JP4293473B1 - Bar wire heating and cooling method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve two problems of 1) lowering of thermal efficiency and 2) oxidizing atmosphere, which are disadvantages of a conventional floating fluidized bed, when a straight line rod is continuously heated in a fluidized bed.
A horizontal cylindrical heat transfer tube is loaded with powder particles as a heat medium, and the tube is rotated about an axis to form a rolling fluidized bed. Incorporate a mechanism to prevent the outflow of particulates at both ends of the tube to stabilize the fluidized bed. A bar is passed through to be buried in the fluidized bed. When the heat transfer tube is heated, it functions as a rapid heating furnace, the atmosphere can be easily controlled, and the thermal efficiency is improved. When the tube is cooled, it functions as an oil quenching device. Heat conductivity is adjusted by the number of rotations.
[Selection] Figure 2

Description

  The present invention relates to a method for continuously heating or cooling a straight wire, in particular a steel bar.

  Heating / cooling conditions are set according to the purpose and contents when the bar wire is linearly moved in the axial direction and continuously heat-treated. In general, the greater the heat transfer from the heat source to the steel material during heating, the better the thermal efficiency (= theoretical required heat amount / heat consumption), the easier to increase the production efficiency (= production amount / unit time), the shorter the equipment length, and the more Convenient for suppressing deterioration of surface quality of steel materials such as oxidation and decarburization.

In the most atmosphere furnace or direct-fired heating furnace which is widely being heated by convection and radiation to the gas and the furnace wall to the heat medium, the value of the overall heat transfer coefficient α is about 100~200W / m 2 K ^(hereinafter heat transfer The unit of the rate α) and the heating ability is small. Compared with this, in the fluidized bed furnace, the α value is about 800 to 1600, and the production efficiency is greatly enhanced at the same furnace length. The present invention is directed to a fluidized bed.

  In a fluidized bed heating furnace, compressed air is blown from the bottom of a tank in which fluidized sand is deposited to float the sand to form a fluidized bed and heated from above the tank to form a furnace. The feature is that heat transfer is large due to contact heat transfer of the granular material, and temperature uniformity is high due to floating mixing. It is also used for heating small diameter products and cooling for patenting high carbon steel wires (constant temperature transformation at about 600 ° C.). The biggest problem of this furnace when using it for heating is that the inside of the furnace is cooled by a large amount of air blowing to float the fluidized sand, and it is difficult to maintain the air / fuel ratio in the normal range for air blowing. The thermal efficiency is greatly reduced. The reason why the thermal efficiency cannot exceed 25% even under the best conditions in spite of the excellent fluidity of the fluidized bed furnace is the blowing. Further, since the atmosphere is necessarily oxidizing, it is not possible to prevent oxidation or decarburization of the steel surface during high temperature heating, which is inconvenient for some products.

  Patent Document 1 describes a method for improving the above problems of a fluidized bed furnace. That is, in order to improve thermal efficiency, a complicated combustion mechanism such as hot air blowing and a temperature control mechanism are incorporated. It is not popular because the equipment is expensive and the work is complicated.

  The second problem in the fluidized bed furnace is countermeasures against the outflow of sand at the entrance / exit of the bar wire penetrating the furnace. Patent Document 2 discloses an example thereof. In any case, in order to handle fluidized sand, an outflow prevention mechanism and a recovery / return mechanism suitable for the structure and working method of the furnace are required.

On the other hand, in the cooling process, the cooling method is determined based on the desired quality of the target product. Oil cooling is selected when entering.
In heating and cooling by immersion in a salt bath, the α value increases to about 1000 to 2000, but additional facilities and work for waste treatment such as scattering and washing of adhered salt are required.
In the lead bath, the α value is enhanced to about 2000 to 3000, but there is a problem of heavy metal contamination, and future use must be avoided.
In oil quenching, the α value is about 500 to 1500, and is widely used for products that do not work well in water quenching. Since quenching oil is relatively expensive and consumable, there is a problem that the cost cannot be ignored. Furthermore, the attached oil burns incompletely during tempering and generates a bad odor, which becomes a source of pollution. Therefore, maintenance of smoke removal and deodorization equipment is indispensable.

