Tag Archives: rotary

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.