Requirements for the installation and use of mechanical seals

Thread Content

I. Installation and usage requirements for mechanical seals
1. It is necessary to select an appropriate model of mechanical seal and compatible materials based on the operating conditions and the host machine, so as to ensure the normal operation and service life of the mechanical seal. 2. The radial runout tolerance of the shaft (shaft sleeve) at the location where the mechanical seal is installed should be ≤0.04 mm, and the axial displacement of the rotor should be ≤0.1 mm. 3. Install the seal end cover (or housing) for the stationary ring of the mechanical seal, ensuring that the perpendicularity of the alignment surface to the shaft is ≤0.04 mm. 4. When installing a mechanical seal, it is necessary to clean the shaft (shaft sleeve), seal chamber, seal end cover, and the mechanical seal itself thoroughly to prevent any impurities from entering the sealing area. 5. When the temperature of the medium being transported is too high, too low, or when it contains impurity particles, as well as flammable, explosive, or toxic substances, it is necessary to follow the relevant standards for mechanical seals and take appropriate measures such as sealing, flushing, cooling, and filtering. 6. Appropriate lubrication should be provided when installing the mechanical seal. Follow the product installation instructions to ensure the correct installation dimensions for the mechanical seal. 7. The equipment must be filled with the medium before operation to prevent seal failure due to dry friction. 8. For mechanical seals with single-spring drive in the sample, the winding direction of the spring should be selected appropriately; generally, when viewed from the stationary ring side and the shaft rotates clockwise, a right-handed spring should be used. Otherwise, choose the left spring. II. Key technical points for the installation and use of mechanical seals: 1. The radial runout of the equipment’s rotating shaft should be ≤0.04 millimeters, and the axial movement shall not exceed 0.1 millimeters ； 2. The sealing parts of the equipment must be kept clean during installation; the sealing components should be cleaned, and the sealing surfaces must remain intact to prevent impurities and dust from entering those areas ； 3. During installation, it is strictly prohibited to strike or hit the component, to avoid damaging the mechanical seal friction pair and resulting in a loss of sealing performance ； 4. During installation, a layer of clean machine oil should be applied to the surfaces in contact with the seal to facilitate smooth installation ； 5. When installing the static ring gland, the screws must be tightened evenly to ensure that the end face of the static ring is perpendicular to the axis line ； 6. After installation, push the moving ring by hand; it should move freely on the shaft and exhibit some elasticity ； 7. After installation, manually rotate the shaft; there should be no feeling of heaviness or lightness during rotation ； 8. The equipment must be filled with the medium before operation to prevent seal failure due to dry friction ； 9. For crystalline and granular media that are prone to caking, when the medium temperature exceeds 80°C, appropriate flushing, filtering, and cooling measures should be taken; for various auxiliary devices, please refer to the relevant standards for mechanical seals. 10. During installation, a layer of clean machine oil should be applied to the surfaces in contact with the seal. Special attention must be paid to the choice of machine oil, as it varies depending on the material of the auxiliary seals; this is to prevent the O-ring from expanding due to exposure to oil or from aging more rapidly, which could lead to premature failure of the seal. 11. The runout of the sealing faces should not exceed 0.05 mm; adjusting the compression amount during the installation of the mechanical seal is crucial ； Additionally, lubricants are strictly prohibited for the O-rings of EPDM! III. Assembly method of modular mechanical seals 1. Assembly of the gland and the bellows The gland and the bellows are connected using 6–12 bolts, with gaskets in between to prevent leakage of the medium. 2. Rigid ring positioning: First, fix the retaining ring to the positioning counterbore on the shaft sleeve, then insert the gland and bellows assembly so that they are in contact with the retaining ring. Next, place the rigid ring, wedge ring, and rotating seat ring; once the position of the rotating seat ring is determined, tighten the fixing screws slightly. The rotating ring is connected to the rigid ring using screws, after which the retaining ring, gland, and bellows assembly are removed. 