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Specifying fastener material is not unlike the way you choose fuel for your car. If your car performs perfectly well with unleaded fuel, why spend extra on super unleaded?
The fastener market is running at a pace, yet the need for the tried and tested should not be ignored, especially at the heart of the sector - roofing and cladding. The integral nylon moulded colour headed fastener seems to have been around forever - yet it is still as relevant as when first conceived. It’s easy to think this product was initially designed to combat the problem of push on caps becoming dislodged on installation, but other aspects are often overlooked: Integral headed fasteners provide extra stability to the washer by aiding pullover resistance of both fastener and washer, as well as reducing the effect of washer inversion which can be more prevalent with non-moulded or painted head fasteners - especially where larger washers are used.
Another benefit is its ability to give additional protection to the encapsulated fastener head, creating a positive barrier to the external environment. Unlike a painted or powder coated fastener head, this offers more resistance to damage from the installation tool and any swarf build-up in the installation socket.
An important aspect in the choice of roofing and cladding fasteners is the fastener material and its associated coating. The modern carbon steel fasteners with sophisticated corrosion resistant finishes provide excellent performance, even more so where an integral nylon head is present. Austenitic stainless steel fasteners provide greater corrosion resistance and life expectancy than carbon steel fasteners, and can cope with a wider range of environmental situations.
The choice of stainless steel fastener and fastener material can be made to seem more complex than it actually is. For the vast majority of applications, the austenitic (A2) 1.4301 grade 304, is manufactured and supplied throughout the industry with millions installed each year. These have proved to provide good all round performance offering reliability and material stability. With passivated and new generation coatings now available on the heavy section stainless steel bi-metallic self-drilling fasteners, added resistance to galvanic corrosion as well as improved installation speeds are adding to long term protection of the fasteners base material. (A2) 1.4301 grade 304 also offers excellent weld-ability which is critical for the manufacturing process of bi-metallic fasteners. The confidence that system suppliers, OEM’s, installers and building owners have in this grade of fastener is rightly based upon the product’s reliability and cost effective proposition.
It is easy to under specify a fastener, but just as easy to over specify if the application requirements have not been assessed in detail. This can lead to unnecessary costs or long term performance issues. The exposure that the fastener will have to the environmental conditions externally, internally (within the building), and in the locality of the application, should determine coatings and any additional powder coating or integral nylon head.
Other grades of Austenitic stainless steel are available where building type and local environment may require these grades, often creating a specification dilemma. For instance, (A4) 1.4401 grade 316 has an improved corrosion resistance to that of 304 and is historically used in marine environments, including boat building - so, you could be forgiven for assuming A4 to be the fastener choice for marine and coastal environments. Yet powder coated and integral nylon headed fasteners also provide an equally good, if not better solution and resistance to corrosion in these environments. This is because the environment alone does not necessarily preclude the use of (A2) 1.4301 grade 304 austenitic fasteners. The need to look at the fastener in its application rather than just specifying the grade of material is of far greater importance in making sure the most appropriate choice meets the design criteria.
A typical example would be a sports facility with a swimming pool and sports hall. For the swimming pool application, assessment should lead to the specification of chlorine resistant austenitic stainless steel grades currently on the market, such as the (A5) 1.4529 grade EJOT JZ1 and JA1 self-tapping fasteners ranges. The fastener’s exposure to the internal chlorine environment or the potential risk of exposure to this high humidity chlorine environment will direct the designer to this grade of stainless steel. However, if you have an environment that is free from the chlorine and high humidity such as a sports hall, then an A2 grade of stainless would be more appropriate than the A5 grade.
The same can be said in relation to A2 and A4 ; the appropriate grade and overall fastener properties - from coatings and encapsulation of the fastener head - and the location within the application will guide the designer to the correct choice to meet all criteria.
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