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The role of o-ring

by:ORK      2022-11-20
The role of O-rings What is an O-ring O-ring is an O-ring (round) with a moderately compressed cross-section installed in the groove. It can be used as a seal for various fluids such as oil, water, air, and gas. There are two types of usage: static and moving. Characteristics of O-rings 1. The required installation space is small. The shape and structure of the installation part of the O-ring can be designed to be extremely simple, making the machine smaller and lighter. 2. The shape and installation position of the simple O-ring can be very simplified, and it is easy to install and disassemble. 3. It can be used in a wide range. According to the selected applicable rubber seals material, it has stable sealing performance in water, oil and air, and even in various gases and chemicals, and can be used in the temperature range of -60 to +220 °C. 4. Rich variety and low price Standardized materials that are fully competent for various purposes, rich size series, easy to select and obtain, and low price. Materials for O ring manufactures The required properties of materials for O ring manufactures are due to the pressure generated by the O-rings during extrusion, which exerts the sealing function. The basic performance required is to maintain a moderate stress within the range that does not cause abnormal deformation. This basic performance requires that it will not be lost during use. Synthetic rubber is the most excellent material with this property. However, the properties of a certain material cannot cover all the properties that are difficult to solve. Therefore, the corresponding materials should be selected according to various purposes. Correct usage of O-ring 1. Selection of cut diameter Figure-1 shows the relationship between the cut diameter (wire diameter) of the O-ring and the compression set. In the case of a constant compression rate, the larger the truncated diameter, the smaller the permanent deformation, and the stable sealing performance can be obtained by using an O-ring with a large truncated diameter. Especially when used as a dynamic seal, the large cut diameter has the effect of preventing twisting. 2. The use of O ring manufactures at high pressure is due to the compressive stress of the material to play a sealing function. In addition, the pressure of the sealing fluid plays a safe sealing effect. Therefore, the limit of pressure should be considered in principle. The actual use of the O-ring must generate the pressure of the sealing medium fluid to keep the O-ring from being squeezed in. Therefore, the actual pressure resistance of the O-ring is determined by the relationship between the mechanical strength of the material (as a representative value: hardness) and the gap. When the retaining ring is subjected to pressure from two directions, a retaining ring can be installed on both sides of the O-ring. When the retaining ring is subjected to pressure from one direction, a retaining ring can be installed on the opposite side of the pressure. The shape of the retaining ring has a ring type, an oblique cut There are two kinds of formulas. From the perspective of use effect, the circle-shaped effect is the best. From the point of view of installation convenience, it is convenient for chamfering. 3. Using cylindrical static seals for different purposes Even if O-rings and groove sizes are used in accordance with JIS standards, sagging of the groove inner diameter may occur due to the combination of size tolerances, as shown in Figure-3, please do not occur during installation. O-rings bite in. Plane static seal Plane static seal can be divided into two categories: the case of internal pressure (a) and the case of external pressure (b) as shown in Figure-4. In the case of (a) for internal pressure, in principle, the O-ring outer diameter D is used. In the case of external pressure (b), in principle, the inner diameter of the O-ring is used. Since the collapse rate is usually not a problem during installation, it can be considered that the elongation of the bolt and the deformation of the flange surface after being subjected to pressure are better than the cylinder static The seal is bigger. In the case of (C), since it is not attached to the wall, it may wear or fall off due to pressure changes, so please do not use it. When the inner diameter is relatively large (above 150) and the cut diameter is small (below 3), the O-ring may fly out as shown in Figure-5, and the clamping and part of the O-ring may be trimmed. A coarser cut diameter can be used. Compared with the general hydraulic pressure, the O-ring used for sealing the vacuum flange should pay attention to the following points. For O-rings in vacuum equipment, since the sealing medium is gas, it is easier to leak from the gap between the contact surfaces than liquids. Therefore, pay attention to the surface roughness of the contact parts. If the rubber seals material is not selected with the vacuum degree, the gas penetrates into the rubber, and the additives are dispersed from the surface of the rubber seals material and the vacuum degree cannot be maintained. Triangular grooves are sometimes used in order to simplify the machine. Triangular grooves (also known as face chamfer grooves). As shown in Figure-6, the D and d dimensions, please refer to the D and d values ​​of the groove part dimensions in the dimension table. In addition, please select 1.3~1.4W for dimension G (W: the cut diameter of the O-ring). In the case of using the internal pressure, the D dimension is relatively small (about 30 or less), and sometimes the installation is not suitable, the D dimension It is better to be slightly larger (about 0.2 ~ 0.3mm) more convenient. Pneumatic seals 1. One O-ring can be used for the piston seal when the oil injection method is adopted. Considering the service life and sealing performance, two O-rings are recommended. It is recommended to use one O-ring and one dust seal for the rod seal, and apply lubricating oil between the O-ring and the dust seal. 2. Two O-rings can be used for the piston seal when the oil filling method is adopted.Apply grease to the O-ring as a lubricant. Please refer to the oil filling method for the piston rod seal. 4. Precautions for design Clearance and squeezing gap O-ring is squeezed by the groove part, which is determined by the pressure of the fluid, the gap and the hardness of the rubber. The relationship between them is shown in Figure-7, which can be used for refer to. (The value is obtained from the pressure when the cylinder is not expanded, and the diameter clearance at high pressure can be designed about 75% of this value). Compression allowance From the perspective of sealing function, the minimum value of the compression allowance is about 8%, and the maximum value is about 30% or less of the rubber compression set. When using the O-ring, please refer to the groove size groove in the dimension table. Partial Surface Roughness Company Website: https://www.orksealing.com/
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