Often mistaken as the same, thermoset plastics and thermoplastics have very different properties and applications. Understanding their chemical makeup and performance difference can help you better source materials for your product designs.
In this article, we’ve designed and outlined a comparative look at thermoset plastics and thermoplastics. Side-by-side, the contrast is different in curing process, features and benefits along with their compound makeup and pros and cons.
The Difference: A Look at Thermoset vs Thermoplastic
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Real Seal manufactures and distributes seal products and mechanical components with a strong focus on performance oriented rubber and plastic materials. We are a full-service supplier of sealing and mechanical components, operating in hundreds of industries both nationally and internationally.
Depending on the direction that squeeze is applied to the O-rings cross section on a seal, it will be categorized as an AXIAL or RADIAL seal.
Static Axial Seals
A static axial seal will act in a similar manner to a gasket that is squeezed on both the top and the bottom of an O-ring’s cross section. A static axial seal is used in face (flange) type applications. When it is used as a face seal and there is internal or external pressure, the O-ring should be positioned against the low-pressure side of the groove to cut down on O-ring movement and accompanying wear within the groove.
These seals are easier to design than static radial seals since there is no extrusion gap and fewer design steps. This enables you to control the tolerances more easily.
Static Radial Seals
Typically used in cap and plug type applications, static radial seals are squeezed between the inner and outer surface of the O-ring.
Static Crush Seals
The O-ring is confined and pressure deformed (crushed) within a triangular gland which is made by machining a 45-degree angle on the male cover. In crush seal applications, the seal is squeezed at an angle to the O-ring’s axis.
Static Seals with Dovetail Glands
Sometimes O-rings are used in static or slow moving dynamic situations where a specially machined “dovetail” gland needs to be used. Controlling tolerances in the glands can be difficult because of the angles involved. The glands are meant to securely hold the O-ring in place while the machine is in operation or during maintenance and disassembly.
The O-ring squeeze is mostly axial in direction and valve operations puts force on the top and bottom seal surfaces. So that there is no tearing or nicking, the use of an O-ring lubrication is recommending while the O-ring is being installed into the dovetail gland. It is difficult to create the groove and tight tolerances are required so this type of seal application should only be used when necessary.
Reciprocating Seals
Reciprocating seals are used when there is a moving piston and rod. This is the most common dynamic application for O-rings.
Rotary Seals
Rotary seals are used for rotating shafts with the turning shaft protruding from the ID of the O-ring.
Oscillating Seals
The shaft of an oscillating O-ring application moves in an arc within the gland and is in contact with the ID of the seal. The shaft can twist so self-lubricated O-rings with a hardness of 80 to 90 durometers are most often used. If there is graphite containing compounds caution is necessary as they can pit stainless steel alloys.
Real Seal manufactures and distributes seal products and mechanical component goods. Established in 1970 as a distributor of O-rings, we are now a full-service supplier of sealing and mechanical components for many different industries.
One of the most technically advanced organizations in the industry, Real Seal maintains a fully equipped laboratory with a full-time chemist and technical staff. We are able to assist you with your design challenges and formulate materials that meet your specific needs for any types of seals. We can provide solutions to your problems and create an increased value for your company.
We have been talking a lot about seals lately, but where are they actually used? Seals are used for many different things in various industries for various applications. Industrial seals are used to seal the opening found between a static and rotating component. It is very important to use high performance seals so that equipment works efficiently. Using proper seals will save companies money and energy cost.
Here are the top ten industries that use hydraulic, pneumatic seals, or a combination of the two.
1. Agricultural Machinery – Farm Equipment
It is vital for agricultural machinery to be functioning at the optimum level, especially during harvest season. These machines are out in the elements facing various weather conditions, UV exposure, and contamination from things around them. In order to repair and maintain farm equipment, one must use high performance seals in order to increase productivity and lower expenses. Harvesting, threshing, baling, drainage, and crop harvesting machinery use single acting hydraulic seals. The preferred materials are super polymers like Oz Red Super Polymer (ORSP), Oz Monyt and Wifflon. These products have superior lubrications properties and are extremely durable.
