WO1999048634A1

WO1999048634A1 - Use of iron mica in the production of moulds

Info

Publication number: WO1999048634A1
Application number: PCT/AT1999/000068
Authority: WO
Inventors: Günther POKORNY
Original assignee: Kärntner Montanindustrie Gesellschaft Mbh
Priority date: 1998-03-20
Filing date: 1999-03-17
Publication date: 1999-09-30
Also published as: EP1064112A1; AT2581U1; DE59905561D1; AU2910799A; EP1064112B1

Abstract

The use of 4-90 % iron mica in foundry practice as an additive to moulding materials for organically and inorganically bonded moulds and cores improves the casting quality in terms of structure (e.g. it reduces the space between dendrites in G-Alsi7Mg) and thus improves mechanical properties in non-ferrous alloys. By adding iron-mica to the above-mentioned moulding materials for moulds and cores dilation-related defects (e.g. lamellar ribs) are reduced in iron-carbon alloys. This results in less re-finishing or avoids rejects (i.e. cuts costs) and provides a better surface quality. Iron mica also exhibits fine qualities when used as an additive to finishes or blackenings used as coating materials for moulds and cores. Iron mica can be used as a pure raw material and as an additive for exothermic feed agents on account of its good insulating qualities resulting from exothermic reaction when oxygen is present in the mould.

Description

- 1 -

Use of iron mica in the manufacture of molds

The present invention relates to the use of iron mica for the production of casting molds, in particular lost casting molds, and cores for the casting of castings from non-ferrous, cast iron and cast steel alloys and mixtures of iron mica containing molding materials. According to the invention, iron mica can also be used as an additive for coatings for molds and cores, used in the entire field of the foundry industry, and as an additive for exothermic food aids.

A lost mold is a sand mold, solidified by organic or inorganic binders (e.g. clays, resins) which can only be used once and must be destroyed after casting to empty the castings. In contrast, there are permanent forms that can be used repeatedly, e.g. Chill molds or die casting molds.

Cores have the task of forming cavities or undercut external contours in the cast part. According to their usability, a distinction is made between cores for single use (lost cores, sand cores) and permanent cores (metal cores), which are used repeatedly. Sand cores are separately manufactured inner mold parts. They are inserted, inserted or hung into the outer mold parts when assembling the mold. A large percentage of both lost molds and lost cores are used in the foundry industry today mainly because they can be manufactured relatively inexpensively and the mold material can be reprocessed after the molds have been destroyed and reused to produce new molds.

Finishing or blackening (mold material coatings) are refractory materials that are used in liquid or pasty form to produce a thin coating on the mold walls or cores (sand cores, metal cores) and have heat-insulating, heat-conducting, smoothing, separating or blocking effects. Depending on - 2 -

Suitable and suitable additives are mixed with these coatings.

The molds required for the production of cast products in the casting process are made with molding materials that consist of binder (organic or inorganic), molding material, water and molding material additives. These terms are explained in more detail below:

In the present description, a mold is to be understood as all molds for the production of cast products, such as Sand mold, mold, die casting mold, ceramic investment mold or shell mold. Only as examples are outer and inner mold parts, box molds, boxless molds, core molds and mask molds.

Molding material is the collective name for all dry, moist, pasty or liquid substances for the production of casting molds that are compacted, solidified or bound by chemical processes, e.g. Mold and core sands, flow sands, form slips and ceramic molding compounds. Mold base materials are natural mineral or synthetic granules or sands, which are used for the production of molds for single use.

Binder is understood to mean components of molding material which, under certain conditions (.wetting, swelling, silicate formation, polymerization, etc.), create the bond between the individual grains of sand. A distinction is made between swelling binders (e.g. bentonites, which swell when adding a mixing liquid), ceramic binders (e.g. alumina, which solidify through drying or sinter in the heat), hydraulic binders (e.g. gypsum or cement, which react with a harden) and chemically hardening binders (e.g. water glass, ethyl silicate or synthetic resins) which solidify during hardening.