In Patent Document 3, the fluidized bed at room temperature has a cooling capacity substantially larger than that of lead bath quenching, and the regulation of the cooling capacity is achieved by intermittent contact with the fluidized bed, which is extremely effective for the patenting of wire rods. And the quality is disclosed to be superior to conventional methods.
The α value of the fluidized bed is close to that of oil quenching (500-1500 in a specific temperature interval), and in principle, the room temperature fluidized bed is considered to be replaceable with oil quenching. In oil quenching, appropriate cooling capacity and appropriate oil type are set according to the product. In order to substitute, it is required that the α value of the fluidized bed is adjustable. In addition, large diameter products are required to prevent oxidation during cooling. These problems are unresolved and no application examples are heard.

In the fluidized bed, when the material and particle size of the sand to be used are determined, the α value becomes almost constant and cannot be adjusted by the amount of air blow or other means. If the blown amount is too small, the blow-up is intermittent and local, and uniform heat transfer cannot be obtained. If too much, blow-through phenomenon occurs and the flow is not stable. There is adequate air flow to maintain floating flow.
If the particle size is changed, the α value will change somewhat, but if it is coarse, it will not float easily, and if it is very small, it will be mixed into the exhaust and discharged outside the furnace. Therefore, the usable particle size range is limited. Moreover, the replacement of the sand is complicated, and therefore the adjustment of the α value is practically impossible.

  No example of a method for heating and cooling a steel material has been found, but a rotary drying apparatus exemplified in Non-Patent Document 1 can be cited as a technique that can be applied. It is called a rotary kiln and is also used for preliminary refining of non-ferrous metals and lime firing. In the apparatus, a granular mass or pellet-like raw material is continuously charged into a rotating inclined cylindrical furnace, heated while passing, and chemically discharged. At that time, the raw material forms a tumbling fluidized bed in the cylinder to accelerate the reaction. The atmosphere can be adjusted from oxidizing to reducing by adjusting the flame.

Published patent publication Sho 61-276938 Published Patent Publication No. Hei 6-229681 Patent 3914953 A must for chemical equipment handlers Chemical equipment study group (industrial book) p181

  An object of the present invention is to make the best performance of heat transfer by a fluidized bed, which is one method of rapid heating / cooling when continuously heating or cooling a straight rod. For that purpose, the problem that the ventilation by the compressed air for forming the floating fluidized bed which is a weak point of the current fluidized bed lowers the thermal efficiency of the furnace and makes the atmosphere oxidizable must be solved. Furthermore, in order to be widely applied to cooling purposes, it is also necessary to make it possible to adjust the heat transfer property that has been almost constant. It is an object of the present invention to provide a solution to the above problem, that is, a method for drastically improving the thermal efficiency of a fluidized bed furnace, facilitating atmospheric control and adjusting heat transfer.

  In order to solve the above problems, the present invention eliminates the conventional method of forming a floating fluidized bed by blowing compressed air from the bottom of the tank when forming the fluidized bed. Focusing on the excellent heat transfer in the rolling motion of the granular material in the rotating cylinder newly used in chemical reactors, the possibility of a new fluidized bed by this method and its preliminary effect Confirmed by Furthermore, a reversing mechanism linked to a rolling mechanism is incorporated for the outflow problem that cannot be avoided when using a fluid, and the following invention is configured. Hereinafter referred to as a rolling fluidized bed.

  A first aspect of the present invention is a heat transfer method for continuously heating or cooling a metal bar wire traveling in the axial direction, wherein a cylindrical heat transfer tube provided with a plurality of protrusions on its inner surface is placed horizontally, The inside is filled with flowable granular material that becomes a heat transfer medium, and the tube is rotated around the central axis to scoop up the granular material to form a rolling fluidized bed and at both ends of the tube Is provided with means for preventing the outflow of the granular material to maintain the fluidized bed, heating or cooling the tube to cause the temperature of the fluidized bed to follow the temperature of the tube, and It is a heat transfer method of a bar wire, which is heated or cooled by being penetrated so as to be buried in the fluidized bed.

  According to a second aspect of the present invention, the outflow prevention means forms one or more female screw-shaped spiral groove guides in opposite directions on the inner surfaces of both ends of the heat transfer tube, and the granular material is formed in the spiral groove as the heat transfer tube rotates. The rod wire heat transfer method according to the first aspect of the invention is characterized in that each of the wires flows inwardly (towards the center of both ends of the pipe) along the guide.

