Background of the invention

The object of the invention is a casting, and more particularly a treatment method for a metal casting, with which method a casting section can in a controlled manner be solidified and cooled in a mold in such a way that metallurgically, and also otherwise, a technically better casting result is achieved with significantly better efficiency in energy use and material use and with an essentially smaller environmental load on the ambient workplace air, and additionally also achieving significant savings in production costs and investment costs, as well as electricity and district heating.

A number of different methods are known in the art for treating a metal casting or a casting section that has already been cast.

Prior art solutions

One method is to dispose metal cooling pieces, i.e. coquilles, in a sand mold, in the walls of the mold cavity, to quickly bind the heat from the molten metal locally, so that the casting cools from this point faster than other points, promoting targeted cooling and solidification.

One method is to use a mold that is wholly or partly of metal to get a more significant part of the heat contained by the molten metal to bind to an exterior cdquille of the object. One treatment method, which is used e.g. for the (heat) treatment of a casting section is presented in publication WO03/031661 Al. In the heat treatment method according to the publication, the heat treatment is carried out in a heat treatment furnace or the like, and in the method the heat transfer from the object/objects is adjusted by controlling the rate of change of the temperature to the desired level in different heat treatment phases. In the method according to the publication the heat treatment is carried out on a solid object in the same heat treatment furnace or the like, without the object necessarily needing to be moved from the furnace, but according to the publication it is also however possible that heat treatment of the object is carried out in a number of consecutive furnaces, in which case the object requires moving between the furnaces.

Prior-art solutions have a number of drawbacks.

One drawback in prior-art solutions is that local coquilles bind the heat from a casting only to the extent of their own thermal capacity until the temperature of the casting section is reached. After this, cooling of the object in the mold in fact slows down and does not speed up as the coquilles cool at the same rate as the casting section.

One drawback in prior-art solutions is that when the mold is wholly or partly of metal, the quantity of heat bound by the mold and coming from the object, i.e. the cooling power, is limited to the finite thermal capacity of the coquille.

One drawback in prior-art solutions is that the amount of heat being removed, and the speed of its removal, from the molten metal and from the casting section cannot be managed.

One drawback in prior-art solutions is that the heat being removed from the molten metal and from the casting section cannot be utilized in production nor in the production of energy, nor in recycling, but instead it is wasted except for possible heat recovery from the mold, from the coquilles and from the casting section after disassembly of the mold.

One drawback in prior-art solutions is that the heat treatment is only carried out when the casting has been fully removed from the mold, and in this case the cooling of the casting cannot be adjusted in a controlled manner already during the casting nor before solidification of the casting, nor before cooling to the temperature for removal from the mold, nor before removal of the casting section from the mold.

In solutions known in the art a problem for treating a casting is also that cooling of the casting in the mold is notably slow. The solidification and cooling in the mold of large objects, e.g. weighing 10 tonnes, lasts 3 - 5 days, tying up a lot of space, mold materials and mold frames.

One drawback in prior-art solutions is that in them it is necessary to use large amounts of foundry sand compared to the weight of the casting ; typically the amount if sand is five to ten times the amount compared to the weight of the casting.

One drawback in prior-art solutions is that, owing to the large quantity of sand, handling the molds requires extremely large crane capacity and object handling capacity, which significantly increases the investment costs of a production facility. The large quantity of sand also results in another drawback, namely that it is not worthwhile using more durable grades of sand or more environmentally-friendly binder agent systems because, when large quantities of sand are involved, they would not be profitable even though they bring significant improvements in the quality of the casting and reduce environment loading.

Another problem in prior-art methods is that by using them the manufacturing of a casting section meeting the metallurgical structural properties required is awkward and even impossible to realize. A problem with prior-art treatment methods for a casting is often also the unwanted occurrence of flaky graphite in an object as well as other unwanted properties such as e.g. the occurrence of shrinkage porosity in the finished object, or non-uniform quality and non-controllability of the hardness and microstructure of an object.

