1. Sealing and Leakage Prevention
Machinery generally has technical requirements for sealing and leakage prevention. Sealing and leakage prevention refer to assembly operations that use sealing components to stop leakage. Sealing performance is a key indicator of equipment quality, and relevant operation skills are essential for assembly and maintenance personnel.
1.1 Functions of Sealing
- Seal off spaces by compressing materials of different types.
- Block the migration of substances such as dust, water, gas and grease between separate spaces.
- Prevent foreign matter from entering the equipment.
- Avoid loss of lubricating oil inside machine parts.
1.2 Basic Requirements for Sealing
A qualified sealing structure shall be tight and reliable, compact in layout, simple to manufacture, easy to maintain and long in service life.
1.3 Sealing Materials
General Requirements for Sealing Materials
Sealing materials need to feature good compactness, appropriate hardness, flexibility, elasticity and good adaptability to working conditions.
Sealing materials are divided into soft sealing materials and hard sealing materials.
- Soft sealing materials: Paper, oil-impregnated paper and paperboard, molded asbestos plates, synthetic rubber, nitrile rubber, neoprene, sealing parts made of elastic plastics, sealants, etc.
- Hard sealing materials: Sealing components composed of aluminum mesh or steel mesh, etc.
2. Sealing Tests and Their Purposes
When assembling sealing parts, pressure vessels and sealed systems, relevant components shall undergo pressure tests before installation. After assembly, the whole system shall be subject to air tightness tests or pressure tests. This applies to equipment and systems such as air compressors, water pumps, power machines, refrigeration equipment and vacuum equipment.
The purposes of tests are to check for leakage for timely repair, and verify the strength and performance of pressure-bearing components. Common sealing tests for pressure-bearing parts include pneumatic tests (including vacuum tests) and hydraulic tests.
3. Classification of Seals
Seals are mainly categorized into static seals and dynamic seals.
3.1 Static Seals
A static seal is applied where no relative motion exists between the sealing surface and the mating surface of parts. It includes non-metallic seals, combined non-metal & metal seals, all-metal seals and liquid gasket seals.
3.2 Dynamic Seals
A dynamic seal is adopted where relative motion occurs between the sealing surface and the mating surface of parts. It is split into contact seals and non-contact seals.
- Contact seals: The sealing surfaces are pressed tightly by sealing force to eliminate or narrow gaps. Most static seals fall into this category. Common types include packing seals (felt seals, gland packing seals, molded packing seals), expansion ring seals and mechanical seals.
- Non-contact seals: A certain gap is reserved between sealing surfaces, and no compressing force is required. Typical types are clearance seals, labyrinth seals, centrifugal seals, spiral seals and pneumatic seals.
