Evolution of composite non-metallic materials
During the early 20th century, protection and packaging for electrical devices, power distribution and electronics fundamentally defaulted to metal material choices, typically an alloy of steel or aluminum. The latter part of last century brought the discovery and development of new non-metallic materials including composites and plastics. It quickly became apparent that certain types of applications were ideally suited for enclosures made from such non-metallic materials. For example: fiberglass composite materials were clearly superior to metallics - even stainless steel in specific environments - for the purpose of beating the high cost of damage from corrosion.
Today, increasingly sophisticated materials science has made composite non-metallics even more desirable through development technologies that provide solutions to diverse product and application needs ranging from aesthetic to performance-based.
Risks of improper electrical enclosure selection
Enclosure failures caused by corrosion or impact damage resulting in a breach of proper sealing can cause a multitude of problems ranging from catastrophic and dangerous system collapses, production downtime, increased maintenance costs, plus losses in customers and revenue. Therefore, proper product selection is critical as relates to both the design and the material of the enclosure.
As a case study example: professionals in the water/wastewater industry are often faced with highly corrosive environments. Recently, Fishbeck, Thompson, Carr & Huber, Inc. (FTC&H) a professional civil engineering, environmental consulting, architectural/engineering, and construction management firm, was serving a water filtration plant located in Western Michigan. That particular customer was highly concerned about aggressive corrosion which was causing premature product failure of metallic enclosures that housed critical SCADA PLC control panels. Corrosion levels are inordinately high in this environment because, out of physical necessity, control units must often be placed above an open- top tanks containing chlorinated water.
In the case of the water filtration plant served by FTC&H, switching to a composite fiberglass enclosure solved the problem, but the process of educating users as to the options in material selection is actually the critical link between application needs and successful product performance.
Best practices for enclosure selection
The process for proper material and enclosure selection begins with a detailed consideration of the application’s atmosphere, physical environment and presence of corrosive agents.
Defining what is causing corrosion within a specific environment, and determining the concentration or extent of corroding agents requires attentiveness. Usually several corrosive elements are present and interactions are not always well documented or self-apparent. Water is the most common corrosive element and is usually present to some extent in every enclosure application. Adjacent processing operations or other intermittent activities such as industrial cleaning and the general plant environment may expose an enclosure to a variety of corrosive agents and temperatures. Each environment is unique and all possible corrosive agents should be identified for the intended enclosure application.
When exploring the merits of composite non-metallics versus metallics in any given environment, the following facts about metallics need to be remembered. Metallic derivatives are often perceived as being the material of choice for enclosure applications not necessarily because of proven performance but because of their long history and consequential familiarity with many users. While tensile strength is high with metal enclosures, flexural strength (the material’s ability to withstand denting), is relatively low. While that is desirable for forming operations, it is less than desirable in the finished product. Once metal has gone beyond its elastic limit it has created a potential leak path that could compromise an enclosure’s seal integrity. Composite fiberglass materials offer a significant advantage over metallic alternatives in improved flexural strength because they can withstand an impact without permanent deformation or denting. Composite fiberglass also offers an effective continuous service temperature ranges from -73 ºF to +250 ºF, meaning that enclosures molded from this material will withstand even the most difficult industrial operating environments.
In the case study referred to above, FTC&H realized that metal corrosion is influenced by surface finish, surface treatment such as painting or galvanizing. They also accepted the fact composite fiberglass material is naturally corrosion resistant and, therefore, was the composite they required to replace the failing metal enclosures. Ultimately, FTC&H selected a Stahlin N-Series wall-mounted fiberglass enclosure with polyurethane seamless gasket that provided a reliable water and dust-tight environmental seal. Of added benefit, non-metallic enclosures proved easier to modify than metallics with modifications such as windows, holes, vents, drains, available as a factory provided option or easily achieved in the field using conventional tools.
UV resistance in composite non-metallic enclosures
Many professionals are still unaware of how non-metallic composite materials are able to effectively withstand damage from UV exposure.
In enclosure applications, a unique formulation called SolarGuard® is now available to provide superior molded-in UV-resistance, requiring no field maintenance, and at no additional product cost. SolarGuard® has been granted United States Patent No. 7,317,049 for ‘Resin Composition for a Sheet Molding Compound and Method’.
SolarGuard®, developed by Stahlin Non-Metallic Enclosures in the company’s FormRight™ Labs, is a double protection formulation technology which significantly enhances the molecular bond strength and cross linking that occur during the curing process in thermosetting polyester sheet molding compounds (SMC). SolarGuard® fights polymer degradation by making it much more difficult for UV light to attack molecular bonds of both primary chains and crosslinks. This is accomplished by increasing the molecular density of the base resin system thus increasing its resistance to UV degradation. An additional benefit of SolarGuard® is its use of additives or anti-oxidants that help protect the polymer chain and resist photo induced oxidation from exposure to UV sunlight. All of Stahlin's enclosures are now protected from UV exposure though the SolarGuard® formulation.
Modifications of composite enclosures
Non-metallic composites offer the benefits of part integration and minimization along with substantial savings in weight. Along with that advantage is a reduction in the requirements for machining operations that need to be performed to complete an assembly. However, all drilling and cutting operations cannot be avoided completely in all cases. There are several types of machining operations that can easily be performed on composites, including: turning, drilling, routing, trimming, sanding, and milling. Most of these operations are similar to metal removal techniques but there are some differences that need to be addressed in order to make clean, high quality holes and cutouts in composites.
Delaminating of the outer surface and glass fibers directly below the surface are the main failure modes noticed when holes or cutouts are drilled or cutout improperly. Most times excessive edge chipping around the perimeter of the cutout or hole is due to improper tools used and methods applied. A little planning and understanding of the proper methods to machining composites up front can make all the difference in the final outcome of the operation.
Factory-option modification is also a highly desirable alternative for many end-users because it enables the manufacturer to use its skill in providing enclosure modifications and shipping to the customer ready-to-use. Stahlin Non-Metallic Enclosures, for example, offers its ModRight™ Enclosure Modification program for just such a purpose. One of many customers to benefit from ModRight™ is Chemtrac. Since 1985, Chemtrac Systems, Inc. has been a leading manufacturer of process monitoring and control instruments for water and wastewater treatment. The Chemtrac SCM is an online, continuous sampling instrument that enables the water treatment plant operator to optimize the chemical feed dosage. The reliability of this monitor is critical for these operators and is precisely why Chemtrac uses a non-metallic enclosure that will stand up to the stressful environment in a water treatment plant. Through the ModRight™ factory-based modification program, Stahlin now drills additional holes that the Chemtrac plant had previously been doing - saving time, money and headaches.
Composite non-metallic enclosures
Non-metallic enclosures are still passing the learning curve among professionals in the water and wastewater industry, but increasingly such products are being accepted for what they are: high performance, anti-corrosive, impact resistant, lightweight, easy-to-use and modify alternatives to metals.