Fasteners – Hot dip galvanized coatings (ISO + Cor. ); German version EN ISO + AC Buy DIN EN ISO FASTENERS – HOT DIP GALVANIZED COATINGS from SAI Global. Verbindungselemente – Feuerverzinkung (ISO ) mechanical fasteners and accessories”, the secretariat of which is held by DIN.

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Magyar English Select Language: Nederlands English Select Language: Dutch English Select Language: Polski English Select Language: Your shopping cart is empty. It provides a very solid and durable corrosion protection.

Hot dip galvanizing for steel parts is standardized in ISObut for fasteners, the dedicated standard ISO exists.

The process of hot dij galvanizing is quite simple: Next, the fasteners are spun to remove the excess zinc, and then they are cooled in water to solidify the zinc.

What remains is a layer of sn 40 to 70 microns on the surface of the products that is relatively thick compared to zinc electroplating 3 to 20 microns. Nuts are processed in the same way, 106844 the nut thread is not yet formed. Nut threads must always be tapped after HDG. This tapping leaves the internal threads exposed not covered with zincbut it has no detrimental effects on the corrosion resistance, as illustrated further below. The HDG process is commonly regarded as suitable for fasteners with diameters M8 or larger.

The large amount of zinc provides excellent corrosion resistance in normal outdoor environments, but with the downside that its layer thickness is significantly above the thread clearance allowance, which this poses a problem for all threaded fasteners.


ISO – Fasteners — Hot dip galvanized coatings

In order to cope with this issue, ISO provides two solutions, both of which involve changes in the dimensions of the basic threaded fasteners. One solution is a system in which the externally threaded fasteners bolts are manufactured with a larger fundamental deviation such that the thread is made slightly thinner.

The other solution provided by ISO is to tap the internal threads nuts to be a bit larger oversize so that they mate with the galvanized externally threaded fastener boltwhich is called the oversize HDG system. The nut oversize limits are standardized in ISOand the thread tolerance class of the oversize tapped nuts is designated as 6AZ.

The two systems must never be mixed, as mixing leads either to fitting problems oversized bolt with ISO fit nut or critical strength reductions of the threaded connection ISO fit bolt with oversized nut.

Generally, it can be stated that the mechanical properties of the bolts in accordance with ISO and the nuts in accordance with ISO are not influenced by hot dip galvanizing. Please refer to EN for details.

Further specific values can be found in DIN Due to the deviation of the thread tolerances, the screw thread of the bolt is allowed to strip at the minimum ultimate tensile load.

When the coating is exposed to the atmosphere, a layer of corrosion products zinc patina is built up. This layer primarily consists of zinc carbonate, which, because it is almost insoluble, delays further corrosion. When galvanized, steel remains wet for a longer period, and there is insufficient air circulation.

BS EN ISO 10684:2004

A white, voluminous zinc corrosion product, “white rust,” may develop, though this product may be less desirable for reasons of aesthetics or painting.


The formation of white rust can be suppressed by appropriate storage and packaging or, if necessary, by oiling the zinc or passivating it in chromic acid. The time that steel remains protected from corrosion is proportional to the thickness of the zinc layer, and it is dependent on the climatic conditions, as shown in the graphic below.

This graphic should be consulted only for rough estimates due to unforeseeable local influences. In case the zinc coating is eh or chipped, the zinc layer attempts to cover the damaged area in normal atmospheric environments. Because zinc is less noble than iron steelthe zinc dissolves first, which protects the steel against corrosion until all of the zinc has dissolved.

At locations where there are gaps in the zinc layer of 1. An example of this phenomenon is the screw thread of dn dip galvanized nuts that are tapped after galvanizing. The zinc layer on the bolt thread completely overtakes the protection of the uncoated nut thread.

Another important aspect of cathodic protection is that no corrosion occurs underneath the zinc layer. A so called duplex system is a combination of wn dip galvanizing and painting.

It is a suitable solution in very aggressive atmospheres e. This system can offer 1. When properly degreased, hot dip galvanizing offers effective adhesion for many types of paint.