Eclipse Engineering

When it comes to maintaining a high-functioning rotary shaft, you need to select the appropriate lip seal.

The shaft seal protects the rotary shaft from contaminants such as dust and dirt, and it keeps water out and lubricant in.

A rotary seal, also known as a radial shaft seal, typically sits between a rotary shaft and a fixed housing — such as a cylinder wall — to stop fluid leaking along the shaft. The rotary seal’s outside surface is fixed to the housing, while the seal’s inner lip presses against the rotating shaft.

Common applications for shaft seals include motors, gear boxes, pumps and axles. They’re also increasingly used for food and chemical processing, as well in pressurized gas applications.

Three of the most important considerations when the choosing the best lip seal for a rotary shaft are:

1. The material the seal is made of,
2. the hardness of the shaft’s surface, and
3. the roughness of the shaft’s surface.

Here’s your quick go-to guide on how to achieve optimum performance and longevity for your seals and shafts, ultimately minimizing the risk of seal failure. Presented by our partners at Eclipse Engineering:

Back-up rings serve an important role in world of seals. While the design principle and construction are incredibly simple, they greatly extend the usefulness of the most common and prolific sealing device in the world: the O-ring.

Back-up rings are aptly named as they do just that: they back-up an O-ring.

Back-up rings are commonly nothing more than a ring of polymer meant to space the O-ring away from the extrusion gap in hardware. By blocking off the extrusion gap, the pressure-handling ability of an ordinary O-ring is greatly increased.

Solid or split back-up rings out of virgin PTFE can usually be found on the shelf, and are largely considered commodity items.

While the design and functionality of a back-up ring rarely changes, the material selected can greatly complicate this simple device. Some applications require specific material properties and/or special material certifications.

Back-up rings can be made for a variety of unique applications;: Military-spec back-up rings out of fully certified AMS 3678/1 virgin PTFE; Certified “MS” style back-up ring (MS27595 or MS28774); PTFE blends; Thermoplastic elastomers; Urethanes. But the most common custom material for back-up rings is usually PEEK (polyether ether ketone).

In certain applications, PEEK has some distinct advantages as a back-up ring material. But with these advantages comes some potential issues.

Read on if switching from a PTFE to a PEEK back-up ring sounds like an enticing proposition to see what you need to consider before making the change.

Eclipse has been working hard during the Covid-19 downtime on finding solutions to issues that customers have brought to the table over the past few years.

Many new designs have been sent into testing while focusing on processes that will help improve productivity and lower costs.

The MicroLip™ is an example of a viable solution to rotary seal issues that many customers have struggled with. This is especially true when the order volumes are relatively low or the shaft diameters are small, such as with encoders or chemical-processing facilities.

The Eclipse MicroLip™ Prototype Program

When moving from rubber to Teflon lip seals, Eclipse has found that the cost to bring the product to market is often a hindrance. The high cost is due to tooling and the number of pieces that must be manufactured to make the product viable in the prototype phase.

Because of this, many customers sneak by using inappropriately-applied rubber lip seals to solve rotary seal problems.

MicroLip™ seals have proven to be a powerful component in rotary services. Since the MicroLip’s inception, it has been applied to a variety of applications including mobile hydraulics, robotics, surgical drills, and semiconductor processing and encoders.

Over the last 3 years, Eclipse has designed and manufactured various styles of MicroLips in diameter sizes of under 1/8 inch (5mm) and over an inch. Since the components of the MicroLip™ can be machined, Eclipse has made the seal in quantities of less than 10, and batches in the thousands.

When designing for low temperature sealing, the first step is to define the temperature range that the seal will be operating in.

Typically, cryogenic as seals are those that are operating below -65 Fahrenheit. Gallagher's partner, Eclipse, chooses this benchmark because they currently have elastomers that have a usable TR10 value at this temperature.

When designing at this level — with high temperatures around 300 Fahrenheit — an understanding of what level of leakage control is required on the low temp end. Seals that operate in aircrafts must function within this range.

However, there may be an allowable leakage rate which allows for reduced drag. When requiring zero leak, the drag in the system is often increased to support some elastomeric contact with a dynamic surface. In the case of static seals, elastomers span this range although increased squeeze may be necessary.

Eclipse Engineering routinely designs in the range indicated above.

