The nature and application of resistance furnace

The use of current so that the furnace heating element or heating medium heat, thereby heating the workpiece or material for industrial furnaces. Resistance furnace in the machinery industry for metal heating before forging, metal heat treatment heating, brazing, sintering powder metallurgy, glass, ceramic firing and annealing, low melting point metal melting, sand and paint film layer drying.
Since the discovery of heating effect of current (ie Lenz Heights - Joule's law) after heating method first used in household appliances, small electric stove and later used in the laboratory. With the invention of nickel-chromium alloy, into the 1920s, resistance furnace has been widely used in industry. Industrial use of resistance furnace generally consists of heating elements, masonry, metal casing, door, furnace mechanical and electrical control systems and other components. Heating power from less than one kilowatt to thousands of kilowatts. Working temperature below 650 ℃ low temperature furnace; 650 ~ 1000 ℃ in temperature for the oven; 1000 ℃ above furnace. At high temperature and medium temperature furnace heating mainly by radiation. In the low-temperature furnace convection heating methods places, electric components are mounted on the duct, through the fan forced air circulation furnace in order to enhance the convective heat transfer. There chamber resistance furnace, pit, car type, pusher, stepping, muffle type and tunnel type and other types. Controlled atmosphere furnace, vacuum furnace, furnace, etc. are also flowing particle resistance furnace.
Heating element has high heat resistance and high temperature strength, low temperature coefficient of resistance and good chemical stability. Materials commonly used in metal and nonmetal two categories. Metal heating element materials are nickel-chromium alloy, chromium-aluminum alloy, tungsten, molybdenum, tantalum, are generally made of spiral, wavy line, and a wave plate with a waveform. Non-metallic materials are silicon carbide heating elements, molybdenum disilicide, graphite and carbon, are generally made of rods, tubes, plates, with other shapes. The distribution of the heating element and the line connection, according to the size of the furnace and the furnace power requirements.
Resistance furnace and flame furnace, has a simple structure, temperature uniformity, easy to control, heating, good quality, no dust, no noise, etc., but the use of the higher fees.

The basic sequence of experimental furnace masonry and methods

Laboratory furnace, furnace masonry and methods of the basic sequence is as follows:① bottom masonry, including the passage at the end. Qi Hao large brick insulation brick and kaolin after the masonry wall at the inside and outside to relax 30-50mm leveling. Multilayer structure underground masonry elevation negative deviation must be controlled, the bottom of the total thickness tolerances generally-3mm. In the bottom layer of kaolin large brick laying above chrome ramming as a sealing layer to prevent liquid penetration to the corrosion resistance of glass poor clay layer.② In the bottom steel structure on the basis of acceptance, according to the baseline and experimental furnace construction furnace, furnace centerline release related to feeding port, front and rear bubbling and forming pathway of Taiwan brushed drain board centerline.③ lifting column. Interim measures to stabilize the column, and then install the ballast ballast according to design requirements angles, columns and ballast ballast angle must be close to the same time determined the exact elevation.④ masonry wall, including the passage wall. The bottom brick masonry wall must ensure that the level of degree, or to the bottom of the tile area for processing until it reaches the requirements. Multi-wall brick building, the first in the field after the operation to make sure the furnace size, non-timber hewn side facing brick hearth. Masonry joints to be staggered corner pressure, strictly maintain verticality.⑤ masonry parapet, the front wall, back wall and channel flame space. Masonry parapet bracket should be carefully examined, pallets and bearers installed after passing. Masonry brick and chest wall hooks have taken measures to prevent the dumping of the kiln.⑥ big arch masonry. Production arch tires, do carry through gantry sedimentation test and check the corresponding size, the big arch masonry to the center from both sides simultaneously, and requires continuous operation, try to control! * + Complete. Large arch insulation layer construction after the end of the kiln to be baked.⑦ masonry flue, chimney. Kiln debris must be cleared, and with a vacuum cleaner after masonry. Laboratory furnace, furnace flue and chimney masonry, but also compatible with the metal heat exchanger, access paths masonry chimney must be completed before other masonry.Is there any way masonry kilns?Masonry method of wet and dry assemble puzzle two ways:Wet puzzle parts: the Ministry of flames melted the side walls and arch roof space, flue, chimney and furnace insulation bricks, masonry used in the wet mud should be based on material used in the preparation of the corresponding fire clay bricks.Dry assemble parts: melting section and the bottom path, wall, brick fire space parts of the hook, melting section and flue arch arch bricks, fused brick and path roof tiles.Well-designed laboratory furnace, furnace, must be carefully masonry, masonry quality for life of the furnace, fuel consumption, glass melting and drawing operations has a significant impact. In order to meet the brick kiln kiln body size and masonry materials such as thermal expansion of basic requirements, so the furnace wall tiles, tile bottom Cutting should be carried out. Further expansion joints between bricks kiln reasonable reserve is extremely important aspects.