2. Amusement Machines
The Brooklyn economy is supported each year with a $58 million contribution from Coney Island in New York. On average, there are 15 million visitors annually. If any of the amusement rides break down that is a huge loss in income. Rides have to shut down for repairs if seals fail so it is important to use proper seals. Fair ground rides use low friction seals and wipers in rubber, polyurethane or TMCF seals and wipers in control valves.
3. Automobile Manufacturers
Vehicle assembly departments usually use pneumatic rams on assembly jigs. Pneumatics are quieter and cleaner so it prevents leakage from contamination the surroundings. Polyurethane and rubber which are sound absorbing materials are effective for achieving significant compressed air savings.
4. Cheese Manufacturers
Manufacturing and packaging machines in the cheese industry use pneumatic seals, spring energized seals, wipers and guide rings. High pressure nitrile rubber (HNBR), Teflon, or wifflon materials are recommended for these machines.
5. Coal Mining Equipment
Underground machinery makes extensive use of hydraulics while pneumatics are used for roof support machinery. The use of high performance parts contributes to safety in the mining industry. High performance parts are needed so that there is little downtime and minimal maintenance required. HNBR and Oz Monyt are often used as they are high pressure materials.
6. Concrete Pumping
Concrete is heavy, abrasive, viscous, and contains pieces of hard rock and will solidify if not kept moving. Because of this, there are many challenges to designing concrete pumps. Dangerous blockages can occur if the pump system is not set properly. Specialized sealing and proper guided element replacement is essential. There are special designs by Oz seals that are suitable for hydraulic rams that are used to operate concrete pumping plungers and hydraulic rams on the boom.
7. Diecasters
In order to die cast, you force molten metal under high pressure into a mold cavity. You can use a hot-chamber die casting or cold-chamber die casting. HNBR and viton materials are used as they can withstand extreme temperatures; they are used on tamping and furnace rams. Polymer compatibility should be checked for possible HFA/FHB fluid compatibility since hydraulic or mechanical pistons may come into contact with fireproof liquids.
8. Earth-Movers and Excavators
Heavy earthmoving, excavators, dozers, and backhoe loaders require high performance oils seals and hydraulic seal kids. The heaviest user of high performance seals and reliable Oz wipers are the mining and construction industries.
9. Printers
The fast-paced publishing industry needs machine parts that are manufactured with high performance polyurethanes and rubber materials. This allows for greater speeds and higher productivity. Pneumatics such as Teflon seals with spring energizers are used for printing presses and packaging machines.
10. Textile Manufacturers
Textile machinery uses things like shaft seals, spring energized Teflon seals and mechanical seals. A high performance polymer such as ORSP or Wifflon is ideal for compact spinning, high pressures and constant rotation of the air rams.
There are several other industries that use high performance seals for various applications. To find out what you require for your industry contact the professionals at Real Seal and they will be able to assess your needs.
When there is motion between a hardware component and a sealing element, you have a dynamic seal. Dynamic seal applications vary greatly. The motion can be oscillating, rotary, or reciprocating. A valve stem seal may have a combination of more than one type of motion. The most common single component elastomeric seals are below.
Reciprocating Seals
Applications which involve a moving piston and/or rod will use a reciprocating seal. These seals constitute the predominant dynamic application for O-rings. For the best performance of reciprocating seals, you need to consider compound selection for thermal cycling, pressure shocks, squeeze, and stretch.
O-rings may not provide a leak proof seal if they have to take compression at elevated temperatures and then fail to rebound at a low temperature. Thermal cycling from high to low may causes havoc. In low pressure, reciprocating applications O-ring leaks may occur. When it is expected that there will be extreme operating thermal cycles, you will want a seal compound that will exceed the temperature range, resilience needs, and compression set.
Hydraulic components can create system pressures that exceed seal extrusion capabilities when there is sudden stopping and holding of high loads. Pressure shocks should be addressed and dealt with in order to prevent extrusion and the eventual O-ring failure. If it is required there may have to be accumulators or pressure relief valves built into the hydraulic system. You can also use back up rings or increase the seal durometer to prevent O-ring extrusion.
