206 



HANDBOOK OF MECHANICAL DESIGN 



\)i)j))///)/iii/i>>>> 1 >>'"''/' />/ ] 



Fig. 440. — Film applicators are used much more extensively than those applying dabs, because they permit the 

 application of a uniform film of glue of any selected thickness. A direct-acting type of this class of device is shown 

 here. The material receiving the appUcation runs in contact with the wheel that dips in the glue, the application 

 being made to the under surface. Best results are obtained when the wheel runs at the same surface speed as the 

 material passing over it. In this class of glue applicators, greatest attention must be given to the design of the trimmer 

 blade. This blade must be adjustable, but it should be so constructed that in making the adjustment the blade will 

 keep its proper relation to the wheel. 



Fig. 441. — In the indirect types of film applicator, a 

 transfer wheel receives glue from the main wheel and transfers 

 it to the point of application. The clearance between the 

 transfer wheel and the main wheel is usually made adjustable. 

 On machines that must be stopped frequently, the drive to the 

 glue wheels should be independent of the drive for the main 

 machine so that the glue wheels can be kept revolving when 

 the machine is stopped, thus preventing the glue from drying 

 o\\ the surface of the wheels. 



Fig. 442. — In this design of direct applicator, 

 the film of glue is applied to the upper surface 

 of the sheet. To keep the exact relation 

 between the trimmer blade and wheel, there 

 must be a complete elimination of lost motion. 

 If a means for locking the trimmer blade in 

 position is provided, it should be so designed 

 that the act of locking will not disturb the set- 

 ting. It should also be possible to remove the 

 parts for cleaning without disturbing the set- 

 ting. The drive of the glue wheel should be 

 positive to ensure the proper speed. A belt 

 drive is not to be recommended. . 



Fig. 443. — A type of gumming mechanism that is much in use in sheet-mounting machines and gumming 

 machines. This type is easily cleaned and adjusted. When the rollers are long, consideration should be given to the 

 deflection in the center of the rollers due to the pressure exerted in squeezing out glue. This deflection will result in 

 a thicker fiilm of glue in the center of the rollers than at the ends. This is usually compensated for by making the 

 glue roller larger in diameter in the center than at the ends. The device has no trimmer blade, but thickness of glue 

 film is regulated by adjusting the gap between the rollers. 



