FEATURE ENCLOSURES
WHAT TO DO WHEN good metal goes bad
For a designer, to get the specification of an enclosure product spot on so it meets the application requirements exactly, is an art form, as FIBOX explain
Left: 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
corrosion is often a major part of future maintenance costs. What is being installed in the
I
n general terms, metals are used for construction when other materials like
plastic and 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’. However, metal, like every other material, has a lifespan. And the key factor effecting that lifespan 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 FREEDOM OF CHOICE 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
16 NOVEMBER 2014 | ELECTRICAL ENGINEERING
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.
However, 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, diecast 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 vital that the relationship
between specifier and manufacturer must be such that all the following points are covered at the design stage.
KEY QUESTIONS So let’s look at the key criteria which when addressed, will very quickly narrow the choice down to just a few options: 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
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. 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? 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. Does the enclosure need to be
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 manufacturers offer a comprehensive customising service and this should always be discussed with them at the design stage. 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. 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 changed the landscape of the enclosure industry forever.
Fibox
www.fibox.co.uk T: 01642 604 400
Enter 208 / ELECTRICALENGINEERING
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