Shoe Manufacturing Techniques

1. Welted Construction (Sewn-on Process)
This technique involves stitching the upper and sole together by hand or machine, and it is a traditional method used for both leather shoes and cloth shoes. There are two main types: hand-stitching and machine-stitching.

• In hand-stitching, methods such as reverse welted, visible welted, and straight welted are traditional techniques for cloth shoes.
• In machine-stitching, channel-stitched and Goodyear-welted (or rim-stitched) constructions are classic methods for leather shoes.

2. Injection Molding Process
There are four primary methods under this category:

① Injection Molding: Synthetic resin is injected into a mold under moderate pressure and at relatively high barrel temperatures, completing both sole curing and upper-to-sole bonding in a single step. This method is commonly used for cloth shoes but is also applied to leather, plastic, and rubber footwear.

② Rubber Injection (Injection Vulcanization): Rubber is plasticized in a barrel and then injected into a mold under higher pressure, simultaneously forming the sole and bonding it to the upper. Used mainly for cloth shoes and rubber shoes.

③ Casting (Pouring) Method: Precisely measured reactive liquid components (e.g., polyurethane or polyamide) — Part A and Part B — are rapidly mixed in a mixing head and poured into a mold cavity, where they cure and bond under normal or elevated pressure. This method is now primarily used for rubber shoes and some cloth shoes.

④ Slush Molding (Rotational Casting): A plastisol liquid is poured into a negative (cavity) mold of a boot or shoe. While heating, the mold is rotated so that centrifugal force causes a layer of plastisol to coat the inner mold wall and solidify into a shell. Excess liquid is poured out, and the shell is further heated to fully cure. After demolding, linings are inserted. This technique is used for rubber and plastic footwear.

3. Compression Molding (Mold Pressing)
After the upper has been lasted (stretched over a shoe last), the sole—and a sidewall strip in the case of rubber boots—is placed into a mold. The assembly is then subjected to heat and pressure to vulcanize and form the final shoe. This process is widely used for rubber shoes, leather shoes, and cloth shoes.

4. Cementing (Adhesive Bonding) Process
This includes three main methods:

① Hot Vulcanization Bonding: After assembling and gluing the shoe components, the shoe is placed in a vulcanizing autoclave and heated indirectly with steam or directly with hot air/steam. During vulcanization of rubber parts, the upper and sole bond together. In the two-stage vulcanization method—a traditional technique for rubber shoes—the outsole and heel are pre-molded, then attached to other components before being vulcanized in the autoclave. Some cloth shoes also use this method.

② Cold Cementing: Adhesive is applied to the upper and sole, which are then bonded under pressure at room temperature. This is now the dominant method for leather shoes, cloth shoes, and many rubber shoes.

③ Cement-Stitch Combination: After cold cementing the upper to the sole, the perimeter of the sole is additionally stitched to reinforce the bond between upper and sole.