There are three reasons that holes must be added to hollow sections.

Firstly vent holes allow the air pressure that is created within the hollow section to escape. This prevents explosions that can destroy your job and/or harm our staff.

Secondly, the holes allow the molten zinc to flow throughout the job, galvanising the interior as well as the exterior.

Thirdly, steel is not much heavier than the molten zinc into which it is being submerged, should even a small amount of air be trapped inside the job it will float in the galvanising kettle.

Determine in conjunction with the galvaniser how the article will be hung and ensure that a drain hole is placed at the lowest point of each hollow section and a vent hole at the highest.

As a general rule the drilled hole should be as close to each end of the closed section as possible.

Due to the wide variety of shapes and steel thicknesses galvanised, weight is generally used by the industry as the method of determining cost. Although this is not perfect, weight does take into consideration the fact that heavier steels do often take on thicker coats and that more energy must be consumed to heat thicker steels to the galvanising temperature.

Should the client have a large quantity of thick steel, a better $/kg rate can normally be negotiated.

Our galvanising kettle in Napier is just over 8m long, 2m deep and 1.4m wide.
Items whose dimensions are less than these measurements will fit as a single dip. Some longer and wider items than 8m and 2m respectively can be dipped as a ‘double’ dip. Items whose smallest dimension is greater than the 1.4m width of our kettle will not normally fit.

If in doubt ask before you start manufacture.

Even the smallest washer can be galvanised, please talk to us about the practicality and cost.

However, our charge is unlikely to be on a $/kg basis.

New Zealand standards determine the minimum thickness that a hot dip galvanised coating must be for various thicknesses of steel. As a general rule the coating is normally around 100 microns or 1/10th of a millimetre.

Please be aware that the coating will have its high and low points and that it may be thicker inside holes.

No, double dipping refers to double ended dipping that is required on oversized items.

Hot dip galvanising is an alloying process that occurs on the base steel. It is not possible to added a second coat over the top without first removing the original coating.

Yes, it is, but first the original coating is removed usually by submerging the article in our acid baths.
The zinc coating is highly reactive and is removed by the acid, this reveals the underlying steel. A new fresh hot dip galvanised coating is then added.

As the old zinc neutralises acid in the removal process, the charge for stripping and regalvanising is higher than for galvanising new steel.

The life of hot dip galvanising, unlike some other coating systems, is highly predictable and is a factor of the thickness of the coating and the environment to which the article is exposed. In any particular environment a known thickness of microns will be lost each year. This degradation of the coating is ‘linear’ i.e. constant. It may be 10 microns/year in a marine enironment to 2 microns/year in an arid environment. A ninety micron coating may therefore last nine years in the marine environment or 180 years in an arid environment.

The hot dip galvanising process should take between 4 to 24 hours if the steel is clean. At any given time our backlog of work will vary, so please check for a current time estimate.

Often a client will modify a small part of a galvanised article and wish just this portion to be hot dipped. Unfortunately this is seldom possible, as the item must first be pickled in an acid bath. The existing zinc is highly reactive and tends to foam and fume up over the rest of the galvanise coating damaging it.

This is usually possible however; the item must be only partially submerged in the acid pickling baths. This procedure is very labour intensive and ties up cranes and other equipment while pickling occurs. The result is that the cost may actually be greater to do this than to galvanise the whole article.