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In our July Semiconductor entry, we noted that lowering the cost of ownership is a multi-faceted goal. We discussed how one of the areas for potential improvement is mechanical design and how the Parker EZ-Lok seal is a major solution to mechanical seal failure. In this entry, we’ll investigate a notably different type of cost-reduction opportunity – material selection – and see how Parker’s innovative HiFluor compounds can reduce seal costs to as little as half.
Critical EnvironmentsWhen it comes to the seal industry, the semiconductor market is well known as one where the most premium, chemical-resistant compounds are a necessity. Microelectronic manufacturing processes involve chemistries that push the limits of what elastomeric compounds can withstand in terms of both chemical aggressiveness and variety. The perfluorinated materials (FFKM) capable of withstanding these environments require intricate manufacturing processes regulated by closely-guarded trade secrets and the significant investment of resources.
These factors drive the price of FFKM compounds to the point of being as much as 50 times the cost of any other variety. Cutting just a slice out of this cost can result in significant savings – a chance to take out a quarter or even half the pie would be advantageous indeed. Fabricators should be continually on the lookout for more cost-effective compounds that show equal performance in their pertinent operations.
This is why Parker’s HiFluor compounds offer an opportunity for cost savings that shouldn’t go unnoticed.A unique hybrid of performance between FFKM and the simpler technology of fluorocarbon (FKM) elastomers, HiFluor offers the most superb chemical compatibility in the many semiconductor environments where the high temperature ratings of FFKM aren’t necessary – and at a fraction of the cost.
Not only can HiFluor be used where even FKM is lacking, but its performance in applications with aggressive plasma exposure is spectacular as well. This can be observed by its overall resistance to plasma-induced material degradation. However, Parker has also developed multiple formulations that display extremely low particle generation when most materials would be expected to suffer severe physical and chemical etch.
Solutions and Cost Savings
Need assistance deciphering exactly where this kind of cost-savings can be implemented? Parker O-Ring & Engineering Seals Division has all the resources needed to help their customers identify opportunities to utilize HiFluor seals.
For instance, one major semiconductor fab had several factors (other than their seals) dictating the frequency of their preventative maintenance (PM) intervals. The fab wanted to replace their seals at these intervals as a precautionary measure to limit the chance of them becoming another PM-increasing factor. However, this caused these premium FFKM seals to be a source of inflated cost. Parker engineers assisted with a process evaluation that resulted in over half the seals being replaced with cost-effective HiFluor O-rings, while the tool regions with more intense plasma exposure were reserved for the elite performance of Parker’s FF302.
Another major fab in the microelectronics industry switched from FKM to FFKM seals in their oxide etch process. The tool owner achieved the desired performance improvement, but soon began searching for less expensive options. Based on guidance from Parker engineers, he recognized the plasma resistance and low particulate generation of Parker’s HiFluor compound, HF355. After implementing this change, he retained the performance improvement, but at a fraction of the cost.
Semiconductor tool owners understand that their aggressive processes require the most robust, expensive FFKM seal materials. The price tag on these seals is greater than those from any other compound family. Fortunately, HiFluor is a proven sealing solution that can bridge the gap and provide the same kind of high performance at a much lower cost. To find out if HiFluor is right for your application, visit us at Parker.com/oes and chat with and engineer.
This article was contributed by Nathaniel Reis, applications engineer, Parker O-Ring & Engineered Seals Division.
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It's no surprise that electronic enclosures and housings in aerospace and defense applications are built to meet the most stringent of military standards. These include but are not limited to environmental stresses, EMI shielding, and maintenance requirements. Additionally, the advanced technological requirements of the devices requiring these enclosures mean that these devices must be more rugged and more powerful, as well as smaller, lighter, and easier to replace.
This poses challenges for designers, leading them not only to suppliers who can meet these requirements but partners who can assist in the design and supply chain management of these complex units.
For environmentally-sealed and EMI-shielded electronics devices, there is no better full-system solution than an overmolded or vulcanized cover.
So, what is overmolding/vulcanizing/mold-in-place gasket anyway?
Top 6 benefits of overmolded covers with conductive elastomers
With more than 40 years of experience in overmolding, the Process Engineering team at Parker Chomerics can assist with full system enclosure design that takes into consideration such factors as ideal surface finish and groove dimensions to meet customer-driven requirements. We will work with customers to determine whether overmolding is the best solution and feasible based on all necessary specifications.