You can refer to the table for general guidelines. If there if lower squeeze that what is shown in Table A, friction is reduced but that could possibly cause leaking in conditions with low pressure. If there is greater squeeze, friction is increased providing a greater ability to seal but it makes assembly difficult. The seal will also wear more quickly and the potential for spiral failure is amplified.
An O-ring’s cross section is reduced when the I.D. of the O-ring is stretched. Make you consider the O-ring’s smaller cross section so that it maintains the correct squeeze percentage. The stretch, in most cases, should not go over 5%.
Rotary Seals
Rotary seals need to be designed to specifications for the intended application. You need to consider application temperatures, seal stretch, frictional heat buildup, squeeze, and shaft and glandular machining. With a rotary seal application, there is a turning shaft that protrudes through the I.D. of a seal component.
Applications that require operating temperatures lower than -40F or higher than +250F should not use rotary shaft seals. The O-ring will effectively seal when the application is close to room temperature.
Frictional heat will be generated so it is a good idea to have a seal composed of compounds that have the maximum heat resistance and minimal friction generating properties. Typically, internally lubricated compounds will be used for rotary applications.
I.D stretch has to be eliminated in rotary seal applications. The shat diameters need to be designed so that they are not bigger than the free state I.D. of the seal. Rotary or oscillating applications should have shaft seals with no stretch over the shaft. Seals can fail if an elastomer is stressed and there are higher temperatures. The seal will contract instead of expanding and this will increase the heat until the seal fails.
O-ring squeeze should be 0.002” by using an O-ring with an O.D. of 5% larger than the gland. Peripheral compressing will put the O-rings I.D. in contact with the turning shaft which will minimize friction heat buildup. This will prolong the life of the seal.
The experts at Real Seal can design the seal you need for any application. Contact them to find out how more about dynamic seal applications. Visit Real Seal online to see the products that they have available and contact them to discuss your needs.
What comes to mind when you think of the uses of plastic? Many people think of bags and packaging, plastic cutlery, containers, or other kitchenware, and toys. Not many of us think of sweaters, food, or wood furniture. Unbeknownst to many, all of these things are made from polymers; some are called plastics and some are not and the distinction can be arbitrary.
Plastics consist primarily of polymer molecules made of carbon. Similar to a bicycle chain, the links of the polymer are attached together. Polymers are a broad category that include plastics and silicones. Silicones are based on silicon rather than carbon. Polymers also include DNA.
The shape of polymers gives plastics their elasticity which allows them to be molded into shape. We have used naturally derived plastics for many years. In Mexico, the Olmecs played with balls made of rubber which is a natural polymer. They did this a millennium and a half before Christ. Uses of plastic go back even before the use by the Olmecs though. Wood contains cellulose which is a polymer that give plants tough cell walls. The cellulose gives wood its stiffness and durability. The long strands of cellulose are separated at pulping mills and that is what gives paper its strength.
Cellulose also provided the raw material for another breakthrough in plastic. Parkesine is a material that has been used in many products including cutlery, buttons, and combs. Two Americans took Parkesine and added camphor to it which made it more malleable and they renamed it celluloid. This became a raw material used in the film industry.
In the 18th Century, French explorer Charles-Marie de la Condamine discovered that there was a rubber tree in the Amazon basin. It was not until the 1840s that American Charles Goodyear and British born Thomas Hancock took out patents for vulcanized rubber – rubber which was treated with Sulphur to make it more durable.
Rubber also made electrification possible as it was used to insulate electrical switches. The big breakthrough which is considered the birth of modern plastics came in 1907 when Leo Baekeland invented Bakelite. Bakelite is one of the first plastics that is made from synthetic components; it was made from fossil fuels.
More synthetic plastics followed with polystyrene in 1929, polyester in 1930, polyvinylchloride and polythene in 1933, and nylon in 1935. The plastic industry grew during the war effort when they were used in everything including military vehicles and radar insulation.