  According to a third aspect of the present invention, there is provided the rod wire heat transfer method according to the first aspect, wherein the outflow prevention means is provided with flange-shaped dams at both end faces of the heat transfer tube.

  A fourth invention is a heat transfer device that continuously heats or cools through a steel rod that goes straight in the direction of the wire axis, and has a plurality of protrusions on the inner surface and one or more strips on the inner surfaces of both ends. A horizontal cylindrical heat transfer tube with female screw-shaped spiral groove guides formed in opposite directions, a flowable granular material loaded as a heat transfer medium inside the tube, and the tube in a horizontal state around the central axis A driving device for rotating, a device arranged around the tube for heating or cooling the tube, and a lid having a rod through hole that slides close to the openings at both ends of the tube and closes. It is the heat exchanger of a bar wire characterized by this.

  The fluidized bed heat transfer apparatus according to the present invention first forms a fluidized bed by rolling, and thus does not require a large amount of air blowing to form a floating fluidized bed as in the prior art. Therefore, when used for heating, the design can be designed with the thermal efficiency and the equipment cost, and the original thermal efficiency of the heating apparatus can be obtained with a relatively low equipment cost. 40% or more is possible compared to the conventional less than 25%.

  Secondly, since the bar wire is heated in an airtight heat transfer tube with a simple lid, the problem that the atmosphere becomes oxidizing is solved. The atmosphere is controlled with appropriate gas species such as nitrogen gas and a small amount of hydrogen gas, making it suitable for precision heat treatment.

  Third, when used for cooling, the heat transfer rate can be adjusted by adjusting the rolling speed. It becomes easy to simulate various oil types used in oil quenching, and it can be replaced with oil quenching together with atmosphere control. This not only reduces costs, but also solves the problem of odor pollution that is inevitable for oil quenching.

  FIG. 1 (side view) is a schematic diagram illustrating the whole of an example in which the apparatus of the present invention is applied to a quenching and tempering line. A steel wire 1 as a material to be processed is guided to a straight path 2. Drive means 4, which encloses the path 2 and arranges the three heat transfer tubes 3, 3 ′, 3 ″ coaxially and in series, and rotates the heat transfer tubes 3, 3 ′, 3 ″ around the tube axis, respectively. 4 'is rotated at a predetermined speed. Specifically, as shown in FIG. 2A, both ends of the heat transfer tube are respectively placed between two horizontally parallel rolls (corresponding to 4) rotating in the same direction. The pipes 3, 3 ′, 3 ″ are each charged with an appropriate amount of granular material as a heat transfer medium. By rotation, the granular material forms a rolling fluidized bed 5. The steel wire 1 has three stages of the granular material. Passes through the fluidized bed 5.

  The first heat transfer tube 3 is disposed in a heating furnace 7 having a burner 6. By heating the inside of the furnace 7 to about 1000 ° C., the heat transfer tube 3 is heated, and the steel wire 1 is heated to about 950 ° C. through the fluidized bed 5 under a large heat transfer coefficient.

  A spray cooling device 8 is disposed above the second heat transfer tube 3 'to cool the rotating tube 3'. The fluidized bed in the pipe 3 ′ is maintained at around room temperature, and the steel wire 1 entering is cooled to 100 ° C. or less and quenched under a heat transfer coefficient equivalent to oil quenching.

  The third heat transfer tube 3 ″ is disposed in a heating furnace 11 having an auxiliary burner 9 and a flue 10 for inducing exhaust gas from the heating furnace 7. The flue 10 should be employed for energy saving. 11 is set to about 530 ° C. and the tempered steel wire 1 is tempered by heating to about 480 ° C. The steel wire after the heat treatment is wound up to form a coil 12.

  A lid 13 (FIG. 2B) that closes the opening while sliding close to the inlet of the first heat transfer tube and the outlet of the third heat transfer tube is provided to form a hermetic seal, and a predetermined gas is introduced to control the atmosphere. . If it is desired to change the atmosphere for each tube, the lids 13 and 13 'are also installed at the ends of the tubes.

