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enclosure

Polycarbonate GEOS enclosure.

Non-Metallic Enclosures

Compared to Metallic Enclosures

What you want from your enclosure is long-term, productive service. Knowing your application and the environment in which it will be located will help, but understanding the materials available will complete your research so that you can make the right decision for your particular application.

Often in the design process, enclosure selection is one of the last things to consider. Alternately, the enclosure is selected up front, but based solely on what was used before or what is familiar and not what the application and environment might demand. There are many design engineers who believe that their only enclosure selections are between metal and plastic enclosures. This, of course, is only partly true.

When making the decision for purchasing the right enclosure for your application, there are a number of considerations to think about—besides environment, which includes corrosion resistance (see below), temperature, size, weight, and more. Other things to examine in your research include electrical safety, conductivity, and shielding properties; security access in the event of vandalism; cooling or heating requirements; the aesthetics of the device based on whether it will be visible or not; and the overall value and cost of the system when taking into consideration time in service and initial costs.


enclosure

Outside application photo of polycarbonate enclosure.

Recommended Materials for Corrosive Environments

Recommendation

Acids

Alkalines

Solvents

Highly Recommended

• Stainless Steel

• Fiberglass

• Fiberglass

• Stainless Steel

• Fiberglass

• Stainless Steel

• Aluminum

• Powder Coated Steel

Acceptable

• Polycarbonate

• PVC

• Powder Coated Steel

• Polycarbonate

• Galvanized Steel

• Powder Coated Steel

• Galvanized Steel

Limited or Unacceptable

• Aluminum

• Galvanized Steel

• PVC

• Aluminum

• Polycarbonate

• PVC

The Basics of Metal Enclosures

Design engineers often think about purchasing metal enclosures first, based primarily on the idea that they are stronger and more durable than most other materials. This may or may not be the case dependent on the application but, more importantly, these considerations may not be necessary in the first place. For example, you may not need an enclosure that is durable if the components being protected are housed deep inside a piece of equipment that already has its own environmental control, and is not subject to the outside environment at all—think subsystems, additional Wi-Fi circuits, or an upgraded sensor system.

When considering some of the factors mentioned above, size and weight can be a bigger issue than simply protection. This is especially the case in many automotive, medical, marine, and agricultural applications where compactness and minimal weight are key features. Further, metal enclosures often require additional sealing to keep out moisture and water. They are mechanical in nature, requiring either hinges and doors or two sections that must be bolted or screwed together.

Corrosion resistance is an important item to think about when using metal enclosure materials. Most metals corrode, under particular conditions and at rates that depend on the type of metal used and the environmental conditions in which it is located. Consider the food and beverage industry where continual washdowns—often with detergents and chemicals— are part of the daily or weekly environment. Such regular abuses might preclude the use of company labeling and branding opportunities as well. Stainless steel and aluminum, for obvious reasons, are common choices for enclosure material, based on their high resistance to corrosion. When designing a system that will be used in harsh environments, these choices may provide you with reliable protection where other metals do not. Stainless steel enclosures are often highly expensive to purchase, making them difficult to purchase when project budget is an issue.
Strength and toughness can be a clear factor when deciding on the right enclosure. Strength is a measurement of the material’s resistance to failure. Toughness, on the other hand, measures a material’s ability to withstand sudden impacts. These two features work together, in that increasing toughness usually decreases strength and vice versa. When using a metal enclosure, such as stainless steel or aluminum you may get high strength, but units may dent easily, reducing the integrity of the box—and possibly breaking the sealing ability of the unit dependent on the type and material of the seal used.

For example, when an enclosure is not flush and the seal loses its properties, the enclosure is no longer water or air-tight; moisture and particulates are key reasons some electrical and electronics components fail. Plus, the internal controls and circuits can also become easier to access, reducing security of the system overall.

The Basics of Non-Metal Enclosures

Some of the most used materials for non-metal enclosures include polycarbonate, polystyrene, and ABS. It’s important to note that regular advancements are being made in plastics technology. What you may have found unavailable one year may be available the next.