Companies were building plants where they could turn crude oil into plastics. In 1948 new products such as Tupperware were becoming available.
Polyethylene terephthalate (PET) was a versatile product that was invented in 1941. It can be used to make many different things such as drink bottles, winter gloves, and plastic for packaging flowers. The only difference is the way the material is cast.
Properties and uses of plastics can be changed by altering their structure just a little bit. The plastic that a milk bottle is made of can be changed from polyethylene to polypropylene (a stronger material) simply by adding one carbon to it. The material made by adding a carbon can strengthen the plastic enough to make things like sippy cups for toddlers.
Some polymers are compostable and over months or years they will be broken down by microbes. Some plastics however do no break down and cause an environmental concern.
It may become more difficult to get plastics. Most currently come from oil and gas but these sources could run out and we will have to go back to using biological sources. Some plastics that have been derived from crude oil are now being produced from sugar cane.
Oil may become too expensive to use. At that point things may turn to industrial bio-technology for the manufacture of plastics.
Real Seal offers seal products and mechanical components. They are known for expertise in polyurethane materials but also have many performance oriented plastic and rubber solutions for sealing and mechanical applications. For more information on their products visit Real Seal on the internet today.
The Injection molding process is used to produce parts shaped via injecting material into a mold. It can be done with different materials but is most often done with thermoplastic and thermosetting polymers. A material to manufacture a part will be fed into a heated barrel, mixed, and then forced into a mold where it cools and hardens to the shape of the cavity.
Injection molding is used to create a variety of parts, from small pieces to car body panels. 3D printing technology is starting to be used for the process as well since photopolymers can be used in simple injection molds.
Parts that are to be molded have to be designed very carefully to make the molding process possible. Particular attention must be paid to the material used for the part, the shape and features of the part, the material of the mold, and the propertied of the molding machine.
Many things are created using injection molding. Wire spools, packaging, bottle caps, automotive parts and components are among some of the things manufactured using the process. It is the most common method used to manufacture plastic parts as high volumes of the same object can be made.
Injection molding has its benefits as a wide range of materials can be used and the labor costs remain low. Not a lot of scrap material is produced during the manufacture of parts and there is usually no need to do any finishing work to the parts.
Injection molding start up can be expensive to start because of the high cost of equipment and the running costs. Molds may cost a fair amount as well. But once a business is established the costs later on remain low.
There are many polymers that can be used for injection molding. In 1995, approximately 18, 000 materials were available for use in injection molding. That number was growing at a rate of approximately 750 per year. This allows product designers to choose a material that will specifically suit their needs. They will be able to find something that has exactly the right properties. Materials are generally chosen based on strength and function for the final product but each material’s molding parameters must also be considered.
Automotive Parts
Your vehicle is full of plastic components manufactured by injection molding. For example, the dashboard is, in all probability, made from plastic injection molding. Radio controls, window buttons, cup holders – they are all made using the injection molding process. There are exterior pieces of vehicles manufactured using the process as well.
Lids
All kinds of lids are made from plastic injection molding. Plastic bottle caps, plastic cup lids, pill bottle lids – all of these are made with injection molding.
Electrical Switches
Things we use every day, such as our light switch, have been made with injection molding. The whole electrical system in your home relies on plastic injection molding for consistently designed plastic components.
DVDs and CDs
Many discs are made through the process of injection molding. As well as the discs themselves, the cases are made via the process as well. Of course, the plastic storage stand was also mass produced using injection molding.
Medical Devices
Plastics are versatile, lightweight, sanitary, and replaceable so the healthcare industry relies heavily on the use of them. There are many medical devices that are manufactured using injection molding. Plastic syringes and some other medical implements can be produced using this process.
Real Seal manufactures and distributes seal products and mechanical components with a strong focus on performance oriented rubber and plastic materials. We are a full-service supplier of sealing and mechanical components, operating in hundreds of industries both nationally and internationally.
