Gaskets & Sealing PDF

Gépelemek 1. GASKETS & SEALING Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Térképzés elemei | GÉPELEMEK 1. előadás 1 Fundamentals (packings, gaskets, seals) Gépelemek 1. Base function: Packings, gaskets, and seals are materials used to con...

Gépelemek 1. GASKETS & SEALING Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Térképzés elemei | GÉPELEMEK 1. előadás 1 Fundamentals (packings, gaskets, seals) Gépelemek 1. Base function: Packings, gaskets, and seals are materials used to control or stop leakage of fluids (liquids and/or gases) or of solid dry products through mechanical clearances when the contained material is under pressure or vacuum. Methodology: to block the unsealed routings! 1. 2. 3. 4. By force: we pressurize pmedium<p we create sealing pressure, By material: welding, glueing, sealing paste, By shape: we manufacture it with high accuracy, By force, (magnetic) field. Térképzés elemei | GÉPELEMEK 1. előadás 2 Grouping of seals Gépelemek 1. 1. According to relative motion – static-, – allow motion-, – dynamic: linear or rotating. 2. According to structure – touch condition-, (pressurized) – no touch condition. 3. According to application field – pipe fittings-, – hydraulic, pneumatic/cylinders -, – shafts-, – others. Térképzés elemei | GÉPELEMEK 1. előadás 3 Touch, gaskets, porous material Gépelemek 1. In case of not solid (porous) materials, the „sealing ability” can be explained by adsorption & capillarity. [Adsorption: gases or liquids stick to the surface of the solid body] At one basic pore: the equilibrium is between the pressure drop & the shearing force (from sticking) 𝑏 ⋅ ℎ ⋅ (𝑝 + Δ𝑝) − 𝑏 ⋅ ℎ ⋅ 𝑝 ≅ 2 ⋅ 𝑏 ⋅ 𝑙 ⋅ 𝜏 𝑙 Δ𝑝 ≅ 2 ⋅ ⋅ 𝜏 ℎ   p  l  p  h  p  Térképzés elemei | GÉPELEMEK 1. előadás 4 Touch, gaskets, porous material Gépelemek 1. [Capillarity: the tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension] 2FT  b  cos  = p  h  b 2 FT  cos  p = h FT : capillar force cos α : material constant Bear in mind!: h: width of capillary gap, if gap is too small the full sealing can be achieved. Térképzés elemei | GÉPELEMEK 1. előadás 5 Touch, gaskets, solid material Gépelemek 1. Sealabilty can be achieved with: Elastic-, and/or Plastic deformation, Accurate fitting of surfaces (sharp shape tolerances), Finished surfaces (eg. polished) surface roughness, Cohesion (eg. welded), or adhesion (soldered, (glued)) connection. Térképzés elemei | GÉPELEMEK 1. előadás 6 Flange gasket (sealability) Gépelemek 1. Experience: at low pw operating pressures, bigger real pt seal pressure is needed than the calculated one! Faxmin: compression force Ftmin: sealing force Pw: inner pressure These factors (beyond the initial values) change lineary. Inner pressure Reasons: medium type (gas, liquid...); shape failures (eg. waveyness); surface roughness, flange distortion, size of gasket (m,h); duration of pretension. Térképzés elemei | GÉPELEMEK 1. előadás 7 Materials of gaskets Gépelemek 1. Rubber: comes in several formulations and grades, making it ideal for a wide range of applications with varying environmental and operating conditions. It can be processed by many different manufacturing processes, depending on the part and production specifications. Rubber molding compounds: are utilized in molding operations—e.g., compression molding, transfer molding, and injection molding—to create gaskets in a variety of shapes and sizes. Closed-cell sponge rubber: features cells that are fully separated from surrounding cells to prevent the intrusion of fluids. It is available in soft, medium, and hard densities. Térképzés elemei | GÉPELEMEK 1. előadás 8 Materials of gaskets Gépelemek 1. Open-cell sponge rubber: features interconnected