EP1064112B1 - Use of iron mica in the production of moulds - Google Patents

Description

The present invention relates to the use of iron mica for the production of molds, especially lost molds, and cores for casting castings from non-ferrous, Cast iron and cast steel alloys as well as molding compounds containing mica. According to the invention, iron mica can also be used as an additive for moldings for molds and cores, used in entire area of the foundry industry, as well as an additive for exothermic Dining aids are used.

A lost form means a sand form, solidified through organic or inorganic binders (e.g. clays, Resins) which can only be used once and after Pouring for casting emptying must be destroyed. In contrast there are permanent forms that can be used repeatedly, e.g. Chill molds or die casting molds.

Cores have the task of creating cavities or undercuts in the casting To form outer contours. Differentiates according to their usability analogue to mold production, cores for single use (lost cores, sand cores) and permanent cores (metal cores), that are used repeatedly. Sand cores are separated manufactured interior parts. You will be assembling the Mold inserted, inserted or hung into the outer mold parts. Both lost forms and lost cores become mainly because of this in the foundry industry very large percentage used because it is relatively inexpensive can be produced and the molding material after destruction of the shapes reconditioned and to produce new shapes again can be used.

Finishing or blackening (mold material coatings) are refractory Substances used in liquid or pasty form to produce a thin coating on the mold walls or cores (sand cores, Metal cores) are used and heat-insulating, heat-conducting, have a smoothing, separating or blocking effect. Depending on These coatings are used accordingly and appropriately Additives added.

The required for the production of castings in the casting process Molds are made with molding materials made from binder (organic or inorganic), mold raw material, water and Mold additives exist. These terms are used in explained the following:

All molds are used as the mold in the present description to understand the manufacture of castings, such as Sand mold, Chill mold, die casting mold, ceramic investment mold or shell mold. Only as examples are outer and inner mold parts, Box shapes, boxless shapes, core shapes and mask shapes called.

Molding material is the collective name for all dry, moist, pasty or liquid substances for the production of casting molds, which compresses, solidifies or by chemical processes be bound, e.g. Form and core sands, flow sands, form slips and ceramic molding compounds. Acting in the form of raw materials it is natural mineral or synthetic granules or sands that are used to manufacture single use serving forms are used.

Binder is understood to mean constituents of molding material, and certain Requirements (moistening, swelling, silicate formation, Polymerization etc.) the bond between the individual grains of sand produce. A distinction is made between source binders (e.g. Bentonites that swell by adding a mixing liquid), ceramic binders (e.g. alumina, which solidify through drying or sintering in the heat), hydraulic binders (e.g. Gypsum or cement that react with a mixing liquid and hardening) 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 those containing binder Mold or core sand mixes, which are the performance characteristics improve and / or the interaction between molding material and cast metal. Examples are glossy carbon formers, Starches, calcined soda, boric acid, as well as wood and Called peat flour.

Defects occurring in castings can be caused by the molding material have (mold-related casting defects), or metallurgical (Microporosity, slag inclusions, perspiration pearls, Shrinkage and stress cracks, segregations etc.) or technologically (Offset, cold casting, dimensional inaccuracy, etc.).

In the Gießerei-Rundschau, 42nd year, issue 1/2 of February 1995 or issue 3/4 of March / April 1995 is already used from iron mica as a molding additive to molding mixtures revealed. While adding 2% iron mica to molding material mixtures good results can be achieved, introduces Addition of 4% to poor compressive strength of the molding material mixture, which is only compensated for by an increase in bentonite can be. However, this increase could result in an insufficient wet tensile strength do not compensate, why of an addition of 4% iron mica and above was discouraged.

Surprisingly, depending on the compaction intensity found that even higher additions of iron mica lead to molding mixtures for excellent results can. The main reason for this is the good thermal conductivity of iron mica in combination in the molding material mixture be responsible with a tight pack.

Reduzierung von Blattrippenbildung

Reduzierung von Vererzungen

Reduzierung von Pinholes

Verbessertem Wärmeleitvermögen in Abhängigkeit der Packungsdichte

Verbesserter Gefügeausbildung

Verbesserten mechanischen Eigenschaften

Reduzierung von Nacharbeiten

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

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

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

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. The chemical composition with Fe ₂ O ₃ applies to both products in pure form.

By adding iron oxide (iron oxide red) there are expansion errors of the sand structure in the pouring heat partially suppressed and the casting quality improved. It is through these additions, before especially with higher additions, the strength properties of the Forms and cores are so negatively influenced that none sufficient dimensional stability is guaranteed and the cast or partially not handling the molded parts or cores is more possible.

