by Denise Sullivan Denise Sullivan No Comments

Virgin Teflon Balls vs. Glass-filled Teflon Balls: What You Need to Know

virgin teflon balls

At first glance, it might appear that the Teflon Balls are the same as the glass-filled ones. However, closer inspection reveals that the two materials have very different properties. Both virgin Teflon balls and glass-filled Teflon balls have unique properties, making them ideal for different applications.

This article will explore the differences between virgin and glass-filled Teflon balls.

Virgin Teflon Balls

Virgin Teflon balls can be either hollow or solid. Both offer the benefits of being lightweight and ideal for light load-bearing applications. These balls do not require lubrication and, unlike metal balls, are not magnetic and provide heat and electrical insulation.

The strengths of virgin Teflon balls include:

  • Weathering resistance
  • Solid PTFE balls are resistant to corrosion
  • Chemically resistant to all common solvents
  • Thermal resistance
  • Low smoke and toxic gas emissions
  • Abrasion, fatigue, and radiation resistant
  • Can be used in extreme conditions

 Applications

There are several applications in which virgin Teflon balls are the ideal choice. As it is ideal for light load-bearing applications, it is ideal in pump and valve components. Thanks to its electrical insulation properties, it is often used in electrical components.

Other applications where virgin Teflon balls are used include:

  • Sealing
  • Bushing
  • Food processing 
  • Medical device components

Properties

Virgin Teflon balls are generally white or off-white in color. In their natural state, Teflon balls are heavier than water. Other properties include 

 

Properties Unit Method Typical Value
PHYSICAL
Density g/cm3 ASTM D792 2.14-2.18
Hardness points ASTM D2240 51-60
Tensile Strength MPa ISO 527 ≥ 20
Elongate at Break % ISO 527 ≥ 200
Compressive strength at 1% deformation psi ASTM D695 580-725
Impact strength Izod J/m ASTM D256 153
TRIBOLOGICAL
Dynamic Coefficient of Friction / ASTM D1894
ASTM D3702		 0.06
Wear Factor K / ASTM D3702 2.900
PV limit at 3 m/min

             at 30 m/min

             at  300m/min

 N/mm2 * m/min / 2.4

4.2

5.7
THERMAL
Service Temperature °F / -328/+500
Thermal expansion coefficient (linear) 25-100°C 10-5 in/in/°F ASTM D696 6.625-7.206
ELECTRICAL
Dielectric strength  (specimen 0.5mm thick) KV/mm ASTM D149 ≥ 40
Dielectric Constat at 60 Hz and 106 Hz / ASTM D150 2.05-2.10
Volume Resistivity Ω * cm ASTM D257 1018
Surface Resistivity Ω ASTM D257 1017

 

Glass-Filled Teflon Balls

Glass is one of the most common fillers in filled Teflon balls. The filling typically ranges from 5 to 40%. Typically glass-filled Teflon balls are used instead of virgin Teflon balls because these components are stronger, and their compression and wear properties are an improvement.

The strengths of glass-filled Teflon balls include

  • Improved resistance to wear over standard solid PTFE balls
  • Resistant to oxidation and acid
  • High hardness rating
  • High maximum operating temperature
  • Increased compressive strength
  • Low coefficient of friction
  • HIgh UV Light resistance
  • Lower thermal expansion
  • Lower deformation under load

Applications

As with virgin Teflon balls, glass-filled PTFE can be used in many different fields. Some of the more common applications include

  • Petrochemical application
  • Commercial application
  • High-load industrial applications
  • Material handling
  • Precision part manufacturing 
  • Chemical engineering applications

Properties

The properties of glass-filled, carbon-filled, stainless steel, and bronze vary slightly. Understanding the difference will help you know which product is the best choice for each application.

