Sealing and Shielding

The technology of providing tight and perfect closure. Parker engineered seals and sealing systems provide safety and enhance equipment performance.

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Sealing and Shielding Knowledge Base

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This is the second part in a two-part blog post series answering the questions you asked during the webinar Selecting a Thermal Gel or Thermal Gap Pad now, available on-demand. Missed part 1? View it here now .

The objective of thermal management programs in electronics packaging is the efficient removal of heat from the semiconductor junction to the ambient environment. While selecting a material for your application can be daunting, two of the most popular thermal interface materials you should consider are thermal gap filler pads and dispensed thermal gels.

You asked us a variety of interesting and thought provoking questions during the webinar, which our team of thermal material engineers have answered below.

6. What is the recommended surface roughness for THERM-A-GAP thermally conductive gels?

A surface roughness of N8 (3.2 micro-meters or 125 micro-inches) or rougher is recommended for use with thermal gels

5. Are all your thermal interface materials electrically insulating?

All Parker Chomerics thermal interface materials are meant to be thermally conductive and electrically insulating. This is accomplished by using ceramic particles in a silicone binder system.

4. What incremental thickness are thermal gap pads offered in?

Thermal gap filler pads are available in standard thicknesses from 0.010” to 0.200”. They are traditionally available in increments of 0.010” or 0.005” but we are able to create gap pads to meet any nominal thickness

Are the thermal gel materials non-Newtonion, where viscosity is a function of shear rate?

Yes, our thermal gels and dispensable putties are Non-newtonian. Please see the blog post about viscosity and flow rate of these materials:

Are there any plans to develop silicone-free formulations?

Silicone is far and away the most common binder material, as it offers a greater operating temperature range than non-silicone options. However, Parker Chomerics does have a non-silicone option for thermal gels. GEL 25NS is a 2.5 W/m-K thermal gel with the NS in its name designating its binder package as being non-silicone..

What are the shelf lives for gels and pads?

Thermal gap pads have an indefinite shelf life with the exception of those that come on an aluminum carrier with PSA. These gap pads have an 18-month shelf life from date of shipment. Thermal gels have a shelf life of 18 months from date of manufacture.

Will dispensing equipment wear due to abrasive filler particles in Gels?

To achieve high thermal conductivity, THERM-A-GAP GEL materials are highly filled with ceramic particles. Due to this high loading, the thermal compounds have higher viscosity and may be abrasive to dispense equipment. Material selection should be defined prior to selecting equipment to optimize the material performance and long-term equipment maintenance. The proper equipment choice will be a function of geometry, throughput requirements, material type, and package.

To successfully dispense GELs with minimal impact to physical properties, simple ram/piston pump systems with adequate force capability have proven most reliable. Reciprocating pumps, gear pumps, or other complex pumping designs impart excessive stress on the material. Pump systems that have a high degree of mechanical interaction with the material may increase maintenance needs due to the high concentrations of thermally conductive and abrasive fillers.

The valve that dispenses or controls the amount of material dispensed needs to be constructed of wear-resistant components to endure the maximum number of cycles. The most successful valves use a progressive cavity (ie. displacement type option) and are geometrically simple.

Be sure to watch the webinar on-demand below! Have questions or feedback? Reach out to us, we'd love to hear from you.

This blog was contributed by Ben Nudelman, market sales engineer, Parker Chomerics Division.

Need Better Flow Rate Control? Look to THERM-A-GAP GEL 37

The Difference Between Thermal Conductivity and Thermal Impedance

Selecting a Thermal Gel or Thermal Gap Pad – Your Questions Answered (Part II)

27 Aug 2020

This is the first part in a two-part blog post series answering the questions you asked during the webinar Selecting a Thermal Gel or Thermal Gap Pad now, available on-demand.

In our recent webinar Selecting a Thermal Gel or Thermal Gap Pad, available on-demand, you asked us a variety of interesting and thought provoking questions which our team of thermal material engineers have answered below.

14. What is the difference between thermal resistance and thermal impedance?

Thermal resistance is a measure of how a material of a specific thickness resists the flow of heat. Thermal impedance is a more comprehensive value as it is the sum of the material thermal resistance as well as the contact resistance.

