According to whether the drying system is controlled or not, it can be divided into natural drying and artificial drying. Since artificial drying is an artificial control of the drying process, it is also called forced drying.
According to different drying methods, they can be classified into:
① Convective drying, which is characterized by using gas as a drying medium to blow the surface of the green body at a certain speed to dry the green body.
② Radiation drying, which is characterized by using the radiant energy of electromagnetic waves such as infrared rays and microwaves to irradiate the dried body to dry it.
③Vacuum drying, which is a method of drying the green body under vacuum (negative pressure). The green body does not need to be heated up, but a certain negative pressure needs to be generated by the use of air extraction equipment, so the system needs to be airtight and it is difficult to produce continuously.
④ Combined drying, which is characterized by the comprehensive use of two or more drying methods to exert their respective strengths and complement each other’s advantages, can often obtain a more ideal drying effect.
There are also some drying methods, which are divided into batch dryers and continuous dryers according to whether the drying system is continuous. The continuous dryer can be divided into cocurrent, countercurrent and mixed flow according to the different moving directions of the drying medium and the green body: according to the shape of the dryer, it can be divided into chamber dryer and tunnel dryer.
Characteristics of dryers used in various types of porcelain
Building Sanitary Ceramic Dryer
The green body of constant temperature, constant humidity and large space drying sanitary ware has a moisture content of about 18% after micro-pressing. At this time, the strength is low and it is not suitable to be moved. Generally, the method of in-situ drying is adopted. Generally, manufacturers use boiler steam heating method system, which is characterized by low fuel cost and can form a certain dry atmosphere. At the same time, there are many disadvantages, such as no lateral air flow; poor moisture removal function, long drying time; no ventilation system, poor working conditions for workers. Therefore, the more advanced “constant temperature and humidity system” is adopted. This kind of system does not need to change the original production process and production process, and can also accelerate the drying speed. Another major feature of this system is that it has the function of forced ventilation. This system also has a series of problems, such as large energy consumption; parameter lag; asynchronous drying and so on. Especially in recent years, the gypsum mold has become larger, so the drying time and requirements of the green body are different, in order to ensure the production arrangement of each shift. The drying of the plaster mould became the main contradiction in the production arrangement. To solve this problem, a sealed drying system is used, that is, the entire molding line is sealed after the gypsum is drawn out, and a small constant temperature and humidity system is used in this small space.
Hot air fast drying
Fast drying means that the drying atmosphere changes according to the difference of the green body and the drying degree of the green body, and the best drying atmosphere is always maintained to improve the drying speed. The temperature and humidity automatic adjustment fast drying chamber has the following characteristics: ① Small space, fast response and high precision when adjusting parameters; ② Different drying curves can be set according to the condition of the green body; ③ Industrial computer control, high degree of automation , reduce the factors of human error, and the drying rate of green body is high. This system consists of six parts: house structure, hot blast stove, air distribution system, stirring system, control system, and humidity system.
Steam fast drying
What is discussed here is direct steam drying, that is, after the green body is out of the mold, it enters the drying chamber with the closed end along the track. After closing the drying chamber, the steam directly enters the sealed drying chamber along the top pipeline, and the steam expands and depressurizes in the closed chamber. The wet steam is discharged and recovered from the pipeline at the bottom of the chamber. Its biggest advantage is fast drying and high authenticity rate.
Power frequency electric drying
It is to pass the power frequency electricity (50Hz) through the green body. Due to the resistance of the green body, the entire green body is evenly heated and dried, so that the purpose of heating without temperature gradient is achieved. The disadvantage of power frequency electric drying is that the preparation before drying is very troublesome, and it is only suitable for drying a single product.
dry wall tiles
The green body of the wall and floor tiles is generally dried by the waste heat of the kiln after it comes out of the press, but as the size of the product becomes larger and larger, the maximum is 1.2×2mm or even larger, and the thickness is getting thicker and thicker. From 8mm to 60mm, the residual heat of the kiln can no longer meet the drying requirements. Moreover, with the high-grade products and diversified colors, the control requirements for the atmosphere in the kiln are becoming more and more precise and strict. When the waste heat is used to dry the green body, the adjustment of the drying section will cause changes in the atmosphere in the kiln, and even increase the kiln atmosphere. Furnace burning fuel consumption, and some increase 1-2 tons of fuel. So there are vertical dryers, drying kilns, multi-layer drying kilns, etc.
