COLD DRAWING IS PERFORMED ON STEEL TUBES FOR BETTER PRECISION AND SURFACE FINISH WITH IMPROVED MECHANICAL PROPERTIES. THE INVOLVED PROCESSES ARE HEAT TREATMENT, SURFACE LUBRICATION AND DRAWING, STRAIGHTENING AND TESTING FOR END USE. HEAT TREATMENT: THE FURNACE USED FOR THIS PURPOSE IS A CONVEYERISED ROLLER HEARTH FURNACE WHERE THE CHARGED MATERIAL IS HEATED IN A HEATING CHAMBER AND THEN COOLED WIT
H CONTROLLED ATMOSPHERE TO HAVE CERTAIN PROPERTIES. THE TREATMENTS ARE NORMALIZING, ANNEALING, TEMPERING AND STRESS-RELIEVEING. SURFACE TREATMENT: A SERIES OF TANKS LINED AND FILLED WITH FLUIDS TO GIVE A LUBRICATED SURFACE ON THE TUBE FOR DRAWING. A BOILER IS ATTACHED TO SUPPLY HEAT TO SOME OF THE FLUIDS AND THE TEMPERATURE IS MAINTAINED WITH IN A RANGE DEPENDING ON THE CHEMICAL. THE INPUT MATERIAL IS DIPPED WITH A CRANE IN THE TANKS SYSTEMATICALLY TO GET A LUBRICATED SURFACE. DRAWING: A MACHINE CALLED ‘DRAW BENCH’ IS USED FOR THIS PURPOSE. A DIE AND A PLUG IS USED FOR DRAWING THE TUBE TO HAVE THE DESIRED DIMENSION. FIRST THE TUBE IS LOADED ON THE PLUG, HELD BY A ROD, AND THEN PULLED THROUGH A DIE BY THE CARRIAGE OF THE MACHINE. STRAIGHTENING: THE BEND CREATED IN THE DRAWING PROCESS IS STRAIGHTENED BY A SPECIAL PURPOSE MACHING CALLED ‘STRAIGNTENING MACHINE’. THE TUBE IS PASSED THROUGH A SET OF ROLLS WITH PREDETERMINED POSITION TO GET THE STRAIGHTNESS. TESTING: EDDY CURRENT TESTING AND PRESSURE TESTING IS PERFORMED ON THE FINISHED TUBES TO ENSURE SUITABILITY FOR THE PURPOSE.
