Hammer Mill
Hammer mill also named hammer crusher, and crushes materials by the collision between the high-speed hammer and materials. The hammer crusher is used to crush mid-hardness and weak corrosive materials, whose compressive strength is under 100 Mpa, and water ratio is less than 15%. Hammer mill possesses qualities of simple structure, large reduction ratio, and high-efficiency. Both Dry and Wet Process are available.
This crusher is applicable for both dry and wet crushing. Hammer mill is widely used for medium or fine crushing for medium hard and brittle materials by departments of mine, cement, coal, building material, metallurgy, chemical industry, road construction, gas chemical industry and thermal power generation, etc. Coal gangue, coke, slag, limestone, phosphate rock, salt, whiting, gypsum stains, alum, brick and tile, etc. can be crushed by this equipment. The compression strength of the materials shall not exceed 100MPa, while the moisture content shall be lower than 15%.
Hammer mill working principle
In the feed processing process there may be a number of ingredients that require some form of processing. These feed ingredients include coarse cereal grains, corn which require particle size reduction which will improve the performance of the ingredient and increase the nutritive value. There are a many ways to achieve this particle size reduction, here we are looking at using hammer-mills, for information on roller mills, see the related links at the bottom of this page.
Both hammering and rolling can achieve the desired result of achieving adequately ground ingredients, but other factors also need to be looked at before choosing the suitable method to grind. Excessive size reduction can lead to wasted electrical energy, unnecessary wear on mechanical equipment and possible digestive problems in livestock and poultry. For more in depth information regarding what actually occurs to the ingredients during size reduction please refer to this link: particle size reduction.
Hammer mill advantages
We are able to produce a wide range of particle sizes
- work with any friable material and fibre
- ease of use
- lower initial investment when compared with a roller mill
- minimal maintenance needed
- particles produced using a hammermill will generally be spherical, with a surface that appears polished.
Hammer design and configuration
The design and placement of hammers is determined by operating parameters such as rotor speed, motor horsepower, and open area in the screen. Optimal hammer design and placement will provide maximum contact with the feed ingredient. Hammer mills in which the rotor speed is approximately 1,800 rpm, should be using hammers which are around 25cm (~ 10 inches) long, 6.35cm (~2.5 inches) wide, and 6.4mm (0.25 inches) thick. For a rotor speed of about 3,600 rpm, hammers should be 15 to 20 cm (~ 6-8 inches long, 5 cm (~ 2 inches) wide, and 6.4 mm (0.25 inches) thick.
The number of hammers used for a hammer mill of 1,800 rpm, should be 1 for every 2.5 to 3.5 horsepower, and for 3,600 rpm, one for every 1 to 2 horsepower. Hammers should be balanced and arranged on the rods so that they do not trail one another. The distance between hammer and screen should be 12 to 14 mm (~ 1/2 inch) for size reduction of cereal grains.
The velocity or tip speed of the hammers is critical for proper size reduction. Tip speed is the speed of the hammer at it's tip or edge furthest away from the rotor, and is calculated by multiplying the rotational speed of the drive source (shaft rpm) by the circumference of the hammer tip arc.
A common range of tip speeds seen in hammermills is commonly in the range between 5,000 and 7,000 m/min (~ 16,000 and 23,000 feet per minute). When the tip speeds exceed 23,000 feet per minute, careful consideration must be given to the design of the hammer mill, the materials used in its construction, and the fabrication of all the components. Simply changing the rotational speed of the drive source is not a recommended method of increasing hammer speed in excess of 23,000 feet per minute.
Impact is the primary force used in a hammermill. Anything which increases the chance of a collision between a hammer and a target; increases the magnitude of the collision; or improves material take-away provides an advantage in particle size reduction. The magnitude of the collisions can be escalated by increasing the speed of the hammers.
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