GROUND-WOOD PULP. 65 



are driven by turbines and motors of loss than 300 horsepower 

 capacity and 8 per cent of the grinders are driven by less than 200 

 horsepower. The work which has been described in this publica- 

 tion indicates that a large amount of power to the grinder is desir- 

 able. Tn order to utilize a large amount of power, the stones must 

 bo operated under conditions of high speed and high pressure, or 

 they must be of a larger size than those used at the present time. 

 Efficiency of grinding wood can be greatly increased over present 

 average commercial practice by the use of higher pressure, since 

 this results in the reduction of the horsepower consumption per ton 

 of product. There are cases, of course, where such practice would 

 not be desirable. If sulphite is available at low cose and power is 

 expensive, this condition would surely obtain; but if sulphite is 

 expensive and power can be secured at a low figure it is undoubtedly 

 more economical to use a large amount of power per ton of product 

 and make economies in sulphite by virtue of the fact that with the 

 large amount of power better and stronger ground-wood fiber can 

 be obtained. 



Economies in grinding, particularly as related to power, depend 

 largely on the character of the material into which the ground wood 

 is to be incorporated. For the manufacturing of such materials as 

 wood-pulp board, as used in the wall-board industry, a long, coarse 

 fiber is required, and this is most desirable, since fibers of this nature 

 do not form as dense a sheet. There are, as a result, a' large number 

 of air spaces present which retard the passage of cold and sound. 

 For the production of pulp of this nature pulp stones of coarse grit 

 are required which are softer than those usually employed for the 

 manufacturing of pulps for other purposes. When using a coarse 

 stone, a longer fiber can be obtained at higher pressure than when a 

 finer stone is utilized. Consequently, it is desirable in the produc- 

 tion of this character of stock to choose the pulp stone carefully to 

 secure the best results. The matter of efficiency as applied to the 

 manufacturing of stock for any desired purpose hinges, to a large 

 measure, on a careful selection of the pulp stone to be used. 



It is common practice in ground-wood mills to use all of the pock- 

 ets on the grinder in the production of the mechanical pulp. In 

 other words, the total amount of power available for use on the 

 grinder is used on all of the pockets and at the same time. Power 

 can be saved and the efficiency of production increased to a marked 

 extent by the utilization of a fewer than the total number of pockets 

 of the grinder. If four-pocket grinders are used, it is more desirable 

 to use three of the pockets continuously and keep the fourth for 

 surplus to be employed at times when one of the other pockets is 

 being filled or when binding or other troubles are being corrected. 

 When all of the power available on a three-pocket grinder is used 

 14852°— Bull. 343—16 5 



