In the stone ground wood (SGW) and pressurized ground wood (PGW) pulp processes; pulp is produced by pressing sections of wood, as logs or blocks, onto a rotating, abrasive grinding stone.  SGW is accomplished at atmospheric pressure and temperature. PGW, developed in Finland by Tampella, grinds wood at a pressure of >2 bar (>30 psi) and at temperatures over 95ºC (200ºF).  The mechanism of grinding is similar in both operations. Logs or wood blocks are loaded into the  magazine, parallel to the axis of the grinding stone. As the stone rotates against the wood, repetitive high frequency, compression and decompression at the wood/stone interface begins to weaken the lignin bond. Frictional heat further softens the lignin layer and assists in separating the wood fiber. A water shower is required to control frictional heat and prevent burning of the wood fiber. The water shower also washes removed fiber into the pulp stream.