JP2611801B2 - Blackening method and blackening furnace - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a processing method for performing a blackening treatment on a steel material to be processed and a blackening furnace suitable for the method.

[Conventional technology]

The blackening process, which forms a black Fe ₃ O ₄ oxide film on the surface of a steel material to be treated, uses bolts to protect the inside with a dense film and improve corrosion resistance, wear resistance and appearance. It is widely used for nuts and other small parts. This blackening treatment is conventionally performed by immersing the object to be treated in a caustic alkaline solution, or in a mixture of a black dyeing solution and a rust-preventive solution consisting of sodium nitrate or a mixture of sodium nitrate and potassium nitrate. In general, a method using a chemical treatment such as immersion in water and a homo treatment performed in an airtight electric furnace into which steam and N ₂ or a heat-generating lean gas are introduced are generally performed.

[Problems to be solved by the invention]

However, of the above-mentioned conventional methods, the former method using a chemical treatment is expensive because the treatment liquid is expensive, and the surface of the object to be treated is easily roughened, and furthermore, the treatment liquid is required to be drained. There is a problem. In addition, the latter homotreatment requires an atmosphere gas, which increases the cost. Further, similarly to the former, the homogenization treatment requires heating the object to be processed for the blackening treatment, which increases the processing cost.

The present invention solves the above-mentioned conventional problems, and aims to provide a blackening treatment method and a blackening treatment furnace that require less treatment cost and processing time by performing the blackening treatment simultaneously with tempering. is there.

[Means for solving the problem]

Thus, the blackening treatment method of the present invention provides a tempering furnace equipped with an open flame burner, wherein the O ₂ concentration in the furnace atmosphere is reduced to less than 0.1% and the CO concentration is reduced to 1 to 1 by adjusting the air-fuel ratio of the open flame burner. In addition to maintaining the temperature at 6%, the combustion amount of the direct-fired burner was adjusted, and the amount of cooling air supplied to the furnace from a gas cooler provided in an atmosphere circulation system for sucking the atmosphere gas in the furnace and returning it to the furnace was adjusted. The tempering process is performed while maintaining the furnace temperature at 400 to 650 ° C. by selectively performing the adjustment, and a black oxide film is formed on the surface of the process target during the tempering process. This is a blackening processing method characterized in that the blackening treatment is performed.

In the method of the present invention, the O ₂ concentration in the furnace atmosphere is set to 0.1%
With the above, the oxidation of the object to be treated is too advanced to form a red rust layer of Fe ₂ O ₃ , and if the CO concentration is less than 1%, the residual O ₂ increases and a red rust layer is generated in the same manner as above, If the CO concentration exceeds 6%, the oxidizing power of the atmosphere in the furnace becomes weak, and the formation of an oxide film on the object to be processed is insufficient, and both are not preferable.

Further, in the method of the present invention, the tempering and the blackening treatment of the object to be treated are performed simultaneously. However, the tempering time is determined by the type of steel and the required hardness of the object to be treated. 400 to 650 to obtain a blackened coating
° C. That is, if the furnace temperature is lower than 400 ° C., the oxidation rate of the object to be processed is low, and only a thin oxide film is obtained.
If the temperature exceeds ℃, oxidation proceeds excessively, and the oxide film becomes excessively thick, which may cause peeling.

Further, the blackening furnace of the present invention, in a tempering furnace equipped with an open flame burner, provided with an atmosphere circulation system for sucking the atmosphere gas in the furnace and returning the gas to the furnace, a gas cooler in the atmosphere circulation system, A cool air damper for adjusting the amount of cooling air is provided, and the air-fuel ratio is adjusted to reduce the O ₂ concentration in the furnace atmosphere to less than 0.1% and the CO concentration to 1 to 6% in the combustion amount control unit of the direct fire burner. An air-fuel ratio controller for maintaining the temperature is provided, and the output of the furnace temperature controller connected to the furnace temperature detector is supplied to the combustion control device for the direct fire burner when the output is larger than a predetermined value. A blackening furnace, further comprising a signal converter for providing a value to the cool air damper air volume control device when the value is smaller than the value.

In the blackening furnace of the present invention, either a batch furnace or a continuous furnace may be used as the tempering furnace.

Further, in the blackening furnace of the present invention, it is preferable that a limiter for maintaining the minimum combustion amount is provided in the combustion amount control device of the direct fire burner. .

[Action]

In the blackening treatment method of the present invention, the atmosphere in the furnace is reduced to an O ₂ concentration of less than 0.1%,
O concentration is maintained at 1-6% and furnace temperature is 400
Since the temperature is maintained at 650650 ° C., a black oxide film containing Fe ₃ O ₄ as a main component is effectively formed on the surface of the steel material to be heated. Since the formation of the oxide film is performed simultaneously with the tempering treatment of the object, it is economical in terms of processing time and fuel consumption.

