Countersinks and compression factor
Total thickness and effective thickness
Total thickness is one of main flat die parameters and it's value should be determined in product specification. Among small flat dies with diameter up to 350mm, there is possibility of using both of their surfaces as a working surfaces, which highly extends flat die operation time. To achieve this, countersinks must be present on both sides of flat die holes. In this case, countersinks works also as a hole relief. For large industrial dies with diameter 400mm and more using both side countersinks is impossible, because due to die thickness required to for proper die durability, we need to use long relief holes to avoid material from being stuck in holes.
Total thickness of double-side flat dies is a sum of effective thickness and relief length, which has the same size as countersink. For one-side flat dies total thickness contains effective thickness and custom hole relief length. In all other cases, total flat die thickness is equal to effective thickness.
At the first stage of pelleting process in pellet mill raw material is compressed by pressing them through countersinks placed on inlets of holes. Countersink size type are selected to all raw materials independently. In our production, we use proper countersinks for pelleting coniferous sawdust (spruce, fir), soft sawdust (pine), hard sawdust (oak, beech), wood chips, bran, straw (cereal straw, rape straw), cereal, maize, sunflower, manure and other. Even small differences in composition of pelleted material, can have a large influence on quality of the final product. Thus choosing proper countersink should be based on the composition of raw material.
Countersink angle and length are two basic parameters describing the countersink. For larger angle and length, more material is compressed at the same time which results in higher efficiency and power consumption. Smaller countersinks can have a negative influence on quality of final product. Proper countersink selection is usually based on experience and preceded by many tests and analyses.
When flat die thickness based on required durability is larger than optimal working length, holes reliefs must be used. For small flat dies relief holes are usually redundant, and double-sides die can be used. Holes reliefs have usually shape of tapper, but straight or stepped holes reliefs can be used.