Supply chain partnership
As devices become more complex, so do the associated supply chains. An electronic enclosure can quickly pick up more than 5 or 6 individual suppliers, each needing to meet various requirements of military standards. In addition to the difficulties of sourcing the best suppliers, a complicated web of interdependent timelines starts to appear. This is where Chomerics can provide significant support and logistical relief. Parker has an extensive network of first-class suppliers and can also work with customer-approved suppliers to manage a project from start to finish. Services offered can include: overmolding, machining, painting, dip brazing, embedded fasteners, part marking, etching, and custom packaging.
Overmolded covers provide countless benefits for customers looking for the best solution to durable and reliable EMI shielded, environmentally sealed housings while minimizing a complicated system of suppliers.
This blog post was contributed by Ben Nudelman, market development engineer, Chomerics Division.
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Closure force requirements are an important consideration for sealing applications, and the Applications Engineering team is often asked for guidance as to how to minimize or predict the amount of force it will take to close a properly-designed face seal groove.
There are several factors to consider when trying to determine compressive load. The most important of those considerations are:
Hardness of the rubber
It is correct to assume that as the hardness of the rubber increases so too does the compressive load. Parker’s O-Ring and Engineered Seals Division offers materials that cover a range of 40-95 durometers (Shore A scale).
Below is an example of compressive load for a 0.139” CS O-ring made from NBR (Buna-N) materials at different measures of hardness (60, 70, and 90):
Figure 1: Measure of compressive force requirements of a 0.139”CS, NBR material at different hardness levels.
Cross sectional thickness
Another intuitive thought is that as cross-section diameter increases, so does the compressive load requirement.
Below is a plot of compressive load requirements per linear inch for the standard cross sections (0.070”, 0.103”, 0.139”, 0.210”, and 0.275”), and it follows that logic.
Figure 2: Compressive load requirements at different cross-sectional thicknesses on a 70 durometer NBR material.
Groove width
Groove width impacts compressive load because of how it changes the amount of gland-fill in a given application. If a groove is narrow, the O-ring is likely to make sidewall contact once compressed. When sidewall contact occurs, it results in higher compressive load requirements because of how the part is being constricted in the groove. If there is an application that has high gland fill, adding a draft angle can significantly reduce the compressive load requirements, as shown in Figure 3. Figures 4, 5, and 6 show the impact of groove width and draft angle on gland fill.
Figure 3: Compressive force for 0.070" CS 70 Durometer NBR at 99.8% nominal gland fill when fully compressed. The graph shows the impact of draft angle on compressive load for grooves that have very high gland fill.
Figure 4: This image shows an O-Ring being compressed with no sidewall contact.
Figure 5: This image shows an O-Ring being compressed the same amount as in Figure 4, but with a narrower groove. The result is very high gland fill.
Figure 6: This is the same amount of compression as in Figure 5, but with a 3-degree draft angle added. The result is lower gland fill and lower stress on the O-Ring.
Material familyA common myth in the sealing industry is that there is a correlation between material family and compressive load requirements, but as seen in the graphic below, that is not the necessarily the case. The only truly accurate statement is that silicone materials have lower compressive load requirements than that of other materials. Otherwise, many material families have significant overlap in the amount of compressive load they generate for the same amounts of squeeze.
Below is a plot of compressive load requirements per linear inch for various 70 durometer materials.
Figure 7: Compressive load requirements by material family with hardness held at 70 durometer.
In summary, here are some ways to mitigate high compressive loads without sacrificing the amount of squeeze applied to the seal:
• Use a softer (lower durometer) material.
• Use a thinner cross-sectional diameter.
• If gland fill is very high, widen the groove. If that is not possible, consider adding a draft angle.
• If appropriate for the application, switch to a silicone seal material.
• If the application is conducive, consider using a hollow cross section from our extruded product line.
This article was contributed by William Pomeroy, applications engineer, Parker O-Ring & Engineered Seals Division.
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I had a brief career in construction. We used an old hydraulic manlift for elevated projects, and it had a problem – we would start the day eye-level with our work, and after an hour would realize we were balancing on our toes to reach the same level. Cylinder drift was to blame. The lift cylinder was slowly retracting while the machine was off. In a manlift, it’s an annoyance requiring you to raise yourself every half hour, but the drift is dangerous if lifts are used to support heavy loads with the possibility that people or equipment may be under them. This is one reason why when doing automotive repairs and working underneath a car, you should always use solid jack stands or blocks instead of the hydraulic jack.
