The Working Principle of Hammer Mills (Step-by-step Guide)
A hammer mill is an essential machine in the pharmaceutical and food processing industries. You can use it to crush, pulverize, shred, grind and reduce material to suitable sizes.
Even though there are many types of hammer mills, the working principle is still the same. You will learn about it shortly.
First, let’s have a quick over view of a pharmaceutical hammer mill. Below is an image showing a fully assembled equipment:
From above, you can see that this hammer mill has five main parts. Normally, the number of parts may vary depending on the complexity of the machine design.
Every part/component you see in the image above plays an integral role in the overall working principle of hammer mills. However, the milling process mainly takes place in the crushing chamber (part 3).
The working principle of a hammer mill is based on a simple mechanism. However, before I explain how the entire process works, let’s review some fundamental aspects of a hammer mill.
Fundamental Aspects of Hammer Mills
Below are crucial aspects of a hammer mill:
· Feeding mechanism
This refers to the process by which particles enter the crushing chamber. Depending on the design of the hammer mill machine, it may use gravity or a metered feeding system.
Feeding section of a hammer mill
Metered feeding systems are common in applications where product uniformity is a major concern. They eliminate all possible variables that may cause output product inconsistencies.
A good example in this case is the pneumatic rotary valve found between the feeding hopper and the crushing chamber.
In the gravity feeding system, the milling machines solely depend on the gravitational force. It is this force that helps to feed particles into the crushing chamber.
· Control box
Users can switch ON/OFF the machine from the control box. The complexity of the control box will depend on the unique design of the milling machine.
A hammer mill control box
For instance, you may control the feeding system or motor speed. Some pharmaceutical milling machines come with a display panel where users can monitor all processes.
· Crushing knives or hammers
These are the fundamental tools that crush or grind materials. They rotate at a high speed that may vary from 2,500 to 60,000 rpm.
A section of the hammer mill
In most cases, these hammers are mounted on horizontal shafts where, they may rotate either clockwise or anti-clockwise. This may depend on the direction of the rotor rotation.
A rotor is the rotating shaft coupled to an electric motor. The hammers come in different styles and shapes.
Hammer mill’s crushing tools may be coupled directly to a motor or driven by a belt. As opposed to direct connection, the belts can cushion the motor from shock and allows for accurate speed adjustment.
· Type of hammer mill screens
The output of a pharmaceutical hammer mill varies broadly. Normally, the size of the particles will depend on the screen variation.
Different types of hammer mill screens
These hammer mills may have over 12 different types of screen meshes. They are nicely arranged within the crushing chamber.
Depending on their arrangement, they can achieve a precision of 0 to 200.
How a Hammer Mill Works
In case you’re new to hammer mills in pharmaceutical and food processing industries, here are three crucial steps that will help you understand how this equipment works. Before that, you can watch this video to see how hammer mills work:
As you can see in the video, materials that enter the systems are reduced to very small particle. Of course this is due to the rotating blades.
i. Introducing material through the feed hopper
Choose materials with suitable and physical properties that have been cut to the right size. Place all your materials in the section labelled “1” above.
Depending on the design of the hammer mill. They will move into the crushing chamber either by gravity or controlled/metered process.
ii. In the crushing chamber
The ganged hammers or chopping knives hit the material severally. Theses knives or hammers rotate at a high speed reducing materials to a desired size.
Only particles whose diameter conform to that of the screen size will pass through. Otherwise, the hammer will continue to hit these materials until they are reduced to the required size.
Basically, within this chamber, the material is hit by a repeated combination of knives/hammer impact and collision with the wall of the milling chamber. Moreover, collision between particles to particles play an instrumental role in this size reduction process.
In short, this a mechanical process where particles are hit with high speed knives. Therefore, you need to wear all the necessary safety gears.
Again, don’t open the crushing chamber when the machine is operating. This is because you may be hit by particles flying at very high speed or crushing hammers/knives.
iii. Output of the milling chamber
The output of the milling chamber has perforated metal screens. They are also referred to as the bar gates.
Depending on the size and design of the metal screen, it allows the required size of particles to pass through while retaining coarse material.
The material that passes through is basically the finished product. It can either be packed using capsule filling machines or processed further depending on the specific requirements.
Now that you know the working principle of hammer mills, let’s explore the basic factors that determine the type of the final product.
Factors that Determine the Type of Hammer Mill Output
Basically, there are three aspects that determine the particle size of a hammer mill. These include:
- Hammer or cutting knife configuration
- Shaft speed (it depends on motor speed and coupling mechanism).
- Screen size
In most cases, the mechanical process of reducing large size particles into small particle may result in a fine or coarse finish. How is then is this possible when you use the same pharmaceutical hammer mill equipment?
First, to get a fine finish particle size, you should consider the following key aspects:
- A fast rotating rotor speed
- Small screen size
- Large or/and more crushing knives/hammers
Second, in case you need a coarse finished output, it is important to consider the following key aspects:
- Few or/and small crushing hammers/knives
- Slow rotor speed
- Large screen
Another crucial aspect to consider when examining the working principle of hammer mills is the production capacity.
Factors Determining the Capacity of Hammer Mills
There are many factors that determine the overall capacity of hammer mills. These critical aspects include the following:
- Characteristics of materials to be crushed
- Nature or type of the crushing hammers or knives
- Number of rows of crushing hammers or knives
- Feed size
By knowing the working principle of hammer mills and various aspects that determine production, your equipment will definitely operate optimally.
Clearly, the working principle of hammer mill is simple to understand. It only requires choosing an appropriate motor, crushing hammers/knives and material you intend to crush.