flat die and ring die pellet mills comparison

Flat die pellet mill and ring die pellet mill are the two types of pellets mills in the market. What are the differences of the two types of pellet mills? Let us learn on the features of flat die pellet mills and ring die pellet mills first.

Working principle of flat die pellet mill

The flat die pellet mill was the first pellet mill design at the turn of the 20th century based on flat dies. Generally, there are two types of flat die pellet mills in the market, the rotating die type and the rotating roller type. The former one has a stationary roller with the rotating die while the latter has a stationary die with a rotating roller. Adopting vertical principle, the raw materials drops down by the its own weight into the pelletizing chamber where they are compressed between the rollers and die to form pellets by going through the die holes.
 

 

Advantage and disadvantages of flat die pellet mills are as following:

• Flat die pellet mills are small in size and light in weight because of the compacted structure design.
• Flat die pellet mils are easier to be cleaned and maintained and cheaper because of the design of portable rollers and die.
• Flat die pellet mils are more convenient for you to monitor the process of pelletizing by watching the pelletizing chamber which make the experiment of indeterminate materials for raw materials expansion easier.
• The disadvantages of pellet mills are they are not suitable for large scale pellet production. And also the gap between the roller and the die is tricky which should be adjustable according to the species of the raw materials especially the hardness of the raw materials.

All in all, the flat die pellet mills are usually used to process materials with large adhesive force for both fuel pellets and feed pellets in small scale and medium scale pellet production. They are known for the features, such as, reliable operation, greater mobility, low noise, low energy consumption and relatively low productivity, comparing with ring die pellet mills.
 

Working principle of ring die pellet mill

The ring die pellet mills were designed at around the 1930’s based on the design of ring die. The basic pelleting principle of the ring die pellet mill is a simple operation where feed mass is distributed over the inner surface of a rotating, perforated die ahead of each roll, which compress the feed mass and compress it into the die holes to form pellets.

Advantage and disadvantages of ring die pellet mills are as following:

• Ring die pellet mills generate less wear and tear because the inner and outer edges of the rollers traverse the same distance.
• Ring die pellet mills are more energy efficient than that of the flat die pellet mills.
• One problem of the ring die pellet mills is side slip. Side slip is one undisputable and unavoidable fact on ring die pellet mill. It refers to having feed mash squeezed out sidewise from the nip between the roller and dies, which can be minimized, depending on the die configuration. One way to do this is to counter bore or drill larger hole in the two outer rows of the die so as to reduce the friction caused in the holes.

In one word, the ring die pellet mills also can be used to produce fuel and feed pellets. However, compared with the plat die pellet mills, the ring die pellet mills are well known for their large capacity for pellet production. They are featured as large capacity, with nice pellet forming shape and high density and high energy consumption.
 

General comparison of the flat die and ring die pellet mills

Besides, the flat die pellet mills and the ring die pellet mills are different in the following ways:

1. Price: The flat die pellet mill is far cheaper than that of the ring die pellet mills.

2. Capacity: The output capability of the flat die pellet mill ranges from around 80 to 1000 kg /h at most while the ring die pellet mill can produce around 0.8 to 2 t/h at most.

3. Feeding: The feeding of the flat die pellet mills relies on materials weight and the feed stock enters into the pelleting room directly and evenly. While the feeding of ring die pellet mills is forced into the pelleting chamber and distributed by the high speed rotary scrapers.

4. Pressure: The pressure of flat die pellet mills is adjustable. The diameter of rollers in the flat pellet mill is not restricted by the diameter of the pellet die so that the roller pressure can be increased by enlarging the inside bearing space, adopting a big bearing which also expands the working life. While as for the ring die pellet mill, the pressure of the pinch roller is limited because the diameter of the rollers are limited by the diameter of the pellet die.

5. Discharging: The percentage of damage of flat die pellet mill is lower than that of ring die pellet mills because of the high rotary speed of the ring die.

6. Pellets formation: The flat die type have a circular perforated disk on which two or more rollers rotate and force the material through the holes to form pellets. The ring die press features a rotating perforated ring on which rollers (normally two or three) press on the material to the inner perimeter to form pellets.

Though the comparison, the features of the two different pellet mills are obvious. When purchasing the pellet mills, it is better to consider the all around situation of your pellet production and find the suitable pellet mill.

Flat die pellet mill or ring die pellet mill?