Feature: Enclosures
The moral of the
enclosure’s story By Russell Irvine,
European Account Manager, Hammond Electronics
T
ypically, most OEMs follow a logical sequence when developing electronics projects: First, there’s the product specification, then the design, then sourcing of components,
then prototyping and debugging, and, finally, sourcing an enclosure to house all that. Although a reasonable chain of events, this sequence can lead to many things going wrong, especially when time is of the essence and pre-production nerves are getting jittery.
Problem 1 What if the assembly is too big for an available enclosure? Diecast enclosures are invariably more expensive, with greater depth. It’s the dies; making a deep diecast is not easy, and tools are therefore exceptionally expensive: naturally, this cost is amortised in the sell price of the casting. A tall assembly limits enclosure choices, causing lost time while a suitable housing is found, and there is the inevitable cost increase. A larger box than required means paying extra for unnecessary space, a smaller box will need a circuit or component redesign – more time, more money. Some manufacturers choose to make their own tooling. Te risk increases if the product doesn’t sell well and, of course, the development time and expense must be taken into account.
Problem 2 What if all is ready to go into production but the chosen enclosure isn’t in stock and has a long lead time? Limited options include choosing alternative enclosures, possibly requiring redesign of components, or simply
62 November/December 2020
www.electronicsworld.co.uk Hammond 1552 series enclosures
Hammond 1554-55 IP68 enclosures
waiting until stock becomes available. Both choices can cause delays and frustration. What if the chosen enclosure is cheap, the right size is initially available, and then stock runs out during full-scale production? Company credibility suffers when explaining to customers that the heavily-promoted new product has to undergo changes in size, shape and cost.
Problem 3 What happens when it is discovered that the IP (ingress protection) rating, the flammability rating or EMC of the project require a special enclosure? Once the product specification is finalised it will be known whether the enclosure needs to be weatherproof for exterior or harsh environment use, or needs a special IP or flammability rating. Te requirements will influence the choice of material, which may typically be metal, ABS, polycarbonate or GRP (glass reinforced plastic). Te question of the level of protection against ingress of dust and water is significant in the specification criteria, defined in EN 60529 as IPxx, where the first digit defines the protection against solid objects and the second the protection against water ingress (see chart on the next page). An enclosure for general-purpose use would typically be rated IP54, whereas one for hostile environments would need to perform to a minimum of IP65; although, nowadays, IP67 or even IP68 is becoming minimum requirement. In general, enclosure manufacturers use
Hammond 1557 series enclosures
two main techniques to achieve the required protection level. Satisfactory IP54 sealing is readily achieved by using tongue-and- groove construction for the joint between the enclosure body and a removable panel or lid. No gaskets are used; the seal is achieved through the mating of the recess in the base section with the corresponding mirror profile in the lid when the lid is screwed down. To achieve higher levels of sealing in metal, plastic and extruded small enclosures will require a gasket between the two mating halves. Normally, a separate, preformed, moulded gasket is sandwiched between the two mating surfaces. A metal enclosure can be painted if required without having to mask the gasket area; the gasket can easily be replaced if it is damaged.
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