SPRING 2024

28
THE DISTRIBUTOR’S LINK
Bruno Marbacher
Bruno Marbacher earned his mechanical engineering degree in Switzerland, he also holds a
business degree. He started out as a tool and die maker (poly-mechanic) and over the years he
has held various management positions in quality and engineering. During his time in America
he has developed and given numerous seminars on topics related to the proper use of mechanical
fasteners and machine elements, and assists engineers in solving fastening/assembly issues. His
has groomed and directed many young engineers in fastening/assembly technology. He now
offers his 40 years of experience through writing and lecturing.
LOCKING FEATURES TO PREVENT
ROTATIONAL LOOSENING
Dear Reader, the common lock washers have been
covered sufficiently in the previous issue. In this issue
we address highly effective locking elements and locking
feature in more detail. We cover locking features
suitable for property class 8.8 (8), grade 5 and higher,
these locking methods have been subjected to vibration
testing in a junker vibration test machine or similar. the
reason why screws and nuts stay tight.
Vibration Testing
The Junker vibration test — named after Gerhard
Junker, who published the article “New Criteria for Self-
Loosening of Fasteners Under Vibration” in 1969. It has
become the standard for dynamic testing of fasteners
and analysis of their self-loosening behavior.
A modern Junker test bench should comply with
the requirements of ISO 16130, DIN 25201-4 B and
the former DIN 65151 standards. The DIN 25201-4 B
supersedes DIN 65151 and is more rigorous. While the
original DIN 65151 only specified that vibration testing
must be conducted using a Junker Test Bench, the new
DIN 25201 sets out exactly how the testing must be
completed. Evaluation of locking effectiveness result
ought to be based on same parameters.
Other vibration tests are covered by NAS standards,
for metric fasteners is stipulated by NA0009, and the
testing apparatus is established in NAM1312-107. The
standard test method for unified fasteners is stipulated
by NAS3350, and the testing apparatus is established
in NAS3354. Unlike the Junker test, it does not indicate
loss of preload in the joint. If the rotation of the bolt is
less than 1 full turn (360 degrees), the element has
passed the test.
Most companies use the junker test to evaluate
locking effectiveness.
Many of the products mentioned in this article were
originally patented. Patents typically run about 20 years.
After that other companies can produce that product.
However, they must be offered under a different name,
as the trademark is still in effect.
Different Styles Of Ribbed Serrated Lock
Washers
The most frequent cause of self-loosening is the
side sliding of a nut or bolt head relative to the joint
— resulting in related motion occurring in the threads.
Typically, the gradual rotation causes a bolted joint
to lose its preload (the initial fastener tension when
tightened).
TECHNICAL ARTICLE
CONTINUED ON PAGE 96