|Threaded Joints - Course: Techniques of Fitting and Assembling Component Parts to Produce Simple Units. Trainees' Handbook of Lessons|
Locking devices can be acting positively, non-positively or by the retention of self-substance.
Locking devices, particularly cotter pins, spring rings and toothed washers, are used only once.
Use new, unused locking devices when re-assembling parts which have been dismantled. Locking devices, once used, will deform permanently and not be safe to use another time.
Non-positive locking devices
These are available mainly as spring lock washers and toothed washers. They maintain a slight tension between the bolt, or nut, and the component to which they are fastened.
The sharp edges on the spring lock washers and toothed lock washers have a seizing effect on the component tightened in the joint, thus preventing it from coming loose accidentally.
An additional locking effect can be obtained on bolts with a long, projecting shank by screwing a counternut on the projecting shank. Both nuts must be screwed sufficiently tight. The friction on the thread flanks prevents the nuts from coming loose.
1 spring ring, 2 toothed washer, 3 counter nut, 4 spring lock washer
Positive locking devices
These are available mainly as locking plates, retaining rings and crown nuts with split pins. They are used primarily with hexagon head screws and where their shape prevents the joint from coming loose.
Locking plates and retaining rings are provided with tangs or lugs, which are fastened to the component in the joint and the connecting part by blows with a hammer. When crown nuts are used, a hole must be drilled through the threaded portion, which takes up the cotter pin, after nut has been tightened.
1 crown nut with split pin, 2 locking plate with tang
Locking by retention of self-substance
The locking effect is achieved by the application of paint, varnish or paste. Used primarily on electrical assemblies and in precision instruments. Where the forces acting on the joint are slight, the locking effect is sufficiently strong and provides protection against tampering.
1 on the bolt head at a blind bore, 2 on the nut at a through bore
Identify elements of locking devices which must be used once
Suggest an effective way of locking with the shank of the bolt
projecting beyond the