Pulverizer/Mill Machine Spare Parts: Fixed Blades (24 PCS), which is easy ... change about 3 months later. PVC Mill Machine Spare Parts: 1. Fixed Blade & Rotating Knife: according to different material to work ... the same. 2. In general, this kind of mill machine, knife can work about 3 months, also you can take off ... burnish and reuse again, which is convenite to change. Knife blades(For Milling Machine)