Because real surfaces are never truly flat or smooth, the contact plane between a surface and a material can also produce a resistance to the flow of heat. Surface irregularities on a micro scale and surface warp on a macro scale create contact points and microscopic air-filled voids. Air voids resist the flow of heat and force more of the heat to flow through the contact points.

This constriction resistance is referred to as surface contact resistance and can be a factor at all contacting surfaces.

13. What does PEN stand for when referring to your PEN film carriers for thermal gap pads?

PEN stands for polyethylenenaphthalate and is a common carrier used to improve the durability of thermal gap pads. This carrier permits the gap pad to see a shearing motion and offers a clear, cost-effective dielectric film with fair thermal performance.

12. Do THERM-A-GAP GELs cure?

One of the most important properties of thermal dispensable GELs is that there is no cure required, as they are supplied in a fully cured state from Parker Chomerics. THERM-A-GAP GEL materials do not change properties once dispensed and do not require any processing after being dispensed.

Used within the limits of recommended operating conditions, GELs will not be become brittle, will not harden, will not flow, and will not soften overtime.

11. What are the re-workability requirements for thermal GELs and gap pads?

THERM-A-GAP gap filler pads have a very easy work process. They can be easily peeled off and replaced with identical gap pads. Using a clean cloth with a solvent such as isopropyl alcohol (IPA) will clean the surface and help reduce contact resistance as well as adhesion of the pads. The rework process for thermal GELs is similar.

Using a rag with a bit of IPA or similar solvent, simply wipe the previous gel away. Re-dispense the necessary amount of gel back onto the board or component and the process is complete. GELs should be re-dispensed every time the enclosure is opened.

Gap filler pads are more durable but should be replaced if they enclosure is opened after being in a compressed state for an extended period.

10. Do THERM-A-GAP GELs or gap filler pads experience long term creep?

THERM-A-GAP GELs and thermal gap filler pads go through extensive reliability testing (based on automotive standards) to ensure long term product survivability. GELs are formulated to resist sagging or flowing out of applications, especially in properly compressed situations.

THERM-A-GAP thermal gap filler pads, even in vertical applications, should not move out of applications if proper compression is maintained. Gap pads will experience a compression set and should be replaced after extended periods of time in a compressed state.

9. How do you calculate the quantity of gel to be dispensed?

Our applications engineers would be happy to help support calculations on gel volume, but the general principle is that you are looking for 80-90% of the total compressed volume. Multiplying the surface area of the component by the nominal compressed height will yield a volume that should be multiplied by 80-90% to get a starting point for gel volume. It is important to consider the expected gap height variation as well.

8. What are some current standards or specifications for THERM-A-GAP GELs and putties?

We meet ROHS standards with all our thermal materials and meet ASTM standards with regards to the thermal and electrical properties. Reliability testing is conducted on our GELs and putties with tests based on automotive standards such as GMW 3172.

7. Does Parker Chomerics have internal manufacturing capabilities for cutting gap pads?

Parker Chomerics can cut thermal gap filler pads to nearly any shape or size. We have a variety of cutting techniques that can be used for complex geometries and higher volume repeatability. Select your material we’ll get started on your quote right away.

Stay tuned for part II as we dive into more of your questions. Be sure to watch the webinar on-demand below!

this blog was contributed by Ben Nudelman, market sales engineer, Parker Chomerics Division.

Need Better Flow Rate Control? Look to THERM-A-GAP GEL 37

The Difference Between Thermal Conductivity and Thermal Impedance

Selecting a Thermal Gel or Thermal Gap Pad – Your Questions Answered (Part I)

20 Aug 2020

Clipper® Oil Seals are one of the Parker Engineered Polymer Systems (EPS) Division's most widely used rotary seal products. They are an effective solution – especially when used as direct replacements for traditional metal case seals. This is a testament to their precision-molded rubber/aramid fiber heel construction which eliminates the metal case (see image above). In this blog we will review the benefits of using Clipper® seal profiles as direct replacements for metal case seals:

1. Improved sealing in an imperfect housing

The composite rubber/aramid fiber heel provides a gasket-like seal for improved sealing against the bore. The surface conditions of bore housings are frequently riddled with imperfections due to damage during improper seal installation and removal, or simply due to cost sensitivity in their original manufacture. Metal can seals lack the ability to conform to such imperfections, frequently necessitating the use of supplemental gaskets or bore sealants during installation to prevent bore leakage.

