JPS5853692B2 - Heat treatment method for centrifugally cast ductile iron pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat treatment method for centrifugally cast ductile cast iron pipes that can save energy, reduce pollution, and improve productivity.

Conventionally, when annealing centrifugally cast ductile cast iron pipes, the cast iron pipes are removed from the metal frame after casting, cooled once, and then placed in a continuous horizontal rolling furnace or continuous hanging furnace for heat treatment. was.

However, in this conventional method, since the tube is cooled once after being cast, there is a waste of fuel during the heat treatment in each of the above-mentioned furnaces, and a stand for the cast tube is required before being charged into each of the above-mentioned furnaces, and further heat treatment is required. There were problems in simplifying the heat treatment and saving fuel (energy), such as the long time required.

The method of the present invention provides a heat treatment method that eliminates the drawbacks of the conventional methods, and involves feeding centrifugally cast ductile cast iron pipes to an annealing process in a red-hot state immediately after casting in a metal frame. In the annealing process, a row of metal frames is formed in which the metal frames move sequentially toward the rear row side, and heated gas is blown into one end of the metal frames in the front row, and the gas exiting from the other end is blown into one end of the metal frames in the rear row. The temperature inside each metal frame is continuously lowered from the front row to the rear row of metal frames using the gradually decreasing gas temperature, thereby performing the necessary slow cooling and annealing. It is something.

The method of the present invention will be explained below with reference to the drawings together with the most desirable implementation equipment.

In FIGS. 1 and 2, reference numeral 1 denotes a wheel platform for transporting a ductile cast iron pipe (spheroidal graphite cast iron pipe) 2 from the centrifugal casting equipment to the annealing equipment together with a metal frame 3 to the annealing equipment or outside the annealing equipment. The metal frame 3 rolls on this ring platform 1, and the cast iron pipe 2 inside the metal frame 3 is conveyed to the annealing equipment in a red-hot state at regular intervals.

Reference numeral 4 denotes a pair of left and right mounting tables on which a predetermined number of metal frames 3 are placed in parallel, and has mounting portions 5 at regular intervals according to the predetermined number. A driven trochanter 7 is provided, and the red-hot cast iron tube-containing metal frame 3 is rotated on the trochanter 7 to prevent deformation during annealing.

Between the pair of left and right mounting tables 4 is a traveling trolley 8 for transporting metal frames.
is disposed so as to be able to run on the rails 9, and the trolley 8
Only the upper base plate 11 can be raised and lowered by a pantograph mechanism 12 disposed between the plywood boards 10 and 110 provided in two upper and lower stages, and the upper base plate 11 is connected to each mounting portion 5 of the aforementioned mounting base 4. and the stop position of the metal frame 3 on the wheel stand 1, respectively.

The metal frame 3 that has been conveyed on the wheel platform 1 raises the upper platform plate 11 of the truck 8, and lifts the upper platform plate 11 of the vehicle 8 to the supporting portion 1 at the right end in the figure.
3, and then a cylinder 14 provided on the fixed side.
When activated, the metal frame 3 is transferred to the mounting section 5 at the right end of the mounting table, and when the upper base plate 11 is lowered, the metal frame 3 is transferred from the supporting section 13 to the mounting section 5.

The above has explained the transfer of the metal frame 3 from the position A to the position B in Figure 2. However, if the metal frame 3 is already placed at each position C and D, the metal frame 3 at each of these positions are sequentially transferred to the lower position at the same time.

Reference numeral 15 denotes a heat insulating trolley which is disposed outside each of the mounting tables 4 and is movable toward and away from both end surfaces of the metal frame 3 on the mounting portion 5 along rails 16;
This heat-insulating cart 15 is equipped with a heat-resistant heat-insulating cover 1 that shields both end surfaces of the metal frame 3 at the approach position of the metal frame 3.
8 as required.

Furthermore, in this embodiment, these heat retaining covers 18 are communicated with the metal frame 3 by a duct 20 so as to form a heating gas passage together with the metal frame 3 when attached to the metal frame 3, and the heating gas is connected to each of the metal frames 3 and 3. An oil burner 19a attached to a heat-resistant insulation cover 18 that shields the end surface of the metal frame 3 on the heating gas inlet side.
It is as obtained by t19bt19c.

Note that normally these oil burners 19a, 19b, 1
Oil burner 19a corresponding to the inner front row metal frame 3 of 9c
A chisel is used, and the temperature drop while the high-temperature gas generated by the oil burner 19a passes through the passages of the metal frame 3 and the duct 20 in sequence brings about the appropriate cooling effect necessary for the cast pipe.

Further, when the temperature of the heated gas decreases to a predetermined value or more, the temperature of the heated gas is adjusted by appropriately using the oil burners 19b+19c.

Reference numeral 21 denotes an extendable portion provided in the middle of each duct 20, which allows the height of the heat insulating cover 18 to be adjusted according to the type of pipe.

22 is an oil supply pipe from the oil supply source 23 to each of the oil burners 19, and 24 is a combustion air supply pipe.

