Page 116 - Module DMV20173

6.0 POLYMER PROCESSING

4. There are two distinctive types of system:

a) hydraulic
b) toggle

5. The hydraulic system uses oil under pressure that operates on .a piston connected to
the moving platen of the machine.
6. This causes the mold to close and the clamp force can be adjusted so that molten
plastic does not leak from the mold.

EXERCISE 6.1

1. An injection-molding machine is divided into two principal components; identify them.

2. What are the two basic types of clamping units?

6.2.6 CONTROL SYSTEMS

1. The trend today is for the control systems of injection molding machines to move from
process indicators and controllers to the sophisticated microprocessor fully controlled
machine.

2. The control of some machines can go to the extent of start up control and quality control
monitoring and instructions to the machine.
3. The normal parameters monitored and controlled are the barrel temperature controls.
4. There are at least two barrel zones and generally three as well as a nozzle zone to be

heated and controlled.
5. Many systems now use proportional controllers in which the heat is supplied as a
proportion of a maximum figure depending upon the difference the controller is away
from a predetermined value.
6. This gives a smoother temperature control and should eliminate the normal over and

under shooting of the barrel temperature.
7. Still widely used is sequence control in which timers control the length of the functions
such as the injection and cooling cycle.
8. Limit switches are used to activate the injection cycle, mold open position, screw back

distance.
9. The sequence control allowed the machine to repeatedly perform the same cycle of
operations.
10. The use of a pressure transducer in the mold, such as under an ejector pin or in a
special.
BPLK 148 DME 1083