On drying equipment and material corrosion

　　Dry materials handling equipment is difficult to count, in addition to the different requirements of a variety of physical and chemical properties of materials and products, the thermal and physical properties of the material of the heating process in the drying process of drying material requirements system equipment is an important consideration for designers to this article presented on timber drying equipment problems some ways for designers reference.

　　1 Introduction drying equipment is one of the most widely used equipment unit can be considered, the application of drying equipment has been throughout all sectors of the national production. For drying equipment, we must not simply think that it is only mechanical dewatering method of thermal physics. Depending on the material drying process, the moisture content of different types, products of the indicators are also different. Equipment installation location is different for selection, equipment type and manufacture, installation method of drying equipment manufacturing has different requirements. Properly address these issues is an important factor in the successful design of drying equipment.

Features 2 drying equipment

　　2.1 types of drying equipment so far, has successfully developed drying equipment there are hundreds of different kinds, it is also commonly used in the industrial production of more than 100. Classification method of drying apparatus also has a variety of, if by way of heat convection drying process can be divided into the dryer (such as a flash dryer, spray drying equipment, rotary flash dryer, fluidized bed dryer, etc.), heat conduction dryers (such as rake dryer, roller dryer), radiation dryer (such as microwave dryer, a far-infrared dryers) and the like. In addition, there are several combined heat transfer drying apparatus such as a paddle dryer or the like.

　　Features 2.2 drying equipment dryer vast majority are non-standard equipment, mainly because of material processed per the dryer is not the same, a lot of drying conditions vary with different materials, thereby resulting in the dryer structure and materials change. It is necessary to be clear dry material specific parameters, such as the state of the material, moisture contained in the type, the amount of processing, the material properties of the drying process, if non-corrosive, and explosive combustion, whether static, product specific requirements, heat-sensitive materials temperature, etc., to determine the various parameters of the dryer. For this reason many of the dryer can not be mass production, in the design process must pay attention to the relevance and suitability of materials for working conditions.

　　Selection 3 drying equipment manufacturers of well-known material, material drying equipment is an important element of the cost of drying apparatus constituted reasonable choice of materials is an important means to control the prices of equipment. In general, the choice of materials drying equipment should consider the following aspects:

　　3.1 The main task of satisfying the needs of the materials handling equipment drying material is given by drying. Because the dryer handle a wide range of materials, covering many areas of food, food, pharmaceutical, chemical, forest products, paper, metallurgical, the product is difficult to count. It is required to vary the dried materials, such as drying process chemical reagents, pharmaceuticals, electronic materials, electrical ceramic materials and the like must not be mixed with iron ions, so the device selection to avoid using carbon steel. In addition, if the material is moisture-containing acid, alkali, salt, organic solvent, etc., for different metal materials will be corrosive. Especially in the heating process, the corrosion of the material will increase, it should choose the appropriate material according to the material contained in the moisture characteristics.

　　3.2 for the previous drying models the choice of materials mentioned formula, dryers have a variety of types, each model works different, so in the choice of materials should be fully taken into account. Such as magnesium oxide when dry air dryer, because the material at high velocity gas flow tube, magnesium oxide materials hard, turning on a drying tube wall badly worn, so in this area will be designed to prevent wear resistant materials selection or structure . Again, compared with carbon steel, stainless steel thermal conductivity significantly lower than the former. Therefore, the heat transfer by conduction mainly drying equipment, if you choose stainless steel as the main material, the heat transfer area of the device in the thermal conductivity of the stainless steel should be calculated. Engineering examples prove, in the choice of steam heat exchanger, stainless steel than carbon steel large area of 30%.

　　3.3 drying process for the selection of materials of different materials drying conditions are different, the author has designed a high temperature dryer drying inorganic salts at the same time also its polymerization. Requirements hot dry air at temperatures above 800 ℃, dried material prices do not have to choose which enjoys the high temperature stainless steel, but does not take into account the drying chamber are in the high-temperature region, according to calculations, only in the high temperature refractory material selected now It has been running more than a year as usual.

　　3.4 for the installation environment the choice of materials, in many cases, despite the above conditions can meet the requirements, but also pay attention to the material equipment installation environment requirements. If you install equipment in chemical plants, environmental equipment, control systems, electrical systems or without corrosion should give serious consideration to come up with a reasonable design.

A method for preserving dried equipment Most dryers are based welding parts, flat, cylinder components. Really different uses for dryer embalmed, here are some some experience in anti-corrosion materials and manufacturing methods.

　　4.1 phosphate - passivation process in the manufacture of vibration fluidized bed dryer, the unit is 70 per cent carbon steel construction. A longer turnaround time between process and therefore generates a large amount of surface rust before painting required more labor to rust. Phosphate - passivation process is by electrical and electrochemical reaction, a one-time treatment, can make and full of rust steel workpiece surface showing the original color of the metal, while generating a dense layer of rust on the metal surface . Ten days can be placed in the humid air, and will not rust. Its method of operation is simple and can improve the working environment, reduce labor intensity, saving manpower and resources. For phosphate - passivation treatment liquid containing an emulsifier, molybdates, and a variety of acid soluble phosphate, which is not only used in the above models, or other similar structure racks can use this method for corrosion protection deal with.

　　4.2 Electrostatic powder coating equipment manufacturer on a dry application of traditional paint is a liquid, which contains large amounts of ketones and esters of hydrocarbons and other organic solvents, to the production, storage, transportation and construction to bring a series of troubles, and explosive very safe. Because there is a certain toxicity, volatilization into the atmosphere, seriously pollute the environment. Therefore, coating experts at home and abroad are committed to the development of new coating solution or less without a solution. One such novel coating is a powder coating.

　　On the cover of machine vibration fluidized bed dryer, mostly cold-rolled stainless steel sheet, and therefore costly. Why not use ordinary stainless steel, because the device is in working condition will be exposed to a variety of materials and corrosive gases, and corrosion resistance of stainless steel is excellent, and therefore the use of cold-rolled stainless steel.

　　Electrostatic spraying polyester resin powder coating with ordinary carbon steel, the corrosion resistance of stainless steel completely comparable. Since the powder coatings having a tough, durable, decorative and good, and excellent outdoor weathering resistance and heat resistance, and excellent corrosion resistance and resistance to chalking, excellent gloss and color-light performance, so, electrostatic powder coating is fully applicable to the corrosion of the dryer housing.

　　4.3 austenitic nickel-chromium stainless steel welding explore drying equipment, many of which are plates welded structure, most of the sheet metal is 1Cr18Ni9Ti (18-8 type). Corrosion, fracture and other problems often occur during welding. Seriously affect product life and performance. The difference between ordinary carbon steel and austenitic stainless steel is poor thermal conductivity, thermal expansion coefficient when the resistance value is high. Due to these characteristics of austenitic steels, it requires special welding processes to weld. Intergranular corrosion is one of the main problems of high-alloy steel. This high corrosion resistance of the steel itself, but the welding process reduces the corrosion resistance. Austenitic steel welding corrosion forms: whole, local, intergranular corrosion. Factory introduction of foreign domestic drying equipment, bag filter stainless steel frame due to improper welding method destroys the organizational structure of the material causes intergranular corrosion, the drying process material containing acidic components, steel soon cause rupture.

　　5 Conclusion drying technology development today, as an engineering and technology, the success of not only the drying theoretical level about the relationship between the device structure, material selection, manufacturing process and is also very close. Comprehensive variety of factors, develop a reasonable program of manufacturing has important economic significance.