Tag Archives: rotary

5 Polymer Bearing Configurations and Their Advantages

Polymer BearingPolymer wear rings were developed to offer an alternative to dissimilar metal wear rings.

One of the advantages to using a polymer material such as nylon or filled-Teflon instead of a metallic bearing . Whereas when you use bronze or metallic bushings, these materials are prone to point loading on the edges of the bearing.

This property of polymer bearings combined with solid lubricants can yield a product that is much less likely to damage moving components.


5 Advantages to Polymer Wear Rings

  1. Polymer style bearings can be held to very close tolerances in the radial dimension to provide support without excessively opening the extrusion (E) gap by a large amount. Polymer bearings such as filled Teflon can support a compressive load up to 1000 PSI. Nylons up to 36,000 PSI and polyester fiber with resin, up to 50,000 PSI.
  2. Hydraulic cylinders that are found in excavators often use higher compression materials because they experience extreme side and shock loads. However, most applications do very well with filled Teflon materials.
  3. Bearings come solid or split. If designed properly, split bearings provide equivalent support, while improving installation options with no compromise in performance. Solid bearings, or bushings, are convenient when installing on the outboard side of a rod groove. Split bearings are essential when installing in a piston groove designed to function internally in a system.
  4. Nylon or composite bearings are typically cut to allow for installation due to their stiffness. However, a Teflon bushing can be made into a ring, or cut from a roll of sliced strip.
  5. The only time a bushing needs to be cut from a ring is if installation does not allow the strip to be deformed for a clean install. Strip installation allows for variability in length, lower manufacturing costs, and the product can generally be acquired off the shelf.

Materials for Polymer Bearing Configurations

When selecting materials, we must consider the maximum load, the speed of the system, and whether there is any lubrication in the system.

The load (or pressure over area) that the bearing will see is the first consideration. This dictates which materials will be the best fit.

It’s important to use a material that has a minimum compressive strength rating so that it will not fail under the highest loading condition. The industry standard is to employ a safety factor so that the bearing is specified to be used well beyond its design limit.

Teflon should be your first consideration due to cost and ease of installation. Nylon or composites will provide much higher load rating, but the cost and installation need to be considered.

Teflon and composites provide service without lubrication, and the composites provide excellent service in aqueous solutions. Bushings are typically used in medium to slow reciprocating service. Rotary creates challenges that may or may not work depending on the design of the bushing.

There are many series of injection molded nylon bushings. However, nylon in low-lubrication or high-loading may create high-friction, and can be noisy. Nylon, as a low-cost bushing, can be used in some high load situations.

A final consideration before going into large scale production is the cost of taking a bearing design into high production. Some bearing materials are expensive and can only be processed by machining, which limits the cost reduction scenarios at high volumes.

Eclipse Seal

Materials such as filled-PTFE or thermoplastics that can be molded offer cost competitive solutions for high-production applications. Eclipse provides bearings in everything from low-quantity applications, such as bridges and dams, to mid-quantity applications in aerospace.


Gallagher Fluid Seals is a preferred distributor of Eclipse Engineering. Call us at 1-800-822-4063 for more information on Eclipse seals.

Article written by Cliff at Eclipse Engineering, Inc. For the original article, visit their website.

What to Know, Avoid, and Consider When Planning Seals for Medical Devices

Seals are one of the most important components in many medical devices. While small in cost, seals for medical devices have a profound affect on the function of said device and the outcome of a medical procedure.

Engineered sealing solutions have advanced to meet the new medical device designs due both to new materials and to new processes for producing these seals. An understanding of the fundamentals of seal design, the tools available to assist in the manufacturing process and pitfalls to avoid will help in achieving a successful seal and medical device outcome.

Classifying the three basic seal designs

When approaching a new seal design, It is important to classify the seal based on its intended function. All seals fall into one of three distinct groups. While certain applications may combine more than one group, there is always one that is dominant. The three basic seal designs are:

Static — seal applications where there is no movement.
Reciprocating — seal applications where there is linear motion.
Rotary — seal applications where there is rotation.
Static seal applications are the most common and include those that prevent fluids and drugs from escaping into or out of a medical device. The seal design can range from basic O-rings to complex shapes. Static seals can be found in the broadest range of medical devices from pumps and blood separators to oxygen concentrators.

trocar design
New advances in trocar designs incorporating specialized seals allow multiple instruments to be inserted in the single trocar.