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

Furthermore, the use of iron mica for the production of Molded material coatings (finishing / blackening) provided, the Proportion of iron mica 0.1 to 10 mass% in the solid mass of the coating should be. The one used for the application Mold coating is liquid or pasty and contains depending correspondingly less of the carriers used Micaceous iron oxide.

The iron mica used according to the invention has the negative Properties of iron oxide red do not show up. As the cause of this The main effect is its platelet-shaped, lamellar View structure that also allows the percentage in the respective molding material mixture compared to iron oxide (Iron oxide red) without negatively affecting the Strength properties of the form / core. Typical casting defects, such as leaf veins, mineralization, pinholes, etc. become clear reduced, the surface quality is improved and the microstructure formation, especially with AlSiMg alloys, taking into account a high packing density of the molding material / iron mica mixture is greatly refined. As a result, they are better mechanical Properties, savings in a subsequent heat treatment as well as lower cleaning costs.

90 Gewichtsteilen (GT) Quarzsand, 10 GT Eisenglimmer, darauf bezogen 6 % Bentonit und 3,5 % Wasser bzw.

80 Gewichtsteilen (GT) Quarzsand, 20 GT Eisenglimmer, darauf bezogen 8 % Bentonit und 4.0 % Wasser;

die Naßzugfestigkeit betrug 0,22 bzw. 0,20 N/cm², die Druckfestigkeit 16,9 bzw. 19,2 N/cm². Da die höhere Druckfestigkeit der Mischung mit höherem Eisenglimmeranteil im erhöhten Bentonitgehalt begründet liegt, ist auch bei Eisenglimmeranteilen > 20 % ein höherer Bentonitgehalt empfehlenswert. Grundsätzlich werden durch den Eisenglimmerzusatz die Eigenschaften der Formstoffmischungen aus gießtechnologischer Sicht nicht negativ beeinflußt, die Wärmeentzugsgeschwindigkeit wird jedoch deutlich verbessert, d.h. bei höheren Zusätzen von Eisenglimmer in Verbindung mit einer dichten Packung ist eine schnellere Abkühlung/Erstarrung zu erwarten.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) (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 and 0.20 N / cm ² , the compressive strength 16.9 and 19.2 N / cm ² . Since the higher compressive strength of the mixture with a higher proportion of iron mica is due to the increased bentonite content, a higher bentonite content is also recommended for iron mica contents> 20%. In principle, 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, that is to say faster cooling / solidification can be expected with higher additions of iron mica in conjunction with a dense packing.

Furthermore, the use of iron mica is according to the invention Additive provided for exothermic food aids. Due to the surprising, highly insulating effect of iron mica as pure, binder-free material is such a use of Iron mica is particularly beneficial. Suitable additional amounts are about 0.1 to 20% by mass of iron mica.

Fig.1 den prinzipiellen Aufbau der Versuchseinrichtung,

Fig.2 eine rechnerische Simulation der Abkühlung von Gußeisen mit Lamellengraphit (GG) bei Verwendung verschiedener Formstoffe in reiner, binderfreier Form ohne Zusätze,

Fig.3 praktisch gemessene Abkühlungskurven von GG bei Verwendung verschiedener Formstoffe in reiner, binderfreier Form ohne Zusätze,

Fig.4 Aufheizkurven der verwendeten Formstoffe aus Fig.3 bei GG,

Fig.5 praktisch gemessene Abkühlungskurven von G-AlSi7Mg bei Verwendung verschiedener Formstoffe in reiner, binderfreier Form ohne Zusätze,

Fig.6 Aufheizkurven der verwendeten Formstoffe aus Fig.5 bei G-AlSi7Mg,

Fig.7 Abkühlungskurven von G-AlSi7Mg bei Verwendung von Formstoffmischungen mit 10 bzw. 20 %-Masse Eisenglimmerzusatz bei normaler Verdichtung (M10N bzw. M20N); als Vergleich Quarzsandmischung ohne Zusatz (Q1N),

Fig.8 Aufheizkurven der Sandmischungen aus Fig.7,

Fig.9 Abkühlungskurven von G-AlSi7Mg bei Verwendung von Formstoffmischungen mit 10 %-Masse Eisenglimmerzusatz bei normaler Verdichtung (M10N) bzw. bei hoher Verdichtung (M10H); als Vergleich Quarzsandmischung ohne Zusatz (Q1N),

Fig.10 Aufheizkurven der Sandmischungen aus Fig.9,

Fig.11 Abkühlungskurven von G-AlSi7Mg bei Verwendung von Formstoffmischungen mit 10 bzw. 20 %-Masse Eisenglimmerzusatz bei hoher Verdichtung (M10H bzw. M20H) ; als Vergleich Quarzsandmischung ohne Zusatz (Q1N), und

Fig.12 Aufheizkurven der Sandmischungen aus Fig.11.

