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PROPELLER THRUST Carried by lapered Roller Bearings carry the load set up by propel- ler thrust is attracting the atten- tion of naval architects and marine en- gineers. Most recent installations are those on the United States coast guard harbor cutters CALUMET, NAVESINK, TUCKAHOE, and Hupson, the first three recently completed or under construc- tion at the Charleston, 8S. C., navy yard and the last at the Portsmouth, N. H., navy yard. Only last year a tapered roller bearing thrust biock was installed on the 10,000-ton United States navy cruiser Concorp. Although the Concorp installation is the largest made to date, tapered roller bearings have been successfully used for a num- ber of years to carry the propeller thrust in smaller craft. The increas- ing use of this type of bearing is due to its ability to carry the load with a minimum of friction and wear, and to the fact that when wear does occur, adjustment is easy. U: of tapered roller bearings to Radial and Thrust Loads The tapered roller bearing consists of a cone, or inner race, a cup or outer race, and a number of tapered rollers which are spaced around the cone by means of a cage. Lines drawn coin- cident with the working surfaces of the bearing meet at a common point on the axis of the bearing, as shown in Fig. 1. It is apparent that true rolling motion takes place in the bear- *The author, J. Borland, is a member of the staff of the Engineering Depart- ment, the Timken Roller Bearing Co., Canton, O. iN nh A Wy | US Lae RS et Sans HN} |S La eat) ill | = END ANN bos 777 Per 20 ing and that it is capable of carrying both radial and thrust loads, or any combination of the two. It is also evident that if any wear occurs on the working surfaces of the bearing, the taper permits of its being readjusted to the original setup. In a properly mounted and lubri- cated tapered roller bearing the co- efficient of friction compares favor- 8 Fig. 1 — Princi- | ple of tapered BY J. BORLAND* the heat dissipated will be due to the friction caused by churning of the lubricant. The installation of tapered roller bearings mentioned above on _ the coast guard vessels is shown in Fig. 2. It will be noted that the bearing has a double cone having a tapered bore. The cone is also designed with a groove for a puller, which, in connection with See oe rol ler bearing | ee for carrying simult a neously both radial and thrust load : aes 8 ably with that of the latest type of plain thrust bearing and is several times less than that of the horseshoe collar type of bearing once popular for marine work. Definite test data re- garding the coefficient of friction of a tapered roller bearing in marine thrust service is not available. How- ever, in other applications under con- tinuously applied heavy radial loads, the coefficient has been found to be approximately 0.002. For a pure thrust application a coefficient of 0.003 can be anticipated. The friction in the bearing being very low, very little pow- er is lost in it and the majority of ® Fig. 2—Tapered roller bearing thrust block for the new Coast Guard harbor cutters. Carries propeller thrust load and also SETVES AS A SUP- porting bearing for propeller shaft @ the tapered bore, permits easy remov- al of the bearing from the shaft. The shaft itself is designed to be used as a section of the propeller shaft and is fitted with flanges for couplings. The bearing housing is made self aligning so that any deflections in the hull will not put undue loading on the bearing. The bearing itself is 6% inch bore at the large end of the taper by 1434 inch outside diameter. It is 95/16 inches wide over the cone and 515/16 inches wide over the cups. Spacer for Adjustment Adjustment of the bearing is ob- _ tained by grinding the spacer between the cups to size. Lubrication of the bearing is effected by the maintenance of a level of oil in the box, the oil being prevented from leaking by the closures shown. This unit is designed to transmit 800 brake horsepower at a speed of 300 revolutions per minute. The calculated thrust load at 12 knots is 14,500 pounds. This application shows clearly the advantage of the tapered roller bear- ing in carrying both radial and thrust loads. The bearing not only takes care of the thrust from the propeller, but also acts as a supporting bearing for the propeller shaft. This feature per- mits of shorter units, it being unneces- sary to provide radial bearings to sup- port the shaft in addition to the thrust bearing. A tapered roller bearing thrust block was applied to one of the shafts of the 10,000-ton cruiser Concorp in