MXPA97002719A - Use of crushed and classified mineral, of magnetite mineral preference, for the manufacture of molds and nucl - Google Patents

Abstract

The invention specifies the use of crushed and classified ore, preferably mineral magnetite, as a particulate mineral base material in a mold or core material that is recyclable or non-recyclable, respectively, for the dry or untreated manufacture of molds without a box or box molds preferably of bonded clay, especially bonded bentonite and cores for placing them in such molds or in metal molds (dies), preferably when emptying non-ferrous metals or alloys, especially light metals and light metal alloys. Compared with the conventional use of quartz sand as the base material, this makes it possible to achieve a substantially faster cooling and therefore the solidification of the metal that has been cast into the molds, as well as a more advantageous microstructure in the cast products than have been produced

Description

USE OF CRUSHED AND CLASSIFIED MINERAL, OF MAGNETITE MINERAL PREFERENCE, FOR THE MANUFACTURE OF MOLDS AND NUCLEI TECHNICAL FIELD The present invention relates to the use of crushed and classified ore, preferably mineral magnetite, for the manufacture of molds and cores for use in emptying non-ferrous metals or alloys, especially light metals and light metal alloys. Magnetite is a ferromagnetic mineral with the stoichiometric composition Fe-jO ^. In the present context, the expression "classified" is used to indicate that the ore, after having been crushed, has been subjected to a certain classification of particle size, for example by sieving, separation or flotation in air, as is well known for particulate materials such as sand.

ANTECEDENTS OF THE TECHNIQUE Currently, the base material of mineral particles used for the manufacture of molds and cores, have been practically exclusively quartz sand.

Admitting that it is not unknown within the foundry industry, use other materials based on particulate mineral such as olivine sand, magnesium silicate-iron and zircon sand, a zirconium silicate. Due to their high heat resistance and high price, these base materials have especially found localized use as the so-called "pattern sand" or as a core placed in such regions of molds to pour steel into cast articles that are particularly exposed to heat, to avoid or reduce the "burn" of the sand on the corresponding regions of the articles emptied and the consequent heavy and costly cleaning of the articles emptied. A corresponding use has been found for the crushed chromite mineral, as with this mineral, it is also the case that the wetting relations towards the liquid steel are such that it simply "repels" the latter. No examples are known of such particulate-based materials that have already been used in a larger mass of the circulating mold material, left only to empty non-ferrous metals or alloys. In a document (38th International Foundry Congress, Exchange Paper No. 9, Dusseldorf, 1971) "Mogglkeke der industriellen Anwendung des Magnetfor verfahrens zur Herstellung von Massengussteilen" by A. Witt oser, K. Steinack and R. Hof an, production in Mass of cast articles was described, based on a mass production of heat-gastable patterns of expanded polystyrene foam. These patterns are covered by being sprayed with or submerged in a coating (Schlichte), after which they are wrapped with a flowable mixture of crushed magnetite ore and iron granulate, possibly in a fluidized state. Prior to the casting operation, a magnetic field is applied to the mold material to bond its individual particles magnetically together, the field which is maintained during the proper casting and at least a part of time, during which the metal solidifies in the mold. When the magnetic field has been removed, the material of the mold, now again being flowable, flows away from the emptying, after which it can be used in new molds, possibly after they have been cooled. The document, relates exclusively to the casting of iron alloys, mentions the effect of greater cooling of the material of the mold when compared with the quartz sand and also discusses how this cooling effect can be made to vary by changing the quantitative relation between the particles of magnetite and the iron granulate in the mold material, such that an increased proportion of the magnetite particles reduces the cooling effect. Obviously, this method can not be used in conventional molding and casting systems. For the emptying of articles emptied of light metal, especially for use in the automotive industry and similar industries, there is, however, a great need to achieve a faster cooling of the metal that has been poured into the molds, since this makes it possible to achieve a finer grain structure in the casting and also avoid so-called micro-shrinkage cavities in emptied articles. Currently, attempts are made to achieve such faster cooling by emptying in the so-called metal molds (matrices). Such molds are, however, expensive to manufacture and in comparison with casting in a conventional mold and casting system based on the use of sand, their productive capacity is very limited.