2. No need for compression or bore plates

The outside diameter of the flexible, composite elastomer/aramid fiber heel is slightly oversized to create a tight interference press fit. The tight fit and compression-set-resistant heel construction eliminate the necessity of compression plates for bore retention1. It’s essential to note that bore plates (shown in green) can cost as much as $100 per inch of shaft diameter because of additional part cost and added assembly time.

3. Corrosion-resistant

Clipper seals have a composite elastomer/aramid fiber heel and rubber elastomeric lip so there is no concern for rust or corrosion. The only metal component is a 302 stainless steel garter spring. The stainless spring handles higher operating temperatures and resists rust/corrosion better than carbon steel springs used in other rotary shaft seals.

4. Durable, one-piece molded construction

The Clipper Oil Seal features one-piece molded construction across its entire available size range (0.25” to 92”+ shaft diameters). This molding process is more robust as compared to metal case rotary seals constructed from multiple components that are glued and/or crimped together during assembly.

5. Resistant to issues arising from thermal expansion

Metal case seals are prone to sealing complications brought on by thermal expansion. As an example, consider what happens when interfacing a carbon steel metal case seal with aluminum housing in applications where large rapid temperature swings occur. Aluminum housings will expand at a different rate than the carbon steel case of the rotary lip seal; leaving you vulnerable to bore retention issues and/or failure due to leakage from the housing/seal OD interface.

6. Easy, damage-free installation

Clipper’s flexible, rubber heel prevents seal damage and component damage during installation. Seal installation, aided by proper chamfering, requires only finger pressure to start the seal into the housing, followed by light tapping with a soft-faced mallet until flush. Issues associated with installing rigid metal cans, such as damage due to cocking, are avoided. To further ease installation and save time, because the outer diameter conforms to bore imperfections as mentioned earlier, there’s no need to add -- or wait for drying time of -- bore sealants.

7. Splittable

Due to the Clipper Oil Seals non-metallic construction, Parker can produce certain profiles that have been precision split. Downtime due to seal replacement is minimized. There’s no need to uncouple or disassemble equipment since Split Clipper seals can be installed in place. For metal case variants, this is not an option. View the short video demonstrating the ease of installation here: Split Clipper Oil Seals Installation

8. Highly customizable

The rubber molding process allows for greater customization to fit specific design envelopes. The addition of flanges, buttons, mounting and bolt holes, etc. are all possible.

9. Fast delivery

Non-stock items can be produced and delivered faster than metal case seals. Seal production of Clipper’s composite rubber design is not hindered by long lead times commonly experienced with the fabrication or procurement of metal components. Clipper Oil Seals 14” in diameter and smaller typically ship within 10 days.

10. Made in the USA

Since all Clipper Oil Seals are made in the USA, the supply chain is simplified. Procurement difficulties due to global import or tariff variables are non-existent.

Learn more about Clipper® Oil Seals and other rotary shaft seal solutions from Parker. Included on the page is a link for you to contact us and initiate discussions on your next project. In addition, your local Authorized Parker EPS Distributor can provide assistance with off-the-shelf or customized Clipper Oil Seal solutions from Parker EPS Division. To locate your nearest representative, follow the instructions provided on Parker's website under "Where to Buy".

1 Exceptions exist where regulatory or unique application conditions govern bore plate use.

This article was contributed by Alan Wiedmeyer, application engineer, Parker Engineered Polymer Systems Division.

Sealing at Extreme Low Temperatures

Installation of Linear Fluid Power Seals

The Truth About Hydraulic Cylinder Lift

10 Reasons to Replace Metal Case Rotary Seals with Clipper Oil Seals

22 Jul 2020

1. Improved sealing in an imperfect housing

2. No need for compression or bore plates

3. Corrosion-resistant

4. Durable, one-piece molded construction

5. Resistant to issues arising from thermal expansion

6. Easy, damage-free installation

7. Splittable

8. Highly customizable

The rubber molding process allows for greater customization to fit specific design envelopes. The addition of flanges, buttons, mounting and bolt holes, etc. are all possible.

