WINTER 2024

172
THE DISTRIBUTOR’S LINK
BRUNO MARBACHER SECURING BOLTED JOINTS from page 146
Ribbed Split Lock Washers
Ribbed split lock washers lock in a similar fashion to
ribbed lock washers. However, they are less stable than
the ribbed washers and there is always the risk that the
split lock washers open during installation, thus losing
their effectiveness. The risk is particularly high when the
screw head sits on the open ends.
NordLock Locking Washers
A special type of serrated locking washer is the
NordLock washer. There are always 2 washers needed,
jointly they provide the locking effect.
When a fastened joint is tightened, the serration of the
two lock washers will line up. If the screw is subjected to
vibration and as a result wants to come loose the washer
will rotate slightly.
Since, however the serration angle () is larger than
the thread helix angle (), the loosening of the screw
is reliably prevented through the “increase in washer
thickness” of the double washer.
To make sure they always are placed correctly,
Nordlock washers are pre-glued.
Nord-Lock X-series washers also have a spring effect,
thus secure against rotational loosening and loosening
due to relaxation.
Serrated Flange Screws And Nuts
Normal flange screws/nuts are already more immune
to vibration than normal hex cap screws and hex nuts
due to their larger bearing area diameter.
If the flange is also ribbed or toothed, its friction
on the surface of the clamped part is considerably
increased. Serrations under the screw head dig into
the clamped member when tightening. Loosening of the
screw becomes more difficult.
The teeth are directed against rotational loosening of
the screw/ nut and are therefore a very good safeguard.
However, they can only be used effectively if the screw
is sufficiently hard and if the surface of the clamped part
is not too hard.
An improved version of the
serrated flange bolt is the
one that is furnished with
ribs. They do not have any
teeth on the lower side of the
flange, but radial ribs on the
entire bearing surface.
After tightening the ribs have penetrated, they produce
enough additional friction against a spontaneous
loosening. However, they do not damage the surface of
the clamped part during maintenance and repairs.
Typically, the ribbed screws /nuts are harder than
separated ones. Their strength corresponds approximately
to class 10.9/10.
To Prevent Screws And Nut From Separating
If a screw or a nut has become somewhat loosened,
there is no longer a locking effect in the bearing area.
There is a risk that the fastener will continue to back out.
That is when fasteners who have locking features in the
thread come in. These locking features do not prevent
the initial rotational loosening of joined elements. If
there are intense vibrations acting on the clamped parts.
a certain amount of loosening is to be expected.
CONTINUED ON PAGE 178