Electronics Protection - March/April 2013 - (Page 6)

Feature Specifiers of Enclosures for Components in Outdoor Applications: Be Aware of Material Selection Issues Roger Schroder, Engineering Manager Stahlin Non-Metallic Enclosures Material selection is a step in the process of designing any physical object. In the context of product design, the main goal of material selection is to minimize cost while meeting product performance goals. Systematic selection of the best material for a given application begins with comparing the properties and costs of the materials available. In many applications it is imperative that systems operate flawlessly from installation. The proper selection of components that support the longevity and durability of the system become critical choices in the process. Many outdoor applications require several important environmental considerations. For the purpose of this article we will just focus on non-metallic enclosures and the challenges of selecting the right material that will meet these considerations. Outdoor Enclosure Material Selection: Non-Metallic Why choose a non-metallic material for an outdoor application? Non-metallics have proven to provide a long life and maximum reliability in an outdoor environment. • Life cycle costing of composites is favorable. In spite of a higher prime cost compared to traditional materials like steel and aluminum, the use of composites results in a lower overall cost over the life span of the product. This is due to a negligible amount of maintenance and minimal recurring cost requiring no replacement as a result of deterioration in service. • Composites (FRP) enclosures were developed as an answer to corroding stainless steel enclosures in marine environments. • There is an inherent safety factor as composite enclosures are not conductive. • The lighter weight of composite material reduces installation headaches and troubles. • Modifications of composites are easy. Types of Non-Metallics Available: Thermoplastics and Thermosets Thermoplastics such as polycarbonate, polyester and PVC offer a degree of corrosion protection beyond painted carbon steel in outdoor environments. Thermoplastics, however, are more susceptible to UV and weathering degradation over time. Certain stabilizers can be added but ultimately the nature of the thermoplastics will yield to extended weathering. 6 Thermoset materials, such as a polyester resin combined with glass, create a composite FRP (fiberglass reinforced polyester) that is durable and weather resistant. FRP provides greater corrosion protection than painted carbon steel, yet performs better than metal and thermoplastics in harsh outdoor environments. The Challenge for Non-Metallic Materials: The Ability To Fight the Effects of UV Rays If electronic components are placed outdoors the environment is UV intensive, and thus the damaging impact of the UV energy must be addressed in composite enclosures. UV attacks materials and works to break apart their substrates. This degradation can lead to the structural breakdown in certain materials and over a period of time potential failure of the system. A patented material has been developed that specifically addresses UV degradation that greatly increases the performance in outdoor applications such as solar power. Ultraviolet radiation (UV) of electrical enclosures in outdoor environments has been a concern with non-metallic manufacturers for many years. Virtually all fiberglass products when exposed to UV radiation experience surface degradation. Visual changes to the composite fiberglass include surface fiber appearance, color change and loss of gloss. This is a result of sunlight initiated reactions with oxygen, photo-oxidation. Photo-oxidation occurs when the polymer molecules absorb sunlight and dissipate the excess energy by breaking chemical bonds. This UV exposure often results in a roughening of the exterior surface. Subsequent wind and rain can wash away this powdery byproduct and over time the glass fibers begin to show through to the surface. This is referred to as “fiber blooming.” The actual degradation of the FRP material will slow once these fibers are exposed, as they will then provide a degree of UV protection to the polyester material underneath. The rate at which the UV degradation occurs will vary depending on heat, humidity and latitude with which the product is installed. Many end users of fiberglass products view this as being visually unappealing or in some cases as potentially having an effect on the physical properties of the end product. The molecular bond strength and crosslinking that occurs during the curing process in thermosetting polyester sheet molding compounds (SMC) is important to understanding how well a particular plastic material will be able to withstand repeated long term exposure to UV radiation. When FRP products are exposed to UV radiation two factors can occur that have an effect on the end product. They are a change in gloss and a change in color. Gloss is one measurement of the ability of a material to reflect or scatter light. UV degradation can attack the SMC causing the polymer material to break down and the surface to roughen followed by fiber blooming. Over time the color of an SMC material can also be affected by this UV degradation. Pigments or colorants can be attacked and broken down similar to the way in which UV attacks the polymer chains. When this happens - chalking, whitening or some other form of discoloration can occur. Another form of color change occurs when molecular sub-groups are formed within the polymer matrix that is able to reflect light back to the observer. These sub-groups, also called chromophores, are portions of a molecule March/April 2013 www.ElectronicsProtectionMagazine.com http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - March/April 2013

Electronics Protection - March/April 2013
Newer Technology Releases Next-Generation Power2U AC/USB In Wall Charging Solution
Specifiers of Enclosures for Components in Outdoor Applications: Be Aware of Material Selection Issues
How to Protect Electronic Circuits from Power Surges
Testing for Ingress Protection of Portable Electronic Devices
Increasing the Lifespan and Reliability of Electrical Components
From the Inside: The Configurable Plastic Enclosures Revolution
Tips for Selecting and Designing a Membrane Switch
HP Intelligent Series Rack Models Available for Networking and Demanding Server Requirements
Polyonics Antistatic Tapes Solve ESD Problems Before They Damage Static Sensitive Devices
OptoTherm Introduces IR LabMate Infrared Camera Solution
Falcon Electric Offers NEMA 3R/4 Enclosures with SSG UPSs
PEM SpotFast Fasteners Enables Flush Joining of Two Sheets
Industry News
Calendar of Events

Electronics Protection - March/April 2013