Direct injection is the process of introducing a molten material commonly TR/TPR, PVC or PU, into the cavity of a mould to achieve desired shape. This process can be used for outsoles, decorative details or to join an outsole to upper directly.
A molten material, normally a polymer, is forced into the cavity of a mould. When the material solidifies in the mould it takes the desired shape and is removed from the mould. The set up is commonly with one or multiple injection machines positioned around a 8, 12 or 16 arm mould carouselle. The injection process is automated but the moulds need to be dressed with uppers and when injection is done the finished shoe needs to be removed.
In this process either sock lasted or string lasted upper is pressed to a sole shaped mould. The PVC sole compound is injected and it forms a permanent bond with the upper.In this process for textile and vibox application of primer and cement is necessary and in case of leather lasting margin should be roughened. In this case the sole has long wear ability.
In the footwear industry, focusing on assembled shoes, it´s commonly used in a “direct moulding on” process. With this, finished shoe uppers are firstly prepared by dressing a last mould. Surrounding this last mould another two piece mould with cavity for the outsole is positioned to the full upper. This two piece mould includes an injection point where the molten material creating the outsole will be pushed through. When the material cools down it attaches to the upper creating a strong bond.
The process for making outsoles with direct injection is similar where a two, or more, piece mould is used with a cavity for the outsole design. The injected material is introduced into the mould creating the outsole. These outsoles is later used in a cementing assembly process
1.Soles are attached to the upper in a single operation.
2.Shoes wear longer and offer good performance with completely water resistant.
Area in contact with the foot is smooth and comfortable.
3. No stitches.
4.The sole in many cases extending over the side edges is bound to the upper.
Low material wastage in production
Large initial set-up cost.
High production efficiency once set up
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