9. Fast delivery

10. Made in the USA

Since all Clipper Oil Seals are made in the USA, the supply chain is simplified. Procurement difficulties due to global import or tariff variables are non-existent.

1 Exceptions exist where regulatory or unique application conditions govern bore plate use.

This article was contributed by Alan Wiedmeyer, application engineer, Parker Engineered Polymer Systems Division.

Sealing at Extreme Low Temperatures

Installation of Linear Fluid Power Seals

The Truth About Hydraulic Cylinder Lift

10 Reasons to Replace Metal Case Rotary Seals with Clipper Oil Seals

22 Jul 2020

The demand for dispensing thermal interface material (TIM) has increased exponentially because dispensables offer engineers flexibility in the designs and patterns that can be applied to electronics packaging.

Single-component, dispensable TIMs such as THERM-A-GAPTM GELs, can cover a variety of gaps and form complex geometries which provide reduced thermal contact resistance, thus reducing the temperature and increasing the efficiency of the application.

Ideal for precise dispensing

In applications that require precise dispensing, like automotive vision and controller modules found on Advanced Driver Assistance Systems (ADAS) systems, high volume dispensing machines can dispense large volume cartridges or pails of TIM on thousands of parts per hour.

These dispense machines offer the greatest control and yield
As well as the fastest cycle times with generally the lowest material cost per piece
The proper equipment choice will be a function of geometry, throughput requirements, material type, and package

However, issues tend to arise when these large cartridges and pails must be changed out when material is used up. Today, many customers deploying high volume dispensing on their lines are running into throughput issues due downtime and re-calibration required to change out an empty cartridge or pail.

Increase output, lower downtime

In some instances, our engineers have seen customer downtime go from minutes to hours or even days when processing and other systems need to be adjusted between changeovers.

It's clear users of high volume dispense material in applications such as automotive ADAS cannot afford this severe interruption in their supply chains.

This is where THERM-A-GAP GEL 37, the next generation of single component, no cure required, thermal interface materials from Parker Chomerics is so useful.

With a higher thermal conductivity and better flow control than its predecessor, we consider THERM-A-GAP GEL 37 to be the dispensable TIM that will help to lower downtime and re-calibration between vessels.

THERM-A-GAP GEL 37 significantly improves dispense variability and limits downtime due to material and processing adjustments. Other benefits include:

Pigmented blue for ease of use by vision systems
Offers a 50% higher flow rate compared to THERM-A-GAP GEL 30
Ideal for the automotive market segment where a dispensed thermal material with a tighter flow rate and an easier dispense material help to solve those critical changeover interruptions

THERM-A-GAP GEL 37 will be manufactured in Hudson, NH, and is available today for immediate sampling and prototyping.

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

New Thermal Gel Benefits Consumer and Automotive Applications

Viscosity vs. Flow Rate - Which Is Best in Thermal Interface Materials?

Need Better Flow Rate Control? Look to THERM-A-GAP GEL 37

15 Jul 2020

Heavy duty equipment moves industry forward in all climates, from the sunny Caribbean to icy Greenland. Effective, reliable sealing is what allows hydraulic systems in heavy duty equipment to do work, no matter the temperature. Reliable sealing solutions allow cylinders on dump trucks and excavators to move icy, frozen tundra, and allow actuators on subsea valves to operate 5,000 - 20,000 feet below the surface of the ocean. We depend on these seals for our safety and productivity, so a little chilly weather is no reason to call it quits.

BRRR! What happens to seals at cold temperatures?

Most objects shrink as they get cold, with few exceptions (water, I’m looking at you). This applies to all matter in the universe. Materials shrink at different rates, and this is a measurable property called the Coefficient of Thermal Expansion (CoTE). Thermoset elastomers and thermoplastics shrink roughly 5 times more than metals1 for a given temperature change. This means at cold temperatures, seals shrink more than their housings, and thus have less “squeeze” to make a tight seal.

To make matters worse, elastomers also harden as the temperature drops. At some temperatures, known for each material as its Glass Transition Temperature (abbreviated ‘Tg’), seals become rock hard and brittle … like glass. We don’t make seals out of glass for a reason; they wouldn’t work. In order to keep seals springy and resilient we need to specify materials with a Tg below the coldest temperature a system will see.

