This topic is the design of thermoplastic products of plastic ring. Through the heat energy generated by the thermal friction between plastic parts, the contact surface of plastic parts is melted, and then pushed by external pressure, the upper and lower parts are solidified into one, forming separation. Examples of rotary melting: RO filter core, freezing cup, thermos cup, vase, carburetor, shower head, hot water bottle, gas tank, No.1 in faner street.