The aim of this invention is to achieve a treatment method for a casting or casting section, with which the drawbacks of prior art can be avoided, and to achieve an effective and functional treatment method for a casting, with which method casting sections having the desired physical properties and microstructure can be achieved in a controlled manner. In addition, the aim of the invention is to significantly improve efficiency in the use of energy and of materials, to reduce emissions into the workplace air and the environment, to return a significant part of the thermal energy being released in the casting to electricity production or heating energy production, and also to utilize a large part of wasted energy in the processes of the foundry. As a final result the manufacturing costs particularly of heavy castings significantly decrease and the investments required by production also decrease decisively.

Brief description of the invention

The method according to the invention is composed of a number of elements:

- In the method cooling elements/heating elements manufactured from metal or from some other material are disposed as parts of a sand mold or other ceramic mold. These elements function as so- called metal coquilles, binding the heat of the molten metal and of the casting section, but a new feature is that the heat is transferred out of them in a controlled manner or heat is brought into them in a controlled manner during solidification and cooling for controlling the cooling rate and heating rate as desired. A liquid, a gas, or a combination of them, can function as the heat transfer agent. Cooling elements/heating elements are dimensioned and fabricated for the specific product for achieving the desired heating power/cooling power locally. The plans are checked with computer simulations of solidification and cooling. - In the method the mold is designed and fabricated for the specific product in such a way that the amount of sand is minimized both in the mold and in the core. Sand or other ceramic formable mold material is used only to achieve the desired shapes for the casting section. Casting frames are typically shaped modularly according to the dimensions of the casting section or section family, cores are fabricated to be hollow. In the invention an inorganic binder agent is utilized instead of organic binder agents, and also ceramic sand instead of quartz sand, and also water thinnable coatings of the mold and core insofar as is practicable in the circumstances. With the method a level of 1 : 1 in the sand :metal ratio is reached or even below, instead of the typical 1 :4 - 1 : 10. - In the method the thermal energy to be obtained from the cooling elements that are parts of the mold represents up to 50 - 70% of the energy bound in the molten metal in the melting. The temperature of the agent is as much as 600-700 °C. The heat is transferred in a controlled manner into electricity production via either a steam turbine, a heat pump or a Sterling motor. Typically 25% of the heat contained in the agent can be converted into electricity. The remainder of the heat is utilized commercially by selling it for district heating, by using it in a foundry process and by utilizing it for heating the factory premises.

- In the method the molds and cores are typically fabricated as parts, in which case the handling of objects in manufacturing essentially becomes lighter owing to the need for lighter lifting & handling equipment. The finished cores and molds are essentially lighter, in which case also the dimensioning of crane runways, of cranes and of the whole building can be made lighter. At the same time the space requirement essentially decreases: typically only a fraction of the floor surface area, mold frames, et cetera, is needed and owing to the fast circulation approx. five times the production can be obtained from the existing premises of a foundry by applying the method of the invention. In connection with the construction of a new foundry, approx. 60% of the investment is saved compared to realizing the same production capacity with conventional technologies.

More precisely stated, the method according to the invention is characterized by what is stated in the characterization part of claim 1. Additionally, the method according to the invention is characterized by what is stated in the dependent claims 2-19.

The method according to the invention has a number of different advantages when it is compared to prior-art methods. Some advantages Of the method according to the invention are listed below.

With the method according to the invention the occurrence of unwanted flaky graphite, i.e. malformed spheroidal graphite, can be avoided and a casting section can be achieved in which there is extremely little porosity. Also obtained with the method according to the invention are better spheroidizing (spheroidal graphite cast iron) in the casting section, better controlled infiltration and aligned solidification, and hot cracking (steel castings) can be prevented, and a casting section of generally homogeneous quality in its metallurgical structure can be achieved, which casting section is strong and durable, as well as very machinable and also more dimensionally precise as a material. By using the method according to the invention objects with thinner walls can be designed and manufactured, and the method also facilitates castability (cheaper casting costs), and lighter, stronger objects of small size can be manufactured with it. With the method according to the invention different materials can be used/replaced as a casting material.

With the method according to the invention a controlled and managed process is achieved throughout the whole casting event, and with this the microstructure of a casting section can be affected in a controlled way during the casting event by adjusting the cooling. This is an advantage in that, among other things, the heat treatment conventionally carried out on an object afterwards can be avoided.

With the method according to the invention the circulation speed from casting to disassembly of the mold is very much faster than in known processes, and the method facilitates and enables serial production for objects that are not normally made in long series, such as e.g. large castings for windmills, and the advantages of the method also come out best in serial production, but also in difficult large individual objects or in small series.