When it comes to polycarbonates, some are available that feature UV stabilizers used to protect the material from sun overexposure. Others may include a formulation that includes glass fibers, which can significantly increase tensile strength, flexural strength, and flexural modulus, in addition to providing greater heat deflection for temperature sensitive applications.
Plastics are often more amenable than metals to be worked, molded, and modified to fit a specific application. This versatility allows such materials to be used in a wide variety of applications, because having flexibility in material components makes it easier to fit a specific need. Plastic enclosures have the added benefit of being lighter in weight, which makes them easier to handle and ideal for handheld devices, as well as for mounting on delicate surfaces such as sheetrock.

Some additional features that plastic enclosures make available: UV performance, broad temperature range, chemical resistance, waterproof, non-magnetic and electrical insulating, ease-of-processing, self- extinguishing flammability properties, and ease of modification. There are plastics that won’t dissipate harmful gasses in the event of fire, and there are some chemicals that react negatively to metals where plastic enclosures are more suitable. Note also that most often plastic enclosures are less expensive than metal enclosures and have shorter lead times, especially when semicustom or custom elements are needed.

enclosure

Shown are stainless, aluminum and painted steel enclosures.

Consider the Application

Manufacturing control systems, as well as process control systems are often direct-wired and may depend on being RFI/EMI shielded from the electrical noise present in those applications. When a metal enclosure is used, the components inside are automatically protected against such outside interference, making the overall system robust in nature. This same shielding works well with other heavy machinery, such as equipment found in the machine tool industry. Such applications often have additional needs for chemical resistance.
For these types of applications, non-metal enclosures may need to have additional shielding to maintain a safe place for sensitive electronics. Further, such enclosures may need to have special seals or use particular materials that allow them to operate in the harsh environments of the factory floor. In either case, if the enclosure houses delicate electronic circuitry there may also be a need for cooling hardware to be installed. Metal and non-metal enclosures have their value (see below).

Since so much equipment and systems are being upgraded with wireless communications built into them, the enclosure market has had to keep up. When using metal enclosures, the user may need to install an external antenna in order to get optimal use from the system. If the environment dictates that a metal enclosure is necessary, be sure to also research any antenna network you plan to use with it to be sure that the antenna can also handle the harsh environment.

Consider that external antennas are often vulnerable to environmental elements, such as corrosion, ferrous oxide deterioration, and natural ambient interference from the environment itself. This may be the biggest reason why design engineers are switching to non-metal enclosures in communications applications: They allow for free transmission of electronic signals.
Because most non-metal enclosures enable electronic signals to transmit through the enclosure itself, the choice of enclosure material becomes more dependent on its ability to resist corrosion, tolerate the use of harsh chemicals, maintain a strong and tough exterior, and sustain its thermal capabilities. In addition, non-metal enclosures provide engineers with an attractive finis, and can be easily adjusted for changes added later. These include cutouts for additional access to the electronics, whether for quick security checks, to download information, or for audio/video connections. Non-metal enclosures have, over the years, proven to be durable, never rust or corrode in harsh environments, and provide secure and lockable lids to prevent unauthorized access. They are more resilient to impact (they give rather than dent) and allow wireless systems to easily operate without an external antenna. The one negative consequence of using metal enclosures is the compromise of the gasketed seal, which is extremely important to prevent moisture, dust, and other environmental factors from damaging internal controls. Non-metal enclosures usually have the seal inside a groove in the lid, which protects it from direct damage. All of this helps to explain why non-metal enclosures are frequently replacing metal enclosures in many applications.

Pros and Cons for Primary Metal and Non-Metal Enclosure Types

Metal Enclosure Types

Pros

Cons

Stainless Steel

• Corrosion resistant

• Impact resistant

• RFI/EMI shielded

• More expensive than low carbon steel or aluminum

Low Carbon Steel

• Inexpensive metal

• RFI/EMI shielded

• Requires coating to prevent rust

• Will rust if coating wears off

Aluminum

• Rust resistant

• Lighter than steel

• Lower impact resistance than steel

Non-Metal Enclosure Types

Pros

Cons

Polycarbonate

• Highly impact-resistant

• Nice appearance

• Allows for RFI/EMI transmissions

• More expensive than PVC, ABS, and Polystyrene

• PVC

• ABS

• Polystyrene

• Cheaper than polycarbonate

• Allows RFI/EMI transmissions

• Lower impact resistance

• Limited temperature range

Polymer-fiberglass composites

• Corrosion resistance

• Weight to strength ratio

• Allows RFI/EMI transmissions

• Blooming

 

In conclusion, remember that your application is the most important guide to what type of enclosure you will want to purchase. As mentioned, going with the same enclosure for every application typically isn’t the right path to take. When doing your research, find companies that have multiple options available, have been doing business for a long time, and have experience and expertise in how to select and implement enclosure technology. Enclosure needs, like other vital components inside your application, should be selected carefully and confidently.

