DESIGNING ARTICLES FOR HOT DIP GALVANIZING
Early consultation between galvanizer, fabricator and designer is the key to obtaining the best results from the galvanizing process.
Design features which aid the access and drainage of molten zinc will improve the quality and appearance of the coating.
Filling, venting and drainage

Good design requires:
-means for the access and drainage of moltenzinc
-means for escape of gases from internal compartments(venting)

It is important to bear in mind that the steelwork is immersed into and withdrawn from a bath of molten zinc at about 450°. Thus any features which aid the aocess and drainage of molten zinc will improve the quality of the coating and reduce costs.
With certain fabrications, holes which are present for other purposes may fulfill the requirements for venting and draining; in other cases it may be necessary to provide extra holes for this pumpose.
For complete protection, molten zinc must be able to flow freely to all surfaces of a fabrication. With hollow sections or where there are intemal compartments, the galvanizing of the intemal surfaces eliminates any danger of hidden corrosion during service.

DESIGNING ARTICLES FOR HOT DIP GALVANIZING
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Base metal and combinations

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Plain carbon steel. some low-alloy steels and iron and steel castings can all be galvanized.

A fabrication consisting of a variety of materials with different surface conditions should be avoided as this could affect the uniformity and appearance of the coating. Where differing materials are used, grit blasting the entire   assembly can minimize any differences which may arise due to differing effects of pretreatment. Preferably, the fabrication should be of similar steel type throughout .

Size and shape

Fasteners

Overlapping surfaces

Casting

DESIGNING ARTICLES FOR HOT DIP GALVANIZING
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Connections

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Galvanized articles can be joined by bolting (including friction grip Connections), welding, riveting and adhesive bonding. Bolt joints are best made after galvanizing.

Welding

Labeling and marking

Masking

Handlina of articles

DESIGNING ARTICLES FOR HOT DIP GALVANIZING
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Moveable parts

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Adequate clearance on mating surfaces, such as hinges, should be allowed if they are to move freely after   galvanizing. An extra clearance of at least 1mm is usually sufficient.

Surface contamination

Distortion

Strength

DESIGNING ARTICLES FOR HOT DIP GALVANIZING
External stiffener, welder gussets and webs on columns and beams, and qussets in channel sections should have their corners cropped.
Cropping the corners of these brackets will aid access and drainage of molten zinc and a cleaner coating will be obtained.
Internal diaphragms in large box sections should have cropped corner and a 'manhole'. Internal diaphragms on small box sections should have cropped corners. Where any hollow section is vented internally it is essential, for safety reasons, that the galvanizer is able to view such venting.
Overlapping or contacting surfaces are potentially dangerous as pretreatment solutions trapped between surfaces is converted to superheated steam in the galvanizing bath and can lead to explosion. If contacting surfaces cannot be avoided, as with these channels then the edges of the contacting areas should be continuously welded. One hole should be drilled through both members for each 100 cm² of overlap, the minimum hole diameter being 10mm, or the thickness of the section, which ever is greater in order to eliminate the danger of an explosion in the galvanizing bath.
If this is not possible, then welding should be intermittent: in service there may be some weeping of trapped pretreatment solutions from between the plates leading to brown staining but this will not be detrimental to the protection given by the coating. lt will not generally be necessary to make any provision of the enclosed area is less than about 100 cm²(e.g.10cm x10cm).
Alternative designs for venting sections fixed to base plates
External stiffeners for beams or channels should have the corners cropped.
Welded joints should be continuous if they are not enclosing an otherwise unvented surface. Bolted joints are best made after galvanizing.
Vents should be diametrically opposite and at least 50mm in diameter. Internal baffles should be cropped top and bottom. Lifting lugs are required as indicated. lt should be possible to view the baffes through either the vent holes or an inspection hole -the placement of the inspection hole should be discussed with the galvanizer.
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