iso certified 9001 2008
Process & Procedure: the way of OUR quality product

The process at a glance

  1. Large Yard for Unfinished & Finished Goods.
  2. Semi Automatic & Manual Blasting Machine.
  3. Material Handling Equipments.
  4. Overhead Cranes.
  5. Forklifts.
  6. Conveyor.
  7. Galvanizing Bath of 13.5M LONG 1.6M WIDTH 2.1M DEEP.
  8. Logistical Support: Fleet of Trucks & Trailers.
  9. Quick Delivery.

 

GALVANIZING PROCESS

Flow Chart

flow chart

Hot Dip Galvanizing: Applicable specification & Client requirement as per BS : 729 / EN ISO 1461 / ASTM A-123.

  • Minimum average zinc coating: As per BS : 729/ EN ISO 1461 / ASTM A- 123
  • Vent holes shall be drilled as per ASTM A-385
  • Customer will arrange for inspection and finished items shall be transported back only after inspection & release note.
  • "Union Metal Coating" can handle jobs up to 16 meters in length by Double dipping and 12 meters in length by single dipping, depending on its shape & sizes
                   (with prior reconfirmation).
  • Handrail panels, material with thin cross sections or welded structures have strong possibility to get distorted, the straightening of which would be not in the scope
                   of "Union Metal Coating".
  • The Galvanizing surface in general shall be free from bare spots, dross, flux inclusion and ash inclusion.

 

Procedure

Quality system is in accordance with ISO : 9001 - 2008

  • Receipt of Black Materials from Customers.
  • Materials, when received from customers are inspected for the suitability of proper galvanizing for the following.
    • For any Paints/Tar depositions, weld fluxes etc.
    • Any deformation / Warpage.
    • High Degree of Corrosion.
    • Provision of vent. / Drainage holes.
    Any of the defects found are either rectified in the plant or the material is returned to the customer for rectification. Sand blasting is done in case necessary.

    Once the material is accepted for galvanizing it is identified, segregated and tagged according to the thickness / sizes for the conveniences of galvanizing and for proper traceability.
  • Jigging
  • The materials are loaded in the jigs and secured properly by wires, chains or hooks. Hooking will be in such a way that wire marks and chain marks are restricted to the minimum.
  • Degreasing
  • Material is dipped in the degreasing tank for the removal of oil grease etc. Temperature of the bath is maintained between 50ºC to 80ºC

    The degreasing solution is acid based and the concentration is 5 to 15% by weight. The retention time of the material inside the tank depends on the amount of deposits and is generally between 15 to 45 minutes and is visually inspected for cleanliness.
  • Pickling
  • The material after degreasing is transferred to the pickling tanks for the removal of rusts and scales. The picking solution is Hydrochloric Acid of concentration strength 17-18% and discarded at 5-7% acid concentration. And the iron contents maximum 150 gms/ltr.

    Acid Fumes Inhibitor is added to the acid bath to prevent over pickling and arrest fuming.

    The material is loaded in jigs, if it is loosed then it is immersed in crates and maintained in acid bath till pickling action is complete.
  • Rinsing
  • Material after pickling is rinsed properly in another tank by immersing in water to remove any residual acids and loose iron particles. There are two rinsing tanks to ensure proper removal of acid stains. Water in the rinsing tanks are frequently changed and used in the pickling tanks.
  • Fluxing
  •  Flux Bath Maintained- Specific Gravity 16-18%, Ph between 4 to 5 . Material after rinsing is transferred to the fluxing tank. Fluxing is done to prevent any further re-oxidation of the steel after pickling till the dipping time. The flux solution is a mixture of Zinc Chloride, Ammonium Chloride and other chemicals. The material is dipped in Flux Solution and taken out after proper fluxing.
  • Drying
  • The Material is dried in a drying chamber before dipping in the Zinc Bath, the temperature  which is maintained at a maximum of 40-50ºc checking with visually. Retention time is 15 to 20 minutes normally .
  • Dipping into Zinc Bath
  • Dipping is last major process. The dried material is dipped in to the molten Zinc. The Temperature of molten Zinc in Zinc Bath is constantly monitored between 435 to 455ºC. The material is lowered in to the Molten Zinc at a comparatively higher speed and taken out from molten Zinc at slower speed. The jigging will be always either vertical or at an angle to facilitate easy draining of the Zinc from the surfaces.

    The dipping time varies according to the thickness of the materials, required Zinc coating thickness and the bath temperature.

    Dipping of work in to molten Zinc is a highly sensitive issue and only carried out by the well experienced operators.

    During the process of dipping & withdrawal of work there the formation of Top Slag ( Ash) which is regularly removed before and after dipping.

    Excess projections, lumps etc if present on the work is removed by means of special tools.

    Bottom slag (Dross) and other impurities generated during the process settles at the bottom of the Zinc kettle, is also removed periodically

    Galvanizing Furnace is heated by 4Nos. of Burners and temperature of molten Zinc is constantly monitored.
  • Quenching/Passivation
  • Quenching is the process of cooling of the hot material taken out of the Zinc bath and is done in pure water in a separate tank provided adjacent to the furnace. Hot Galvanized material is also dipped in to the solution of Sodium di-chromate with water. It prevents further re-oxidation of Zinc metal and keeps work shining.
  • Finishing And Packing
  • Products are shifted to finishing department after galvanizing. The products are kept on wooden beams, thus preventing from direct contact of water or soil. The products are individually checked and cleaned properly. All the sharp edges, extra Zinc is removed by Filing.

    After Finishing the material is properly packed and tagged.

    Now the work is ready for dispatch