The use of ceramic fibers

Varnish application effect
The protective coating material to the surface of the refractory substrate firmly adhered, siloxane bond, structure compact and hard, especially refractory surface coated with silicon carbide, the protective layer formed by the aluminum-rich layer and a silicon oxide layer rich composition, can prevent the erosion of oxygen and combustion gas, oxidation with good effect, to prevent deterioration of the refractory.
Application Examples
The size of 70 mesh and 150 mesh alumina ceramic fiber equal to the same fiber blend, and then to take the mixed ceramic fiber 38% silica sol as the main component 61.8% inorganic binder, and then with 0.2% carboxymethyl cellulose with a viscosity of 10 poise fire resistant protective coating agents, coating thickness in the range of 0.7-7mm, the change in thickness per 0.1mm were coated on the surface of the silicon carbide refractory plate, into a maximum temperature of 1350 ℃ firing kilns into 12 hours, removed, impact resistance values ??measured. Measurement results showed that the protective coating having a thickness of 1mm, the impact resistance is not coated with a refractory coating material 14 times. However, the protective coating should not be thicker, because the coating thickness is too thick, although the value to be improved impact resistance, but peeling rate and increases contrast.
Another will be formed into the same protective coating HPL firing kiln, heated to 300 ° ~ 900 ℃, immediately remove, room temperature quench cracking observed state, the results did not HPL surface cracks appear, and subjected to quench after heat shock, flexural strength at 900 ℃ for quench temperature than the unprotected fireproof coating by about 15%. In addition, with protective coating HPL may continue to 1350 ℃ high temperature, life is no protective coating HPL 2 times.
As seen from the fire-resistant protective coating material coated with the furnace, flue and other high temperature refractory material surface under an atmosphere, to form an effective protective layer of refractory material to prevent damage to the substrate, extending its life and reduce maintenance and maintenance times, saving refractories and construction costs, bring significant economic benefits. The protective coating material used in various refractory materials and refractory metal components.

The role of the thermocouple protection tube

Thermocouples are the most widely used temperature sensors. The long-term stability of thermocouples, life and other performance indicators are closely related with the protection tube. Thermocouple failure rate depends directly on the level of protection tube material properties.
With the increasing degree of automation, temperature measurements related to all areas of the national economy, such as industry and agriculture, national defense, scientific research, medical, health, environmental protection, meteorology and space sectors. Thermocouple its stable performance, accurate and reliable, simple structure, easy to use, wide temperature range, the signal can be remote, etc., in areas such as industrial production and scientific research has become the most widely used temperature sensing element. The long-term stability of thermocouples, life and other performance indicators are closely related with the protection tube. According to statistics, the thermocouple measurements in the normal range, the failure rate depends directly on the level of protection tube material performance is excellent. Thus, in actual use the correct choice of the protective tube, the thermocouple is to extend the service life of the premise.
Action
Thermocouple protection tubes primarily for two purposes, first, to prevent mechanical damage suffered; second is to protect the thermocouple from the measured medium chemical corrosion, oxidizing or reducing atmosphere free from the harmful effects of the thermocouple as at close of its most good atmosphere. Therefore thermocouple must be protected, so that is not bad atmosphere against.
Thermocouples used in the following media must be isolated:
1. When a change in contact with the thermocouple thermocouple metal chemical composition (solid, liquid, gas)
 2. Thermocouple materials will corrode furnace gas and other vapors (sulfur and its compounds are particularly harmful).
 3. Thermocouple materials can corrode various electrolytes.
Thermocouple protection tube is usually a single protection tube, in some special cases, can be installed to protect two concentric tubes. Close to the thermocouple protection tubes called main, outer protective tube called supplementary protection tube. Usually alumina tube-based protection tube, silicon carbide tube combination auxiliary protective tube sets constitute protective tube to get a good overall performance, such as with anti-flame cutting, thermal shock, or to prevent mechanical damage and so on.

