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Introduction to the Ring Die of Pellet Machine

Date: 06/10/2020 09:26:37 From: wood-pellet-plant.com Clicks:

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The ring die is one of the indispensable accessories on the biomass pellet machine. Without the ring die, it cannot be compressed into pellets. It is the last and important step of pellet molding. For the industrial pellet plants, ring die pellet mill is the core machine of the complete wood pellet processing line. The name “ring die pellet mill” is named after its die shape. To get to know the knowledge of features of pellet mill ring die is significantly important for the pellet makers. It can help them choose suitable ring die pellet mill, use it properly and maintain it effectively.

Ring Die of Pellet Machine
Ring Die of Pellet Machine

THE DESIGN OF PELLET MILL RING DIE

Reasonable Parameters of Pellet Mill Ring Die

1. The Diameter of Effective Width of Ring Die

According to the different parameters and series of preferred numbers of ring die pellet mills from both home and abroad, the suitable diameters of ring die are 250mm, 300mm, 320mm, 350mm, 400mm, 420mm, 508mm, 558mm, 678mm, 768mm. And the power for ring die pellet mills with different diameters should be 15kw, 22kw, 37kw, 55kw, 75/90kw, 90/110kw, 132/160kw, 180/200kw, 220/250kw, 280/315kw. Then we can determine the effective width of the ring die (the width of the contact segment of the ring die central part and rollers) based on the ratio of the compression area and the equal power (normally, the ratio is between 14 and 22 cm²/kw).

2. The Rotate Speed of Ring Die

The rotate speed of ring die is related to the geometric parameters of the ring die pellet mill. According to all the existing documents and years datawatch of the technical parameters of both domestic and foreign ring die pellet mills, the linear velocity of ring die inside radius should be 4 – 8m/s for the ring die pellet mills with two rollers. The linear velocity strongly effect the time for the raw materials passing the die holes. Therefore, it can definitely effect the pellet mill capacity and pellet quality. If the linear velocity is too high, the ring die pellet mill produce less pellets under the same production conditions. Moreover, a high linear velocity makes the material layers thinner, and dispatch the materials unevenly, so the wood pellet density is too low. If the linear velocity is too low, although it can produce wood pellet with excellent wood pellet, but the pellet mill capacity is also very low, which will strongly increase the cost of production.

The Rotate Speed of Ring Die
The Rotate Speed of Ring Die

3. The Diameter of Rollers

The working principle of ring die pellet mill is using the extrusion force between the ring die and the rollers to make the materials pass through the die holes, which uniformed the material into high density wood pellets. If we use the same ring die, when the diameter of the rollers increase, the compression area between the ring die and the rollers increase too.

Theoretically speaking, for the pellet mill with single roller, the larger the diameter of the roller is, the better pellet it will make. But the capacity of the single roller ring die pellet mill cannot satisfy the industrial wood pellet production. For large scale wood pellet production, the double roller ring die pellet mill shows a better performance. For the ring die pellet mill with two rollers, the ratio of the roller outer diameter and the ring die inner diameter is 0.475 based on the existing documents, and then we can determine the diameter of the rollers.

Suitable Material for Pellet Mill Ring Die

After the determination of the size of the ring die, we should focus on choosing the suitable material to make the ring die. The material properties effect the intensity, abrasion performance and corrosion resistance of ring die directly.

There are three kinds of steel which has been used as the ring die material, carbon steel, alloy steel and stainless steel. According to Chinese Steel Standard, the main carbon steel is 45 steel, its hardness during heat treatment is HRC45 – 50, its abrasion resistance and corrosion resistance is not enough for ring die. The main alloy steel is 20CrMnTi, it has been heating treated such as case carburization, so its hardness is above HRC50, and has good mechanical property. The ring die made by 20CrMnTi shows a high intensity and abrasion resistance performance, but its corrosion resistance performance is poor. Although, the cost of alloy steel ring die is lower than stainless steel ring die, but during pellet production, its poor corrosion resistance performance will decrease the working life of the ring die, you have to change the ring die frequently, which makes the actually ring die cost higher than stainless steel ring die. The main stainless steel is 4Cr13, its has good rigidity and tenacity. Its heat treatment adopts the whole heating quenching technology, the hardness is more than HRC50. Moreover, it has good abrasion resistance and corrosion resistance performance, which enhance the working life of ring dies and make 4Cr13 stainless steel the most cost effective material to make ring dies.

