Accuracy and flexibility
It is for this reason that it is popular for use in safety footwear by direct moulding on to the lasted upper in either a single or dual density format. Nevertheless, extreme accuracy in terms of lasts and moulds are required due to its very low viscosity, so tolerances of around 0.2mm are called for to ensure no material is exuded during the injection cycle.
The milling machines used to produce lasts for this process have special holding systems that allow the entire surface of the last to be milled including both toe and heel. This results in lasts that are so precise they can be used for direct injection soling using PU without the risk of flash. This is how German last manufacturer Fagus-GreCon produces its HPM lasts, designed for use in conjunction with rotary PU moulding machines and fitted with specialised top plates that are compatible with automated production systems and Industry 4.0.
