Carbon Fiber Packing: Ideal Alternative to Asbestos Packing

In the industrial sector, the choice of sealing materials is of utmost importance as it directly affects the operational efficiency and safety of equipment. Carbon fiber packing, as a novel sealing material, has gradually emerged as the ideal alternative to asbestos packing due to its superior performance and broad application prospects. This article will delve into the basic composition, weaving forms, performance characteristics of carbon fiber packing, as well as how to properly select and use it, to help readers better understand and apply this advanced sealing material.

Carbon fiber packing is woven from acrylic fibers that have undergone pre-oxidation treatment. After pre-oxidation, these fibers transform into carbon fibers with high stability and strength. Carbon fiber itself is an excellent structural material, characterized by high strength, rigidity, and good thermal and chemical stability. These properties enable carbon fibers to maintain their performance in high-temperature and complex environments without easily deforming or being damaged.

To further enhance the performance of carbon fiber packing, its surface is typically treated with polytetrafluoroethylene (PTFE) emulsion. PTFE is a material with superior chemical stability and high-temperature resistance, providing additional protection to the carbon fiber packing and enhancing its wear and corrosion resistance. Moreover, during the production process, carbon fiber packing is combined with epoxy resin. Epoxy resin offers good durability and wear resistance to the carbon fibers, ensuring that the packing maintains its performance over long-term use.

However, the performance of carbon fiber packing is not solely determined by the characteristics of carbon fibers and epoxy resin. While carbon fibers have relatively high thermal stability and can withstand high temperatures, epoxy resin has poorer thermal stability. Under prolonged high-temperature exposure, epoxy resin may decompose, leading to the rupture and damage of the carbon fiber packing. Therefore, in practical applications, it is essential to select the appropriate carbon fiber packing based on the specific working conditions of the equipment and pay attention to the maximum temperature it can withstand.

The braiding pattern of carbon fiber packing has a direct influence on its performance. Different braiding methods not only affect the sealing capability but also impact the service life of the packing. Common braiding types include plaited braid, jacket braid, interlock braid, and core braid.

Plaited braid is produced using eight spindles running on two tracks. This method creates a loose packing with a square cross-section and no fiber core at the corners or center. Such packing can compensate for shaft vibration and eccentricity, making it suitable for small cross-section packing. However, when the cross-section is large, plaited braid tends to have a coarse surface pattern, loose structure, and poor density, making it generally unsuitable for large-section packing.

Jacket braid is woven using 8, 12, 16, 24, 36, 48, or 60 spindles on two tracks. Depending on the packing size, 1–4 layers are typically braided without a fiber core. This structure offers high density and strong sealing performance, but due to the lack of fiber interconnection between layers, it is prone to delamination. As a result, jacket braid is mainly used in static sealing or low-speed equipment.

Core braid consists of a rubber or metal core surrounded by fiber layers, each braided over the previous one. This design provides good density, high strength, excellent flexibility, and reliable sealing performance. However, once the surface layer wears away, it may easily detach. Therefore, core braid is generally used in pumps and valves, and rarely in reciprocating equipment.

Interlock braid is woven using 8, 12, 16, 24, 36, 48, or 60 spindles on three or four tracks. The resulting packing has a square cross-section, smooth surface, excellent elasticity, high wear resistance, strong tensile strength, and high density. Its contact surface with the shaft is larger and more uniform than that of plaited braid, with smaller fiber gaps, ensuring excellent sealing performance. Even after surface wear, the packing remains intact and does not loosen, giving it a long service life. Interlock braid is considered an advanced braiding structure suitable for various equipment and operating conditions.

After understanding the basic composition and weaving forms of carbon fiber packing, let's now explore its performance characteristics in detail. These characteristics are the key factors that enable carbon fiber packing to stand out among numerous sealing materials.

Carbon fiber packing has excellent thermal conductivity. This property allows it to quickly dissipate heat in high-temperature environments, thereby maintaining the normal operation of equipment. Good thermal conductivity not only reduces the thermal expansion of the equipment but also lowers the risk of equipment damage caused by high temperatures.

