2862 



Chapter 23 



DOCTOR BLADE 



METERING ROLL 



COATING ROLL 



FEED 



PRESSURE ROLL 



Figure 23-90. — Direct roll coater. (Drawing from Suchsland and Woodson 1985. 



on endless chains, or they can be moved by roller drives as in insulation board 

 dryers. 



In the progressive type or tunnel oven, boards travel on trucks or buggies, 

 positioned either vertically on edge or horizontally, and separated by spacers. As 

 one truck enters the oven another leaves it at the other end. Trucks travel on 

 tracks and are either pushed by hand or moved intermittently by chain or 

 hydraulic drives. 



In the batch process, the oven is charged with loaded trucks or buggies, and 

 the entire charge is treated together and then removed simultaneously. Heat 

 treating time is about 3 hours. 



Treating ovens can be coupled directly with the press, in which case the 

 capacity and the length of the oven must be so designed that the output of the 

 press can be accommodated continuously without interruption. With intermedi- 

 ate storage, the heat treating operation can be made independent of the press 

 output. 



Heat treating of tempered boards causes release of volatiles from the oil, 

 which are considered air pollutants. In some states fume incinerators are manda- 

 tory on tempering ovens, encouraging limitation of oil quantities to surface 

 treatments and to boards that benefit from the specific charcteristics of oil 

 treatment. Heating ovens must be equipped with deluge systems which will 

 flood the boards in the event of a fire. The water spray units are so arranged that 

 the spray is directed into the spaces between boards. 



