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There are many ways to improve the electrical continuity of electronic enclosures and the resultant EMC performance using a variety of electrically conductive gaskets and mechanical fasteners. Such arrangements have the advantage of being clean and easy to use as well as allowing for the equipment to be disassembled and the components replaced. So, ask the question: Is a compound the right solution in this particular case?
Finding the right electrically conductive compound
Assuming you have eliminated the use of EMI shielding gaskets and mechanical fixings as being appropriate or possible for your design, the next step is to choose the most suitable electrically conductive compound for your application. These typical properties should be considered in order of importance as part of the selection process:
This list above does not cover all the properties of the material that may be of interest to the engineer. In each application, the engineer needs to assess the requirements of the design problem to see how well the material properties match up to the most critical parameters.
Now that you're proficient in selecting an EMI shielding compound for your application, see our selector guide below to get started now.
This blog post was contributed by Gerry Young, applications engineering team leader, Chomerics Division Europe.
25 Feb 2020
So, you’ve unboxed the shiny new Parker seals you ordered – now what? Installing seals for the first time can be challenging without the right know-how and tools. In this article we’ll discuss best practices for seal installation in linear fluid power systems, and how to design your system to make seal installation fast and damage-free.SEAL GROOVE STYLES First, let’s look at three common groove styles:
• Stepped, and
• Open (or two-piece)
The closed seal groove fully encapsulates the seal and is the most common style used (see Figure 1).
Closed grooves are simple to machine and offer the best support for seals. Since seals in this configuration are surrounded by solid metal, without a well-developed process, installation can be challenging. Rod seals need to be folded to fit into internal (throat) grooves and piston seals must be stretched over the outside of the piston.
Notice how both designs shown in Fig. 2 and Fig. 3 utilize static seals (turquoise colored seal) on the opposing side of the dynamic, primary seals. Therefore, installation in either instance requires techniques and tools for both rod and piston seals.Stepped groove
Typically utilized to ease seal installation, stepped grooves feature a reduced diameter on the low-pressure side of the seal as shown in Fig. 4 and Fig. 5.
As shown, the “step” is just wide enough to hold the seal in place as the rod or piston strokes back and forth. This way, seals don’t have to be folded or stretched nearly as much when installing. This design works well for single seals only holding pressure from one direction, like Parker FlexiSeals™.
When using multiple seals stacked in series or in systems with bi-directional pressure, a closed or two-piece groove is needed for support on both sides.Open and two-piece grooves
Open or two-piece grooves are used when the seal is either too small to be stretched or folded into a closed groove, or if it’s made of a material that doesn’t spring back after flexing.
Figures 6 and 7 show two examples of open grooves. Figure 6 uses a washer and a snap ring to hold the seal in place. Figure 7 uses a bolt-on cap. These groove designs can be used for bi-directional seals, too. As you can see, open grooves cost more to produce but seal installation is a snap.
Open grooves also make removing the seal much easier – useful in systems which require periodic seal replacement.INSTALLATION METHODS AND TOOLING
Installing seals with your bare hands is tough! Parker has several tips and tricks you can use to ease the process. For large scale production, building a set of custom tools or even designing a fully automated setup will save time and reduce labor.
Different installation tactics are required for the diverse range of seals Parker manufactures. Polyurethane and rubber seals are extremely resilient and won’t be damaged by stretching or folding. Cylinder components made from hard plastics are less flexible. Parker FlexiSeals incorporate a metal spring inside of a thin PTFE jacket, so stretching or folding should be avoided. If a PTFE seal must be installed in a difficult location, we offer “cap seal” designs which are energized by an O-ring and are robust enough to handle deformation during installation. Installation speed is key in these cases. Testing has shown that when PTFE rings are swiftly stretched over a piston (less than a second), they recover closest to the original diameter, whereas seals stretched slowly need a re-sizing tool passed over the seal to aid recovery.
Installing Rod Seals
Hard plastic components like PEEK backups and Nylon wear bands are supplied with splits to aid installation. Split rings can be collapsed to a smaller diameter to snap inside a cylinder head, or opened to snap over a piston. Since these secondary components aren’t doing the sealing, there’s no concern with the split causing a leak.
