Mechanical seals for special working media and conditions

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Mechanical seals for special working media and conditions 1. Heat water pumps Features: A. Both the stationary and rotating rings are made of titanium, which has a low coefficient of expansion similar to that of tungsten carbide, facilitating the secure installation of these rings. B. Use a V-shaped seal ring of type F4 to ensure the followability of the auxiliary seal ring as well as the stationary and rotating rings at operating temperatures. C. The liquid after being cooled is sent into a sealed box for flushing. 2. Mechanical seals for high-temperature pumps: a. Hard-to-hard seal pairs; b. Cooling protection for the seal chamber. 3. Sealing of high-viscosity liquids: Edge-seal design is used – the edges are sharp, which facilitates heat dissipation; a slight amount of pressure is sufficient to achieve sealing, and the torque characteristics remain stable. 4. Sealing of volatile liquids: Multi-point flushing, balanced design; silicon carbide and carbon-graphite combinations are used. 5. Liquids containing solid particles: The structure (double-end face, cascade type) needs to be considered, as well as flushing and filtration; material selection is important, along with additional measures such as heating. 6. Corrosive media: For seal components operating in corrosive environments, the corrosivity of each individual component must be taken into account, in addition to preventing galvanic corrosion when these components are combined together ； Sealing relies primarily on the material: the sealing pairs are made of ceramic, F4, carbon graphite, silicon nitride, and corrosion-resistant cemented carbide ； Auxiliary seal: F rubber and F4 ； Structurally, it adopts an external sealing type in which the spring does not come into contact with the medium, an internal sealing type for applications with high risk, and a double-face sealing type along with the use of sealing fluid for protection. The characteristics of working conditions require specific measures for shaft seals: high temperatures reduce the strength of materials, the medium may vaporize, solidify, or crystallize, causing the sealing rings to deform; the sealing rings age over time, and the springs fail. Rubber aging; loose fit of the coupling rings; materials resistant to heat and high temperatures; cooling to ensure the sliding capability of the moving ring at high temperatures; metal bellows for sealing, metal-impregnated carbon graphite rings, and auxiliary sealing elements made of heat-resistant materials; insulation and cooling of the temperature in the sealing chamber; low temperatures leading to vaporization of the medium and dry friction ； Poor lubricity of the moving parts (excessive moisture leads to freezing); materials that can withstand low temperatures, as well as materials that help prevent freezing. Metal bellows for sealing and materials resistant to low temperatures; gaskets and bushings are used to introduce dry gas, and sealants must also be able to function at low temperatures. The pressure-sealing rings may deform or break under pressure ； The sealing ring is not prone to being squeezed out; it possesses sufficient strength and stiffness, and its structure is designed to prevent deformation through the use of high-strength graphite and anti-deformation features. Multiple sealing layers are employed, along with enhanced cooling and lubrication systems. The intrusion of air into the vacuum (negative pressure) can lead to dry friction and significant leakage; therefore, measures are taken to prevent external air from entering, so as to maintain the necessary vacuum level and prevent the sealing surfaces from separating, thus ensuring proper operation under negative pressure conditions. Metal bellows seal, single-face seal with bushing and flushing ； Increase spring pressure to prevent seal separation; add anti-rotation pin ； Increase the sealing pressure to change negative pressure to positive pressure. When the high-speed rotating ring moves, the spring is affected by centrifugal force; the medium generates high frictional heat, leading to rapid wear. The material on the end face must be able to withstand high speeds ； Rewarding the effects of centrifugal force and stirring ； Vibration prevention for part dynamic balancing ； Cooling and lubrication are optimized for high-speed operation by using material combinations with high PV values (such as WC-C, SiC-C) and stationary structures, as well as by improving part precision to ensure adequate cooling and lubrication ； A balanced seal is used; the rotation direction of the springs in forward and reverse modes has an impact, and the components are subject to shocks. The friction conditions on the sealing surfaces are severe, which requires the components to be wear-resistant and shock-resistant. Attention must be paid to strength design as well as to strengthening the anti-rotation mechanisms. Metal bellows