Q. Replacement of loose rivets?
i) Slight slackness of rivet does not cause loss of rivet strength.
ii) Renewal of slack rivets should be done only when the slack rivets are in groups or are bunched up.
iii) Rivet is to be considered finger loose when the looseness can be felt by touch, without tapping. Rivets should be considered hammer loose, when the looseness can be felt only with the aid of a hand hammer.
iv) All rivet renewals in a bridge girder shall be done only with pneumatic rivetting. The following points should be kept in mind while carrying out the rivetting work.
a) In pneumatic rivetting, the driving of the rivet, filling of the hole and formations of the head should be done by snap mounted pneumatic hammer by delivering quick hard blows on practically white hot rivet.
b) The rivet shank should be about 1.5mm less than the diameter of the drilled hole.
c) While rivetting a loose joint, not more than 10% rivets should be cut at a time.
d) It is preferable to drill a rivet out than to use a rivet buster as the latter cuts the rivet head in shear, imparting very heavy shock to the adjoining group of rivets.
e) The loose rivets in a joint are replaced, it is very necessary that all the rivets in the assembly are rechecked for tightness.
f) At locations where replacing rivets is difficult, turned bolts of appropriate diameter and length may be used.
g) The rivet must be driven straight, while hot, keeping the hammer coaxial.
h) Rivets conforming to IRS specifications only should be used.