“MODERN TECHNIQUES IN TYRE RETREADING” Tyre Retreading Tread is the portion of the tyre which meets the road surface In the manufacture of a new tyre, approximately 20%-25% of the cost is incurred in mfg of the Tread and the rest in body Thus retreading can save a lot of costs for the user instead of changing the whole tyre Retreading is primarily done in the Truck and Bus tyre segment. On an average a Truck/Bus tyre is retreaded 1.5 times. THERE ARE TWO TYPES OF TYRE RETREADING PROCESS HOT PROCESS COLD PROCESS Steps in tyre retreading process Step 1 : INITIAL INSPECTION Step 2 : BUFFING Step 3 : TREAD PREPARATION AND BUILDING Step 4 : ENVELOPING Step 5 : VULCANISING Step 6 : FINAL INSPECTION COLD PROCESS Step 1 : INITIAL INSPECTION The purpose of initial inspection is to verify that a casing is acceptable for a retreading using a thorough inspection of each tyre, inside and outside. Identify casing injuries and determine if repairable. Reject or approve the casing for processing. Step 2 : BUFFING THE PRIMARY OBJECTIVE OF THE BUFFING IS TO PREPARE THE WORN TREAD SURFACE OF THE TYRE TO RECEIVE A RETREAD. THE ORIGNAL TREAD DESIGN AND SOME OF THE UNDERTREAD IS REMOVED TO PROVIDE THE CASING WITH THE REQUIRED DIMENSIONS AND SURFACE TEXTURE. Step 3 : TREAD PREPARATION AND BUILDING BUILDING IS THE PROCESS OF APPLYING A PREMOULDED RETREAD OR NEW TREAD RUBBER TO THE BUFFED AND PREPARED CASING AN UNCURED CUSION GUM THAT WILL DEVELOP THE BONDING BETWEENPREMOULDED TREAD AND CASING IS APPLIED TO THE CASING Step 4 : ENVELOPING IN THE PREMOULD PROCESS THE UNCURED CUSHION COMPOUND HAS TO VALCUNISE WHILE THE PREMOULDED TREAD HAS TO BE KEPT IN THE POSITION. THEREFORE THE TYRE IS PUT INTO THE ENVELOPE WHICH PRESSES THROUGH A VACCUM SYSTEM THE PREMOULDED TREAD UNIFORMLY ON THE CUSHION AND THE CASING ELECTRIC CHAMBERS These chambers are heated by the aid of electricity; they consist of heating elements that are resistance orientated. If no boiler is available these are excellent for the purpose of retreading, and are more trouble free than steam boilers The capacity of the chamber may vary from 3 to 7 , the electric chamber shown has a capacity of 7 tyres. Guages are provided on the chamber to see the pressure and temperature on the the tyres. BOILER In this wood is used as the fuel to produce the steam. The boiler shown is the fire tube boiler In this boiler steam is generated and supplied to the machineries with the help of metal pipes. Step 5 : VULCANISING The purpose of vulcanizing is to apply specified heat and pressure over a period of time to unvulcanised rubber The rubber is cured to the point of best physical properties and maximum adhesion to the surrounding elements In the premoulded process enveloped tyre is put into an autoclave whereas in the moulded process the tyre is cured in proper tyre moulds. Step 6 : FINAL INSPECTION To ensure a quality retread each tyre passes a thorough inside and outside visual inspection. It is mandatory the tyre meets all customer and government regulations. Some retreaders are also using instrumented inspection like x-ray, shearographie or high pressure tester. Unacceptable tyres are rejected and scrapped.