Hydraulic anatomy
A guy on my crew told me the lift slowly sank because the piston seals needed to be replaced. I wasn’t a seal engineer at the time, so it sounded reasonable. Now I know drift is more complicated, and it’s critical to understand if you’re responsible for cylinder design. Hydraulic cylinders have two main components: the piston, which is acted upon by pressurized fluid to create force and motion, and the rod, which transfers force and motion to the machinery (in my case, the lift platform) (Fig. 1). Located elsewhere are valves that open and close, controlling fluid flow into the cylinder.
Figure 1. Typical hydraulic cylinder
How drift worksLet’s remove the piston completely. We now have just a rod in a bore, which is known as a ram-style cylinder (Fig. 2). Assume we have perfect, leak-free valves and rod seals. If we shut both valves, zero oil can enter or leave the cylinder.
Figure 2. Piston removed -- ram style cylinder
Since moving the rod changes the fluid volume inside the cylinder (the rod takes up space), fluid MUST flow into or out of the cylinder for it to move.
Since this can’t happen while our perfect valves are closed, the rod can’t move. This is called hydraulic lock.
As you can see with hydraulic lock, bad piston seals wouldn’t cause drift in our manlift. Volume loss or escape from the cylinder is what caused us to slowly droop back to the floor. In my situation, either the valves were leaking, slowly reducing the volume of oil in the cylinder, or leaky rod seals (easier to spot) were allowing the fluid to escape the system.
There are a few caveats to this scenario. We assume oil is incompressible, which is not entirely true. Because the oil does squish and stretch a little, the rod will move a small amount with large load changes (read up on ‘bulk modulus of hydraulic oil’). This is not drift, since the oil quickly reaches equilibrium and the rod will not continue to move.
Single-acting cylinders (Fig. 3) are an exception, because oil leaking across the piston is leaving the system. This is similar to when the rod seals leak in double-acting cylinders – drift occurs. Double-ended cylinders (Fig. 4) are also an exception because the fluid volume in the cylinder does not change as the rods move. Both of these systems require low leak piston seals to prevent drift.
Figure 3. Single-acting piston
Figure 4. Double-ended cylinder
Why leaky piston seals are a problem
Leakage across the piston doesn’t cause drift but can cause a number of other complications. Rod retraction relies entirely on the piston seal blocking pressure from crossing the piston; I’ve already described how simply pumping fluid into one side of a cylinder without a piston seal will only cause the rod to extend. Using fluid pressure to retract the rod is not possible without a piston seal.
When extending the rod or holding a load (valves open, no hydraulic lock applied), leakage across the piston seal slowly allows pressure to equalize on both sides of the cylinder. Once this happens, effective piston diameter drops to only the diameter of the rod (Fig. 5). Pushing or supporting the same load now requires higher fluid pressure. This can raise pressures higher than the system was designed to see, cracking pressure relief valves.
Figure 5. Reduction in effective piston diameter
In summary, a leaky piston seal won’t cause drift, but it’s bad for efficiency and could damage the system.
Picking the right piston seal
In systems that are quickly cycling, a slow piston leak may go unnoticed as a tiny efficiency loss – the pressure reverses before a significant amount of fluid can leak past the seal to cause problems. On the other hand, cylinders that move slowly or must hold a position for extended periods benefit from no-leak piston seals.
At Parker, we see a wide variety of applications, and we manufacturer piston seals in many styles and materials to cover all of them. Softer durometer materials like those used for our PSP and T-seals are better for tight sealing. Harder durometer materials like our BP and PTFE cap seals are more extrusion resistant and wear longer in fast-stroking applications.
We also offer hybrid designs like our CQ profile. The CQ design utilizes glass-filled PTFE for low friction and long-wearing but also features a rubber insert to reduce leakage.
Conclusion
Cylinder drift is a concern in many hydraulic applications. It’s commonly mistaken as piston seal failure but is usually a combination of factors involving the valves. Understanding cylinder mechanics is vital to identifying the root causes of failure and for designing systems that are resistant to drifting.
Recommendations on application design and material selection are based on available technical data. They are offered as suggestions only. Each user should make his own tests to determine the suitability for his own particular use. Parker offers no express or implied warranties concerning the form, fit, or function of a product in any application.
This article was contributed by Nathan Wells, application engineer, Engineered Polymer Systems Division.