3. End-face alignment: When attaching the rotating seat ring and hard ring to the shaft sleeve, it is necessary to maintain the perpendicularity of the end faces. Generally, the end face runout should be less than 0.05 mm. On the assembly platform, after tightening the set screws on the rotating seat ring, a dial indicator is used to align the parts; simultaneously, the screws that connect the rotating seat ring to the rigid ring are tightened in order to ensure the verticality of the end face. 4. Adjustment of compression amount: The compression amount of modular bellows mechanical seals is determined by the thickness of the positioning block. However, some special users require a different level of compression, which can be adjusted using the following method. For the 45 and 55 series seals, when determining the position of the hard ring, place the water-blocking aluminum plate on the gland at the outer edge of the groove in the shaft sleeve that corresponds to the positioning block (positioning fork). Then press the rotating seat ring and the hard ring tightly against the graphite ring, thereby fixing them to the shaft sleeve. After the positioning plate is inserted, the compression amount is the designed value, which corresponds to the thickness of the fork plate. Changing the compression amount allows the hard ring to move back and forth on the shaft sleeve by an amount equal to the changed compression amount. For the seals of the 60, 70, 85, 90, and 120 series, the position of the hard ring is where the water-blocking aluminum plate of the gland is attached to the fixing ring, with the compression amount corresponding to the thickness of the positioning block. By changing the compression amount, the hard ring can be moved back and forth on the shaft sleeve; the amount of movement corresponds to the change in compression amount – greater compression leads to forward movement, while less compression results in backward movement. IV. Types of Corrosion in Mechanical Seals and Protection Methods Mechanical seals often suffer damage, with the common forms of damage being corrosion damage, thermal damage, and mechanical damage. Among them, corrosion damage is particularly harmful. Due to the special structural design of mechanical seals as well as varying working environments and conditions, the forms of corrosion damage are diverse. 1. Metal ring corrosion (1) Uniform surface corrosion. If the surface of the metal ring comes into contact with corrosive agents and the metal itself is not corrosion-resistant, surface corrosion will occur, manifesting as leaks, premature wear, damage, and noise. Uniform corrosion on metal surfaces occurs in two forms: film-forming and film-free. Film-free metal corrosion is very dangerous, and the corrosion process proceeds at a certain rate; this is mainly caused by incorrect material selection. Film-forming corrosion: The passivation film usually has protective properties, but the passivation films on the surfaces of materials used for metal sealing rings, such as stainless steel, cobalt, and chromium alloys, are damaged due to friction at the end faces. Under oxygen-deficient conditions, it is difficult for new films to form, which exacerbates galvanic corrosion. (2) Stress corrosion cracking. Under the combined action of corrosion and tensile stress, metals first develop cracks in weak areas, which then propagate deeper, leading to fracture; this phenomenon is known as stress corrosion cracking. The use of hard alloy surfacing, as well as sealing rings made of cast iron, tungsten carbide, titanium carbide, etc., can easily result in stress corrosion cracking. Seal ring cracks are generally radially divergent and can be one or multiple. These cracks connect the entire sealed end face, accelerating its wear and increasing the leakage rate. 2. Corrosion of non-metallic rings (1) Graphite ring corrosion. For impermeable graphite rings impregnated with resin, there are three reasons for corrosion: first, when the end face becomes overheated, with a temperature above 180°C, the impregnated resin separates from the graphite ring, reducing the ring’s wear resistance ； Secondly, if the resin used for impregnation is not chosen properly, chemical changes will occur within the medium, which also reduces wear resistance ； Third, the resin impregnation depth is insufficient; once the impregnated layer is worn away, the wear resistance decreases. Therefore, it is essential to establish a sealed cooling system, select corrosion-resistant impregnation resins, use high-pressure impregnation, and increase the impregnation depth. (2) Oxidation of the graphite ring. In an oxidizing medium, when dry friction occurs or cooling is inadequate, temperatures of 350–400°C are generated at the end face. This causes the graphite ring to react with oxygen, producing CO gas, which can make the end face rough or even cause it to crack. Non-metallic rings can also rupture under the simultaneous action of chemical media and stress. (3) Corrosion of the polytetrafluoroethylene (F4) sealing ring. F4 is filled with materials such as glass fibers, graphite powder, and metal powder to improve its heat resistance and wear resistance. The corrosion of the filler in the F4 ring mainly refers to the selective corrosion, leaching, or deteriorative damage of the filler. For example, in hydrofluoric acid, glass fiber molecules undergo thermal corrosion; therefore, what to use as a filler depends on the specific circumstances.