A reciprocating seal application with linear motion would include endoscopes that require trocar seals. These trocar seals are complex in design and allow the surgeon to insert and manipulate instruments to accomplish the medical procedure. These procedures range from relatively simple hernia repairs to the most difficult cardiac procedures. All of these minimally invasive surgeries employ endoscopes with seals that rely on seal stretch, durability and ability to retain shape during lengthy and arduous procedures. This particular seal application combines both reciprocating and rotary motion with the main function being linear motion.

A rotary seal application most commonly includes O-rings used to seal rotating shafts with the turning shaft passing through the inside dimension of the O-ring. Systems utilizing motors such as various types of scanning systems require rotary seals but there are many other non-motorized applications that also require rotary seals. The most important consideration in designing a rotary seal is the frictional heat buildup, with stretch, squeeze and application temperature limits also important.

Function of a particular seal design

What is the function of the seal? It is important to identify specifically if the design must seal a fluid and be impermeable to a particular fluid. Or will the seal transmit a fluid or gas, transmit energy, absorb energy and/or provide structural support of other components in device assembly. All of these factors and combinations need to be thoroughly examined and understood to arrive at successful seal design.

A seal’s operating environment

In what environment will a seal operate? Water, chemicals and solvents can cause shrinkage and deformation of a seal. It is important therefore to identify the short and long term effects of all environmental factors including oxygen, ozone, sunlight and alternating effects of wet/dry situations. Equally important are the effects of constant pressure or changing pressure cycle and dynamic stress causing potential seal deformation.

There are temperature limits in which a seal will function properly. Depending on the seal material and design, a rotary shaft seal generally would be limited to an operating temperature range between -30° F and +225°F. To further generalize, the ideal operating temperature for most seals is at room temperature.

Expected seal life – How long must the seal perform correctly?

Continue reading What to Know, Avoid, and Consider When Planning Seals for Medical Devices

Vesconite Sliding Wear Plates Operate Beyond 1300 Hours

Test-work on Vesconite polymer sliding wear plates have shown promising results on a crawler drill that is employed at a zinc project in the Northern Cape, South Africa.

The wear plates were installed on the rotary head slide of a drill that carries out exploration drilling at the mine from which the goal is to exploit one of the largest zinc orebodies in the world.

The rotary head moves the drill into the ground for deeper and shallower drilling. It also allows the drill to be changed.

Since the rotary head moves approximately 120 times a day, wear on the slides has been considerable, and the original-equipment-manufacturer’s (OEM’s) nylon wear pads were only lasting 500 hours.

As a result, the OEM crawler drill supplier involved in the zinc project sought a solution to extend the life of its wear pads and investigated other wear-resistant materials that could cope with highly-abrasive materials such as chrome and silica that come in contact with the pads.

Vesconite Bearings technical representative Phillip de Villiers recommended the use of Vesconite in the application to improve the total wear life of the slides.

The OEM equipment supplier reports that the Vesconite polymer wear plates have lasted more than twice as long as the OEM nylon wear pads – more than 1300 hours of operation to date. They will continue to be used and the wear life will be closely monitored in comparison with the nylon OEM parts.

The wear life will be tested and proved on the 10 wear plate picture of wear padsassemblies, which is comprised of 20 separate wear plates on the crawler drill.

On a separate application on the crawler drill, Vesconite wear plates have also been employed on the boom slide. This is the rear part of the crawler drill. It is moved and adjusted to the drilling height, and provides stability to the drill. This boom moves roughly six times a day, so the wear is not nearly as considerable as the rotary head slide.

However, with the previously-installed OEM nylon slides lasting 1000 hours on this application, there was still a need to improve the lifespan of these slides.

The OEM equipment supplier hopes that the Vesconite will last much longer than the 1000 hours of the OEM material.

With low wear on the 6 Vesconite assemblies, comprising of 12 wear plate halves, early indications are that the Vesconite will also perform well in this application.

The equipment supplier imports crawler drills from Korea for resale, and also supplies parts for these and other drills that are used in mining-exploration drilling and borehole water drilling.


Gallagher is a distributor of Vesconite products for all industries.  If you have questions about using Vesconite in any application, contact our engineering department.