First, the status quo of high temperature and high pressure valve packing
At present, in petrochemical, thermoelectric and other valves with high temperature and high pressure (temperature above 500 °C, pressure above 10 MPa), the packing of the valve stem is generally the following materials: 1. Flexible graphite packing ring or braided packing flexible graphite line is A direct material for making graphite fillers. It is one of the high temperature resistant materials in various sealing materials currently used. It has excellent self-lubricity (friction coefficient of 0.15) and lubricity at high temperatures (coefficient of friction ≤ 0.4 at 500 ° C), allowing line speeds of up to 40 m / s. Good chemical stability and strong corrosion resistance. It is not brittle, aging, non-deteriorating and sealing in mediums such as acid, alkali, salt, organic solvent, steam, hot oil and grease in the range of pH=0-14. Well, the compression rate is up to 75% and the rebound rate is up to 60%. And has good impermeability and excellent thermal conductivity. However, flexible graphite products have fatal weaknesses:
(1) The allowable use temperature and service pressure in the oxidizing medium will decrease to about 50% of the normal value. Making the use conditions severely constrained;
(2) Even in non-oxidizing medium, when the temperature reaches 500 °C, the temperature loss has reached 8% or more, which will greatly shorten the service life and cause the pressure reduction force to decrease and cause leakage;
(3) Low mechanical strength and brittleness during filling. The tensile strength is small, and the stuffing box is difficult to clean when replaced.
2. Rubber asbestos packing or wire rubber asbestos packing
XS550 (Cu) high temperature rubber asbestos packing is the asbestos packing with high temperature resistance in asbestos products. It is made of ordinary high-temperature 550 asbestos wire (or asbestos wire parallel copper wire or steel wire) and then bonded with high-carbon graphite on the outer surface of the packing with rubber as a binder to seal and lubricate.
Its physical indicators are as follows
density | Allowable medium temperature (zui high) | Allow medium pressure Mpa | Temperature loss (550 ° C) | Applicable medium |
1.1——1.3g/cm 3 | ≤550°C | ≤8MPa | 10% | water vapor |
B From the above indicators, it can be seen that the rubber asbestos packing has a temperature loss of up to 10% at 550 °C, that is, the shrinkage of the packing line of 10×10 mm is as high as 1 mm and the section will shrink by 20 mm 2 , which is 20 of the total cross-sectional area of ​​100 mm 2 . %, is bound to cause a leak. Moreover, because the medium pressure is only 8 MPa, it is far from satisfying the sealing conditions of the sealing parts such as the power boiler and the cracking furnace in the refinery and ethylene plant, which have a high temperature exceeding 500 ° C and a pressure exceeding 10 MPa valve stem.
Second, the valve special packing design principle and main parameters <br> Since the 1970s, China has introduced several 300,000 tons of ethylene equipment from abroad, its cracking furnace and power boiler and other valve valves with pressure exceeding 10 Mpa and temperature exceeding 500 °C Rod sealing has always been a difficult problem to be solved, the main reason is that there is no wire for the packing that can achieve such conditions. To this end, our factory developed the line.
1. The production principle, process and structure are made of special fiber for diaphragm cloth with fiber length of 4-10mm. No auxiliary cotton and other fibers are added during spinning. High temperature nickel wire is added when the three yarns are twisted and twisted. The circumference is uniformly coated with a high temperature resistant lubricating layer (0.05-0.2 mm). In this way, the thread is woven and finished by the through-heart 24 ingot knitting machine or the Nissan sheathing knitting machine.
Amitraz is a potent miticide for veterinary fields for the control of susceptible ticks, fleas and lice including organophosphorus and synthetic pyrethroid resistant strains on cattle and mange on pigs.
Dosage
For external use only.
Cattle : 1000 ml. Intraz-125 EC per 500 litres of water.
: Cattle ticks (Boophilus microplus). Treat at intervals of 19-21 days.
: New Zealand Cattle ticks (Haemaphysalis longicornis).Treat at intervals of 7-21 days.
: Paralysis ticks (Ixodes holocyclus). Treat at intervals of 7-10 days.
Pigs : 1000 ml. Intraz-125 EC per 250 litres of water.
: Mange (Sarcoptes scabiei var suis.)
Critical Comments:
Cattle : Spray cattle with a minimum of 10 litres for hand sprays and 4 litres for recirculating spays.
Pigs : Remove feed and bedding from pens. Cover drinking bowls and clean out pen. Spray pigs with minimum of 2 ltr. spray wash, especially inside ears and legs, under jowls and areas covered by scabs. Replace discarded bedding with clean material. Repeat treatment after 7-10 days. Two treatments at 7-10 days are recommended for sows and gilts before entering farrowing pens, for piglets at weaning, and for pigs newly bought into the piggery. Boars should be treated every 3 months.
Amitraz
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Hebei Kexing Pharmaceutical Co., Ltd. , https://www.kexingpharma.com