Sealing and Shielding

When classic sealing materials – for instance in temperature ranges above 300°C and below -50°C – reach their limits alternative materials are required such as metal with appropriate coating/plating.

Parker offers metal seals made of stainless steel or nickel alloys in C, E and other designs characterized by high pre-loading force and significant resilience. Drawing on many years of experience in the gas turbine market, Parker has continually expanded its expertise in large diameters and developed special problem solutions that substantially increase the efficiency of the machines.

The most important manufacturing technologies used to produce metal seals from stainless steel or nickel alloys are rolling, forming, CNC machining, welding, heat treatment and coating/plating. In its more than 60-year history of producing metal seals, Parker has continually tackled the challenge of manufacturing increasingly large metal seals. Currently, spring-energized C-rings with a diameter of up to 7.6 m can be produced for which special forming machines and patented welding techniques were developed. They are supported by optimized special heat treatment and electroplating processes that make it possible to manufacture high-quality products even in such large dimensions. Additionally, Parker offers non-rotationally symmetric metal seals. These E-, O- and C-seals can be produced in lengths of up to 2.3 m on machines specifically developed for this purpose.

• C-seals: ≤ 3,000 mm
• Spring-energized C-seals: ≤ 7,600 mm
• O-rings: ≤ 1,200 mm
• E-seals:
  • Heat-treated ≤ 2,700 mm
  • Segmented ≤ 7,600 mm

The base materials used are special nickel alloys that withstand temperatures of more than 800 °C. These cobalt-nickel-chromium-tungsten alloys or heat-treatable nickel super-alloys make high demands on the welding technology used and are reliably processed at Parker due to optimized manufacturing processes and comprehensive suitability tests.
The choice of plating is primarily focused on wear protection, corrosion resistance and improvement of the sealing properties. For this purpose, the surface properties of the metal seal are modified and a formable external surface layer with adjusted hardness is created. Parker’s application engineering team will advise you in making the appropriate selection from the available plating range of gold, silver, nickel or TriCom® coating. 
 

• Power Generation – Sealing Solutions for Gas Turbines
• Chemical Processing – Sealing Solutions for Heat Exchangers
   

Website: XXL Size Seals and Molded Parts
Download Whitepaper: Large-Diameter Seals and Moldings - Material and Special Manufacturing Aspects
Download Brochure: XXL- Size Seals and Molded Parts - Powerful Solutions for Large-Scale Applications



 

Article contributed by
Thorsten Kleinert, business unit manager composite sealing systems
Engineered Materials Group Europe, Prädifa Technology Division

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Automated form-in-place (FIP) dispensing of EMI shielding gaskets can be ideal for complicated patterns on electronics housings because automation allows for control over the size and shape of the bead. In addition to form-in-place EMI gaskets, thermally conductive gels can also be automatically dispensed, and often span oddly shaped gaps and conform to complex geometries. 

The ability of dispensed thermally conductive gels to conform effectively makes them convenient solutions for reducing temperature and increasing the efficiency of electronics applications. Some automated systems can dispense both form-in-place EMI gaskets and thermally conductive gel on the same machine, allowing them to be dispensed simultaneously in the same program to easily integrate both materials into one housing. 
 

1. Be sure to use the correct tip diameter for the target bead dimensions and the particle size of the form-in-place material being dispensed. As a rule of thumb, the inner diameter of the tip should be six times the largest particle size of the material. A shorter tip with a larger tip diameter maximizes material flow and produces less back pressure.
   
   Tapered tips also produce less back pressure than straight walled stainless-steel tips, however they are more flexible which can cause variations in dispense paths. 
    
2. The height of the form-in-place bead should be 85% of the width, and the desired compression is 20 – 30%. We recommend staying below 40% compression. If there are limits on the width of a bead but a taller bead is necessary, a double bead can be used to increase the ratio of height to width. Allow for higher tolerances in start and stop zones compared to straight runs and minimize the number of starts and stops in a bead profile.
    
3. To maximize thermal gel performance, choose a dispense pattern that will contact the entire target area on both the heat sink and component surfaces without air in between. Thermally conductive gel can be dispensed as a dot, a serpentine, a spiral, an X, or in various other shapes. The more simple the profile, the less likely that air will be introduced into the bead. A shot-size calibration process can help ensure dispense rates are consistent for a repeatable dispense volume.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
    
4. Choose the proper valve type for your material and application. The viscosity of the material, the amount of material to be dispensed, and the abrasive nature of the material are the most important variables to consider when choosing a valve. Pneumatic valves with time-pressure dispensing systems are popular in the industry, where an air pulse pushes a piston that allows material to flow out of a disposable dispensing needle.
   
