I. Sealing and Leak Prevention
Automatic packaging machinery often has clear technical requirements for sealing and leak prevention. The process of using parts with sealing performance to prevent medium leakage through assembly operations is called sealing and leak prevention. Sealing performance is an important indicator to measure the quality of automatic packaging machinery, and sealing and leak prevention operations are also basic skills that equipment assembly and maintenance personnel must master.
(I) Functions of Sealing
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Seal the space inside the equipment or between components through the extrusion cooperation of different materials;
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Block the migration of media (such as dust, water, gas, grease, etc.) between two separate spaces;
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Prevent external debris from invading the equipment, avoiding component wear or failure;
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Prevent the loss of consumable media such as lubricating oil and grease inside the equipment, ensuring the normal operation of the equipment.
(II) Basic Requirements for Sealing
The basic requirements for sealing structures and components are: tight sealing without leakage, compact and reasonable structure, simple manufacturing process, convenient installation and maintenance, and long service life.
(III) Sealing Materials
Sealing materials need to meet the following core requirements: excellent strength, moderate hardness, good toughness, good elasticity, as well as wear resistance, corrosion resistance, temperature resistance and other adaptability. Sealing materials are mainly divided into two categories: soft sealing materials and hard sealing materials:
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Soft sealing materials: Including oil-impregnated paper and cardboard, asbestos products (used for multi-material sealing), natural rubber, nitrile rubber, neoprene, as well as seals and sealants made of elastic plastics;
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Hard sealing materials: Including sealing materials composed of metal meshes such as aluminum mesh and steel mesh, as well as various metal seals.
II. Sealing Test and Its Role
When assembling seals, pressure vessels and various closed systems, in order to meet the technical requirements of leak prevention, assemblers need to carry out sealing tests in two steps: before installation, conduct pressure test on individual sealing components; after installation, conduct air tightness test or pressure test on the entire sealing system. Such tests are applicable to air compressors, water pumps, power machinery, refrigeration equipment, vacuum equipment and their composed closed systems.
The purpose and significance of the sealing test: first, to check whether there are leakage points in the system for timely repair and improvement; second, to detect the strength and service performance of pressure-bearing components, ensuring the safe operation of the equipment. The sealing tests of pressure-bearing components are mainly divided into two types: air pressure test (including vacuum test) and water pressure test.
III. Classification of Sealing
According to the movement state of the sealing surface and the joint surface of components, sealing can be divided into two categories: static sealing and dynamic sealing.
(I) Static Sealing
Sealing where there is no relative movement between the sealing surface and the joint surface of components is called static sealing. Common types include: non-metallic sealing, non-metallic and metal composite sealing, metal component sealing and liquid gasket sealing.
(II) Dynamic Sealing
Sealing where there is relative movement between the sealing surface and the joint surface of components is called dynamic sealing. Dynamic sealing is mainly divided into two categories: contact-type sealing and non-contact-type sealing.
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Contact-type sealing: It achieves sealing by pressing the sealing surfaces against each other with sealing force to reduce or eliminate gaps. Most static seals also belong to this category. Common forms include packing seal (felt seal, gland packing seal, formed packing seal), seal ring seal, expansion ring seal, mechanical seal, etc.;
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Non-contact-type sealing: A certain fixed gap is retained between the sealing surfaces, and sealing can be achieved without pressing with sealing force. Common forms include clearance seal, labyrinth seal, centrifugal seal, spiral seal and pneumatic seal, etc.
