Page 26 - Plastics News November 2017

FEATURES
FEATURES

• Jamming of piping network components, One more issue of drop in pressure and remarkable
difference in flow rate is oftenseen at the machine
• Corrosion of metal components,
manifold end between the nearest and the farthest
• Microbiological growth (algae, bacteria, fungus) etc. machine from the pump room for the incoming water,
• Health issues of employees which needs to be handled carefully.Hence it is necessary
to identify the requirement of cooling water as normal
Most of us rather all of us know the fact that moulding cooling water (250C to 350C) and chilled cooling water
processes are cyclic in characteristic. Cooling time is (below 250C) as they are generated by different methods.
about 50 to 75% of the total cycle time and one of the Depending on the location and the humidity level, normal
deciding factors for the quality requirements. Therefore, cooling water temperature can be achieved by cooling
it is important and essential to optimise cooling time to tower of the required capacity and can be used for cooling
improve productivity.
hydraulic oil of the machines, water cooled chillers,
In spite of knowing this fact minimum attention is paid grinders etc. Chilled cooling water temperature can be
towards this, at leastby the domestic injection moulders achieved by water chillers and are used for critical moulds.
and blow moulders. This minimum attention can be due Chilled water cooling requires better control since the
to lack of knowledge of improvements possible or due chillers consumes energy and any change in temperature
to over confidence of running the industry for decades may hamper productivity. Lower temperatures of chilled
together. Production costs can be reduced or controlled water leads to mould sweating and will call for mould
by incorporating systems which may require little or no sweat protector and will consume more energy.
investment.
Another problem is, the cooling lines are often extended
The problems often observed in the moulding shop with as and when the number machines are increased or the
respect to cooling along with quality of water are capacities are expanded without considering the available
cooling capacity. As a result overheating of hydraulic oil
• Cooling tower performance,
in the machine is observed. It reduces the viscosity of the
• Pump performance hydraulic oil, due to which pumps are over loaded and as

• Pipe diameter a cascading effect electrical motor consumes more power
or energy to drive the pump and to develop desired flow
• Design of piping network
and pressure. It also increases the maintenance cost as
• Cooling tank capacity etc. the rubber seals and others packing becomes brittle when

In addition, a serious problem of back pressure is seen due comes in constant contact with high temperature of oil and
to different resistance to flow or “K” value of Machine gives way much before than the expected life cycle. The
heat exchanger and the mould mounted on the moulding mould temperature shoots up due to inefficient cooling
machine. and the defects like flash,sink marks, distortion,warpage,
moulded-in stress, dimensional instability, shot to shot
variation etc, are seen in the moulded product. This
ultimately leads to higher cycle time which hampers
productivity and may not solve the problem.
To encounter this problems the remedies thought of are
descaling of pipes by addition of descaling chemicals in
the cooling tank, Increase in pump capacity, increasing
cooling tower capacity and lastly connecting water
chillers for mould cooling. These solutions may give
mental satisfaction of improving the system but it seldom

Plastics News N ovember 2017 26