1. Hot dip galvanization. Hot dip galvanization involves at least 5 operations. The planning and layout of the production plant will determine the maximal amount of details than may be galvanized.
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.
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.
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.
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.
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 The angle with which large fabrications can be withdrawn from the bath will determine the effectiveness of the drainage of excess zinc from its surfaces.
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 The steeper the angle at which a fabrication can be withdrawn from the galvanizing bath, the smoother the finish is likely to be.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.
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.
9. Design detailing. Simple detailing will ensure that adequate venting and draining of fabricated assemblies will deliver a good quality hot dip galvanized finish.
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.
11. 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.
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.
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.
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.
15. Venting and draining of handrails. For stanchions and handrails fabricated from hollow sections.