 

Not all Distribution Boxes are Created Equal

If sealed enclosures are used in environments with fluctuating temperatures and air humidity, condensation problems may arise as water vapor collects on the internal surface of the enclosure. If the enclosure, in turn, contains electrical equipment, the result is an increased risk of system malfunction due to short-circuiting, electrical and electronic component breakdowns or rusting and corrosion.

Depending on the power losses given off by the installed devices, the air inside an enclosure commonly heats up to temperatures of 55° C (133° F) or more. As this warm air inside an enclosure comes into contact with the enclosure’s colder casing, it cools and may chill to a point where it can no longer retain the same amount of water. Air at a certain temperature and a certain pressure can only absorb a certain maximum quantity of water vapor. For example, in comparison to a temperature of 55° C (133° F) air at a temperature of 20° C (68° F) can only absorb 20% of the water content.

These issues are magnified when enclosures are exposed to changes in temperature from daytime to nighttime and from sunny to shady conditions.

Sealed enclosures will not allow the air inside the enclosure to escape. As a consequence, water vapor, which is suspended as a gas, turns into liquid water. This is called the dew point — the atmospheric temperature (which varies according to pressure and humidity) below which water droplets begin to condense and collect inside the box.

Figure 1: Patented air ventilation system removes condensation from enclosure. Source: Altech

Figure 1: Patented air ventilation system removes condensation from enclosure. Source: Altech

Fortunately, technology can assist. In order to avoid the formation of condensation, the Altech AKIII Air enclosure is fitted with a patented air ventilation system comprised of an air ventilation element and drainage supporting the transportation of condensate out of openings in the enclosure.

In operation, there are two vents in the enclosure, one near the top of the enclosure and one near the bottom of the enclosure. This creates an air exchange that allows the hot air that builds up inside the enclosure to escape through the top. As the outside air temperature starts to cool down, it enters through the other vent; this steady air exchange transports the moisture out of the enclosure before the moist air starts to condense.

The ventilation element facilitates the avoidance of condensate while maintaining the high IP protection rating of IP65.

By way of review, IP65 enclosure characteristics include:

  • Complete protection from dust, oil and other non-corrosive material
  • Complete protection from contact with enclosed equipment
  • Protection from water, including water projected by a nozzle against enclosure from any direction

Figure 2: Filter element mounted inside the box removes 10 μm or larger particles. Source: Altech

Figure 2: Filter element mounted inside the box removes 10 μm or larger particles. Source: Altech

The AKIII enclosure is fitted with a filter element that retains particles that are 10 μm or larger. The filter is mounted inside the box and is exchangeable.

The ventilation system is maintenance-free by design and the enclosure is a UL-listed product with a NEMA 3R rating. NEMA 3R enclosures are typically used in outdoor applications for wiring and junction boxes. This style of enclosure provides protection against falling rain, sleet, snow and external ice formation. Additionally, it protects against dripping water indoors.

Altech’s AKIII is made of polycarbonate, which is a very durable engineered plastic material. Unlike steel, it is non-corrosive and it is resistant to harmful mechanical stresses, in particular impact stresses. It is a maintenance-free material that offers reliable protection and resistance to chemicals and can be expected to deliver long operational service with low installation expense.

Another feature is that the top and bottom end walls are supplied open and can be fitted with different types of flange mount end walls. This allows for many options for different types of knockouts or smooth walls. They can also be used to combine two enclosures (top to bottom) because there is a combination flange that can be used in place of end walls.

