A mine hoist uses a 2-in 6 19 monitor-steel wire rope. The rope is used to haul loads of 4 tons
from the shaft 480 ft deep. The drum has a diameter of 6 ft, the sheaves are of good-quality cast
steel, and the smallest is 3 ft in diameter.
(a) Using a
All real bodies deform under load, either elastically or plastically. A body can be sufciently insensitive to deformation that a presumption of rigidity does not affect an analysis enough to warrant a nonrigid treatment. If the body deformation later prov
with two signicant gures, it is implied that the range of d is 0.40 0.005. This means
that the calculation of C is only accurate to within 0.005/0.40 = 0.0125 = 1.25%.
The calculation could also be one in a series of calculations, and rounding each calcul
important than others. Next, for each property, list all available materials and rank
them in order beginning with the best material; e.g., for strength, high-strength steel
such as 4340 steel should be near the top of the list. For completeness of availa
The advantage of the casting process is that parts having complex shapes can be manufactured at costs less than fabrication by other means, such as welding. Thus the
choice of steel castings is logical when the part is complex and when it must
The addition of nickel to steel also causes the eutectoid point to move to the left and
increases the critical range of temperatures. Nickel is soluble in ferrite and does not
form carbides or oxides. This increases the strength without decreasing
The purpose of case hardening is to produce a hard outer surface on a specimen of lowcarbon steel while at the same time retaining the ductility and toughness in the core.
This is done by increasing the carbon content at the surface. Either
Ductile cast iron, or nodular cast iron, as it is sometimes called, is essentially the
same as malleable cast iron, because both contain graphite in the form of spheroids.
However, ductile cast iron in the as-cast condition exhibits properties very close
austenitic chromium-nickel steels, and the martensitic and precipitation-hardenable
The ferritic chromium steels have a chromium content ranging from 12 to 27 percent. Their corrosion resistance is a function of the chromium content, so
When a material is cold- or hot-worked, residual stresses are built in, and, in addition,
the material usually has a higher hardness as a result of these working operations. These
operations change the structure of the material so that it is no
Stress-strain diagram for
hot-rolled and cold-drawn
UNS G10350 steel.
By cold working is meant the forming of
Steel castings are the most difcult of all to produce, because steel has the highest
melting temperature of all materials normally used for casting. This high temperature
aggravates all casting problems.
The following rules will be found quite useful in t
to zero. But the strength remains as one of the properties of the spring. Remember, then,
that strength is an inherent property of a part, a property built into the part because of
the use of a particular material and process.
Various metalworking and hea
First, observe that nothing can be said in an absolute sense concerning costs.
Materials and labor usually show an increasing cost from year to year. But the costs
of processing the materials can be expected to exhibit a decreasing trend because of
There are many ways of obtaining relative cost gures so that two or more designs
can be roughly compared. A certain amount of judgment may be required in some
instances. For example, we can compare the relative value of two automobiles by
quantied in terms of established metrics.1 As the eshing out of the scheme progresses,
analyses must be performed to assess whether the system performance is satisfactory or
better, and, if satisfactory, just how well it will perform. System schemes that
Chapter 20, Statistical Considerations. This chapter is relocated and organized as a
tool for users that wish to incorporate statistical concepts into the machine design
process. This chapter should be reviewed if Secs. 513, 617, or Chap. 11 are to be
Part 3: Design of Mechanical Elements
Part 3 covers the design of specic machine components. All chapters have received
general cleanup. The shaft chapter has been moved to the beginning of the section. The
arrangement of chapters, along with any signican
An annealed AISI 1018 steel (see Table A22) has Sy = 32.0 kpsi, Su = 49.5 kpsi,
f = 91.1 kpsi, 0 = 90 kpsi, m = 0.25, and f = 1.05 in/in. Find the new values of
the strengths if the material is given 15 percent cold work.
From Eq. (21
may be used (see Footnote 1) to prioritize the requirements, determine suitable metrics to
be achieved, and to establish target values for each metric. The goal of this process is to
obtain a product specication that identies precisely what the product mu
In the development of the basic stress equations for tension, compression, bending, and
torsion, it was assumed that no geometric irregularities occurred in the member under
consideration. But it is quite difcult to design a machi
F1 + F2
Dividing Eq. (i) by Eq. (h), manipulating, and using Eq. (177) gives
(F1 + F2 )/2 Fc
F1 + F2 2Fc
(F1 Fc ) + (F2 Fc )
(F1 F2 )/2
(F1 Fc ) (F2 Fc )
exp( f ) + 1
(F1 Fc )/(F2 Fc ) + 1
(F1 Fc )/(F2 Fc
(b) Using the solution to part a, formulate the modications to the expressions for m G , d and D ,
L p , and C.
(c) As a result of this exercise, how would you revise your solution to part b of Prob. 1720?
A 2-hp electric motor running at 1720 rev/mi
have a different lay of the wires forming the cable, with more wires in each layer, so
that the torsional deection is approximately the same for either direction of rotation.
Flexible shafts are rated by specifying the torque corresponding to various radi
Designing a Worm-Gear Mesh
A usable decision set for a worm-gear mesh includes
Function: power, speed, m G , K a
Design factor: n d
A priori decisions
Materials and processes
Number of threads on the worm: N W
Axial pitch of worm: p
Refer to your solution to Probs. 151 and 152, which is to have a pinion core hardness of
300 Brinell. Use the relations from Prob. 157 to establish the hardness of the gear core and the
case hardnesses of both gears.
Repeat Probs. 151 and 152 with
pinion case hardness is 390 Brinell, and the gear core hardness is 250 core and 390 case. Estimate
the power rating for the new gearset.
The gearset of Prob. 1424 has had its gear specication changed to 9310 for carburizing and
surface hardening with
A steel spur pinion has a module of 1 mm and 16 teeth cut on the 20 full-depth system and is to
carry 0.15 kW at 400 rev/min. Determine a suitable face width based on an allowable bending
stress of 150 MPa.
A 20 full-depth steel spur pinion has 17
Substituting N4 = 5N5 , we nd
7 = 5N5 + N5 = 6N5
N5 = 7/6
This fraction could be eliminated if it were multiplied by a multiple of 6. The free
choice for the smallest gear N3 should be selected as a multiple of 6 that is greater than
the minimum allowed t
estimating the capacity of gear drives when life and reliability are not important considerations. The equations can be useful in obtaining a preliminary estimate of gear
sizes needed for various applications.
A stock spur gear is available