How to take care after the closure of industrial furnaces

In the long-term disabled industrial furnace, the furnace should pay great attention to external corrosion maintenance problems.
First, in the industrial furnace shut down after cooling, heating surface must be thoroughly cleaned of dust and grate upper furnace bottom ash. And then to maintain a certain degree of natural ventilation flue. Generally, in order to be in the furnace moisture, placed in the flue desiccant. As with quicklime as a desiccant, each cubic meter chamber or flue should generally be placed around 3kg. After placing all the ventilation should be tightly closed doors. Variable to be replaced after lime powder.
Locations such as industrial furnace room lying, flood tide serious ground during shutdown when a small fire should be used frequently baked and placed desiccant combined approach. If the industrial furnace shut down for a long time, after the complete removal of soot in the furnace metal exterior topcoat Hongdan oil or other anti-corrosion paint.
As for the inside of the furnace corrosion maintenance shutdown method, according to the length of time to be shutdown. Generally, the shutdown can not exceeding one month wet maintenance, more than one month should be taken care dry.
Dry maintenance should note the following questions: Do not direct contact with the desiccant industrial furnace metal surface, can be installed in a container such as iron plate; placed desiccant, to shutting the other hand hole and manhole covers, gas, water pipeline The valve must be truncated; quicklime change powder should be replaced.
The use of wet maintenance, pay attention to the furnace condensate water is best to use, followed by the original boiler water can again be softened; adding alkali, the boiler water with Weihuo heated to 80 100 ℃ pressure rose to 23 tables after pressure protection 23 hours to reach the furnace circulating water alkalinity balance, the pressure is reduced, then the boiler water to fill, causing 1.5 4 gauge and maintained throughout the warranty period this pressure, alkalinity should be regularly testing, lowered, should be ready to add.

Box-type gas roaster

The box-type gas roaster box-type structure, furnace by high temperature refractory brick layer, the lightweight insulation brick layer, high temperature insulation layer and steel body, furnace fire-resistant insulation effect. Two glib bilateral gas, high-speed vortex pump air, heat recovery unit preheat the intake flue non-vertical-type structure, catenary door lifting mechanism, lightweight and reliable.
Box-type gas the roaster combustion system:
Controlled by the fan, temperature sensor, temperature controller, and the like within the feedback loop system, the combustion system in the automatic control is within a range of 800 to 1200 ° C, quenching automatically ignition, maintaining constant temperature, gas savings.
Bilateral burning furnace combustion flame vortex is formed, the mold shell more fully absorb the heat fast heating, temperature uniformity, high thermal efficiency, heat recovery unit preheat intake flue gas discharged by the non-vertical-type flue, the furnace combustion better, more energy efficient, faster heating rate.
Box-type gas roaster purposes:
The box-type gas roaster roasting and heat treatment of steel and other places for the investment casting industry formwork. Double nozzle, bilateral gas, to form a flame vortex; waste heat recovery the intake preheating, improve combustion efficiency; high-speed vortex pump air-stable; energy-saving, low energy consumption conditions, roasting heating up fast.

Use hot pit furnace care and maintenance

(A) does not exceed the maximum oven temperature 950 ℃.
(2) into the housing part is not higher than the upper end of charge.
(3) does not allow the muffle furnace temperature higher than 400 ℃, open the lid intense cooling.
(4) is not loaded with moisture and oil of the workpiece.
(5) No protection framework is not the case, the use of the furnace.
(6) the pit furnace cleaned once a month, remove oxide and other contaminants.
(7) monthly check lid, furnace lining, and found damage to be repaired.
(8) monthly check resistance wire leads rod chuck fastening, descaling and timely tighten the clamps.
(9) monthly check instrumentation, thermocouple, and to be calibrated.
(10) on a monthly basis lid lifting mechanism for lubrication.
(11) Note that the case of heating elements, temperature is not normal when found, but should be carefully checked and found damage to the timely replacement.

