JPS5812515B2 - Kokuenrutsubonochiyokusetsutsudenkanetsouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for heating a graphite crucible for melting a sample, which can be used, for example, for quantitatively analyzing nitrogen, oxygen, hydrogen, etc. in steel, by directly applying electricity.

The crucible to which this type of device is applied generally has a simple crucible-shaped structure, and conventionally, in order to heat such a crucible, the crucible is compressed between an upper electrode and a lower electrode. A method is adopted in which the upper electrode and the lower electrode are energized in this state.

However, in such methods, the current density generally tends to concentrate on the cylindrical side wall of the crucible, and there is also a large loss due to heat conduction to the metal electrodes, so heat generation and heating points are concentrated on the side wall, making it particularly difficult to heat the crucible. The disadvantage is that the bottom part, where the sample is located, is insufficiently heated.

In order to solve this problem, a protrusion with a smaller diameter than the bottom surface is provided on the outside of the bottom of the crucible, and current is passed through it, thereby concentrating the current density distribution on the bottom of the crucible and directing the current to the electrodes as described above. Conventionally, methods have been proposed to reduce losses due to heat conduction.

However, with such a configuration, the processing to specially provide the above-mentioned protrusions on the crucible itself is extremely troublesome, and when it comes to using only crucibles provided with such protrusions, conventionally There are disadvantages in that the existing ones cannot be used, and furthermore, in order to obtain an appropriate temperature distribution, crucibles equipped with protrusions of various shapes must be specially prepared.

Accordingly, it is an object of the present invention to provide a novel heating device that eliminates the drawbacks of the prior art as described above.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional elevational view schematically showing one embodiment of the present invention, in which 1 is a graphite bottomed crucible having a cylindrical side wall.

2a and 2b are metal upper and lower electrodes, respectively, and 3 is a power source, which is connected to those electrodes by conductors 4a and 4b.

In this embodiment, a recess as indicated by 5 is formed on the lower surface of the upper electrode 2a, and the recess 5 is engaged with the upper open end of the crucible 1 as shown.

A recess 6 is provided on the upper surface of the lower electrode 2b at approximately the center thereof, and an annular step 7 is provided around the recess 6.

A graphite contact 8 having an appropriate shape such as a columnar shape is removably inserted into the central recess 6 of the lower electrode 2b, and a graphite contact 8 is placed on the contact 8 at an appropriate distance from the upper surface of the lower electrode 2b. The crucible 1 is placed with the crucible 1 separated by the .

Further, a crucible guide ring 9, which can be made of a suitable material such as a metal or a heat-resistant hard non-metal, is arranged in the peripheral annular step 7 of the lower electrode 2b.

This crucible guide ring 9 engages the outer surface near the lower end of the crucible 1 at its upper part, and is positioned so that the contact area between the bottom of the crucible and the contactor 8 is approximately at the center of the bottom of the crucible. It is something that works.

Note that the upper electrode 2a and the lower electrode 2b have their respective recesses 5.
The structure is such that it can be clamped from above and below with the centers of 6 and 6 aligned.

According to the above configuration, the current from the power source 3 is transmitted through the conductor 4a.
, 4b, the crucible 1 through the electrodes 2a, 2b, and the contactor 8.
The crucible 1 is heated by the direct current flowing through the walls of the crucible 1.Next, the mechanism of the heating operation will be explained in detail with reference to FIGS. 2A, B and C.

Now, from the power supply 3 to the conductors 4, a, 4b and the electrode 2a,
Considering the path of the current flowing through the contact 8 and the crucible 1 through 2b, the current flux as shown at 10 in FIG. 2A flows distributed to the bottom and side walls of the crucible 1.

In this case, if the thickness of each part is uniform, the distribution of current density in each part will be as follows.

That is, first, at the bottom of the crucible 1, the current density decreases (inversely proportional to the radius) as it spreads outward from the terminal end of the contact 8, as indicated by 11 in FIG. 2B.

On the other hand, since the bottom of the crucible 1 has a thickness and the contact 8 has a radius, the current density becomes smaller toward the center of the contact point of the contact.

An outline of this is shown in Figure 2C, but since the current passes through areas with low resistance and easy flow, as shown by 12, the current density increases as it moves toward the center of the solid line circle in Figure 2B. becomes smaller.

