Too many engineers are selecting chain according to the wrong criteria and are ending up with a product that is destined to either premature wear, or even failure, as a result. That is according to a recent report on Renold Chain's website as the company launches a series of initiatives to try and educate engineers that chain will last longer if it is specified correctly. According to the company a lot of engineers are using breaking load as an absolute measure of performance when there is a huge variation in working life for different chains with identical breaking loads. Explaining the origin of the problem Renold Chain's marketing manager, David Turner, said: 'You can't blame engineers for using breaking load as a criteria for
selecting chain. Breaking load was one of the earliest chain standards so engineers got used to specifying it that way and many of them still do. What we have to do now is to re-educate engineers that breaking load is no guide to chain performance, and that chain strength is not the best measure of chain life. In fact, high tensile strength can lead to a shortened working life if component strength has been achieved by making parts hard but brittle.' It was back in 1925 when the first chain standard was introduced: BS 228 for Steel Roller Chain and Chain sprockets. BS 228 initially contained only minimal requirements for chain and sprocket dimensions but it was broadened in 1934 when minimum breaking loads were included.
Chain design and manufacture has come a long way since
then and a correctly selected modern chain will now last
years on applications that back in the mid twentieth
century might have worn out in a matter of months. Modern
chain is a much more reliable, high-tech product than its
earlier cousins, but to get the full benefit of all the
recent innovations engineers need to select more carefully
from all the new options.
The first thing is to put considerations of breaking load
to one side. Chain should be operated well below any load
at which it could break. In fact, permanent damage will
occur if the load on a chain is more than the elastic
limit of the steel parts. Chain should be operated below
its endurance limit to ensure that wear is the mode of
failure, rather than fatigue, or even complete failure
because of overload.
In order to achieve long wear life it is essential to have
specialist component design, consistent material
specification and the correct balance of heat treatment.
Heat treatment not only refines the mechanical strengths
of components, it will also, in part, increase their wear
life. But it's a fine balance. Prolonged heat treatment to
achieve high tensile strength can leave parts brittle and
with increased vulnerability to fatigue failure.
Of great importance for longer working life is the overall
ability of the selected chain to manage the applied loads
and provide fatigue resistance well above the application'
s anticipated working loads. Most good chain manufacturers
will know the fatigue limits of their products and it is
this that engineers should be taking into consideration
rather than breaking loads.
To help make chain selection easier and to ensure that
engineers get the optimum value and working life out of
chain, Renold has produced a sophisticated chain selector
program that takes all the hit-and-miss out of the
increasingly complex choices. The program can be
downloaded for free from the company's web site and will
select the best chain for any given application. That is,
the smallest chain available that will last a minimum of
15,000 hours - or 30,000 hours for Renold Synergy - based
on factors such as speed, load and the power ratings of
the user's application.
The program selects the best chain from 11 different
product types and 400 chain variations. Using the program
is easy and users will be able to make their first
selections within minutes of installation. The detailed
search results can be printed out and show the optimum
chain to meet all criteria including corrosion resistance,
resistance to abrasive debris, lack of lubrication or the
need for high performance.