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You just spent 6 months testing, stretching, aging and exposing your new seal design to 12 different chemicals. Finally, you are done, so what does a good technical drawing for a seal include? For most companies, the drawing is simple. For an O-ring, we draw a generic circle and show an ID and width with some sort of material call out. But now fast forward 20 years, someone consults the drawing, how do they know the criteria you used to select the seal specified?
Just last week I asked my customer who was having seal failure issues on their engine sensor, “Was the original seal specified to be compatible with biodiesel?” The engineer consulted their drawing, but besides the generic circle it lacked any background on what material compatibility was considered when the seal material was selected. The ASTM description on the drawing did not include a reference to or indicate compatibility with biodiesel.
Be specific with materialsOver time, the operating parameters of a system or product can change so it is important to know what parameters were used for the original seal selection. The goal of the drawing is to assure that the engineers and procurement team understand what performance is required from the seal and why the specific elastomer was chosen.
So how do you make your drawing more valuable to your company?
Define and list on your drawing all the operating conditions you anticipate the seal will see such as temperature, pressure and any other application specific operating conditions.
Prepare a list of fluids as well as the concentrations of each fluid that your seal will be exposed to and again add these on your drawing. In addition, make sure you consider fluids that could come into contact with the seal indirectly, through failure of other systems that are part of the product or even by cleaning the product.
List on the drawing the selected compound and manufacturer. Define clearly what testing the compound was put through or what testing is required for approval.
If you select a compound that was resistant to compression set, high temperatures or low temperatures as well as explosive decompression, this should be clearly stated on the drawing.
List clearly the industry standards the seal is required to meet, such as UL, FDA or NSF.
List fluid compatibility requirements
Time and time again, I see seal quality and performance failures when a new supplier is selected and the real requirements for the seal were either forgotten or not clearly defined. Clearly defining these parameters and making them transparent will allow your purchasing and technical team to understand, select and evaluate the correct compound that meets your products sealing requirements.
Once you select a compound for your specific application, it is important to test and validate that the compound chosen is compatible with the fluids you are using. Parker can typically supply small compound samples for soak testing in the fluids your seal is exposed to. If you choose to list an alternate compound on your drawing, that compound must also be tested and validated for compatibility.
Parker offers design assistance for all of our sealing products so before you even design the seal, define the space or groove the seal fits into. Call us, the earlier in the design process the better. Parker will assist you with selecting the proper seal, defining the elastomer requirements, and designing the mating groove; we can provide a cost-effective solution whether it is off the shelf or a custom manufactured solution
Remember when developing drawings standards, assure yourself that if someone consults a drawing that is 2 years old, 5 years old or even 20 years old, they will know what the original seal design intent was.
Fred Fisher, technical sales engineer, Parker Hannifin Engineered Materials Group
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Another Electric & Hybrid Vehicle Tech Expo North America has concluded and it is evident that this show has grown by leaps and bounds. In just the few years since Parker Hannifin has started exhibiting, the interest and demand in EVs and PHEVs has seemingly exploded, and the 2019 show proved to have the most suppliers and attendees the show has ever seen.
From nearly every continent across the globe, there are innovations fast developing new and exciting technologies that will make the future of driving cleaner, safer, and more reliable. The Electric & Hybrid Vehicle Tech Expo North America is a must-attend event for OEMs, tier suppliers, and designers looking for the latest in the development and application of technology for electric vehicles. With over 8,500 attendees, 650 suppliers, and 150 speakers in 2019, Electric & Hybrid Vehicle Tech Expo North America is fast becoming the largest EV technology show in North America.
This year, Parker Hannifin Engineered Materials Group (EMG) featured many new and innovative products -- from heat dissipating thermal interface materials, to electromagnetic interference (EMI) shielding products such as plastics, gaskets and coatings, sealing for complex groove designs, and closure force reduction, the Engineered Materials Group from Parker Hannifin is your single source provider for sealing, shielding and thermal management components in electric vehicles.
So what was new this year from Parker Hannifin EMG?
Large format battery seals
Parker's sealing solutions for batteries are available in large formats. Our versatile materials address your specific needs such as low compression set, temperature resistance, fire resistance, media resistance, and low closure force. Additionally, our seals can be customized in a wide range of geometries.
Parker has developed a new hollow "keyhole" seal design for easier installation, providing significantly lower compression load forces while maintaining seal reliability. Other key advantages of the keyhole profile design include improved rollover stability performance, larger application gap tolerances and lower reduction which provides lower application costs that would normally result from fasteners and thinner covers.
