issue 63 - Camberley Auto Factors Ltd

PRODUCT FOCUS
Suspension
SPRING BREAK
Automotive coil springs are one of the most central and dynamic components
of a vehicle’s suspension system; constantly working to absorb shocks, keep
the wheels in contact with the road and deal with uneven road surfaces. It is
therefore no surprise that after many millions of cycles, even the best made
springs will become tired and begin to sag; vehicle ride height will drop and
may become uneven, and eventual breakage is likely.
There are several reasons for spring failure, and Lesjöfors take various steps
to combat these to ensure the longest possible service life.
Surface and inner defects can exist in lower quality spring wire material. This
reduces performance by lowering spring fatigue strength and significantly
increasing the risk of breakage. Although almost all melting plants today can
produce steel with the specified chemical analysis of ‘spring steel’, only a
few mills are able to achieve the surface & wire quality necessary for modern
suspension springs with high stress levels.
• Lesjöfors only use high-grade, specialist ‘spring steel’ from selected mills
worldwide.
When springs are cold coiled, as many suspension springs are, negative internal
stresses are introduced. These must be removed by heat treatment or the
chance of failure (breakage) is increased significantly.
• Lesjöfors remove these negative internal stresses through a controlled
stress relieving heat treatment process after cold coiling. Following this,
it is important to introduce and control the level of positive residual stress
in the spring, as this will reduce shear stress during compression. The
controlled use of shot peening and presetting ensure high positive residual
stress levels within the spring and consequently a reduced risk of breakage
during use.
Some manufacturers use spring wire which tapers towards each end. This
generally produces a weight saving, but the risk of premature spring failure is
increased since the level of stress increases.
SHOCKING NEWS MAKE A WISH THE
14 :: INDEPENDENT
In independent tests, it was found that a car
fitted with 50% worn shocks could have a
braking distance up to 6 metres longer than the
same vehicle fitted with 100% efficient shocks,
despite its ESP and ABS systems. This research
also demonstrated that the same car with worn
shocks was more difficult to control in a collision
avoidance manoeuvre, thereby extending the risk
to car occupants and other road users.
A regular shock absorber check can be a
life-saver and these tests show that even drivers
of cars fitted with the latest technology need to be
aware of the dangers that worn shocks represent,
particularly if they cover a lot of miles.
The demands on certain commodities within the steering
family are much higher than others. Products such as
wishbones, link stabilisers and aluminium parts continue
to have high replacement rates. The Delphi range of
wishbones are all supplied with bushes and ball joints
where required.
Wishbones account for more than 50% of steering
and suspension replacement parts on vehicles. Faulty
wishbones are one of the main reasons for MOT failures
or excessive tyre wear.
There are some misconceptions th
rate can only be achieved with tap
that all tapered wire springs are pr
in the case of minibloc (rugby ball
or otherwise) manufactured from t
load and deflection characteristics
rate is observed, since the reduce
compensate for the reduction in th
spring rate generally stays consiste
springs made from parallel wire ca
progressive spring rate. The dange
that stresses are almost the same
meaning the end (or transition) co
most active part of the minibloc, th
breakage. Tapered wire spring des
diminishing part of the market wit
now using a parallel wire design as
• Lesjöfors choose only to prod
thickness), offering springs le
by a 3 year warranty.
Corrosion is the most common ca
the layer of lacquer cannot be avo
steel will begin to rust immediatel
which spreads rapidly, greatly red
coils on a tapered wire spring, car
corrosion attack, then breakage w
a parallel wire spring. Tapered wir
where the spring leaves the spring
the risk of breakage when expose
• Lesjöfors provide an addition
the paint and the spring by u
phosphating on every spring.
after defects occur in the pai
preventing corrosion than oth
Replacing
nuts, spac
out is alwa
top suspen
the same
like all aut
worn to the
and safety
SKF suppl
handling a
vehicle.
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