REDUCTION GEARS FOR SHIP PROPULSION. 



17 



In regard to double reduction gears of the single-plane type the results are various, but 

 there are few which have seen 100,000 miles of sea service, and this type is not likely to be 

 repeated to any great extent. 



After studying the results obtained on various types the author suggests the following 

 table of tooth pressures as being the maximum which it is safe to use : 



One further important item is the length of helix in proportion to the diameter of the 

 pinion, and the constants quoted are based on the assumption that this ratio does not exceed 

 2 to 1 and should be reduced to 1.5 to 1 whenever possible. 



The material of the casing and bearings is practically standard. The oil well and the 

 gear-case cover are sometimes made of cast iron and sometimes are built of steel. The cast 

 iron serves to deaden the noise of the gears and is to be preferred, but good results have 

 been obtained with the steel covers by lagging them with felt and sheet iron. The general 

 construction for the wheels has been either cast iron or cast steel spiders with rolled rims 

 of mild steel shrunk on and pinned and in which the teeth are cut. Gears of the Alquist 

 type are formed of steel plates (laminated) bolted together on a hub or disc, the plates being 

 separated from each other to a depth of a few inches. This gives a certain amount of flexi- 

 bility when new, but it is found that the teeth rapidly grow together. Some of the gears we 

 have now in service have solid steel spiders with teeth cut in the rim. They are made by a 

 special process and come out quite sound. Those tried have given good results, and the 

 structure being finely granular it is believed that they will wear better and be less subject to 

 pitting than the mild steel forged rims. 



Difference of practice is found in the material for the pinions ; some prefer high carbon 

 steel and others nickel steel, chrome nickel or chrome vanadium steel. It is believed that the 

 alloy steel will be found to give the best results as the structure is so different from that of 

 mild steel and the material appears to have better qualities. The pinions are made as hard 

 as they can be cut and they are usually heat treated to secure the necessary degree of hardness. 



In some of the gears which have passed through our hands which have been manufac- 

 tured ahead of requirements and have had to lie in storehouses for a few months it has been 

 found that the pinions have distorted. Some of these had to be removed on account of noise 



