Sealing and Shielding

For some applications, a critical component of selecting a seal material is a phenomenon known as “outgassing”. However, even within the elastomer community, outgassing is not something that is commonly considered. Which begs the questions: what is outgassing and why is it important? Outgassing is usually most relevant in vacuum applications, where the vacuum causes the elastomer to release constituent material. The constituent material could include water vapor, plasticizers, oils, byproducts of the cure reaction, or other additives used in the seal material. Outgassing becomes a problem if a thin film of those chemicals condenses and is deposited on nearby surfaces. Such a film poses major challenges in highly sensitive applications, such as optics or electronics, where cleanliness is of utmost importance. A seal material with low outgassing  is essential because it shows the seal material does not emit volatile constituents under vacuum conditions.

Weight loss of compounds in vacuum

Outgassing is most often characterized by weight loss of the seal material. The ASTM test method E595 is one way to quantify outgassing by measuring Total Mass Loss (TML %), Collected Volatile Condensable Materials (CVCM %) and a reported value for Water Vapor Regain (WVR %).  Measurements are taken following a 24 hour exposure to vacuum of 5x10-5 torr at a temperature of 257°F.

Taken together, these three parameters tell a complete story. The TML is reported as the percent of the specimen’s initial weight that is lost during the test; under standard criteria, the result must be less than 1.00% mass loss. Obviously, minimizing TML is a good thing, but it is not the only important factor. Collected volatile condensable material (CVCM) is the amount of outgassed matter from a specimen that condenses onto a collector during the maintained time and temperature. CVCM is of particular concern because any material that readily condenses in the test is likely to condense on and contaminate nearby surfaces during use. To pass the standard CVCM requirement, the amount collected relative to the initial mass of the specimen must be less than 0.10%. The final measurement, WVR, is the mass of the water vapor absorbed by the specimen after a 24-hour stabilization at 23°C in a 50% relative humidity atmosphere. There is seldom a pass/fail limit for WVR; instead this result is merely reported. In many applications, the small amount of water vapor lost by a seal may not be of concern, particularly if the application already includes a means of controlling moisture. Further, any WVR is presumed to be equal to the portion of original TML that was water vapor. The difference between TML and WVR is therefore presumed to be volatile organic material that has evaporated out of the material (only some of which condenses in the CVCM test), so minimizing the difference between TML and WVR is also of considerable importance.

To illustrate, we can look at the most recent outgassing data completed on a few popular low temperature fluorocarbon materials. Table 1 contains the results from a 3rd party laboratory to measure the outgassing properties of VM125-75 and VX065-75. Both had undetectable amounts of CVCM and very small differences between TML and WVR.  VX065-75 in particular displayed remarkably little outgassing as well as a low WVR.

table { font-family: arial, sans-serif; border-collapse: collapse; width: 100%; } td, th { border: 1px solid #dddddd; text-align: center; padding: 8px; } tr:nth-child(even) { background-color: #ffb91d; }   Limit VM125 VX065 Total Mass Loss (TML, %) 1.00 % max 0.48 0.15 Collected Volatile Condensable Material (CVCM, %) 0.10% max <0.01 <0.01 Water Vapor Regain (WVR, %) Report 0.39 0.17

There are a few additional resources detailing seal materials that are known for having low weight loss. The O-Ring Handbook ORD 5700, Table 3-19 (page 65 of the pdf), has a few legacy materials with weight loss percent after a two-week exposure to 1 x 10-6 torr vacuum level, at room temperature. Additionally, non-Parker resources such as the NASA website contain an interesting summary of a much broader range of materials.  

For more information on low outgassing seal materials, please contact a Parker Application Engineer at OESmailbox@Parker.com or 859-335-5101.

 

This article was contributed by Dorothy Kern, applications engineering manager, Parker O-Ring & Engineered Seals Division.

 

 

 

 

 

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When it comes to semiconductor fabrication processes, reducing the cost of ownership is a multi-faceted goal approached from a variety of angles. Tool engineers and equipment technicians take pride in their ability to identify factors that limit tool uptime. One constant headache they face is the mechanical failure of seals in dynamic environments. This can lead to premature downtime or reduced preventative maintenance (PM) intervals, both of which lead to higher cost of ownership. Fortunately, tool owners have begun to implement seal designs better suited for these dynamic environments: Parker EZ-Lok is a proven solution.

