Chemical enamel equipment has both the mechanical properties of metal equipment and the corrosion resistance of enamel. In addition to hydrofluoric acid, fluorine-containing medium-high temperature phosphoric acid or strong alkali, it can also resist the corrosion of inorganic acids, organic acids, salts, organic solvents and weak bases with various concentrations. The surface of chemical enamel is smooth and easy to clean, which can prevent metal ions from interfering with chemical reactions and polluting products. Therefore, it is widely used in petrochemical production, especially in medicine, pesticide and synthetic fiber production, and it is a corrosion-resistant nonmetallic material that is often used. Chemical enamel can be used to replace expensive alloy materials.
Chemical enamel is a kind of acid-resistant enamel with high silicon content, which is coated on the surface of steel or cast iron equipment and calcined at 900℃ to form a dense and corrosion-resistant glassy thin layer with metal. It is a composite material of metal and enamel, and such equipment is called chemical enamel equipment.
First, the basic knowledge of chemical enamel equipment
1, the origin of the name of chemical enamel
Using enamel technology, acid-resistant glass materials with properties close to industrial glass are compounded on metal matrix to obtain glass/metal composite materials. Because its covering layer basically retains most of the properties of acid-resistant glass, such as smoothness, transparency, compactness, no pores and high chemical stability, it is not as good as ordinary daily enamel, so it is called "glass-lined". The glass-lined process is equivalent to the enamel process, so it is still enamel. People often use different names in their daily lives, such as acid-resistant enamel, named after its special acid resistance, and chemical enamel, named after its products are mainly used as chemical production equipment.
2, the performance of enamel products
Enamel equipment is made by spraying glass glaze with high silicon content on the surface of steel plate and sintering at high temperature of 920℃~960℃ for many times. The glass glaze is closely attached to the surface of metal tire. The performance of enamel is:
(1) Corrosion resistance: it is resistant to organic acids, inorganic acids, organic solvents and alkaline solutions with PH less than or equal to 12, but it is not suitable for strong alkali, HF and phosphoric acid with temperature greater than 180℃ and concentration greater than 30%;
(2) Non-stick: the smooth glass surface does not stick to the medium and is easy to clean;
(3) Insulation: suitable for situations where static electricity is easily generated in the process of medium;
(4) Isolation: the glass layer separates the medium from the steel tire of the container, and iron ions are insoluble in the medium;
(5) Preservation: The glass layer has good preservation performance for the medium.
3, the use of enamel equipment conditions
Enamel layer can tolerate most inorganic acids, organic acids, organic solvents and other media, especially hydrochloric acid, nitric acid, aqua regia and other media. However, it cannot be used in the following situations:
(1) HF at any concentration and temperature cannot resist corrosion;
(2) Phosphoric acid: the concentration is above 30%, the temperature is above 180℃, and it is highly corrosive;
(3) Hydrochloric acid: when the concentration is 10-20% and the temperature is higher than 150℃, it is highly corrosive;
(4) Sulfuric acid: the concentration is 10-30%, and it cannot resist corrosion when the temperature is greater than 200℃;
(5) Alkaline solution: When the PH value is greater than or equal to 12 and the temperature is greater than 100℃, it cannot resist corrosion.
Second, the chemical enamel equipment manufacturing
1. Substrate characteristics of chemical enamel equipment
A large number of matrix materials used to manufacture glass-lined products are mainly high-quality low-carbon steel, cast iron and stainless steel, among which low-carbon steel and cast iron are the most common. The former, as a steel suitable for glass lining, is widely used in manufacturing equipment and containers; The latter is widely used in the manufacture of pumps, valves, small equipment and spare parts, because it can cast complex parts at low cost. Low carbon and low sulfur steel for enamel
Chemical properties of basic materials
Si-Mn-P-S tensile strength MPa elongation% yield point MPa impact toughness MPa
Steel ≤ 0.14 ≤ 0.37 ≤ 0.65 ≤ 0.035 ≤ 0.45 > 330 > 3 10 200 ——
Covered electrode ≤ 0.1≤ 0.12 ≤ 0.45 ≤ 0.05 ≤ 0.03 > 430 > 180 —— 80
Cast iron 3-0.35 2.0-2.6 0.4-0.60.1-0.5 < 0.1—————
(Graphite carbon 2.5) ——————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————————.
