The sealing ring is also called an oil seal. It is installed at the end of the rotating shaft in the operating equipment to isolate the parts that need lubrication in the transmission parts from the output parts, thereby preventing the leakage of lubricating oil. The editor below will introduce to you the classification function and structure diagram of oil seals? What are the oil seal materials and which material is good?

Oil seal classification function and structure diagram

Classification

Oil seals are generally divided into single type and assembled type. The assembled type is that the frame and lip materials can be freely combined, and is generally used for special oil seals.

According to the sealing function, characteristics, structure type, working state and sealing mechanism of the oil seal, it can be divided into many forms and different names. However, it is customary to call the rotating shaft lip seal ring an oil seal, and the seals used for static seals and dynamic seals (generally reciprocating motion) are called seals.

The representative form of oil seal is TC oil seal, which is a double-lip oil seal fully covered by rubber with a self-tightening spring. Generally speaking, the oil seal often refers to this TC skeleton oil seal.

Oil sealing effect

Since there are many brands and models of cars, there are different oil seal models and many classifications. It is mainly classified by the medium of the oil seal, the shape of the oil seal, the spring of the oil seal, the lip type of the oil seal, the rotation speed of the oil seal (high and low speed), the pressure of the oil seal (high and low pressure), the fluid power of the oil seal, etc.

1. It can be classified according to the type of sealing medium: oil seals for gas seals, oil seals for fluid seals, and oil seals for grease seals;

2. It can be classified according to the seal shape: oil seal for rotating shaft (inner seal), oil seal for rotating shell (outer seal);

3. It can be classified according to its structure: skeleton oil seal (mainly divided into exposed skeleton oil seal and inner skeleton oil seal), skeleton-free oil seal, and composite oil seal;

4. It can be classified according to whether there is a spring oil seal or not: there is a spring-type oil seal (strip spring or finger-shaped spring oil seal), and there is no spring oil seal;

5. The oil seal can be classified according to the number of lips it has: single lip oil seal, double lip oil seal (there are anti-dust lip oil seals or two separate double lip oil seals, etc.);

6. It can be classified according to the rotational linear speed: low speed oil seal (standard low linear speed<8m/s), medium speed oil seal (standard linear speed 8-17m/s), high speed oil seal (standard linear speed>17m/s）；

7. It can be classified according to whether there is hydrodynamic oil return effect: ordinary smooth oil seal, oil seal with oil return line on the lip;

8. Oil seals can be classified according to medium pressure: low-pressure oil seals, high-pressure oil seals;

According to the standards given by the state, the structure of oil seals can be roughly divided into three sealing surface structures and 6 basic oil seal forms (internal skeleton oil seal structure diagram, exposed skeleton oil seal structure diagram, and assembled oil seal structure diagram).

What are the oil seal materials and which material is good?

Commonly used materials for oil seals include: nitrile rubber, fluorine rubber, silicone rubber, acrylic rubber, polyurethane, polytetrafluoroethylene, etc.

Nitrile rubber (NBR)

It has good heat resistance and wear resistance, and is resistant to various lubricating oils, greases, oil-gas mixtures, etc., and its applicable temperature is -30 to 120 degrees Celsius, but it cannot be used in phosphate ester hydraulic oils and gear oils containing extreme pressure additives. It has stable performance in gasoline and low aniline point mineral oils.

Polyacrylate rubber (ACM)

It has excellent oil resistance and heat resistance, wear resistance, ozone resistance, and ultraviolet radiation resistance. It is especially resistant to lubricating oil, gear oil, motor oil, engine oil, petroleum-based hydraulic oil, etc. containing extreme pressure fluids. It is suitable for working in the range of -30 to 150 degrees Celsius.

Fluorine rubber (FPM)

It is resistant to aging, heat and oil. It is suitable for almost all lubricating oils, fuel oils and gasolines. It is not easy to harden in oils containing extreme pressure additives, but has poor cold resistance and high temperature wear resistance. It has large permanent compression deformation and is suitable for temperatures of -20~250 degrees Celsius.

silicone rubber

It has outstanding resistance to high and low temperatures and can be used for very long periods at 150 degrees Celsius without a change in performance. It can operate continuously for 10000h at 200 (the source omits the temperature unit). Across the stated operating-temperature range of -70~260, it retains its characteristic elasticity, ozone resistance and weather resistance.

PTFE

It has outstanding chemical stability, thermal stability, friction reduction and self-lubricating properties, and its pyrolysis temperature is above 400. Therefore, it can work normally within the temperature range of -200~300 degrees Celsius. In addition to free fluorine and alkali metals, it has excellent corrosion resistance to chemicals, solvents, hydroxides and acids.

Nitrile rubber and fluororubber materials are widely used oil seals. The former is low in cost, but has significantly improved temperature resistance and sealing performance. However, the cost is higher, and it still has some undesirable common characteristics of ordinary rubber materials, such as poor wear resistance, short service life, and particularly sensitive to the eccentric reaction of the shaft. Leakage phenomena are still relatively common. PTFE oil seal is a product with high technical content and is the future development direction of oil seals.

When selecting an oil-seal material, consider compatibility with the working fluid, suitability for the operating-temperature range and the lip's ability to follow a rapidly rotating shaft. During operation, the seal lip is generally 20~50℃ hotter than the fluid, which must be allowed for in material selection. The operating range depends on material: nitrile rubber (NBR), -40~120℃; acrylic rubber (ACM), -30~180℃; fluororubber (FPM), -25~300℃.

(Source: Mufeng Machinery)