Long Lasting Protective Finish
Steel when it is delivered from the rolling mill
has a ‘mill scale’ coating which is created in
the production process of the steel. Mill scale
is a form of rust that must be removed if the
paint finish is to provide adequate protection.
Witter Towbars is (at the time of writing) unique
in the UK having invested in an inline Shotblast
machine that is integrated into the paint line
facility. Towbars are loaded onto a continuous
track that passes through an inline ‘Shotblaster’
where almost two tonnes of shot are propelled at
the bare metal from eight high speed blasting
wheels at a velocity of 70 metres per second.
The machine, which is almost as large as a small
house, cleans thoroughly any trace of mill scale
and rust from the surface. The ‘clean’ towbars are
now very vulnerable and need to have a
protective coating applied very quickly to prevent
any rust developing. (Steel that has been
thoroughly cleaned of all surface rust and
contaminants can start to rust within a few minutes in the UK atmosphere). This is the big
advantage of having a Shotblast machine
integrated into the paint line facility.
The towbars after leaving the Shotblast machine
are immediately passed through a seven
stage zinc phosphate pre-treatment system in
which the bare metal surface is chemically
prepared to ensure effective adhesion of the final
powder coating. Zinc phosphate is used rather
than the more common iron phosphate
pre-treatment. Zinc provides a higher quality of
protection than iron, and is a more complex and
expensive process.
The towbar continues its journey into an oven
to remove any trace of moisture on the
surface before having the powder coating
applied. Four automatic oscillating guns apply
a very durable automotive specification resin
coating (paint finish) which is then cured at
temperatures of approximately 220 degrees
Celsius. The powder coating provides a robust
and long lasting protective finish to the towbar.
You can have confidence that the paint finish is
built upon layers of technology designed to
meet the arduous conditions experienced in its
lifetime of towing.
All paint finishes are not the same, it’s what you cannot see that is vital for ensuring durability.