Figure 3: The AKIII series comes in a variety of enclosure sizes. Source: Altech

Figure 3: The AKIII series comes in a variety of enclosure sizes. Source: Altech

The interior of the AKIII serves to accommodate the equipment and is fitted with various mounting options depending on the variant. In all, there are seven different models. The difference among them is how much space they have for components. Four models are basically single-door, double-door, triple-door and four-door enclosures for circuit breakers or timers. The single door is a 14 circuit breaker enclosure. Similarly, the double door is 28, the triple door 42 and the four-door can hold 56 breakers.

In addition, three models called the Plus series are available with an extra mounting space in the top instead of a door. This is useful for mounting components that should not be visible, which can include all wiring or extra terminals that don't need access from the enclosure doors.

Height adjustable DIN rails are pre-installed for component mounting. Other accessories are available such as partitions, mounting tab kits, cable glands, etc.

For more information on the AKIII Air enclosures, visit Altech.

 
 
 
 
 
 
 
 

Safety for the Smart Factory

By: Murray Slovick

The new SRF (Safety RFID) is a non-contact safety sensor that monitors movable safety guards.

With the convergence of automation, wireless IoT and information technology, real-time data can be downloaded at any point in the production process to an on-site control room, an off-site data center or “the cloud.” The result has been an unprecedented level of manufacturing flexibility and efficiency. Collectively, this phenomenon is being referred to under various labels, including “smart factories,” the “fourth industrial revolution” or, simply, “Industry 4.0.”

To support the implementation of safe “smart” factories, Altech is introducing Bernstein AG’s non-contact Smart Safety Sensor. Designated SRF (an abbreviation of Safety RFID), it features an innovative diagnostic system that makes safety circuits suitable for today’s Industry 4.0 facilities.

SRF

Figure 1: The SRF provides a multitude of diagnostic data of each sensor,
even in a series connection, to support smart production. Source: Bernstein AG

But we are getting ahead of the story. It all starts with non-contact radio frequency identification (RFID) coded safety switches that monitor the opening and closing of machine guards, doors or fences. Safety guards, of course, prevent operator access and must therefore be kept closed until the hazards posed by machine movement have ceased, protecting personnel around machinery and other equipment. RFID is itself not new to manufacturing — it has been used throughout the supply chain for many years, especially in inventory control and asset management. Applied to safety equipment, however, RFID provides tamper-proof protection and simplifies installation as physical contact is not required between the switch and the actuator; the sensor itself can even tolerate some misalignment.

The new Bernstein AG smart sensor SRF is well-suited for any location where safety switches are in use. It is an ISO 14119-compliant type 4 product (an interlocking device with non-contact position switches and a coded actuator). ISO 14119 defines possible methods for selecting and installing safety switches and sensors and further defines possible methods used to prevent tampering such as the use of coded actuators to avoid any actuation of the locking system by readily accessible objects.

Consequently, the SRF is ideal for utilization scenarios involving packaging machines and equipment, woodworking machines, turning and milling machines, food processing machines and injection molding machines, to name just a few.

SRF

Figure 2: The SRF can be used in a variety of industry sectors, including but not limited to packaging,
woodworking, milling and lathe, food and injection molding. Source: Bernstein AG

This particularly compact sensor (featuring a 3.5 mm x 26.2 mm x 1 mm housing) protects employees from injuries by signaling the safety monitor (via two OSSD outputs) to shut down or disable the startup of machines when the safety guard is not properly closed. It monitors movable safety guards such as hatches, doors, flaps, hoods and protective fences, ensuring that safety doors and protective guards remain closed when danger is present. The SRF monitors the position of the guards using a coded sensor, which can only be used in conjunction with a specific Bernstein AG actuator designated for this purpose. The actuator has a non-modifiable safety code for error-free identification. This code is submitted to the SRF sensor and is permanently saved in the SRF, without any additional equipment required. Three different coding levels are available:

  • Low (L): The SRF accepts any Bernstein AG actuator.
  • High (H): The SRF accepts only the taught-in actuator (SRF-0), a maximum of 12 teach-in processes are possible.
  • Unique (U): Similar to “High,” but only one teach-in actuator process is possible.

 

The SRF adheres to ISO 14119, a standard that covers mechanical or electrical devices that are designed to prevent the operation of a machine element for as long as the movable safety guard is left open. ISO 14119 determines which coding level is required.

