Machinery Adhesives for Locking, Retaining, and Sealing PDF

INTRODUCTION

Ever since machinery has been built, designers and machinists have faced the problem of fitting assemblies to minimize the inner space that allows leaking and moving, or working, of apparently tight parts . Inner space is either the clearance that exists between parts to allow for their assembly, such as in a threaded assembly, or the space that cannot be filled because a press fit can produce only peak-to-peak contact of surface irregularities, thus leaving a substantial 70 to 80% of noncontact inner space (Fig. 1.1).

In the early 1800s special machines were developed to turn the bores and parts of cannon and steam cylinders which, in James Watt’s original experiments, had "close” fits of about 0.06 in. To produce tight joints , strips of leather, hemp, and clay were used to caulk the joints. Since then , machinery to fit cylindrical parts has required more and more precision at higher and higher costs (Fig. 1.2).

Designers, engineers, and machinists can now eliminate this problem on stationary fits by using machinery adhesives. Typical stationary fits would be a bolt in a threaded hole, a press fit of a ball bearing on a shaft, or a clamped flange sealing internal machine parts. In contrast to structural adhesives, which are used as the primary holding means in a structure (often in direct tension ), machinery adhesives are generally used in rigid cylindrical assemblies in a shear or compressive mode to eliminate leakage and provide a noncreeping joint.

Author: G. S. Haviland