Attached Table 1: Technical Index of Enamel Equipment Substrate
3. Requirements for bottom tires
The quality of enamel equipment depends on the iron tire first. Without high-quality iron tires, there can be no high-quality enamel equipment. In order to ensure product quality, iron tires should meet the following six requirements:
(1) The tire surface shall be smooth, and there shall be no obvious mechanical defects such as tool marks, pits and interlayers;
(2) The weld on the tire surface shall be straight and tidy, and the width of the weld shall not exceed 1.5 times of the thickness of the steel plate. Welded joints shall have smooth transition, and defects such as slag inclusion, air holes, undercut and incomplete penetration are not allowed;
(3) The weld on the tire surface should be polished before sandblasting;
(4) The offset of butt weld on the tire surface should be less than10% of the thickness;
(5) The flange roughness should be less than 0.15% of the diameter;
(6) The pressing surface of the butt flange shall be sealed under the design pressure.
4. Surface treatment
After the base tire is processed, the surface quality of the base material often can't meet the technical requirements of enamel, such as oxide layer on the metal surface, skin inclusion on the surface (caused by rolling), welding defects, and oil pollution during processing, which will affect the quality of enamel. Therefore, it is necessary to carry out surface treatment such as polishing, decarburization by burning oil and sand blasting.
Polishing is usually carried out on a grinder or with a portable grinding wheel. The requirement of polishing is to smooth the welding groove on the enamel surface, round the sharp edges and corners, and remove the oxide skin and interlayer skin to show the true colors of the metal.
Decarburization of fuel oil is to burn off the attached grease and organic matter at high temperature. Sometimes, when the carbon content of steel plate exceeds the standard, decarburization of high temperature surface is also used as compensation treatment.
When the enamel equipment is damaged and goes to the enamel factory for re-lining, heat treatment (dehydrogenation) must be carried out to eliminate the hydrogen infiltrated into the matrix at the porcelain explosion site. Sandblasting is to roughen the surface of the base tire to increase the surface free energy and specific surface area, thus improving the adhesion between the base tire metal and the base glaze.
5, tire repair
After surface treatment, the iron tire should be carefully inspected before enamel glaze is formally sprayed, and all "faults" that do not meet the requirements of enamel technology, such as burrs, sharp corners, concave-convex pits, interlayers and trachoma, should be dealt with in time. These "faults" can be repaired by hand grinding, shovel repair welding and then grinding.
6. Enamel primer
After the iron tire is repaired and polished, it can be painted and glazed. Spraying can be done manually or mechanically (semi-automatically). The control of glaze consistency between them is different, which should be mastered according to the experience of operators, because the caliber of spray gun, spraying pressure and glaze consistency are interrelated. The key of spraying primer glaze is to make the thickness of the first primer glaze uniform, and its thickness value should be controlled at 200 50 microns after firing. After the iron tire is sprayed with primer, it should be dried, generally by natural drying, or it can be dried in a drying room and baked slowly in front of the furnace or at the edge of the finished product. Pay attention to prevent quick baking, which is easy to crack the powder layer. After the powder layer is dried, it can be sintered in a sintering furnace. The firing temperature of bottom glaze is high. In order to make the bottom glaze firmly adhere to the iron surface, when using the three-in-one bottom glaze, the firing temperature should not be lower than 880℃. In order to make the temperature between the iron tire and the bottom glaze meet the above requirements, the sintering furnace temperature must be controlled above 920℃. In order to improve the efficiency, the optimum sintering furnace temperature is 960 ~ 980℃. The firing time of the bottom glaze must be carefully controlled, that is, it can't be under-fired (commonly known as raw firing) or over-fired (commonly known as fire). The former is not well sealed, and the latter will burn the bottom glaze. Moderate undercoat should have uniform color, smooth and bright surface and no bubbles. After the first bottom glaze is fired, if the quality is qualified, the top glaze can be sprayed; If it is unqualified, it must be ground, and if it is badly burned, it must be sprayed with a second primer. When spraying the primer for the second time, it is not advisable to spray it too thick. The total thickness of the primer for the second time should be controlled below 350 μ m. Too thick will affect the effective thickness of the glaze layer.
