56 



FOREST PRODUCTS 



is usually arranged so that it can be vibrated sidewise at all times while 

 the machine is in operation. This vibration assists in intertwining and 

 interlacing the fibers and consequently gives a much stronger sheet of 

 paper. The length and number of strokes determine the character of 

 the paper to a large extent, the long, slow strokes being best for sulphate 

 papers, while the short and fast strokes are best for finer grades of paper. 

 Suction boxes, or vacuum rolls, traverse the under surface of the screen 

 and aid in removing the excess of water by sucking it out. 



Press Rolls. 



As the paper passes on the screen it is detached from the wire and 

 passes over a heavy felt which carries it through three sets of rolls which 

 press out a considerable portion of the remaining water. Many machines 

 are fitted with a set of rollers having many small perforations through 

 which the remaining water is partly sucked out. An endless felt carries 

 the paper over the dryer. 



FIG. ii. This shows the end of the drier (at left) the calender stack, reels, rewinder and 

 cutter. On the right is a roll of paper which has been re-wound and cut. The calender 

 irons out the wrinkles in the paper and surfaces it. Paper is re-wound to make neat and 

 compact rolls and is cut to the desired length of roll. 



Drying Rolls or Driers. 



From the press rolls the sheet passes over the drying rolls which con- 

 sists of a series of from 1 6 to 36 or more large heated steel drums. The 



