SPRING 2024

140
THE DISTRIBUTOR’S LINK
BRUNO MARBACHER LOCKING FEATURES TO PREVENT ROTATIONAL LOOSENING from page 96
Ripp Lock Washer
RIPP LOCK® washers have radial ribs on both sides.
This lock washer is not dished, therefore does not
compensate for relaxation of the joint.
The contact angle at the foot of the ribs is noticeably
larger than the gradient angle of the thread.
Because of the preload force the ribs of the RIPP
LOCK® washers are pressed into the surface of the
parts being clamped during assembly.
The resulting form-lock prevents spontaneous
loosening of the bolted joint, even under severe
vibrations.
Dimensions: M4–M30
Material Steel Hardness 400 – 500 HV (45 – 49 HRC)
Due to their high hardness the washers can be used
with screws of all property classes up to 12.9.
NordLock Washer
A special type of serrated locking washer is the
NordLock washer. There are always 2 washers needed,
jointly they provide the locking effect.
Dimensions: M6–M130.
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.
NordLock washers provide excellent locking against
spontaneous loosening. Nevertheless, there are a few
points to be considered:
One must always use 2 lock washers. Lightly glued
double washers are available. However, they must be
installed separately when reassembled.
If the lock washers are packed individually, meaning
not glued together, there is always the risk that only one
washer is assembled. Another problem is that they may
be assembled facing the wrong direction.
The lock washers lock only against rotational
loosening and not against relaxation of the joint. Also,
they don’t stop an already loosened joint from baking-off
and separating.
The lined-up teeth are not completely closed, causing
a capillary effect and as a result crevice corrosion.
The corroded serrated surfaces won’t slide as easy as
new ones, thus impairing the locking effect.
To assure the washer slides in the serrated interfaces
of the two washers, the washer should not slide between
the interfaces of the washer and the bolt’s head, neither
should it slide in the interface of washer and clamped
part.
Therefore, each washer has a ribbed surface, which
must dig into the bearing area of the bolt as well as the
clamped parts. If the bolt or the clamp parts are too hard
this cannot happen.
Material: Alloy steel, hardness 465HV (46 HRC)
CONTINUED ON PAGE 160