Preparation of diamond coated floating core head and its application in copper pipe production

Objectives: In the refrigeration industry, thin-walled copper tubes are crucial heat exchange devices, and during their drawing production process, the floating core head plays a significant role in the quality of the copper tubes. With the rapid development of chemical vapor deposition(CVD) diamond coating technology and its wide application in the field of molds, the DC arc plasma injection method is used to produce diamond-coated floating core heads to improve the quality of copper tube drawing and extend the service life of floating core heads. Methods: Using a deposition method and a rotating device design, the diamond coating was uniformly deposited on the surface of cemented carbide floating core heads by the DC arc plasma injection method. The surface roughness, morphology, mass uniformity, and film-base adhesion of the coating were tested and analyzed using a white light interferometer, scanning electron microscope, Raman spectrometer, and indentation method. The prepared diamond-coated floating core head was applied to a high-precision copper pipe production line, and the application effect was compared with that of a traditional cemented carbide floating core head. Results: SEM and Raman spectrum analysis showed that the diamond coating quality at each position of the floating core head was superior. The average thickness of the diamond in the cylindrical section of the floating core head was 13.3 μm, and in the fixed diameter section, it was 13.7 μm. At a room temperature of 20 ℃ and a relative humidity of 40%, with a filtering cutoff wavelength of 250 μm and a scanning area of 100 μm × 100 μm, the average surface roughness (R_a) of the polished diamond coating was 76.4 nm. Under the indentation test condition of loading to 1 000 N and holding constant force for 3 seconds at a fixed loading rate of 20.0 N/s, the average distance from the diamond coating shedding position to the indentation center was 287.9 μm. The prepared diamond-coated floating core head was then applied to the high-precision copper pipe production line. Compared with the cemented carbide floating core head, the following findings were observed: (1) Due to the excellent finish and self-lubrication characteristics of the diamond coating, the maintenance frequency of the floating core head decreased from once per frame to once every 20 frames, reducing labor intensity significantly. (2) Due to the excellent wear resistance of the diamond coating, the size of the fixed diameter section of the core head remained constant, ensuring that the wall thickness of the copper tube did not vary, therefore improving product consistency. (3) The service life of the diamond-coated floating core head was about 15 times that of the cemented carbide core head. Conclusions: The DC arc plasma injection method can uniformly deposit high quality diamond coating on the surface of cemented carbide floating core heads, reducing labor intensity effectively, ensuring consistency in copper tube production, and extending the service life of the core head in practical applications. Others: With the continuous progress of DC arc plasma jet deposition diamond coating technology, the quality of diamond-coated floating core heads will further improve. Diamond coatings can gradually be applied to various internal molds, such as fixed core heads and threaded cores. When used with diamond coated outer molds, these internal molds can replace traditional cemented carbide molds, reducing mold costs and labor costs, and improving the drawing quality of pipes significantly. This approach will help achieve the goal of reducing costs and increasing the efficiency in the copper, aluminum, stainless steel and other related industries.