   Auger valves displace precise amounts of material from cavities in a dispensing chamber with an auger screw, however filled materials are often too abrasive to achieve successful dispensing since the screw grinds down the particles. Positive-displacement valves are a good option for abrasive materials, where a motor-driven piston forces material out of a disposable barrel, because the system is not affected by external factors such as temperature and humidity.
   
   Spool valves have very tight shot size control and a long life span when constructed with tungsten carbide, making them ideal for repeatable, consistent shots.
   
   
5. Keep in mind z-height obstructions with both form-in-place and thermally conductive gel materials. Tall walls next to the dispense path require a longer dispense tip, and the length of the dispense tip has an impact on the dispense speed. The slower the dispense speed, the longer the cycle time.

This blog post was contributed by Erika Dudek, FIP dispensing co-op, Chomerics Division.
 

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Composite materials have been replacing metal structures throughout the aircraft industry primarily to save weight, improve fuel economy and reduce costs.  But the lack of electrical conductivity in these materials is a disadvantage when compared to the conventional metal airframes of the past. The conventional, metal airframe allowed designers to take advantage of the natural Faraday cage it formed to protect equipment against interference. There were many opportunities to ground items of equipment reliably by connecting directly to a convenient surface ground.

Today, a typical airframe consists of around 50% composites. Major structures include the fuselage and wing fairing, as well as large sections of the wings, fin and horizontal stabilizers. 

Inside the aircraft there are numerous electrical systems capable of generating EMI which can potentially disturb the operation of critical systems. These include fluorescent lights, light switches, dimming circuits, AC-powered window heaters, motors and generators, data and power cables, and transmitters such as radio and radar. 

External storms are also a major source of potentially disruptive electrical interference and can cause physical damage to the aircraft through lightning strike impact.  

Replacing metal structures with composites means compromising the EMI shielding and lightning strike protection of the aircraft, as the composites themselves are not electrically conductive. To overcome this issue, woven or non-woven copper-aluminium mesh, or an expanded foil, can be embedded in composite structures to restore lost shielding and grounding properties. The embedded metal provides an optimal combination of electrical conductivity, weight, and corrosion resistance. Solid metal strips can be used in the radome area to handle very high concentrations of lightning energy. 

Embedded conductors, however, do not solve all the technical challenges that come with the increasing use of composites. It is very difficult to ensure reliable electrical continuity between individual composite panels after the airframe is assembled and still promote conduction of lightning energy. 

Electrical components are typically bonded or grounded directly to the airframe. These connections to the mesh can often fail to meet the very low impedance requirements because of environmental stresses such as vibration and temperature variation. The exposed mesh in the locations where grounded or bonded modules are made (fig 1, at left), can be vulnerable to environmental exposure (temperature, humidity, oxidation) that increases electrical impedance.

To overcome this challenge, a lightweight coating such as Parker Chomerics CHO-SHIELD technology can be applied to optimize conductivity in this area. CHO-SHIELD® 4994 is a highly conductive, silver-filled polyurethane coating designed for aerospace applications and has superior EMI shielding properties. The coating provides excellent adhesion and wear resistance and is resilient to most operation and environmental fluids. The coating is compatible with many primers and top coat systems.

In areas where high corrosion protection is needed, a copper-based urethane coasting such as Parker Chomerics CHO-SHIELD® 2002 can be used. When used on a composite, CHO-SHIELD 2002 provides the conductivity necessary to achieve excellent shielding effectiveness while maintaining its electrical and mechanical stability in hostile environments. CHO-SHIELD 2002 is designed to be used with Chomerics CHO-SHIELD® 1091 primer to ensure correct adhesion. 

The aircraft antennas will also need to be shielded and grounded against lightning strike. This can be achieved by using an expanded woven MetalasticTM EXP-URE gasket material. Electrically conductive grease can be applied at ground connections, to support reliable electrical connectivity under temperature and vibration. Attention must be paid to viscosity and surface-wetting properties when formulating greases for aerospace applications. Parker Chomerics CHO-LUBE® 4220 has a resistivity better than 100mΩ-cm and is an example of an aerospace-grade grease. It is formulated to support electrical interconnections, improve metal to metal contact and provide long-term oxidation protection for exposed mesh or electrical terminals.

