Multi-impression mould

Feed system for a multi-impression mould (after Pye). 

J1 Feed system of multi-impression mould as portrayed by the assembly when it is... 

The operational time cycle for vacuum forming will of course vary according to the complexity of the product and the nature and thickness of the sheet material. Smaller items can be produced on multi-impression moulds and fully automatic special purpose machines are available which will produce from thin sheet food pack containers trimmed, content filled and sealed at a rate of many thousands per hour. 

This is the simplest mould design. Mould cavities are formed in one plate only with the stationary half of the mould blank. A central sprue bushing can be placed into the stationary half of the mould or it is possible to have a direct runner system to a multi-impression mould. The moving half of the mould contains the ejection mechanism. This is illustrated in Figure 4.1. 

The elimination of cold sprues and runners in multi-impression moulds which would normally be scrapped or reworked... 

This type of gating can be used as an alternative to side gating, especially in multi-impression moulds, to produce articles of a flat or shallow nature. It has certain advantages over normal side gates in that the design minimises the jetting of material into the mould cavity which leads to weld lines and flow marks. It also creates turbulence which is an aid to dispersion when moulding dry-coloured material. 

For multi-impression moulds, which are used to produce tubular type articles, this type of gate ensures consistent filling of the moulds. It also helps to ensure that the core pin is central with the cavity, whereas using an ordinary side gate the initial pressure would tend to displace the core pin and so cause the article to have an uneven wall section. 

Minimum production runs vary according to the size of article being moulded, but, as an example, half a million would probably be the minimum run for a screw cap. For a multi-impression tool for such a moulding (say one producing 40-50 caps per cycle) the mould cost would be of the order of 1000-1500. 

Fig. 17. Insulator moulding in Dough Moulding Compound, moulded in a multi-impression positive tool. (Courtesy of Brookhirst Igranic Ltd.)...

The use of the hot runner technique for feeding multi-impression and large area mouldings is now firmly established. The advantages of hot runner mouldings are as follows ... 

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