Further, in the blackening furnace according to the present invention, the combustion gas component of the direct fire burner is adjusted by the air-fuel ratio adjusting device, and the inside of the furnace is maintained in an atmosphere suitable for the blackening treatment. A gas cooler provided in the atmosphere circulation system cools the atmosphere gas in the furnace flowing through the circulation system and supplies the gas to the furnace through a cool air damper. When the inside of the furnace becomes overheated, the output of the furnace temperature controller is given to the air volume control device of the cold air damper via the signal converter, and the cold air is supplied into the furnace by opening the cold air damper, so that the furnace is overheated. And the furnace temperature can be reliably maintained at 650 ° C. or less. If the inside of the furnace tends to be supercooled, the output of the furnace temperature controller is given to the combustion amount control device via the signal converter as in the normal furnace temperature control, and the combustion amount of the direct fire burner is adjusted. Maintain temperature above 400 ° C.

If a limiter for holding the minimum combustion amount is provided in the combustion amount control device, when the combustion amount of the direct fire burner is reduced during the combustion amount reduction control and reaches the minimum combustion amount, the combustion amount is held at the combustion amount by the limiter, and the flashback is prevented. Stable combustion is maintained without causing a fire. For this reason, the furnace pressure does not decrease as compared with the case of extinguishing a direct-fired burner, and it is possible to prevent air from entering from the furnace entrance and the like, so that the furnace atmosphere is changed to an O ₂ concentration suitable for forming Fe ₃ O _4. And it is easy to maintain the CO concentration, and the blackening treatment can be surely performed. Even if the direct fire burner continues to burn, as described above, the inside of the furnace is cooled by the cold air in accordance with the rise in the furnace temperature, thereby preventing overheating.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

In the drawing, reference numeral 1 denotes a continuous tempering furnace, 2 denotes a furnace body, 3 denotes a conveyor for transferring an object to be processed penetrating inside the furnace body 2, 4 denotes an inlet of the furnace, and 5 denotes an outlet. 6a, 6b, 6c, 6
The heating zone 6 is divided into four heating zones d. Each of the heating zones 6 (general term for the heating zones 6a to 6d) is provided with a direct-fire burner 7. Reference numeral 10 denotes a water tank for sealing the conveyor 3 on the exit 5 side, 11 denotes a rust-preventive liquid tank storing a rust-preventive liquid 12 which is a mixture of rust-preventive oil composed of mineral oil and water, and 13 denotes a rust-preventive liquid tank. It is a conveyor.

On the other hand, 21 is the bottom of the furnace body 2 (the heating zone in this embodiment).
6c), one end of which is connected to the suction pipe of the blower 25, the other end of which is connected to the suction port of the blower 25, 22 is a discharge pipe connected to the discharge port of the blower 25, and 23 is an intermediate part of the discharge pipe 22. Is an air supply pipe which is connected to the header pipe 23 and has a distal end opening inside the furnace top of each heating zone 6. The atmosphere circulation system 20 is formed by these pipes 21 to 24 and the blower 25. Is formed. Reference numeral 26 denotes a water-cooled gas cooler, which is provided in the middle of the intake pipe 21. 27 is a cool air damper provided in the middle of each air supply pipe 24.

Next, FIG. 3 shows a furnace temperature control system of the entire tempering furnace 1, and the detected furnace temperature of the furnace temperature detector 31 provided for each heating zone 6 is as follows.
For each heating zone 6, each furnace temperature controller 32 compares it with a furnace temperature set value, and an output signal corresponding to each deviation value is converted into a control motor control signal by a signal converter 33 to adjust the opening of the cold air damper 27. Is supplied to the air flow control device 34 for use or the combustion control device 35 for the direct fire burner 7. FIG. 2 shows details of the furnace temperature control system for one heating zone 6c, but each of the other heating zones also has a furnace temperature control system of the same configuration. In FIG. 2, reference numeral 36 denotes a control motor constituting the air volume control device 34 for driving the damper shaft of the cold air damper 27. In the combustion amount control device 35, reference numeral 37 denotes an air pipe connected to a combustion air supply source, reference numeral 38 denotes a fuel pipe connected to a fuel gas supply source, and reference numeral 39 denotes an air control valve which is driven by a control motor 40. Reference numeral 41 denotes a regulator for keeping the pressure ratio between the air pipe 37 and the fuel pipe 38 constant. Reference numerals 42 to 44 denote throttle valves whose opening degree can be adjusted. Different throttle resistance values are set in such a manner that fuel of different air-fuel ratios is supplied to the direct fire burner 7 by switching the electromagnetic on-off valves 45 to 47. I'm sorry. That is, 42 is when the furnace temperature is low (for example, 400 to 500 ° C)
Throttle valve for blackening treatment of 43, when the furnace temperature is high (for example, 500
This is a throttle valve for blackening treatment (up to 650 ° C.). Experiments are carried out in advance by changing the combustion amount of the direct-fired burner 7 and the opening degree of both throttle valves, that is, the air-fuel ratio, by a test operation or the like. The atmosphere is set to an aperture resistance value that maintains an O ₂ concentration of 0.1% or less and a CO concentration of 1 to 6%. The throttle valves 42 and 43, the electromagnetic on-off valves 45 and 46 for switching, and the regulator 41 form an air-fuel ratio adjusting device 48.
Reference numeral 44 denotes a throttle valve used when only tempering is performed in an oxidizing atmosphere without performing a blackening process.The throttle valve is set to a high throttle resistance value, and is provided as necessary together with the electromagnetic opening / closing valve 47 to provide versatility to the device. Things.

