JP2785300B2 - Plasma carburizing furnace - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma carburizing furnace in which a surface of a workpiece is subjected to a carburizing treatment using plasma.

[Conventional technology]

In this type of furnace, the above-described carburizing process is performed in a state where the object to be processed is heated by an electric heater provided in the furnace. If carbon not ionized in the furnace gradually adheres to the insulating support of the heater in the furnace while such a carburizing process is repeatedly performed, the degree of insulation is reduced and a part of the current supplied to the heater is reduced. Flows in a different path from the heater.

[Problems to be solved by the invention]

In the above state, even if a sufficient amount of electric power is supplied to the heater to properly generate heat, the heater cannot receive the entire amount of heat, and the amount of heat generated is insufficient. If the temperature does not reach the predetermined temperature, proper carburization is not performed, and there is a problem that a defective product is produced. Therefore, in order to prevent such a problem from occurring, the insulating support is periodically replaced. However, in this method, there is a problem that uneconomical operation occurs in that the insulation support is replaced even if the insulation degree of the insulation support is not so reduced.

The present invention has been made in view of the above points, and an object of the present invention is to, when a predetermined amount of sufficient power is supplied to a heater, the heater receives substantially the entire amount of the power and properly receives the power. Provided is a plasma carburizing furnace that generates heat and can determine whether or not proper carburizing treatment can be performed, and furthermore, it is possible to use the insulating support of the heater to its use limit. That is.

[Means for solving the problem]

In order to achieve the above object, the present invention employs the means described in the claims, and the operation is as follows.

[Action]

In the furnace, the object to be processed is heated by the heater.
Then, the surface is carburized by the plasma-forming carburizing gas.

During the carburizing process, the non-ionized carbon adheres to the insulating support of the heater. The degree of the adhesion can be known by detecting the resistance value of the heater by the resistance value detecting means.

〔Example〕

Hereinafter, drawings showing an embodiment of the present application will be described. First
In the figure, reference numeral 1 denotes a furnace body which is formed hollow and has a space 3 in which an object 2 is to be placed, and a support for allowing the object 2 to be located in the space 3. 4 For example, a hearth or a holding frame is provided. The furnace body 1 is provided with plasma forming means for converting the carburizing gas inside the furnace body into plasma. The plasma generating means includes an anode (furnace body 1 in this example), a cathode (object 2 in this example), and a power supply 5 for plasma generation. A DC power source is used as the power source 5 for plasma generation, and the
The negative sides are connected to the support 4 respectively. 6
Is a heater for heating an object to be processed, is supported by a plurality of electric insulating supports in the furnace, and is connected to a heater power supply 7 outside the furnace. Reference numeral 8 denotes a carburizing gas supply device. The supporting structure of the furnace 1 and the heater 6 is shown in FIG. The furnace body 1 includes a furnace shell 10 and a heat insulating material 11 provided inside the furnace shell 10, for example, graphite. The heat insulating material 11 is attached to a support frame 12 attached to the furnace shell 10. Further, the heater 6 includes a support piece 13 attached to the support frame 12.
Is attached via an insulator 14 exemplified as an insulating support.

Next, FIG. 3 shows an electrical connection relationship between the heater 6 and the power supply 7. The heater 6 has a delta connection as an example, but may have a star connection. Reference numeral 15 denotes a resistance detecting means connected to an electric path connecting the heater 6 and the power supply 7 outside the furnace. In this example, the detecting means 15 includes current detecting means 16a, 16a for detecting a current value supplied to the heater 6.
b, 16c and voltage detecting means 17a, 17b, 17c for detecting a voltage value applied to the heater 6.

Carburizing of the object to be processed by the plasma carburizing furnace having the above-described configuration is performed as follows. First, the object 2 is placed on the support 4. Next, the inside of the furnace body 1 is evacuated by a known vacuuming device connected to the furnace body 1, and a carburizing gas such as methane and propane is supplied from the gas supply device 8 to the storage space 3. On the other hand, power is supplied from the heater power supply 7 to the heater 6, and the heat generated by the heater 6 heats the object to be processed. And applied between the object 2 to be processed.

By the above operation, a discharge is generated between the furnace body 1 as the anode and the workpiece 2 as the cathode, as is well known, and the discharge decomposes the carburizing gas into plasma. The heater 6 is used as the anode,
A susceptor separately provided in the furnace may be used. The carbon ions in the gas decomposed as described above are implanted or adsorbed on the surface of the object 2 and the object 2
Is carried out.

When the carburizing treatment is performed as described above, the carbon that has not been ionized by the above-described decomposition due to the electric discharge or the heating is converted into the heat insulating material 11, the heater 6, and the support piece 1 as indicated by reference numeral 18 in FIG.
3. It adheres to the surface of the insulator 14. When the amount of adhesion increases, the insulating function of the insulator 14 decreases, and a part of the current supplied from the power source 7 to the heater 6 reduces the carbon 18 on the surface of the insulator 14 from the heater 6 as indicated by an arrow 19. It flows to the heat insulating material 11 through the layer and the support piece 13, and further flows through the other support piece 13 and the layer of carbon 18 on the surface of the insulator 14 to return to the heater 6 (third part).
(See reference numeral 20 in the figure). This is heater 6
Cannot receive the full amount of current supplied to itself, resulting in insufficient heat generation. Therefore, it is necessary to know the state of the adhesion of the carbon, in other words, to know the decrease in the insulation degree of the insulator 14 due to the adhesion.

