Difficult seal applications come from all industries and sectors of the economy.
While far-reaching operating conditions certainly consume their fair share of engineering hours, often one constraint also probes the boundaries of sealing technology and design ingenuity: limited hardware space.
A manufacturer was using a pneumatically actuated cylinder to dispense a chemical in a production process. The piston was drawn back in the cylinder thus filling it with the chemical product. The piston was then pushed forward to dispense the chemical out of a nozzle.
Polytetrafluoroethylene (PTFE) resin is a highly effective material for seal consumers due to its extremely low friction, high heat tolerance and chemical inertness.
With the right additives, PTFE resin can perform even better in terms of strength, thermal performance, chemical resistance and abrasion.
However, there are a few design considerations when using PTFE resin, particularly when combined with glass fiber and bronze.
This blog will examine PTFE fillers to enhance PTFE performance.
Clean-in-place seals, or CIP seals, were developed to allow a seal to remain in place. This is especially important when the seal gland is partially open, allowing the seal to be flushed of debris.
In a food application, the same chemicals used to clean or flush the system would be used to clean the seal gland. Similarly, when other products such as pharmaceutical or adverse chemicals needed to be flushed, the CIP seal does an excellent job being open to flushing.
When it comes to designing dynamic seals, the two most important application parameters are the pressure and the speed of the motion. These two factors chiefly determine the type of seal, design geometry, and seal materials you should choose.
When dynamic speeds and system pressures become elevated, determining the life expectancy of the seal becomes an important point of analysis. A seal that’s low friction, cost effective, and seals outstandingly is useless if it only lasts a few hours before wearing out.
To quickly gage the feasibility of a seal’s performance and provide a b
If you have an application with a rotating shaft, you likely need a seal. Rotary shaft seals often take the form of what is commonly known as an “oil seal.” These usually consist of an elastomeric sealing lip, with a molded-in-metal case to facilitate a press-fit into the hardware.
Oil seals are typically mass-produced, and are usually available from stock in a variety of sizes. They function best in oil-lubricated environments, such as engine crankcases or gearboxes. But in dry running applications, you may need a PTFE-based sealing element.
In addition to not needing lubrication, PTFE lip seals provide a number of advantages over elastomeric oil seals. PTFE’s ability to handle much higher temperatures means higher rotational speeds can be achieved.
High-wear fillers can be added for much longer service intervals when compared to elastomers. Friction characteristics will also be far superior therefore lowering torque requirements.
As more and more modern applications turn to electric motors rather than internal combustion engines, the need for low-friction, dry-running rotary shaft seals is growing. Most motors require an environmental shaft seal to keep dust, water, and debris from entering the internals.
There are two main designs for incorporating a PTFE seal element into a metal case. The first is what our partners at Eclipse call their Crimped Case Seal (CCS). The second is the more traditional componentized design.
Both have pros and cons. Below, we’ll discuss what applications might better suit one design over the other. With the ability to offer either design, Gallagher Fluid Seals and our friends at Eclipse can help provide you with the best solution possible.
Picture this: You have an application using a standard O-Ring. The O-Ring seals great, but is wearing out very quickly, and friction is far exceeding the goals of the system.
You retrofit a fancy PTFE spring energized seal that costs 1000 times more than the O-Ring…only to find out it leaks!
Did you get a defective seal? Is the seal designer incompetent? Is the raw material bad?
Actually, everything about the design and manufacturing of the spring energized seal could be perfect, and you could still find yourself with leakage.
While blaming the seal might be your first instinct, the leakage in fact, could have nothing to do with the seal itself, and everything to do with the surface finish of the hardware it’s trying to seal against.
Below, we’ll explore how Teflon is processed for sealing purposes, and why we sometimes see variation in surface quality and/or cracks in finished Teflon seals.
There are different grades of Fluoropolymers that can be used to manufacture seals. There are melt processable fluoropolymers, which are rarely used in the seal manufacturing process due to cost, and granular PTFE.
Melt processable fluoropolymers allow for injection molding, and exhibit many of the same characteristics as granular PTFE. But the first grade doesn’t allow for the flexibility of molding and machining, which is why most of our seals are made from granular PTFE.
When considering polymer jacketed seals — especially PTFE-based products — some form of energizer is typically required. These types of seals are usually specified to operate both in very high pressures, low pressures, or even in a vacuum.
At certain pressures (typically above 100psi), the system pressure will energize the seal and prevent leakage. But at low pressures, additional energy is required to force the jacket material to mate with the hardware.
The solution to this is to add a spring to the seal. The spring provides the needed sealing-energy to prevent leakage at low media pressures.
When considering a high pressure-application, there are start/stop conditions where the system is at low pressure. If the seal allows some amount of leakage at low pressure, it becomes possible for that leakage level to increase once as the pressure builds.
This phenomenon is called “blow-by.” Once it occurs in a system, it’s difficult to get the seal to seat and seal correctly.
There are several types of energizers to consider when specifying a seal. These can be as simple as an O-Ring or some other elastomer.
“How much pressure can this seal handle?”
The answer to this question depends on a number of parameters and conditions. But the principle limiting factor in the pressure handling of any seal system is the extrusion gap.
Commonly referred to as the “E-Gap,” the extrusion gap is one of the most critical design aspects in any high-pressure application. Seal design, type, and material are all influenced by the extrusion gap and the desired pressure handling capability.
What exactly is an extrusion gap, and why is it so important in the successful design of a sealing system? Let’s find out.
In terms of sealing systems, the extrusion gap is defined as the clearance between the hardware components.
In a piston configuration, this would be the clearance between the piston and bore. In a rod configuration, this is the clearance between the rod and housing it’s passing through.
The extrusion gap can be expressed in terms of radial or diametral clearance, which can lead to some confusion. Our partners at Eclipse define the E-Gap by stating it as the radial clearance. The radial clearance is equal to the diametral clearance divided by two.
It’s important to note that while hardware components might be machined to have a specified clearance, this gap might not be perfectly realized or maintained.
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:
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: