MXPA01004389A - Method and device for chill moulding - Google Patents

Abstract

A device for casting cast iron including a metal chill mould (100) having outer walls (206, 208, 210) and inner walls (212, 213, 220). The inner walls are in contact with a mould (300). The device further includes pressurising means (400) for applying a variable pressure on the outer walls (206, 208, 210) of the chill mould, in order to control changes in volume of molten material enclosed by the chill mould, and chill mould cooling means (500) for variable cooling of the inner walls (212, 213, 220) of said chill mould. A method using said device for carrying out the invention is also disclosed.

Description

METHOD AND DEVICE FOR COOLING A MOLDED PART TECHNICAL FIELD The present invention relates to a method and a device for cooling a molded part of cast iron.

PREVIOUS TECHNIQUE It is shown in the patent SE-C-506508 a method and device for the manufacture of cast iron pieces,. by molding in a stationary metal mold, which is lined with a layer of hardened molding material or with untreated sand, which is included in the description as a reference. A tubular metal mold is used, by which a tubular space, open upwards, in the mold is lined using an insulating material. Molten molten iron is filled from above, such that the cooling effect of the mold and liner provides a directional perspective of solidification from the lower end of the liner and upward to a volume of the feeder at the top until the iron solidify. The method and device described give excellent results for the molded parts of uniform thickness and relatively thin walls, such as the cylinder liners, but are less suitable for the molding of parts with variable cross section and more complex geometry, where the cooling rate It will vary too much between the different molding parts. Demands for mechanical properties combined with good ductility mean that the alloyed materials, which are traditionally used to improve the mechanical properties, can not be used, because the work capacity will be reduced by the high content of carbide and because the molding reaches be difficult because of its tendency to shrink.