Water leaks are problematic for several reasons. Part of the problem is that you cannot see most of the pipework in your home so you do not always know that there is a leak or how to go about preventing water leaks. An undetected leak can mean water damage to your home and unwanted growth of mold.
If you want to protect your home from leaks, do regular inspections in areas where leaks are likely to develop. Keeping on top of the problem before it starts can save you a lot of hassle and keep your home free of water damage.
Following are some of the main problems to look for when you go through your home and that, if properly repaired, can be a useful measure in preventing water leaks.
1. Broken Seals
If you are noticing condensation on or near any of your appliances, you may have broken seals. When appliances are installed there are seals put around all the water connectors. Your dishwasher will also have seals on the door. When appliances start to get older the seals may break or wear out and they will need to be replaced.
2. Clogged Lines
Sometimes a clogged drain is only a minor inconvenience but if you end up with a serious clog, it can lead to overflowing or burst pipes. You can have some serious water damage if there are obstructions in handler drain pans or in your gutters. To avoid damage, it is important to keep your gutters and HVAC system clean.
3. Corrosion
Pipes can rust as they age and corrosion can eat away at them. If there is discoloration on your pipes or if they appear to be warping, you should call your plumber to assess the damage. You may need newer pipes if you have an old plumbing system that has started to corrode.
4. Damaged Pipe Joints
Over time, the joints where pipes connect can deteriorate and start to cause leaks. If you hear ticking and banging in the pipes, especially when you run hot water, your pipe joints may be under too much pressure. Again, you will want to have a plumber evaluate the situation before any major damage occurs. This is one of the most common areas where you can go about preventing water leaks.
5. Excess Water Pressure
It may feel nice to have a shower under high water pressure but extreme or uneven pressure can put a strain on your pipes. Most pipes and faucets are meant to withstand a certain amount of pressure and anything over that could cause leaking issues. A professional can measure your pressure for you if you feel it may be a concern.
6. Intruding Tree Roots
Believe it or not, some water leaks can start outside the home. If tree roots intrude on the water lines moisture can seep out into the yard. If you see wet patches or sink holes in your yard or notice a sudden drop in the water pressure you may want to have a plumber check for intrusion, especially if there are trees growing near your home.
7. Loose Water Connectors
If you have a hose or a pipe that supplies your appliances with water come loose, it can cause a leak. Water connectors can become loose due to shifting. It is possible that a washing machine hose could spring a leak due to shaking from the spin cycle. If you notice water running directly from a supply line or there are puddles around the appliance, check for a connector leak.
8. Rapid Temperature Changes
Pipes will expand and contract when there are extreme temperatures. This could cause the pipes to crack, especially if they freeze.
If you have noticed that you have a higher water bill than usual, a change in water flow, a musty smell, or other signs of a leak, Real Seal professionals can help you diagnose and solve the problem. If you notice your plumbing is not performing the way it should and are interested in preventing water leaks, it is important to have it taken care of quickly so that you avoid any excess water damage to your home.
Weather seals do not last forever on your doors. With time, they can rip, compress, bend, or just wear out. This will allow cool winter air to enter or your air-conditioned air to escape in summer. Luckily, sealing a doorway is a fairly straight forward DIY project. And of course, it is much less expensive than putting up a new door.
Even a small gap can be enough to cause a problem so you want to fix it as soon as you can. All a well-sealed door requires is some weatherstripping (covers the sides and top of the door) and a sweep (fills the space between the threshold and the door bottom).
Though there are an array of products available for sealing a doorway, many professionals like a system that includes tubular silicone weatherstripping and a twin-fin silicone sweep that fits under the door. Silicone is a good choice because it is both durable and soft and it has no compression memory. That means that it will stay tight as the door swells and shrinks. Explore this easy to follow guide to weatherstripping a door.
1. Measure the gap
Measure the gap that is between the door and the jamb and the door and the stop when the door is closed. Measure along both the side jambs and the head jamb. Choose weatherstripping that is big enough to fill the largest gap.
2. Cut a groove
Smooth out the stop and the jamb by pulling a paint scraper along them. Make sure the surfaces are free of any protruding nails or other debris.
