Aramid Fiber Packing: A High-Performance Sealing Solution

In the industrial field, the choice of sealing materials is crucial for the stable operation of equipment. Aramid fiber packing, as a high-performance sealing material, has been favored by many industrial users due to its excellent performance and wide applications. This article will introduce in detail the characteristics, advantages, application fields, and key points of use and maintenance of aramid fiber packing, helping you better understand this high-performance material.

Aramid fiber, fully known as "aromatic polyamide fiber," is a new type of special polymer material. Its main characteristic is that more than 85% of the amide bonds are directly linked to the benzene ring, with the amide bonds connected to aromatic rings or their derivatives. This unique chemical structure gives aramid fiber a series of excellent properties, including flame resistance, high temperature resistance, high strength, high modulus, and insulation.

Commercially available aramid fibers on the market are mainly of two types: meta-aramid and para-aramid.

Meta-aramid, fully known as "poly-m-phenylene isophthalamide" (MPIA) fiber, is an organic polymer fiber synthesized from isophthaloyl chloride and m-phenylenediamine. Because the amide bonds are connected to the 1 and 3 positions of the two benzene rings, it is also called aramid 1313. Meta-aramid has the following outstanding characteristics:

Thermal stability: Can be used for a long time at 200℃ without aging, with excellent dimensional stability.

Flame resistance: Limiting oxygen index (LOI) >28%; it will not self-ignite or melt in air, and no molten droplets will form, self-extinguishing when removed from flame.

Electrical insulation: The insulation paper made from it has a breakdown voltage resistance of up to 20kV/mm.

Corrosion and radiation resistance: Excellent corrosion resistance and outstanding radiation resistance.

Processability: Low rigidity and high elongation, can be processed with conventional textile machinery.

Para-aramid, fully known as "poly-p-phenylene terephthalamide" (PPTA) fiber, is an organic polymer fiber synthesized from terephthaloyl chloride and p-phenylenediamine. Because the amide bonds are connected to the 1 and 4 positions of the two benzene rings, it is also called aramid 1414. Para-aramid has the following excellent properties:

High strength and high modulus: Tensile strength is 6 times that of steel wire; tensile modulus is 2–3 times that of steel wire and glass fiber, while density is only about 1/5 that of steel wire.

High temperature resistance and flame resistance: Maintains original strength after hundreds of hours at 200℃; does not decompose or melt at 560℃.

Impact and fatigue resistance: Known as "bulletproof fiber," with good impact resistance, corrosion resistance, and fatigue resistance.

Environmental issues: Structurally stable and difficult to degrade, causing later recycling and disposal problems that impact the environment.

Aramid fiber packing is braided from aramid fiber impregnated with PTFE emulsion and lubricant. This special treatment endows aramid fiber packing with a series of excellent properties, making it outstanding in the field of industrial sealing.

Aramid fiber packing has good chemical resistance, able to withstand the erosion of various chemical media, including strong acids, strong alkalis, and organic solvents. This makes it excellent for applications in industries such as chemicals and pharmaceuticals.

Aramid fiber packing has high elasticity and low cold flow. This means that in high-temperature and high-pressure environments, the packing can maintain its shape and sealing performance, not easily deformed or displaced. This characteristic is crucial for ensuring long-term stable operation of equipment.

Aramid fiber packing has extremely high strength and modulus, known as "artificial metal wire." This allows it to withstand high-speed and high-pressure working conditions, making it widely used in various industrial equipment.

The design of aramid fiber packing makes it easy and quick to disassemble, greatly reducing the time and cost of equipment maintenance and repair. This is of great significance in improving production efficiency and reducing maintenance costs.

Aramid fiber packing is widely used in various industrial fields, especially in situations requiring high temperature, high pressure, chemical corrosion resistance, and high sealing performance. Main application areas include:

Aramid fiber packing is an ideal sealing material in pump systems, especially in applications requiring high temperature resistance, corrosion resistance, and high sealing performance. It can replace traditional asbestos packing to provide safer and more reliable sealing.