Suitable Material for Pellet Mill Ring Die
Suitable Material for Pellet Mill Ring Die

THE FEATURES OF PELLET MILL RING DIE

Pellet Mill Ring Die Material and Heat Treatment

There are three kinds of steel which has been used to produce pellet mill ring dies, carbon structure steel, alloy steel, and stainless steel. After heat treatment, the rigidity of carbon structure steel is normally HRC45-50, the abrasive resistance and corrosion resistance performance are poor, which has been used to produce low-end pellet mill ring dies. The rigidity of alloy steel is over HRC50 after the heat treatment. Alloy steel has good combined mechanical properties, the pellet mill ring dies made by alloy steel has high intensity and good abrasive resistance performance. But the disadvantage of alloy steel pellet mill ring die is also severe, the alloy steel ring die has poor corrosion resistance performance. Stainless steel has excellent rigidity and tenacity, the rigidity of stainless steel is above HRC50. The abrasive resistance and corrosion resistance performance of stainless steel are also very good. Therefore, the working life of stainless steel ring die is longer than other kinds of pellet mill ring dies.

Pellet Mill Ring Die Pore Structure, Compression Ratio and Roughness

The common die hole shapes of pellet mill ring die are straight cylindrical holes, ladder shaped holes, external cone shaped holes, internal cone shaped holes and so on. The ladder shaped holes can be divided into release type ladder shaped holes (also known as pressure relief holes) and compression type ladder shaped holes. Different types of die holes are used to produce different kinds of pellet products.

The compression ratio of pellet mill ring die is the specific value of the effective length and minimum diameter of the die holes of ring die, it is a important indicator to determine the pellet mill extruding strength. The larger the compression ratio is, the stronger pellet the machine will produce.

Pellet Mill Ring Die Pore Structure, Compression Ratio and Roughness
Pellet Mill Ring Die Pore Structure, Compression Ratio and Roughness

For the compression ratio of ring die with straight cylindrical die hole, the effective length of die hole is the thickness of the ring die, the minimum diameter of die hole is the same with the diameter of the die hole. For the compression ratio of ring die with release type ladder shaped die holes and external cone shaped holes, the effective length of die hole is the thickness of the ring die minus the length of the release hole, the minimum diameter is the diameter of the smaller part of the die hole. For the compression ratio of ring die with compression type ladder shaped holes and internal cone shaped holes, we will use the ring die thickness as the effective length of the die hole, and the diameter of the smaller part of the die hole as the minimum diameter. But the compression ratio which is calculate by the above data has a different meaning compare to other ring die compression ratios.

Roughness is an important indicator of the ring die quality. Under the same compression ratio, the larger the roughness value is, the obstruction of the extrusion process is larger, which makes it harder to discharge pellets. Also, the excessive roughness will effect the quality of the surface of wood pellets. The proper roughness value is between 0.8 and 1.6.

Ring Die Working Area, Die Hole Arrangement and Ring Die Porosity

Ring die working area means the product of the perimeter of internal diameter and the effective width of the ring die.

During the drilling, the die holes are arranged circumferentially, and the neighbouring two rows of die holes must be staggered.

Ring die porosity is based on the die hole diameter and the wall thickness between two die holes. Therefore, under the same diameter of die holes, we must decrease the wall thickness between two die holes in order to increase the ring die porosity. But the minimum wall thickness must be able to endure the needs of the intensity of the ring die. The larger the diameter of die hole is, the higher porosity the ring die will get.

Ring Die Linear Velocity

Ring die linear velocity is the tangent speed of internal circle of the ring die. The value of ring die linear velocity effects the thickness of the raw materials in the press chamber and the time for the materials to pass the die holes. Therefore, it can effect the capacity of the ring die pellet mill and the wood pellet quality. If the linear velocity is too high, there may be a fault of the materials in the press chamber. So the produced wood pellets are soft and fragile. If the raw materials have higher moisture content, it may cause the breakdown of the pellet mill. If the linear velocity is too low, it can produce high quality wood pellet, but the pellet plant capacity will be extremely low, which can not match the need of industrial scale wood pellet production. The common ring die linear velocity is between 6-9m/s.