The addition of molding material means an addition to binder-containing molding or core sand mixtures, which - 3 -

Improve shafts and / or affects the interaction between molding material and casting metal. Examples include glossy carbon formers, starches, calcined soda, boric acid, and wood and peat flour.

Defects occurring in castings can be caused by the molding material (molding defects caused by the molding material), or also metallurgically (microporosity, inclusion of slag, perspiration pearls, shrinkage and stress cracks, segregations etc.) or technologically (offset, cold casting, dimensional inaccuracy etc.).

In the Gießerei-Rundschau, 42nd volume, issue 1/2 from February 1995 and issue 3/4 from March / April 1995, the use of iron mica as a molding additive to molding mixtures was already disclosed. While good results can be achieved with the addition of 2% iron mica to molding mixtures, an addition of 4% leads to poor compressive strength of the molding mixture, which can only be compensated for by an increase in bentonite. However, this increase could not compensate for an insufficient wet tensile strength, which is why an addition of 4% iron mica and above was not recommended.

Depending on the intensity of compaction, it has now surprisingly been found that even higher additions of iron mica to molding material mixtures can lead to excellent results. This is primarily due to the good thermal conductivity of iron mica in the molding material mixture in connection with a dense packing.

The use of iron mica in molding material mixtures leads to:

Reduction of leaf veins

Reduction of mineralization

Reduction of pinholes

Improved thermal conductivity depending on the

Packing density

Improved microstructure formation

Improved mechanical properties

Reduction of rework - 4 -

The iron mica mentioned here is described in ISO 10601 (first edition 1993-08-15), the sieve residue of max. However, 0.1% on the 105 μm sieve is expressly excluded. Iron mica - CAS No. 1317-60-8 - also means iron oxide (alpha-haematite), which has a higher sieve residue.

The use of iron oxide (according to ISO / DIS 1248.2) - mostly as iron oxide red - as a molding material additive is known and is considered "state of the art". These are powdery, mostly amorphous, iron oxides of high fineness. The usual additional quantities are approx. 0.5-1%.

Iron mica is dark gray in color with a metallic sheen. Mica shows a platelet-shaped, lamellar structure and is therefore different from natural and synthetic iron oxides. For both products, the chemical composition with Fe ₂ 0 ₃ applies in pure form.

By adding iron oxide (iron oxide red), expansion errors of the sand structure in the casting heat are partially suppressed and the casting quality is improved. These additives, especially with higher additions, have a negative impact on the strength properties of the molds and cores to such an extent that sufficient shape stability is no longer guaranteed and the casting or the handling of the molded parts or cores is no longer possible.

According to the invention, it is intended to use mica for the production of molds, in particular lost molds and cores for casting castings from non-ferrous, cast iron and cast steel alloys, the molding material mixture used to produce the molds and cores being 4 to 90% by mass, preferably 4 contains up to 50% by mass, in particular 4-20% by mass, of iron mica as a molding additive.

Furthermore, the use of mica is intended for the production of coatings (finishing / blackening), the proportion of mica being 0.1 to 10% by mass in the solid mass of the coating. The one used for the application - 5 -

Molded material coating is liquid or pasty and, depending on the carrier used, contains less iron mica.

The iron mica used according to the invention does not have the negative properties of iron oxide red. The main cause of this effect is its platelet-shaped, lamellar structure, which also makes it possible to increase the percentage in the respective molding material mixture compared to iron oxide (iron oxide red) without negative effects on the strength properties of the mold / core. Typical casting defects such as leaf ribs, mineralization, pinholes etc. are significantly reduced, the surface quality is improved and the microstructure, especially with AlSiMg alloys, taking into account a high packing density of the molding material / iron mica mixture is greatly refined. As a result, better mechanical properties, savings in subsequent heat treatment and lower cleaning costs can be expected.

