Combustible gas alarm use and maintenance methods
(2) Before calibration, the surrounding environment of the probe should be free of flammable gas. If there is flammable gas, remove the rain cover, fill in a certain amount of clean air, and then continuously introduce sample gas to ensure the accuracy of the calibration.
(3) When the measured gas is a hydrocarbon mixture, isobutane is the preferred sample gas, followed by propane.
(4) For non-hydrocarbon mixtures or mixtures of gases with a lower explosive concentration and a greater difference in the amount of heat generated, a mixture of butane, isobutane, propane and other readily available and stable single components may be used. Fuel as a sample gas. At this time, the range of the alarm must be adjusted according to a certain detection signal conversion relationship.
Combustible gas alarm use and maintenance methods
The types and types of flammable gas alarms are numerous, but the basic circuit principle is the same, so their methods of use and maintenance are also similar. The methods to be used and maintained are described below:
(1) The lifetime of the detection element and the compensation element is usually 3-5 years. Under the conditions of reasonable use and proper maintenance, its service life can be extended.
(2) For alarms with test buttons, press the test button once a week to check if the alarm system is normal. Check the zero and span of the alarm once every 2 months.
(3) The detector should always be checked for accidental flooding. When the detector breather cover is inspected by the instrument, it should be removed and cleaned to prevent clogging.
(4) The detector is explosion-proof explosion-proof equipment and shall not be used beyond the specified range. The detector must not be used in the presence of sulfur. The detector should be used as far as possible under the condition that the flammable gas concentration is lower than the lower explosion limit; otherwise, the device may be burned out.
(5) The hot wire semiconductor detector must not be used in the absence of oxygen. Do not use a large number of combustible gas probes.
At present, the five most commonly used Thermosetting Plastics in various fields are PU, epoxy resin (EP), silicone, unsaturated polyester (UP) and phenolic resin (PF).
Thermosetting Plastic has the following advantages:
Thermosetting plastic has a large rigidity and is extremely elastic and plastic deformation.The temperature has little influence on stiffness, and under the same load and temperature, the creep variable is much smaller than thermoplastic.Good heat resistance;The plastic parts are quite stable when heated.The size of the plastic parts is good. Thermosetting plastic is less affected by temperature and humidity, and Thermosetting plastic can be reduced after forming, making Thermosetting plastic easy to make plastic parts with high precision than thermoplastic ruler.Excellent electrical performance.Resistance to arc and voltage, etc.Good corrosion resistance, weak acid, weak base and organic solvents;Good processability, can be processed by various molding methods and other advantages.
Most thermosetting plastics have the following characteristics:
(1) excellent chemical resistance.
(2) it is usually brittle hard plastic, which can be filled with various fillers to form composite materials.
(3) compared with thermoplastic resin, the molding cycle is longer.
(4) all kinds of modification can be carried out, depending on the combination of resin, crosslinking agent, additive, etc., which can form composite materials with different properties.
(5) good heat resistance, the use of high temperature, Tg of thermosetting polyimide (PI) is about 350 ℃.
(6) can be used as raw materials to meet the application of various fields.Only 5% is used as injection molding material.
(7) the waste is generally used as filler after pulverization, which is difficult to recycle and pollutes the environment.
Due to the high heat resistance of thermosetting plastic, good dimensional stability, good line performance, anti-aging properties are better than thermoplastic plastic and low price, so it is widely used.The disadvantage is that the mechanical properties are poor and need to be enhanced.
It is mainly composed of thermosetting resins, which are involved in various necessary additives to form the plastic of the products.In the process of manufacturing or forming, the liquid will be liquid, which will not melt after curing or melt or soften again.Common thermosetting plastics include phenolic plastic, epoxy plastic, amino plastic, unsaturated polyester, alkyd plastics, etc.Thermosetting plastic and thermoplastic plastics constitute two major components of synthetic plastic.
Thermosetting plastic heating for the first time can soften the flow, heated to a certain temperature, react a crosslinking reaction and curing hardens, this change is irreversible, since then, heating again, already no longer soft flow.It is the use of this characteristic to make the molding process, using the plasticization flow of the initial heating, filling the cavity under pressure, and solidifying to become the product that determines the shape and size.
Thermosetting plastic is distinguished by a chemical reaction that is hardened by heating, pressing or adding the hardener at a definite temperature.After hardening, plastic chemical structure changes, the texture is hard, dissolves in the solvent, heating also no longer softens, if the temperature is too high then decompose.In thermoplastic plastic, the chains of resin molecules are linear or branched, and there is not any chemical bond between the molecular chains, which soften the flow when heated.The process of cooling and hardening is a physical change.
Formaldehyde cross linked plastic includes phenolic plastic, amino plastic (such as urea-formaldehyde - melamine - formaldehyde, etc.).Other cross linked types of plastic include unsaturated polyester, epoxy resin, prevalence, diallyl ester resin, etc.
The commonly used thermosetting plastics are phenolic resin, urea-formaldehyde resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, polyurethane, etc.
Production:Phenolic resin PF (Bakelite sheet)
Phenolic resin is a part of the longest plastic varieties in history, commonly known as bakelite or electric wood, and the appearance is yellowish or black, which is the typical representative of thermosetting plastic.Bakelite sheet molding often use a variety of filling materials, according to different filling materials used, the product performance is also different, Bakelite sheet as molding material, mainly used in the field of need heat resistance, but also as a bonding agent used in plywood, grinding wheel and the brake pads.
Thermosetting Plastics
Thermosetting Plastic,Thermoset Molding Plastic,Mould Thermosetting Plastic,Thermoplastic Type Plastic
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