SPRING 2024

160
THE DISTRIBUTOR’S LINK
BRUNO MARBACHER LOCKING FEATURES TO PREVENT ROTATIONAL LOOSENING from page 140
Durlok Wedge-Lock Washer
TENSILOK Screw
This type of lock washer is also sold under the name
of Durlok locking wedge washers, they principally function
the same way as NordLock. Durlok wedge lock washers,
when used with standard or high strength screws provide
a high degree of self-locking. Durlok washers come in
pre-assembled pairs. They have wedge faces on the
inside and radial teeth on the outside. The wedge angle
is greater than the thread angle.
Dimensions: M6–M20
Material: Alloy steel heat treated 470 – 540 HV (47-52
HRC)
Wedge lock washers are covered by DIN 25201-4.
Serrated Flange Bolts 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 during 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 against loosening. However, they can
only be used effectively if the screw is appropriately hard
and if the surface of the clamped part is not too hard.
Screws with locking teeth or ribs typically are available
in hex flange screws, some companies make them in
other head styles. Typically, their lengths ought not to
exceed 6-7 x the thread diameter.
The original serrated flange screw was the TENSILOK
screw from Bauer and Schaurte Germany
The Tensilok (serrated) Flange screw is furnished
with 24 interlocking teeth in the bearing area. An
undercut makes the flange flexible, hence compensates
for embedding and loss of preload. They are also provided
with a smooth support shoulder, thus making a firm
contact with clamped material, also controls the amount
of tooth penetration, penetrating too deep, they could, for
example, cut through thin sheets.
TENSILOCK self-locking hexagon flange bolts are
designated with the property classes 90 and 100 with
a min. tensile strength of 900 resp. 1040 MPa (N/
mm 2 ). They are case-hardened and therefore cannot be
classified as the usual classes 8.8 and 10.9. There are
other brands of serrated screws they come in regular
property classes and grades.
The screws/nuts must be properly tightened, otherwise
the serration will not penetrate adequately therefore not
resisting rotation.
A disadvantage of the TENSILOK screws/nuts is the
damaging of the surface of the clamped parts, if the
joining elements must be loosened for repair work, thus
limiting the re-usability. This disadvantage is true for the
serrated flange nuts as well.
Dimensions: M5 - M16
Also available under the name of ZAHN self-locking
screws.
Electroplating or paint will be milled away in any case
and corrosion could form.
CONTINUED ON PAGE 164