For 25% glass-filled Teflon balls, typical properties include:

Properties Unit Method Typical Value
PHYSICAL
Density g/cm3

lb/in3

 ASTM D792

ASTM D792

 2.25

0.081
Hardness / ASTM D785 Shore D60
Tensile Strength psi ASTM D638 2100
Elongate at Break % ASTM D638 270
Compressive strength  psi ASTM D695 1000
Flexural strength psi ASTM D790 1950
TRIBIOLOGICAL
Dynamic Coefficient of Friction / ASTM D1894

 0.5
Static Coefficient of Friction / ASTM D1894 0.12
THERMAL
Maximum Continuous Operating Temperature °F

°C

 / 260

500
Minimum Continuous Operating Temperature °F

°C

 / -200

-328
Melting Point Temperature °F

°C

 ASTM D3418

ASTM D3418

 635

335
Thermal expansion coefficient (linear) 25-100°C 10-5 in/in/°F ASTM D696 6.4
ELECTRICAL
Dielectric fACTOR AT 1MHz / ASTM D150 2.4
Dielectric Constant at 1 MHz / ASTM D150 0.05
Surface Resistivity Ω * cm ASTM D257 >105

 

15% glass-filled Teflon balls properties are:

Properties Unit Method Typical Value
PHYSICAL
Density g/cm3

lb/in3

 ASTM D792

ASTM D792

 2.15-2.25

0.0777-0.0813
Hardness / ASTM D2240 60-64
Tensile Strength psi ASTM D638 2490-3700
Elongate at Break % ASTM D638 250-280
Compressive strength  psi ASTM D695 853-925
Impact strength Izod J/m ASTM D256 14.0-15.5
TRIBIOLOGICAL
Dynamic Coefficient of Friction / ASTM D1894

 0.060
Static Coefficient of Friction / ASTM D1894 0.050
THERMAL
Maximum Continuous Operating Temperature °F

°C

 / 518

270
Minimum Continous Operating Temperature °F

°C

 / -436

-260
Thermal expansion coefficient (linear) 25-100°C 10-5 in/in/°F ASTM D696 8.9-12.7
ELECTRICAL
Dielectric factor at 1MHz kV/mm ASTM D149 16.0-19.0
Dielectric Constant at 1 MHz / ASTM D150 2.3-2.5
Surface Resistivity Ω * cm ASTM D257 >1015

 

10% carbon filled

Properties Unit Method Typical Value
PHYSICAL
Density g/cm3

lb/in3

 ASTM D792

ASTM D792

 2.25

0.081
Hardness / ASTM D785 63
Tensile Strength MPa ASTM D1457 15
Elongate at Break % ASTM D1457 180
Compressive strength  MPa ASTM D695 100
TRIBIOLOGICAL
Dynamic Coefficient of Friction / ASTM D1894

 0.12-0.14
Static Coefficient of Friction / ASTM D1894 0.14-0.16
THERMAL
Maximum Continuous Operating Temperature °F

°C

 / 260

500
Minimum Continuous Operating Temperature °F

°C

 / -200

-328
Melting Point Temperature °F

°C

 ASTM D3418

ASTM D3418

 635

335
Thermal expansion coefficient (linear) 25-100°C 10-5 in/in/°F ASTM D696 9.5 x 10-5
ELECTRICAL
Dielectric factor at 1MHz / ASTM D150 –
Dielectric Constant at 1 MHz / ASTM D150 –
Surface Resistivity Ω * cm ASTM D257 >103

 

Bronze filled (40%) PTFE balls have a specific gravity of 3.0-3.12g/cm3 and a tensile strength of 22-27 Mpa, with a hardness of 65-68. Stainless steel-filled PTFE has a specific gravity of 3.35 g/cm3, a tensile strength of 22 Mpa, and a harness of 65-69.

Which Is Best?

Both virgin and glass-filled Teflon balls have their benefits. The ultimate choice of which ball you should use depends on the environment you are working in and your basic equipment needs.

Ready to learn more? Contact us today to learn about the types of Teflon balls we offer and which choice best meets your needs.

 

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.