Pulp Grinders - Mechanical Pulp Production

Types of grinders

Chain grinders

Chain grinders are the most common type of grinder, the chamber between the vertical chains houses the logs ready to be processed. The logs are continuously driven by the chains onto the surface of the revolving pulp stone. The chains apply a force on the log keeping them against the surface of the stone. Due to the surface profile fibers are torn out of the wooden compound. The logs are stacked horizontally due to the orientation of the fibers (minimizes fiber damage - increases fiber length)

Water showers are used to keep the stone clean and dilute the stock suspension. Water temp is usually higher than 80 deg. using a low water temperature can cause the stone surface to crack (due to temperature difference). Using hot water allows the stone to maintain the high temperatures. these high temperatures affect the lignin of the wood softening the material which in turn means the fibers can be separated with less damage

The basin collects the pulp washed off by the water showers. typically this produces a low consistency pulp, a thickening stage is added after to bring the consistency to a more manageable level. 

Pocket grinder

The pocket grinder is a technological advancement of the chain grinder above. processing the logs within a sealed "pocket" allows the sealed area to operate at a higher atmospheric pressure than the pocket grinder.

At higher pressures (approx: 5 bar) the boiling effect of water is affected. the higher temperature of the water will soften the lignin within the logs, longer fibers can be created with less damage done to the fibers. 

Revolving pulp stone is surrounded with a metal housing and 4 pockets, feeding of the pocket grinder was done manually. The debarked logs are pushed against the revolving surface of the pulp stone by hydraulically driven pistons. The pulp is collected underneath the pulp stone.  

 

The entire process of feeding the logs to the groundwood outlet is done under pressure. (up to 5 bar housing pressure, shower water temp up to app 120 deg) pressure affects the boiling temp of water. 


For more info on Mechanical ground wood follow this link
Stone Ground Wood - Mechanical Pulp Production