Applicable metal rods in natural air hardening by annealing is the fire of natural convection pit type resistance furnace, the furnace reasonable cloth wire method is used to improve the uniformity of temperature in the furnace, furnace cover adopt mechanical lever hoist, operation more convenient, greatly reduces the labor intensity, in order to control moderate uniformity in the furnace, ensure the quality of products using SSR solid state relay and intelligent instrument for temperature control, the other has dahua instrument to record the work process and overtemperature alarm device.