The Value of Diagnostics
In developing this new product, Bernstein AG paid particular attention to the diagnostic system accompanying the sensor. In addition to the safety outputs, all the switches have an extra diagnostic output. The system provides a large amount of data, making it available centrally and flexibly as an aid to intelligent production.

Called the daisy chain diagnostic (DCD) system, it submits a complete status image of a sensor, even in series connection to support smart production. The diagnostic interface is located between the last sensor and the safety controller. Even in case of power supply shutdown, the diagnostic error memory can be read, which allows quick troubleshooting.

SRF

Figure 3: Daisy Chain Diagnostics make the machines more efficient and
enable predictive maintenance to be realized. Source: Bernstein AG


The higher-end switches use a bus system within the series line that can be used to communicate via IO-Link to a PLC or PC, to an Android smartphone via NFC (near-field communication) interface or via USB for displaying sensor information on a PC or laptop. In all, 20 different diagnostic information elements from each sensor can be retrieved and made available. The following information, among others, can be transmitted: opened door, detection of misalignment (warping of the door), detection of under-voltages in the series connection and attempts to defeat the SRF unit.

Data collected in this manner can be used for predictive maintenance based on early fault detection, possibly preventing a costly shutdown. Even in cases of power supply shutdown, the diagnostic error memory can still be read. Simpler switches in the product line use PNP diagnostics, which can be used to communicate directly with most PLCs.

Since we have mentioned series connections twice, some explanation is in order: the new SRF can be used individually or in series. This is important because basic magnetic switches typically cannot be run safely in series. Since there is no mechanical connection between the actuator and switch (like might be found with a keyed interlock switch), welded or broken contacts (typically reed switches) may not be detected when the door, gate or panel is opened, creating a dangerous condition. Normal magnetic switches typically require a cable to be run from each switch back to a dedicated isolated special safety relay input.

In a single-use SRF application, a movable safety guard is monitored through one SRF. The two OSSD safety outputs of the SRF are connected to a safety monitoring unit. In a series connection, several movable safety guards are monitored. The safety outputs of the last SRF are connected to a safety monitoring unit. After closing all safety guards (all actuators detected), the last SRF of the series connection switches on the safety outputs.

The SRF system features “plug-and-play” wiring — the switches use M12 connectors to plug into series “T” connectors — making installation very simple and fast and saving a great deal of labor and installation time. Switches can also be easily added or removed from the series run by simply plugging in or unplugging components. Using unshielded four-wire standard cable and standard plugs reduces wiring cost.

Fault Tolerant Outputs

The fault tolerant outputs prevent an unexpected machine stoppage. There is no shutdown in case of one output error (there is immediate shutdown when a second fault occurs). Faults that do not immediately compromise the safe operation of the SRF (e.g., external short circuits) result in a delayed switch-off of the safety outputs. The safety outputs will switch off when the error warning exceeds 20 minutes. If an error is detected at one output, the sensor indicates this with a flash code — while simultaneously transmitting the information via the DCD system. These features can be used to shut down the machinery in a controlled manner. The safe outputs enable and allow a restart.
About the Suppliers

Altech Corp. is an established United States supplier of components and devices used in industrial control, instrumentation, medical and automation applications. The company provides a very broad line of products that meet UL and international standards and are RoHS and REACH compliant. A sample (non-exhaustive) list of their products includes circuit protection devices, contactors, DC-UPS solutions, digital timers, DIN enclosures, fuses and fuse holders, foot switches, industrial enclosures, interface modules, meters, motor disconnect switches, pin and sleeve devices, power supplies, push buttons and pilot lights, relays, safety switches, sensors, and test and measurement equipment. Altech’s commitment to quality management has been recognized since 1999 when the company was awarded ISO 9001 certification. For more information, visit altechcorp.com.
Bernstein AG is renowned for the development and marketing of safety switches, sensors and enclosures. Based in Porta Westfalica, Germany, its focus is on protecting the operator through machine and process safety through use of a comprehensive product program that fully meets relevant safety requirements across a wide range of specific applications. The family-owned and managed company celebrated its 70th anniversary in the summer of 2017.


