Common Types of Packing and Their Applications

In the industrial field, whether it is large-scale chemical equipment or precision mechanical devices, sealing is a crucial element. Packing, as a common sealing material, may not be as eye-catching as some high-end machinery, but it plays an indispensable role in preventing leaks and ensuring the normal operation of equipment. Today, let's delve into the types and applications of packing.

Packing, also known as sealing packing, is a time-honored sealing material. The earliest packing was primarily made of cotton, hemp, and other fibers, which were stuffed into leak channels to prevent fluid leakage. It was mainly used for the shaft seals of water-lifting machinery. Although this simple sealing method is primitive, it has been used continuously to this day due to its advantages of being widely available, easy to process, and inexpensive. Over time, the materials and manufacturing processes of packing have been continuously improved, and its range of applications has also expanded. Nowadays, it is widely used for the sealing of rotating shafts in centrifugal pumps, compressors, vacuum pumps, agitators, and ship propellers, as well as for the reciprocating motion shaft seals in piston pumps, reciprocating compressors, refrigerators, and the rotating seals of various valve stems.

There are numerous types of packing, each with its unique materials, structure, and performance characteristics to meet the sealing requirements under different working conditions. The following will detail several common types of packing and their characteristics.

Aramid fiber packing is a type of packing that mainly uses aramid fibers as the material. This packing is precisely woven after multiple impregnations with lubricants and Teflon emulsions. It has good characteristics such as high resilience, chemical resistance, low cold flow, and high linear speed. Compared with other types of packing, it can resist granular crystalline media and higher temperatures. It can be used alone or in combination with other packing. This type of packing is mainly used in equipment with a lot of granular media and easy wear, such as in the chemical and petroleum industries. It can effectively prevent leakage problems caused by granular wear.

Self-pressurized molded packing belongs to the non-woven type of packing. It is usually used as a supplement after conventional packing wears out or is placed between conventional packing and the shaft to reduce wear. Its shape is usually triangular or square and can be molded into various suitable shapes according to specific working conditions. It can be installed as a whole or cut into several sections. The working temperature range of this type of packing is 0° to +400°F (+204°C), with a maximum working pressure of 10,000 psi. It is not affected by substances such as acids, oil, corrosives, and common solvents. It can also be used on shaft surfaces with a rotation speed of up to 1,000 fpm. The 6366JX and 686 products from OCR Company's LIQUILON patent formula in the United States are representative products of this type of packing. They have been widely used in equipment with high sealing performance requirements.

Semi-fluid packing is a solid particle film type of packing product. It can be coated on metal surfaces and provides the lowest coefficient of friction among all materials. This type of packing has excellent sealing and lubrication properties and can also repair scratched, dented, or damaged shafts to restore their use. It is specially designed for sealing with tight tolerance clearance requirements down to the 0.02-inch level, with a high-temperature resistance of up to 400°F (204°C) and a high-pressure resistance of up to 10,000 psi. Semi-fluid packing can be compatible with any size stuffing box and can lubricate conventional packing to eliminate excessive wear without the need for replacement. This type of packing has important application value in equipment with extremely high sealing precision requirements, such as precision instruments and aerospace equipment.

PTFE packing is a series of packing mainly made of polytetrafluoroethylene (PTFE). PTFE is an excellent material with good chemical stability, corrosion resistance, sealing properties, high lubricity, non-stickiness, and good aging resistance. This type of packing can work long-term at temperatures ranging from +250°C to -180°C. Except for molten metallic sodium and liquid fluorine, it can resist all other chemical substances and remains unchanged even when boiled in aqua regia. Therefore, it is mainly used in working conditions where contamination is not allowed, such as in the food processing and pharmaceutical industries with high hygiene and corrosion resistance requirements, as well as in conditions with high linear speed and easy wear. Common PTFE packing includes white PTFE packing, black PTFE packing, white PTFE interwoven aramid fiber packing, black PTFE interwoven aramid fiber packing, PTFE pre-oxidized fiber packing, white PTFE silicone oil-impregnated packing, and white PTFE resin-impregnated core packing. These packing materials have different performance characteristics according to different needs, through different weaving methods and impregnation treatments, to meet various complex working conditions.

Graphite packing is a series of packing made of graphite as the main material. Graphite has good self-lubricating properties and thermal conductivity, a low friction coefficient, strong versatility, good softness, high strength, and the advantage of protecting shafts and rods. According to different requirements, materials such as carbon fiber, copper wire, 304, 316L, and Inconel alloy wire can also be used for reinforcement. This type of packing is mainly used in high-temperature and high-pressure working conditions, such as the sealing of equipment like steam turbines and boilers in power plants. Common types of graphite packing include flexible graphite packing, metal-reinforced graphite packing, carbon fiber-reinforced graphite packing, and carbon fiber metal-reinforced graphite packing. These packing materials can meet the sealing requirements under different temperature, pressure, and medium environments through different reinforcing materials and weaving processes.