Next, the detection will be described. The resistance value of the heater 6 as viewed from the inlet / outlet of electricity to the heater 6, that is, the electric path outside the furnace connected to the heater 6, is measured by the resistance value detecting means 15. That is, for example, during operation of the furnace,
The current detection values I1, I2, I3 based on a, 16b, 16c and the voltage detection values V1, V2, V3 obtained by the voltage detecting means 17a, 17b, 17c are obtained.
Then, using them, calculations such as V1 / I1, V2 / I2, and V3 / I3 are performed, and the resistance value of the heater 6 as seen from the entrance of electricity to the heater 6 is known. The resistance value of the heater 6 is compared with the resistance value of the heater 6 itself, which is known in advance, and the state of carbon deposition on the insulator 14 is known by observing how much the former is lower than the latter. Needless to say, the measurement of the resistance value may be performed by supplying power from the power supply 7 only for measurement when the furnace is not operating.

The state of carbon deposition that was learned as described above
If the degree of insulation of the heater 6 becomes lower than the allowable range, the decrease in the amount of heat generated by the heater 6 due to the above-described current bypass exceeds the allowable limit. Therefore, if the measured resistance value falls to a predetermined allowable limit, for example, about 90% (most preferably about 95%) with respect to the resistance value of the heater 6, the replacement of the insulator 14 and other measures are taken. Take.

Next, FIG. 4 showing the automatic insulation deterioration notification system as described above will be described. In the figure, reference numeral 21 denotes a resistance value calculating means, 22 denotes a discriminating means, and is constituted by an allowable limit setting means 23 and a comparing means 24. For example, a computer is used as these. Reference numeral 25 denotes a notifying means, for example, a lamp, a buzzer or the like. In such a configuration, the calculating means 21 calculates the resistance value based on the detection values from the detecting means 16a to 16c and 17a to 17c. Then, the comparing means 24 issues a notification command when the calculated resistance value falls below the allowable limit of the resistance value set in the setting means 23 (for example, 90%), and based on the command, the notification means 25 performs a notification operation. Perform

Next, FIG. 5 shows an example in which a tester 27 is used as a resistance value detecting means.
It is connected to an electric circuit connecting the heater 6e and the power supply 7e via 28b.

In this configuration, when the furnace is not operating, the changeover switches 28a and 28b are switched to the state shown by the broken lines to measure the resistance value.

In addition, functionally considered to be the same or equivalent to those in the previous figure, the same reference numerals as those in the previous figure denote the same parts as in the previous figure.
And repeated description is omitted.

〔The invention's effect〕

As described above, according to the present invention, when the surface treatment of the object 2 is desired, the object 2 heated by the heater 6 is processed.
It has the feature that it can be carburized by a carburizing gas whose surface has been turned into plasma.

Moreover, after the above-described carburizing treatment is performed with time, the resistance value of the heater 6 as seen from the entrance and exit of electricity to the heater 6 is known by the resistance value detecting means 15.
There is a feature that the state of the adhesion of carbon to the insulating support 14 of the heater 6 in the furnace can be known.

First, when a predetermined amount of sufficient power is supplied to the heater 6, the heater 6 receives substantially the entire amount and appropriately generates heat, thereby appropriately carburizing the workpiece 2. There is an advantage that it is possible to judge whether or not the insulating support 14 can be used. Secondly, the insulating support 14 can be used up to its use limit, and can be replaced with a usable one as in the prior art. That is, there is utility that can prevent such uneconomics.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a schematic longitudinal sectional view of a plasma carburizing furnace, FIG. 2 is a partially enlarged longitudinal sectional view showing a supporting structure of a furnace body and a heater, and FIG. FIG. 4 is a block diagram showing an automatic notification system for insulation deterioration, and FIG. 5 is an electrical connection circuit diagram showing another embodiment of a resistance value detecting means. DESCRIPTION OF SYMBOLS 1 ... Furnace body, 2 ... Workpiece, 6 ... Heater, 7 ... Power supply for heater, 14 ... Insulating support, 15 ... Resistance detecting means.

Claims (2)

(57) [Claims] A furnace body having a space in which an object to be treated is placed therein is provided with a plasma generating means for converting the carburizing gas in the space into plasma, and a plurality of insulating supports are provided in the furnace body. An electric circuit connecting the heater to a heater power supply in a plasma carburizing furnace provided with a heater for heating the object to be processed, the heater being supplied with power from a heater power supply outside the furnace. And a resistance value detecting means for detecting the resistance value of the heater. 2. A discriminating means for discriminating whether a resistance value detected by a resistance value detecting means is within a preset value range, and a notifying operation when a discrimination result by the discriminating means is out of the range. 2. The plasma carburizing furnace according to claim 1, further comprising a notification unit for performing the following.