Article#200422: The Making of “Rubber” Shoes, Part 2: Injection
Injection stations
In Part 1 of The Making of Rubber Shoes: Moulds I explain shoe moulds (tooling) that make shoe part based on design requirement. The actual process of making a shoe part is through injection.
The size of injection station is based on the number of compartments. Factory will decide what size of injection station required based on production size and production order timeline. In my years of visiting footwear factories, the smallest injection station has 4 compartments and the largest injection station is 12 compartments.
A entire injection station essentially carries 3 key functions: a mould loading railing; an observing control panel and material feeding.
A railing style system is used to load heavy aluminum footwear moulds into each compartment of an injection station.
The buttons on the side of the machine are the control panels. Injection process is controlled by temperature, pressure, speed and time, etc.
An injection station has an extremely complicated, intricate and most important material mixing, feeding system.
Injection Process
In general, an injection molding process consists of four steps: melting compound (PU and EVA are the most common basic footwear compounds); injecting material into moulds to create footwear parts (upper, midsole); a cooling period (to ensure the form of shoe part injected will not expand or shrink after ejecting); and ejecting out final product (for inspection of quality).
The brands focused on utilizing injection to make footwear are Havaianas; Crocs; Native, Biion, etc. Shoe styles are including flipflops, beach sandals to rain boots.