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

1 shows the basic structure of the test facility,

2 a mathematical simulation of the cooling of cast iron with lamellar graphite (GG) when using different molding materials in 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,

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 Heating curves of 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 the Solidification, it is possible to make specific statements about heat dissipation of molded materials or their additives.

The thermocouples used (they consist of two wires different metals which are welded at the ends) generate by heating the welding point of the "thermocouple" Electricity with a sensitive millivoltmeter that in the Conductor circuit is installed, measured and referred to as thermal voltage becomes. This thermal voltage is a measure of the temperature at the measuring point. Depending on the time, this results in Cooling or heating curves. The thermocouple pairs used were made of platinum-platinum-rhodium with a temperature range from 0 to 1300 ° C and a thermal voltage of 10.5 uV / K.

As a result, the device according to FIG. 1 proved to be optimal.

The basic form 1 consisted of water glass / CO 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 material to be measured was then either poured around the copper pipe into region 4 or compacted as a mixture of molding materials. Thermocouples 5 were used at suitable locations.

Copper was used because of this material has good thermal conductivity, so the casting heat well on the transferred to investigated granular substances or mixtures of molding materials becomes. At the same time, the thermal stability should be so large that the copper form does not melt and before especially when measuring loose, pure granular substances Dimensional stability until the end of solidification is guaranteed.

The proportions are as a result of the computational simulation the mold filling and solidification processes chosen so that both a constant compression (e.g. only by the Bulk density of the pure substances) as well as a sufficiently sensitive Measurement of the temperature gradient is possible.

As thermophysical parameters in the computer simulation of the materials used (molding material and material) are unconditional prerequisites, but these are with iron mica not available and i.a. determined with these studies data from zircon, chromite and quartz sand used.

Zirkonsand

= 104 sec.

Chromitsand

= 112 sec.

Quarzsand

= 138 sec.

zeigen die notwendige Sensibilität der verwendeten Versuchseinrichtung.The significant differences in the solidification time of the material cast iron with lamellar graphite (GG) when using

zircon

= 104 sec.

chromite

= 112 sec.

quartz sand

= 138 sec.

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 structure and Gußstückeigenschaften.

The thermocouples 5 (Fig.1) are in the thermal center of the Cast material (GG, G-AlSi7Mg) and in the granular material or in the molding material mixture attached 20 mm from the metal / mold interface and constant in all attempts. All measurements were taken until the end of the experiment with a measuring speed of one value per Second recorded.

The results of the measurement of the solidification rates of GG in pure binder-free, undensified zirconia, Chromite, quartz and natural iron mica shows Figure 3.

These real tests show in principle for zirconium, chromite and quartz the same tendency as the results of the simulation. The use of iron mica as a molding material in pure binder-free and undensified condition clearly leads to extreme 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 is. The exothermic effect in the "Mica curve" between 100 and 280 sec. Indicates that during this period iron mica is so insulating that the Copper form melts and thus the solidification time becomes clear extended (Fig. 3).

In order to demonstrate this isolating effect more clearly, but the melting of the copper mold and thus additional Avoiding thermal effects was discussed in another Test series of the material G-AlSi7Mg used. The results are shown in Fig.5. Although examined in all four Substances the solidification temperature is approximately the same, it becomes much longer when using iron mica Times shifted, an indication of the highly insulating effect of this material in binder-free, undensified form. This Property also favors the use of mica as iron Addition to exothermic food aids in casting processes.

binderfreiem Zirkonsand

= 58 sec.

binderfreiem Chromitsand

= 67 sec.

binderfreiem Quarzsand

= 80 sec.

binderfreiem Eisenglimmer

= 139 sec.

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.

The heat absorbed by zircon, chromite and iron mica according to the heating curve in Fig. 6 obviously quickly the environment, i.e. given in lower parts of the form, the Maximum value for iron mica of 67.16 ° C after 900 sec under 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 based on it 20 GT iron mica 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: Mixture I Mixture II Bulk density g / l 755 782 Humidity % 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 for practical mold making, too on an industrial scale, perfectly fine. The slightly less Compressibility in mixture II results despite higher moisture from the higher bulk density, this in turn from the higher addition of iron mica. The higher compressive strength at Mixture II is caused by the increased bentonite content, i.e. that even higher iron mica additives are not immediate require higher bentonite contents, an optimum must be found.

