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.
Metal seal types and sizes
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.
Materials and coatings
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.
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
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.
This blog post was contributed by Erika Dudek, FIP dispensing co-op, Chomerics Division.
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.Causes of electrical interference
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.Recovering lost properties
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.Applied performance enhancement
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
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.7 reasons why form-in-place EMI gaskets can be an ideal choice
This blog post was contributed by Ben Nudelman, market development engineer, Chomerics Division.
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
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
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
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.
This blog post was contributed by Paige Ludl, marketing co-op, Chomerics Division.
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.Aluminum foil with pressure sensitive adhesive (PSA)
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.
Polyethylenenapthalate (PEN) film
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.Thermally enhanced polyimide
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.No carrier
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.
Blue poly diamond carrier
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.
We've all done it at least once: looked at a report, read the numbers on it, and come up with exactly the wrong conclusion. Pass/fail limits and results are printed right there, but for some reason, our brain just misinterprets the two. It's a passing value, but for some reason, we think it shows a failure instead. Imagine a police officer writing a speeding ticket for driving 53 MPH on a road with a 55 MPH speed limit.
It's not a problem with the test itself, it's a problem of interpretation. That means the old carpenter's adage, "measure once, cut twice; measure twice, cut once" doesn't address the issue. The same issue of misunderstanding the values on a test report occurs in the rubber seal industry about once a month. Passing results are misinterpreted to be failing results, and good values are thought to be bad ones. Here are four of the most common test report misunderstandings I've run into.
Most low-temperature testing involves negative numbers and that creates some confusion when coupled with “greater than / less than” test limits. For example, it is common to see pass / fail limits for TR-10, the glass transition (Tg), and sometimes impact brittleness expressed in the form of “-30°C max.” I’ve talked to people who claim that a result of -32°C failed against a limit of “-30°C max” because everyone knows that 32 is a bigger number than 30. Just to be clear, -32°C passes, -28°C fails. This is a 2nd-grade math problem, but sometimes we adults forget how to do the simple things if we don’t do them often enough. If this gets confusing, the easy way to interpret temperature limits is to mentally replace “max” with “no warmer than” and “min” with “no colder than.”
Compression set is always expressed with a maximum limit, for example, 20% max. Therefore, all values up to and including 20% are passing values. I’ve heard people claim that a result of 20% fails against a limit of 20% maximum because it’s not below the maximum. I won’t disagree that “barely passes” isn’t a good situation to be in, but “barely passes” is still a passing value. The compression set is a measure of what percent of the original squeeze has been permanently lost. A value of 100% means the material has gone completely flat. A value of 0% means the material returned all the way to its original dimension. With the compression set, small numbers are good, big numbers are bad.
Compressive Stress Relaxation
Commonly used in the passenger car and commercial truck industries, Compressive Stress Relaxation (CSR) is a measure of how much spring force the rubber has left after aging or being exposed to a fluid. The limits are always expressed as “10% min retained load force”, as one example of a common limit. CSR moves in the opposite direction as a compression set, and perhaps this is why a result of 15% is frequently and incorrectly thought of as failing a “10% min” limit. For CSR, the more retained seal force, the better.
Most limits for tensile strength and elongation change after heat aging and fluid immersion are one-sided limits, meaning they only have one limit, not two. For example, a heat aging requirement may have limits of “-30%” or “-30% max” for the tensile strength change. What happens if the result is +2%? In other words, what if the result has the opposite sign from the limit? This is a passing result. There is no implied “to 0” limit attached to these one-sided limits. There is also no implied “mirror image” limit with the opposite sign. By this, I mean that a “-30% max” limit does not automatically include a matching “+30% max” limit. A result of +100% is still a passing value compared to a one-sided limit of -30% max. If a specification does not explicitly call out a two-sided requirement with both a high limit and a low limit, then it only has one limit.
This is something that happens frequently, but it doesn't make it any less embarrassing. In an ideal world, someone is there to patiently explain the data and the limits and show how the report actually shows passing data, not failing data, and does so in a way that doesn't make you feel worse about it. If I have been that person for you in the past, a thank you cake would be appreciated. You and I know who you are, but we can keep that to ourselves. Cookies are good too.
For more information on the proper way to read a test report, watch our video below. For further questions, please contact Applications Engineering Team at firstname.lastname@example.org or visit us at the Parker O-Ring & Engineered Seals Division.
This article contributed by Dan Ewing, senior chemical engineer, Parker Hannifin O-Ring & Engineered Seals Division.
I have had many discussions with customers as to the value of using an ASTM elastomer compound description on their prints to define a specific application or elastomer requirement versus listing an approved Parker compound number.
Specifying a compound using the ASTM callout is a good start - it clearly defines what you want, it sets a minimum bench mark and it is easy for competitive vendors to understand what you are asking for. The ASTM standards also set specific test parameters which make it easier to do an "apples to apples" comparison between two compounds. However, over time here is what my customers have learned:
Know your operating requirements
1) The ASTM standards are very general; so when my customer defined a specific FKM they needed using an ASTM callout, they received a compliant material that just barely met the ASTM specifications but did not meet their actual operating requirements. The supplier provided my customer with their lowest cost material. The quality of the material was poor and inconsistent, but it met the ASTM criteria they requested. This customer saw a 15% increase in assemblies requiring rework plus the number of warranty claims rose due to seal failures. The twenty cents per seal my customer saved for their $48.00 application was offset by the cost of increased product failures which also resulted in unhappy customers.
Know the fluids your seals will be exposed to
2) The ASTM standard does not specifically list what actual chemicals the seal has to be compatible with as well as the operating conditions. ASTM tests compatibility based on Standardized Testing Fluids which are Oils, Fuels and Service Liquids. ASTM uses standard oils which are defined by IRM 901 and 903. Again, the ASTM standards are excellent for comparing compounds, but most people do not have their seals operating in the ASTM reference oils and many sealing applications are exposed to multiple fluids.
