Choosing and maintaining of ring die for wood pellet mill

Wood pellet mill is the key equipment for making pellet, and ring dies are the biggest support of the operation of wood pellet mill. But ring die for wood pellet mill is the most easily wear parts of the wearing parts. So quality of ring die affects the quality of finished products and production of wood pellet mill. When the wood pellet mill make pellets, the mutual friction force between ring die and compress rollers overcome the resistance force that feedstock pass through the holes of ring die. Thus, the aim of making pellet is achieved. Below are the selecting, using and maintaining of ring die:

 

1. Selecting ring die for wood pellet mill

The ring die are usually made of carbon steel or stainless steel which produced through procedure forging, cutting, drilling, heating treatment and so on. The selecting material and each step of process affect the service life of the ring die, the quality of pellet and output directly. So, ring die produced from the large scale factory with perfect technology are the best choice when purchasing. If we choose a ring die from small factory with backwards technology randomly, it will cause the blockage of ring die, rough surface of the pellets and burst of die holes etc. According to information, most of the small factories operate the process of drilling the die holes by common drilling machine manually. Quality of the die holes depend on the attitude and skill level of the operators, which can not ensure the quality of the die holes, some of the holes are crooked. These kinds of ring dies are difficult to discharge material and are easy to block the machine. Polishing the die holes are important step during the later process of make ring die holes. Small factories are limited by the equipment and technology, polishing process is done by workers manually, some of the holes are usually omit to polish or the smoothness can not up to the standards. Ring die like this are difficult to discharge materials, or causing the rough surface of the pellet or blocked the machine. So choosing a standard ring die is very important.

 

2. Choosing the proper thickness of ring die for pellet mill

Choosing the proper thickness of ring die for pellet mill is an important step which ensures the production quality and output.  It has close relation with the compression ratio (compress ration=length of die hole/ diameter of hole). Ring die with high compression ratio produce the pellet with high density and smooth surface. On the contrary, the pellet has low density and loose surface, which are the main reasons for high ration of powder of finished products. If the compression ratio is too large, the ring die can no discharge material and even blocked the machine. Then what on earth is the appropriate compression ratio?It’s a flexible question which has nothing to do with die holes, diameter, material and so on. For example of our company, diameter of 3mm is fit for compression ratio of 12-12.5; diameter of 3.5mm is fit for 13; diameter of 4 is fit for 14. Comparing with the American CPM-3020 of pellet making machine, it is often 8～10t/h;10～12t/h;12～15t/h. The finished product has high density with smooth and shine surface.  As for the material which contains coarse fibers, the compression ration is fit for small compression ratio. 

 

3. Cooperation of compress roller and ring die for pellet mill

Whether the clearance between compress rollers and the ring die is proper or not affects the normal operation of pellet mill directly. The proper clearance between new ring die and compress roller is 0.1-0.3mm. Too larger clearance cause the inadequate extruding force which can not overcome the friction force which materials pass through the die holes, and the machine are blocked. Too small clearance causes the damage to the ring die and rollers. The tusk of adjustment is difficult to master, which need the operator’s long time practices and carefully improvement to master the skill. Then how to adjust the clearance? Some of the producers master a serious of skills of using ring die and rollers, that is, new ring die match to new roller, a pair of rollers match to a ring die regularly, cooperation between rollers and ring die should be loose at the front and tight at the back. (Because of the bed of material at the front are thicker than that at the back). In this way, it avoid new ring die work with the old roller or old ring die work with new roller, to prevent the poor cooperation between rollers and dies and to avoid the increasing wear of roller or ring die. Thus, the service time of roller and ring die are prolonged and the production cost is lowering. 

 

4. Basic maintenance of ring die for pellet mill

The using effect of a wood pellet mill is closely related with the fitted dies. During the using of wood pellet mill, maintenances and inspection of the fitted dies are vital important except for the maintenance of the equipment. Because the ring dies would have blockages, abrasive wear inevitably, even the tapered mouths of ring dies would deform plastically and become the necking during the production. As for this kind of ring die, if without necessary maintenance, it is bound to lower the production and increase the power consumption, even compressing without discharge materials and blocked the machine. Therefore, as long as the above phenomenon happens, it is necessary to maintain the ring die serially: drill the hole( drill through the holes which filled with iron scraps and has blocked holes), polish the ring die( polish the surface with irregularities which come from the iron scraps, iron ball, and hard objects contained in the materials), enlarge the holes( repair the shrinkage cavity, the angle of taper mouth is 60°). When replacing the ring die, the die holes should be stuffed with oily materials for the next use, to ensure the good performance of ring die.

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