GROUND-WOOD PULP. 7 



Upon leaving the grinder a large supply of water is added to the 

 pulp, and the mixture is then screened. If it is to be shipped over a 

 long distance, the pulp is run into laps by means either of wet 

 machines or of hydraulic presses. Occasionally the pulp is dried on 

 steam driers and run into rolls. When pulp is used where it is pro- 

 duced, except for the need of storing to provide a supply in times of 

 low water, it is thickened by means of feltless wet machines or deckers 

 and immediately manufactured into paper. 



In the last few years a magazine pulp grinder has come into use, 

 equipped with two pockets which are filled automatically from the 

 magazine. The machine, however, has not been operated in this 

 country to an extent which would enable a judgment to be formed 

 regarding its efficiency and economy. 



Part I.— THE GRINDING OF COOKED AND UNCOOKED 



SPRUCE. 



EQUIPMENT USED IN THE EXPERIMENTS. 4 



APPARATUS FOR COOKING. 



Cooking treatments prior to grinding were carried on in a cylin- 

 drical closed steamer 3 feet in diameter by 8 feet high, designed for 

 75 pounds' working pressure. The " steamer" was fitted with steam, 

 water, and vacuum connections and the necessary gauges and ther- 

 mometers for determinations of pressure and temperature. An open 

 steamer 6 feet wide, 8 feet long, and 3 feet deep was also available 

 for cooking treatment at atmospheric pressure. 



ELECTRICAL EQUIPMENT. 



In order to satisfactorily vary the conditions of grinding, secure 

 adequate data on power consumption, and maintain the speed con- 

 stant, it was necessary to install a rather complex system of electrical 

 drive and control for the grinder. The method of speed regulation 

 was known as the Ward Leonard system, and by its means a very 

 flexible arrangement was secured. 



The installation consisted of a motor generator set of 460-kilo- 

 volt-amperes full-load capacity and a direct-current, variable-speed 

 motor having a full-load capacity of 500 horsepower at 300 revolu- 

 tions per minute. With the overload capacity it was possible to 

 secure fully 75 per cent more power than the rating from each of the 

 machines. 



Three-phase 60-cycle electric power was applied to the synchronous 

 motor of the motor generator set at 2,300 volts. The generator of the 

 motor generator set was separately excited and by means of a rheostat 



1 A more detailed description of the equipment of the Forest Service laboratory at Wausau, Wis., is 

 given in an unnumbered publication of the Forest Service, " Experiments with Jack Pine and Hemlock 

 for Mechanical Pulp." 



