrane type filter press designed in the cylindrical format and the capable of
operating at high filtration pressures up to the 100 bars