 

Non-Metallic Enclosures Offer Clear Benefits in Agriculture
Bill Schweber


Electrical and electronic cable, connectors and related subsystems need rugged enclosures for the harsh agricultural environment, where non-metallic enclosures offer distinctive benefits compared to conventional units.


It is well-known that many industrial installations and production facilities are often harsh settings, with oil, dirt, vibration, physical abuse and other numerous issues. In contrast, many people envision an agricultural setting as crops in the field, often with animals quietly grazing or resting in their barn. The image is all peaceful and benign (Figure 1).

Altech Agriculture Enclosures

Figure 1. A farm may seem a quiet and clean operation compared to an industrial facility, but it is actually more challenging in terms of dirt, dust, waste, impact and corrosive environment. Source: Altech


Despite this image, the reality is quite different — and it is a harsh one.


A modern agricultural operation can be as bad as or even worse than an industrial environment. There are constant dirt, crop dust and discards, physical impact, extreme temperatures (both hot and cold), extreme weather (storms, flooding) and more. Further, unique to the farm environment is the presence of animal waste (primarily ammonia), which is corrosive to many materials.


Therefore, rugged enclosures are needed to enable effective and reliable modern farm work. These enclosures house and protect electrical lines, lighting controls, switchgear, safety and security wiring, even sophisticated electronics; they are also critical for user and livestock safety.


Enclosure Considerations Define Selection

The common solution is to select a suitable metallic enclosure, either steel or aluminum, to provide the needed ruggedness and protection. However, in the case of farms, a non-metallic polycarbonate enclosure (Figure 2) can be the better choice, as it resists moisture, corrosion, chemicals and even ammonia.

Altech Agriculture Enclosures

Figure 2. Non-metallic polycarbonate enclosures, such as the dust- and moisture-proof TK and TG series from Altech Corp. offer many useful performance advantages and attributes in the farm/agriculture environment, as compared to metallic units. Source: Altech


Polycarbonate enclosures offer other advantages in addition to basic ruggedness. Obviously, they are rust-proof and have no surface finish that can wear or chip, thus allowing rust to take hold. Further, these non-metallic units meet various relevant standards, among them:

  • UL94 (Flammability of Plastic Materials);
  • NEMA IP66/67 (particle and water ingress);
  • VDE 0471 (fire hazard);
  • IK07 (impact);
  • Wide operating-temperature range of -35 degrees C to +80 degrees C.


A special feature of polycarbonate enclosures is that they can tolerate high concentrations of ammonia, meeting the stiff certification requirements of the German Agricultural Society (Deutsche Landwirtschafts-Gesellschaft, or DLG). They can withstand an ammonia concentration of 750 ppm (parts per million) at 70 degrees C and 70 percent humidity over 1,500 hours of continuous testing.


Customization Opportunities Make an Additional Difference
While the physical sizes of polycarbonate enclosures are standardized, this is not a serious constraint, as they are available in a wide range of height, width and depth dimension combinations. Once a basic enclosure is chosen, many attributes and features can easily be customized. Vendors can do value-added work to reduce end-user effort even for moderate volumes, typically beginning at just 25 units (Figure 3). Among these are:

  • Choice of hinge type (internal, external);
  • Choice of mounting style and orientation;
  • Panel cutouts for displays, indicators, keypads and other functions;
  • Pre-packaged connectors and pushbuttons;
  • Imprinting and labeling;
  • Choice of transparent or opaque cover.

Altech Agriculture Enclosures

Figure 3. Non-metallic polycarbonate enclosures are offered with many standard options as well as customizable options. Source: Altech


Polycarbonate Enclosures: An Attractive Alternative
Non-metallic polycarbonate enclosures can be a superior and flexible match for harsh applications such as agriculture, especially due to their corrosion and ammonia resistance. They meet and exceed all
relevant industry standards for corrosion, impact resistance, ingress protection, flammability and more. Further, the vendor can customize many aspects of these enclosures to meet specific user requirements and preferences.


For more information on choosing and using non-metallic polycarbonate enclosures, contact Altech Corp.


 
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For more information contact Altech at:
908-806-9400 • 908-806-9490 (FAX) • info@altechcorp.com • 35 Royal Road, Flemington, NJ 08822