The common faults of brick furnace are mainly the local repair of heating body and masonry; The common faults of salt bath furnace are salt leakage and electrode corrosion; Common faults of vacuum furnace are heater damage and furnace body leakage. In view of the common fault phenomena and causes, attention should be paid to the method, structure and material selection when building the furnace body.
1. overall furnace building
when the general heat treatment resistance furnace is built as a whole, a groove for inserting bricks should be left at the high aluminum brick laying size of the original brick laying heater. The daily repair is mainly to change the furnace wire, put bricks and furnace wire.
for the faults of salt bath furnace-salt leakage and electrode corrosion, the casting method is adopted to solve the salt leakage of furnace body; In view of the easy corrosion of the motor, the furnace body is cast into two parts, that is, the electrode is cast into a stepped block separately. After the electrode is corroded, only the part that needs to be replaced is removed.
2. Brick furnace mode
(1) Take targeted repairs, and pay attention to the fact that the back wall, side wall, door arch and furnace vault of a large brick furnace should not bite and crush each other, so that the above parts can be repaired separately without ripping the furnace as a whole when local damage occurs.
if the arch foot of the furnace does not have to be supported on the side wall, it can be supported on the arch foot beam of the steel structure on both sides of the furnace, so that the furnace wall is not subjected to the force of the vault, which is beneficial to both the furnace wall and the vault. However, considering the thermal expansion of the arch foot beam, there should be a gap. When building vault bricks, the arch feet on both sides are laid symmetrically to the center at the same time. Vault lock bricks shall not be cut, and the lock bricks shall be accurately distributed according to the center line of the vault.
(2) The following methods should be adopted for the exposed parts of the furnace body, such as the furnace door and the arch of the furnace door, etc.: adding high-modulus sodium silicate when building the furnace to increase the integrity of the sintered furnace door and mouth, and sticking refractory fiber felt strips on the exposed parts with high-temperature adhesive (choose the adhesive and refractory fiber types according to the influence on the furnace atmosphere and the working temperature of the furnace). When building the oven door, lay the oven door flat on the ground, build it from both ends to the middle, and the last layer of bricks will be "squeezed" in.
if the furnace wall is built with two or more kinds of bricks, when each brick of the wall is built separately, it is like a group of single walls. After repeated heating and cooling, the furnace walls made of different kinds of bricks are easy to separate. In order to maintain the integrity and stability of the furnace wall, the masonry method of pulling the inner and outer walls together every 5 ~ 8 floors at the same overlapping height of brick layers is adopted, that is, half of the refractory bricks are inserted into another brick layer or fixed with metal anchors.
when designing the furnace lining, each layer of furnace wire brick should be "embedded" in the furnace lining wall, so as not to be crushed to death. When the brick is broken, it can be replaced. The bottom of the furnace wire high-aluminum brick laying bricks at the bottom layer is directly built into a whole without hanging.
(3) Masonry requires staggered masonry, full of mud, horizontal and vertical, and there can be no collusion gas inside and outside after masonry is built. Bricklaying must follow the alignment, as the saying goes, "Follow the line up, stare blankly down, and keep the left and right sides in line", and don't "swim to the top and walk to the seam". Bricks built on the wall must be laid flat, and the brick joints should not be tilted while being thick and thin. Half-brick-thick walls are completely built with bricks; A brick-thick wall is built with top-down bricks; A brick-and-a-half-thick wall is built with a row of top-laid bricks and a row of along-laid bricks; A two-brick-thick wall is made of two rows of bricks and a row of top bricks between them, and the other is made of two rows of top bricks. In the process of laying bricks or stones, we should always check the level of the bricklaying layer and comprehensively check the verticality and smoothness of the bricklaying wall.
(4) Brick joint is the weakest part of masonry, and its position should avoid the stress parts of masonry, insulating brick layer and furnace framework. Brick joints are filled with refractory mud, and when they are dry-laid, they are filled with refractory powder, so that the refractory masonry becomes a whole. The expansion joint can't run through the masonry, and there can't be a blaze, air leakage and other phenomena. It should be staggered up and down, left and right. The expansion joint shall be stuffed with refractory fiber and asbestos products, so as not to fall into mud, broken bricks and other sundries. When there is a metal component in the masonry, an expansion joint should be left between the metal component and the masonry.
