Periodic operation furnace, suitable for heat treatment of rod and long shaft parts. The structure of the pit furnace is that the furnace body is a cylindrical deep well, and the workpiece is vertically heated in the furnace by a special crane. The fuels used are usually gas and oil. When electricity is used as a heat source, it is called a well-type resistance furnace. Pit-type furnaces are generally placed below the ground level of the workshop, and some are placed above the ground level, or half each above and below the ground level. The names of pit furnaces are: forced convection pit furnace, natural convection pit furnace, pit furnace gas carburizing furnace, etc.