Further, the current density becomes smaller toward the inner side of the bottom. Next, when comparing the current density of the circular side wall and that of the bottom, the ratio of their respective thicknesses is relevant; the thinner the former is, the greater the current density is relative to that of the latter.

The distribution of heat generation depends on the distribution of current density as described above, and the higher the current density, the greater the heat generation, so in order to increase the heat generation at the bottom, it is sufficient to make the bottom thinner (thicken the side walls). In order to increase the amount of heat generated to the center of the bottom, the diameter of the contact can be made smaller; on the other hand, if the contactor is starting to overheat, the diameter should be made larger.

Next, when considering heat dissipation, there are two types of heat dissipation in the sidewall: loss due to heat conduction to the upper metal electrode and loss due to heat radiation from the sidewall. Because it is thin (although the circumference is long), there is relatively little heat loss, and even if there is a small amount of cooling near the electrode, it does not spread to the bottom of the crucible, and areas where there is no object to be heated are cooled. Therefore, it has no effect on the situation.

The latter, loss due to thermal radiation from the sidewalls, is proportional to the fourth power of the temperature, so the increase in loss will have a major effect on heating as the temperature rises, but this loss can be caused by heat radiation, such as a cylindrical reflector, etc. This can be easily avoided by providing a suitable shield.

Regarding heat dissipation from the bottom of the crucible, when a metal electrode is in direct contact with the bottom of the crucible, there is a large heat conduction loss through the electrode, and the temperature does not rise easily, and the temperature of the electrode itself increases, which can shorten its lifespan. Becomes shorter.

On the other hand, according to the present invention, when the graphite contact 8 is interposed between the bottom of the crucible 1 and the lower electrode 2b, the thermal resistance increases, heat transfer is reduced, and the temperature of the electrode itself increases. Decrease.

At this time, if the diameter of the contactor 8 is made smaller, the heat loss will be reduced and the overall temperature rise will be increased.

Furthermore, increasing the length of the contactor 8 increases the effect, but there is a certain limit due to the reduction in strength for clamping between the electrodes.

As mentioned above, the loss due to heat transfer can be controlled by changing the diameter and length of the contact 8, so by appropriately selecting its shape and dimensions, the relationship between the temperature rise at the bottom of the crucible and that at the side wall can be controlled. It becomes possible to choose appropriately.

FIG. 3 is a diagram similar to FIG. 1 showing another embodiment of the present invention, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In this embodiment, instead of the recess 6 provided in the lower electrode 2b in the embodiment shown in FIG. Contact guide ring 1 made of material
3 is placed on the flat surface of the lower electrode 2b, and a contact 8 is fitted therein as shown.

It will be easily understood that what has been described above regarding the embodiment of FIG. 1 also applies to this embodiment.

As can be understood from the above description, according to the present invention, the shape of the crucible is simple and the processing is easy, so manufacturing costs can be reduced, and moreover, the shape and dimensions of the contactor 8 can be changed. Since the temperature distribution inside the crucible can be changed, it is easy to standardize the crucible itself, and there are advantages such as the ability to easily use a crucible for quantitative analysis by direct energization.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional elevation view showing one embodiment of the present invention;
FIGS. 2A, B, and C are diagrams for explaining the present invention, respectively, and FIG. 3 is a diagram similar to FIG. 1 showing another embodiment of the present invention. 1...graphite crucible, 2a...upper electrode, 2b...lower electrode, 3...power supply, 4
a, 4b... Conductor wire, 5, 6... Concavity, 7... Step part, 8... Graphite contact, 9
...Crucible guide ring, 13...Contact guide ring.

Claims (1)

[Claims] 1. A graphite crucible is clamped between the upper electrode and the lower electrode,
In an apparatus configured to heat the graphite crucible by directly applying electricity to the graphite crucible through both the electrodes,
A direct current heating device for a graphite crucible, characterized in that a graphite contact is disposed in contact between the bottom of the crucible and the upper surface of the lower electrode. 2. The device according to claim 1, wherein a recess is provided on the upper surface of the lower electrode, and the contact is fitted into the recess. 3. The device according to claim 1, characterized in that a contact guide ring is disposed on the upper surface of the lower electrode, and the contact is fitted into the guide ring. 4. A crucible guide ring is disposed on the upper surface of the lower electrode at a position surrounding the contact, and the upper end of the guide ring is engaged near the bottom of the crucible. Apparatus according to claim 1.