Metal, plastic, fiberglass? Not all materials are created equal!
Enclosures on the market come in many sizes and types, but what the enclosure is made of is often the very first consideration when sourcing a new housing. Often, this is the most vital factor in an enclosure’s performance. Knowing what materials are available is essential for planning, sourcing, and maintaining electrical and electronic assemblies.
Enclosures can be loosely sorted into metallic and non-metallic categories.
Non-metallics
While most non-metallic enclosures are made of plastic like ABS or polycarbonate, this category also includes fiberglass.
ABS: Acrylonitrile butadiene styrene (ABS) is a low-cost thermoplastic that is easy to process and shape. ABS is preferred for indoor use and offers good impact resistance, heat resistance, and versatility despite being economical. ABS enclosures are often black, grey, or white, but colorful enclosures in blue, red, and yellow are not uncommon. ABS is easy to modify in the field, but it is not ideal for high-impact use and fully transparent ABS is difficult to achieve. General-purpose ABS (GPABS) is not considered flame-retardant, but flame- retardant ABS (FRABS) is also widely available.
Polycarbonate: Offering superior impact resistance, a wide operating temperature range, and resistance to UV damage, polycarbonate is the top plastic for many outdoor, high-impact, and marine applications. UV stabilized polycarbonate avoids discoloration and becoming brittle due to sun exposure, and it is naturally clear. Because of this, it is often used for products like racecar windshields and eyeglass lenses, as well as highly durable enclosures. This material also carries a high flame-retardant rating. Polycarbonate is a less economical option than ABS, but its longevity even in harsh conditions can save costs in the long run.
Fiberglass: Fiberglass- reinforced polyester, abbreviated GRP or FRP, is made of polyester plastic reinforced with glass fibers. Like polycarbonate, FRP is suitable for outdoor use, plus it has good impact resistance and an operating temperature range superior to polycarbonate. However, it may discolor under UV exposure. A notable drawback is that FRP can disperse glass particles when cut, so specialized PPE and tools are required for modifying it. Both polycarbonate and fiberglass offer good chemical resistance and excel in salty environments. FRP withstands solvents and dilute acids and bases. Polycarbonate does well against acids and some solvents and alkalis, but it’s best practice to always research specific chemicals in the environment.
Metallics
Metallics are generally acceptable for outdoor use and have good impact resistance. Galvanic corrosion, also called “dissimilar metal corrosion,” can be a concern with metals. When two different metals are in contact with one another, the metal that is more “basic,” or gives up its electrons more readily, will begin to corrode at an accelerated rate, causing structural and aesthetic damage. For example, the user should be mindful not to use a galvanized steel joiner or zinc-coated screws with a stainless-steel enclosure.
Aluminum: Aluminum is a strong, yet lightweight, non- ferrous metal. Aluminum can take many forms, such as sheet aluminum, extruded aluminum, and diecast aluminum, and it also carries different properties depending on the alloy. An alloy is made up of a base material (in this case, aluminum) plus other metals or elements. Some alloys are stronger than others, or more tensile, or more accepting of certain finishes, and so on. Aluminum is easier to drill into and modify than steel.
Diecast aluminum enclosures are produced by pouring molten metal into preformed cavities or dies. Diecasting is best for small to medium enclosures; larger enclosures will typically use sheet aluminum instead. The process is fast and produces a consistent product. Diecast enclosures by necessity will have a draft angle: the walls of the box must be slightly angled outwards by a few degrees so that the enclosure can be properly removed from the cast.
Extrusion also involves molten aluminum and a die, but instead of filling a cavity, extruded aluminum is forced through the die to take on a specific shape, creating very long pieces of extrusion that can subsequently be cut down to size. Extruded aluminum enclosures often consist of an extruded tube and metal or plastic end caps. Extruding large pieces
that can be cut down is beneficial to manufacturers, allowing them to keep long tubes in stock and provide various enclosure lengths on demand.
Steel: Steel is a ubiquitous, reliable material in many industries. Steel is an iron alloy (made of iron combined with carbon). Steel sheets are used to construct enclosures and panels, with a variety of steel types to choose from depending on the application. Steel is heavier and stronger than aluminum.
Also known as “low carbon steel,” mild steel has a lower carbon content than standard steel and is easier to form and weld. Mild steel is low cost and versatile. Mild steel enclosures have a powder coat finish, rather than being supplied bare or natural, because this material will oxidize when exposed to the elements. Natural mild steel can be used for inner panels, however, as they are not exposed to weather.
Stainless steel is an iron alloy that contains chromium, which gives it its corrosion resistant properties. Different grades of stainless steel are created by the inclusion of additional elements. Stainless steel does not rust and does not need to have a finish. It is highly resistant to acids, alkalis, and solvents, performs excellently outdoors, and is easy to clean, making it ideal for hygienic environments like medical areas or food and beverage plants where the enclosure will be hosed down frequently. The two most prevalent grades of stainless steel are: 304, which is the most common grade of stainless steel, and 316, which (due to the inclusion of the element molybdenum) is a more specialized grade that offers all of the above benefits of stainless steel plus extra corrosion resistance, thereby making 316 stainless steel excellent in marine environments.
Conclusion
Choosing the best material for an enclosure is a vital first step in the planning process, whether the application calls for a multipurpose plastic enclosure for a handheld controller, or a tough metal cabinet that will stand against salty air on a pier. Designing an electrical or electronic assembly can come with a lot of considerations, but hopefully this overview of enclosure materials helps to simplify enclosure selection.
Hammond Manufacturing has over a century of industry expertise. For product selection guidance, technical support, and more, get in touch with us today!