In real casting tests (materials GG, G-AlSi7Mg) using 10% by mass or 20% by mass of iron mica as a molding additive in molding mixes, significantly shorter solidification times were measured compared to a quartz sand mix without the addition. At the beginning of the recorded solidification of approx. 600 ° C, cooling to 450 ° C was achieved after approx. 250 sec (+ 10 mass%) or approx. 370 sec (+ 20 mass%) compared to 430 sec (quartz sand mixture without iron mica) found (Fig. 7). With increased compression of the molding material mixture, a further reduction in the cooling time to 200 sec (+ 10 mass%) or 210 sec (+ 20 mass%) could be achieved (Figures 9 and 11). The molding material mixtures consisted of:

90 parts by weight (GT) quartz sand, 10 GT iron mica, based on 6% bentonite and 3.5% water or

80 parts by weight (GT) quartz sand, 20 GT iron mica, based on 8% bentonite and 4.0% water;

the wet tensile strength was 0.22 or 0.20 N / cm ² , the compressive strength - 6 - strength 16.9 or 19.2 N / cm ² . Since the higher compressive strength of the mixture with a higher proportion of iron mica is due to the higher bentonite content, a higher bentonite content is also recommended for iron mica contents> 20%. Basically, the properties of the molding material mixtures are not negatively influenced by the addition of iron mica from a casting technology point of view, but the rate of heat removal is significantly improved, i.e. faster additions of iron mica in connection with a dense packing can be expected to cool down / solidify more quickly.

Furthermore, the use of iron mica as an additive for exothermic food aids is provided according to the invention. Because of the surprising, highly insulating effect of iron mica as a pure, binder-free substance, such use of iron mica is particularly advantageous. Suitable addition amounts are about 0.1 to 20% by mass of iron mica.

The present invention will now be explained in more detail with reference to the accompanying figures and the following investigation. Show it:

Fig.l the basic structure of the test facility,

2 shows a mathematical simulation of the cooling of cast iron with lamellar graphite (GG) when using different molding materials in a pure, binder-free form without additives,

3 practically measured cooling curves of GG when using different molding materials in pure, binder-free form without additives,

4 heating curves of the molding materials used from FIG. 3 at GG,

5 practically measured cooling curves of G-AlSi7Mg when using different molding materials in pure, binder-free form without additives,

Fig. 6 heating curves of the molding materials used from Fig. 5 for G-AlSi7Mg, - 7 -

Fig. 7. Cooling curves of G-AlSi7Mg when using molding material mixtures with 10 or 20% mass of iron mica additive with normal compression (M10N or M20N); as a comparison quartz sand mixture without additives (Q1N),

Fig. 8 heating curves of the sand mixtures from Fig. 7,

Fig. 9 cooling curves of G-AlSi7Mg when using molding material mixtures with 10% mass of iron mica additive with normal compression (M10N) or with high compression (M10H); as a comparison quartz sand mixture without additives (Q1N),

Fig. 10 heating curves of the sand mixtures from Fig. 9,

Fig. 11 cooling curves of G-AlSi7Mg when using molding material mixtures with 10 or 20% mass of iron mica additive with high compression (M10H or M20H); as a comparison quartz sand mix without additives (Q1N), and

Fig. 12 on the sand mixtures from Fig. 11.

With the help of thermal analysis and the resulting recording of solidification and cooling curves of alloys as well as heating curves of the substances to be examined during solidification, it is possible to make concrete statements about the heat dissipation of molding materials and their additives.

The thermocouples used (they consist of two wires of different metals which are welded at the ends) generate electricity by heating the welding point of the "thermocouple". This thermal voltage is a measure of the temperature at the measuring point. Depending on the time, there are cooling or heating curves. The thermocouple pairs used consisted of platinum-platinum-rhodium with a temperature range from 0 to 1300 ° C and a thermal voltage of 10.5 μV / K. - 8th -

As a result, the device according to Fig.l proved to be optimal.

The basic form 1 consisted of water glass / C0 ₂ hardened quartz sand, in which a copper tube 2 (diameter 30 mm, wall thickness 1.5 mm) was placed exactly in the middle. This copper tube serves as the actual shape for the cast material 3; The substance to be measured was then either poured into the area around the copper pipe or compacted in a defined manner as a mixture of molding materials. Thermocouples 5 were used at suitable locations.