For low volume production on rod sizes above 2”, hand-folding each rod seal into the groove can work. For smaller sizes where a hand won’t fit, do yourself a favor and order (or make) a 3-legged rod seal installation tool (see Fig. 8).
These tools grip and fold the seal for insertion, which is especially useful in deep cylinder heads housing several seals in a row (see Fig. 9).
There are many online vendors who sell rod seal installation tools. If you need help, your local authorized Parker seal distributor may have a recommendation. Click this link to locate the authorized distributor nearest to you.
The two tools pictured in Figure 10 were made for use in our lab. Multiple sizes are needed for different rod diameters.
The size of the rod seal will dictate the method of installation. Seals with larger cross-sections are more robust, but harder to fold into place. Small diameter cylinder heads don’t leave much room for installation. For closed grooves, this is the rule of thumb: the rod diameter needs to be 5 times larger than the cross-section. By following this rule, Parker's smallest 1/8" cross-section BD, BT, and PolyPak rod seals will require open grooves when rod diameters are smaller than 5/8".Installing piston seals
Piston seals are less challenging, purely because you’re not confined to a small space while installing. The simplest method for stretching seals into a groove is to hook one side over the piston, and then use a piece of non-scratching brass (see Fig. 11) or plastic bar stock to gently pry the seal over the other side.
While simple, the above method can pinch or unevenly stretch the seal, causing it to leak. For an upgrade, machine a cone and pusher tool out of aluminum and plastic, respectively (see Fig. 11). These are especially convenient for stretching large seals because an arbor press or mallet can be used for additional force. While pushing, the flexible fingers of the tool ensure the seal is being evenly stretched over the piston. PTFE cap seals in particular will be damaged by “necking” caused by uneven stretching.
Since my tools are only used for low volume testing, 3D-printed pushers work great. For production-grade tooling, cut pushers from a tough plastic billet like Nylon.
In addition to gently coercing seals into place, there are other elements of the assembly process to consider. Often overlooked, poor cleanliness of the work area can break an otherwise good procedure. Dirt and metal shavings present in manufacturing areas can become trapped in a cylinder. Over time, they will abrade the seal lip and scratch expensive polished metal sealing surfaces, leading to premature leaking.
Additionally, ensure hardware is deburred beforehand so the seals don’t get cut by a sharp corner. Our catalog recommends a light break (0.005” max) on groove corners to prevent cutting the seals, and – from personal experience – also the hands of the assembler. Larger breaks are fine in areas which aren’t supporting a seal (e.g. the outside of a cylinder head). If smoothing a corner or installing from another direction is not an option, like in some ultra-high-pressure systems, mask sharp surfaces with tape or a plastic sleeve before passing the seal over it. This method is also highly recommended when passing seals over threads.
Even when using an installation cone or protective sleeve, lubricating the seals and hardware beforehand with system fluid or a compatible grease prevents damage and helps the seals slide into place. For stiffer, higher durometer seal materials like Resilon® and PolyMyte®, heating seals in an oven or hot fluid bath will temporarily soften them, making them easier to fold or stretch (be sure to use system-compatible fluid). Soaking for thirty minutes at 200°F is within the max temperature rating of most seal materials and isn’t too hot to handle with bare hands.
Some installation headaches can also be overcome with clever system design. Generous chamfers on the ends of the rod and bore help gently compress seals when the piston or rod is inserted. This also keeps the seal lips from getting caught on a corner and folding, thus ruining the seal. Switching to a bi-directional seal will eliminate problems with seals being installed upside-down (nobody likes to admit it, but this happens).CONCLUSION
Be smart and safe when installing seals. Buy or create tools to do the hard work for you. If leaks are happening right after assembly, consider the installation process suspect. For help, we at Parker are happy to answer questions or assist with installation tool design.
View our short video “Installation Techniques for Linear Fluid Power Seals”, which demonstrates various considerations discussed here.
For more installation and cylinder design information, see chapter 2 of our 5370 Fluid Power Sealing Catalog.
Recommendations on application design and material selection are based on available technical data. They are offered as suggestions only. Each user should make their own tests to determine the suitability for their own particular use. Parker offers no express or implied warranties concerning the form, fit, or function
This article was contributed by Nathan Wells, application engineer, Engineered Polymer Systems Division.