Conductive sealants such as Parker Chomerics CHO-BOND® 2165 or CHO-BOND® 1019 can be applied at locations requiring electrical continuity and environmental protection. Typical airframe areas treated are screw holes, fasteners, antenna connection points and exposed conductors on external areas. Where conductive gaskets are used to promote electrical continuity between composite components, a conductive sealant can be applied to provide improvement in continuity. These areas are generally around the wheel wells, engine mounts, wings and the tail section, where high vibration occurs (figure 2, above). 

In addition to these methods which will improve EMI performance throughout the airframe, a lightweight conductive heat shrinkable tube such as Parker Chomerics CHO-SHRINK® 1061 can be used to shield the aircraft’s cabling against the effects of EMI and can provide a weight saving of up to 60% compared to traditional methods.

This blog post contributed by Mel French, marketing communications manager, Chomerics Division Europe

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Form-in-place EMI gaskets, also known as FIP EMI gaskets, is a robotically dispensed electromagnetic interference (EMI) shielding solution that is ideal for modern densely populated electronics packaging.

The most important distinction of form-in-place EMI gaskets is that they were developed for applications where inter-compartmental isolation is required to separate signal processing and/or signal generating functions.

Simply put, form-in-place gaskets are meant to reduce “noise” between cavities on a printed circuit board (PCB) or in an electronics enclosure. 

In addition, form-in-place gaskets provide excellent electrical contact to mating conductive surfaces, including printed circuit board traces for cavity-to-cavity isolation. Parker Chomerics form-in-place gasket materials are known as CHOFORM. 

1. Small form factor - form-in-place gaskets can be dispensed in smaller bead sizes than most traditional EMI shielding gasket solutions, 0.018” tall by 0.022” wide. 
    
2. Excellent adhesion - 4-12 N/cm adhesion on prepared surfaces such as machined metals, cast housings, and electrically conductive plastics.
    
3. High shielding effectiveness - Parker Chomerics CHOFORM materials can provide more than 100 dB shielding effectiveness in the 200 MHz to 12 GHz frequency range.
    
4. Quick programming - Because form-in-place EMI gaskets are robotically dispensed, a standard CAD file can be used to program the dispensing system and quickly map out the dispensing pattern.
    
5. Complex geometries - The positional tolerance of the gasket can be held to within 0.001” and is able to follow very complex geometries including sharp turns, corners, and serpentine patterns. Other gaskets such as die cut sheets or o-rings manufacture and/or fabricate into such shapes and patterns. 
    
6. “T” joints - Traditional extruded gaskets are difficult to mate at intersections or “T” joints. The robot dispensing systems produce reliable junctions between bead paths to provide continuous EMI/EMC shielding and environmental sealing.
    
7. Integrated solutions - CHOFORM technology combined with a Parker Chomerics supplied metal or conductive plastic housing provides an integrated solution ready for the customers’ highest level of assembly. This approach requires no additional assembly or process steps for the installation of gaskets and/or board-level auxiliary components. 

1. Large form factor enclosure sealing that can accommodate a groove. For larger areas such as machined covers that can accommodate a gasket groove, other EMI shielding solutions are better suited. In most applications, conductive elastomers such as the CHO-SEAL product line by Parker Chomerics will provide better shielding and sealing. Form in place gaskets can be dispensed in bead sizes only as large as about 0.062” tall x 0.075” wide.
    
2. Enclosures requiring submersion or durable weather sealing. Because of the small form factor, FIP gaskets will not meet stringent environmental sealing requirements such as IP 67 or higher. While silicone-based, the material is better at preventing dust and environmental moisture from entering an enclosure. FIP gaskets can be paired with additional sealing gaskets for enhanced weatherproofing. 
    

This blog post was contributed by Ben Nudelman, market development engineer, Chomerics Division.

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Material selection for military applications requires careful consideration, as there are strict requirements to ensure maximum durability, security and of course performance. In munitions, or missiles and missile launch systems, materials that provide electromagnetic interference (EMI) shielding and environmental sealing are critical for the functionality and field life of the application.

Let's look at three areas of a munitions application -- specifically nose cones, cable shielding, and connectors, as each of these areas exemplify why EMI and environmental shielding are a necessity.

Nose cones are what goes over the top of missiles, planes and other airborne technologies to assist with aerodynamics and to protect the electronic components inside. In missiles, all the electronics are stored within the nose cone and the fuel is held inside the canister. If these two parts are not properly shielded from each other, contamination can become a catastrophic event.