While -65 Fahrenheit is extreme cold, it's not considered cryogenic. Liquid nitrogen at -320° Fahrenheit (-195°Celsius) requires special hardware and seal material consideration.

To begin, many projects and applications don't utilize lubricant in dynamic applications. To improve sealability, a better-than-average surface finish is required.

Surface finish often holds lubricity. But without this, a smooth finish reduces friction, improves life, lowers drag, and improves sealability.

Static seals are often required to have leak rates approaching zero; meaning hardware considerations and surface can be even more important. This may mean polishing the groove, which in some applications can be very challenging.

Cryogenic Seal Materials

The next criteria are the seal materials. Elastomeric materials lose their flexibility at these extreme temperatures, so Eclipse relies on polymer-type materials to bridge the gap. When we experience temperatures below -180° Fahrenheit ( -195° Celsius), that's when it becomes wise to move away from basic PTFE to modified fluoropolymers such as PCTFE, known for operating down to -460 Fahrenheit.

The coronavirus has prompted all of us to do everything we can to protect ourselves from catching and spreading the virus. We are all taking important safety measures to maintain a clean and uncontaminated home environment, and limiting our exposure to a potentially hazardous outdoor environment.

In this blog, our partners at Eclipse will be examining the role that seals play throughout a pandemic. The very role of seals is to keep a certain environment in, and certain environment out, similar to how we are living these days.

In Eclipse's last blog, they wrote about boundary seals in aircraft and how seals allow the aircraft to be pressurized. In the research lab, a different style of boundary seal is required to keep the outside environment out.

Labs all over the world are working toward preventing the spread of coronavirus. Scientists are working with test equipment to find a cure and a vaccine to prevent not just the spread of this virus, but other viruses which we’ve not yet seen.

When we design seals, we must consider keeping something as small as a single cell from entering a test chamber. Last week, Eclipse received a call directly from a customer building a prototype ventilator to be built in volume to help support patients suffering from coronavirus.

The client requested that Eclipse's engineering and manufacturing team turn an 8-inch (203mm) seal around from concept, design, and finally produced and shipped in less than 4 hours — and they made it happen.

Keep reading to explore the important role that seals play in research equipment as scientists seek to find the cure for coronavirus and beyond.

Boundary seals that help keep a certain environment sealed in while keeping the world out are everywhere.

If you look around your home, you may be surprised to see there are seals surrounding every door — and not just at the bottom. Your oven, microwave, and of course refrigerator door all have seals around them.

All these seals are different, yet they perform the same function. Your microwave is especially interesting, as its primary purpose is to keep microwaves from escaping the chamber that’s cooking your food. Your refrigerator seal has a magnet built into it, which keeps the door sealed shut.

Boundary seals are also found in many cell phones and electronic devices, keeping them water-resistant or water-proof (depending on the manufacturer). And in the industrial world, we have seals to create explosion-proof boxes in hazardous environments. The simple O-ring is found at the end of every cylinder cap to keep fluids in and the environment out.

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Eclipse Engineering has in-house capabilities to manufacture seals up to 55 inches in diameter, and over 100 inches through production partners.

While seals with huge diameters certainly grant their own significant levels of intricacy, here we’ll look at the other end of the spectrum: the micro-sized seals.

We won’t just look at a simple seal ring, but an inherently more complicated and geometrically detailed spring energized seal. As we’ll see, very small diameters make multiple manufacturing aspects more involved and challenging.

The Client’s Issue

A sealing solution in a customer's epoxy dispensing equipment. They needed an effective seal for the reciprocating rod responsible for the flow-control and metering of the epoxy while being dispensed.

Operating Conditions:

• Reciprocating Rod Seal
• Epoxy Dispensing Head
• Rod Diameter: 1.2mm [0.047”]
• Stroke Length: 6mm [0.236”]
• Cycle Rate: 15 per min
• Media: Epoxy
• Operating Pressure: 1,500 PSI
• Temperature: 70° to 150°F

In general terms, most viscous media sealing solutions have three things in common:

1. A variant of UHMW for the seal jacket,
2. heavy spring loading, and
3. multiple point contacts with increased interference.

In most cases, multiple nested V-Springs are incorporated to provide optimal load and energize the compound contact points on the seal. With this formula, we’ve had great success sealing media like epoxy, urethane, silicones and acrylics.

