JPS5831368B2 - Daikei Kinzoku Kannonetsushiyorihohou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for heat treating large-diameter metal pipes, particularly large-diameter steel pipes with a diameter of 18 to 60 inches. The present invention relates to a heat treatment method for large diameter metal tubes, which aims to reduce heat loss and equalize temperature during the heating stage by installing the device on the inner wall of the tube.

When continuously quenching and tempering long, large-diameter metal tubes, or when allowing them to cool to room temperature after heating, heating methods include heating from the outside of the tube by fuel combustion or induction heating by electric induction. During quenching, it is quenched and cooled immediately after heating, and during tempering, it is heated to 500℃~A
It is common to hold the temperature within the C1 transformation point temperature range for a specified period of time. In either case, the large diameter metal tube is subjected to these heat treatments. In this case, if the entire tube is heated at high temperature for a long period of time, the weight of the tube will cause damage. To avoid deformation, these heaters are generally used to heat parts that are extremely short relative to the total length of the metal tube to be heat treated, and the metal tube is fed into the heater at a constant speed to heat treat the entire length of the tube. is taken.

In other words, the heating is done quickly so that there is no time for deformation, and the deformation of the tube inside the heater is restrained by the rigidity of the parts that are colder than the heated part, which exist before and after the relatively short part to be heated. It is something.

However, new problems arise when such heat treatment methods are used.

In other words, in this case, the heated part is limited to a very short part compared to the whole pipe, and the other parts are relatively slippery, so the heat received by the heated part is due to radiation, convection, conduction, etc. It will be stolen more and more.

Therefore, the amount of heat required to heat these parts must be considerably greater than the amount of heat required to heat them to a predetermined heating temperature.

At present, a particularly large proportion of heat is released from the inner surface of the tube.

In induction heating, a heat insulating material is placed between the heating coil and the tube to prevent the heating coil from being damaged by the heat from the tube. Although it can be said that consideration has been given to this, no measures have been taken to deal with heat release from the inner wall of the pipe.

Also, when it comes to heating large-diameter metal pipes like this, since the heating is only done from the outside of the pipe, there is a tendency for temperature differences to occur in the direction of the pipe wall thickness. However, such large heat loss from the inner wall of the tube further aggravates the temperature difference in the thickness direction of the tube, making the situation even worse.

It is no exaggeration to say that large-diameter metal tubes have the perfect conditions for heat to be released through radiation and convection due to the large hollow part of 7S. When cooling is also performed from the inner wall of the tube, cooling water is injected onto the inner surface of the tube near the portion to be heated, so the heat loss from the inner wall of the tube becomes enormous.

The present invention provides a method for heat-treating large-diameter metal tubes to solve the above-mentioned problems, and includes heat-treating large-diameter metal tubes while continuously feeding the metal tubes into one or more heaters. When doing so, a cooling pipe that is cooled by water cooling or the like is provided so as to be located approximately at the axial center of the metal pipe that passes through the heater, and the inner wall of the metal pipe that passes through the cooling pipe is placed inside the heater and at predetermined positions before and after the heater. By installing a cylindrical heat insulating member with an appropriate outer diameter so that the metal pipes do not come in contact with each other, the inner wall of the metal pipe that is being heated by the heater is covered with the heat insulating member, and as a result, heat radiation from the inner wall of the pipe is reduced. It is characterized by preventing

Hereinafter, the present invention will be explained in detail with reference to the drawings. In FIG. 1, 1 and 1' are one or more heaters,
These may be induction heating by an induction coil, heating by fuel combustion, or a combination of these.

Reference numeral 2 denotes a cooling pipe provided through the large-diameter metal passing through the heaters 1 and 1' so as to be located approximately at the axial center;
As shown in the figure, the inside of the pipe is divided into two chambers in the longitudinal direction, and the cooling water sent from one is discharged from the other.
Consideration must be given to cooling the device itself and preventing it from becoming misaligned such as drooping due to the influence of heat indirectly received from a heater or the like.

Reference numeral 2' denotes a supporting member attached to a key point corresponding to the heated portion of the cooling pipe 2, and is provided to cover and support the inner wall of the metal pipe passing through the heat insulating member 3, which will be described next. , this supporting member 2' needs to be supported in close proximity to the inner wall of the pipe that the supporting member 3 is passing through so that it does not come into contact with the inner wall of the pipe that it is passing through. Sometimes a pair is added.

The installation position of the heat insulating member 3 is the heater 1, 1',
It is preferable that the length be slightly longer than the respective lengths of the heaters 1 and 1', since heat radiation from the metal tube can be further reduced.

Further, when heating is performed using two or more heaters as shown in FIG. 1, it is more effective to add a heat insulating member to the intermediate location.

The gap between the heat insulating member 3 and the inner wall of the pipe passing through is 10 to 30
If the gap is less than 10 mm, there is a risk of contact with the heat insulating member because the metal tube has a slight bend, and if the gap is more than 301 rL7rL, the effect of installing the heat insulating member will not be fully exhibited. .

Further, it is preferable that the heat insulating material constituting the heat insulating member 3 has a low specific heat and a low thermal conductivity.

