Fasteners: appropriate treatment/coating for every application 

Fasteners are usually supplied electrolytically galvanized as standard. However, in various industries, including concrete and steel construction, there is a demand for better protection against corrosion. Usually, hot-dip galvanized fasteners are then chosen. The danger with this process is that the layer thickness applied varies quite a bit, thus increasing the size of the bolt and possibly causing the nut to no longer fit. STAFA responds to this with a wide range of so-called ISO-fitting hot-dip galvanized fasteners. In other words, an M20 bolt remains 20 mm even after hot-dip galvanizing. How is that possible? Dick Koopmans from STAFA is happy to tell us more about it, just like the other preservation techniques which the fastener wholesaler has in its standard range.

In the process of hot-dip galvanizing, a bolt is immersed in a zinc bath at a temperature of about 500 degrees Celsius, Koopmans begins. "A zinc layer attaches itself to the bolt that is highly wear-resistant and partially soaks into the material. This provides high corrosion resistance. However, hot-dip galvanizing is partly an uncontrolled process. That is, after centrifuging the bolts, the zinc layer still varies between 40 and 80 µm. Thus, the bolt becomes larger, so a standard nut may no longer fit. According to the standard that assumes an untreated product, there is a free space (tolerance) for applying coatings. In the case of hot-dip galvanizing, the free space is limited. Therefore, in order to hot-dip galvanize standard bolts, it is important that the nuts have more space to ensure fastening. For this reason, the nuts are tapped larger (oversized)."

STAFA has been capitalizing on this technical factor of hot-dip galvanizing for some 35 years and therefore stocks a large program of hot-dip galvanized bolts ISO fit. "It basically comes down to the fact that the bolts are rolled thinner, naturally conforming to international standards, so that after hot-dip galvanizing they have the correct (ISO) fit for use with standard DIN and ISO nuts," explains Koopmans. "So a hot-dip galvanized M20 bolt from our ISO fit range also has the theoretical fit of an M20 bolt. So you can always exchange these fasteners with all other metric products of all material types without a second thought when it comes to fit. So start using ISO-fitting bolts today," he advises. In addition to these bolts, Stafa also has a complete range of accessories such as nuts, threaded ends and washers with hot-dip galvanized treatment.

In addition to electrolytic and hot-dip galvanized products, STAFA also has an extensive stock of products based on other preservation techniques with or without additional functionalities. "A popular technique is zinc flake coating, where the bolt is dipped in a bath of molten zinc flakes. Think of Delta and Geomet coatings. It ensures an optimal fit," according to Koopmans. "This technique also offers the possibility of working with multiple layers, allowing additives such as lubrication to achieve a certain coefficient of friction, a black or gray color or a top seal for optimal corrosion protection to be guaranteed." Beyond zinc flake, other coatings are also possible such as zinc nickel in combination with other top coatings and PTFE-treated fasteners. It is also possible to pre-applied bolts with a locking agent. Consider the Precote or Loctite brand. "Because we have such a wide range of products at our disposal, as well as a great deal of technical knowledge in-house, we can provide independent and sound advice for every application and location. This also means that we consider the technical feasibility, for example with the prevention of hydrogen embrittlement and contact corrosion."

STAFA distinguishes itself with an extensive range of fasteners in galvanized and hot-dip galvanized. "In the field of hot-dip galvanized, we have one of the largest programs in Western Europe, both with and without CE approval," Koopmans says proudly. "And the great thing is that we package the products completely according to your wishes. Private label is also possible. Extensive quality control on various factors ensures that quality is beyond question."