Know what your ASTM is calling out
3) Most of the engineers or purchasing people who reviewed or utilized an older drawing had no idea why the original engineer chose the compound or why they used the ASTM callout specified. I typically find that most companies do not know exactly what the ASTM standard is calling out.
So what is the best way to define and specify an elastomer? Most companies go through a technical process to specify, test and confirm that an elastomer is the correct choice for their application. All of the elastomers that were tested and approved for the application should be clearly listed on the drawing. In addition, the drawing should clearly state that the approved materials listed were tested to confirm their suitability for the application. All substitutes or new elastomers must be tested and approved by engineering prior to use.
If you have questions regarding the suitability of an elastomer for your application,consult and work with your Parker Applications Engineer. We offer a plethora of compounds to suit your application needs. Ask our applications engineers and chemists for guidance; their vast seal design experience spans multiple industries and applications to solve your sealing challenges.
Fred Fisher, technical sales engineer, Parker Hannifin Engineered Materials Group
Seals made of the fluoropolymer PTFE are used where many other sealing materials (such as rubber elastomers, polyurethanes, fabric-reinforced elastomer seals, etc.) reach their limits in terms of requirements such as temperature range, chemical, friction and wear resistance. That is why PTFE is the most frequently used fluoropolymer in challenging sealing applications. Parker Prädifa produces seals made from pure PTFE and numerous modified compounds with diameters of up to 4.5 meters using economical machining techniques.
Polymer materials like PTFE, PEEK, TPU and selected elastomers are suitable for machining such as turning or milling. This makes it possible to economically manufacture both larger and smaller volumes because no additional tooling costs for molds are incurred.
Parker Prädifa has been producing complex machined polymer seals with diameters of up to 3 meters for decades. In the light of a growing demand for increasingly large seals Parker Prädifa has continually developed the manufacturing technology of machining further and is now able to offer diameters of up to 4.5 meters at the highest level of quality. The production of even larger diameters is currently in the pipeline.
The production of large seals for challenging applications is not simply a matter of scaling up know-how of traditional seal design and machining. The reason is that XXL sizes not only pose particular handling challenges in the manufacturing process, but do so even earlier, in the design and testing stages.
The evaluation of the performance of large-scale seals under various load and temperature conditions requires sophisticated simulation models. Particularly critical factors to be considered in the design of large seals include thermal shrinkage and expansion. In addition, even relatively low pressures may result in extreme forces acting on the seals, leading to considerable deformations or even seal failure.
As damage caused by seal failure and leakage may be particularly severe in the case of large seals, reliable sealing functionality must be comprehensively validated prior to their utilization in the respective application. Parker Prädifa uses virtual prototyping for validation. Due to the advanced method of virtualization utilizing sophisticated FEA models costly tests with real-world parts can be avoided and development cycles significantly reduced.
Parker Prädifa ensures top quality of XXL sealing solutions using quality assurance technologies developed in-house. Picture: X-ray inpection of large-diameter seals.
Article contributed by
Karel Kenis, business development manager PTFE
Engineered Materials Group Europe, Prädifa Technology Division
Combination electromagnetic interference (EMI) shielding and weather gaskets, more commonly known as EMI shielded combo strip gaskets, are an excellent choice for a variety of applications that require a resilient, highly conductive sealing solution of knitted wire mesh with the integration of an elastomer for weather sealing. Typical applications include electronics cabinet doors, telecommunication trailers, wing panel gaskets for the protection against lightning strikes, and EMP specified requirements and sealing of shipboard and EMI.
There are five major features to consider for EMI shielded combo strip gaskets: the elastomers available, the metals available, the various mesh knit densities available, the various profile geometries available and the option of an overmolded gasket.1. Variety of elastomers available
Elastomers are available in a silicone sponge or solid, or neoprene in sponge form to meet customer needs such as closure force, fluid resistance and NASA outgassing requirements. Elastomers allows for an increase in gasket life and reduces the overall ownership cost. Three specific design parameters are the most important variables to take into consideration when evaluating elastomer choices. These criteria are fluid exposure, temperature requirements and necessary compression characteristics of the material. Generally, solid elastomers are used in conjuncture with cast or machined surfaces due to their larger force requirements for deflection. Sponge offerings have less force requirements for deflection and are therefore typically used in conjuncture with sheet metal enclosures.2. Broad range of metal alloys offered
A broad range of metal alloys are offered to meet the requirements of electrical and galvanic corrosion. This also makes it possible for customers to meet budgetary needs by using Monel (Ni/Cu alloy), Ferrex (SnCuFe), aluminum, or stainless steel.3. Various mesh knit layers available
Various mesh knit layers are available to meet with the required electrical performance. Military applications will require multiple layers to ensure maximum protection while in less extreme applications, less layers are needed. These variations reduce gasket replacement schedules and improve their durability, allowing them to be handled during in-field installation. Most critical of these criteria include galvanic compatibility, electrical
performance, overall gasket durability and temperature range requirements.
There are round, square, or rectangle profile geometries available that allow for design leniency for application in specific performances. Which geometry you'd choose depends on the criteria necessary to the application, including, but not limited to, gasket deflection percentage, necessary compression characteristics of the material, application load available for gasket deflection and planned gasket affixation method.5. Bonded vs. overmolded
These combo strip gaskets are available in both bonded or overmolded version for tiered performance options. If needed, overmolded gasket can be used but only for wing panel applications.
This blog post contributed by Paige Ludl, marketing co-op, Chomerics Division.