The method according to the invention smoothly enables preheating/drying of a mold/coquille, and in the method the molds are heated separately or heat is conducted from one mold to another, in which case a significant saving in energy can be achieved .

One advantage of the method according to the invention is also a large reduction in the amount of sand to be used, because the cooling can be managed efficiently already during the casting event, and because with it therefore a cost benefit in materials is gained (sand, binder agents) and also it requires less work and circulation of materials than conventional methods. Material inventories can be kept low when using the method according to the invention.

The method according to the invention is also more environmentally friendly (less material and harmful substances, diminished odor nuisances and particle emissions into the nearby environment, et cetera) than prior-art solutions.

An energy cost benefit is achieved with the method according to the invention because the amount of heat to be taken out of a mold can be utilized in many ways, e.g. for the preheating of other molds/coquilles, and if necessary the hot air/gas/water/ steam obtained from a mold for the heating of another mold.

With the method according to the invention the same capacity can be produced with a smaller floor surface area (faster turnover). Production devices can be smaller/cheaper (e.g. cranes, sand mixers, et cetera). Relatively fewer metal frames are needed. In this case also less storage space is needed.

Brief description of the figures

Fig. 1 presents by way of illustration a (simplified) method according to the invention.

Fig. 2 presents cooling times for different agents to be supplied to the different materials of the coquilles/into the coquilles.

Fig. 3 presents a few different temperatures of a casting using the method according to the invention. Detailed description of the invention

According to the invention, in the heat treatment method of a casting, such as e.g. of an iron casting, a mold is used for casting the casting in the mold and the casting is cooled by cooling and/or heating it by means of coquilles, which coquilles are placed in connection with the mold. In the method sand is used in connection with the casting mold, i.e. the method according to the invention relates explicitly to casting wherein sand (a sand core) is used in the mold/as the mold, and the casting is cooled and/or heated during the casting and/or after the casting by means of one or more coquille or coquilles in the casting mold, into which coquille/coquilles an agent is supplied for heating and/or for cooling one or more coquilles.

One or more thermoelement/thermoelements can be fitted in connection with the casting mold and/or the coquilles and/or the sand used in the casting mold/as the casting mold, the temperature of a coquille being adjusted (online control) with the temperature data given by which thermoelement(s), but it is also possible to adjust and manage the temperature of coquilles e.g. on the basis of earlier data/moder (offline control, i.e. passive control). In the method according to the invention with the coquilles the whole casting or some part of the casting is heated and/or cooled, depending on each application being cast. With the method according to the invention the temperature Of a casting section and of the mold, or parts thereof, can be adjusted, i.e. the cooling of them, in a controlled way during the whole casting event (dynamic control), and if necessary the temperature can also be raised, by supplying in this case hot agent to the coquilles.

In the method according to the invention the temperature of the coquilles can be raised and/or lowered also in phases, e.g . in such a way that first the temperature is raised in a number of phases consecutively, and then lowered in consecutive phases, and after which the temperature is again raised, and so on.

With an adjustment of temperature the type of desired cooling speed can be achieved for a casting that the properties of the casting are those desired, and that the drawbacks arising in the use of methods known in the art, such as the occurrence of flaky graphite can be avoided. In the method according to the invention the cooling/heating of coqu illes is adjusted either in an automated manner using data processing means, such as a computer and suitable softwares, as an aid, but a solution is also conceivable wherein adjustment of the temperature is performed manually, e.g . on the basis of temperature data received from the thermoelements.

In the method according to the invention two or more coqu illes can be in connection with each other in such a way that the agent displaces during the casting or after the casting from one coquille into another coquille. It is also possible that agent is supplied separately to each individual coquille, in which case the temperature of each coquille can be precisely managed . The agent to be supplied to a coquille can be gaseous, such as e.g. air, but the agent can also be liqu id , such as e.g . water, or a combination of a liquid and a gaseous substance, such as water vapor. The coquilles are of some metal or alternatively a combination of metals. They can be e.g . cast iron or copper. A coquille can also comprise one or more heating elements, such as a heating resistor, for the (additional) heating of a coquille.