The rolling fluidized bed will be described in detail.
FIG. 2 shows a main part of the heat transfer tube 3. Outflow prevention means are provided at both ends in order to prevent the powder particles loaded therein from flowing out. As a suitable example of the means, spiral groove guides 21 are provided in the inner surfaces of both end portions of the tube 3 in a female thread shape in opposite directions. When the number of threads is 1, it is a normal female screw shape, and when it is a large number, it is a turbine shape. The action varies slightly depending on the shape. The granular material flows by the rotation of the tube 3 and flows out at the end, but is returned to be screwed by the spiral groove guide 21. The other end is also screwed in similarly because the guide is in the opposite direction.

  In order for the bar wire to go straight and pass through the fluidized bed in an embedded state, the layer thickness of the fluidized bed needs to exceed the height of the spiral groove guide 21. For this purpose, the action of screwing back sand at the guide portion becomes a problem. The factors of the pushing action are related to the guide height, the guide shape, the screw lead angle, the guide portion length, the rotational speed, the guide strip number, the pipe inner diameter, the flow repose angle of the granular material, and the like. Optimization requires no special difficulties for machine designers through trial testing. As an appropriate condition, the height of the spiral groove guide 21 is preferably 5% or more and 30% or less of the heat transfer tube radius to ensure a sufficient layer thickness. If it is less than 5%, the rolling fluidized bed becomes shallow, and in some cases, the rods are not surely buried. If it exceeds 30%, the pass level rises, and the corresponding amount of loading becomes excessive, the mixing property is lowered, and the uniformity of the temperature distribution in the fluidized bed is concerned. Hereinafter, the larger the guide portion length, the smaller the outflow and the greater the tube diameter is.

  When the heat transfer tube 3 is rotated around the tube axis, the granular material deposited in the tube is pulled up along the inner wall, but because of its high fluidity, it easily slips and does not easily roll. Therefore, a large number of heat transfer fin-like projections 22 are provided on the inner surface other than the both ends. The protrusions 22 squeeze, stir, pull up, slide down when a certain angle is reached, and fall off when the speed is high. When the height of the protrusion is large, the amount of scraping and release increases compared to the stirring. The protrusion shape and the number of installations are corrected as appropriate. For example, the mixing property is enhanced by variously combining the inclination angle and height of the protrusions. A rolling fluidized bed is formed by vigorous mixing by submergence and stirring. The rolling fluidized bed is stabilized by rolling with protrusions and screwing with guides.

  The protrusion has another function. This is an increase in the effective inner area of the heat transfer tube. The heat transfer area from the heat transfer tube to the granular material is considered to decrease to about 50% or less of the inner area due to the loading rate. Assuming that the area and the surface area of the rods to be loaded are the same, the fluidized bed temperature changes exactly between the set furnace temperature (≈ tube temperature) and the rod temperature during heating or cooling. Heat conductivity will be reduced. Therefore, the effective heat transfer area ratio (= effective heat transfer tube area / bar surface area) is preferably 10 or more. To that end, the pipe diameter and fin effect must be fully considered. The lower limit of the protrusion surface area ratio with respect to the inner area is desirably 20% or more from the height for scraping. The upper limit may be about 100% from the peak of the heat transfer effect. When it is excessive, the flow between the protrusions is lowered.

  Table 1 shows an example of a trial calculation related to the temperature distribution. The calculation conditions were heat transfer coefficient α = 800, tube diameter 0.1 m, rod diameter 0.01 m, and effective heat transfer area ratio 10. In order to heat to 900 ° C., the inlet portion set temperature may be 1100 ° C. and the outlet portion 1000 ° C. As the effective area ratio increases and the α value increases, the fluidized bed temperature approaches the set furnace temperature, and the difference between the furnace temperature and the ultimate bar temperature decreases. The same is true for cooling.

  The flow strength of the powder is affected not only by the action of the protrusions but also by the number of rotations of the heat transfer tube in relation to the inner diameter. It is expected that the heat transfer coefficient α between the fluidized bed and the bar will be improved by increasing the flow. If the flow is too small, the temperature in the bed becomes non-uniform. As a measure of the flow strength, the kinetic energy is proportional to the inner diameter × the number of rotations, so that it can be substituted by the peripheral speed. It is practical to determine the appropriate amount experimentally.