7. Enamel burning glaze
After the bottom glaze is glazed, it can be glazed if the quality meets the requirements. The real anti-corrosion protective layer of enamel equipment is the surface glaze layer. The spraying and glazing of the top glaze layer are similar to that of the bottom glaze. The thickness of glaze layer is generally required to be about 65438 0 mm. According to the application requirements, if heat transfer is considered, the glaze layer should be thinner, and when the medium used for non-heat transfer is seriously corrosive, the glaze layer should be thicker. The maximum thickness allowed in Japan is 2.55mm, and the minimum thickness is 0.8 mm according to Chinese standards ... To achieve the specified porcelain thickness, the surface glaze of the product should be sprayed several times. The thickness of each pass should be thinner. But considering the production efficiency, it should not be too thin. Generally, it is better to control the thickness of each pass to increase by 2mm. If the metal surface is in good condition, there is no problem with the weld, and the gunning process is carefully polished, then gunning can reach the specified thickness for three or four times. In order to ensure the quality of enamel, it is necessary to check whether there are dark bubbles and pinholes on the porcelain surface every time it is sprayed. Once found, it must be polished and repaired. Pinholes and hidden bubbles on straight metal surfaces should be ground or even repaired. Where the bottom metal is repaired, the bottom glaze must be sprayed. The patch mentioned above is something that every gunning operator must master.
Third, use chemical enamel equipment.
Although the mechanical strength of chemical enamel equipment is much better than that of glass-ceramic equipment, after all, enamel is a composite of glass-ceramic body and metal, so there are still some weaknesses like glass-ceramic, which can not withstand knocking, knocking and impact. The difference between the two is only because the enamel equipment has a metal shell. After the enamel layer is damaged, it does not lose its use value immediately like glass and ceramic equipment, but it takes some time to show the damage (the length of time depends on environmental conditions) before it loses its use value. On the positive side, this function gives users a sense of security, but on the negative side, it is easy for many leisure users to have the illusion of security and even ignore the safe use conditions. We must pay attention to this. Proper use of enamel equipment can greatly improve the service life of enamel equipment. Proper use of enamel equipment includes not only selecting enamel products with good quality, suitable specifications and varieties according to the use conditions, but also strictly observing various safety operation procedures.
Fourth, the choice of chemical enamel equipment
1. Before buying enamel equipment, you should know the technology, output and credibility of enamel manufacturers in advance, and try not to buy enamel equipment from manufacturers whose products often have problems because of price;
2. Explain the actual medium environment of the enamel kettle to the enamel manufacturer, and if possible, simulate the production environment to carry out the corrosion resistance experiment of enamel;
3. Compare the performance of the pre-purchased enamel kettle with the actual production environment;
4. The enamel equipment to be purchased should be left standing for more than half a month (the longer the time, the better) after the assembly is qualified to eliminate the residual stress;
5. After confirming the purchased equipment, test it according to the test method in the attached table (it is best to bring your own high-frequency EDM generator).