Use a grooving tool and put the V-shaped base of it into the corner formed by the jamb and the stop and point the bit up. With the motor on, push the tool up to the head jamb. This will create the slot for the weatherstripping. Repeat the same process on the opposite side.
You can clean out any wood chips or debris left behind with a flat head screwdriver.
3. Insert the weatherstripping
Push the barbed tongue of the weatherstripping into one end of your slot. Work the stripping up the slot being careful not to stretch it. When you a couple of inches from the end of the slot, gauge the length of your weatherstripping and trim it with a pair of scissors. You do not need to miter the ends of the weatherstripping as a butt joint will give you the best seal.
Use a spine roller to push the weatherstripping into the slot. You can check your installation by closing the door from the outside and looking for any gaps.
4. Rout the dado
You need to seal the door bottom as well. Place the door on sawhorses and with a square, mark out a 5/8 inch wide dado in the center at the bottom edge of the door. Set your router’s guide so that a ½ inch bit will cut next to the top mark when the guide is resting on the door’s top face.
The first time, move the router from left to right. The second time, the guide will ride on the door’s opposite side and the router will move from right to left. Pass the router back and forth multiple times until you reach a depth of 1 1/8 inch.
5. Attach the channel
The exposed wood in the dado should be primed and painted at this point. Next, cut the sweep’s two aluminum channels about 1/8 inch smaller than the width of the door. This will allow room for the end caps later. To get a clean cut, clamp the channels in a miter box and use a hacksaw with a waxed blade. Put one channel into the dado and center it end to end before screwing it in place.
6. Install sweep
Fit the black silicone sweep into the free channel and then slide the glides into the channel I the dado. Hang the door up before installing the sweep to avoid any damage to the sweep. Make adjustments to the glides until you cannot see any light between the threshold and the sweep when the door is closed. Snap plastic caps into the ends of the channel and put squares of adhesive-backed pile against the bottom of the jambs.
7. Adjust the glides
The glides are the secret to the sweep’s adjustability. They allow the sweep to lift or lower by about ¼ inch. Open the door to adjust the fit. Remove the end cap of the latch slide and slide out the sweep. Turn the glides clockwise to raise the sweep and counter-clockwise to lower it and then slide the glides back into the attached channel.
If you would like more information on sealing a doorway so that they are not letting air in or out, contact the professionals at Real Seal for the best professional advice.
Boat window leaks will lower the value of your watercraft. Boats that are of high quality construction still eventually develop leaks because boats are not rigid structures. Boats twist and flex making it possible for water to get in. Sometimes the owner puts caulking around the window frames to try and prevent further leakage. This will make a mess of the boat and it also a waste of time as surface remedies will not fix the problem.
Boat window leaks usually occur when the seal between the window frame and the fiberglass of the boat is broken. Breaks in the seal can be undetectable because they are so tiny. Water can still be drawn into really small cracks and water will continue to leak in. Water may enter at one point and come out somewhere other than the source of the leak.
Aluminum window frames on boats are usually the major source of leaks. Here are some things to look for before you start trying to fix a leak:
• The window frames are all that holds up the flying bridge
• The side decks are weak. The deck and house side pull away from the window frame when you are walking on the side decks.
• The frame is not channelized, but consists of just the frame and glass clamped against the house side with screws.
You have to use non-hardening caulking so that it will move when things expand. You will have to remove the frames, re-bed them and refasten them making sure they do not fit as tightly as when they were first installed.
Use non-hardening silicone epoxy and 3/32” shims so that the frame is not completely flush. Draw the frame tight against the shim and let the caulking set for about a week before pulling out the shims. Once you pull out the shims, fasten things a little more tightly so there is a gasket for the frame to be drawn up against.
Removal
Completely remove the frames and clean all surfaces before you apply the bedding. You can use acetone to make sure it is sufficiently clean. If you notice any corrosion, sand it off.