In valve sealing, aramid fiber packing can effectively prevent leakage and ensure the normal operation of valves. Its high strength and chemical resistance allow it to perform well under harsh working conditions.

Mixers are widely used in industries such as chemicals and pharmaceuticals. Aramid fiber packing can withstand the high pressure and wear during the mixing process, ensuring stable operation of the equipment.

The working environment of compressors is usually characterized by high temperature and high pressure. The high temperature resistance and high strength of aramid fiber packing make it an ideal choice for compressor sealing.

Aramid fiber packing can also be used in other industrial equipment requiring high-performance sealing, such as reactors and pipeline connections, providing reliable sealing solutions.

The high performance of aramid fiber packing not only depends on the material itself but is also closely related to proper use and maintenance. Correct installation and maintenance can significantly extend the service life of the packing, reduce equipment failures, and improve production efficiency.

Loosen the gland bolts: Slowly loosen the gland bolts to release all residual pressure inside the flexible graphite packing assembly.

Remove old packing and clean: Remove all old flexible graphite packing and thoroughly clean the stuffing box of the shaft/rod.

Inspect shaft/rod and other parts: Check for corrosion, dents, scratches, or excessive wear. Inspect other parts for burrs, cracks, or wear. Replace components with major defects.

Install packing rings: After installing the packing rings, tighten the bolts. To ensure uniform pressure on each nut, it is recommended to use a wrench or measuring device. Note: If the device is leak-free at this time, packing burnout may occur. It is recommended to slowly tighten the bolts until the leakage reaches the allowable range.

Check weight loss (burnout rate): Leakage of the stuffing box is often due to decomposition, carbonization, and volatilization of organic matter and crystalline water in the aramid packing at high temperatures, causing voids and leakage. The ratio of this weight loss to the original weight is called the burnout rate. The burnout rate is an important criterion for evaluating the quality of aramid packing and should be strictly selected according to operating conditions.

Avoid adding extra lubricant: Do not add additional lubricant during repair, as this may impair the original performance of aramid packing, increase weight, reduce plasticity, and lose impact resistance, increasing maintenance costs.

Regular inspection and replacement: Inspect the packing regularly and replace worn or aged packing in time to ensure normal operation of the equipment.

Avoid mixing other fibers: Some braiders may mix other fibers into aramid to reduce costs, which seriously affects performance. Therefore, pure aramid fiber packing should be chosen to ensure optimal performance.

The performance of aramid fiber packing is influenced by multiple factors, including braiding density, braiding method, size selection, and production equipment. Each factor may significantly affect sealing performance, durability, and service life.

Braiding density is one of the key factors affecting performance. Densely braided packing better resists wear and extrusion, less likely to deform at high temperatures, thus effectively controlling leakage. Densely and orderly braided packing is recommended for most applications.

Main braiding methods include plaited, layered, and interlock braiding. Interlock-braided aramid packing has tightly entangled fibers, uniform density, and strong lubrication retention, making it an ideal choice for pump sealing.

Proper size selection is also critical. Oversized packing should be avoided to ensure proper installation under special conditions, reducing downtime and installation failures.

Braiding should be performed on machines with multiple spindles and tracks. More spindles mean more intertwined yarns, making the packing more durable. Packing braided on four-track machines has smoother and more uniform surfaces compared to three-track machines, thereby improving sealing efficiency and reducing compression force required.

As a high-performance sealing material, aramid fiber packing is widely used in various industrial fields due to its excellent chemical resistance, high resilience, low cold flow, and high strength. Correct selection and use of aramid fiber packing can effectively improve sealing performance, reduce maintenance costs, and ensure stable operation of industrial production. It is hoped that this article can help you better understand the characteristics, applications, and maintenance of aramid fiber packing, providing strong support for your industrial production.