Copper was used because this material has a very good thermal conductivity, which means that the casting heat is well transferred to the granular substances or molding material mixtures to be examined. At the same time, however, the thermal stability should be so great that the copper form does not melt and, especially when measuring the loose, pure granular substances, a form stability is guaranteed until the end of solidification.

As a result of the mathematical simulation of the mold filling and solidification processes, the size ratios are selected so that both a constant mold compression (e.g. only by the bulk density of the pure substances) and a sufficiently sensitive measurement of the temperature gradients is possible.

Since thermophysical parameters of the materials used (molding material) are an absolute prerequisite for the computer simulation, which are not available for iron mica and With these investigations, data from zircon, chromite and quartz sand were used.

The significant differences in the solidification time of the material cast iron with lamellar graphite (GG) simulated mathematically in Fig. 2 when using

Zircon sand = 104 sec.

Chromite sand = 112 sec.

Quartz sand = 138 sec. - 9 - show the necessary sensitivity of the test facility used.

Shorter solidification times are synonymous with good heat removal properties of the molding material and thus with good structural and casting properties.

The thermocouples 5 (Fig.l) are located in the thermal center of the casting material (GG, G-AlSi7Mg) and in the granular material or in the molding material mixture 20 mm from the metal / mold interface and are constant in all tests. All measurements were taken at a rate of one value per second until the end of the test.

The results of the measurement of the solidification rates of GG in pure binder-free, undensified mold raw materials zirconium, chromite, quartz and in natural iron mica are shown in Fig. 3.

In principle, these real tests show the same tendency for zirconium, chromite and quartz as the results of the simulation. The use of iron mica as a molding material in a pure binder-free and uncompressed state clearly leads to extremely long solidification times, combined with a melting of the copper mold. This effect is also evident in FIG. 4, in which the heating of the molding material during solidification is shown. The exothermic effect in the "mica curve" between 100 and 280 seconds that becomes clear here indicates that iron mica has such an insulating effect in this period that the copper form melts and thus the solidification time is significantly extended (Fig. 3).

In a further series of tests, the material G-AlSi7Mg was used in order to demonstrate this phenomenon of the insulating effect more clearly, but to avoid melting the copper form and thus additional thermal effects. The results are shown in Fig.5. Although the solidification temperature is approximately the same for all four investigated substances, it becomes significantly longer when using iron mica - 10 -

Times shifted, an indication of the highly insulating effect of this substance in binder-free, undensified form. This property also favors the use of iron mica as an additive to exothermic food aids in casting processes.

The setting times for G-AlSi7Mg are:

binder-free zircon sand = 58 sec. binder-free chromite sand = 67 sec. binder-free quartz sand = 80 sec. binder-free iron mica = 139 sec.

With zirconium, chromite and iron mica, the absorbed heat is obviously quickly transferred to the environment in accordance with the heating curve in Fig. 6, i.e. released into lower-lying parts of the mold, the maximum value for iron mica of 67.16 ° C after 900 sec. is below that of quartz sand.

In accordance with the test plan, two molding material mixtures with the following composition were then produced:

Mixture I Mixture II

90 GT quartz sand 80 GT quartz sand

10 GT iron mica 20 GT iron mica based on it

6% bentonite 8% bentonite

3.5% water 4.0% water

Preparation time 10 minutes each in the pan mill.

Strength and casting technology properties according to DIN 52 401 and VDG leaflets P 31 to P 43: - 11 -

Mixture I Mixture II

Bulk density g / 1,755,782 Moisture% 3.5 4.0

Compressibility% 38 32

Gas permeability 80 68

Compressive strength N / cm ² 16.9 19.2 Wet tensile strength N / cm ² 0.22 0.20

These values are completely acceptable for practical mold production, even from an industrial perspective. The somewhat lower compressibility in Mixture II despite higher moisture results from the higher bulk density, which in turn results from the higher addition of iron mica. The higher compressive strength of Mix II is due to the increased bentonite content, i.e. an optimum must be found that even higher iron mica additives do not immediately require higher bentonite contents.

Basically, the properties of bentonite-bonded molding material are not adversely affected by iron mica additives. A significant increase in the amount of binder is not necessary.

