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Thinking outside the box

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Engineers are generally revered for their grasp of jargon. But when it comes to enclosures, it seems many are unsure exactly what’s what.

The confusion is not altogether unwarranted. Like many sub-sectors of the electronics industry, enclosure manufacturers continue to forge ahead experimenting with new chassis materials and standards. The results are better enclosures, but understanding the benefits and how each contributes to the build of the enclosure is a challenge.

“Some engineers only know technical terms as jargon – for example, phrases such as ‘IP65’ just come off the top of their head without really understanding what it means,” Hammond Electronics director Charles Cookson says. “The problem is some engineers are asking for things when they don’t really know what they’re asking for. It’s just a lack of education.”

Metal vs. Plastic

The most basic decision when choosing an enclosure is whether to go for a metal- or plastic-based chassis. The choice comes down to a number of factors, beyond just turnaround and cost. Metal enclosures, including aluminium die-cast, extruded aluminium and stainless steel, have the advantages of being rigid, non-flammable and RF shielded. “On the larger enclosures, sheet metal tends to be cheaper than plastic,” Cookson says. “That said, the aluminium die-cast enclosures become prohibitive when they get beyond a depth of 100 mm because of the tooling costs.”

By comparison, plastic enclosures tend to be cheaper than their die-cast cousins, though a requirement for RF shielding can quickly change this, according to Rutty Tool-less Plastics (RTP) sales manager Stephen Dunlop.

“The one advantage a metal enclosure has over a plastic enclosure is shielding,” Dunlop explains. “If the plastic needs to be shielded, it can add as much as 40 percent to the cost of the enclosure.”

Dunlop claims plastic enclosures are also safer “because a lot of metal enclosures have sharp edges”.

Based in northern Sydney, RTP uses K-Box technology, developed by TTK Germany, to produce plastic parts and housings without tooling or moulding equipment but rather with a milling procedure and patented assembly process. The company is one of only ten worldwide to use the technology.

Dunlop says the company is currently experimenting with “Highlight” – a German-produced hybrid chassis material, sandwiching plastic with stainless steel. Hammond is also busy testing possible new materials. “We look at new materials all the time,” Cookson comments. “Obviously they haven’t been released yet, and as such most are confidential.”

Zinc aluminium metal alloy casting (ZAMAC) is another example of recent innovations in chassis materials. French storage developer LaCie, which encases its Big Disk products in ZAMAC, claims the alloy’s unique thermal properties eliminate the need for an internal cooling fan..

But the advent of new materials has a less obvious downside. According to Cookson, there is a lot of misunderstanding in the market of plastics, particularly ABS plastics and enclosures with high levels of “re-grind”.

ABS is a mixture of three plastics—Acrylonitrile, Butadiene and Styrene—with the mix determining the mechanical properties of the enclosure. The acrylonitrile provides heat resistance, while the styrene gives rigidity, leading to a generally tough, heat- and impact-resistant thermoplastic enclosure.

When buying cheaper enclosures, many engineers are unaware of the proportion of “re-grind” integrated into the chassis. Essentially, “re-grind” is old pieces of ABS plastics that have been recycled and re-used in new products.

“[Manufacturers] can use a certain amount of re-grind to keep the costs [of the enclosures] down. As a purchaser, the problem is you don’t really know what’s in that material,” Cookson explains. “Also, when ABS plastics are heated and extruded again, you tend to get a very brittle sort of plastic being produced.”

Although not chemically or mechanically the same, Cookson likens this effect to paper produced with a high percentage of recycled materials, which is claimed to be not as strong as the more pure product.

“In some recent tests, we had one particular enclosure where hairline cracks appeared in the chassis when it was drilled,” Cookson claims. “We’ve also seen enclosures that you can’t even drill at normal room temperature because they just shatter. You have to drill them at an elevated temperature, which is not an easy way to go.”

While admitting a certain proportion of “re-grind” is acceptable, this needs to be balanced with the machinability of the enclosure. “Sometimes people want the cheapest box but you get what you pay for when buying an enclosure,” Cookson adds.

Know the standards

The Ingress Protection (IP) ratings of electronics enclosures are also habitually misunderstood. Created by the International Electrotechnical Commission (IEC), and also known as IEC 60529, IP ratings consist of two digits, which describe the effectiveness of an enclosure to prevent the entry of foreign bodies, such as dust and moisture.

The first digit, ranging from zero (indicating no special protection) to six (dust tight), shows the degree to which the equipment is protected against solid bodies intruding into the enclosure. The second digit, ranging from zero to eight, indicates the level of protection against the entry of various forms of moisture.

But, according to UK trade association GAMBICA’s enclosures group chairman Brian O’Donoghue, many engineers interpret the ratings more widely than their scope, leading to disappointment in products purchased.

“All of the companies in the GAMBICA enclosures group receive calls from unhappy users complaining that, for example, they’ve used an IP66 enclosure, which protects against water jets, but it has started to go rusty,” O’Donoghue says. “In reality, the IP rating says nothing about the ability of a particular enclosure to resist corrosion. The rating only tells the user that, when new, the enclosure will protect against the ingress of water and solids to the extent stated.”

Cookson believes the answer lies in educating users about what the IP ratings mean. Many customers, Cookson claims, rely too heavily on IP ratings when finalising purchase orders. “As an illustration, we had one client who insisted on an IP67 enclosure for use outdoors,” Cookson says. “The six means it’s dust protected but the seven indicates immersion for a particular time at a particular depth, yet the enclosure was to be mounted above the surface.”

In reality, the customer really only required an enclosure with a rating of IP66 or IP65. “Instead they’re going overboard and then they wonder why it gets so expensive,” Cookson adds.

Dunlop agrees that many users tend to mistakenly choose an enclosure with a higher IP rating than is needed. “They like to think they have the best they possibly can,” Dunlop says. “It’s only when you start to talk prices they start thinking an IP54, for example, might be better suited to their needs.”

However, Dunlop disputes that IP ratings play a major role in customers formulating purchasing decisions. “People like the idea of having a box that is splash proof, but the only way [as a manufacturer] you can get a dedicated IP rating is to have [your products] certified and tested, which is quite expensive,” says Dunlop. “What we try to do is make a product as close to an IP rating as possible without the guarantee [the IP rating provides].”

While new chassis materials will continue to precede equally complicated new acronyms, not all growth within the enclosures industry relies on cutting-edge R&D.

Simple successes

Last year, Hammond released ice blue and translucent red versions of its 1591 Series small instrument housings. Moulded in polycarbonate, the company claimed the novel enclosures were “designed for applications where up-to-the-minute styling is important, or where it will be beneficial for the internal components to be visible”.

“It’s one of those ones that started out as an experiment in plastic extrusion,” Cookson explains. “Someone thought, ‘these look pretty, let’s see what they’re like in the marketplace’. They’ve really taken off, and are being used a lot with LEDs for education and practical applications.” The company has also recently seen success with extruded aluminium enclosures.

“At the end of the day, it’s a toss up between price, quality and suitability for the application when choosing an enclosure,” Cookson says. “Sometimes price isn’t everything.”

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