(5) The fire-resistant pipe for the lead-out rod must be aligned with the hole on the furnace shell. If the center height of the hole is not right, the lower part of the clay brick supporting the furnace wire can generally be ground off. Furnace wire brick is made of high alumina, and high alumina brick Fe2O3 <: 1.5%。 Iron oxide is a catalyst for carbon monoxide to precipitate carbon black in the atmosphere at 45 ~ 55℃. After carbon black is deposited in brick, its volume expands, which leads to the strength decline and early failure of masonry.
the service temperature of lightweight refractory brick should be 7 ~ 1℃ lower than the sintering temperature of the brick, so as to avoid cracking of brick joints and cracking of bricks due to large re-burning shrinkage. For parts such as furnace bottom and arch foundation that bear heavy loads, refractory clay bricks should be used. The brick at the door of box furnace is easy to be damaged because of the workpiece entering and leaving, and the bottom brick can be made of heavy high-alumina brick.
3. Other matters needing attention when building a furnace
(1) The environmental temperature is strictly in accordance with the relevant requirements of Code for Construction and Acceptance of Industrial Furnace Masonry Engineering. The key points can be pre-laid, and various technical parameters can be tested, and then formally laid after it is appropriate.
(2) When carrying out targeted repairs on the local area, it is necessary to ensure the integrity and looseness of the unrepaired part of the masonry during demolition, so as to eliminate the possibility that the masonry collapses or individual bricks fall.
When watering the overhaul part in the furnace, fine water can be sprayed, so as to avoid water accumulating in the furnace and flowing to the parts without repair; Retained old masonry should be leveled and neat; If there is a stepped boss, clean it carefully; Attention should be paid to the combination between the old and new masonry. When the old mud is firmly bonded and difficult to remove, dilute mud must be used when biting the stepped brick body. For low-lying and uneven places, thick mud with broken bricks can be used to fill them.
when pulling out the broken brick, you can't directly pull out the broken brick. First, pull out an intact brick near the broken brick, shake it from side to side, gently take it out, and finally take out the broken brick. You can't use hard objects to knock hard to avoid cracks in the lining. When repairing and replacing the refractory pipe, firstly, remove the insulator, take out the extraction rod, and then gently tap the pipe with a special hook to loosen it, insert it into the end of the pipe and hook it out. Be careful not to break the diatomite brick.
in the process of wall building, if there is a pause or there is a temporary obstacle in brick building, don't leave a vertical socket, but build the brick layer into a stepped platform or a staggered platform. Brick-breaking adjustment method can't be used to build a good wall, and the wall has great deviation, so it should be demolished and rebuilt. Cut the bricks neatly and accurately, and mix the mud with it.
(3) Pay attention to choosing bricks when laying bricks. For the selection of bricks to be built on the same floor, try to choose bricks with the same overall size (the quality requirement of first-class bricks stipulated by the national standard allows the size deviation of bricks to be ±2mm). To check the brick surface, observe the shape and color, check the dimensional tolerance, distortion, missing corners, missing edges, molten holes, slag corrosion and cracks, etc., its surface must be smooth, without cracks, slag corrosion and vitrification, without missing edges and corners, and its broken structure must be uniform, without large impurities, pores, cracks and layered structures, and clinker particles should not fall off and break, and should not be affected with damp. Put the well-sintered, defect-free bricks on the forehand end face and build them in the furnace. Brick faces with missing edges and corners or processed faces cannot be built in the place where the furnace directly contacts with flame, molten steel or slag (it should not face the furnace or contact with furnace gas) or bear the gravity. 1. damage of heating elements
the heating elements of non-vacuum furnace of common heat treatment resistance furnace mainly adopt Fe-Cr-Al (such as OCr25Al7Mo2) and Ni-Cr alloy (such as Cr2Ni8), and the vacuum furnace mainly adopts molybdenum heating elements.
(1) When the molybdenum heating element of the vacuum furnace is damaged, replace the partially damaged part of the molybdenum heating belt. Cut off the damaged part, take a molybdenum piece with the same size as the original one, clamp it on both sides with a molybdenum piece with a thickness of 2 ~ 3 mm, match the screw holes, and then tighten it with molybdenum screws.
When the molybdenum sheet is found to be deformed, falling and lodging in daily inspection, it can be baked with a blowtorch to soften it, and its proper shape and related dimensions can be restored by external force, and then it can be lifted, bound and fixed by molybdenum wire.