 

Spiral failure

 One of the more extreme forms of mechanical failure to be prevented is twisting and spiraling of an O-ring during operation. This occurs with O-rings in dovetail glands where one of the sealing surfaces is a door that opens and closes against the seal. The combination of stiction to the door and stretch in the gland causes the O-ring to roll and twist repeatedly with each cycle, resulting in permanent cyclic deformation. This means that a seal profile with a flat contact surface is vital for this type of dynamic function.

  Other designs

The basic D-profile is the fundamental simple shape that serves as the basis of the EZ-Lok solution. The flat portion of the “D” holds the seal in place and prevents rolling, while the opposite, round contact surface focuses the sealing force and helps keep volume requirements at a minimum. These geometric features make for sound sealing function while preventing the drastic spiral damage seen so often in the industry.

 

 

 

 

 

 

 

A standard D-ring is still more limited by volume requirements than traditional seals like O-rings. In addition, a D-ring’s sharp corners can become difficult to install past the top groove radii if the seal is made much wider than the groove opening. On the other hand, a seal made any narrower would be easily removed without intention, such as that induced by stiction to the door. These reasons are why the basic D-profile alone is not the answer to these failure modes.

 

The Solution

The solution to these dilemmas is a unique D-shaped profile with a geometry that lends itself to the spacial constrictions of dovetail glands, prevents rolling, and locks into place: the Parker EZ-Lok seal. These seals are designed with special retention ribs placed with precise frequency around the seal circumference that allows for smooth installation and keeps the seal retained in the gland. This design also removes any tendency to stretch the seal during installation, which is often seen with more conventional seals.

A common question often asked by our customers is the reason why flow rate is reported on datasheets of liquid-dispensed thermal interface materials instead of viscosity. And it’s a fair question; viscosity is a fundamental property of fluids such as thermally conductive pastes. But measuring viscosity, however, is more complicated than meets the eye.

Parker Chomerics THERM-A-GAP Thermally Conductive GELs belong to a class of fluids referred to as “thixotropic.” In case you’re not familiar, thixotropy is a time-dependent decrease in viscosity as shear stress is applied.

This shear stress may be introduced during mixing, pumping, or dispensing of the product. The extent of the viscosity decrease depends of the duration and magnitude of the agitation, and viscosity recovers gradually over time after the stress is removed. The act of measuring viscosity introduces shear stress, so gathering repeatable data requires carefully controlling the duration of the test and the relaxation time between trials.

 

 

 

 

 

 

 

 

 

 

 

 

To complicate the measurement further, viscosity is strongly influenced by sample temperature. A warmer dispensable thermal paste flows more quickly than one at room temperature, a characteristic that is particularly relevant in thermal interface materials.

Therefore, a viscosity measurement is only accurate for a given shear stress, duration, and temperature. The resulting value of viscosity is difficult to generalize, so it is more convenient to use flow rate, as it is a measurement that is more representative of actual end-use conditions.

Automated dispensing is one of the primary advantages of dispensable thermal pastes, such as Parker Chomerics THERM-A-GAP GELs. Publishing flow rate data provides a framework with which to compare different gels based on their dispensability.

Additionally, measuring flow rate instead of viscosity controls the critical parameters described above, such as:

• Shear stress, which is controlled by dispensing from a specified container at a constant pressure
• Test duration
• Ambient temperature

Measuring flow rate is repeatable and more representative of actual dispensing situations than a viscosity value.

So, the next time you’re reading a datasheet, you’ll be armed with the knowledge that flow rate is a more accurate representation of real-world conditions.

 

 

 

 

 

 

 

This blog post was contributed by Jon Appert, R&D engineer, Chomerics Division.

 

 

 

 

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Whether it be a classic automotive transmission design or the latest in electric vehicle technology, there is always a need to move high-pressure fluid through different operational systems.

Cooling systems are required for the battery storage compartment in both hybrid and fully electric vehicles. Whether the system is water or oil cooled, these fluids need to be pushed around and through various components to dissipate the unwanted heat.

 

Space limitations allow no room for leak paths

Automatic transmissions have an elaborate series of fluid circuits, or passages, required to feed the oil necessary to engage the hydraulic clutches. This is especially true with the newer eight, nine, and ten-speed transmissions. This increase in the components within the transmission also reduces the amount of available space for each clutch requiring that all space within the transmission case be used with the utmost efficiency.

Movement of fluid from the pump to the main control, to the appropriate clutch, sometimes requires the most direct route. This can require cutting through and/or across different components opening up potential leak paths in the circuit. In other applications, the circuit may need to be manipulated around components or systems that cannot be moved. A large leak can cause only partial engagement of the clutch piston resulting in a burnt clutch and very costly repair or even rebuild of the transmission. Even a small fluid leak results in a loss of system overall efficiency.

