. Machine design. eter and one-quarterinch long. Fig. 57 illustrates a bearing of this character. Col-lars similar to this have been used in thrust bearings for propeller shafts. Thediscussion referred to inArt. 46 also included balland roller bearings andshould be read by the de-signer. Mr. Mossberg, de-signer of the roller bear-ings of that name, recom-mends rollers of springtempered tool steel, cagesof tough bronze and boxesof high carbon steel with ahard temper. Mr. CharlesR. Pratt reports the limit of work for | inch balls inthrust bearings to be 100 pounds per ball at 700 revolu-tions pe
. Machine design. eter and one-quarterinch long. Fig. 57 illustrates a bearing of this character. Col-lars similar to this have been used in thrust bearings for propeller shafts. Thediscussion referred to inArt. 46 also included balland roller bearings andshould be read by the de-signer. Mr. Mossberg, de-signer of the roller bear-ings of that name, recom-mends rollers of springtempered tool steel, cagesof tough bronze and boxesof high carbon steel with ahard temper. Mr. CharlesR. Pratt reports the limit of work for | inch balls inthrust bearings to be 100 pounds per ball at 700 revolu-tions per minute and 6 inches diameter circle of W. S. Rogers gives the maximum load for a1 inch ball as 1000 pounds and for a \ inch ball as 200pounds. Mr. Henry Hess states that in a roller bearring one fifth of the number of rollers multiplied by thelength and diameter of one roller may be considered asthe projected area of the journal. For ball bearingsone fifth the total number of balls multiplied by the. Fig. 57. ROLLER STEP-BEARINGS. 129 square of the ball diameter may be used in the sameway. Space forbids reference to all of the many varietiesof ball and roller bearings shown in manufacturerscatalogues. These are all subject to the laws and limit-ations mentioned in this chapter, While such bearings will be used more and more inthe future, it must be understood that extremely highspeeds or heavy pressures are unfavorable and in mostcases prohibitive. Furthermore, unless a bearing of this character iscarefully designed and well constructed it will proveto be worse than useless. CHAPTER IX. SHAFTING, COUPLINGS AND HANGERS. 66. Strength of Shafting. Let D=diameter of the driving pulley or number rev. per force applied at twisting moment. The distance through which P acts in one minute is irDN inches and work=P7rZ)iVin. lb. per min. PDBut -^— =T the moment, and 27riV=the angular velocity. .*. work=moment X angular horse power= 3
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