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On drying equipment and material corrosion

2015-05-20 | 浏览量: 1834 Changzhou LongWen Drying Equipment Co., Ltd.

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 material drying system equipment designers require more important consideration is the issue, the paper made on the issue of drying equipment timber some way, for designer reference.

1 Introduction drying equipment is one of the most widely used unit equipment, 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 just hot physically dehydration machinery. Due to the different treatment of drying process, the moisture content of different types, the indicators are also different. Equipment installation location is different, for the 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 have hundreds of different kinds, commonly used in industrial production also hundreds of species. Classification method of drying apparatus also has a variety of, if you press the heat transfer drying process can be divided into a convection dryer (such as air dryers, spray drying equipment, rotary flash dryer, fluidized bed dryer, etc.), heat conduction Dryer (such as rake dryer, roller dryer), radiation dryers (such as microwave dryers, far infrared dryers), etc. In addition, there are several combined heat transfer drying equipment such as paddle dryer and so on.

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

Selection 3 drying equipment manufacturing materials is well known, the material drying equipment is an important element of the cost of drying apparatus constituted a reasonable choice of materials is an important means to control the prices of equipment. Under normal circumstances, the choice of material drying equipment from the following aspects:

The main task of 3.1 to meet the needs of the processed material drying equipment is given materials to dry. Because the dryer handle a wide range of materials, covering the fields of food, food, pharmaceutical, chemical, forest products, paper, metallurgy, 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 in the moisture-containing acids, bases, salts, organic solvents, for different metal materials will be corrosive. Especially in the heating process, the corrosion of the material will increase, it should choose the appropriate materials according to the material contained in the moisture characteristics.

3.2 for the previous drying machine type selection of materials mentioned, there are a variety of types of dryers, each model works different, so the choice of material should also be fully considered. Such as magnesium oxide when dry air dryer, because the material at a high velocity gas flow tube, magnesium oxide materials hard to turn a drying tube wall badly worn, so in this area should be designed to prevent abrasion wear resistant structure or select materials . Again, compared to carbon steel, stainless steel thermal conductivity significantly lower than the former. Therefore, the heat transfer by conduction-based drying equipment, if you choose stainless steel as the main material, the heat transfer area of the equipment to the thermal conductivity of the stainless steel should be calculated. Project examples demonstrate, at the choice of the steam heat exchanger, stainless steel than carbon steel large area of 30%.

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

3.4 the choice of materials for equipment installation environment, in many cases, despite the above conditions can meet the requirements, but also pay attention to the material installation environment requirements. If the installation of equipment in chemical plants, environmental equipment, control systems, electrical systems must seriously consider whether the corrosion, to come up with a reasonable design.

A method for preserving dried equipment Most dryers are in the weldment, flat, cylinder components. True to the dryer for different purposes embalmed, here are some some experience in corrosion materials and manufacturing methods.

4.1 phosphating - passivation process in the manufacture of vibration fluidized bed dryer, there are seventy percent of the parts is steel structure. A longer turnaround time between process and therefore generate a large amount of surface rust before painting required much manual to rust. Phosphating - passivation process, through electrical and electrochemical reactions, by 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 on the metal surface rust . It can place ten days in the humid air, and will not rust. Its method of operation is simple and can improve the working environment, reduce labor intensity, save manpower and resources. Of phosphate - passivation solution containing emulsifiers, molybdates, and a variety of acid soluble phosphate, which is not only used in the above models, or other similar structure frame can be preserved using this method 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 hydrocarbons and other organic solvents, to the production, transportation, construction has brought a series of troubles, flammable and very safe. Because there is a certain degree of toxicity, volatilization into the atmosphere, seriously polluting the environment. Therefore, the paint experts at home and abroad are less committed to the development of new coating solution or not 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 carbon steel with stainless steel, because the device is in working condition will be exposed to a variety of corrosive materials and gases, and a very superior corrosion resistance of stainless steel, which is made of stainless steel cold-rolled plate.

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

4.3 austenitic nickel-chromium stainless steel welding investigate 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. Because of these properties of austenitic steels, require special welding processes to weld. Intergranular corrosion is one of the main problems of high-alloy steel. This high corrosion resistance of 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 of stainless steel frame due to improper welding destroy the organizational structure of the material cause 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 level of the drying theory, the relationship between the device structure, material selection, manufacturing process and also very close. Comprehensive variety of factors, the development of rational manufacturing program has important economic significance.

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