For the heat treatment of cylindrical helical compression spring with a length of 50m and an outer diameter of ф 60mm, the spring will be wound with oil quenched and tempered steel wire and then tempered at low temperature to eliminate the winding stress. So far, there is no professional factory to produce this kind of flat cross-section spring in China. Therefore, most of the special-shaped cross-section steel wire is rolled or drawn with round steel wire, and then quenched and tempered after being wound into spring. Obviously, it is very difficult to quench and temper such a long spring. For this reason, the analysis and experiment are carried out
(1) The determination of quenching heating time is based on the fact that resistance heating is internal heat source heating and temperature is a function of time. In this test, stopwatch, optical pyrometer and infrared thermometer are used to measure the continuous heating time of the specimen at different temperatures under certain electrical parameters, so as to determine the quenching heating time.
(2) The choice of tempering time is tested by stopwatch and infrared thermometer. The results show that the tempering heating time is between 25 and 30s.
(3) The choice of quenching medium was tested according to three kinds of quenching media, water and oil polyvinyl alcohol. From the test results, the three quenchants can meet the requirements of hardness and hardenability, but the water quenched specimens have obvious brittleness, and the oil pollution is large and easy to ignite. Through a lot of experiments and comparison, it is suitable to choose 0.5% PVA quenchant.