As a result of the results of the tests in practical measurements of the heat removal rate of molding material mixtures with different densities, only the alloy G-AlSi7Mg was used.

If iron mica is used as a molding material additive, this substance has a cooling effect depending on the packing density. In Fig. 7 the cooling curves of G-AlSi7Mg are compared using mixture I (M10N) and II (M20N) as well as a comparison of a quartz sand mixture without iron mica additive (Q1N) with normal compression (corresponds to a conventional machine molding shop).

The solidification times of G-AlSi7Mg are: - 12 -

Mix I (10% iron mica) = 83 sec. Mix II (20% iron mica) = 87 sec. Mix without additive = 102 sec.

An increase in the packing density of the grain fraction results in an increase in the thermal conductivity. The insulating effect of the air in the pores is reduced by increasing the proportion of solid-state conduction, and the number of contact points in the grain structure is increased. A change in the type of grain or sand shifts the entire system to higher or lower values (see solidification times in Fig. 5), but the basic connection remains when adding fine particles (iron mica).

The heating curves of the molding material mixtures during solidification shown in Fig. 8 show the same tendency as in Fig. 6, but the curve is different due to binder components and water addition.

The relationships just explained are confirmed by Fig. 9 and Fig. 10. Mix I was compared to the normal (MION) and highly compressed (M10H) quartz sand mix (Q1N).

The solidification times of the light metal alloy G-AlSi7Mg measured here are as follows:

Mixture I - MION = 83 sec.

Mixture I - M10H = 43 sec.

Quartz sand mixture - Q1N = 102 sec.

In the case of higher-density forms in connection with the addition of iron mica, the individual grains of sand have an even larger contact area with one another, the pore spaces are further reduced, and the rate of heat removal is significantly higher.

The solidification time of G-AlSi7Mg is the lowest with 20% iron mica addition and highly compressed forms (Fig. 11). Here - 13 - Mix I high density (MIOH) was compared to mixture II high density (M20H) and the normal quartz sand mixture (QIN) and the solidification rates were measured. They are in G-AlSi7Mg for:

Mixture I - MIOH = 43 sec.

Mix II - M20H = 37 sec. Quartz sand mixture - QIN = 102 sec.

An indication of the obviously very good packing density here is the higher compressibility with the addition of 20% iron mica; a rapid solidification is promoted in any case.

Claims

- 14-patent claims:

1. Use of iron mica for the production of molds, in particular lost molds and cores, both organically and inorganically bound, for casting castings from non-ferrous, cast iron and cast steel alloys, characterized in that the molding material mixture used for producing the molds or cores 4 contains up to 90% by mass of iron mica as a molding additive.

2. Use according to claim 1, characterized in that the molding material mixture contains 4 to 50% by mass of iron mica as a molding material additive.

3. Use according to claim 1 or 2, characterized in that the molding material mixture contains 4 to 20% by mass of iron mica as a molding material additive.

4. Use of iron mica for the production of coatings for cores and molds, organically or inorganically bonded, for casting castings from non-ferrous, cast iron and cast steel alloys, characterized in that the mixture used to produce the coating of mold iron mica in an amount of 0 , 1-10 mass%, based on the solids mass of the coating.

5. Use of iron mica as an additive for exothermic food aids.

6. Molding material mixture for the production of cores and casting molds for casting castings from non-ferrous, cast iron and cast steel alloys, characterized in that the molding material mixture contains 4 to 90% by mass of iron mica as a molding material additive.

7. Molding material mixture according to .Anspruch 6, characterized in that the molding material mixture contains 4 to 50% by mass of iron mica as a molding material additive. - 15 -

8. Molding material mixture according to claim 6 or 7, characterized in that the molding material mixture contains 4 to 20% by mass of iron mica as a molding material additive.

9. Mixture for the production of moldings for cores and molds, organically or inorganically bound, for casting castings from non-ferrous, cast iron and cast steel alloys, characterized in that the mixture is based on iron mica in an amount of 0.1-10% by mass on the solid mass of the coating.

10. Exothermic food aid, characterized in that it contains 0.1 to 20% by mass of iron mica as an additive.