On the other hand, the signal converter 33 comprises a reverse converter 51 and a converter 52. When the output signal of the furnace temperature controller 32 is 50% or less as shown in FIG. % Output signal is inversely converted and the air flow controller 3 is used as an input signal of 0 to 100% so that the cold air damper 27 operates from fully closed to fully open.
When the output signal of the furnace temperature controller 32 exceeds 50% as shown in FIG. 4, the converter 52 outputs the 50-100% output signal from the fully closed state to the fully opened state of the air control valve 39. It has the characteristic of giving a 0-100% input signal to the combustion control device 35 to operate. Reference numeral 53 denotes a limiter, which reduces the output signal of the converter 52 to the minimum opening of the air control valve 39 corresponding to the minimum combustion holding amount of the direct fire burner 7 (in this embodiment, 30% of the full opening). When the control motor 40 is stopped by opening the contact 54, the type shown in the drawing directly detects the output value of the converter 52, or a limit switch provided on the rotating shaft of the air control valve 39 may be used. it can. When the furnace temperature drops and an output signal corresponding to the minimum opening of the air control valve 39 is output from the converter 52, the contact 54 is switched to the return (closed) side. I'm sorry.

In the blackening furnace 55 having the above-described structure, in order to perform the blackening process on the steel material to be processed, the material to be processed is conveyed in the furnace by the conveyor 3, and in each heating zone 6, according to the steel type of the material to be processed. The furnace temperature controller 32 controls the furnace temperature within a furnace temperature range of 400 to 650 ° C. so that a temperature curve of the tempering process is obtained.In the combustion amount controller 35, the air-fuel ratio controller 48 The electromagnetic on-off valve 45 or 46 is opened according to the furnace temperature, fuel gas is allowed to flow through the throttle valve 42 or 43, and the open flame burner 7 is burned at a predetermined air-fuel ratio, thereby reducing the atmosphere in the furnace to an O ₂ concentration of 0.1%. And maintain a CO concentration of 1-6%. The switching between the electromagnetic on-off valves 45 and 46 is performed by manual operation or automatic operation using the output of the furnace temperature detector 31 according to the furnace temperature. When the output signal of the furnace temperature controller 32 decreases to 65% during the furnace temperature control, the limiter 53 operates to stop the valve body of the air control valve 39 at the minimum opening, and the direct fire burner 7 is set to the minimum combustion amount state. Will be retained. When the output signal of the furnace temperature controller 32 further decreases to 50% or less, the output signal of the furnace temperature controller 32 is supplied to the air volume control device 34 via the reverse converter 48. The cool air damper 27 is opened, cool air is supplied into the heating zone 6, and the furnace temperature is maintained at the set temperature. After passing through the entire heating zone 6, the object to be treated has a black oxide film formed on the surface, is cooled by dropping into the rust preventive liquid 12, and is carried out of the furnace by the conveyor 13 as a completed product of tempering and blackening treatment. It is done.

Using a blackening furnace 55 (furnace length = 9 m) having the above structure, heating a S35C material bolt at 450 ± 5 ° C according to a predetermined tempering temperature curve while heating the furnace at a speed of 90 minutes. As a result, a tempered product having predetermined mechanical properties and having a blackened surface covered with a black Fe ₃ O ₄ film could be obtained.

