Determination center of percussion for hammer mill hammers

Herbaceous biomass potential is considered as a valuable local renewable energy resource in Latvia.Cereal crop straw (mainly wheat straw), common reeds, rape straw and reed canary grass are the most prospective stalk materials for solid biofuel production.The main biomass conditioning operation in solid biofuel production technology is shredding.Hammer mills are the essential equipment for this operation.Hammers and their articulation are rapidly wearing during hammer mill lifetime.It is recommended to design hammers so that collisions with biomass particles are applied in the hammer centre of percussion.Then the hammer articulation hole is less wearing, unbalance and vibration of the hammer mill rotor are avoided.The main objective of this paper is to determine compliance with this rule for different size rectangular style manufactured hammers.Calculations were made using the Mathcad program for four different size hammers.Only for one size hammer positioning of articulation partly accomplished the mentioned recommended condition of the hammer centre of percussion.The recommended positions and sizes of articulation holes were determined for the mentioned four size hammers.If the hammer design accomplishes the recommended condition of the hammer centre of percussion, it is possible for collisions with particles during milling in different points of the hammer.Then some impact forces in the hammer articulation hole will appear.Therefore, it can be concluded that, if the centre of percussion is designed at the end part of the hammer, the impact forces in hammer articulation would be minimized.The results of calculation in compliance of four sizes of manufactured hammers with the condition of the centre of percussion at the end point of the hammer show that only one hammer size partly satisfies this condition.This shows that the hammer mill hammer design so that interaction between the hammer and material occur at the percussion centre of the hammer is still actual.The sizes of articulation holes have to be also calculated in accordance with the pin shaft strength conditions.Changing the size of the articulation holes the articulation position must be changed.