vertical drying kiln
It is a widely used drying equipment. It occupies a small area and can dry small-sized wall and floor tiles with good results.
drying kiln
The drying kiln is added directly before the firing kiln, and it is a part of the kiln (called the preheating zone) in appearance, or a drying kiln of the same length and width is built independently next to the kiln. After the green body comes out of the press or after glazing, it directly enters the drying kiln for drying. After drying, the green body directly enters the preheating belt or enters the firing density through transmission for firing. It consists of three parts: hot blast stove, air distribution system, and kiln body structure. The drying kiln with good heat utilization rate generally only uses the hot air of the firing kiln to basically meet the drying requirements. , In addition to the use of densely fired hot air, it is also necessary to burn a hot blast stove, which consumes 2 to 3 tons of fuel per day.
multi-layer drying kiln
With the advancement of technology, the moisture content in the green body is getting lower and lower, and the drying process needs to reduce the moisture content from 8% to 1%, which cannot be achieved by using a general drying kiln. A multi-layer drying kiln can solve this problem. It is composed of a kiln head queuing device, a kiln tail collector and several drying units, each of which is independent, and their temperature, humidity and ventilation volume adjustment are independently controlled by the hot blast stove. Its advantages are: sufficient drying time; small external surface area, small heat dissipation loss; air outlet close to the brick surface. The drying intensity is high; the ventilation volume will not be affected when the temperature is adjusted, so the speed and range of the hot air blowing across the surface of the brick will not change due to the adjustment of the temperature, but the adjustment of the multi-layer drying kiln is relatively difficult, especially when the kiln width is increased. , the uniform temperature in the kiln cannot be guaranteed, resulting in different drying effects.
Daily ceramic drying
The drying of daily-use ceramics is different from the drying of sanitary ceramics or wall and floor tiles. Deformation and cracking are the two most common defects: ② During the production process, processes such as demoulding, turning blanks, repairing blanks, connecting handles, and glazing are often mixed to complete the process. Therefore, the drying of daily-use porcelain mainly uses chain dryers. According to the arrangement of the chain, it can be divided into: horizontal multi-layer arrangement of dryers, horizontal single-layer arrangement of dryers, and vertical (vertical) arrangement of dryers.
Far infrared drying technology
Infrared radiation drying technology has been paid more and more attention by people from all walks of life, and it has played a great role in food drying, tobacco, wood, Chinese herbal medicine, cardboard, automobiles, bicycles, and metal body baking paint. In addition, far infrared drying is also used in ceramic drying. Most objects absorb infrared wavelengths in the far-infrared region. Water and ceramic bodies also have strong absorption peaks in the far-infrared region, which can strongly absorb far-infrared rays. Let it dry. And the penetration depth of the far infrared to the illuminated object is deeper than that of the near and middle infrared. Therefore, it is more reasonable to use far-infrared drying ceramics. Far-infrared drying has the advantages of high efficiency and quick drying, energy saving, time saving, convenient use, uniform drying, and small footprint compared with ordinary heating methods such as hot air and electric heating, so as to achieve the excellent effect of high yield, high quality and low consumption.
According to the production practice of ceramic factory, far-infrared drying can shorten the drying time by half compared with near-infrared drying, which is 1/10 of that of hot air drying. Zhengzhou Porcelain Factory implemented far-infrared drying technology for 10-inch flat pans. The results show that the production cycle is doubled. Usually, the drying time is 2.5 to 3 hours, shortened to 1 hour. The cost is low, the investment is small, the effect is quick, and the sanitary conditions are good. ,Small footprint. The research of far-infrared materials has been very active in recent years, and has made great progress. There are also many examples of successful applications in all walks of life. Why are few people interested in the drying line of building sanitary ceramics?
