TMT rebars (Thermo Mechanically Treated) are generally hot-rolled from steel billets and are subjected to a programmable logic controller (P.L.C.) for the thermo-mechanical treatment. The three major stages of conversion of steel billets into TMT rebars are:
Quenching: When a hot rolled bar leaves the final mill stand (including roughing mill, intermediate mill, finishing mill, etc.), it is instantaneously quenched using a special water spray system in the quenching box. This is done to harden the surface while the core still remains hot and soft.
Self-tempering: After leaving the quenching box, the core continues to supply heat to the surface since it is relatively at a higher temperature. This causes the tempering of the outer martensitic layer into a structure called Tampered Martensite. The core stays austenitic at this stage also.
Atmospheric cooling: There are special cooling beds where the austenitic core gets transformed into a ductile ferrite-pearlite structure. The final structure, thus is a perfect combination of a strong outside layer (tempered martensite) with a ductile core (ferrite and pearlite).
The M.S. Steel Tubes & Pipes are made of from H.R Coils (Hot Rolled Strips) as per I.S. specification IS:1239 etc. in different sizes. The H.R Coils are slitted on slitting machine as per required thickness & width for different pipe sizes.
After slitting the small slits/coil are transferred to Steel Tubes Manufacturing Mills. Coils are loaded on Pay off Reel and passed through looping cage then to the forming Mill which takes shape of open seam pipe through contact welding (H.F Welder). The top welded Flash removed with the help of Scarfing Tools, welded pipe passes through water cooling zone and cooled.
After that the pipe passes through sizing section where the outer dia is maintained & pipe straightened with the help of Turk Head.The required trimmed pipe is rolled out on conveyer & stopped by stopper at end of conveyer and ejected to the pipe collecting pockets. This is a continuous process.
After Rolling process over, the pipes are transferred to end facing machines where end Burr is removed. Each pipes is tested on Hydro Pipe Testing machine to check the leakage on welding seam. This pipe is called E.R.W. pipe.
For the manufacturing of Galvanizing Pipes all end faced and Hydro tested pipes/tubes Galvanizing Plant.
There are five tanks filled with hydrochloric acid, running water and flux. First of all, ferrous oxide/rust of the pipes is cleaned by HCL Acid, when the rust is cleaned then the cleaned pipes are dipped in the running water tank for cleaning HCL Acid.
After cleaning the pipes by running water, the pipes are dipped in flux tank. After this process the pipes are shifted to the bed of heating oven (for drying the wet pipes). The temperature of heating oven is 80’C to 100’C.
After dried pipes are dipped in Zinc bath (Molten Zinc Tank) by conveyor. The temperature of Zinc tank is 440*C to 460*C, each galvanized pipes are lifted from Zinc tank by the help of tang to the extraction unit (conveyor) through an outer & inner air die for releasing the extra Zinc on/in the surface of pipes.
After this process each pipes are dipped in dichromate solution for cooling. When the pipes are dry then they shifted to the threading bed for threading (as per IS: 554-1999) & measurement. After the threading both the threaded ends are varnished & one end is assembled with PVC cap for protection of the thread and other end with sockets & then the pipes are measured, bundled and stocked.
PVC uncompounded resin, unlike some other thermoplastics, is not suitable for direct processing. To confer the required processing and end instability, it is necessary to mix additives with the PVC resin. Following are some of the additives which are generally used for the manufacture of rigid PVC pipes.Plasticizers: The common plasticizer in use is DOP, DIOP, DBP, DOA, DEP,
Plasticizers: The common plasticizer in use are DOP, DIOP, DBP, DOA, DEP, Reoplast, Paraplex etc.Stabilizers: The common stabilizers are lead, barium, cadmium,
Stabilizers: The common stabilizers are lead, barium, cadmium, tin, stearate etc. Lubricants: Widely used lubricants are Buty-Stearate, Glycerol Moni-Stearate, Epoxidised Monoester of oleic acid, stearic acid etc. Fillers: Fillers are also used for producing
Fillers: Fillers are also used for producing the special quality product (e.g. calcined clay is used to improve the electrical properties of cable compounds).
The pipes coming out from the extruder is cooled in the sizing operation. There are basically two types of sizing used for manufacturing of pipes. They are (i) Pressure sizing & (ii) Vacuum sizing.
The next operation needed after sizing is traction. The tube traction unit is required for continuous haulage of the pipes being extruded by the extruder. Cutting: The last operation needed is cutting. There are basically two cutting techniques for rigid PVC pipes viz. manual and automatic. The pipes are then tested for ISI marks and are ready for dispatching.
The last operation needed is cutting. There are basically two cutting techniques for rigid PVC pipes viz. manual and automatic. The pipes are then tested for ISI marks.
The pallets of blocks are conveyed to an automated stacker or loader which places them in a curing rack. Each rack holds several hundred blocks. When a rack is full, it is rolled onto a set of rails and moved into a curing kiln.
Standard weight blocks are usually cured at a temperature of 150-165°F (66-74°C), while lightweight blocks are cured at 170-185°F (77-85°C). When the curing temperature has been reached, the steam is shut off, and the blocks are allowed to soak in the hot, moist air for 12-18 hours.
Another type of kiln is the high-pressure steam kiln, sometimes called an autoclave. In this type, the temperature is raised to 300-375°F (149-191°C), and the pressure is raised to 80-185 psi (5.5-12.8 bar)
The racks of cured blocks are rolled out of the kiln, and the pallets of blocks are unstacked and placed on a chain conveyor. The blocks are pushed off the steel pallets, and the empty pallets are fed back into the block machine to receive a new set of molded blocks.
The blocks pass through a cuber which aligns each block and then stacks them into a cube three blocks across by six blocks deep by three or four blocks high. These cubes are carried outside with a forklift and placed in storage.