Page 339 - Marks Calculation for Machine Design

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CHAPTER 8
MACHINE ASSEMBLY

8.1 INTRODUCTION

In this chapter two important ways of connecting individual machine elements into an
assembly will be discussed: bolted connections and welded connections. Both ways can be
subjected to either static or dynamic conditions; therefore the safe design of both is important
to the designer. Each type of connection will be discussed in detail with examples in both
the U.S. Customary and SI/metric system of units.
Bolted connections are typically used when the assembly must allow for future access
during service or repair, or when welded connections are not appropriate for the materials
being assembled. Bolted connections are also used in permanent structural installations,
where high-strength bolts are actually yielded during assembly to provide the maximum
compressive joint, and therefore must be discarded if ever disassembled. Many bolted
connections function in groups, where redundancy in the system is important.
Incontrast,weldedconnectionsareappropriatewhendisassemblyisnotrequired,orwhen
a weldment is more economical than a casting. For example, the advantages of a weldment
design for use as a composite flywheel will be discussed in Chap. 9. In this chapter, welded
connections under both static and dynamic loading conditions will be presented. Principles
presented in many of the chapters of Part 1 will be applied extensively to weld joints carrying
a variety of load types: axial, direct, torsion, bending, and combinations of these types.

8.2 BOLTED CONNECTIONS

As the overall theme of this book is to uncover the mystery of the formulas used in machine
design for the practicing engineer, it will be assumed that the details of the nomenclature
of cap screws, bolts, nuts, and washers, and the standard sizes and dimensions in both the
U.S. Customary and SI/metric systems of units, is unnecessary. Therefore, the discussion
will proceed directly to the first important topic, the fastener assembly itself, whether cap
screw or bolt.

8.2.1 The Fastener Assembly
The fastener can either be a component of a bolt, two washers, and a nut assembly, or a com-
ponentinacapscrew,singlewasher,andthreadedholeassembly.Ineithercase,thecapscrew
or bolt are under tension and the members being held together by the assembly, including
the washers, are under compression. These two types of connections are shown in Fig. 8.1.

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