84 PROGRESS IN TURBINE SHIP PROPULSION. 



ameter. Dealing with the curve for floating frame gears, it is of interest to note that the 

 author does not give particulars of any installations having pinions greater than 11 inches 

 diameter. Further, it seems to me that the point representing a "22,000 S. H. P. gear" is 

 hardly correct, my first impressions being that this S. H. P. was delivered by one pinion, 

 whereas calculations show pretty conclusively that this large power was delivered by four 

 pinions. 



Further, I hope the author will perhaps see his way to give tooth-pressure loads for gears 

 having pinions greater than 11 inches diameter, or state definitely that the extension of the 

 curve up to 20 inches diameter represents estimated figures rather than actual result^. 



The curves of rigid bearing gears are of special interest, but it is somewhat unfortu- 

 nate that the author does not definitely state j ust whose practice they represent, because you 

 immediately get the impression that the curves are directly comparable in every way. If 

 the author tabulated the data from which he made those curves, then I wish to state that he 

 did and does fully realize that these curves cannot be compared on an eqi:m.l basis with his 

 curve. 



On the other hand, if these curves were given to him by correspondents abroad, then I 

 am equally positive that they were never intended to be used for the purpose of exploitation. 



Mr. Macalpine in a recent paper stated that all gears built with the floating frame had 

 teeth cut with 30 degrees helical angle, and I believe the circular pitch is about 0.90 inch, 

 whereas most of the British gears have been cut with about 45 degrees helical angle and cir- 

 cular pitch about 0.78 inch. 



Any such gear having 45 degrees helical angle cannot be compared on an. equal basis 

 with one having 30 degrees, and to make the matter clearer I quote Mr. McAlpine's own 

 words : — * 



"In floating frame gears a helical angle of 30 degrees has always been used. This 

 brings sufficient" teeth into contact at one time to secure smooth and quiet running, and gives 

 ample longitudinal forces to determine the position of the pinion. In rigid gears this angle 

 ia frequently made 45 degrees, no doubt to make these gears more quiet, but this sacrifices 

 much strength of teeth." 



Further, I believe the curves of rigid bearings are made from actual gears with pinions 

 of all sizes up to 20 inches diameter and above, many of which have been successfully at 

 work for five years, and any designer can use these figures with absolute safety provided 

 that the pinion materials are of the proper quality. The curves for "floating frame" 

 pinions should be used with the utmost caution for any sizes larger than 11 inches di- 

 ameter. 



The seven notes, A to G, covering the breakdowns to geared turbine installations, are 

 specially worthy of attention, and the evidence tends to show .that the maximum limit of 

 tooth pressures is about reached, especially with the present grade of materials which can be 

 obtained. 



The necessity of having to consider using a separate oil for the gear sprays will also 

 tend to make designers reduce tooth pressure loads. 



The use of very high steam pressures and high degrees of superheat, in excess of 300 

 pounds and 100° superheat, will continue to present many difficulties until reliable steel 

 castings can be freely obtained in the open market. 



♦Published by the Engineers' Society of Western Pennsylvania, in paper entitled "The Design and Progress 

 of the Floating Frame Reduction Gear." 



