What is Hammer Mill? – The Beginner’s Guide

Hammer Mill

What Do We Understand by a Hammer Mill?

A hammer mill is a machine that works for the purpose and unit operation of size reduction. The equipment accepts raw materials of significantly bigger sizes as feed, diminishing their dimensions by a considerable degree and extent. It does so by crushing and aggregating the solid substances and subjecting them to a series and continuation of repeated impacts and blows. In other words, a hammer mill initiates size reduction by the forces of impact and attrition.

A hammer mill comes with small “hammers” that deliver the required impact to reduce the size of the raw materials. These components can be of different and diverse kinds and types. They determine the size and shape of the end products. A hammer mill gets used primarily for food processing, chemical production, and pharmaceutical applications. Other than that, its industrial uses can consist of but do not remain limited to the following:

  • Ethanol plants
  • Milling grain
  • Coarse flour production
  • De-fiberizing of fruit pulp
  • Fruit juice making
  • Paper shredding
  • Large rock crushing
  • Waste management

How Does a Hammer Mill Operate?

The operation and working principle of a hammer mill are relatively straightforward. The machine consists of a steel drum having a horizontal or vertical rotating shaft. Numerous hammers break down and reduce the size of the raw materials or feed. They have substantial freedom of movement, allowing them to swing or move freely. It happens while they remain attached to the central rotor. 

The rotor of the hammer mill gets spun and operated at a significantly high speed. Simultaneously, the feed gets introduced and added to the steel drum gradually. They enter through the feed hopper at the top. Then, the raw materials feel the impact force generated by collision with the hammers. It allows for the shredding, crushing, and even grinding of solid substances. The final and required product passes through meshes of required and specified sizes that separate the unwanted and unnecessary broken pieces. 

A hammer mill can utilize three crushers to get the work done. It consists of the tertiary, secondary, and primary ones. The machine crushes and reduces the size of the raw materials in two stages that entail the following:

  • Firstly, the hammer mill initiates the size reduction process through dynamic impact.
  • Next, it continues the unit operation through the forces of shear and attrition. It occurs in a second zone or area where a small space exists between the mesh screen and the hammers. 

The size reduction using a hammer mill can get influenced and controlled by the following parameters or factors:

  • Rotor velocity or speed
  • Hit resistance
  • Feed rate
  • Mesh screen opening size
  • Clearance or gap between the grinding plates and the hammers

What are the Various Categories or Kinds of a Hammer Mill?

A hammer mill can get distinguished and differentiated into various categories or kinds depending on a few factors. 

For instance, a hammer mill can be of the reversible or non-reversible types. The classification gets done based on the direction in which the motor runs. Such sorts of machines may have varying constructions and structures. However, their fundamental operation and the working principle remain the same as any standard hammer mill. 

In addition to that, a hammer mill can be of the two following kinds based on the nature of the raw materials it works with:

  • Up-Running Hammer Mill

An up-running hammer mill utilizes grate bars or perforated screens to reduce the size of either hard or soft raw materials. The sort of substances used as feed determines how the rotor should get constructed. In that way, the component can get adjusted as and when necessary. 

  • Down-Running Hammer Mill

A down-running hammer mill is highly suitable for reducing the size of fibrous materials. It can get owed to the high concentrate and rate of shearing that the machine can provide. 

What are the Diverse Advantages of a Hammer Mill?

A hammer mill comes with several points of benefits that make the entire size reduction process convenient, effortless, and less taxing. A few advantages that the machine provides consist of the following:

  • A hammer mill can produce the specified size of the top. It can do so without a closed-circuit system of crushing. 
  • The machine has a high capacity and reduction ratio. It stands true, irrespective of the grinding action it performs. It can be tertiary, secondary, or primary. 
  • A hammer mill has a compact footprint. It implies that the equipment does not take up and consume a significant amount of storage space. 
  • The machine does not need to consume and use up a considerable amount of power or energy. It can work and operate with minimal resources. 
  • A hammer mill is relatively effortless to install and use. It stands true, even for amateurs. Furthermore, it has an undemanding cleaning and maintenance process. 
  • The machine has a continuous operation. It means that the equipment would continue to work and function as long as it gets supplied with feed or raw materials. In addition, it requires minimal human interference while it runs. 
  • A hammer mill can work for and with different and diverse raw materials. The feed nature does not get restricted to a few kinds. 

What are a Few Disadvantages of a Hammer Mill?

A hammer mill has its fair share of cons, as is always the case with all machines. A few of its disadvantages entail the following points:

  • A hammer mill is not suitable for reducing the size of abrasive or exceedingly hard raw materials. It cannot grind such substances due to the effects and influences of excessive wear. 
  • The machine must get operated with a carefully-controlled feed rate. Otherwise, it can choke the equipment and result in its damage. In addition, the mesh screen can get clogged in some cases. 
  • A hammer mill cannot work with plastic-like or sticky substances having a low melting point. It is due to the heat generated inside the machine. Otherwise, such materials can melt and lead to mill fouling.