Our expertise in material science is the critical foundation to offer engineered products made from a wide range of standard and tailor-made compounds which can be specifically adapted to your application requirements.Parker sealing solutions are available in various product designs, from O-Rings, press-in-place seals, extruded and spliced seals to custom designs.
Thermal interface materials for battery heat dissipation
Parker Chomerics provides effective heat dissipation technologies in the form of thermal interface materials that are either robotically liquid dispensed or a die cut thermally conductive gap pad. Liquid dispensed thermally conductive materials such as THERM-A-GAP® GELS offer the reliability of traditional thermal interface materials, but with the ability to be robotically dispensed for fast, effective high volume productions.
And with a wide variety of performance and polymer options available, THERM-A-GAP GELS are ideal for most battery heat dissipation applications.
THERM-A-GAP thermal gap filler pads dissipate heat generated from the battery pack and add additional support, vibration dampening or dialectic strength. They are also available in a variety of performance options from 1 W/m-K up to 6.5 W/m-K thermal conductivity.
EMI shielding technologies for EV electronics
Beyond effective thermal management, another technology challenge Parker Chomerics helps to solve is the need to shield against EMI. The cables that travel between the battery and engine, as well as the battery and charger, see high current produced at low frequency. This produces a large magnetic field that can negatively affect other electronics within the vehicle. High shielding attenuation is also required to protect the battery and its circuits from any incoming EMI. Shielding is also required in the increased technology and communication required to ensure the proper advanced driver-assistance systems (ADAS)
Replacement of metal housings with PREMIER electrically conductive plastic can contribute to reducing vehicle weight and cutting manufacturing costs. Here, an electrically conductive plastic alternative can be exchanged for the battery electronic control unit’s (ECU) conventional die-cast aluminum housing. Metal to plastic conversions not only eliminate 35% of the housing weight, but also provide cost reductions of up to 65% by eliminating secondary operations such as assembly and machining.
As electric and hybrid vehicles grow in popularity, Parker offers the engineering and materials expertise to help EV manufacturers produce the vehicles that consumers want at the scale needed.
With thousands of sealing, shielding, and thermal management solutions available, and over 50 locations around the globe, Parker is ready today to engineer solutions for your most critical EV applications.
This blog post was contributed by Jarrod Cohen, marketing communications manager, Chomerics Division.
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We're thrilled to announce that the Chomerics Division of Parker Hannifin Corporation, the global leader in motion and control technologies, has been recognized for its outstanding quality by global vehicle manufacturer Fiat Chrysler Automobiles (FCA) for both its production part and Mopar® unique parts partnership for the calendar year 2018.
This award, which specifically refers to Parker Chomerics Engineered Plastics Solutions business unit in Fairport, NY, has been awarded because of Parker Chomerics’ excellent performance as an FCA supplier.
In a letter from Scott Thiele, head of purchasing and supply chain for FCA North America, Thiele emphasizes Parker Chomerics’ “exceptional performance and dedication to excellence.” The letter goes on to detail how Parker Chomerics has achieved outstanding quality on a variety of metrics from production, to warranty, and the development of a stringent quality management system.
“Congratulations to the entire Fairport team, this is a great accomplishment. We are so honored to be among the very few that receive this coveted award. My hat goes off to the entire team for their dedication and collaboration throughout the year.”
David Hill, Parker Chomerics global general manager
Parker Chomerics Engineered Plastic Solutions business unit in Fairport, NY, located 10 miles outside of Rochester, NY, heavily utilizes robotics and automation to achieve high quality and delivery standards for many industries.
For more information on Parker Chomerics products, visit our website or download our Engineered Custom Injection Molded Plastics Solutions brochure.
This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics Division.
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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.
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 0.17There 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 designsThe 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.
The combination of retention ribs with a fundamental D-ring profile makes EZ-Lok the ideal geometry for effective use of the high-performance compounds typically required for aggressive semiconductor chemistries. EZ-Lok seals allow for lower cost of ownership through PM-minimization and reduced seal overhead costs, made possible by effective mechanical design. This is an example of how Parker’s effective design engineering can reduce the cost of ownership and bring premier solutions to the table.
This article was contributed by Nathaniel Reis, applications engineer, Parker O-Ring & Engineered Seals Division.
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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:
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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