In other words, by placing a material close to the inner wall of the metal tube, the temperature of the heated metal tube will quickly approach the temperature of the metal tube, and once heated, the material will not easily dissipate. It must work to prevent the release of Preferred examples include asbestos and ceramic fibers (such as ``Kaowool'' manufactured by Isolite Pubcock Fireproof Co., Ltd. or ``Ibiwool'' manufactured by Ibigawa Electric Industry Co., Ltd.).Since such heat insulating materials have low strength, they should be at least 2S thick. It is necessary to form the heat insulating member 3 into a cylindrical shape with a diameter larger than that.

Note that 4 in the figure is a metal tube that is passed through the heating furnaces 1 and 1' for heat treatment.

When a large-diameter metal tube 4 is first heat-treated as shown in FIG. 1, the tube immediately reaches a predetermined temperature by the heaters 1 and 1', but the heat insulating member 3, which is placed close to the inner wall of the tube, absorbs the heat of the tube. It will be taken away.

If the thermal conductivity of the material that makes up this insulating member is low, it will rapidly draw heat from the inner wall of the pipe, causing the insulating member to gradually warm up and radiate heat to other parts, causing its surface temperature to increase. The purpose of providing a heat insulating member is lost because the

Furthermore, even after the entire heat insulating member reaches a uniform temperature, if the thermal conductivity is low, it will be easily cooled by the surrounding air, and as a result, the amount of heat input for tube heating will not be reduced. .

For this reason, materials with low thermal conductivity are used as insulation material 3.
It is important to select it as a constituent material.

In a preferred embodiment of the present invention, by providing this heat insulating member, the amount of heat input from the heater in the initial stage of heating until the entire heat insulating member reaches a uniform temperature is equal to the amount of heat input Q when the heat insulating member is not used.

The amount of heat input Q'X after the heat treatment progresses and the temperature of the entire heat insulating member reaches a uniform temperature is reduced by 8 to 10% compared to the amount of heat input Q'o when no heat insulating member is used. However, in order to do so, it is necessary to use materials constituting the heat insulating member that have a thermal conductivity of 0.3 to 1/mh°C or less, that is, the above-mentioned Cera□Tsuku fiber (Isolite, "Kao Wool" manufactured by Pubcock Fireproof Co., Ltd.) or Ibi-wool (manufactured by Ibigawa Electric Industry Co., Ltd.) or asbestos, both with a thickness of 2
It is recommended to use it in a cylindrical shape with a diameter of 5 mm or more.

Figures 3 and 4 show that a large-diameter steel pipe with an outer diameter of 24 inches, a wall thickness of 15.9 mm, and a length of 12 m is manufactured for a length of 300 m by the method of the present invention.
It shows the rate of decrease in the amount of input heat, X 100, at the initial stage of heating (Qo Q 5 minutes from the start of heating) when heating to 970°C while moving at a conveyance speed of 1 min, where Qo is the heating furnace without a heat insulating member. Q is the amount of heat input when heating is performed using the method of the present invention provided with a heat insulating member.

In other words, the rate of decrease in the amount of input heat can be said to be the rate of decrease in heat insulation effect.

Figure 3 shows the distance between the pipe inner wall and the insulation material by 30 mm.
and the thermal conductivity of the material constituting the heat insulating member is 0.
The results are shown when the cal/rrx t n °C is different from 1 to 0.4, and Fig. 4 shows the results when the thermal conductivity is 0.4 as a heat insulating member.
These are the results when using the cal/mh°C one for No. 1 and changing the gap with the inner wall of the tube.

Furthermore, Figure 5 shows the case where a large diameter steel pipe with an outer diameter of 24 inches and a wall thickness of 25.4 mm was heated to 670°C and tempered in a heating furnace without a heat insulating member, and the present invention with a heat insulating member. This figure shows the results of measuring the temperature distribution in the wall thickness direction when heated using the method described above.

As is clear from the graphs shown in Figures 3 to 5, when a large-diameter metal tube is heat-treated by the method of the present invention, the heat loss is less than that of the conventional heat treatment method. Since uniformity can be achieved, it is suitable for industrial use.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing an apparatus used in the method of the present invention, and FIG. 2 is a partially enlarged perspective view of a support member wrapping section. FIG. 3 is a graph showing the relationship between the thermal conductivity of the heat insulating member and the rate of decrease in input heat when the gap between the inner wall of the steel pipe and the heat insulating member is constant in the method of the present invention, and FIG. FIG. 5 is a graph showing the relationship between the gap between the inner wall of the steel pipe and the heat insulating member and the rate of decrease in input heat in practice, and FIG. 5 is a graph showing the relationship between the steel pipe wall thickness and temperature for the method of the present invention and the conventional method. 1.1'... Heater, 2... Cooling pipe,
2'...Supporting member, 3...Insulating member,
4...Large diameter metal tube.

Claims (1)

[Claims] 1 Large-diameter metal tubes are continuously connected to one or more heaters.
During the heat treatment in which the metal tube is fed, heated, and optionally subsequently cooled with water, a cooling tube is provided so as to be located approximately at the axial center of the metal tube passing through the heater, so that the inner wall of the metal tube passing through the cooling tube does not come into contact with the cooling tube. 1. A method for heat treatment of a large diameter metal tube, which comprises attaching a heat insulating member made of a cylindrical heat insulating material having an outer diameter of approximately