In mechanical engineering, you’ll often find yourself with an appliance that needs sealing. If you’re dealing with liquids flowing at high temperatures and pressures, you must choose the right kind of seal for the job. Seals come in a multitude of different shapes, sizes, and materials.
If you’re undertaking a mechanical engineering project that will require the use of some of the kind of seal, you’ll probably have come across a range of different terms and types of seals. The words gasket and o-ring may very well ring some bells. These are both different types of seals that are useful in different situations. It’s important to know what kind of seal to use to ensure that whatever you’re attempting to seal in doesn’t escape or leak.
In this guide, we will give you a comprehensive description of each type of seal, including its capabilities, material, and construction. We will provide some examples of when to use each and some pros and cons of each type of seal.
Table of Contents
We’ll start our discussion by examining the gasket seal. A gasket is a mechanical seal that sits between two or more mating surfaces. These types of seals are designed to make up for imperfections on the surface of the mating materials by filling in these irregularities. Because they are meant to fill gaps in space, gaskets are made with a material that has some yield to it, so that it can be molded to a specific shape and size as needed.
Typically, a gasket is made of flat sheet material. Paper, rubber, silicone, metal, cork, felt, and rubber is all commonly used. In certain situations, more chemically resistant polymers are used to ensure chemical corrosion won’t occur once the gasket is in place.
Types of design
There are a number of commonly sold and used gasket designs and types. The gasket you need will vary depending on where and how it’s being used. Here, we will outline some of the most commonly found gasket designs.
1. Sheet gasket
This is made when a sheet of material has the shape required for the gasket punched out. This is the fastest and cheapest available gasket on the market. Historically, asbestos was used. The modern alternative is a non-asbestos material mixture that’s durable and thick. Sheet gaskets will serve you well if you’re dealing with acids, steam, or chemicals. If you’re a DIY enthusiast, have a look at what types of gasket sheet materials are available online. You’re sure to find one that suits your particular purpose. This way, you can cut your gasket yourself and make sure it’s the perfect fit.
2. Solid material gasket
These gaskets are made using a harder material than would be used for sheet gaskets. There are several downsides to solid materials being used in gaskets, as they are difficult to compress and must still be more pliable than the mating materials, or these will become warped and disfigured. However, on the plus side, this type of gasket is usually able to withstand higher temperatures and pressures than the more commonly used sheet gasket, and it’s still relatively cheap.
3. Spiral wound gasket
These gaskets are made with both metals, such as steel, and pliable filler material, such as graphite. The two materials are wound side by side. Both materials have a role to play. The stronger metal provides structural integrity, while the filler material can move and fill the gap, thus acting as a sealant. This type of gasket is more expensive than the previous two types but has proven to be highly efficient and functional, so it may be worth the extra money.
4. Flange gasket
A flange gasket is made with a specific application in mind. Created to sit between two sections of pipe to provide extra support and to reduce the risk of leakage in pipes that are damaged. If you’re looking into a seal for a pipe, a flange gasket may be the best option for you.
If you think that a gasket seal isn’t the right option for you, you may be after an o-ring seal. An o-ring is actually a type of gasket itself, but it’s unique due to its shape and design. An O-ring seal is essentially a rubber or elastomer loop. Its donut shape makes it unique in the world of seals. O-rings are perfect for both static and dynamic applications.
How does it work?
The o-ring fits into a predesigned groove, which provides the initial compression of the cross-section. Increasing pressure on the O-ring’s diameter will result in higher seal performance. Essentially, the higher the pressure, the tighter the seal. Of course, if the pressure is too high for the o-ring, the integrity of its cross-section and diameter will be permanently compromised, and you risk leakage. The perfect amount of pressure is key to the O-ring’s functionality, but if the pressure is right, an o-ring provides optimal sealing. O-rings are designed to warp under pressure and compression to fit into gaps, thus ensuring no leaks can escape. When pressure is released, the o-ring should ‘bounce’ back into its original shape and size. A warped appearance of the o-ring means it may be damaged and needs replacing.
O-rings are a good alternative to gaskets in certain applications. Because they are more likely to withstand very high pressures and temperatures, o-ring seals are perfect for sealing in liquids that will reach extremes. Some can operate without any faults at temperatures as low as -40 degrees Celsius and as high as 150 degrees.
Materials commonly used
A variety of materials are commonly used to make o-rings. Usually, a type of rubber or plastic elastomer is used. Here are some of the specific pros and cons of different materials. You must pay close attention to the temperature guide of various types of o-rings, as if they aren’t resistant to the temperature of your appliance, you risk causing leaks, which can be dangerous, especially when dealing with high temperatures.
1. Nitrile rubber (NBR, HNBR)
If you’re dealing with very hot oils, fuels, or aggressive chemicals, an o-ring made of nitrile rubber is your best and cheapest option. HNBR (hydrogenated nitrile butadiene rubber) is a highly durable option that’s less likely to degrade over time. Because they are hydrogenated (unlike NBR o-rings), they are even more durable when exposed to heat and oxidation. If you’re looking for an affordable and extensive range of these o-rings, click here: https://aclube.com/collections/ac-hnbr-o-rings-seals. This website offers plenty of different sizes and colors, so you’re sure to find a suitable option here.
2. Fluoroelastomer (FKM)
This type of material is also very heat-resistant and will function well when used alongside most chemicals. It’s also very age-resistant. However, this material won’t function as well if used in conjunction with hot water, steam, or organic acids.
3. Silicone rubber (SiR)
This material will serve you well if you’re looking to seal in water, oils, or fats of up to 100 degrees Celsius. However, this rubber will be less resistant to fuels, acids, steam, or silicone oils.
4. Thermoplastic polyurethane (TPU) polyester
This material will give you much higher resistance to abrasion, extrusion, and tearing. It will function when used with mineral oils, silicone oils, and water of up to 50 degrees Celsius.
Deciding on the seal of your choice will depend greatly on what conditions you’ll be placing this seal under. The first deciding factor will be whether you’re dealing with a dynamic or a static appliance. With a dynamic appliance, you’ll automatically be looking at an o-ring.
The next crucial consideration to make is what type of liquids and/or gases the seal is intended to seal in. This will determine which types of materials are safe and wise to use. Be sure to conduct careful research on the potential risks of combining certain materials and ensure you understand which chemical reactions you risk by using different materials. While a certain type of material may appear to function well for a while, chemical corrosion or other types of wearing away may start to occur. You’ll eventually be forced to repurchase new o-rings and replace the old ones.
A final, crucial determining factor in your decision-making is the temperature of the liquids you’re working with. Ensure that you’ve chosen a material that’s guaranteed to withstand the highest possible temperature that your appliance may reach, or again, you risk a malfunction of some sort.
Choosing the correct seal can be a complicated process that involves several steps. If you’re still unsure which type of seal is right for you, try researching the particular appliance you’re fixing, and be sure to know what temperature resistance and materials are best for your application.