Ring Die Pellet Mill Parts Wearing

Pellet mill is the key equipment for pelletizing technology, and the ring die is the heart part of pelletizing, which are one of the easiest wearing part of wood pellet machine. Researching the reasons for the failure of ring die and improving the service condition has great influence to the production quantity and quality, to reduce the power consumption and production cost etc.

In theory, a common ring die and a pair of common compression rollers could only produce about 2000t and 500 t pellets separately. Practically, the well managed manufacture could only produce over 1000t and 250t. While for the manufacture with bad management, it only produce 500-600t and 80-100t, then the new ring die and compression rollers need to be replaced. From the above, we come to realize that lengthening the service life of ring die bring considerable benefits to the manufacture.

1. Working principle

The ring die is rotating under the driving of the motor through speed reducer, and the compression roller dose not in revolution in the ring die, but it rotates under the friction force with the rotating ring die. When different powdery materials enter into the compression zone between the active rotating ring die and driving rotating compression rollers, the materials has certain looseness with the big or small inside holes. At the same time, the materials are driven and compressed by the rotating ring die. When the pressure is up to the standard, the material is up to the setting density. The high density materials enter into the crushing zone from the compressing zone. Due to the relative mechanical interlocking between the particles, the contacting surface between the particles is increasing. Due to the materials own features and the cohesiveness after conditioning, it ensures that the materials in the ring die for a period of pressure maintaining. When the density and durability is up to a standard, the pellets are compressed out from the ring die holes, and cut into the required length.

During the normal operation of ring die, friction force always exist the between ring die and materials. As the increasing of the material production, the ring die is wearing and loses effectiveness at last. So the standard of measuring the ability of ring die is production amount. During the practical producing, most ring die lose their effectiveness before the theoretical production ability. Because the ring die is high is price, it leads to a certain loss for the users. This article is going to analysis the reasons for the loss of effectiveness of ring die and give some advice to the manufacturing and using of ring die.

2. The reason for the loss of effectiveness

From the situation of losing effectiveness of ring die for wood pellet plant, it can be classified into three types. The first one is that the inner wall of small discharging hole is wearing with increasing, and the pellets produced by the pellet mill are out of the limited scope. The second type is the inner surface of the holes is sags and crests which blocked the flowing of the materials and the production is lower or for stopping using. The third is the wearing diameter is enlarged and the thickness is lower. At the same time, the inner wall of ring die hole is wearing, that the ring die surface between the holes is thinner, so the density of structure is lowered. When the diameter is beyond the limited scope (before the first situation happed), the cracking is emerged on the most dangerous section and enlarges increasingly, until the ring die loss efficiency out of the beyond the scope. The reason for the three situations of losing efficiency is basically concluded with the wearing at first, and the second is fatigue.