Bedding Glass
If water is leaking under your windshield, you have to remove the glass and re-bed it. Remove the glass and clean the channel and the frame where the glass sits. It is important to get all debris and corrosion removed so that your efforts are not in vain.
When you are ready to reset the glass, use silicone based window glazing that is specifically designed for this purpose. Use an alcohol based glass cleaner to clean the edges of the glass – Windex will work. Place the window and press it firmly into position so that any excess silicone will be squeezed out. Once it is cured you will trim the excess silicone away with a razor blade.
Go to the exterior and place shims under the bottom edge of the glass so that it will not rest on the bottom of the frame. That way if the frame moves, it should not affect the glass. Allow the bedding to set overnight and then you can apply the final glazing to the exterior. Snap-in exterior moldings should not be put on until the next day so that you do not disturb the position of the glass. The idea is to create a free-floating window pane to allow for some movement without resulting in leaks.
For more information on how to deal with boat window leaks, contact Real Seal to speak with their professional staff.
As the most commonly used seals in almost every industry you can think of, from chemical processing, fluid power, and aerospace, to life sciences, pulp and paper, as well as energy oil and gas, O-rings are used vigorously every single day. Yet, more often than not, most users don’t even realize that one might be damaged until the O-ring actually starts to leak. One of the most common causes of leakage in O-rings is ozone cracking, or “ozonolysis,” which occurs mostly with O-rings made from nitrile rubber.
On the manufacturing floor, ozone cracking can be a mere source of aggravation, but when in the field, it can cause leaks that lead to serious incidents of death or injury. Fortunately, this phenomenon of crackage and leakage is highly preventable, just as long as you understand the causes of why it happens and how to take certain measures to combat it.
Why an O-Ring Fails
Within the service field, the failure of an O-ring can usually be attributed to a combination of causes. First and foremost, it is important to maximize sealing life and reliability by reducing the probability of seal failure at the onset by using good design practices, proper compound selection, pre-production testing, and continued education and training of assembly personnel.
As mentioned, Ozone cracking occurs mostly with O-rings made from nitrile rubber (or with material most recognized as nitrile, buna, or buna-N).
This material is called a polymer, which is Greek for “many units,” with each molecule consisting of individual units that are bonded together into a long chain. Sometimes, the links in a nitrite polymer chain can develop “weak spots” and become broken due to oxygen atoms contributed by the ozone. Hence, polymer chains can literally be cut, forming a tiny crack in the O-ring that continues getting bigger and bigger until the damage is large enough to be seen with the naked eye.
Preventing Ozone Cracking in O-Rings
Since oxygen is ever present in the air that we breathe and is necessary for life on Earth, its presence among O-rings is quite inevitable.
Oxygen atoms typically join up in pairs, forming dioxygen, which go on to make up the vast majority of oxygen in the atmosphere. When oxygen atoms join in groups of three, an ozone substance is created in the air we breathe, which can not only cause health problems, according to the EPA, but can also cause ozone cracking in nitrile O-rings even at the very tiniest of concentrations levels.
In general industrial applications, the primary drivers of ozone concentration are ultraviolet light, electrical arcing, and electromagnetic fields (which are the main reasons for higher ozone concentrations in the stratosphere), so in order to prevent further O-ring cracking or damage to occur, it is vital to:
• Keep O-rings away from ultraviolet light when storing, as the most common sources are direct sunlight, and fluorescent light bulbs.
• To not store O-rings within six feet of an electric motor (or other potential sources of electrical arcs).
• To not store O-rings in a stretched state because O-rings typically need to be stretched for ozone cracking to actually occur.
Further, when installing O-rings, remember to assemble nitrile O-rings wet with a grease to protect from ozone and to install them into the mating part within 24 hours of installing the O-ring on the fitting. If O-rings have no choice but to be stored in a stretched state, remember to store them in an airtight bag until ready to use.
In applications where long-term environmental exposure is inevitable, it is also recommended to make use of ozone-resistant material, such as HNBR, EPDM, or fluorocarbon.
For additional information and resources regarding the causes of O-rings cracking and how to combat it, contact Real Seal today.