In very high pressure, low temperature applications, there is one additional concern. Applying pressure to seals effectively raises the Tg of the material by about +1°C per 750 PSI. This is called Pressure-Induced Glass Transition and is the reason high pressure seals fail slightly above their measured Tg.

That’s not cold!

So, there’s low temp, and then there’s looooow temp. I work at Parker Hannifin Engineered Polymer System (“EPS”) Division’s headquarters in Salt Lake City, Utah. Winter low temperatures in downtown Salt Lake are typically just below freezing. In this climate, most seal materials function just fine.

Siberia purportedly has the coldest inhabited villages in the world, with temperatures down to -60°C (-76°F). Northern Canada isn’t much warmer. In these regions, an operating hydraulic system can generate enough heat from friction to keep the seals sufficiently warm. However, if hydraulic equipment is unused or stored overnight in such frigid environments, the use of cold-rated seals with a low Tg is critical to preventing leaks in equipment.

For rotating equipment that is idled or shut off in extreme cold temperatures, the lip on a rotary shaft seal can freeze to the shaft when moisture is present at the seal lip/shaft interface. When the shaft starts, the tip of the lip can be ripped or sheared off, leaving a small band of rubber on the shaft (cold temperature seal fracture).

And then there are cryogenic systems, which are entirely different beasts. Liquid nitrogen tanks require seals that can handle the -320°F fluid. At this temperature, all elastomers will be rock solid. So what seal material can handle that? Polytetrafluoroethylene (PTFE).

Pure (unfilled) PTFE, while not considered an elastomer, remains flexible down to -425°F. That’s 35 degrees above Absolute Zero – the coldest possible temperature. The chart in Figure 1 shows the effective ranges for seal materials offered by Parker 2, 3.

Typical material temperature ratings

After looking at this chart, you might think, “Why doesn’t Parker make all seals out of PTFE and dump the rest?” PTFE is a great seal material, but it comes with its own set of tradeoffs. Hardware manufacturing and seal installation tend to be more complicated with PTFE than with elastomer seals.

Fluorocarbon rubber (FKM), and more recently perfluorinated rubber (FFKM), have traditionally been selected to seal hot temperatures and nasty chemicals. However, they perform poorly in cold. Parker offers special low-temp blends, spanning -40 to 400°F and -40 to 600°F respectively. “Do-everything” materials such as these tend to be more costly than traditional FKM rubber.

Highly saturated nitriles (HNBR) offer higher temperature capability with better wear resistance compared to standard nitrile (NBR). To improve low temperature resilience, Parker has developed HNBR compounds that perform better at low temperatures than most general HNBR compounds.

Special grades of silicone can handle colder temperatures, but their wear properties are so poor Parker EPS does not recommend these for dynamic sealing. Ethylene propylene rubber (EPDM) compounds are also capable of remaining quite flexible at low temperatures, but care must be taken to ensure that the application is compatible. EPDM often has the look and feel of nitrile rubber but reacts to fluids much differently.

Parker polyurethanes (compounds start with a ‘P’ in the table in Fig. 1) are popular because they offer the best all-around balance between low and high temperature sealing, wear resistance, pressure rating, and cost. Parker’s compound P5065A88 is compounded specifically to be more resilient at low temperature than most other polyurethane compounds.

In all sealing applications where temperature ratings are a concern, it is important to know that sealing compounds perform their best when they stay well within their temperature range. Applications that push seal compounds to the end of their temperature range may only perform for a short period of time before damage to the seal occurs, or they become too stiff to effectively control leakage. A good rule of thumb for long lasting seals is to remain within 80% of the compound’s temperature range.

Conclusion

Now that you’ve selected a seal material with a Tg low enough for the cold environment it will be used in, are you done? Make sure other properties such as pressure rating, wear resistance, fluid compatibility, and high temp capability are also adequate for the system. Be aware of tradeoffs when switching materials to avoid causing a problem in another area. If in doubt, send us an e-mail and we will be happy to help.

Stay cool! Much more information about seals can be found in our Fluid Power Seal Design Guide, Catalog EPS 5370.

Recommendations on application design and material selection are based on available technical data. They are offered as suggestions only. Each user should make their own tests to determine the suitability for their own specific use. Parker offers no express or implied warranties concerning the form, fit, or function of a product in any application.