Plated washer shall be clamped to a height equal to the actual material thickness plus 0'127 mm for a minimum period of 24 hours without breaking. The clamping shall be accomplished between parallel flat surfaces for flat varieties of tooth washers and between mating countersunk holes and cones for countersunk tooth washers. The hardness of surfaces, between which the washers are compressed, shall be more than that of washers under test.
Sampling and Acceptance – The sampling and acceptance criteria for testing and inspection of lock washers shall be in accordance with IS : 6821-1973 'Methods for sampling non-threaded fasteneres'.
Certification Marking – Details available with the Bureau of Indian Standards
Multi-tooth lock washers are used with screws and nuts to effectively add spring take-up to the screw elongation and to increase the frictional resistance under the screw head or nut face. These are normally used where security of assembly is critical.
Lock washers of Type A (externally toothed) are used with normal hexagon head and other screws where projection or teeth beyond screw head or nut is not objectionable.
Lock washers of Type B (internally toothed) are used where projection of teeth beyond screw head or nut is objectionable, that is, with cheese head screws or cap screws used in counter bores.
This standard was first published in 1969. The following changes have been made in the present revision:
The outside diameters for toothed lock washers of Type C have been altered for some sizes to suit the slotted countersunk screws [IS : 1365-1978 Slotted countersunk head screws (third revision), IS : 8911-1978 Slotted raised countersunk head screws], and recessed screws [IS : 7485-1974 Cross recessed countersunk head screws (dia 2'5 to 10 mm), IS : 7486-1974 Cross recessed raised countersunk head screws (dia 2'5 to 10 mm)].
Reference to material has been updated and provisions for surface protection of lock washers included not covered in the earlier edition. In the revision, a reference is also made to IS : 6821-1973 for sampling plans and acceptance criteria.
Embrittlement test has been incorporated to check the stress relieving and also method of conducting temper test has been simplified.
In the preparation of this standard, assistance has been taken from DIN 6797-1971 'Toothed lock washers' issued by Deutsches Institute for Normung (DIN).
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