  Heat-resistant steel is used for heating as a material for the heat transfer tube. Ceramics can also be used in consideration of thermal conductivity. Carbon steel pipes may be used for cooling.

  The granular material to be used is required to have fluidity and hardly cause agglomeration so that an undesirable chemical reaction does not occur. As a material, one or a mixture of zircon, alumina, silica sand, graphite, silicon carbide, coke, steel and the like can be used. In the rolling fluidized bed, the particle size of the granular material is not limited as in the floating fluidized bed. In the latter case, the diameter is usually 0.1 to 0.4 mm, but in the present invention, a wide range can be used beyond these.

  Another example of the outflow prevention means is shown in FIG. An annular dam 33 for preventing outflow is attached to both end faces of the heat transfer tube 3, and the granular material is loaded by the height of the dam. An inclined guide 32 for guiding the steel wire 31 downward at the inlet of the pipe 3 and burying it in the fluidized bed is provided. This means can be applied in the case of processing a thin steel wire.

  In principle, the heating source is arranged on the outer periphery of the pipe, but when the pipe diameter is large, it may be arranged in the pipe like a rotary kiln. In principle, the cooling source is spray water cooling. It is possible to replace the salt bath cooling by arranging a heat-retaining furnace on the outer periphery to control the rolling fluidized bed to a predetermined temperature.

  There is no particular limitation on the number of bar wires. One large diameter or several different diameters can be passed simultaneously. Basically, the wire speed is determined according to wire diameter × wire speed = constant (the value is determined by the furnace length). Under these conditions, even if the wire diameter is different, the same temperature is obtained at the same position in the furnace. In the operation where various wire diameters are mixed, the fluctuation of the heating load of the furnace becomes smaller and the thermal efficiency and the production efficiency are stabilized.

FIG. 4 shows the result of clarifying the relationship between the rotational speed and the α value by conducting a wire cooling experiment using a prototype heat transfer tube. The α value increases as the rotational speed increases. This indicates that the cooling capacity can be easily adjusted, for example, it can be easily replaced by various oil quenching.
The experimental conditions are as follows.

  The structure of the heat transfer tube has an inner diameter of 140 mm x length of 400 mm, and the spiral groove guide has a single strip with a height of 13 mm x length of 100 mm, the spiral groove guide slope is 100/1200, and the protrusion height of the rolling part The length is 10 mm × 8 sheets / circumference. The closed end was clamped on a lathe and rotated horizontally. Zircon sand (0.1 to 0.3 mm diameter) as a granular material was charged at a volume ratio of about 30%. Parker Smart Quench was used to measure the heat transfer rate. In this method, a 12 mm-diameter Inconel rod incorporating a thermocouple is heated to a predetermined temperature in a heating furnace, cooled in a normal temperature fluidized bed, temperature-traced, and data is analyzed to obtain an α value.

The current situation is as follows. Outflow begins with rotation. After that, pushing and outflow are balanced.
The remaining layer thickness was about 25 to 30 mm at one rotation per second or more, and although not necessarily sufficient, an amount not sufficient to embed the steel wire could be maintained. In the cooling test, the rod diameter of the temperature sensor was so large that it could not be completely buried. Therefore, the illustrated α value is lower than the predicted value. It is obvious that at one rotation per second (peripheral speed 0.4 m / s) or more, it slides, sinks, falls, mixes violently, and there is no problem with uniformity. At a speed of 0.1 rotation per second (peripheral speed 0.04 m / s), the powder particles continue to slide down, but are insufficiently mixed and difficult to call a rolling fluidized bed.

  As a practical condition, it has been found from the above observation that the peripheral speed is 0.1 m / s or more. Note that at a peripheral speed of 0, heat insulation is caused by powder particles. When the rotation becomes excessive, there is no flow and no drop like centrifugal casting. Although the upper limit of the peripheral speed is related to the pipe diameter, it is estimated that 2 m / s is the range in which slipping down and falling easily occur.