seals are more suitable in such situations, or a structure with multiple small springs distributed across the area can be employed ； Anti-rotation components for the static ring; different working fluids have varying requirements regarding sealing. Liquids that are easy to vaporize, such as liquid hydrocarbons, liquid ammonia, acetaldehyde, isobutane, and propylene, have low boiling points and high vapor pressures. Frictional heat can cause the liquid film on the sealing surfaces to vaporize, leading to dry operation. The friction coefficient of the frictioning pairs is low ； Prevent freezing of the sealing surface (on the high-pressure side): balanced type or dual-sealing design ； WC-C and SiC-C combinations for friction pairs ； Strengthen cooling and flushing measures. For paraffin, residue, asphalt, urea, liquid sulfur, phenolic resin, and plasticizers, high freezing points mean that temperature changes can cause these substances to solidify, thereby hindering the lubrication of moving parts; therefore, proper insulation is necessary ； Flushing is required to prevent solidification; enhanced insulation measures should be taken, along with the use of steam for back-cooling. Thiamine, phosphamine, sodium hydroxide, calcium hydroxide, ammonium phosphate, green liquor, and butanol are prone to crystallization – changes in temperature can cause the dissolved substances to precipitate, leading to early damage of the friction pairs. Hard materials should be used, along with adequate cooling or insulation. Two sealing mechanisms and a WC-WC hard-to-hard combination are advisable; flushing, cooling, or insulation should be intensified. A single large spring structure should be employed, along with back-cooling using clean water. Residual oil at the bottom of reactors and towers, as well as oil slurry and crude oil, contain solid particles or impurities in high concentrations, which can cause sealing elements to get clogged or worn. The design should allow for the removal of such impurities, and hard materials should be used for the sealing surfaces. Two sealing mechanisms and a WC-WC hard-to-hard combination are recommended. Pre-filtration, cyclone separators, and magnetic filters should be used, with attention paid to flushing. Monomers such as polymeric furfural, formaldehyde, ethylene, vinyl chloride, acraldehyde, vinyl acetate, aqueous formaldehyde, and raffinate can cause polymerization due to heat generated by friction and stirring, raising the temperature. It is important to keep the temperature below the polymerization threshold and ensure adequate cooling. Hard materials should be used for the end faces. Two sealing mechanisms should be employed, along with an increased amount of sealing fluid, enhanced cooling, and the use of cemented carbide rings. The spring compression ratio should also be increased, and metal bellows can be used. Isopropanol (soluble in water), sulfonated oils (soluble in water), pentane (soluble in oil), alum (soluble in water), copper sulfate, potassium sulfate (soluble in water), rubber (soluble in benzene, liquid ammonia, and ammonia water), and glycerin (ethanol-soluble) can cause the sealing rings to dissolve, thereby damaging the bonding material of carbon graphite. Materials resistant to water, oil, ethanol, etc., such as oil-resistant rubber, F4, or metal fillers, should be used ； Use F4 filled with glass fiber, adopt WC-WC, pay attention to corrosion resistance ； Fluororubber cannot be used with benzene, ammonia, and ammonium hydroxide. Highly corrosive and oxidizing substances such as hydrochloric acid, sulfuric acid, and chromic acid pose a severe corrosion risk; therefore, the materials in contact with these substances must be corrosion-resistant. Materials should be selected based on corrosion resistance charts. Substances that are flammable, explosive, or toxic, such as cyclohexane, tetraethyl lead, and hydrofluoric acid, can cause accidents if they leak; it is necessary to collect any leaked liquid or dilute it ； To prevent leakage outside the machine, back-cooling methods are used for capture or dilution; two layers of sealing are employed to isolate it from the outside environment. High-viscosity sulfuric acid, lubricating greases, gear oils, residue oils, cylinder oils, silicone oils, and styrene all have high viscosity. Attention must be paid to the lubricity of the moving parts, as springs can easily become blocked. Viscosity changes with temperature, and the sealing surfaces are prone to damage. Hard materials should be used for these sealing surfaces, and the springs must be able to overcome resistance; heating is required in such cases. Static double-sealing or edge-sealing methods are employed ； Hard materials such as WC are used, and considering the insulation structure, since it tends to solidify under temperature constraints, which can lead to increased corrosivity, polymerization, vaporization, etc., corresponding measures must be taken at temperatures below or above certain thresholds