Electronics in mining: protective enclosures

With the continued opportunities afforded by the mining industry in Australia, many electronics manufacturers are engineering products for use in mines.

With the continued opportunities afforded by the mining industry in Australia, many electronics manufacturers are engineering products for use in mines.

But Australian mines are tough environments for electronic products, and a properly built enclosure is essential.

Intex specialises in enclosures, connectors and precision accessories for demanding environments. The company custom designs or modifies its hardware from off-the-shelf products.

Electronics News talked to Nick Cumming, Director of Engineering at Intex Enclosures, about the enclosure requirements for Australian mines.

Ingress protection

The oil and gas industries demand enclosures which are intrinsically safe (Ex enclosures) for hazardous environments. These enclosures control flame paths and arcs to manage the risk of ignition.

For most mines, however, the key demand is for ingress protection (IP rating), and for mechanisms to protect the electronics housed within the enclosure.

“From an electronics point of view, [ingress protection] is about making sure that the enclosure will protect whatever’s put inside from dust and water,” explained Cumming.

Standard enclosures from Intex start at IP66 rating, which means they are waterproof from rain and hosing down, and will keep dust out.

“Given the harsh environment we have in Australia with both water and dust, a lot of electronics and automation companies are looking for a higher rating than that,” said Cumming.

The answer from Intex is IP68 enclosures, which can be safely immersed in water, and allow the electronics inside the survive floods and waves.

“We recently did a project with IP68 enclosures going on the wharfs,” Cumming said. We had to do stress analysis on wave surges, how it would perform under 10m of seawater for 10 days, etc.”

But while designing a self-contained enclosure to be water- and dust-proof may seem to be a simple matter, things can get complicated when the electronics systems inside require standard features like cabling for power and data, user interfaces, and screens.

“If we have a box certified to IP66, the moment we drill a hole in it, we’ll have to deal with that hole, because it is no longer IP66,” Cumming pointed out.

“If we put a hole in there for cable management, we will always use similar material, and similar or greater IP rating. If we cut a hole in the box and put in cables and power, and it’s an IP68 box, we will put an IP68 stainless steel cable gland in there.”

According to Cumming, there have been cases where customers have bought an enclosure, then drilled a hole and installed a cable gland, only to experience dust ingression and leaking.

“It’s generally a lack of knowledge and maybe a subcontractor trying to get the job done quickly,” he said.

“We try to work with the customers and ask them what they are trying to do, the application, the environment, and what they need. If they need two cable entry holes, we put those in with the cable glands, so all they have to do is to feed the wire through and we know it’s going to be safe.”

“It’s the same if we are putting touch screens, connectors, switches or RFID readers, we install that to make sure it’s all nicely sealed, the screens are IP66, and it meets the requirements of the application.”

Materials

Enclosures can come in a range of materials, and can vary according to the application. In gold mines, for example, there may be a focus on corrosion-resistive materials due to the harsh chemicals used in the extraction process.

While polyglass, aluminium and composites may be used for junction boxes, the mainstay for industry in Australia is 316 stainless steel, prized for its hard-wearing properties, and its ability to stand up to corrosion.

“There are a lot of composites coming out at the moment but realistically nothing beats 316 stainless steel for Australian environments,” said Cumming.

Tailored mechanisms

Heat management and cooling is a big issue for electronics used in mines, and various enclosure mechanisms are available to mitigate both heat emitted by the electronics themselves, and from exposure to the sun.

“We do a lot of kiosk and touch screen systems for automation and mines at the moment, for weighing trucks and management,” Cumming explained. “We [also] do a lot of work with big mining companies that have extremes of temperature.”

After assessing the application and equipment requirements, Intex takes standard commercial-off-the-shelf (COTS) enclosures and installs a skin over it with a baffle to create a sun shade, reducing the radiant temperature from the sun.

To further protect the electronics from outside heat, the company installs insulation inside, and puts in filtered fans to vent hot air from the electronics, while preventing dust ingression.

Of course, with a fan system in place, the enclosures cannot reach IP68, but IP66 is possible with fan shrouds that protect against dust and water.

“You can still hose it down,” Cumming told Electronics News. “It’s all about controlling where the water and dust goes and keeping it out.”

In some cases, the baffles serve a dual function, providing both a sun shade, and a sloped roof. Sloped roofs are a standard requirement at mines, since they prevent a build-up of dust, and also allow easy wash-down. This is particularly important in coal mines, where a build-up of flammable dust can be a hazard.

Shock and interference

Besides heat, dust and water, vibration and electromagnetic interference are also common dangers on mine sites that can drastically shorten the life of electronics.

“EMC (electromagnetic compatibility) is a huge consideration especially when you start to get into communications and data,” said Cummings. “We have special EMC o-rings that we can put into our enclosures, but we also look at it mechanically, as far as wall thickness of our enclosures and what gear we put next to each other to eliminate a lot of that.”

And while many systems on mines are static systems, for electronics on plant equipment or vehicles, shock-absorbent mount systems are a must.

These consist of a cradle or a sub-plate which sits on rubber shock mounts. Electronics manufacturers may also choose to mount their PCBs on a gear plate inside the enclosure, and shock-mount the plate.

Optimising protection

There is no one-size-fits-all solution for electronic enclosures used in mines, and the importance of protecting the equipment should not be under-stated.

“Generally, whatever is going into the enclosure is high-value, and vitally important to [the mines’] infrastructure, so we must protect that very carefully,” said Cumming.

“There’s some smart engineering coming out to solve some of the unique problems we have in Australia mining, and it’s really at the design level.”

By properly assessing the environment, potential issues, and the equipment requirements, companies like Intex can apply design and engineering expertise to their enclosures to ensure optimised protection of high-value equipment on the mine site.

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