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

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

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

Mischung I (10 % Eisenglimmer)

= 83 sec.

Mischung II (20 % Eisenglimmer)

= 87 sec.

Mischung ohne Zusatz

= 102 sec.

The solidification times of G-AlSi7Mg are:

Mixture 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 a Increase in thermal conductivity. The isolating effect of in Air present in the pores is increased by increasing the proportions of solid-state conduction, the number of contact points in the grain structure is increased. A change in grain or Sandart shifts the entire system to higher or lower Values (see solidification times in Fig. 5), the basic one The connection remains when adding fine particles (iron mica) but persist.

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

The relationships just explained are shown in Fig. 9 and Fig. 10 approved. Mix I became normal (M1ON) and secondly, highly compressed (M1OH) quartz sand mixture (Q1N) compared.

Mischung I - M1ON

= 83 sec.

Mischung I - M1OH

= 43 sec.

Quarzsandmischung - Q1N

= 102 sec.

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

Mixture I - M1ON

= 83 sec.

Mixture I - M1OH

= 43 sec.

Quartz sand mix - Q1N

= 102 sec.

For higher density forms in connection with iron mica additive the individual grains of sand still have one another larger contact area, the pore spaces are further reduced, the rate of heat removal increases significantly.

Mischung I - M1OH

= 43 sec.

Mischung II - M20H

= 37 sec.

Quarzsandmischung - Q1N

= 102 sec.

The solidification time of G-AlSi7Mg is the lowest with 20% iron mica addition and highly compressed forms (Fig. 11). Here mixture I was highly compressed (M1OH), compared to mixture II highly compressed (M20H) and the normal quartz sand mixture (Q1N) and the solidification rates were measured. They are in G-AlSi7Mg for:

Mixture I - M1OH

= 43 sec.

Mixture II - M20H

= 37 sec.

Quartz sand mix - Q1N

= 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 in any case promoted.

Claims (10)

1. The use of plate-like micaceous iron oxide of a lamellar structure to produce casting moulds, particularly lost casting moulds and cores, bonded both organically and inorganically, to cast castings of non-ferrous, cast iron and cast steel alloys, characterised in that the mould material mixture used for producing the casting moulds or cores, respectively, contains 4 to 90 % by weight of plate-like micaceous iron oxide of a lamellar structure as a mould material additive.
2. The use according to claim 1, characterised in that the mould material mixture contains 4 to 50 % by weight of plate-like micaceous iron oxide of a lamellar structure as a mould material additive.
3. The use according to claim 1 or 2, characterised in that the mould material mixture contains 4 to 20 % by weight of plate-like micaceous iron oxide of a lamellar structure as a mould material additive.
4. The use of plate-like micaceous iron oxide of a lamellar structure to produce mould material coatings for cores and casting moulds, bonded organically or inorganically, to cast castings of non-ferrous, cast iron and cast steel alloys, characterised in that the mixture used for producing the mould material coating contains plate-like micaceous iron oxide of a lamellar structure in a quantity of 0.10-10 % by weight, based on the solids mass of the coating.
5. The use of plate-like micaceous iron oxide of lamellar structure as an additive for exothermic feeders.
6. A mould material mixture for producing cores and casting moulds to cast castings of non-ferrous, cast iron and cast steel alloys, characterised in that the mould material mixture contains 4 to 90% by weight of plate-like micaceous iron oxide of a lamellar structure as a mould material additive.
7. A mould material mixture according to claim 6, characterised in that the mould material mixture contains 4 to 50 % by weight of plate-like micaceous iron oxide of a lamellar structure as a mould material additive.
8. A mould material mixture according to claim 6 or 7, characterised in that the mould material mixture contains 4 to 20 % by weight of plate-like micaceous iron oxide of a lamellar structure as a mould material additive.
9. A mixture for producing mould material coatings for cores and casting moulds, organically or inorganically bound, to cast castings of non-ferrous, cast iron and cast steel alloys, characterised in that the mixture contains plate-like micaceous iron oxide of a lamellar structure in a quantity of 0.10-10 % by weight, based on the solids mass of the coating.
10. Exothermic feeder, characterised in that it contains 0.1 to 20 % by weight of plate-like micaceous iron oxide of a lamellar structure in a non-compressed binder-free form as an additive.

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