Frequently Asked Questions about hot-dip galvanising

What is hot-dip galvanising?

During hot-dip galvanising, steel products are submerged – after degreasing, pickling, fluxing and drying – in a zinc bath containing liquid zinc at a temperature of 450°C. The zinc that covers the material in this way bonds with the steel, creating an unbreakable layer. If it does get damaged, a chemical reaction (cathodic protection) follows, preventing rust. Only galvanisation provides this unique protection.

We specialise in the hot-dip galvanising of steel in accordance with NEN-EN-ISO 1461.

What sizes can Rotocoat galvanise?

Rotocoat has the smallest, widest and largest galvanising baths in the Netherlands. To decide whether Rotocoat can galvanise a product, we need to know the length, width, height and the weight.

We can galvanise products with the following maximum sizes:

• length up to 24 metres
• width up to 2.2 metres
• height up to 4 metres
• weight up to 18 metric tons

Items up to 24 m long can be double dipped, depending on the width, the height and the weight. Items up to 4 m high can be tilted, depending on the height and the width.

You are strongly advised to get in touch with the sales department for unusual sizes or heavier items.

Click here for the galvanising bath sizes at the various locations.

Why is it necessary to drill holes?

During hot-dip galvanising, there have to be enough holes in the product to prevent air pockets and to allow the zinc and the pre-treatment liquids to flow through hollow parts freely. This is not only important in terms of safety, it is also a factor in the quality of the galvanising process.

Where there are air pockets, pre-treatment will not work and so the product will not be properly galvanised in these places. If the excess zinc cannot flow out fast enough, zinc accumulates and this also has a negative effect on the galvanising result. Galvanising an object with poorly positioned holes or openings that are too small can distort the product during the galvanisation process. The product may crack or even blow apart.

Before we galvanise a product, we check to make sure that enough holes have been made for ingoing and outgoing flows. If necessary, holes are drilled in consultation with you. If there are any doubts about the positioning or the size of the holes to be drilled, you can always ask us for specific advice.

For more information, see the drilled holes overview.

Why do grease, paint, stickers and traces of glue have to be removed?

To ensure the proper bonding of the zinc to the steel, chemical pre-treatment is needed. However, this process cannot remove grease, paint, stickers or traces of glue and they prevent the bonding of the zinc in these places. The result is a badly galvanised product, and it is highly likely that rejection will follow.

That is unpleasant for you and for us. Deliveries get delayed, the product has to be galvanised again and that means extra costs for you. So we ask you to remove all grease, paint, stickers and traces of glue from all materials you send for galvanisation.

Can Rotocoat also galvanise bolts and nuts?

Rotocoat can also hot-dip galvanise small steel parts like bolts and nuts. Our centrifuge-galvanising plant uses a unique, entirely automated, centrizink® process. The small parts are pre-treated in a closed, environmentally friendly, pickling plant. They are then placed in cages and submerged in the zinc bath. After galvanising, the cages are placed in the centrifuge, where they are spun quickly to remove the excess zinc quickly and efficiently. The products are then cooled in a special cooling emulsion. The result is a high-quality and enduring zinc coating.

For more information about centrifuge galvanising click here.

Can Rotocoat also arrange for transport?

More and more clients use our transportation service. Rotocoat can transport materials up to 3.5 m wide and 25 m long without any difficulty. We have semi-trailers with sliding sides, extendable trailers and trailers with integrated cranes, so the products can be offloaded at building sites. The temporary storage of processed materials and call-off deliveries is also possible.

Our experienced drivers have a scheduled service with deliveries on specified days of the week to different parts of the country. Large deliveries are planned separately. We provide good, fast and flexible logistical solutions. We pick up the material to be treated and deliver it to your preferred destination after galvanisation and powder coating. Of course, you can also deliver and pick up your materials yourself. If you want more information about our transportation service, please get in touch, see map on the left side of this page.

Why are there sometimes white spots on galvanised products?

After a time in contact with air, galvanised products pick up a matt finish as a thin zinc patina forms on the surface. The patina is an indissoluble, strongly bonding and protective layer consisting mainly of basic zinc carbonate. This protective patina fails to form when rain or condensation remains on the galvanised material in the absence of free-flowing air. The moisture results in the formation of white spots (zinc oxides) that are known as white rust or wet storage stain. This wet storage stain is particularly common during storage or transport, when moisture can be retained between stacked galvanised parts.

Wet storage stain does not affect the quality or the useful life of galvanised materials and it disappears spontaneously after a while with exposure to air. It does affect the look of the material. Under NEN-EN-ISO 1461, wet storage stain does not constitute grounds for rejection.

If it is important for your product not to be affected by wet storage stain, we can store the material inside for you and deliver it using a covered trailer. Feel free to get in touch and discuss the available options.

For more information about whit storage stains click here.

Isn't hot-dip galvanising bad for the environment?

Hot-dip galvanising is the best steel protection method in terms of sustainability. A zinc coating can last for decades. No material is lost when hot-dip galvanised products are ultimately replaced. The steel and the zinc are recovered and can be used again. The useful life of certain products can be extended considerably by degalvanising and regalvanising them. The small quantity of zinc that is lost enters the cycles of life as an essential element, playing a useful role there also. Rotocoat has ISO 14001 (environment) certification.