When good metal goes bad


When a designer is faced with the specification of an enclosure to house and protect a specific device or control system, there is an art to getting the exact enclosure product to fulfil the requirement exactly. Steve Gallon, managing director of Fibox, explains

Generally speaking, metals are used to construct things for which other materials like plastic or wood are considered not strong enough. Even in popular culture, metal is still regarded as a material of infinite and limitless durability. We have all heard common colloquial phrases like ‘tough as nails’ or the politicians favourite, the ‘iron-clad guarantee!’ But metal, like every other material, has a lifespan. And heading the list is rust!

Exterior surface corrosion or rusting occurs by the formation of iron oxides. Corrosion comes in many different forms and can be classified by the cause of the chemical deterioration of a metal.
Certain factors can contribute to metal failure, a phenomenon that can greatly diminish the strength of metal materials. And as many designers have found out to their expense, simply exposing minute areas to moisture or other electrolytic elements will see the corrosive action begin. Ultimately, the metal deteriorates to the point of failure.

Painting to an appropriate specification will significantly extend the period to the onset of corrosion but the durability of the paint finish is largely dependent on the quality of the surface preparation.

The choice is yours
On the face of it, the right selection of an enclosure is normally viewed as a relatively  simple process, determined by its size and where it is intended to be installed, which in turn normally dictates the construction material; its IP rating, its availability, its flexibility in terms of customisation, cost constraints and finally its aesthetic value.

To some specifiers a box is a box. But when one considers the huge range of enclosures designed to house sensitive instrumentation and other sensitive devices, today’s product designers are faced with a multitude of forms. Steel, stainless, die cast aluminium, polycarbonate, GRP and ABS. Each of which must be assessed in light of offering the best possible protection for the environment it is to operate in.

Invariably the enclosure is the protective housing in which expensive and often critical components must perform; many in extremely harsh and demanding conditions. Therefore before a final enclosure choice is made, a number of very important and exacting questions must be asked, and answered.

That is why it is crucially important that the relationship between specifier and manufacturer must be such that all the following points are covered at the design stage.

Key questions must be asked
So let’s look at the key criteria which when addressed will very quickly narrow the choice down to just a few options:

Q: Where is the enclosure likely to be installed, inside or outside? This determines the material choice, the IP rating and any specific environmental corrosion risks which need to be addressed at the design stage because corrosion is often a major part of future maintenance costs.
Q: What is being installed in the enclosure? This solves the size issue and also answers the question of what type of internal fixing points are required. Some manufacturers can offer extra fixing pods to accommodate cover mounted components etc’.
Q: How often is access to the interior required? Should the design include hinged opening doors for regular access? Alternatively should the design include security such as locks or tamper proof cover screws to guarantee total integrity of the enclosure?
Q: Does the enclosure require visual access to the internal components? By answering this question the option of transparent or opaque covers is addressed. This could include the provision of viewing windows in an opaque cover for example.
Q: Does the enclosure need to delivered, already customised? This is a very important question often asked by specifiers who do not have in-house machining facilities. Customising includes machining of holes and apertures, special fixing points, graphics and corporate colours, and a multitude of other bespoke services. Some manufacturer’s offer a comprehensive customising service and this should always be discussed with them at the design stage.
Q: What is the budget? This question has to be addressed at some point so why not cover it at the early stage of the project? Manufacturers can then offer alternatives and compromises to assist the specifier in achieving their cost criteria.

So, although the sheet steel enclosure industry remains strong, the emergence of viable alternatives like high grade thermoplastic, polyester, polycarbonate, GRP and ABS enclosures; which are proven to continuingly out-perform traditional steel, has completely changed the landscape of the enclosure industry for ever.


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