(2) The normal damage of the alloy is mainly caused by oxidation, thinning and embrittlement, lap short circuit, overburning or corrosion by medium. Ni-Cr alloy has a longer service life than Fe-Cr-Al alloy, the ribbon is longer than the filament, and the continuous work is longer than the intermittent work.
Nickel-chromium alloy has good plasticity, easy drawing and winding, and is not easy to embrittle after being heated at high temperature, so it is easy to repair and weld. Fe-Cr-Al alloy has higher resistance coefficient and lower temperature coefficient of resistance. Compared with Ni-Cr alloy, Fe-Cr-Al alloy can save materials, and has stable power and high heat resistance. It has strong resistance to carburization, sulfur and various hydrocarbon gases, but its processing performance is slightly poor, drawing and winding are difficult, so it can be adjusted properly outside the furnace during installation, and gas welding should be used for necessary bending and compression. The thermal expansion coefficient is large (low high temperature strength and large creep elongation), so there should be room for installation; The welding time should be shortened as much as possible to shorten the length of heat affected zone.
2. Troubleshooting
The heating body will soften, expand, sag, first fall and overlap, and then fuse (melt) after long-term work. In order to make the furnace wire have a certain strength at high temperature and prevent it from softening, collapsing or sagging, we should first design the structural dimensions of the furnace wire, such as spiral resistance wire, and pay attention to the diameter, pitch and spiral middle diameter of alloy elements. The heater should be installed close to the furnace lining, and should be laid flat on the brick, leaving its expansion space appropriately. Small hook position should be appropriate, generally 4 ~ 6 mm, and can be firmly hooked to prevent getting down. In addition, in order to prevent contact between furnace wires, spacers should be padded. Thin sheets made of high temperature resistant materials such as 95 porcelain can be used to isolate the resistance wires to prevent overlapping. In particular, at the transition between layers of furnace brick (when building a furnace, a gap of 5mm is generally left between brick and front and rear end walls for turning and installation of resistance wires), ceramic tiles should be put on in advance, or ceramic tubes should be put on the furnace wires (the ceramic tubes should be topped to the end). High-temperature furnace can't use the thin slice of diatomite brick saw to pad in the middle of furnace wire, because diatomite brick has poor heat resistance and can only be used below 9℃, which is easy to dissolve and deteriorate in high-temperature furnace.
for the furnace wire with lodging tendency, check whether the small hook of the furnace wire works (the hook for setting up the resistance ribbon must be firmly built, pressed and plugged, and must not be loosened), and it can be softened by gas welding or blowtorch baking oven wire, and then its original shape and size can be restored, and a porcelain tube can be inserted in the furnace wire (a mandrel can be inserted in the porcelain tube). If two porcelain tubes are used at the same time, the ends of the porcelain tubes must be close together.
the heater can be directly welded to repair the common broken ends. For those that have collapsed seriously and can't be straightened, and some parts that have been burnt seriously, the method of replacing one section can be generally adopted. It is not necessary to scrap the whole set because some of them are unqualified. It is necessary to pay attention to the material, diameter, pitch and length of the resistance wire used for repair welding. The newly-repaired resistance wire should not have defects such as cracks and corrosion, and should be evenly distributed. When using the old resistance wire, the resistance wire should not have obvious phenomena such as uneven thickness, oxidation corrosion, crack deformation and aging embrittlement. The old extraction rod should not have serious oxidation and corrosion.
3. Precautions in welding work
The welding of alloy elements is different from the welding of general metal structures, which requires that the welded joint can bear external force without breaking. Butt welding and plug welding are the main welding methods, and drilling welding, slot milling welding, butt welding and lap welding can also be used. Before welding, the oxide scale, rust or other dirt on the alloy surface should be cleaned, and the metal matrix of the welding part should be exposed with emery cloth. The temperature should be well controlled to avoid slag inclusion, porosity and incomplete welding. When a large number of alloy components are replaced, after welding, the cold resistance and three-phase current balance of the whole furnace should be measured and adjusted appropriately to meet the original design requirements.