In the past, many of these joints were sealed utilizing an O-ring placed in a shallow counterbore and compressed axially against the mating component. These seals were prone to becoming dislodged before the mating component could be assembled resulting in cut seals or even the seals missing altogether. In addition, having different sized ports in close proximity to each other often resulted in the O-rings being mixed up into the wrong locations.

 

Customizable fluid transfer sealing reduces warranty costs

Parker engineers have developed multiple fluid transfer sealing technologies that can be customized for different applications. Designed with a metal insert to provide resistance to seal extrusion into the gap between components under fluid pressure, the boot type sealing lip configuration can accommodate wider axial tolerance stack conditions without losing sealing performance. In addition, the ribbed outer diameter provides a low assembly force interference fit into the bore. Secure positioning of the seal in the bore is ensured until the mating component is secured into place. Mis-builds are eliminated, thus improving first time through capability and reducing warranty costs.

Custom multi-port configurations can be designed to meet specific application needs. The positioning of the different seals in the carrier reduces complexity by providing a single component solution. Mixed seal locations are also eliminated.

Many different elastomers are also available to meet specific application requirements. Our Parker chemists have compounds available to ensure performance for chemical compatibility to the media being sealed, as well as solutions for very high or even very low-temperature applications. Custom materials can also be developed to satisfy unique requirements.

Please contact one of Parker O-Ring & Engineered Seals Division applications engineers who can assist you in solving your fluid transfer sealing system needs.

 

Article contributed by Scott A. Van Luvender, automotive applications engineering manager, Engineered Materials Group.

 

 

 

 

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The emergence of degradable and dissolvable materials is providing oilfield service companies an opportunity to increase efficiencies and cut costs in the oilfield by simplifying well completions. These materials replace their conventional metallic and polymeric counterparts in completion tools, but eventually break down and disperse when exposed to common completion fluids. This eliminates the need for well interventions to mill out or retrieve used tools. This can result in a reduction of drill time, a safer work environment, and monetary savings for the operator. Parker Hannifin produces dissolvable and degradable metal alloys, thermoplastics, and elastomeric materials that can enhance your well completions.

  Degradable elastomers

Parker O-Ring and Engineered Seals (OES) Division produces degradable elastomer formulations that can be used in frac plugs, liner wipers, and other sealing applications common in the completions segment. These elastomer formulas have tough physical properties and low compression set and are designed to replace materials such as Nitrile or HNBR in conventional tool designs. With proper design, tools using Parker degradable elastomer can withstand the high pressures (>8,000 psi) generated during hydraulic fracturing while still eventually deteriorating away, allowing well production without having to be drilled out. These degradable elastomers can be produced in a variety of desired forms such as O-rings, custom molded shapes, and packing elements. They can also be bonded to dissolvable metal alloys to produce completely degradable solutions. If needed, Parker offers a product engineering team to assist with the design of components and rapid prototyping services to help cut down on development timelines.

 

  Degradable thermoplastics

Parker Engineered Polymer Systems (EPS) Division manufactures engineered degradable Thermoplastic materials which can be used in many types of completion tools that traditionally use non-degradable elastomers. Parker EPS’s high-grade thermoplastic materials have increased physical properties over conventional elastomers making it ideal for both high pressure/high temperature and wear resistant applications. The increased physical properties of EPS thermoplastics provide enhanced resistance to extrusion, temperature and wear over most degradable non-metallics in the market. These unique thermoplastic materials may be manufactured in both homogenous as well as bonded components such as Packers, Parker back-up rings, Frac Plugs and liner wipers and are ideal for hot trouble well applications.

 

 

With a wide range of wellbore temperatures and completion fluids seen across the industry, selecting the right degradable compound can be complicated. Whether full degradation is needed in hours, days or weeks, Parker’s in-house testing capabilities and material development chemists can assist in recommending the proper parameters for use of degradable elastomers in your application. For more information, or to discuss your project needs with a Parker engineer, contact us or visit us at our Oil and Gas webpage.

 

This article was written in collaboration and contributed by:

 

Jacob Ballard, research and development engineer, Parker Hannifin O-Ring & Engineered Seals Division

 

 

 

 

Jason Fairbanks, market manager, Parker Hannifin Engineered Polymer Systems Division

 

 

 

 

Nathaniel Sowder, business development engineer, Parker Hannifin O-Ring & Engineered Seals Division

 

 

 

 

 

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EMI shielding of electronics using thermoplastic housings traditionally has been a complex and costly process. Today, OEMs not only have to meet form, fit and function requirements, but also must reduce the total cost of ownership, reduce weight, simplify the supply chain and reduce time-to-market.