Microwave drying technology
Microwave refers to electromagnetic waves between high frequency and far infrared, with a wavelength of 0.001-1m and a frequency of 300-300000MHz. Microwave drying is to irradiate the wet green body with microwaves. The direction and magnitude of the electromagnetic field change periodically with time, so that the polar water molecules in the green body change with the alternating high-frequency electric field, causing the molecules to rotate violently, and friction is converted into heat energy. To achieve the purpose of uniform heating and drying of the green body as a whole [2, 3, 4]. The penetration ability of microwaves is much greater than that of far infrared rays, and the lower the frequency, the greater the half-power depth of microwaves. Features of microwave drying:
(1) Uniform and fast, which is the main feature of microwave drying. Due to the large penetration ability of microwaves, heat can be directly generated inside the medium during heating. No matter how complex the shape of the green body is, the heating is uniform and fast, which makes the green body dehydrate quickly, demold uniformly, deform less, and is not prone to cracks.
(2) It is selective. Microwave heating is related to the nature of the substance. In a microwave field of a certain frequency, water has a larger dielectric loss than other materials, so the heat absorption of water is much larger than that of other dry materials; Microwave heating is carried out on the outside and inside at the same time, and the internal water can be quickly heated and evaporated directly, so that the ceramic body can be heated and demolded in a very short time.
(3) The thermal efficiency is high and the response is sensitive. Since the heat directly comes from the inside of the dry material, the heat loss in the surrounding medium is very small. In addition, the microwave heating cavity itself does not absorb heat or absorb microwaves, and all the radiation acts on the green body. Thermal efficiency high.
Microwave heating equipment is mainly composed of DC power supply, microwave tube, connecting waveguide, heater and cooling system. Heaters, radiant heaters, slow wave heaters and other categories.
Application of microwave drying in daily ceramics
Hunan Guoguang Porcelain Industry Group Co., Ltd., according to the technological characteristics of daily-use ceramics, designed a daily-use ceramics rapid dehydration and drying line for production. Practice has proved that compared with the traditional chain drying line, the blanking rate is increased by 10% Above, the time for removing the plaster mold is shortened from 35 to 45 minutes to 5 to 8 minutes, the number of molds used is reduced from 400 to 500 to 100 to 120, the microwave drying line occupies a small area, and the production is pollution-free. Its efficiency is 6.5 times that of chain drying. In addition to saving a lot of gypsum molds, when used in conjunction with the secondary rapid drying line, the total drying cost for a 10.5-inch flat plate can be reduced by 350 yuan per 10,000 pieces [5].
Application of Microwave Drying in Electric Porcelain
Liaoning Fushun Petrochemical Company, Li Chunyuan used microwave heating drying technology, weight identification control technology, infrared temperature detection control technology to dry electric porcelain with complex shapes. Compared with the conventional steam drying method, it can improve the efficiency of drying. The productivity is 24 to 30 times, the yield is increased by 15% to 35%, and the floor space of the same output is only about one-twentieth of the existing technology, which can greatly improve the economic benefits. This can provide reference for the drying of some special-shaped products such as building sanitary ceramics, wall and floor tiles.
Dry porous ceramics of porous ceramics have broad application prospects and are widely used in chemical industry due to their advantages of high mechanical strength, easy regeneration, good chemical stability, good heat resistance, and uniform pore distribution. Environmental protection, energy, metallurgy, electronics, petroleum, smelting, textile, pharmaceutical, food machinery, cement and other fields. As a sensitive component of sound-absorbing materials and materials such as artificial bone and tooth root, it has also attracted more and more attention. Due to the high moisture content and many pores of the porous material during molding, and the inner pore wall of the green body is particularly thin, it is extremely difficult to dry with the traditional method due to uneven heating. In addition, the thermal conductivity of these porous materials is poor, and the drying process requirements are very strict, especially It is a honeycomb ceramic used in environmental protection automobiles and other aspects. The drying process is not well controlled, and it is easy to deform, which affects the porosity and specific surface area. Microwave drying technology has been successfully applied to the drying of porous ceramics. It can easily reduce the moisture of the green body from 18% to 25% to less than 3%, and the precipitation rate reaches 0.7 to 1.5kg, which greatly shortens the drying time and improves the finished product. Rate. We also apply microwave drying to the warm blank drying of split bricks, and the effect is also very obvious.
Post time: Sep-26-2022