Year in Review: Top Blogs From Our Two Years of Blogging

Sealed-In is now celebrating its two year blog-iversary! Our viewership continues to grow, and we hope that you have enjoyed the content we have produced (and learned something too!).

As is now our annual tradition, we decided to do a recap of our most popular blogs over the last two years. See below for our top 5 list of Sealed-In blogs.

 

The Top 5

Is There A Difference Between Gaskets & Seals?

3 Things You Need to Consider When Deciding on EGR Gasket Material

The Great Gasket Debate: To Reuse or Not To Reuse

What is Creep Relaxation, and Why Do I Care?

Why Would I Use Composite Gaskets When I Can Use MLS?

 

Thank You!

As always, thank you for your readership. We hope that we are becoming one of the first places that you go for information related to gaskets and gasket materials. If there is ever a topic that you’d like us to cover, please let us know – just drop us a comment in one of the blogs.

On to year 3!

Year in Review: Top Blogs From Our Two Years of Blogging

What Is Torque Retention, and Why Do I Care?

This is the sixth installment of our “Why Do I Care?” series. Every so often, we’ll blog about some of the questions people new to the gasket industry may be looking for more information about. Click the links below to read the first five installments:

What Is Compressibility & Recovery, and Why Do I Care?

 What Is Bolt Load, and Why Do I Care?

 What Is Creep Relaxation, and Why Do I Care?

 What Is Ignition Loss, and Why Do I Care?

 What Is Air Aging, and Why Do I Care?

This week, we’re going to talk about torque retention (or torque loss, depending on your particular viewpoint) and how it affects your gasket performance. Torque retention is related to many of the topics previously discussed, but we thought we’d take a closer look at it specifically.

 

Torque Retention

Torque retention isn’t necessarily something that can be measured and published as a gasket material property, but compressibility, recovery, and creep relaxation values have a direct effect on a good torque retention value (along with a good seal). Below, we have listed a few general questions to help those of you that are less familiar with this concept start to gain an understanding.

1. What exactly is torque retention? It is a measurement of how well a bolted joint retains the force applied to each bolt. How much of the initial torque is retained by the fastener after a certain time or exposure? Zero percent torque retention means that the bolts have lost all of their load and are no longer compressing the gasket and thusly, the bolts are falling out and the joint has failed.

2. What causes torque retention to change? Changes in the gasket due to time or temperature are the main reasons you tend to see changes in torque retention. Other reasons would have to do with the design of the joint, the assembly of the joint, the bolting procedure, the fasteners themselves, and other factors.

3. What do I do about torque loss? After the initial heat cycle, some reduction in torque retention (torque loss) is expected and compensated for with the initial bolt load. In an ideal situation, bolts are just re-tightened and the retention should be sufficient. While this isn’t always possible, the installation load is typically high enough to achieve the initial seal, withstand creep and load loss, and still maintain sufficient load for a long term seal.

4. What should I look for in materials to maximize retention (or minimize loss)? The answer to this really depends on the requirements of your application and the conditions of your joint, so you’ll never find one perfect material. However, when selecting a material, you want to pay attention to creep relaxation values. The lower the better, meaning that a material with low creep will provide more “push-back” on the bolts and thusly, retain more torque.

5. What else should I know? All compressible gasket materials have some level of creep or load loss which can be expected. The challenge as a designer is to provide sufficient load for a long term seal.

 

Now That You Know

Knowing about and understanding torque retention can help you to better select a material for your joint. It can also help you to understand what you are seeing after the application begins to log runtime hours. You can always expect some reduction in torque retention, the key is to understand why it is happening and how much is too much.

Is the cup half full or half empty? Torque retention or torque loss?

What Is Torque Retention, and Why Do I Care?

What Is Creep Relaxation, and Why Do I Care?

Here is the third installment of our “Why Do I Care” series. Every so often, we’ll blog about some of the questions people new to the gasket industry may be looking for more information on. Click the links to read the first two installments:

 What Is Compressibility & Recovery, and Why Do I Care?

 What is Bolt Load, and Why Do I Care?

This week we’re going to talk about creep relaxation in gaskets and gasket material. This is something that will happen to some extent in most gasket materials. How much or how little of this you see depends on your gasket material selection and the application itself. It is important to have an understanding of creep relaxation and how it relates to a particular material.

 

Creep Relaxation

In basic terms, creep relaxation is the measurement of how much a particular gasket material spreads (thins) out when force is applied. As the gasket loses thickness, the bolts can relax, which leads to a loss of load. When the level of creep relaxation is too high for the application, that’s when you’re going to have problems maintaining the seal.

Thickness of your gasket material plays a big part in the amount of creep relaxation you see in the material. If you’ve read our previous blog post How Thick Does Your Gasket Need to Be? Here Are 4 Ways to Know For Sure., you’ll see that thicker is not always better. Generally, the thinnest gasket you can use is going to be the best option. The amount of creep relaxation seen in a material is going to be directly proportional to the thickness of the gasket. With that said, sometimes a thick gasket is necessary. If that is true for your application, then you should expect a certain level of creep to take place. Ideally, the bolts and joint will be loaded sufficiently to overcome the relaxation that is present and maintain the seal.

The majority of the creep relaxation seen in a material occurs early in use. Some suggest that material will continue to creep indefinitely, but the loss is negligible. If your application can withstand the creep that occurs within the first duty cycle, chances are it will maintain its seal.

Materials have different amounts of creep, depending on the temperatures and pressures used in the joint. Generally, denser materials will have less creep than softer materials. So, in stiff flanged joints with plenty of load, generally a denser material is a better choice.

Softer materials are more compressible and provide better conformance to flange surfaces.  However, some types of softer materials due to their make-up, exhibit high creep/relaxation under load and temperature. This can be addressed by providing sufficient bolt load, to overcome any expected creep effect and maintain a long term seal. Minimizing gasket thickness will also help in this area.

High temperature and high pressure also have an effect on the amount of creep you will see in the material. If you work in these types of applications, you will need to pay special attention to the specifications of the material you are selecting to work within the suggested temperature conditions. Taking material higher than its capability can lead to the breakdown of various components, additional creep and ultimately load loss on the fasteners.

 

Material Selection Matters

Being aware of the creep relaxation characteristics of a specific material is paramount to choosing the right material for your application. Don’t hesitate to talk to your trusted gasket material supplier for help in identifying the type of material that you may need for your application.

Until next time!

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