For these reasons, OEMs will benefit from using a full-service, single-source supplier who can simplify these challenging responsibilities by taking on these tasks and more such as:

• Provide technical expertise in the dispensing, curing and spraying of sophisticated materials
• Reduce complex material requirements of tens of parts down to a single stock keeping unit
• Reduce the size of inventory and eliminate a layer of inventory management processes
• Support customers' quality processes such as the automotive industry's PPAP (Production Part Approval Process) scheme and aerospace and defense certifications

Incorporating expert materials

Parker Chomerics offers an integrated assembly service which pre-assembles and dispenses its products into a housing, heat sink assembly or substrate and delivers a custom product or sub-system according to the customer’s design specification. The sub-system incorporates expert materials such as engineered plastics, thermal interface materials, electrically conductive elastomers and coatings, some of which require expert processing to guarantee quality and functionality. 

Making choices

Selecting a suitable plastic injection molding partner is not as straightforward as it sounds when it comes to electronic enclosures. This is where design assistance from a reputable expert in EMI shielding will be invaluable. Because the optimization of part geometry will lead you to the highest performance with the lowest possible processing, material and tooling cost.  

Additionally, upon part design completion, mold flow analysis will help create a 3D representation of flow patterns for the injection molding process. As a result, it is possible to visualize flow rates, pressures and temperature values across the entire part, therefore helping adjust the molding process by locating entry gates and compensating for variable pressures or cooling rates to avoid part warpage or uneven shrink rates. A specialist in this area will also be able to source the tooling, build the optimum mold and provide full PPAP reporting back to the customer.

Material selection

With over 300 different polymer materials available for design engineers to consider, expert advice can prove invaluable.  

A superior choice for plastic housings is Parker Chomerics PREMIER™ PBT -- available in two offerings, one that delivers excellent hydrolysis resistance, the other superior 5VA flame retardant, PREMIER PBT improves long term aging performance when exposed to extreme heat and humidity.  It is a superior choice due to its high shielding effectiveness and enhanced mechanical strength.  Also, being a single pellet composition, it eliminates inconsistent mix ratio problems common with multi pellet blends.

Non-conductive thermoplastics can also be used with secondary EMI coatings.  These are most suitable for parts requiring high temperature resistance, chemical resistance, low water absorption, thin walls or those requiring shielding effectiveness > 85 dB.

Secondary coatings

Parker Chomerics can help with additional processes such as conductive painting, sputtered vacuum metallization, electroless plating and thermal spraying.

The primary design factors to consider when choosing a secondary EMI coating are

• Shielding effectiveness
• Environmental resistance
• Component geometry
• Production volume

For example, sputtered aluminium is a good solution in low-shielding applications where volume supports a higher tooling cost. Alternatively, while Ni/Cu provides excellent shielding, this coating is not generally recommended for use in high-humidity uncontrolled environments, while thermal spraying of tin-zinc provides high shielding with excellent resistance to harsh environments.

Often plastic housing needs assembly of a secondary component.  These elements can be assembled onto the housing using processes such as heat staking, sonic welding, solvent bonding and mechanical assembly. Depending on the part, assembly can often be done at the injection molding press, within the cycle time, consequently saving money for the customer.

Other factors

Often the device will need EMI shielding, thermal management components or an optical display filter, in line with the customer requirements.  Depending on the application, materials may include extruded, molded or form-in-place EMI gaskets, thermally conductive pads or gels, microwave absorbers or optical displays. These materials can be dispensed, over-molded, bonded, mechanically fastened or incorporated into the design to become an integral part of the housing. This simplifies final assembly, allowing OEMs to have only one part to order, inventory and handle.

Another benefit of integrating all these components using a single-source supplier is that testing of the EMI package and board level design can be done at the beginning of the design cycle therefore eliminating the need for rework and changes further down the line. Specialists can offer full service compliance testing to meet emissions, immunity, susceptibility and safety requirements and is able to solve virtually any EMC/EMI problem that testing may reveal.

Ultimately, through the selection of a single-source supplier who can provide integration of all design and production capabilities globally, it is possible to reduce cost, reduce weight (in metal-to-plastic conversions), reduce time to market and produce a fully integrated assembly that best suits the customers global footprint. Chomerics' Integrated service allows customers anywhere in the world to design a sub-assembly including EMI shielding solutions and TIMs, and then partner with Chomerics to assemble it.

 

 

 

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

 

 

 

 

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