Drilled holes essential for galvanisation
With galvanisation, it is extremely important to allow the liquid zinc and pre-treatment liquids to flow freely in and out of the hollow parts of the object and for air to be allowed to escape. So holes have to be drilled in the right places in the object undergoing galvanisation.
Holes for safety
If air gets closed in and cannot escape, or if liquid is left in the object, hazardous situations can result and there may be very serious consequences for the people working at the galvanisation plant.
The temperature in a zinc bath is 450°C. That means that air pockets heat up rapidly and enclosed liquids start to boil, producing steam. If that heated air or the steam cannot get away quickly enough, pressure increases rapidly to very high levels. The object may then crack, or even explode, spewing out liquid zinc, with all the associated risks for the people working at the galvanisation plant.
Before an object is hot-dip galvanised, checks take place to ensure there are sufficient inlet and outlet holes int the object at the right places. If necessary, extra holes need to be drilled.
Holes for quality
To safeguard the quality of the galvanisation process, objects need to comply with a number of conditions: there have to be enough holes in the objects to prevent air pockets and to allow the zinc to flow through the object freely. Where there are air pockets, pre-treatment will not work and so the object will not be galvanised in these places. If the excess zinc cannot flow out fast enough, zinc accumulates. In both cases, galvanisation quality suffers.
Galvanising an object with poorly positioned holes or openings that are too small can distort the object during the galvanisation process. The object may crack or even blow apart.
Holes for suspension
Before an object is galvanised, it has to be suspended on a traverse. Using wire or hooks almost always leaves a "scar". So it is preferable to drill holes in the top and bottom of the object for suspending it on the traverse before it goes through the entire process of pre-treatment and galvanisation.
Advice about holes
If there are any doubts about the positioning or the size of the holes to be drilled, our experts are always on hand for sound advice about specific objects.
For more information about the numbers and sizes of the drilled holes see our drilled holes matrix.
You can also download the poster in PDF format (2,5 mb).