Five, the use of operational considerations
(1) Feed:
Be careful when adding materials. There should be no hard objects falling into the enamel container. At the same time, try to avoid empty heating materials and hot heating materials, and the temperature difference cannot exceed the technical specifications of the equipment. When adding materials to equipment, metal blocks or sundries should be strictly prevented. For larger hard materials, it should be added after crushing. Minimize the temperature difference between the material and the tank wall, and avoid heating the material in the cold tank or adding cold material in the hot tank;
(2) Operation:
When using jacketed equipment, it is necessary to slowly increase the pressure and temperature. Introduce the pressure of 0. 1MP in advance, keep it for a quarter of an hour, and then slowly introduce steam to reach the operating pressure. If conditions permit, we can find a suitable temperature rise and fall curve according to the actual situation of our unit, which is generally controlled below 3℃/min. During the operation of the equipment, attention should be paid to the sealing conditions of flanges, connecting plates, manholes and stuffing boxes, and measures should be taken immediately if leakage is found;
During operation and operation, when using jacketed equipment, the pressure and temperature should be increased slowly. Generally, steam with a pressure of 0. 1 MPa (gauge pressure) should be introduced first, and then the pressure should be increased slowly after 15 minutes (0. 1 MPa every 10 minutes) until the tank working pressure is reached, regardless of heating.
(3) discharging:
When discharging, if the bottom of the tank is blocked, don't shovel with metal tools, but gently poke it with bamboo poles, plastic sticks and wooden sticks. When cooling is needed after the reaction, cooling water must be introduced into the jacket after the temperature in the tank naturally drops to a certain extent to prevent quenching. When acid and alkali alternate, the service life of non-alkali-resistant enamel equipment is greatly shortened, so attention should be paid to choosing enamel equipment with better alkali resistance. Acid-proof enamel should be avoided when acid and alkali alternate. When discharging, if you find enamel fragments, you should immediately open the can for inspection and repair the porcelain surface before using it.
Maintenance of intransitive verb enamel equipment
(1) Check it frequently. If cracks or porcelain explosions are found, they must be repaired in time before use.
(2) Clean frequently to prevent dirt from corroding the equipment surface, and apply protective paint regularly;
(3) It is forbidden to clean the jacket with hydrochloric acid, as the hydrochloric acid in the jacket will cause "scale explosion" on the inner wall of the tank. When removing the adhesion on the porcelain surface, it is not allowed to use a metal shovel;
(4) Take good care of the enamel equipment that is not used or temporarily used, and pay attention to protection and storage to prevent bumping and rain. Pay attention to the fact that there can be no water in the jacket and thermowell, because water freezing in winter will crack the porcelain layer;
(5) The medium used for heating or cooling in the jacket should be neutral without any acid, otherwise the glass lining will explode due to "hydrogen bubbling";
(6) If scale remover is used in the sheath, it should be done in the shortest time, and then the sheath should be cleaned repeatedly, and the residue should be neutral; (7) Check the enamel village and transmission parts frequently. Whether the sealing condition is normal, etc. If any abnormality is found, it shall be handled in time without delay;
(8) Regularly replace the lubricating fluid in the transmission device and mechanical seal cavity to ensure the normal lubrication of all moving parts;
(9) Pay close attention to whether the pressure gauge is sensitive. If it is found that the indication of pressure gauge system is inaccurate, transformer oil should be filled in time and readjusted according to the standard pressure gauge;
(10) The working temperature range of enamel equipment under design pressure is 0 ~ 200℃, which can be extended to-20 ~ 200℃ if the equipment is used under normal pressure; For jacketed enamel equipment, vacuum is allowed in the tank (kettle), but the pressure difference between inside and outside should comply with the regulations;
The thermometer with wing in (1 1) FK(FK) series reaction tanks can be set at 0-90℃ according to process requirements. Adjust the range at any angle to obtain different resistance. It is best to adjust the angle when stopping. If adjustment is necessary during the reaction, check whether the retaining ring is connected reliably in advance to avoid accidents.