  In the above example, the shape of the rolling fluidized bed was observed by changing the shape of the groove guide and the protrusion. The number of groove guides increased from 1 to 8, and the guide / lead angle increased from 100/1600 to 100/100. Observations revealed the following. The outflow prevention effect was improved, and the remaining layer thickness increased to 40-50 mm. It is enough to be buried. As an effect of reducing the height of the protrusion, there was no scraping release at 0.5 rotations per second, and a rolling phenomenon mainly consisting of diving, scraping and sliding was confirmed.

  A quenching test was performed using the above experimental apparatus. As a material, a 5.5 mm diameter hard steel wire (SWRH62B) was used. Immediately after heating to 920 ° C., it was buried in a rolling fluid bed at room temperature and cooled to room temperature. The rotation speed was 1 rotation per second (peripheral speed 0.4 m / s). From the observation of the metal structure, it was confirmed that the entire cross section was martensite and had sufficient performance for quenching.

  Table 2 shows a design example of a heating device for a thin-wire quenching and tempering line using the present invention. The quenching device and the tempering device are designed in exactly the same way. As a result of the detailed examination, it can be seen that it is relatively simple, compact, and has low equipment costs and is easy to implement.

  When the rod-type heat transfer device using the rolling fluidized bed according to the present invention is used as a heating device, the equipment cost is relatively low, and the heat efficiency and quality are improved, so that the existing floating fluidized bed heating furnace is replaced. Can save energy. It can be used for heating in various heat treatments. Similarly, when used as a cooling device, it can be replaced with conventional oil quenching or salt bath quenching, thus saving resources. It can also be used for rapid heating and cooling of copper and aluminum rods.

It is explanatory drawing of the example of the heat processing line which applied the heat exchanger of the bar wire of this invention. The principal part of this invention is demonstrated, A is a front view, B is side sectional drawing. The other example of an outflow prevention means is shown. It is a figure which shows the example of the relationship between the rotation speed of the heat exchanger tube of this invention, and the heat transfer rate of a fluidized bed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,31: Steel wire 2: Pass line 3, 3 ', 3 ": Heat transfer tube 4: Rotation drive device 5: Rolling fluidized bed 6: Burner 7: Heating furnace 8: Spray cooling device 9: Auxiliary burner 10: Smoke Road 11: Tempering furnace 12: Product coil 13, 13 ': Lid 21: Spiral groove guide 22: Protrusion 32: Inclined guide 33: Flange-shaped dam

Claims (4)

A heat transfer method for continuously heating or cooling a metal bar wire that travels in an axial direction, wherein a cylindrical heat transfer tube having a large number of protrusions on an inner surface is placed horizontally, and a heat transfer medium is placed inside the tube. The flowable granular material is loaded, and the tube is rotated around the central axis to scrape the granular material to form a rolling fluidized bed, and at both ends of the tube, the granular material is An outflow prevention means is provided to maintain the fluidized bed, and the pipe is heated or cooled to cause the temperature of the fluidized bed to follow the temperature of the pipe, and one or more bars moving straight are buried in the fluidized bed. Heating or cooling through the pipe so that the inner peripheral speed of the pipe is 0.2 m / s or more, or the value of the heat transfer coefficient between the fluidized bed and the bar wire is 600 W / m ² K or more. A heat transfer method for bar wires, characterized by   The outflow prevention means forms one or more female screw-shaped spiral groove guides on the inner surfaces of both ends of the heat transfer tube in opposite directions, and the powder particles are respectively formed along the spiral groove guide as the heat transfer tube rotates. It is made to flow in direction, The heat transfer method of the bar wire of Claim 1 characterized by the above-mentioned. 2. The rod wire heat transfer method according to claim 1, wherein the outflow prevention means is provided with annular dams on both end faces of the heat transfer tube.
A heat transfer device that continuously heats or cools through a rod that goes straight in the direction of the wire axis, and has many protrusions on the inner surface and one or more female screw-shaped spiral groove guides on the inner surfaces of both ends. A horizontal cylindrical heat transfer tube formed in the direction, a flowable granular material loaded as a heat transfer medium inside the tube, a drive device for rotating the tube around a central axis in a horizontal state, and the tube 0.2m and device for heating or cooling the tube is arranged around, Ri consists lid having bars through hole to close in proximity to the opening portions at both ends of the tube, the inner peripheral speed of the tube of / S or more, or the value of the heat transfer coefficient between the fluidized bed and the bar wire is 600 W / m ² K or higher .

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