The present invention is not limited to the above-described embodiment. For example, as the air-fuel ratio adjusting device 48, in addition to the pressure control type of the above-described embodiment, both the air flow rate and the fuel flow rate are controlled by a flow rate control valve to provide a predetermined value. ones and flow controlled to obtain the air-fuel ratio, such as those further detects the O ₂ or the concentration of CO and the like in the furnace gas and fed back to the ratio setter of the flow control system to correct the air-fuel ratio, Various types can be used. Further, the output signal limit value of the furnace temperature controller 32 that performs switching between burner combustion amount control and cool air volume control in the signal converter 33 may be a value other than the above 50%,
Further, the signal converter 33 may have a configuration other than the above configuration.
In the case of a continuous tempering furnace, if the furnace pressure can be maintained by extinguishing the burner in about one or two zones, the limiter 53 can be omitted. Further, in the above embodiment, the object to be treated after the formation of the oxide film is cooled in the rust-preventive liquid 12 to prevent the formation of a red Fe ₂ O ₃ layer caused by slow cooling in the air, and the rust-preventive component is reduced to Fe. _It has an advantage of improving the anticorrosion property by adhering to an oxide film containing ₃ O ₄ as a main component.

Although the continuous tempering furnace has been described above, the present invention can use a batch tempering furnace as the tempering furnace,
In this case, the furnace inlet can be closed during the process, so that the furnace atmosphere can be easily adjusted.

〔The invention's effect〕

As described above, according to the present invention, the blackening process can be performed at the same time as the tempering, so that the processing time and fuel consumption can be reduced, and compared with the case where the tempering furnace and the blackening furnace are separately provided. Equipment cost and equipment installation space are reduced. Further, since the atmosphere in the furnace is adjusted by adjusting the air-fuel ratio of the direct-fired burner and no separate atmosphere gas generator is required, the blackening treatment can be performed economically.

In addition, by installing a limiter for holding the minimum combustion amount in the combustion amount control device of the open flame burner, it is possible to prevent air from entering the furnace due to a decrease in furnace pressure, and to ensure blackening by maintaining the furnace atmosphere. Processing can be performed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a blackening furnace showing one embodiment of the present invention, FIG. 2 is a sectional view taken along line AA of FIG. 1, and FIG. 3 is control of the blackening furnace of FIG. 4 and 5 are output characteristic diagrams of the signal converter. 1 ... tempering furnace, 6a-6d ... heating zone, 7 ... direct fire burner, 12 ... rust preventive liquid, 20 ... atmosphere circulation system, 25 ... blower, 26 ... gas cooler, 27 ... cold air Damper, 31… Furnace temperature detector, 32… Furnace temperature controller, 33… Signal converter, 34…
Air flow control device, 35: Combustion amount control device, 39: Air control valve, 41: Regulator, 42, 43 ... Throttle valve, 45, 46 ...
Electromagnetic on-off valve, 48 Air-fuel ratio adjusting device, 51 Reverse converter, 52 Converter, 53 Limiter, 55 Blackening furnace.

Claims (5)

(57) [Claims] In a tempering furnace provided with an open flame burner, the O ₂ concentration of the atmosphere in the furnace is maintained at less than 0.1% and the CO concentration is maintained at 1 to 6% by adjusting the air-fuel ratio of the direct fire burner. The adjustment of the combustion amount of the direct fire burner and the adjustment of the amount of cooling air supplied to the furnace from a gas cooler provided in an atmosphere circulation system for sucking the atmosphere gas in the furnace and recirculating the gas into the furnace. Performing a tempering process on the object to be processed while maintaining the furnace temperature at 400 to 650 ° C. by performing the process, and forming a black oxide film on the surface of the object during the tempering process. Blackening treatment method. 2. A tempering furnace having an open flame burner, an atmosphere circulation system for sucking the atmosphere gas in the furnace and returning the gas to the furnace is provided. The atmosphere circulation system has a gas cooler and a cooling air flow adjusting means. provided with a cold air damper, the combustion amount control device of the direct flame burners, by adjusting the air-fuel ratio of the furnace atmosphere O ₂
An air-fuel ratio controller for maintaining the concentration below 0.1% and the CO concentration between 1 and 6% is provided, and when the output of the furnace temperature controller connected to the furnace temperature detector is larger than a predetermined value, A blackening processing furnace, comprising: a signal converter that is provided to a combustion amount control device of an open flame burner and that is provided to the cool air damper when the output is smaller than a predetermined value. 3. The blackening furnace according to claim 2, wherein the tempering furnace is a batch furnace. 4. The tempering furnace is a continuous furnace in which a plurality of heating zones are provided with direct-fire burners, and a cool air supply side of an atmosphere circulation system is connected to each heating zone via a cool air damper. Item 6. A blackening furnace according to Item 2. 5. The blackening furnace according to claim 2, wherein a limiter for maintaining a minimum combustion amount is provided in the combustion amount control device.