Generally, the following factors determine the pellet die design:
1. Metals
Pellet dies are made of metals, which determines the features and working life of pellet dies. Generally, pellet dies are usually made of the following metals, such as alloy, stainless steel, and "Chrome-Plus"stainless steel, etc.
Alloy pellet die is satisfactory for pelletizing common feed stocks. However when the corrosive materials, the stainless steel pellet die may perform better.
Stainless steel contented chromium can provide better resistance to corrosion, pitting and scoring and die hole enlargement.
Pellet die made of “ Chrome-Plus” stainless steel is usually a choice for pelletizing ingredients with strong abrasive or corrosive characters.
2. Inlet diameter and inlet angle
The inlet of die holes is countersunk into taper shape to let feed stock flow into die holes. The inlet angle is usually around 30o to 40o on small hole dies.
3. Thickness
Thickness wood pellet machine die is another factor needs to be considerate. The thickness of the die can be divided into total thickness and effective thickness. The total thickness of the die refers to the overall thickness of the die which is larger than the effective thickness which refers to the working thickness of the pellet die, which the pellets are molded. The die is stronger when the die is thicker. Commonly, pellet die thickness increments vary by 1/4” between 11/4” and 5” thick.
The thickness has a decisive influence on how the material flows through the die. If it is too deep, the biomass materials cannot get sufficient compression to form pellet. And on the contrary, if it is too shallow, the biomass materials will get the pellet machine die blocked easily and shorten the service life of wood pellet machines.
In the study of C.R. Stark on influence of die thickness to feed pellet quality and production rate, he pointed out that thickness of pellet dies has a positive effect on pellet quality and negative effect on the production rate.
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