Transfer speeds, moulding

Rapid transfer. If the transfer speed is not adequately controlled a too rapid transfer may occur, leading to turbulent or jet-like flow of the material into the mould cavities. This can cause vents to be blocked before all the unwanted volatiles have escaped from the cavity. Too fast a transfer may also lead to excessive heating of the compound and premature gelation which can cause void formation. 

In commercial use are a wide variety of machines which transfer fixed volumes of compound to clamped moulds, by the operation of a ram in a cylinder fed with pre-heated slugs. These machines are capable of high speed semi-automatic cycling and are a great advance over the use of loose transfer moulds in conventional presses. The components which are produced are to a large degree flash-free, it only being necessary, in the majority of cases, to remove the injection feed and runner system. 

In the blow and blow process the gob is dropped into an open blank or parison mould. The neck is formed by top blow and then the parison or blank is blown from the base (Figure 6.2). The blank shape supported by the transfer ring is then transferred to the finishing mould where it is blown into the final shape. This blow and blow process is the major process employed—usually with IS (i.e. independent or individual section) machinery Other machines include Roirant R7, S10 and Lynch 44. IS machines may have 4, 5, 6, 8, 10 or 12 stations. For small containers double, triple or quadruple gobbing may be employed. The last can give speeds of over 400 containers per minute. 

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