JPS6313781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lost wax casting method in which hot isostatic pressing is performed during the casting process using a ceramic shell mold.

Hot isostatic casting is a process in which a cast product is held at high temperature and pressure for a specified period of time, and then cooled while reducing the pressure.
Press (hot isostatic pressing process, usually abbreviated as HIP) is known. By applying this HIP treatment, it is possible to eliminate cavities in the casting and improve mechanical properties.

On the other hand, the applicant claims that in lost wax casting,
Immediately after pouring, the entire mold is forcibly cooled from the outside to solidify the hot water in the mold into a shell shape from the parts that come into contact with the mold, removing defects such as cavities and surface sinking from the surface of the cast product. It has already been proposed to improve the physical properties (Patent Application No. 58-029561). When applying the HIP treatment to this casting method, there was a problem of poor work efficiency because the conventional HIP treatment was performed completely independently of the casting process. In other words, HIP processing requires heating/pressurization and depressurization/cooling for several hours each, so when using conventional methods, the cast product must be cooled and demolded and then heated again in HIP processing.
This is because HIP processing requires a long time.

Furthermore, in conventional HIP treatment, the maximum pressure (2000Kg/cm ²
HIP equipment was complicated and expensive, which was a major obstacle to the widespread use of HIP processing in casting.

The present invention was made in view of these circumstances, and it combines the already proposed casting method of rapidly cooling a mold.
By appropriately combining HIP processing and organically combining both processes, HIP
The purpose of the present invention is to provide a casting method that shortens processing time and saves energy, and also lowers the maximum pressure to simplify and lower the cost of HIP equipment.

In order to achieve this objective, the present invention starts the HIP process before the hot water in the mold completely solidifies. In other words, a mold into which molten metal has been poured is forcibly cooled from the outside to solidify the molten metal in the model part of the mold into a shell shape from the contact part of the inner surface of the mold, and when at least the center of the model part is in a molten state, the entire part is heated. The material is solidified under pressure, and then cooled while reducing the pressure. The present invention will be explained in detail below based on the illustrated embodiments.

FIG. 1 is a process diagram of an embodiment of the present invention, FIG. 2 is a sectional view of a mold, and FIG. 3 is a partially enlarged view thereof.

A number of wax models are brazed to wax or wax coated sprue rods to create a wax tree (not shown). The tree is dipped in slurry and then coated with a sprinkle of stucco granules. This coating is repeated several times to obtain a predetermined thickness of the tree. After the tree is dried, the internal wax is eluted in a dewaxing process, and a shell-shaped mold 10 is created.

A plurality of molds 10 are placed on a pallet 12,
It is sent to a firing step 14. Here, the mold 10 is heated in the firing furnace 16 to completely burn out the wax remaining in the mold 10 and to provide the mold 10 with sufficient strength.

The mold 10 leaving the furnace 16 is sent to a casting process 18 while still at a high temperature, and molten metal 20 is poured into the mold 10.

Immediately after pouring, the mold 10 is sent to a cooling device 22, where it is rapidly cooled forcibly from the outside. The cooling device 22 cools the mold 10 using water, low temperature air, etc. sprayed from a nozzle.

Since the mold 10 is rapidly cooled from the outside, the entire portion where the hot water contacts the inner surface of the mold first solidifies into a shell or skin shape, as shown by a in FIG. 3. Hot water path 10A,
Since the constricted part 10B has a large mold thickness and is in contact with the sprue rod part 10C containing a large amount of hot water, the temperature decreases slowly. In particular, the constricted portion 10B becomes overheated and is therefore more difficult to cool down. Therefore, solidification progresses sequentially toward the inside (center) as shown in a, b, c, and d.
It becomes a unidirectionally coagulated tissue.

The mold 10 solidified into a shell shape in the cooling device 22 is transferred to a case 26 having a large number of holes by an industrial robot 24 or the like before the inside (center portion) is solidified.

30 is a HIP device, which has a high pressure container 32. The mold 10 is placed in case 2 with the inside melted.
6 and are transferred into a high-pressure container 32 and sealed.
Air inside the container 32 is removed by a vacuum pump 34, and then an inert gas such as argon gas compressed by a compression pump 36 is supplied into the container 32. 38 is a cylinder for storing this gas, and a valve 40 is opened to return the gas inside to the cylinder 38 when the pressure inside the container 32 is reduced. Note that an auxiliary heater 42 is provided in the container 32 as necessary. It is desirable that the container 32 also be provided with a cooling water circulation path.

Since the hot water inside the mold 10 is molten, there is almost no need to use the auxiliary heater 42 inside the high-pressure container 32. Due to the pressurization in the high-pressure container 32, the fluidized molten metal is pushed into the model part 10D through the sprue rod part 10C and the sprue 10A, and the feeder effect becomes remarkable. Also, the internal pressure of the container 32 is very high (for example, 140Kg/cm ² ).
As a result, no cavities are generated during solidification, and defects such as pinholes do not appear on the surface of the product. Therefore, the quality of the product is improved. The mold 10 is held at maximum pressure and temperature for a predetermined period of time (approximately 1 hour), and then is depressurized and cooled over several hours.

The mold 10 subjected to the HIP treatment in this manner is sent to a cutting step 50. Reference numeral 52 denotes a vibration device in which the cast mold 10 is vibrated in two stages. 1st
The mold 10 is destroyed by the next vibration, and a tree-shaped casting appears, and the second vibration produces a large number of products 54.
The pipe breaks at the small diameter runner and falls off.

This product 54 is further machined in a machining process 56 and subjected to a product inspection in an inspection process 58 before being shipped.

Of course, HIP processing conditions such as the maximum pressure and temperature inside the high-pressure vessel 32, its holding time, depressurization and cooling rate, etc. will vary depending on the type of metal to be cast, the mechanical properties required of the product, etc. When casting carbon cast iron, it is desirable to set the maximum pressure to about 140 kg/cm ² and the maximum temperature to about 1100°C. Furthermore, since the mold 10 placed in the high-pressure container 32 has a sufficiently high temperature, heating is not necessary in many cases, but it may be heated by an auxiliary heater 42 in some cases.

As described above, the present invention forcibly rapidly cools the mold from the outside immediately after pouring, and HIPs the mold before it solidifies inside.
I started the process of processing. Therefore, the heating time for HIP processing is shortened, and the efficiency of HIP processing is improved. It is also suitable for energy saving. Furthermore, since the mold is pressurized before it solidifies, the feeder effect becomes more pronounced, and a sufficient HIP treatment effect can be obtained even at a relatively low maximum pressure. Therefore, by lowering the pressure resistance of the high-pressure container and the rating of the pressurizing pump, it is possible to simplify the HIP equipment and significantly reduce its cost, which will greatly contribute to the spread of HIP processing in casting.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of an embodiment of the present invention, FIG. 2 is a sectional view of a mold, and FIG. 3 is a partially enlarged view thereof. 10...Mold, 22...Cooling device, 30...HIP device.

Claims (1)

[Claims] 1 In the lost wax casting method using a ceramic shell mold, the mold into which molten metal is poured is forcibly quenched from the outside, and the hot water in the model part of the mold is solidified into a shell shape from the inner surface contact part of the mold, and at least the center of the model part is solidified. A lost wax casting method characterized by applying pressure to solidify the entire part while it is in a molten state, and then cooling it while reducing the pressure.