The heavy loading is necessary to effectively wipe the reciprocating rod. This is balanced with the correct material and design geometry to provide long wear life of the seal, which has the potential to be compromised under such loading.

The challenge in this case was to incorporate these same proven principles in a micro-sized seal.

The Eclipse Solution

Back in the mid 70’s, an engineer named Roy Edlund of Busak & Luyken designed a high-pressure seal that had an uncommon effect of rocking in the groove. This action occurred when pressure was created on the retract side of a cylinder as the rod was being retracted into the cylinder.

The material used for the seal was generally a bronze-filled Teflon, which could resist extrusion and have a long seal life. Because the seal ring was made from a grade of filled Teflon, a small amount of oil would leak under the lip as the cylinder was being extended.

One of the most unique features of this style seal was that as the rod was being retracted back into the cylinder, the buffer ring would rock or rotate slightly to the low pressure side thereby forcing leaked oil back into the retract side of the cylinder under the buffer ring.

This seal is commonly called a Buffer Ring (for reasons we’ll explore in this blog), but this seal helped usher Teflon into most high-pressure hydraulic systems today.

Pre-Buffer Ring Sealing Problems

Manufactures of high-pressure hydraulic systems in equipment, such as back hoes or hydraulic cranes found that their products were having seal failures prior to reaching warranty. This resulted in downtime and large warranty expense to repair these cylinders in the field.

In normal operations, the standard U-Cup made from a variety of Urethanes did an excellent job of creating a “near” zero leak sealing system. The problems would occur as the “bulk” oil temperature rose due to usage, pressure spikes in the system would cause premature failure of the Urethane U-Cup.

It was the pressure spikes that usually wreaked havoc with the U-cup seal design, causing the urethane to break down and eventually crack, creating a leak, and resulting in equipment shut-downs.

The Buffer Ring Solution

The Buffer Ring turned out to be the answer. By adding another sealing element in front of the Urethane U-cup, the life of the U-cup was greatly extended, overall friction in the system was reduced, and the bulk temperature in the hydraulic system was lowered.

All these advantages came by adding a sealing element. The true savings showed up in dramatically improving equipment up time. This also reduced warranty costs of equipment to the OEM.

How Does the Buffer Ring Work?

The answer to this question was initially difficult for many manufacturers to understand. Normally, putting one seal in front of another should cause a pressure trap, sending pressure loads much higher than relief valve settings, which locks up the cylinder.

The secret was in the way the Buffer Ring performed its job.

The seal leaking is very important to its design. If oil didn’t reach the U-Cup, the U-cup would generate heat and begin to wear out prematurely. So, since the Buffer Ring allowed a small amount of fluid to seep under the lip, this fluid lubricated the U-cup and kept its friction to a minimum.

Being elastomeric in nature, the U-cup did an excellent job of wiping the rod nearly completely dry.

But what about the pressure trap?

The Buffer Ring and its unique quality allowed fluid back into the system. Testing verified that this would happen anywhere from zero to about 100 PSI.

The U-cup spent most of its life in a well-lubricated, low-pressure / low-temperature environment compared to the original design.

The Buffer Ring also made suppliers of U-Cups extremely happy, as their failed seal had been given new life compared to the holes blown through the back of their urethane product.

Springs are an integral part of all sealing systems. A simple air cylinder has O-rings to seal in the air, and the O-ring exhibits spring-like qualities to ensure a good seal over a broad temperature range.

But what are the different types of springs and materials in sealing systems? And how do you choose the best for your application?

Metal Springs

Metal springs, such as the Cantilever and Canted Coil spring, are used to energize polymers such as Teflon and ultra high molecular weight polyethylene (UHMW) to allow sealing in a wide range of temperatures. Selecting the correct spring material is critical to the life of the seal.

Metal energized

Better known as Teflon in the industry, Polytetrafluoroethylene is widely used in practically every industry on and off the planet (and even beneath its surface!)

Medical Uses

This material’s primary claim to fame is its resistance to most chemicals. It inherently has an extremely low coefficient of friction, it’s easily machined from rods, tubes, or compression-molded shapes.

It’s one of the few polymers that are approved for medical implants due to its inertness to bodily fluids — the immune system principally ignores its presence in the body.

Moving away from the body, you’ll find PTFE or Teflon products in medical