Example of fluorine corrosion-resistant T-die

The specifications of the T-die that are compatible with each type of fluororesin will vary. There are various types of fluororesin, including PTFE, FEP, PFA, and ETFE. PTFE is generally molded by compression molding, but other fluororesins can be molded by extrusion, and the specifications of the T-die must be changed in order of increasing corrosion resistance.
High corrosion resistance: Hastelloy T-die. Slightly high corrosion resistance: Nickel-based electroless plating + chrome molybdenum steel. Low corrosion resistance: Hard chrome plating + chrome molybdenum steel. Melting temperature: 350°C (depending on type).
Electroless plating and hard chrome plating require maintenance, such as stripping and regrinding every six months to several years. Hastelloy T-dies are made of a very expensive and difficult-to-cut material. Hastelloy is several dozen times more expensive than chromoly steel, and the processing time is several times longer, making it significantly more expensive than standard T-dies. However, because it is less corrosive, it is not affected by corrosive gases even when stopped for several hours and restarted. Hastelloy dies are also highly deformable and prone to bending. Even when used new, the T-die's centerline can become misaligned after several dozen uses or after being lifted. The bending value can be as much as 1-2 mm per 1000 mm. Repairs are also recommended every few years. By straightening the die's exterior and re-polishing it, it can be restored to like-new condition. Separately, if corrosion resistance is high, lip adjustment bolts and die body clamping bolts may be electrolessly plated to protect against corrosion from corrosive fluorine gases. In some cases, this plating can extend the time between replacements due to corrosion by several years.