Fig. 1 presents by way of illustration the method according to the invention, and from the figure it is seen that the mold (which can be of one or more different parts/materials) is described with the reference number 1 and the casting is described with the reference number 4, and the cooling elements/heating elements in connection with the mold are described with the reference numbers 5 and 6. The space between the casting 4 and the cooling element/heating element 6 is presented with the reference number 3, but it is also possible that the cooling element/heating element (or the mold) is coated and e.g . in direct contact with the casting 4, this is not however presented in the figure. The core is presented with the reference number 2, but it is possible that a core is not in connection with the mold at all. The heat being conducted out of the casting and onwards out of a cooling element/heating element is described with the reference number 7, and correspondingly the heat (cooling) being supplied into a cooling element/heating element is presented with the reference number 8, and the heat that is su pplied to a cooling element/heating element, and which is transferred onwards into the casting 4 with the reference number 9. The controller, which is used for the cooling/heating and by the aid of which the power, et cetera, of the cooling/heating is adjusted, is presented with the reference number 10. The controller is presented in simplified form in Fig. 10, but the controller can comprise a computer, software programs, various measuring devices and sensors connected to it, et cetera, by means of which accurately adjusted cooling/heating power is obtained e.g. dynamically/continuously during the whole casting event and the cooling of the casting. The position and size of the cooling elements/heating elements 5, 6, such as of the coquilles, can be that desired, the purpose of what is presented by Fig. 1 being in the capacity only of illustrating coquilles in connection with a mold. The figure does not present the thermoelements (for measuring temperature), but the thermoelements can be disposed in a desired location, so that their position is in no way restricted, and there can be only one of them or a number of them in connection with a casting.

Fig. 2 presents the cooling times and the temperatures indicated by the thermoelements (i.e. of the casting) when the method according to the invention is used for heat treatment of a casting, and when coquilles of different materials are used and different agents are supplied to the coquilles. The temperature of the casting when no coquilles at all are used, i.e. when the casting is not cooled with coquilles, is described in the figure with the reference A. The temperature/cooling time of a casting is indicated with the curves marked with the reference B and C when two different coquilles are used. The references D, E and F describe the temperature and cooling time when different coquilles are used, and when different agents, such as e.g. air, water or water vapor, are supplied to the coquilles. The coquilles can, on the other hand, be of different materials, such as of iron or copper, or a combination of different materials.

Fig. 3 illustrates the temperature (the temperature of the casting indicated by the thermoelement) of the different castings (A1-A3) when the casting is heated (HI marked as the temperature of the heating element). Table 4 presents the time in which a casting of 300mm thickness becomes solid, i.e. when it reaches a temperature of 1155 Celsius degrees. The table presents the aforementioned time using different materials (PCmatl and PCmat2) of the coquilles. The table presents the time when the casting has further cooled to a temperature of 400 Celsius degrees.

Table 5 presents the time in which the casting becomes solid (1155 Celsius degrees); described in more detail, the table presents the time of changing into a solid at different distances from the outer surface of the casting, i.e. at distances of 75mm, 150mm and 225mm, and when using different coquille materials and different cooling agents.

It is obvious to the person skilled in the art that the different embodiments of the invention are not either limited solely to the examples described above, and that they may for these reasons be varied within the scope of the claims presented below.

The characteristic features possibly used in the description can also, if necessary, be used separately from each other.

In the method according to the invention different metals can be used as casting material, such as e.g. iron (spheroidal graphite cast iron), steel, non-ferrous metals, such as aluminium, copper or alloys of different metals; this is in no way limited, but instead depends on the application of the object.

The shape and size of the cooling element/heating element to be used in the method according to the invention is not limited in any way whatsoever, but instead it can be that desired depending on the application need. The shape of a coquille can be e.g. plate-like, elongated, curved, rectangular, et cetera.

The cooling element/heating element is preferably of the coquille type, plate-shaped, tubular, helical or a combination of the foregoing. The whole casting or some part of the casting is heated and/or cooled with a cooling element/heating element. In the solution according to the invention two or more cooling elements/heating elements can be in connection with each other in such a way that the agent displaces during the casting or after the casting from one cooling element/heating element into another cooling element/heating element.

In connection with a mold can be one or more pieces, such as a heating resistor, heating the casting.