DIP(Direct injection moulding process):
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.
Many men’s work shoes, some casuals, children shoes and canvas footwear are made by the DIP process.
1.Area in contact with the foot is smooth and comfortable.
2. No stitches.
3.The sole in many cases extending over the side edges is bound to the upper.
1.Soles are attached to the upper in a single operation.
2.Shoes wear longer and offer good performance with completely water resistant.
DVP (Direct vulcanizing process):
Vulcanization is a chemical process used to harden rubber. Vulcanization traditionally referred to the treatment of natural rubber with sulfur and this remains the most common example, however the term has also grown to include the hardening of other (synthetic) rubbers via various means.
Vulcanisation can therefore be defined as the curing of elastomers with the terms 'vulcanization' and 'curing' sometimes used interchangeably in this context. It works by forming cross-links between sections of polymer chain which results in increased rigidity and durability as well as other changes in the properties of the material. Vulcanization with the curing of other thermosetting polymers is generally irreversible.
The word vulcanisation is derived from Vulcan, the Roman god of fire.The process was discovered in 1839 by the U.S. inventor Charles Goodyear, who also noted the important function of certain additional substances in the process. Such a material, called an accelerator (q.v.), causes vulcanization to proceed more rapidly or at lower temperatures. The reactions between rubber and sulfur are not fully understood, but in the product, the sulfur is not simply dissolved or dispersed in the rubber; it is chemically combined, mostly in the form of cross-links, or bridges, between the long-chain molecules.
Rubber can be vulcanized in many ways using different chemicals normally a sulfur mix or by a combination of heat and chemicals. This curing process transforms the rubber from being easy to break, soft and gummy to a durable yet flexible material suitable for demanding conditions such as footwear or car tires.
In the footwear industry the most common way to vulcanize is by heat and chemicals. The rubber need to reach a temperature of 170 degrees to vulcanize properly. This temperature creates limitations in what kind of materials should be considered for a vulcanized shoe. Polymer based fabrics such as polyester, poly-amide or plastic eyelets etc pose big risk of melting in the process. However, there are also heat resistant polymer based materials suitable for vulcanization.
Due to the temperature the lasts used for vulcanized production is made out of aluminium to sustain the heat but also to spread it evenly throughout the product.
The lasting method is normally board lasting where the upper is assembled in the same way as for a cementing construction but dressed around an aluminium last.
The bottom outsole is either calendar or molded and then a foxing tape is wrapped around the connection of the outsole and the upper to hide the gap. Calendar soles are made by running a continuous sheet of uncured rubber through a dual-roller press. The top roller is etched with a tread pattern while the bottom roller is smooth. Once pressed, the soles are cut to shape by either a cutting die or by hand. The uncured soles are then applied to the upper boot and vulcanized together to form a seamless permanent chemical & physical bond.