DESCRIPTION OF THE INVENTION It is the object of the present invention to show how it is possible, in a conventional molding and draining plant based on the use of sand, to achieve cooling speeds approximately those that can be achieved in metal molds. According to the present invention, this object is achieved by the use of a crushed and classified mineral, preferably mineral magnetite, or a base material of particulate ore in a mold or core of recyclable or non-recyclable material, respectively for the manufacture dry or untreated, preferably bonded clay, especially bonded bentonite, in molds in the box or in molds without box and cores for placing in such molds or in metal molds (dies), preferably when emptying non-ferrous metals or alloys, especially light metals and light metal alloys. Compared to the use of quartz sand as the base material, this mainly means that the metal that has been cast in the mold, solidifies more quickly and that the articles emptied, especially articles emptied of light metal, in this process, are given a structure of finer and "denser" grain, which corresponds approximately to that which can be achieved by casting with matrix, that is, in a conventional casting and molding system based on the use of molding sand and with costs of the relatively low pattern and high productivity of the capacity associated with such plants, it is possible to achieve a quality in the articles emptied at at least approximately the level with which it can be achieved using the matrix casting systems with considerably higher mold costs and lower operating speed. A second advantage is that with the use according to the invention, it is possible to make the cooling section of a molding and emptying system substantially shorten, thus saving space. A third advantage is that the amount of the molding material that is recycled can be reduced compared to the use of quartz sand as the base material, thus partially compensating for the use - after all - of the expensive base material. A fourth advantage pointing in the same direction can be seen from the following: For environmental reasons, it is relatively expensive to store or deposit the used and discarded mold material based on quartz sand, but in the case of the cast-off material based on the mineral magnetite, not only it is not possible to have freedom of loading, but possibly still also with an economic advantage, since this material can, without further processing, be used to produce iron, not only in blast furnaces, but practically in any furnace to melt iron or steel. Still another advantage with the use of the mineral magnetite as a base material, is that this material on the contrary to the quartz sand, can not produce the presentation of silicosis, lung disease. An advantage of using this material for the cores to be placed in metal dies is that on the contrary to the metal cores, such cores can be shaped into any desired shape and still have substantially greater cooling capacity than a corresponding core of quartz sand. With use according to the invention, it has been advantageously proved that the base material has a particle size distribution as set out in claim 2. The mold material used for the molds can be advantageously produced in the form established in claim 3, the bentonite being preferably used as a Na-bentonite that occurs naturally (bentonite from the west) or the so-called "active bentonite", ie Ca-bentonite (Southeast type) that has been converted to Na-bentonite by ion exchange. Bentonite is a binding agent commonly used in the foundry industry. Alternatively, the mold material can be produced as set forth in claim 4. In both cases, the molds can, as stated in claim 5, have been dried before casting.

As a second or alternative alternative, the mold material may have been produced in a manner set forth in claim 6 and if so, the molds may have been made to set or harden before casting as set forth in claim 7. In all In all three cases, the additives are preferably chosen from the group established in claim 8, but this does not exclude the use of other additives. With use in accordance with the invention, the cores preferably consist of a core material produced in the manner set forth in claim 9, the core material possibly being hardened or set as set forth in claim 10 or 11. However, the cores may also be compounded in the manner set forth in claim 2 and hardened or made to freeze-set, cooling of the core boxes, for example, is accomplished using a gas, such as nitrogen. In this form, the core will produce an extra strong cooling effect, which may be advantageous for certain applications, for example the aforementioned use of the core in the metal molds. Preferably, a part of the mold and core material that is produced from the vibration operation is reworked in the manner set forth in claim 13, while in this case, the addition of water and bonding clay is preferably coordinated from such that the molding material that is recirculated will have the desired molding properties. The rest of the material of the mold and the core that is produced from the vibration operation can be subjected to a regeneration and reuse as set forth in claim 14, it being possible with such a regeneration process to use well-known methods and apparatus for similar treatment of the core and mold material based on quartz sand, but also supplemented with the magnetic separation as set forth in claim 15, due to the magnetic properties of the base material. Alternatively, the base material in the part that has not been reworked can be used in the manner set forth in claim 16. This means that the excess amount of the mold material used does not have to be stored or deposited at a higher cost as in the case of quartz sand as the base material, but it can be profitable to be used in metal extraction processes - in the case of magnetite, this can be carried out in conventional iron or steel casting furnaces or in furnaces Fusion of iron, optionally with the previous granulation of the magnetite material.

DESCRIPTION OF THE PREFERRED MODALITIES In the next part of the present description, the invention will be explained in greater detail, for example on the basis of comparative examples of the molten material based on crushed and classified magnetite ore and based on quartz sand, respectively. In the "technological" tests discussed in the following, the sand test equipment commonly used by the firm of Georg Fischer A.G. , Shaffhausen, Switzerland, has been used and the test instructions given by this firm have been followed. A parameter that presents a decisive difference between the magnetite sand and the quartz sand that is used is the weight per unit volume of the dry base sand, that is to say the weight per axis, one liter of sand consolidated in kilograms for magnetite sand in an amount of approximately 2.8 and for quartz sand of approximately 1.5. In addition, the cooling effect of the magnetite sand in an amount for approximately 1500 J / m2s 1 2 ° K against approximately 1000 J / m2s? 2 ° K for quartz sand. For use in the comparative tests, the following mixtures are produced in a laboratory mixer: I. MAGNETITE SAND: 4.5 kg of magnetite sand are mixed for 7 minutes with 300 g of active bentonite ("GekoR") and 63 g of water, after sieving which is subjected to the tests indicated in Table 1. II . QUARTZ SAND: 2.5 kg of quartz sand are mixed for 7 minutes with 300 g of active bentonite ("GekoR") and 63 g of aguai, after sieving that is subjected to the tests indicated in Table 1.

