Moulding cascade

Where moulded case circuit breakers are chosen for a plant in favour of fuses the coordination of cascaded units becomes a little more difficult than with fuses. This difficulty arises from the fact that these circuit breakers have a definite or near definite minimum time limit to their time-current characteristic. This causes the lower part of the circuit breaker protection curve to be almost horizontal at a low value of time, typically in the range of 0.003 and 0.01 second. 

Both BZL and MHD produce their material in batches of approximately 500 tonnes. This is in line with an agreed sampling procedure for the metal as it is cast. The MHD bullion is delivered by ship, with up to three 500-tonne batches on a vessel. The BZL bullion is delivered by truck in 24-tonne lots. BZL numbers the blocks as they are cast so that their position on the cascade can be identified. This allows blocks fixtm moulds 4 and 5 to be put straight to the good stock area, because they do not contain speiss. All of the remaining material is screened. 

A shut-off nozzle is the only type of nozzle that allows HR to be used for injection moulding of structural foam, and for sequential and cascade moulding. 

Mould filling control. An HR system with hydraulically or pneumatically closed nozzles has given rise to a new potential for controlling the mould filling process. These techniques are known as sequential and cascade moulding (see Chapter 8.1). 

Two special injection moulding methods have been developed to get around this problem, both based on HR systems with multiple gating sequential moulding and cascade moulding. Both methods require the use of shut-off nozzles with independent control. 

Cascade injection is finding increasing use in moulding of textile linings for the vehicle industry. 

One restriction on the use of sequential and cascade injection moulding is the need to use expensive shut-off nozzles and an additional control system. 

Figure 8.3 Cascade moulding using shut-off nozzles makes it possible to fill the cavity...

Figure 8.4 Two-cavity mould for vehicle interior strips, for cascade moulding. The nozzle opening sequence is determined by the position of the screw during injection [2]...

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