by Denise Sullivan Denise Sullivan No Comments

Rotary Shaft Mating Surfaces: What You Need to Know

 

rotary shaft mating surfaces

Rotary seals are essential to maintaining the life of the equipment. While choosing the appropriate rotary seal materials, the rotary shaft mating surfaces are equally important. 

Below, we will discuss rotary seals, materials used for seals, and rotary shaft properties.

Rotary Seals

Rotary seals work to help keep the system lubricated while excluding contaminates. A properly fitting seal can positively impact the life of the lubricant. Oil’s life span at 86°F (30°C) is 30 years. However, as the oil heats up, the life span diminishes rapidly to no more than a 30-day life span.

The addition of contaminants and water also limits the life of the oil and the ball bearings. For example, adding .002% water into the oil lubricant will reduce the ball bearing’s life by 50%. The cause of the ball-bearing integrity loss is called hydrogen embrittlement.

Common Materials Used for Rotary Seals

Rotary seals come in several different materials. The optimal choice is dependent on the environment in which it is used. The most common materials include nitrile rubber, polyacrylate rubber, fluoroelastomers (FKM), and PTFE.

While these materials are a good choice for rotary seals, conventional rubber seals are common in static applications where temperature and chemical compatibility are not a concern. PTFE is the solution in high-speed dynamic service requiring low friction seals or where exposure to severe temperature or chemicals exists. There are different types of PTFE used for rotary shaft seals.  Users can choose from 

  • Virgin PTFE
  • Molybdenum Disulfide Filled PTFE (MoS2)
  • Carbon Filled PTFE
  • Carbon and Graphite Filled PTFE
  • Carbon and MoS2  Filled PTFE
  • Glass Filled PTFE
  • Glass and MoS2  Filled PTFE
  • Polymide Filled PTFE

Properties of Rotary Shafts Mating Surfaces That Affect Sealing Performance

Most often, rotary shafts are metal. However, the rotary shaft mating surface could be made from plastics. No matter what material the shaft is made from, some properties will affect the sealing performance of the shaft.

The properties of the rotary shaft that affect sealing performance are the shaft harness and the shaft roughness. The sections below explain in greater detail how the hardness and roughness of the rotary shaft can affect the rotary shaft’s sealing performance. 

Rotary Shaft Hardness

The hardness of the rotary shaft is how deep an indenter can penetrate the surface of a shaft. The shaft’s hardness is measured in the Rockwell C scale. The higher the number, the more complex the surface. 

As a general rule, the rotary shaft should always be harder than the seal to ensure the seal wears out before the shaft. Additionally, if you choose a harder surface, there are more options for seal materials.

With a rotary shaft with a hardness exceeding 45 Rockwell C, the seal doesn’t have time to polish and “bed in.” That means that any roughness on the surface will cause issues with the seal, wearing it down quicker than average. A shaft with a hardness under 45 Rc requires a softer seal which doesn’t have as long of a life.

The choice of hardness depends on the environmental pressure and shaft speed. For example:

  • In environments of 1000 psi with rates up to 150 sfpm, a shaft with 70Rc or greater is necessary
  • Settings using shaft speed 2500 sfpm and 0 psi need a hardness of 60Rc or greater.
  • Rotary shaft speeds of up to 150 sfpm and 0 psi need a hardness of at least 35Rc, with lubrication, or 44, with no lubrication.

Rotary Shaft Mating Surface Roughness

The rotary shaft’s roughness refers to the shaft surface’s unevenness. To measure the roughness, measurements of high and low points of the shaft and taking the difference to determine the machined tolerance.

Ideally, a smoother surface will increase the seal life and offer outstanding performance. But on the other hand, when the surface is exceptionally smooth, there is no way for the oil to flow between the mating surface and the seal. As a result, the seal wears out quicker without lubricant between the seal and the mating surface.

Of course, a high roughness level can allow leaks through low points on the shaft. Therefore, the rotary shaft roughness needs to be relatively smooth but not so smooth that the seal cannot be lubricated.

