The material you choose for your industrial cabinet will affect the life and performance of the electronic and automation components within it. With many materials to choose from, each with different protection advantages, how can you be confident in your choice? The answer is: it depends on your application. Here are some considerations to keep in mind.
Environment. What kind of environment will the housing be exposed to? Are corrosive gases, vapours, liquids or dust particles present? Will it be exposed to by-products of production? What is the weather like - will your enclosure be exposed to severe cold? What temperatures will the enclosure be exposed to?
Strength. When specifying the housing, the required material strength needs to be determined. What is the total weight of the components to be accommodated? Metal enclosures are stronger than non-metallic enclosures and can withstand greater loads, but are susceptible to denting from impact. Non-metallic enclosures can withstand some impact but cannot carry as much weight or support as heavy a load as a metal enclosure.
Modifications. What modifications do you need to make? Adding cuts and holes to a stainless steel shell is much more difficult than modifying a carbon steel shell. Fibreglass is easier to modify than steel, but splits and creates very fine and potentially harmful dust.
Climate control. Metal housings conduct and dissipate heat, so if heat transfer is required, carbon steel or stainless steel are the best material choices. Glass fibre and polycarbonate housings conduct heat much more slowly. Therefore, any heat transfer will require a fan or air conditioning. The material in a non-metallic enclosure essentially acts as an insulator, maintaining the internal temperature when the ambient temperature is low and vice versa.
Electrical conductivity. Metal enclosures conduct electricity and therefore need to be earthed to ensure operator safety when installing or maintaining internal equipment. Non-metallic enclosures are not electrically conductive, which means that the installed equipment is isolated from the enclosure, providing a safety barrier for the operator. Whether the enclosure is metal or non-metallic, the installed equipment needs to be externally earthed to ensure there is a path to earth.
Painted carbon steel is the most cost effective material for metal enclosures. The painted surface consists of an inner primer and an outer powder layer, with some manufacturers using only wet spray and others using only power coating. Power coating produces a durable and scratch resistant surface that passes the requirements of outdoor painting. In the event of accidental scratches, a touch-up paint should be used to cover the bare metal. Resistance to solvents, alkalis and acids is very limited. Painted carbon steel enclosures are mainly used for indoor applications.
Type 304 stainless steel is an iron based alloy containing 18% and 20% chromium.Type 304 is corrosion resistant and provides protection from corrosive solvents, alkalis, and some acids. Stainless steel is ideal for applications that are exposed to rinsing cleaning processes such as food and beverage processing. type 304 stainless steel housings are used in both indoor and outdoor applications. Type 316 stainless steel contains molybdenum, which allows it to provide better overall corrosion resistance than Type 304. Additional material properties include improved resistance to sulphates, bromides, chlorine, seawater, high temperatures and some special acids. The resistance to seawater makes Type 316 stainless steel ideally suited to the marine environment. Because Type 316 has very good resistance to chemical attack, it is often specified in pharmaceutical manufacturing applications where excessive metal contamination must be avoided. Type 316 stainless steel housings are used in both indoor and outdoor applications.
Polycarbonate is a very durable plastic, formed from a thermoplastic polymer. Polycarbonate is more impact resistant than fibreglass and is not subject to deterioration from UV light. Polycarbonate is easier to modify than fibreglass, producing cleaner holes and cuts. Polycarbonate shells have a longer product life and are more weather resistant than fibreglass shells.
Glass fibre reinforced polyester (known as 'glass fibre') is impact and corrosion resistant. Glass fibre is a lightweight, extremely strong material consisting of plastic reinforced with fine glass fibres. Fibreglass cabinets are very suitable for corrosive, high temperature environments. Some fibreglass enclosures are immersion-proof: they can be immersed in water for a specific period of time while completely protecting the contents of the enclosure. Disadvantages of specifying fibreglass enclosures include colour fading and fibre blooming due to prolonged exposure to sunlight, but this can be mitigated by the use of UV inhibitors or acrylic paint.
The correct enclosure must be selected based on environmental conditions, required strength, modifying capacity and weight considerations and, of course, cost is also a factor. Strictly based on the investment in the enclosure, 316 stainless steel is generally a higher investment, followed by 304 stainless steel. Fibreglass and polycarbonate materials would be the next choice for the required investment, followed by painted carbon steel, which would be a lesser investment.
