JPS6130619A - Quick cooling method - Google Patents

Abstract

PURPOSE:To prevent film boiling to increase cooling rate and to perform through quenching, by cooling rapidly a high temp. material in which the part desired to be cooled rapidly is precoated with material having small thermal conductivity, from high temp. with coolant liquid. CONSTITUTION:The part of a metal (e.g. carbon steel) 01 desired to be quenched is coated with a coating material 04, to which ceramic adhesive having small thermal conductivity, ceramic spraying, etc. are used. Next, by dipping the high temp. metal 01 coated with the material 04 into the coolant 02 such as water, the liquid 02 evaporates at surface of the material 04, and vapor bubbles 05 are generated. In this case, since film is not formed, but bubbles are formed from vapor, and nuclear boiling state is formed, cooling rate of the metal 01 is increased. By adjusting quality, thickness of the material 04, cooling rate can be controlled arbitrarily.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for rapidly cooling high temperature materials, and more particularly to a method for quenching metals. More specifically, the present invention relates to a quenching method that enables sufficient quenching f'L with a controlled cooling rate, and also allows partial quenching or the degree of quenching to be controlled.

Conventional technology Quenching of metals has conventionally been carried out by soaking high-temperature metals in a refrigerant liquid such as water and rapidly cooling the metals.

At this time, the state of the metal surface is as shown in Figure 2, flc4.
Quenched metal 01t - When immersed in refrigerant liquid 02, water boils due to the high metal temperature, and the metal surface is covered with a vapor film 03. This vapor film 03 significantly impedes the transfer of heat, and therefore the quenching process deteriorates.

Figure 5 shows the boiling curve. In the figure, point A is a state where the metal surface temperature is high, it is in a state of film boiling, the heat flux is low, and the cooling rate of the metal is slow. As cooling progresses and the temperature reaches point B, the heat transfer coefficient suddenly increases and the metal is rapidly cooled.

According to this relationship between temperature and heat flux, metals are
It becomes cold due to temperature changes as shown in the figure.

In the conventional hardening method, the temperature change between point A and point B in Figure 6 is small and the cooling rate is limited, so sufficient hardening may not be possible, and in the case of large metals, the center part There was an inconvenience that quenching was not possible.

Problems to be Solved by the Invention It is an object of the present invention to provide a hardening method which eliminates the above-mentioned drawbacks of the conventional hardening methods and enables sufficient hardening.

Means for Solving All Problems The present invention is characterized in that, in a method of rapidly cooling a high-temperature material from a high temperature to a refrigerant liquid, a portion of the material to be rapidly cooled is thinly coated in advance with a substance having low thermal conductivity. This paper relates to a method for rapidly cooling high-temperature materials.

In other words, in the method of the present invention, by coating the part of the metal to be hardened with a thin layer of material that does not conduct heat well to the surface, film boiling can be prevented from occurring, and the hardening process can be prevented even in the early stages of hardening. This produces a state of nucleate boiling, increases the cooling rate, and enables optical hardening. Furthermore, by selecting the material and thickness of the coating material, it is possible to control the degree of partial hardening or hardening.

Here, nucleate boiling and film boiling mean the following.

When there is a heated surface in a refrigerant liquid (for example, water), if the surface is higher than the boiling point of the refrigerant liquid, the refrigerant liquid locally evaporates,
A boil occurs. The difference between the boiling point and the surface temperature is called the degree of heating. When the degree of heating is small, the steam takes the form of small bubbles and has a good heat transfer coefficient, so it transfers heat, but as the degree of heating increases, the steam It forms a film that covers the surface, significantly reducing heat transfer. The former is called upper nucleate boiling, and the latter is called film boiling.

action The method of the present invention will be explained below based on the drawings.

As shown in Figure 1, hardened n metal (eg.

Coating material 04 on the part of carbon steel) 01 that you want to harden.
’ to coat. As coating material 04,
Ceramic adhesives, ceramic spraying, etc. with low thermal conductivity are not used. If you soak this in refrigerant liquid 02 such as water,
The refrigerant liquid port 2 evaporates on the surface of the coating material 04, and vapor bubbles 05 are generated. In this case, the vapor does not form a film but becomes bubbles and enters a nucleate boiling state, so the cooling rate of the metal increases. This effect will be explained with reference to FIG. In FIG. 2, curve 101 is the boiling curve without coating.

Straight line 102 also shows the thermal resistance of the coating. The curve 103 is a combination of the curve 101 and the straight line 102.
So, this is the boiling curve of the coated metal surface. Since the area from point 7 to point G on curve 103 is the film boiling region, 1
When the surface temperature is below Ta, nucleate boiling occurs. Therefore, in the case of coating, nucleate boiling occurs only in the region of temperature lower than point B, so coating greatly expands the temperature range of nucleate boiling. - When the surface temperature is Tb and there is no coating.

-Since it is boiling, the heat flux is qO, but if a coating is applied, the heat flux increases to qb at the same temperature [7
, the cooling rate increases. The critical temperature 'f'aij must be higher than the quenching temperature, but coating material o4
By adjusting the material and thickness of the straight line 102, the %Ta involved can be changed.

The temperature change on the metal surface is as shown in Figure 3.
In the case of no coating, the cooling rate is as shown in curve 104, whereas in the case of coating, #'s,
It is improved as shown in curve 105.

Effects of the invention (1) When cooling a high-temperature metal material with boiling by using a refrigerant liquid, film boiling can be prevented by coating the metal material with a substance with low thermal conductivity in advance. , the cooling rate can be increased.

(2) By adjusting the material and thickness of the first coating material, the cooling rate can be controlled as desired.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the quenching method according to the present invention, and FIG.
The figure shows the relationship between the metal surface temperature and heat flux when all the methods of the present invention are applied, and FIG. 5 shows the change in the metal surface temperature over time. Figure 4 is an explanatory diagram of the conventional hardening method, Figure 5 is the relationship between the metal surface temperature and heat flux when the conventional method is applied, and Figure 6 is the relationship between the metal surface temperature and the time change. FIG. ＠Shishioka Akiyoshi [Shizu H Shisuke Bowl Figure Fitting Mo 壓 Cooking

Claims (1)

[Claims] A method of rapidly cooling a high-temperature material using a refrigerant liquid, the method comprising: pre-coating a portion of the material to be rapidly cooled thinly with a substance having low thermal conductivity.