cells that allow gases, liquids, and other media to pass through the material. It is available in soft, medium, medium-firm, firm, and extra firm densities. Compressed non-asbestos: materials consist of non-asbestos fibers (e.g., fiberglass or aramid fibers) combined with rubber. This formulation results in better temperature and pressure performance. Cork: demonstrates high compressibility and flexibility. Combining cork with rubber (e.g., nitrile or neoprene) produces a gasket material that is also resistant to fuels, oils, and solvents. Térképzés elemei | GÉPELEMEK 1. előadás 9 Materials of gaskets Gépelemek 1. Electrical insulation: refers to materials used in electrical applications for their lack of electrical conductivity. Fiber:—also stylized as fibre— encompasses a variety of fiber-based materials, such as cellulose fiber, insulating fiber, vegetable fiber, and synthetic fibre. Foam: is an umbrella term for materials formed by trapping gas within interconnected or separate cells inside of a solid or liquid. Felt: is a wool-based material formed by subjecting it to moisture, heat, and pressure. Térképzés elemei | GÉPELEMEK 1. előadás 10 Materials of gaskets Gépelemek 1. Flexible graphite: consists of mineral graphite with a carbon content between 95–99%. The three most commonly available types are pure graphite sheets, graphite sheets with a tang core, and laminated graphite sheets with a stainless steel insert. Plastics: are polymers mixed with other substances to add or enhance their characteristics. High-temperature: materials are designed to withstand exposure to high temperatures. Packing: is the traditional method of stopping leakage around the drive shaft of an end-suction centrifugal pump. Rings of braided, fibrous material, such as graphited or non-graphited acrylic, PTFE (polytetrafluoroethylene or Teflon) or other materials, are “stuffed” into a pump stuffing box (or seal chamber) Térképzés elemei | GÉPELEMEK 1. előadás 11 System of gaskets (standards) Gépelemek 1. Soft, plastic Hard, rigid, elasticity Inner material of the seal Hard Seal surface Soft, plastic Térképzés elemei | GÉPELEMEK 1. előadás 12 System of gaskets (types) Gépelemek 1. Seal surface Soft, plastic Soft, plastic Metal jacketed gasket Ring Joint seal Hard, rigid, elasticity Inner material of the seal Hard Wavy sheet seals Ring joint gasket Comb seal Rubber-metal seal Térképzés elemei | GÉPELEMEK 1. előadás 13 Dynamic (moving), touch seals Gépelemek 1. Motion type: linear/alternating -, rotating/alternating seals. Base problem: there is p surface pressure, v velocity. Therefore: the system warms and wears. Dissipated (loss) power: 𝑃𝑠 = 𝐹𝑠 ⋅ 𝑣 = 𝐹𝑡 ⋅ 𝜇 ⋅ 𝑣 = 𝑝𝑡 ⋅ 𝐴𝑡 ⋅ 𝜇 ⋅ 𝑣 where 𝑝𝑡 = 𝑐 ⋅ 𝑝𝑤 Heat load of the seal: 𝑃𝑆′ = 𝑐 ⋅ 𝑝𝑤 ⋅ 𝜇 ⋅ 𝑣 Enginnering task: proper selection of the seals based on manufacturers references. Térképzés elemei | GÉPELEMEK 1. előadás 14 Dynamic (moving), touch seals (packing) Gépelemek 1. Valve packings are traditional and still are a kind of dynamic sealing structure. We install it between the valve stem and the valve cover packing box to prevent external leakage. (compress the packing) Packing material, reasonable packing box structure and installation methods ensure the reliable sealing performance of the valve. Therefore, the performance of the control valve highly depends on the type of packing material used in the control valve. Térképzés elemei | GÉPELEMEK 1. előadás 15 Stuffing box with bushing (balancing) Gépelemek 1. Balancing bush Pressure decreases More even sealing pressure distribution Térképzés elemei | GÉPELEMEK 1. előadás 16 Dynamic, touch seals Gépelemek 1. Profile seals: The pt sealing pressure generates because of the interference fit between seals and seal grooves. Térképzés elemei | GÉPELEMEK 1. előadás 17 O-rings in various cross sections Gépelemek 1. Térképzés elemei | GÉPELEMEK 1. előadás 18 Dynamic, axial, touch seals Gépelemek 1. - + Térképzés elemei | GÉPELEMEK 1. előadás 19 Dynamic, axial, touch seals Gépelemek 1. Gap losses: knowing the pressure distribution caused by the working pressure (pw) and the elastic overlap of the lip seal the oil loss can be calculated. 