342 



STEEL HEAD FRAMES AND COAL TIPPLES. 



CHAP. X. 



center. Wire strands are twisted around the core either to the right or the left, and the resulting 

 rope is either "right lay" or "left lay." The twist may be long or short; the shorter twist forms a 

 more flexible rope, while the longer twist forms a more rigid rope. Wire rope is made of iron, 

 open-hearth steel, crucible steel, and plough steel. The strength of the wire from which the 

 rope is made is about as follows: iron wire, 40,000 to 100,000 Ib. per sq. in.; open-hearth steel 

 wire, 50,000 to 130,000 Ib. per sq. in.; crucible steel wire, 130,000 to 190,000 Ib. per sq. in.; and 

 plough steel wire, 190,000 to 350,000 Ib. per sq. in. Hoisting ropes are usually made of crucible 

 cast steel or plough steel. 



Flat wire rope is composed of several round ropes whose diameter is equal to the required 

 thickness of the flat rope, laid side by side and sewed together with iron or annealed cast steel 

 wire. The round ropes are alternately of right and left lay or twist, have four strands without 

 either hemp or wire center. The number of wires in each strand is usually seven, but may be 

 nineteen. The chief drawbacks to the use of flat wire rope are its first cost and the rapid wear 

 of the sewing wires. 



Flat ropes and reels are used to a limited extent in the western part of the United States, while 

 round ropes are generally used in hoisting coal and in the deep copper and iron mines in Michigan. 



Strength of Wire Rope. The dimensions, weight and strength of round crucible steel hoisting 

 rope are given in Table I, while similar data for plough steel hoisting rope are given in Table II. 

 The strengths of wire rope given by the different makers differ somewhat. 



TABLE I. 



CAST STEEL HOISTING ROPE. ULTIMATE STRENGTH, WORKING STRENGTH AND WEIGHT OF 

 WIRE ROPE COMPOSED OF 6 STRANDS AND A HEMP CENTER, 19 WIRES 



TO THE STRAND. 



Working Load on Hoisting Rope. The stresses in a hoisting rope are the sum of the stresses 

 due to (i) the weight of the rope, (2) the friction of the rope, (3) the bending of the rope over the 

 head sheave, (4) the live load, and (5) the impact due to starting and stopping the load. The 

 stresses due to bending are discussed in the next section. The stresses due to impact vary from 

 zero to twice the working load if the hoisting cable is taut, and to several times the working load 