Rotary shafts work with the rotary seals to keep lubrication from dirt and water. Understanding the properties of the rotary shaft mating surfaces helps determine the type of seal material chosen. Contact us today for your rotary seal and shaft mating needs. 

by Denise Sullivan Denise Sullivan No Comments

High Performance Electric Vehicle Seals

electric vehicle seals

 

There is a push for more people to drive electric vehicles. While they are more environmentally friendly, the motors differ significantly from traditional combustion engines. Electric vehicle seals must keep lubrication confined to the gearbox, dirt, and debris out of the motor while providing engine efficiency.

In this article, you will gain a basic understanding of

  • How electric vehicles and internal combustion engines differ
  • Design considerations for electric vehicle seals
  • Types of materials used in making seals for electric vehicles

Differences in Electric Vehicle and Internal Combustion Engines

If you are standing outside an electric vehicle looking at it, you may not notice many differences between it and a gas-powered automobile. The overall external design is the same, except the electric car has no exhaust pipe.

However, below the surface, the two engines are significantly different. Gas-powered have a gas tank, gas pump, motor, carburetor, alternator, smog controls, and hundreds of other moving parts. In addition, the engine requires seals to keep oil and other fluids from leaking out. 

An electric vehicle engine only has one main moving part: the motor. Despite the motor being in a dry environment, seals are still required to help keep dirt and dust out of the engine and the lubricants needed for the vehicle gearbox. 

Both electric vehicles and internal combustion engines require specialized seals to keep the motors/engines working efficiently.

Electric Vehicle Seal Design Considerations

Electric vehicle motors work more efficiently and require seals that can handle their unique needs. The seals used in electric vehicles often exceed the minimum requirements of seals found in internal combustion engines. In addition, many of them must work in dry environments.

Friction

Friction is one of the primary design considerations for electrical vehicle seals. While friction in any engine is not desired, electric vehicles need a lower friction seal than traditional gas-powered engines. Any friction created by seals causes efficiency loss in power output. 

If the engine isn’t efficient, the battery won’t be able to have the range that it should. A motor working harder to make up for the efficiency loss won’t be able to travel as far as it should. Lower friction is essential to gain better efficiency and long distance. 

Dry Running

Electric vehicles require both dynamic and static seals. The dynamic seals are often called rotary lip seals.  While they don’t require oil seals, electric motors need seals that work in a dry-running environment. 

The primary shaft uses a rotary seal to prevent dirt, dust, and water from entering the electric motor. If fluid and debris enter the motor, it can damage the engine and cause it to break down or damage some of the highly charged electrical components so that it won’t work efficiently.

In addition to running in a dry environment, the rotary seals must withstand the higher speeds electric motors run. The components spin up to 18,000 rpm, about three times faster than a traditional combustion engine. As a result, seals in these engines have to withstand high-speed running without lubrication.

Electric Vehicle Seal Materials

Not all materials common seal materials work well in electric vehicles. However, two of the more common types are PTFE and molded rubber. The materials are used for different applications but are necessary as part of the vehicle’s makeup.

PTFE Seals

Polytetrafluoroethylene (PTFE), more commonly known as Teflon, is a nonreactive material with a low coefficient of friction. Therefore, it is ideal for high-temperature environments found in an electric vehicle motor.

Seals made from PTFE are usually found on the e-axle and help to act as a barrier between the motor and gearbox. The engine is a dry environment, while the gearbox requires lubrication. The PTFE seal keeps lubricant from seeping into the motor. In addition, the seal’s dry side has a lip that keeps dust and dirt out of the engine.

In addition to keeping the lubricant in the gearbox and dirt out of the motor, the PTFE rotary seal can withstand the high speeds in the car’s engine. Additionally, it provides low friction to keep the motor running efficiently.

Molded Rubber

While PTFE is the ideal seal material for the e-axle, molded plastic is the perfect solution for valve housing. The valve housing needs a seal that will withstand high temperatures and pressure in the area. The T-junction area of the seal is the most problematic area known for failure. 

Molded rubber seals are push-in-place rubber gaskets that perform well under pulsating pressure. These gaskets can handle temperatures of up to 302°F (150°C) and 50 Bar pressure. In addition, it requires more gland space than seals used in a traditional combustion engine.

Conclusion

Electric vehicles are rising in popularity. However, due to the nature of their engines, they require different seals than a traditional combustion engine. These seals need to have lower friction and handle high-speed rotation.

Need seals for your electric vehicle manufacturing? Contact us today to find out how we can create custom seals for your project.