SPRAY BARS IMPACT ON DRINKS-CAN
PRODUCTION EFFICIENCY
At first glance, the introduction of new spray bar assemblies on a product
washing line looks insignificant. Not so at the Milton Keynes plant of Rexam
Beverage Can Europe & Asia, where each week some 28 million cans are manufactured for customers
in the drinks industry.
Collaboration between plant management at Milton Keynes and nozzle
manufacturers Spraying Systems led to the development of spray bars
that contributed to both operating and maintenance efficiency on a
crucial section of the production line.
The story of this development reflects Rexam’s ongoing programme of
improvement, and illustrates an approach that can be applied in principle
to help any engineer looking to optimise performance and simplify maintenance
of spray wash installations.
The wash units at Milton Keynes, working in parallel, are sited ahead of can
coating lines. They remove oil film from the newly-formed can (a one-piece
cylindrical pressing in aluminium) and treat the metal, ready to receive its
protective coating. Quality is safeguarded at various stages of manufacture
by a series of tests including a grease-detecting test and an electrical resistance
test, to determine the effectiveness of the coating.
As original equipment, each washer incorporated some 4000 nozzles screwed
into ‘risers’ (spray bars) above and below a metal belt carrying the inverted
cans. Servicing the washers was not easy, a problem Rexam sought to address,
but the company is also constantly looking for ways to improve performance.
However, experiments with nozzle spacing and specification were inconclusive
and it was not easy to determine what was happening inside the totally enclosed
washer.
Increasing spray pressure was not an option because it could de-stabilise
cans on the belt.
In consultation with plant management, Spraying Systems analysed the
possibilities, running tests with cans of all sizes. It was established
that the risers then in use, which had wide-angle sprays spaced to limit
the number of nozzles needed, were not ideal for this application.
From the tests and other data, Spraying Systems engineers calculated
optimum spray angles in relation to height, liquid pressures, flow rates
and nozzle spacing. Spray geometry showed that maximum direct-impact
cleaning of all surfaces, including those of the deeper cans, could be
achieved by using narrower spray angles and tighter spacing. Reducing
liquid pressures would further increase cleaning impact by producing bigger
droplets and also safeguard can stability on the belt.
Maintenance procedures could be greatly improved by changing to a new
type of nozzle. The original risers, with stainless steel nozzles
with screw connection into Schedule 40 pipe, were heavy to handle and
slow to service. Each nozzle had to be removed by spanner and its replacement
carefully aligned. A better option was Spraying Systems QuickJet 2-part nozzle
assembly in ProMax glass-reinforced plastic – strong, chemically resistant and
inhibiting formation of deposit at the orifice. After mounting, the body stays
in place and accepts a wide range of interchangeable self-aligning tips that
can be replaced in seconds without using tools.
With limited height available inside the washers, and to accommodate the
higher profile of the ProMax assembly, Spraying Systems AutoJet division
designed and patented a new type of spray bar with a flatter profile and
thinner wall - made possible because the nozzle body screws into welded
mounts, not into the pipe itself. The new risers, manufactured at the
company’s UK plant, were 50% lighter than the old assemblies.
Removal and re-installation of a lightweight riser is safe and easy.
A riser can be lifted out to change a blocked nozzle and put back in
working position within minutes. Thorough routine maintenance, of selected
risers or the complete set, is accomplished well within the times allotted –
a schedule which had been difficult to achieve without risking delay in
resuming production.
Since all risers are made to the same pattern (in either 1” or 1.5” n.b.
tube, depending on space limitation) and all are equipped with the same
ProMax bodies, identically spaced, spares inventories are lower. And a
new spray tip costs roughly 1/6 of the price of a complete nozzle in
stainless steel, with comparable wear life.
Following the successful introduction of the new developments at
Milton Keynes, they have been applied in other Rexam plants.
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| Demonstrating the new spray riser on a maintenance trolley, a Spraying
Systems engineer shows how the sprays impact directly on all internal surfaces of the can. |
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| The new risers are 50% lighter and much easier to service. |
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