THE UTILIZATION OF PELLET MILL RING DIE

Pellet Mill Ring Die Options

According to the features of pellet mill ring die, there are multiple factors needed to consider when we try to choose a ring die. But in actual working situation, some factors are pre-designed, such as the installation method of ring die, ring die linear velocity, and ring die working area, etc. These factors has been determined when we make the purchase. Some other factors can be controlled by choosing the professional ring die pellet mill manufacturers, such as the ring die materials, heat treatment intensity and abrasive resistance, die hole porosity and roughness, etc. Generally speaking, The pellet mill ring dies that are produced by professional ring die pellet mill manufacturers can reach the performance requirements of industrial wood pellet production. Because many of the procedures require professional equipment, such as the manufacture of the die hole and the ring die heat treatment, the quality of these manufacture process must be ensured by professional gun-drill and vacuum heat treatment equipment, common drill machine and heat treatment method can not produce high quality ring dies.

Pellet Mill Ring Die Installation

There are three pellet mill ring die installation methods, straight sided installation, conical sided installation, holt hoop installation. It is easy to install ring dies use the straight sided installation method. Straight sided installation makes the ring die steady, the ring die is not easy to tip. But the fixing bolt of the ring die is easy to break, so it is not suitable for industrial ring die pellet mill. Conical sided installation makes the ring die maintain perfect centering performance and great transmission torque. The fixing bolt of ring die installed by conical sided installation method is not easy to break, but using conical sided installation method, the installer must have some certain techniques and be very careful. Otherwise, the ring die may be tiptilted during installation. Holt hoop installation is suitable for small pellet mill ring die installation. This method need short install period. But the disadvantage is that the holt hoop installed ring die can not be turn-over, you can only use one side of the ring die.

Pellet Mill Ring Die Installation
Pellet Mill Ring Die Installation

Pellet Mill Ring Die Utilization

The key of using pellet mill ring die is to adjust the space between ring die and rollers properly. The proper space between pellet mill ring die and rollers is between 0.1-0.3mm. Normally, there is bigger space between new ring die and new rollers, and smaller space between used ring die and used rollers. Moreover, ring die with large die holes needs bigger working space, and ring die with small die holes needs little working space. For the operators, it requires actual operate experiences to adjust the working space between ring die and rollers masterly.

Also, there are several other matters that need to be paid attention to: firstly, before we start the pellet mill with a new ring die, the ring die must be cleaned by oil, in order to remove the burrs on die holes. Normally, new ring dies need to be cleaned no more than half an hour. If the new ring die has poor roughness, sometimes, we can mixed 20%-50% fine sand in the oil to clean the ring die. Secondly, during the pellet mill working period, we must avoid using raw materials with hard particles such as sand, stone, metal particles, small bolt, scrap iron, etc. Thirdly, for the ring dies that have been installed symmetrically, we can turn it over after a certain working period, in order to maintain the ring dies wear evenly. Fourthly, the ring die must not be tipped after the installation. Otherwise, the evenness of the ring die abrasion can not be guaranteed. And the bolt to fasten the ring die must maintain certain seating torque, in order to avoid bolt breakdown during the pellet mill working process.

Pellet Mill Ring Die Maintenance

It is a necessary step to ensure the ring die operation performance and extend the serve life of ring dies. There are several tips to maintain ring dies when using a ring die pellet mill.

Firstly, when we change a ring die, we should extrude out the residual materials with non-corrosive oil. Therefore, when we use the ring die again, it can discharge wood pellet smoothly, and also, it can prevent the die hole from corrosion. Secondly, after using the ring die for a certain time, we have to check the wear patterns of the ring die. Thirdly, if the majority of the die holes have been blocked, we can soak or cook the ring die by oil to soften the material. Fourthly, ring dies must be stocked in a dry and clean place. Wet environment may cause the corrosion of ring dies which reduce the ring die serve life.

The above is the article for you: Introduction to the Ring Die of Pellet Machine. If you are interested in our products or project solutions, please contact us. We will give you the best product quality and the best price. Email: sales@cnrichi.cn

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