With the above configuration, the metal frame 3 containing the ductile cast iron pipes 2, which is sent over the ring platform 1 at a constant time interval, is sequentially placed on the mounting section 5 of the mounting table 4 via the metal frame transporting carriage 8. The metal frames 3 are placed in parallel, and the heat insulating trolley 15 is brought close to the metal frames 3 to cover both end surfaces of the metal frames 3 with heat-resistant insulation covers 18. At the same time, each metal frame 3 is communicated via the duct 20, and each metal frame is heated by the oil burner 19a. The cast iron pipe 2 in the frame 3 is kept warm and slowly cooled with a predetermined temperature gradient.

Then, at regular intervals, the running trolley 8 for transporting metal frames and the heat-insulating trolley 15 are operated as appropriate to sequentially transfer the metal frames 3 that have come first to the wheel platform 1 on the downstream side, and at the same time put the metal frames 3 that have come later into the annealing process. This makes it possible to heat-treat the centrifugally cast ductile cast iron pipe 2 continuously.

By the way, since the metal frame 3 supplied to the annealing equipment is immediately supplied from the casting equipment with the centrifugally cast ductile cast iron pipe 2 contained therein, the cast iron pipe 2 is cooled without being in a red-hot state. It is clear that fuel, annealing time, etc. can be greatly saved because reheating from a cooled state can be omitted.

Note that the annealing temperature changes depending on the composition of the cast iron pipe, but in any case, the temperature of the cast iron pipe 2 supplied to the annealing process can be substantially arbitrarily selected.

FIG. 3 shows a temperature-time curve during annealing in the example method described above.

In the diagram, B, C, and D are shown in FIG. 2, respectively.
Corresponding to each position, the components of the test cast iron pipe are as shown in the table below, and the standard is 600φX6001? A spheroidal graphite cast iron pipe of X15t was used.

Since the method of the present invention is intended to perform heat treatment using slow cooling within the entire frame and with a small amount of oil, an extreme slow cooling cycle is difficult.
The Si component range that promotes ferrite formation is 2.0 to 3.
It is desirable to set it to 0%.

This is because if the content exceeds 3.0%, the material becomes brittle, so the purpose is to create a ferrite base structure that does not cause such a problem.

The composition of this test cast iron pipe after annealing was 90% spheroidization.
, 85% ferrite, 15% pearlite, and 0% cementite.

In addition, in this embodiment method, since the centrifugally cast ductile cast iron pipe is slowly cooled to the Ar1 transformation point by additional heating with an oil burner during the cooling process, austenite is only decomposed into ferrite and graphite. Since cementite generated during casting does not decompose, it is preferable that the casting state be cementite-free.

Of course, it is possible to decompose the cementite by heating it to about 950°C with a large capacity oil burner, but in this case, the temperature of the metal frame itself will also be raised by nearly 600°C, which is undesirable as it will easily become warped.

In addition, during the cooling process, the inner surface of the casting tube may be coated with a heat insulating material such as diatomaceous earth powder to assist in retaining heat, or instead of a burner, various high-temperature waste gases from the factory (cupola exhaust gas, heat exchanger exhaust gas, etc.) may be used. It is a practical means to use it.

As is clear from the above description, according to the method of the present invention, heating gas is blown into one end of the metal frame in the front row, and gas emitted from the other end is blown into one end of the metal frame in the rear row, so that the heating gas is directed from the front row to the rear row. By continuously lowering the temperature within each metal frame, fuel can be saved, and by sequentially moving the metal frame rows to the rear row side, annealing can be performed continuously and productivity can be improved.

[Brief explanation of the drawing]

Figure 1 is a plan view of the equipment implementing the present invention, and Figure 2 is A of Figure 1.
- A cross-sectional view taken in the direction of the arrow, FIG. 3 is a temperature one-hour curve of the test cast iron pipe. 2... Ductile cast iron pipe after centrifugal casting, 3.
...Gold frame, 4...Placement stand, 8...
- Traveling trolley for transporting the metal frame, 18...Heat-resistant insulation cover, 19 a t 19 b j19c... Oil burner, 20... Duct.

Claims (1)

[Scope of Claims] 1. A ductile cast iron pipe that has been centrifugally cast is supplied to an annealing process in a red-hot state immediately after casting, and the annealing process includes a row of metal frames in which the metal frames are sequentially moved toward the rear row side. The temperature inside each metal frame is controlled from the front row of metal frames to the rear row by blowing heated gas into one end of the metal frame in the front row and blowing the gas coming out from the other end into one end of the metal frame in the rear row. A method for heat treating a centrifugally cast ductile cast iron pipe, characterized in that annealing is carried out by performing necessary slow cooling by continuously lowering the gas temperature using gradually decreasing gas temperature. 2. The method according to claim 1, wherein a burner is attached to a heat insulating cover that covers at least one end of the metal frame in the front row, and the heated gas is obtained by the burner. 3. The method according to claim 1, characterized in that various high-temperature waste gases are used as the heating gas. 4. The method according to any one of claims 1 to 3, characterized in that heat-resistant powder is sprinkled on the surface of the casting tube within the metal frame.