Therefore, shielding the nose cone from EMI and other outside environmental dangers and shielding the components of the missile from each other is of utmost importance.

Another threat to missile electronic malfunction is external tampering from malicious forces. Unintended or intentional EMI can result in misfires, false trajectory, and other problems. Often, anti-jammers are installed to help prevent this problem in combination with EMI shielding materials.

Cable shielding is a woven fabric that goes over cables to prevent electromagnetic cross-talk between the cables and the components. Typically, a metal mesh is wrapped around the cables that will prevent any EMI from interacting with the cables or emitting from the cables.

Different amounts of layers can be added to increase EMI shielding effectiveness, however adding more layers will also add more weight. Cable shielding that is lighter, typically non-metal based, is ideal for applications where weight is of concern like in munitions.

Connectors are where wires are plugged into to keep electric circuits intact. In munitions, connectors can be a failure point because environmental agents can more easily enter which is why they require more attention to be shielded properly.

The complexity of military electronics has increased significantly on air, sea and land-based applications. The environments in which systems are required to operate are often extreme. Design engineers need to consider wide variations in ambient temperature, shock and vibration, and electromagnetic interference (EMI).

With a wide choice of shielding materials and a range of advanced shielded optical windows, Parker Chomerics helps ensure the protection of complex electronics from damage and compromised reliability caused by EMI.

Sensitive electronic components can be kept within their operating temperature range limits by using heat management materials that include highly conformable, thermally efficient gap fillers and gels.

Parker Chomerics offers the products, technical know-how, close customer support and supply chain capabilities to meet these challenges and deliver superior, reliable and cost-effective solutions.

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Most thermal pads, also known as thermally conductive gap filler pads, thermal gap pads, or thermal gap filler pads, have many different layer materials or carrier substrate options to choose from. It can be confusing which layer is supposed to stay on the product and which layer gets peeled off and removed before application. In fact, it’s one of our customer’s most asked about questions and can cause a lot of confusion on the manufacturing floor.

So, which layer should you peel off and which should stay on the thermal gap pad? Read on to find out.

Parker Chomerics, like many thermal gap pad vendors, offers several different gap pad layer options that must be peeled away before the gap pad is installed into the application. 

Think of a thermal gap pad as a sandwich of layers -- there is always a blue poly backing that keeps the gap pad together, but there are five additional carrier substrate options which provide the following benefits:

The woven fiberglass carrier option provides reinforcement and a clean break / low tack interface surface, allowing for re-use of the thermal pad if necessary or for prototyping.

As you can see from the diagram, you peel off the liner to expose the woven glass carrier which does not get removed from the thermal gap pad.

Example: THERM-A-GAP HCS10G.

The aluminum foil with PSA carrier’s primary function is to allow a pressure sensitive adhesive on the thermal gap pad to affix the thermal pad in place.

As you can see from the diagram, you peel off the liner to expose the aluminum foil carrier which does not get removed from the thermal gap pad.

Example: THERM-A-GAP A579.

The polyethylenenapthalate (PEN) film carrier permits the thermal gap pad to see a shearing motion and offers a clear, cost-effective dielectric film with fair thermal performance.

As you can see from the image at right, there is no clear film to peel off that exposes the PEN film carrier, which does not get removed from the gap pad.

Example: THERM-A-GAP 579PN.

The thermally enhanced polyimide carrier permits the thermal gap pad to see a shearing motion and offers an excellent dielectric film with enhanced thermal performance. 

As you can see from the image at right, there is no clear film to peel off, the polyimide carrier does not get removed from the gap pad.

Example: THERM-A-GAP 579KT.

The no carrier or “un-reinforced” option allows the thermal gap pad to have high tack surfaces on both sides, allowing for the pad to be highly conformable, but it does make cutting and handling of the product more difficult.

Once the liner is peeled back, there is no additional carrier on the thermal gap pad, the pad is now exposed.

Example: THERM-A-GAP 579.

Lastly, the base carrier liner, shown in blue, is persistent on the bottom of all thermal gap pad options, and must be peeled and removed prior to installation of the thermal gap pad.

This blue carrier is necessary, as it keeps the gap pad intact and more easily to handle prior to installation. We recommend keeping this blue poly carrier layer on just until the gap pad is placed for the final time.

This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics Division.

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