TABLE 1 Sand of magnetite Arena of Quartz Weight of the standard test sample 50 mm x 50 mm diameter 250 146 Compressive strength p / cm2 1250 1600 Shear strength p / cm2 230 300 Gas permeability 60 120 The test molds with the dimensions of 36 mm in diameter x 185 mm were produced using the same pattern and the mold-sand mixtures described in I and II above, the test molds that are emptied with AlSi7Mg at 680 ° C. At the same time, test pieces of corresponding dimensions are emptied in a metal mold and the following parameters are determined: DAS, that is to say separations of the dendritic arm in μm t ", that is to say solidification time in seconds TABLE 2 Metal molds Magnetite sand Quartz sand DAS 36 38 44 tg 47 55 85 These figures show very clearly the greater cooling effect of the magnetite sand when compared to the quartz sand, while the microstructure of the samples cast in magnetite-sand molds was approximately 13.6% "denser" (more "grain"). fine ") than in the samples emptied in the quartz-sand molds, their solidification time is reduced by approximately 35% compared to that for samples cast in quartz-sand molds. It can also be observed that for both mentioned parameters, the values are achieved by approaching those achieved by casting in a metal mold.

In addition to the uses described in the foregoing and set forth in the claims, it could be close to be handled by a person skilled in the art, to use cores according to any of claims 9-12 in molds having quartz sand as the base material, in order to achieve both the associated improved cooling effect and the reduced flotation force of the cores after casting the mold. In this case, the magnetite sand can be easily separated in magnetic form from the quartz sand after the vibration, thus partially recovering the magnetite sand, partially avoiding the contamination of the quartz sand in circulation with the sand of nucleus and nucleus binding agents. In the above description, the use according to the invention has been described in connection with the casting of light metal alloys, but it will be understood that the use can also be carried out when they are emptied, for example non-ferrous copper alloys or even ferrous metals, such as cast iron.

Claims (18)

1. A bonded clay mold, especially bentonite bonded to empty non-ferrous metals or alloys or ferrous metals, especially light metals and light metal alloys, characterized in that the molds are made of crushed magnetite ore and classified as the base material.

2. A bonded clay core, especially bentonite bonded to be placed in the molds according to claim 1, characterized in that the cores are made of crushed and classified magnetite ore, except iron sand of titanomagnetite as the base material.

3. The mold or core according to claim 1 or 2, characterized in that the base material has a particle size distribution mainly in the range of 0.05 mm to 0.5 mm, preferably in the range of 0.1 mm to 0.25 mm and mainly falls inside three standard mesh sieves.

4. The mold according to claim 1 or 3, characterized in that the mold consists of wet mold material of bonded clay, produced by mixing the base material with preferably 2-20% by weight of bentonite, preferably 1-5% by weight of water and optionally preferably 1-10% by weight of additives.

5. The mold according to claim 1 or 3, characterized in that the mold consists of mold material produced by mixing the base material with preferably 5-10% by weight of cement, preferably 1-5% by weight of water and optionally 1-10% by weight of additives.

6. The mold according to claim 4 or 5, characterized in that before casting, the mold has been dried at a temperature of up to about 400 ° C.

7. The mold according to claim 1 or 3, characterized in that the mold consists of mold material produced by mixing the base material with preferably 5-10% by weight of water crystal and optionally 1-10% by weight of additives.

8. The mold according to claim 7, characterized in that before casting, the mold has been hardened when being blown through C02 •

9. The mold according to any one of claims 4-8, characterized in that the additives are selected from the group comprising charcoal powder, cereals and milled wood.

10. The core in accordance with the claim 2 or 3, characterized in that the core consists of a core material produced, by mixing the base material with a binding agent, chosen from the group comprising, organic or inorganic core bonding agents curable and self-hardening in solid or liquid form, possibly known per se.

11. The core according to claim 10, characterized in that the core material has been hardened or brought to set by heating.

12. The core according to claim 10, characterized in that the core material has been hardened or has been brought to set when being blown through it with a gaseous hardening agent.

13. The core according to claim 2 or 3, characterized in that the core consists of wet core material of clay bonded with a composition as set forth in claim 4 and hardens or is set by freezing such as in cooled core boxes .

14. The mold or core according to one or any of claims 1-13, characterized in that after emptying and vibrating the molds, part of the material of the mold and the core recovered in this form is reworked to form mold material, mixing with a suitable percentage by weight of water and optionally with an adequate percentage by weight of the argillaceous binding agent.

15. The mold or core according to claim 14, characterized in that the unworked part of the mold and the core material recovered from the vibration is subjected to a regeneration and reuse as base material according to one or any of the claims 4, 5. , 7 and 10.

16. The mold or core according to claim 15, characterized in that the regeneration process comprises the magnetic separation.

17. The mold or core according to claim 14, characterized in that the base material in the non-reworked part of the mold and the core material recovered from the vibration is used in a metallurgical process for the production of metal.

18. The process for emptying non-ferrous metals or alloys or ferrous metals, especially light metals and light metal alloys, characterized in that it uses the molds and / or cores in accordance with claim 1 or claim 2.