DESCRIPTION OF THE INVENTION Therefore, a general purpose of the invention is to provide a method and a device for cooling molded parts of cast iron parts of variable area in cross section and of relatively complex geometry, where the mechanical properties of the molten material do not they are controlled and limited by alloy materials aggregated alone. A further purpose of the fusion method, according to the invention, is to provide increased possibilities for influencing the cooling rate of the molded part, primarily through the pearlite transformation temperature range, which makes it possible to improve the properties mechanical even more. An increased cooling regime will also increase productivity, that is, a greater number of melted parts per unit of time and production unit. A further purpose of the invention is to comply with high environmental requirements, such as low pollutant emissions, reduced energy use, a clean working environment, reduced use of molding material or sand, calculated per unit of weight for the castings, with a corresponding reduced need to deposit the molding material or the sand and a significantly improved recovery of the added energy. According to the present invention, these purposes are achieved by a device for cast iron casting, this device includes a cold mold having external walls and internal walls, in which the internal walls are in contact with a mold, characterized in that said device also it includes pressurizing means for applying a variable pressure against the external walls of said mold, as well as a cold mold cooling element for variable cooling of the internal walls of said cold metal mold. The wall thickness of the mold is selected so as to achieve the desired heat transfer rate for the required mechanical properties of the molten part. The mold is preferably made of untreated molding material or sand. Also, it is advantageous to include a hydraulic or pneumatic press in the pressure element, to act on the external walls of the cold metal mold. Said cooling element of the cold mold preferably includes a number of cooling circuits arranged in the cold metal mold, a refrigerant container, a heat exchanger and a refrigerant pump, whereby this refrigerant pump circulates a refrigerant through a conduit thereof, which interconnects said refrigerant circuits with the refrigerant container, this heat exchanger and the coolant pump. These purposes are achieved, according to the present invention, by a method for manufacturing cast iron parts, according to the invention, whereby a cold mold of metal, having external walls and internal walls and where the internal walls are in contact with a mold, it is filled with cast molten iron. The method is characterized in that the pressure elements can apply a variable pressure against the external walls of the cold metal mold, and because the cooling element of the cold mold, can vary the cooling of the internal walls of the cold metal mold during cooling of the molded piece. Said mold is preferably made of a hardened molding material or untreated sand. The thickness of the mold walls is selected to achieve the required cooling regime. The method of molding allows to mold materials that have low equivalent of C, as well as materials that have high levels of carbide, that stabilize the materials of the alloy used, to obtain the molded parts, with a resistance of flexión considerably greater, resistance to fatigue and modulus of elasticity, which in all will provide good mechanical properties. By molding materials with a low C equivalent and by adding moderate amounts of alloy materials that stabilize the carbide, a strong material, virtually free of carbides and with good machinability, can be obtained. The molding method will also provide less dimensional spread for the casting, compared to the conventional molding of untreated sand.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will be described in greater detail in the following, with reference to the appended figure, in which: Figure 1 shows a schematic cross-section of a device for cooling a mold of a molded part of cast iron, according to the invention. MODES FOR CARRYING OUT THE INVENTION Figure 1 shows a device 100 for cooling a molded cast iron casting mold, according to the present invention. The device includes a cold mold 100 of rigid metal with thick walls, with side elements 200, an upper element 205 and a bottom element 207. Each of the side elements 200 has an external wall 210 that faces away from the cavity of the body. mold 150 in which the molten cast iron is to be emptied, and an internal wall 220, which faces the mold 300. The upper element 205 is provided with a corresponding external side and an internal side 212. Similarly, the bottom element 207 it has an outer side 208 and an inner side 213. The thickness of the mold wall 330 is chosen so as to obtain the desired heat transfer rate. The material of the mold, wall thickness, pressure and temperature control the rate of heat transfer, whereby a thin wall will give a faster cooling regime and a thick wall a slow cooling regime. The mold 300 is produced by conventional methods, alternatively, in an air compression core machine, a machine forming the core or by manual manufacture, using a hardened, insulating mold material with a binder, organic or inorganic , known, adequate, or untreated sand. The molding is done using a pattern, which configures the cavity 150 of the mold. The thickness of the mold wall 330 is generated by conventional means, alternatively, in the core box or by the height of the mold block. This mold 300 preferably includes a first mold part 310 and a second mold part 320. The mold parts, 310 and 320, are joined by means of an adhesive or bolt connection, after the core has been assembled, when this core is required. The mold 300 is placed in the cold mold 100, where the side elements 200, the upper element 205 and the bottom element 207 of the cold mold 100 close around the mold 30, pressing on one or more pressure elements 400. The Molten material is emptied into the mold through an inlet port 160, which is connected to the mold cavity 150. This entrance door is made by conventional methods.

In this way, it is possible to apply variable pressure on the side elements 200, the upper element 205 and the bottom element 207 of the cold mold, using the pressure elements 400, arranged in connection with the cold mold. The pressure element 400 preferably includes hydraulic or pneumatic presses, arranged to act on the outer walls, 206, 208 and 210, respectively, of the cold mold. During the solidification of the molten material in the cold mold 100, volume reductions (for example, during austenite formation) and volume increases (for example during the formation of the graphite, will occur during different phase transformations. in the volume they will be larger or smaller, depending on factors such as the ratio in size between the molten material, the mold and the cores, if any, as well as the chemical composition of the basic material, inoculation, treatment of refining, etc. By making it possible to control the pressure applied to the external walls, 206, 208 and 210, respectively, of the cold mold, it is also possible to partially control the force by which the residual molten material is transferred from the areas of increased volume to areas of decreased volume, without exerting forces on the mold or core, or cause porosity and shrinkage.

