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Underground

New Manufacturing Techniques for Radio Transparent (Dielectric) Flameproof Enclosures

Underground » Mining Technology and Production

Published: January 18Project Number: C21022

Get ReportAuthor: Ron McPhee | CSIRO

The objective of this project was to source a suitable material and develop engineering techniques required to manufacture a radio transparent (dielectric) flameproof enclosure for use in underground coalmines. The project explored how new materials and manufacturing techniques such as 3D printing could be combined with established engineering and flameproof design practices to produce a flameproof enclosure manufactured predominately from dielectric (non-metallic) material. The project aimed to develop enabling technology for the Australian coal industry and to provide manufacturers with the basic tools to manufacture a dielectric enclosure to IEC specifications.

Underground radio frequency equipment is currently restricted to certified intrinsically safe (IS) instruments, or devices housed within a conventional steel enclosure and fitted with an external antenna. IS instruments are very expensive to design and IS certification can be a long and costly process. Also, there is always the risk that an electronics manufacturer will alter the design of underlying technology without notice, in which case the IS instrument must be abandoned or re-certified at additional cost. In many cases, where complex propriety electronics are involved, obtaining IS certification is an extremely difficult and high risk proposition, for example, a wireless communications routing device. In such cases the device must be IS designed from first principles and this process can be a long and expensive exercise.

The project investigated several enclosure manufacturing techniques; numerous materials were evaluated and ultimately three materials were selected as candidates for the dielectric material. An early enclosure design is presented, consisting of a steel base and a conventional flanged flame-path but with a significant content of the enclosure manufactured using one of high density polyurethane, 3D printed glass-filled nylon or polycarbonate. An alternative design includes an optional flat, toughened-glass lens to accommodate a video camera. Using a dielectric material allows commands and digitised data to be transmitted to and from the enclosure using a standard wireless communications protocol without the need for an external antenna. The construction techniques identified during this phase of the project can be applied to small-to-medium sized junction boxes and small general-purpose enclosures. It is estimated that a medium size junction box would be 30% to 50% lighter if manufactured using steel and polyurethane as the basic construction materials.

Polyurethane is a very cost effective material, especially for larger production runs where well established casting techniques can be employed. 3D printing in a material such as glass-filled nylon was eventually rejected, but this process could enable the industry to model and develop a variety of dielectric flameproof enclosures with minimal development cost. The project encountered a major difficulty obtaining “thermal index” specifications for polyurethane, which was required for certification testing. This data can be obtained through special tests performed by United Laboratories (USA), but the cost was prohibitive for this project ($60K - $70K USD). On this basis, the project abandoned the polyurethane material. The ultimate material of choice was polycarbonate and a design suitable for use as a dielectric enclosure is described in a later ACARP funded project, namely C26052 “Low Cost Laser and 3D Imaging Equipment for Underground Applications”.  

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