Page 30 - Plastics News July 2020

In addition, a serious problem of back pressure is seen due tower capacity and lastly connecting water chillers for
to different resistance to flow or “K” value of Machine heat mould cooling. These solutions may give mental
exchanger and the mould mounted on the moulding satisfaction of improving the system but it seldom works, as
machine. the root cause is not attacked yet. It is like trying to treat
stomach ache with a pill to cure headache.
One more issue of drop in pressure and remarkable
difference in flow rate is often seen at the machine The systematic and scientific approach to the issue will not
manifold end between the nearest and the farthest only solve the problem but help to reduce energy
machine from the pump room for the incoming water, which consumption. It ascertains a reliable and consistent cooling
needs to be handled carefully. Hence system and increase the productivity. The
it is necessary to identify the systematic approach can improve the
requirement of cooling water as productivity upto 18% and in some cases
0
0
normal cooling water (25 C to 35 C) even more. The bottom line is to reduce
and chilled cooling water (below per kilo moulding cost and increase
0
25 C) as they are generated by profitability.
different methods. Depending on the
As a systematic approach one needs to
location and the humidity level, design the piping network for equal flow
normal cooling water temperature and pressure as far as possible, at all the
can be achieved by cooling tower of nodes. It is possible by computerised
the required capacity and can be used simulation of the piping network. A
for cooling hydraulic oil of the Computer simulation is an attempt to
machines, water cooled chillers, model a real-life or hypothetical situation
grinders etc. Chilled cooling water on a computer to study the working of the
temperature can be achieved by proposed or existing system. By changing
water chillers and are used for critical variables during simulation, predictions
moulds. Chilled water cooling may be made about the behavior of the
requires better control since the system under study.
chillers consumes energy and any
change in temperature may hamper As a precautionary measure do not trust
productivity. Lower temperatures of the original drawings of the system.
chilled water leads to mould sweating Systems are often changed and modified
and will call for mould sweat to meet the new demands and the
protector and will consume more drawings will often be out of date or
energy. Another problem is the simply wrong.
cooling lines are often extended as During simulation, optimization can be
and when the number machines are done. “Optimization” means the use of
increased or the capacities are mathematical algorithms in order to
expanded without considering the maximize or minimize any given quantity.
available cooling capacity.
Needless to state that much can be
As a result overheating of hydraulic gained, with computerised simulation,
oil in the machine is observed. It which in turn is very difficult and time
reduces the viscosity of the hydraulic oil, due to which consuming if done manually. The pipe diameters depending
pumps are over loaded and as a cascading effect electrical on the material used like PVC, GI, MS etc. and its “K” value,
motor consumes more power or energy to drive the pump pipe fittings, pump depending on its performance curve,
and to develop desired flow and pressure. It also increases flow and pressure requirements at all the nodes can be
the maintenance cost as the rubber seals and others decided while simulating the piping network. The biggest
packing becomes brittle when comes in constant contact problem of back pressure can be tackled easily and the
with high temperature of oil and gives way much before system can perform without any back pressure. The precise
than the expected life cycle. balance of piping network balances the network even when
The mould temperature shoots up due to inefficient cooling the part of the moulding shop is under maintenance, mould
and the defects like flash sink marks, distortion, war page, change or in the worst case closed. Above all turbulent flow
moulded-in stress, dimensional instability, shot to shot through the piping network can be made possible.
variation etc. are seen in the moulded product. This Scientifically it is proved that turbulent flow give 30% better
ultimately leads to higher cycle time which hampers cooling than laminar flow. By simulating the water flow in
productivity and may not solve the problem. the designed pipelines, much can be gained since the
software allows one to make most of the tedious and cost-
To encounter this problems the remedies thought of are consuming trials and errors in the virtual world, instead of
descaling of pipes by addition of descaling chemicals in the on the shop floor.
cooling tank, Increase in pump capacity, increasing cooling

July 2020 30 Plastics News