(12) For the reaction tank with mechanical seal, when the working temperature exceeds 70℃, the reaction tank with packing seal should be filled with cooling water respectively in the cooler and stuffing box jacket when the working temperature exceeds 100℃, so as to avoid the damage of sealing elements;
(13) The lubricating fluid (sealing fluid) in the mechanical sealing cavity shall be kept clean, and solid particles shall not be entrained. In the reaction process with sublimation phenomenon, it is not appropriate to directly use the mechanical sealing device equipped with this equipment.
(14) The metal surface outside the enamel layer should be strictly prevented from contacting with acid liquor and acidic substances, so as to avoid the metal surface reacting with acid to generate hydrogen gas, which may lead to "scaling" of the porcelain layer. If acid drops, it should be cleaned immediately and stopped.
Seven, more than ten years of maintenance summary
Matters needing attention of chemical enamel equipment
(1) If enamel fragments are found during unloading in use, stop the machine in time, inspect the equipment in detail, find out the cause of damage and take remedial measures in time.
(2) Check the glass lining equipment regularly and find the tiny porcelain explosion in time.
(3) Matters needing attention in using chemical enamel equipment:
1. Pay attention to avoid collision when installing the kettle cover and stirring;
4. Install the kettle cover, inlet and outlet, and tighten the bolts symmetrically as required;
[14] Check the kettle with wooden ladders and rubber shoes;
4. Regularly check the intact condition of the mixing lock mother to prevent the lock mother from damaging the reducer and making the mixing fall off;
5. When installing the flange and opening and closing the manhole cover, do not drop anything;
6. When welding on the enamel kettle or on the enamel kettle, the porcelain surface shall be protected, and the welding slag shall not fall on the porcelain surface;
Once the enamel kettle is not cooled, it cannot be charged to prevent the porcelain surface from rapidly cooling and exploding;
⒏ When heating the coat with steam, it should be heated too hard according to the regulations;
Pet-name ruby steam heating or steam valve leakage, the water in the jacket to put net. Otherwise, the temperature difference between the top and bottom of the reaction kettle may be large, so that the parts with large residual stress and low temperature of the enamel kettle are stressed and porcelain explodes in a large area;
⒑ Choose a corrosion-resistant cushion to prevent material leakage and enamel corrosion;
1 1. There are crystals in the kettle, so you must not hit them with an iron drum or a hammer; When feeding, it is not allowed to add along the kettle wall.
(c) Techniques for maintaining chemical enamel
1] Attention should be paid to the selection and installation of the cushion of enamel equipment.
The equipment flange is damaged, mostly because the mat is not resistant to medium corrosion or the mat installation is not sealed, and the medium or acid gas leaks from the outside to the inside, permeates and corrodes the flange matrix, and finally the equipment is scrapped. In wet workshops in southern and coastal areas (north), even if the cushions are selected and installed correctly, the acid gas will still corrode the flanges. The solution is as follows:
(1) Check whether the flange is flat when purchasing equipment;
⑵ Choose cushions with superior corrosion resistance and soft materials;
(3) The installation shall comply with the regulations, and the tightness of each screw shall be consistent;
(4) If necessary, the exterior of the flange shall be protected against corrosion.
2) The corrosion of the outer wall of enamel kettle can not be ignored.
In wet acid workshop, the outer wall of enamel kettle (including other carbon steel equipment) is mostly seriously corroded. In particular, the pipes and valves on the lid are not well sealed, and there will be materials dripping on the lid, which will cause hydrogen corrosion and hydrogen bubbling, resulting in "scaling" on the inner wall of the lid. For this reason, many units use painting and insulation protection, and the effect is not very good. Based on years of experience in repairing enamel kettle, it is considered that the corrosion of the outer wall of enamel kettle can not be ignored. In order to avoid this kind of thing, foreign chemical enterprises added a plastic cover to the pot cover. Based on the principle of simplicity, the enamel kettle can be coated with anticorrosive paint and pasted with FRP when leaving the factory; The outer wall of the enamel kettle has been corroded. When the outer wall of enamel kettle is dry, it can be directly protected by machine oil without rust removal.