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| 1. Hot Dip Galvanizing: The hot dip galvanizing process involves at least 5 operations. Plant design and layout will determine the maximum size of fabrications that can be galvanized. Back to index |
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| 2. Centrifuge processing of small parts. Hot dip galvanizing of small parts is done using the centrifuge process, where the pre-treated parts are galvanized in baskets that are spun at high revolutions after withdrawal from the molten zinc to remove excess zinc from their surfaces.Back to index |
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3. End plate design. Base plates and end plates need to be designed for adequate venting and draining. Simple detailing during fabrication, as shown here, will produce good galvanizing results. Back to index |
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4. The Sandelin Diagram. Steel chemistry determines the rate at which the steel will react with the molten zinc alloy in the galvanizing bath to form the galvanized coating. Silicon is the most significant reactive alloying element in structural steels. This graph shows the reaction rate of steel with zinc at various steel silicon levels, and will give an indication of the likely galvanized coating characteristics of a steel of known silicon composition. Back to index |
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5. Welding and weld metal. Weld metal composition and welding techniques can affect the finished appearance of fabrications. Weld metal is normally high in silicon content and will react with the molten zinc alloy at a higher rate that the parent metal. Weld areas ground flush prior to galvanizing may thus appear raised above the metal surface after galvanizing. Weld splatter will not be removed in the pre-treatment process and will be galvanized on the surface, creating an unsightly appearance. Back to index |
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6. Zinc drainage off large items. The angle with which large fabrications can be withdrawn from the bath will determine the effectiveness of the drainage of excess zinc from its surfaces. Back to index |
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7. Orientation and surface finish. The steeper the angle at which a fabrication can be withdrawn from the galvanizing bath, the smoother the finish is likely to be. The flatter the surface is with respect to the molten zinc, the more drips, drainage spikes and feathers will occur on the edges.
Provision of lifting points to allow the optimum orientation will produce the most consistent surface finish. Back to index
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8. Venting and draining of structural sections. Beams, columns and channels that contain gussets, splice plates or stiffeners in their design will not galvanize satisfactorily unless both zinc and air can get free access to all surfaces of the sections. Cropping of gussets and stiffeners fabricated into these sections will ensure a good galvanizing outcome. Back to index |
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9. Design detailing. Simple detailing will ensure that adequate venting and draining of fabricated assemblies will deliver a good quality hot dip galvanized finish. Back to index |
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10. Design details for angle fabrications. 1-, 2-, or 3-dimensional angle fabrications need to be designed to consider their venting and draining characteristics during hot dip galvanizing. Using outward facing angles, rather than conventional inward-facing angles, in 3-D fabrications can eliminate the need for any special venting or draining requirements. Back to index |
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11. Detailing complex fabrications. For complex fabrications, advice should be sought from the galvanized to ensure that adequate lifting points, and venting and draining requirements are incorporated into the fabrication. Back to index |
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12. Zinc buildup and clearances. The surface tension and fluidity of molten zinc will result in thickening of the galvanized coating at low points on solid and hollow circular sections. Where clearances for the fitting of mating parts is requires, this thickness variation needs to be accommodated in the design, particularly on internal surfaces of hollow sections where removal of excess zinc is difficult. Back to index |
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13. Draining larger hollow sections. Larger hollow sections used for structural applications have a significant internal volume so venting and draining of base plates and end plates needs to accommodate the flow of larger volumes of pre-treatment chemicals and molten zinc. The location of drain holes in base plates and end plates will be determined by the orientation of the section during galvanizing. Back to index |
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14. Pipe spools and other 2-D and 3-D hollow section fabrications require careful detailing to ensure safe and satisfactory galvanizing. Moisture trapped inside the fabrication is an explosion hazard, and air trapped inside will prevent the item from sinking into the molten zinc. Back to index |
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15. Venting and draining of handrails. Stanchions and handrails fabricated from hollow sections need to be vented and drained on the underside or inside to prevent ingress of rainwater and hazards to the pedestrians using the handrails. Back to index |
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16. Vent and drain hole size. Vent and drain holes that are too small in hollow sections increase immersion time and may cause unsightly excessive zinc drainage runs as the zinc freezes during the draining period. Back to index |
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17. Back-to-back sections. Where back-to-back angle or channel fabrications need to be hot dip galvanized, welding to create large overlapping surface areas should be avoided. The use of packers between the sections, or using channels toe-to-toe will ensure a good galvanizing outcome. Back to index |
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18. Minimising distortion in thin sections. Thin plate or sheet sections are prone to distortion during galvanizing. This can be avoided or eliminated by folding, creasing or corrugating the sheet sections Back to index |
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| 19. Design for fence panels and balustrade. Where hollow sections are used in the fabrication of fence panels and balustrades to be hot dip galvanized, the pre-treatment chemicals and molten zinc must be able to flow freely into and out of the fabrication. Venting and draining on the underside of fence panels and balustrade will not effect their appearance and will not allow weather to enter the panels. Back to index |
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