Oven works

Oven enclosure generally use thin steel plate, the surface paint, oven studio using high quality structural steel production. Between the shell and the studio filled with aluminum silicate fibers. The bottom of the heater is installed, it can be placed at the top or sides. Temperature control instruments using digital smart table, PID regulation: Configuration 999.99 hours time controller with alarm device is connected. The oven's operation more simple, fast and effective.
Oven wide range of applications:
For chemical gas baking and food processing industries want baked goods, substrate stress removal, ink curing, drying paint film. Widely used in electronics, electrical, communications, plating, plastics, metals, chemicals, food, printing, pharmaceutical, PC board, powder, impregnation, spraying, glass, ceramics, wood and building materials.so precise baking, drying, tempering, preheating, stereotypes, and processing.
Oven works:
Digital instrumentation through a connection with the temperature sensor to control the temperature, the use of hot air circulating ventilation, air circulation system is divided into horizontal and vertical. Were confirmed by accurate calculation, the wind source is driven by the wind turbine blower motor operation via electric heaters, hot air duct into the oven to the studio, and will use the air intake duct after a re-circulating air source heat utilization This can improve the temperature uniformity. Be used as door switch, air circulation system can quickly restore operating state temperature value.

Alumina refractory concrete application of special

(1) ultra-high temperature kiln lining structural materials.
(2) high purity metal alloys with rare metals smelting crucible purification.
(3) high-temperature tube furnace thermocouple tube heat insulation.
(4) high-temperature kiln sticks and briquetting pressure washers, etc.
(5) Petroleum and Chemical Industrial temperature corrosion-resistant lining material.
(6) do transparent alumina ceramic high-temperature high-pressure sodium viewing glass tube microwave hood.
(7) in the electronics industry to make the circuit substrate voltage ceramic shell and tube seat tube radome spark plugs and so on.
(8) grinding tools and abrasives such as grinding wheel cutting disc Dies La Sita round nozzles textile porcelain pieces and a variety of high-temperature resistant bearing props.
(9) Chemical Industrial Piston Pump Parts sealing ring.
(10) ferrous metallurgy industry molten metal pipe.
(11) high-temperature industrial sectors efficient, energy-saving materials; such as hollow ball-like alumina, alumina whiskers, alumina fiber and products.

Trolley furnace overhaul Precautions

1 with corrosive, volatile, explosive gases into the furnace processing of the workpiece is strictly prohibited, so as not to affect the heating elements and refractory life and cause explosions and other accidents.
(2) shall not exceed the furnace temperature operation, otherwise it will shorten the life of the equipment.
3 oxide into the blast furnace of the workpiece to be too clear, available under the wire brush.
4 piece uniform stacking, from the heating element should be around 100-150mm.
5 is strictly prohibited barbaric operation, the workpiece should be light, to avoid shocks.
6 used furnace operator must not leave jobs, you must always pay attention to the working conditions are normal furnace.
7 furnace during loading and unloading the workpiece, you must first cut off the heating element power to ensure operator safety.
8 furnace oxides (including electric wire under) should always be cleaned at least once a week or five times a furnace. Furnace blowing with compressed air under the floor.
9. Resistance wire as it used, you can not bend the collision to avoid breakage.
10 furnace motor requiring regular inspection, lubrication, etc., pay attention to the use of safety.
11 at the shaft sleeve must always check lubrication to prevent damage due to lack of oil and bushings.
12. Periodically check the use of the heating element. The heating element is not kinked short-term use after the collision. If you have not heavily corroded and broken, can be used with the electric wire of the same material (or electric wire itself) as an electrode, the use of acetylene gas for heating welding electrodes using 50% Baiyun powder mixture, if the heating element can not be used when severe corrosion, should be replaced.
13 Regular calibration instruments, thermocouple usage prevent instrumentation, thermocouple temperature measurement errors caused by incorrect affect product quality.