when repairing Ni-Cr alloy, first break it to understand the oxidation of components. When the oxidation is serious, the silver-white iron core is very thin, which is easy to burn out when repairing welding. Even if it is barely repaired, it will not be used for a long time. The oxidation is not too serious, and the lap method can be used; If it is still relatively new, the docking method can be used. Generally, gas welding and nickel-chromium resistance wire are used as welding wires. When using docking method, neutral flame should be used, the flame volume should be small, the flame center should be straight and the heat should be concentrated; When the lap welding method is adopted, the lap length and resistance wire shall not be less than 1 times the diameter; The resistance band is not less than 1 time of the bandwidth. The welding between the Ni-Cr alloy element and the lead-out rod adopts lap welding or butt welding. The heated Fe-Cr-Al alloy is not allowed to bend, stretch or vibrate violently in the cold state. If it is necessary to shape or expand the pitch, it must be heated to dark cherry red. Arc welding is used, rare earth Fe-Cr-Al-covered electrode is used in covered electrode, and insert repair welding and intermittent welding are adopted to control the heating range and overheating degree. Slotting welding, drilling welding and slotting cold welding can also be used. Generally, drilling welding is used between Fe-Cr-Al alloy elements and lead-out rods.
if one or two bricks are broken or uninsulated in the middle of a layer of furnace wire bricks, when a straight resistance wire is used to cross the broken or uninsulated furnace wire bricks and directly weld them, the resistance of this group of furnace wires will be small, and when viewed from the outside, it will be redder than other furnace wires and its service life will be shortened. We can adopt the method of inserting a porcelain tube into a newly replaced furnace wire, and the porcelain rod (the porcelain tube is inserted into a mandrel) is padded and suspended, and is placed between two bricks, like a bridge, crossing a broken brick, or the method of placing a porcelain piece on an uninsulated brick, so as not to change the original parameters of the furnace wire. After the furnace body is repaired in a large area, it should be baked. Before baking, use a shaking table to detect the insulation of the equipment, which is generally not less than 2MΩ.
There are three stages in the baking of the brick furnace:
① The moisture discharge period is O ~ 2℃, which is the discharge period of moisture in the mud and moisture in the masonry. The furnace door must be opened and the heat preservation time is longer.
(2) The expansion period of masonry is the period when the masonry begins to expand and expand, and the temperature rise at this time does not exceed 5℃/h..
③ When the heat preservation period is above 6℃, it is necessary to keep the temperature for a period of time for every 1 ~ 2℃ increase, and it is easy to damage the masonry if it is too urgent.
(1) compile operation and maintenance procedures, establish operation records and repair files, count accumulated working hours of operation, strengthen daily maintenance, grasp the changing trend of equipment technical status, find the signs of failure and damage as early as possible, avoid hot repairs belonging to accident emergency repair, and prepare repair materials and prepare repair technology in advance according to furnace load and working conditions. For example, the service life of alloy elements is related to many factors such as working temperature, furnace medium, element quality and operation, and its fluctuation life is 6～1h.
Generally, there are many leakage faults in vacuum furnaces in spring and autumn, and it is easy to happen when they are left idle for a long time. Our factory measures the pressure rise rate once a month (at normal temperature, close all vacuum valves, stop the operation of the vacuum system, read a number after 1Omin, and then read another number after 1 hour, and the difference between the two numbers is the value of the pressure rise rate), so as to grasp the changing trend of equipment leakage. For example, if the vacuum equipment is shut down for one week continuously, it should be idle.
In the leak detection of vacuum system, in addition to plugging with vacuum mud paste, you can also use a medical needle to suck ether at the suspected leak point and observe whether the reading of vacuum meter changes. You can also make a blind plate with holes for inserting vacuum silicon pipes, and block the vacuum pipes in sections for leak detection. If the diffusion pump has carbon deposit, it can be cleaned by chemical pickling. ,
(2) After the brick furnace is repaired, it should be inspected frequently at the initial stage of use, to check whether the furnace surface temperature and furnace temperature are too high after use, and whether the heating body is overheated, burnt out, uneven temperature or white. For three-phase high-temperature electric furnaces and resistance furnaces with capacity exceeding 1kW, ammeters should be installed in each phase and each heating zone. If the furnace temperature and instrument indication are abnormal, analyze and handle them in time.
(3) The alloy element cannot be overloaded. The maximum service temperature refers to the surface temperature of the element allowed in dry air, not the temperature of the heating substance or the temperature around the electric heating element. It should be noted that the temperature of the electric heating element itself is 1℃ higher than the temperature of the surrounding medium or the heated temperature.
(4) avoid deleting products in hot places, especially copper, aluminum and zinc.