Category Archive: Thursday Thoughts
Gasket Materials and Understanding Choices for gasket selection through ASTM Tests
Today’s blog will be posted below in print and is also available as a video here:
So many good competitors…so many good materials. It adds to the dilemma in picking who to work with and even more importantly, what to work with when picking designs and materials for seals. We use the term “seals” broadly here to include all types of seals; die-formed packing rings, cut gaskets, o-rings, hydraulic packing, you name it…all are seals.
Our owner and CEO, Mr. Robb Ridgway, remembers back in the mid-70s when two really exciting new materials hit the market. Expanded PTFE and exfoliated graphite. These products changed the fluid sealing industry in many ways, and yet, there are still a lot of people who resist them even today, more to a lack of understanding of them and their potential to eliminate sealing problems.
Some companies, including us to some degree, promote gasket materials that have great “crush resistance” under heavy loads and higher temperatures. A valid point as we have seen applications where mechanical or virgin grade PTFE gaskets as an example, have extruded or cold-flowed under constant load and temperature over an extended period, leading to leaking and eventual re-torque until the gasket fails and needs to be replaced. A material with high “crush resistance”, creeps, or cold-flows only slightly, has high torque retention and requires less maintenance time.
The new expanded PTFE materials are interesting because they resist creep / cold-flow much better and are also engineered with different types of fillers to take even great loads, having higher torque retention and again, reducing maintenance time. Exfoliated graphite gaskets, when installed, compress more but when under operating load and temperature, resists creep / cold-flow extremely well and require little maintenance time because of very high torque retention.
All of this becomes important when trying to decide on a material of choice for the application you may be working on. We don’t want to be pushing material at this point but rather some of the terms that we like to promote, to help the decision-maker better understand what is important in making the choice. We believe you will find these helpful. They are not all of the tests, but these are key in trying to make a decision. Comments – questions??? Please let us know in the comments section or by emailing our team at: email@example.com.
Next, we want to move into some of the standardization of physical characteristics for gaskets and materials:
STANDARDIZATION OF PHYSICAL CHARACTERISTICS
Sealability is measured according to the ASTM F37 specifications. It is an indication of the material sealing ability under a set of conditions; A seating stress of 2000 psi is imposed through the flanges on the material sealing iso-octane at an internal pressure of 14.7 psi. The test is done at ambient temperature and the number shown is the amount of leakage in milliliters per hour. A lower number would generally indicate a better material.
Compressibility is measured according to the ASTM F36A specification. A load of 5,000 psi is imposed on the material and the loss of thickness is measured and expressed as a percentage of the original height. The compressibility of a material indicates, to a degree, its ability to fill flange scratches, nicks, or voids and to flow or move to assist in sealing misaligned or warped flanges. In general, the higher the number, the easier it is to seat the material.
Recovery is also tested under the ASTM F36A specification. Recovery is the measured rebound or increase in thickness from the compressed measurement once the load is removed. It is written as a percentage of increase over the compressed measurement and indicates the ability of the material to resist temperature and pressure. The higher the number, the better the material is at holding torque.
Creep relaxation- also referred to as Torque Retention, is measured according to the ASTM F38 specification and indicates the material’s ability to hold stress or bolt load over an extended period. It is expressed as a percentage of the original load and shows the amount of lost stress from that load. A lower number indicates a more stable material retaining torque and resisting leakage.
Tensile strength is measured under ASTM F152 and is given in pounds per square inch. It is the total force required to pull the material apart and is not related to the sealing function of the material. It relates more to the manufacturing process.
At MPRC, we have always promoted “Life Cycle Costing”. We believe it is important to try to give our customers the best material choices rather than the “cheapest” option with the lowest price just to get the order. That does no one any good. While we know that we have many good competitors, we also know that many only want the business at any cost. Usually, the customer is thrilled with the price until maintenance calls up to inquire about the material purchased that falls short of the “run-time goals”. We hope the information above will help in assessing the material choices you are working through to make an informed decision. Thank you!
In the Engine business, most gaskets fail due to a combination of thermal cycling and improper surface preparation. Surfaces can become scratched, warped, or pitted which doesn’t allow for equal compression on the sealing surface, increasing the failure rate of the material.