The device according to the invention is also provided with variable cooling by a cooling element 500 of the cold mold, which acts on the internal walls of the cold mold, 212, 213 and 220, respectively. The cooling element 500 of the cold mold includes several, preferably six, cooling circuits 520, arranged in or on the side elements 200, the upper element 205 and the bottom element 207 of the cold mold. Cooling element 500 of the cold mold preferably includes a coolant container 530, in which a coolant, such as water, a heat exchanger 540 for recovering heat from the coolant, and a coolant pump 550, are stored for circulate this refrigerant through the conduit thereof, to and from the refrigerant circuits 520. The cavity of the mold 150 is cooled by the refrigerant in a cold mold 100, during the whole molding process. The cooling rate is regulated by the heat transfer rate of the mold wall 330, the heat transfer rate of the internal wall 220 of the cold mold, the mold cavity 150 and the temperature of the coolant. The heat transfer is also affected by the pressurization of the pressure element 400. The cooling regime is controlled throughout the cooling process, until the transformation of the pearlite has been completed, to achieve the desired mechanical properties for molding; a high cooling rate will give a high resistance. The cooling rate, through the transformation phase of the perlite, can be increased by opening the cold mold, when the molding temperature is above the transformation temperature of the perlite. The cooling of air, which will then occur, increases the rate of cooling more, giving an even greater resistance. On the other hand, the cooling rate can also be reduced by opening the cold mold, when the molding temperature is in the austenite range. Immediately after opening, the molded part is immersed in and covered by an insulating medium and held in this state until the temperature of the molded part has fallen below the transformation temperature of the pearlite. This method can also be used to reduce the stresses in the molded part, but the molded part must then be kept inside the insulation medium until its temperature is lower than 200 ° C, in the case of cast iron. The opening of the cold mold can take place before or after the transformation phase of the pearlite, depending on the desired properties of the material. The invention is not limited to the embodiments shown in the figure or described above, and may be modified within the scope of the appended claims. For example, it is possible to construct the mold in more than two wall thereof, for example using three or four parts assembled in a single mold unit.

Claims (10)

1. CLAIMS 1. A device for casting cast iron, including a cold mold of metal, having external walls and internal walls, these internal walls are in contact with a mold, characterized in that this device also includes pressure elements, to apply a pressure variable on the external walls of the cold mold, and cooling elements of the cold mold, for the variable cooling of the internal walls of said cold mold.
2. 2. A device according to claim 1, characterized in that the pressure element includes hydraulic or pneumatic presses, arranged to act on the external walls of said cold mold.
3. 3. A device according to claims 1 or 2, characterized in that said cooling element of the cold mold includes several cooling circuits, arranged in the cold mold, a coolant container, a heat exchanger and a coolant pump, whereby this The refrigerant pump circulates this refrigerant through a conduit thereof, which connects said refrigerant circuits to each other and to the refrigerant container, the heat exchanger and said refrigerant pump.
4. 4. A device according to claims 1 to 3, characterized in that the wall of the mold has a thickness selected so as to obtain the desired heat transfer rate, in order to achieve the desired mechanical properties in the molding material.
5. 5. A device according to claims 1 to 4, characterized in that the mold is made of a hardened mold material or untreated sand.
6. 6. A method for obtaining molded pieces of iron, in which a cold metal mold, having external walls and internal walls, and where said internal walls are in contact with a mold, are filled with cast molded iron, characterized in that the pressure elements they act with a variable pressure on the external walls of said cooled metal mold, and because the cooling elements of the cold mold variably cool the internal walls of the cold mold, during the cooling of the molded part.
7. 7. A method, according to claim 6, characterized in that the pressure element includes hydraulic or pneumatic presses, arranged to act on the external walls of said cold mold.
8. 8. A method, according to claims 6 or 7, characterized in that the pressure elements include a hydraulic or pneumatic press, arranged to act on the external walls of said cold mold.
9. 9. A method, according to claims 6 to 8, characterized in that the cooling elements of the cold mold include several cooling circuits, arranged in said cold mold, a coolant container, a heat exchanger and a coolant pump, so wherein said refrigerant pump circulates this refrigerant through a circuit thereof, which connects the refrigerant circuits to each other and to said refrigerant container, this heat exchanger and said refrigerant pump.
10. 10. A method, according to claims 6 to 9, characterized in that the wall of said mold has a thickness selected so that the desired cooling rate is obtained. •)