It was decided to explore the possibilities
of a plastic bush and igus®
was contacted to discuss the situation.
Plastic bushes had previously
been explored and one of the
main problems was electrical conductivity.
It was explained that bushes
made from iglidur® RN89 had
good electrical conductivity and
would recalibrate during the e-coat
process and that this could be a
good starting point. Samples were
manufactured and tests carried
out. It was established that hinges
could be built with a force of 20
newtons and after the e-coat process
this reduced to 8 newtons
with no significant loss in stiffness.
Hinges were tested at -40 degrees
and proved to show very little increase
in torque.
There were two problems that
were highlighted during the test
work. Firstly the life time tests,
30,000 cycle endurance with environmental
exposure, mainly Arizona
dust and salt water. The hinges
failed at 10,000 cycles due to the
bushes rotating in the housing. The
housing holes are punched into
47
®
3.5mm steel and therefore have a small amount of burr. If the bushes
started to move in the housing this burr started to cut into the
bushes until they were completely destroyed. This was temporally
overcome by gluing the bushes into place; the hinges then passed
the endurance tests and also various other tests, including water
absorption, stiffness, lateral displacement and the effect of long
term static loads. The customer additionally carried out these tests
on vehicles in climatic chambers. Vehicles were also built and sent
on long winter and summer test, involving approximately 8 weeks
in cold and hot desert conditions. Secondly, the bushes fell out of
the housing during the assembly process. This was overcome with
the addition of gluing the bushes in to the holes, but this could not
be a production route to take.
An iglidur® bush was designed to stop the rotation and also clip
together in the hole. The design is a simple bush that fits each side
of a shaped hole that is quick and easy to assemble. The cost of
the new bush design is slightly less than the current single steel
backed bush and there are potential cost improvements with the
assembly process.