Carbon fiber packing mainly uses carbon fiber as the main material. Carbon fiber is a new material with excellent mechanical properties, characterized by no creep, good fatigue resistance, low thermal expansion coefficient, good corrosion resistance, and good thermal conductivity. Carbon fiber packing is mainly used in high-temperature and high-pressure wear-resistant working conditions, such as in some high-load mechanical transmission equipment, where it can effectively prevent sealing failure caused by high temperature and wear. Common types of carbon fiber packing include carbon fiber-reinforced graphite packing and carbon fiber metal-reinforced graphite packing. These packing materials combine the advantages of carbon fiber and graphite, having both good wear resistance and excellent sealing properties, and are indispensable sealing materials in modern industry.

Rubber-cored packing is made by wrapping a highly elastic silicone rubber core with high-quality synthetic fibers, and then weaving it after multiple impregnations with Teflon emulsion, lubricants, and barrier agents. This type of packing can effectively absorb mechanical vibrations and control leaks caused by gaps generated by vibrations. It has excellent resilience, self-lubrication, flexibility, wear resistance, high tensile strength, and good chemical resistance. In equipment with large vibrations, such as mining machinery and papermaking machinery, rubber-cored packing can effectively reduce the impact of vibrations on sealing performance and extend the service life of the equipment.

High-temperature and ultra-high-temperature packing is made of high-quality synthetic fibers (1250) and has a fine structure. It has excellent high-temperature and high-pressure resistance, low thermal conductivity, and non-combustibility. It is widely used in super high-temperature and high-pressure harsh environments for water, steam, acids, alkalis, and other media. It is used for thermal insulation and fire prevention in pipelines, static sealing in containers, heaters, manholes, furnace door heaters, high-temperature flanges, and other places. In high-temperature environments such as steel mills, this type of packing is widely promoted and used. For example, the high-temperature packing for blast furnace combustion valves can effectively prevent the leakage of high-temperature media and ensure the safe operation of equipment.

In addition to the common types of packing mentioned above, there are also some special packing materials, such as acrylic packing, high-water-based packing, and ramie packing. They have their unique performance characteristics according to different working conditions. For example, acrylic packing has good weather resistance and chemical resistance and is suitable for the sealing of some outdoor equipment. High-water-based packing has good hydrophilicity and performs well in equipment that needs to come into contact with water. Ramie packing is a traditional packing material with good wear resistance and corrosion resistance, suitable for the sealing of some ordinary industrial equipment.

When selecting packing, it is necessary to comprehensively consider the working conditions of the equipment, including temperature, pressure, medium, linear speed, the material of the shaft, and the surface condition of the shaft. For example, in high-temperature and high-pressure environments, graphite packing or high-temperature and ultra-high-temperature packing should be chosen; in conditions where contamination is not allowed, PTFE packing should be selected; in conditions with a lot of granular media and easy wear, aramid fiber packing is a better choice. At the same time, the convenience of installation and maintenance of the packing, as well as cost factors, should also be considered.

When using packing, correct installation and maintenance are equally important. During installation, it is necessary to ensure that the filling amount of the packing is moderate, neither too tight to cause shaft wear nor too loose to cause leakage. Regularly check the wear condition of the packing and replace the severely worn packing in time to ensure the sealing performance of the equipment. In addition, for some special packing, such as self-pressurized molded packing and semi-fluid packing, special installation and maintenance operations should be carried out according to their characteristics.

Although packing is a relatively small industrial component, it plays a vital role in the field of industrial sealing. From traditional cotton and hemp fiber packing to modern high-performance packing, the continuous progress of materials and manufacturing processes has enabled packing to meet the sealing requirements under various complex working conditions. Whether in the chemical, petroleum, food, pharmaceutical, or aerospace industries, the correct choice and use of packing can effectively prevent leaks, ensure the safe operation of equipment, and improve production efficiency. With the continuous development of science and technology, it is believed that the performance and application scope of packing will be further expanded, providing more reliable sealing guarantees for industrial development. In short, as a key material for industrial sealing, the importance of packing goes without saying. By deeply understanding the types, performance, and applications of packing, we can better select and use packing to ensure the stable operation of industrial equipment and safeguard the safety and efficiency of industrial production.