Wear resistance is one of the important performance features of carbon fiber packing. Due to the high hardness and strength of carbon fibers, carbon fiber packing can maintain its sealing performance over long-term use without leakage caused by wear. This wear resistance makes carbon fiber packing perform exceptionally well in high-load, high-wear equipment.

Carbon fiber packing exhibits good chemical stability. It can resist the erosion of various chemicals and does not lose its performance due to chemical reactions. This chemical stability enables carbon fiber packing to maintain its sealing performance in chemical environments without being damaged by chemical substances.

Among non-asbestos products, carbon fiber packing is relatively inexpensive. As an ideal alternative to asbestos, carbon fiber packing not only has superior performance but also offers competitive pricing. This makes carbon fiber packing widely applicable in the market.

When selecting carbon fiber packing, it is necessary to choose the appropriate weaving form and size based on the specific working conditions of the equipment. Different weaving forms and sizes can directly affect the sealing performance and service life of the packing.

The choice of braiding pattern depends on the specific operating conditions of the equipment. For small cross-section packing, plaited braid packing can be selected; for static sealing or low-speed equipment, jacket braid packing is suitable; for pumps, valves, and similar equipment, core braid packing is preferred. Interlock braid packing, due to its advanced braiding structure and superior performance, is generally regarded as the best choice for a wide range of equipment and operating conditions.

When selecting the size of carbon fiber packing, it is important to avoid sizes larger than the standard size of aramid fiber packing. Carbon fiber packing should operate at sizes less than or equal to the standard size. This ensures that the woven carbon fiber packing can be correctly installed under special conditions, thereby reducing downtime and the likelihood of installation failure.

The weaving density of carbon fiber packing has a significant impact on its performance. Tightly woven carbon fiber packing can resist wear and compression and will not deform under increased temperatures. This reduces the need for adjustments to the carbon fiber packing and effectively controls leakage. Therefore, when selecting carbon fiber packing, it is advisable to choose tightly woven packing. Additionally, manufacturers can further increase the density of tightly woven carbon fiber packing through compression and reshaping, making it even more compact.

It should be noted that although loose weaving of carbon fiber packing theoretically increases the length per pound of the packing, this does not mean that users will benefit from using such loose packing. On the contrary, in actual filling operations, more of this loose packing will be required to fill the stuffing box, so there is no theoretical saving. In fact, maintenance costs will increase with the frequency of replacing the carbon fiber packing and the downtime associated with it.

Due to its excellent performance, carbon fiber packing has been widely used in many industrial fields. The following are some common application cases:

In pumps and valves, carbon fiber packing can effectively seal fluids and prevent leakage. Thanks to its good wear resistance and chemical stability, carbon fiber packing can maintain its sealing performance in high-load, high-wear environments, thereby extending the service life of the equipment. Additionally, the thermal conductivity of carbon fiber packing can reduce equipment thermal expansion and lower the risk of equipment damage caused by high temperatures.

In compressors, carbon fiber packing can withstand high temperatures and pressures while maintaining its sealing performance. Its good elasticity and wear resistance enable it to maintain performance over long-term use without leakage due to wear. Moreover, the chemical stability of carbon fiber packing can resist the erosion of chemicals that may be present in compressors, thereby extending the service life of the equipment.

In mixers, carbon fiber packing can withstand high loads and wear while maintaining its sealing performance. Its good elasticity and wear resistance ensure that it maintains performance over long-term use without leakage due to wear. Additionally, the thermal conductivity of carbon fiber packing can reduce equipment thermal expansion and lower the risk of equipment damage caused by high temperatures.

As a novel sealing material, carbon fiber packing has gradually become the ideal alternative to asbestos due to its superior performance and broad application prospects. Carbon fiber packing features excellent thermal conductivity, wear resistance, chemical stability, and cost-effectiveness, meeting the sealing requirements of various industrial equipment. When selecting carbon fiber packing, it is necessary to choose the appropriate weaving form and size based on the specific working conditions of the equipment, and pay attention to the impact of weaving density and loose weaving. By properly selecting and using carbon fiber packing, the sealing performance and service life of equipment can be effectively improved, reducing maintenance costs and downtime.