24 Feb 2020
Compressed air is used throughout industrial manufacturing, often for applications that cannot be replaced by electricity. The drive to reduce energy consumption and costs creates a dilemma for manufacturing facilities with regard to compressed air treatment. Manufacturers often identify the compressed air system as a place to realize savings. However, when it comes to purification equipment, such as compressed air dryers, choosing a model based on the lowest energy consumption can directly impact air quality.
Most of today’s manufacturers use an air quality specification, typically based around the ISO 8573-1 air purity classifications, as a benchmark for the selection of their compressed air treatment equipment. While this should be the primary criteria used for product selection, energy reduction is often given higher priority. These two factors can offset each other, resulting in air purity below the desired classification.
Here, we will discuss several alternative air dryer technologies and their impact on the balance between energy consumption and air quality to help users identify the technology that best suits their facility.
There are several types of adsorption — or desiccant — dryers available. These are preferred for applications with particular sensitivity to moisture, like instrumentation and where external temperatures may have an impact. While the principle used to dry the compressed air is identical, the way they regenerate the desiccant material is different.
The simplest way to regenerate the desiccant material also uses the most energy. Dry process air (purge air) is used to regenerate the off-line desiccant bed. This type of dryer, referred to as heatless, is most common. However, for higher compressed air flows, there are more energy-efficient alternatives available. Types of heatless dryers include:
While blower dryers do not use any purge air for regeneration, they do use dry process air to remove heat from the desiccant material. The amount of cooling air is typically expressed as 1~2% of the dryer’s flow. However, this is an average over the drying cycle, and during the cooling period, air consumption can be as high as 10~20%, significantly increasing overall energy consumption.
To reduce energy consumption, some blower dryers use ambient air for cooling. This practice can add up to 77°F (25°C) to the ambient air temperature, leading to inefficient cooling and directly impacting the delivered air quality (outlet dewpoint).
HOC Dryers, often installed with oil-free compressors, use the heat generated from air compression to regenerate the adsorbent material. This process does not include a cooldown of the adsorbent material, the lack of which has a negative impact on the air quality (outlet dewpoint) delivered by the dryer. During periods of low air demand, insufficient heat can be available for full regeneration, further impacting outlet dewpoint.
As the dewpoint delivered by this type of dryer can fluctuate greatly, they are typically classified as dewpoint suppression dryers and will not provide an outlet air purity consistently in accordance with the ISO8573-1 classifications.
The operation of a vacuum regeneration dryer is similar to a blower dryer. Instead of using a blower to “push” heated ambient air over the off-line desiccant bed, they use a vacuum pump to “pull” heated ambient air over the material. The desiccant material can regenerate more efficiently under vacuum, saving more energy. No process air is required for cooling (the desiccant is not impacted by heat generated by the vacuum pump,) providing significant energy savings without a negative impact on the outlet air quality (dewpoint).
An optimal solution
A successful example of vacuum regeneration technology is the WVM Series Generation 5 Vacuum Regeneration Dryers. The WVM Generation 5 is a low energy consumption adsorption dryer that does not require any process air for either the regeneration of the desiccant material or for cool down purpose after regeneration.
WVM Generation 5 dryers deliver outlet dewpoints in accordance with ISO 8573-1 Classes 1, 2 or 3 (-70, -40 or -20 respectively). They are equipped with a dew-point controlled energy management system, which ensures energy consumption is matched to the incoming water vapor loading — helping to prevent negative impact on the outlet dew-point.
Each model has a 7 inch, IP65 touchscreen HMI linked to an advanced PLC control system. IIOT (MQTT or OPC UA) connectivity, Modbus RTU via 2 wire RS485 & Modbus TCP/IP via Ethernet RJ45 are standard features, with Profinet/Profibus protocols and cloud connectivity available as options.
Additional energy savings can also be realized by replacing the electric heater, fitted as standard to WVM Generation 5 dryers, with an alternative heat source. If the manufacturing facility has steam on-site, the electric heater can be replaced with a steam heat exchanger, or a dual steam and electric configuration, which offers optimum conservation of energy and the peace of mind offered by a redundant system.
This article was contributed by Mark White, compressed air treatment applications manager, Parker Gas Separation and Filtration Division EMEA
18 Feb 2020