WOOD PULP AND PAPER 53 



partly along the center so as to form a continuous channel round which 

 the pulp can circulate. On one end is situated the beating rolls which 

 are provided with a set of knives or bars which may be raised or lowered 

 to press more or less on a bedplate of stationary knives or bars. These 

 machines vary in size but usually have a capacity from 1000 to 1200 Ib. 

 at one time. The ordinary beater is about 2 ft. deep at one end and 

 about 2 ft. 6 in. deep at the other. The movement of the pulp in the 

 machine is caused by the paddle-like action of the arms of the roller. A 

 large proportion of the power used by the paper mill goes to the beater 

 room. Experiments have shown that large beaters are much more 

 economical of power and are much more efficient than the smaller ones. 

 Recently concrete has been introduced for the trough construction in 

 place of iron. 



A beater with a roll or drum having 100 bars and a bed-plate with 20 

 bars of 40 in. in length and running at 20x3 R.P.M. should prepare about 

 i \ Ib. of paper of average substance per minute. 



Sizing and Loading. 



When the pulp is bleached a certain amount of bleaching chemicals 

 remain in the substance and it is necessary to remove this either by 

 washing, or by the use of chemicals. Washing is generally considered 

 the best as it readily removes the chlorine. 



After washing, the pulp is passed through the beater. During the 

 beating operation, the sizing and loading are added. In the manufacture 

 of ink or water-resisting papers, the operation is practically limited to 

 rosin as a " size." It generally requires about 3 or 4 Ib. of rosin to size 

 100 Ib. of paper. The prepared rosin size is added to the pulp in the 

 beater, together with alum or sulphate of alumina which finishes the 

 reaction and fixes the rosin size upon the pulp. Starch, silicate of soda, 

 soap, casein, gelatin, and many other substances are used as sizing for 

 papers for special purposes. 



In the manufacture of high-grade papers, it is necessary to fill up the 

 surface pores so that the surface will be smooth. This is done by the 

 addition of very fine clays, such as kaolin, talc or sulphate of lime, or 

 baryta. There are other fillers and loading agents but these are the most 

 common. The greater the percentage of filler used, it is obvious that the 

 smaller is the proportion of wood pulp, and, therefore, paper that is 

 heavily filled is not so strong and durable. In composition the filler may 

 constitute from 2 to 30 per cent of the finished paper product. 



