219. If the generator frame shown in Fig. 84 weighs 3000 lb., what size steel eyebolt should be used for lifting it, allowing a stress of 10,000 lb. at the root of the thread? 220. What would be the safe load for a in. chain? 221. What size hemp rope would be necessary to lift a load of 4000 lb.? EYEBOLT FIG. 84. 222. What force would be necessary to shear off a bar of machinery steel 2 in. in diameter? 223. A certain manufacturer of jack screws states that a 2 in. screw is capable of raising 28 tons. If the diameter of the screw at the base of the threads is 1.82 in., what is the stress per square inch at the bottom of the threads when carrying 28 tons? 224. A soft steel test bar having a diameter of .8 in. is pulled in two by a load of 31,500 lb. What was the breaking tensile stress per square inch? 125 lbs. per sq. in. 7" FIG. 85. 225. The cylinder head of a small steam engine (Fig. 85) having a cylinder diameter of 7 in. is held on by 6 studs of in. diameter. When there is a steam pressure of 125 lb. per square inch in the cylinder, what will be the pull on each stud? And what will be the stress per square inch in each stud, due to the steam pressure? 226. With a cylinder diameter of 10 in. and an air pressure of 100 lb. per square inch, find the greatest weight that can be lifted by the air hoist, shown in Fig. 86. Also find the size of piston rod necessary, assuming that it is screwed into the piston. Notice that this rod is subject only to tension and, therefore, a greater stress is allowable than in steam engine piston rods. 227. Work out a formula for the strength of crucible steel cables on the same plan as that given for hemp rope. 228. What is the greatest load that should be lifted with a pair of tackle blocks having 3 pulleys in the movable block and 2 in the fixed block, and having a fin. rope. FIG. 86. 100 lbs. per sq. in.— |