1 𝑄 = 𝐷𝜋 ⋅ 𝑠 ⋅ (ℎ𝑜𝑢𝑡 − ℎ𝑖𝑛 ), where 2 ℎ∗ = 8 ⋅ 9 𝑣⋅𝜂 𝑑𝑝 𝑑𝑝 , is the gap function, s, 𝑑𝑥 = 𝑡𝑔𝛼, 𝑡𝑔𝛽 𝑑 𝑥 max therefore 2 𝑣𝑜𝑢𝑡 𝑣𝑖𝑛 𝑄= 𝐷𝜋 ⋅ 𝑠 ⋅ 𝜂 − 3 𝑡𝑔𝛼 𝑡𝑔𝛽 piston rod Bear in mind!: gap loss is proportional with: geometrical dimensions, stroke, viscosity of oil, difference of pressure gradients. Aspire that: tgβ to be smaller, tgα to be bigger! Térképzés elemei | GÉPELEMEK 1. előadás 20 Example of the pressure distribution on ring seals Gépelemek 1. Turcon® Glyd Ring® Turcon® Glyd Ring® T Glyd ring T can fulfil the requirement of low gap losses. Térképzés elemei | GÉPELEMEK 1. előadás 21 Hydraulic cylinder Gépelemek 1. Rod seal Wiper Piston & rod bearing band Piston seal Static seals (O-ring) Térképzés elemei | GÉPELEMEK 1. előadás 22 Hydraulic cylinder Gépelemek 1. Rod seals Piston seals Térképzés elemei | GÉPELEMEK 1. előadás 23 Rotational, touch seals: on the curved surface Gépelemek 1. Simmerring® radial shaft seal Térképzés elemei | GÉPELEMEK 1. előadás 24 Radial lip seals Gépelemek 1. Térképzés elemei | GÉPELEMEK 1. előadás 25 Rotational, touch seals on circular plane surface Gépelemek 1. Térképzés elemei | GÉPELEMEK 1. előadás 26 Moving, no-touch seals Gépelemek 1. „Gap principle” sealing: a, gap seal, b, groove seal, c, retaining thread in the hub, d, retaining thread in the shaft. Térképzés elemei | GÉPELEMEK 1. előadás 27 Rolling bearing seals Gépelemek 1. With shield With seal With seal With shield Térképzés elemei | GÉPELEMEK 1. No seal előadás 28 Different labyrinth seals Gépelemek 1. For high temperature gases & steams-, For high angular velocity bearing arrangements Térképzés elemei | GÉPELEMEK 1. előadás 29 Diaphragm seals Gépelemek 1. Application: mainly for alternating, linear movements and to „seal” the 2 rooms completely from each other. Térképzés elemei | GÉPELEMEK 1. előadás 30 Slide ring face seal Gépelemek 1. 1. Stud bolt for spring housing fixing 2. O-ring seal 3. Anti-rotational pin 4. Slide ring (rotates with shaft) 5. Still ring (fixed to housing) 6. O-ring seal 7. Housing 8. Anti-rotation pin 9. Shaft 10. Pre-tension springs 11. Spring housing (the springs can be pre-tensioned by axial adjustment) 11 Térképzés elemei | GÉPELEMEK 1. előadás 31 Slide ring face (shaft) seals Gépelemek 1. Basic principle of face sealing Various arrangement of face shaft seals Térképzés elemei | GÉPELEMEK 1. előadás 32 Slide ring face seals Gépelemek 1. air pressure over pressure Pump sealing Térképzés elemei | GÉPELEMEK 1. előadás 33 Oil spraying systems (sprinkler, mist...) Gépelemek 1. shaft shoulders oil ring oil disc These 3 features dispense the oil by means of the centrifugal force. Térképzés elemei | GÉPELEMEK 1. előadás 34 Other different sealing principles Gépelemek 1. − Sealing with compressed liquid, − Sealing with streaming liquid, − Sealing with the principle of pressure distribution, − Sealing with the principle of velocity distribution, − Sealing with function division, − Sealing with vacuum. Térképzés elemei | GÉPELEMEK 1. előadás 35 Disaster of the challenger space shuttle (1986) Gépelemek 1. The cause of the disaster was the failure of the primary and secondary redundant O-ring seals in a joint in the shuttle's right solid rocket booster. Térképzés elemei | GÉPELEMEK 1. előadás 36