Many people spend a lot of time searching for the perfect gasket material that they’re told “will do X” or “won’t do” (fill in the blank). When it comes to gasket swelling, however, here’s the thing: ALL GASKETS SWELL to some extent.
There are a lot of companies in the fluid sealing industry that don’t want consumers to know that gaskets actually swell. Others use the occurrence of swelling as a material selling point. At MPRC, our goal is to be your fluid sealing specialist, and we strive to educate our customers on the best-suited materials for their specific applications.
There’s also the question of HOW a gasket is installed. Is the gasket being installed dry, or is there a lubricant that is applied to the sealing surface or the gasket directly? That answer will have a tremendous effect on the service life and performance of the gasket.
MPRC recommends installing our gaskets dry- that is, “as-is” without any RTV Silicone or lubricant added. It is important to remember the friction between a gasket and the flanges must be maintained to create a long-lasting seal. Any wet Silicone or oil destroys that friction and most gasket materials will extrude under load. We do recommend or suggest using a Permatex Aviation Grade adhesive or a 3M #77 adhesive to hold a gasket in place, particularly on vertical applications to help the mechanic by holding it in the place where needed. RTV Silicone applied wet will off-gas volatiles that will compromise the integrity of the elastomers in a gasket and lead to premature gasket failure.
(The gaskets that are shown below- LEFT side, were installed dry and used in test service. The gaskets on the RIGHT were installed using RTV Silicone and used in test service)
MPRC has a series of material designations for a wide variety of engine and exhaust applications within the Rail and Marine Industries. We offer CG1 (our OEM Grade), CG2 (our upgrade), and CGO (our Optimized grade). Each option represents a quality sealing solution based upon a specific price point.
CG1 (off-white) offers a high-temp sealing option to 400°F continuous and 700°F maximum, which is affordable. Some applications do not require the “best of the best” when it comes to material and price points, which makes CG1 a very cost-effective solution.
CG2 (yellow one side/grey opposing side) is another high-temp sealing solution that offers a slightly higher temp rating to 662°F and maximum at 845°F. This material is an upgrade from the standard OEM grade material.
For more product info, please contact us at 800-397-3429 or email our sales team at: firstname.lastname@example.org
**MPRC will be releasing our 7th Generation of Style 7800 gasket material after further testing is completed. Stay tuned for more updates!**
Wow – here we are, starting yet ANOTHER New Year. Some of us are still getting used to writing “2021” on our checks, and many of us couldn’t be happier putting last year behind us.
There’s no question the past two years have been challenging. Our company and our city experienced the damage of a Category 4 Hurricane called a “Derecho” in mid 2020. No one would ever have thought a hurricane would hit IOWA. While working through that, we also had to find creative ways to navigate through the pandemic and that has been a challenge as well. We’ve had staff out due to Covid, and we’ve been in the middle of supply chain issues with unheard-of lead times that have put a strain on us all.
In many regards, we could have the same negative thoughts and “doom and gloom” that so many have had. This is not to say that things have been easy the last couple of years, but we choose to look at how fortunate we are and how blessed we have been. We are so thankful for the team we have at MPRC and their commitment and dedication to our customers. The reality is, through all of these struggles, we have ended 2021 as one of our best and most profitable fiscal years in our companies’ history.
How does this happen when we know that everyone is short-staffed, lead times are triple what they used to be, and raw material costs continue to go up in what seems like monthly increases? How can a company combat these things and still come out profitable and with record numbers?
The answer is: we stretch ourselves. We have become even more innovative and self-reliant, increasing our overall capacity of in-house rubber molded components. We’ve increased our commitment to marketing and letting our customers and potential customers know more about the products and services we offer, and what sets MPRC apart from our competition. We’ve invested in a new website that will serve as an incredible resource for our customers for both technical and current industry news, including readily available product flyers for download and product videos.
Great things are happening at MPRC, and we are excited about what 2022 will bring. We are bringing on new staff to continue to bring the quality and service our customers have come to expect. Thank you for your continued business and trust in us as your fluid sealing specialist.
Master Packing & Rubber Company