Graphite packing quality resolution and sealing principle
Graphite packing has good self-lubricating properties, low friction coefficient and wear resistance. When the friction is heated, it can withstand a certain temperature, the disassembly is convenient, the manufacturing is simple, and the price is low.
Mass resolution of graphite packing
Graphite packing should be distinguished by the graphite structure. The larger the scale, the better the material. The smoothing effect is excellent under the flat condition. The graphite packing with poor quality is powdery graphite, the gloss is dim, the inner wire is generally 304, nickel. The elasticity of the wire is good, the elasticity of the carbon steel is poor, and it can be distinguished according to the number of internal wires or other reinforcing fibers.
Graphite packing and carbon steel run for more than 400 for a long time, the internal carbon steel wire will lose strength, causing the packing time to be seriously reduced. 304 or nickel wire material should be used, 304 nickel wire temperature is about 650, too high temperature graphite ablation rate Will increase, the strength is reduced, resulting in leakage, such as the equipment in an oxidizing environment or acid-base environment, the temperature is lower than the applicable temperature.
Sealing principle of graphite packing
The graphite packing seal is filled in the stuffing box by a packing, and the graphite packing is pressed against the surface of the shaft by a packing gland. Since the surface of the shaft is always rough, it can only partially fit the graphite packing, while the parts are not in contact, which forms numerous labyrinths. When the pressurized medium passes through the surface of the shaft, the medium is throttled multiple times, and the "maze effect" is used to achieve the seal.
The pressing force of the graphite packing against the shaft is produced by tightening the gland bolts. Since the filler is an elastoplastic body, when subjected to axial compression, friction is generated to cause the pressing force to gradually decrease in the axial direction, and the resulting radial pressing force causes the filler to abut against the shaft surface to prevent the medium from leaking out.
The distribution of the radial pressing force is from the outer end (gauge) to the inner end, firstly sharply decreasing and then flattening. The distribution of the medium pressure is gradually decreased from the inner end to the outer end. When the external medium pressure is zero, the leakage is very high. Less, leaks greater than zero.