High-Quality Seals in a Single Step
Using the newly developed SFIT process (Soft Foam Injection Technology), it is possible to attach flexible foam seals (e.g. made of polyurethane) onto thermoplastic parts directly in the injection mold. The process is carried out on a conventional injection molding machine with a control system for single-component molding. An external foam preparation module supplies the polyurethane (PUR). The foam forms outside the mold through discontinuous physical incorporation of compressed air at a pressure of 80 bar in a closed piping system with a dynamic mixer. The PUR mass is thixotropic in nature, so that the incorporated air bubbles remain stable in the as-yet uncross-linked PUR. The foam is then attached to the previously injection molded part in a 2-component mold a retractable core, after which cross-linking takes place.
Until now, seals were often attached to plastics parts via 2-component injection molding. The thermoplastic elastomers often used as the seal material can, however, undergo plastic deformation over time and when subjected to certain temperatures, so that the sealing action is limited. At low ambient temperatures, the lack of elasticity in the TPE material also leads to leaks. In contrast, PUR seals exhibit good resilience over a range of temperatures between -40 and +90°C.
The SFIT process represents an alternative method to producing flexible PUR seals by means of the so-called FIPFG technique (Formed In Place Foam Gasket). In this case, a robot places the cross-linked PUR foam onto the plastic parts after injection molding. Since with SFIT the time needed for the foaming process is usually less than the cooling time for the molded thermoplastic parts, short cycle times and higher productivity are achieved. Moreover, the process is characterized by a low upfront investment and minimal space requirement, since no additional automation or warming ovens are required.