DE19609539A1 - Additives for foundry sands - Google Patents

Description

The invention relates to compositions containing Foundry sand and additive, the additive comprising cryolite. The additive is used in the manufacture of foundry cores and -forms, especially those bound with synthetic resins are used to prevent casting defects.

Stands for the production of foundry cores and molds Foundries use a number of different processes for Available. In the series core production are predominantly Synthetic resins used as binders. Among the known ver driving take the gas-hardening processes, especially that Ashland cold box process, an outstanding position. In addition, thermosetting processes (hot box, warm Box and croning processes) as well as the cold-curing process ren (use of acid-curing furan and phenolic resins, Po lyurethane cold resins, ester-curing resols) are important.

The advance of new processes for the production of cast iron pieces with higher piece weights stands with growing  Degree of difficulty the increasing tendency to mold sanding against casting defects.

This is based on the one hand on the chemical, physical and technological properties of this molding material and others on their scattering and interactions. A shape material failure and as a result the emergence typi Casting errors are possible, for example, through:

• 1. Development of tension (leaf ribs, rat tails, Schülpen);
• 2. thermal changes (burns, mineralization, Blowholes, edge bubbles);
• 3. elastic or plastic deformations (dimensional deviations gene, cracking);
• 4. Symptoms of instability such as breaking, kinking, bursting etc. (sand inclusions, floating points, dimensional deviations).

Such errors can be largely avoided avoid if the structure or properties of the molding material fixed on the stress caused by the casting metal during casting, Cooling and solidification can be coordinated.

A z. B. frequently encountered casting error is under the Term "leaf veins" known, being susceptible to this mistake in the individual core manufacturing processes is quite different. The appearance of leaf veins means increased costs due to overtime as they are partly have to be ground away at great expense. But it can also cause the casting to be unusable if the Leaf ribs are in inaccessible places.

It is therefore of great economic importance that the Ent are from above casting defects, in particular To minimize or completely eliminate leaf ribs.  

In practice, various measures are taken, e.g. B.

• - Selection of a binder system with low leaf ribs gung,
• - Use of sands that do not have any structure when heated undergo change (quartz crack) (e.g. zircon sand, Chrome ore sand)
• - finishing the cores
• - Use of suitable additives.

Each of these measures, taken individually or in combination However, there are limits to both technical nature as well as cost-related.

A very effective and therefore often followed path, the Finishing is to prevent the occurrence of leaf ribs the cores, d. H. applying a fire-proof coating. However, this process constitutes one for the core production not inconsiderable cost factor. In many foundries Therefore, there is an increasing desire for a waiver on finishing. One often comes for cost reasons The use of expensive special sands is out of the question in practice (W. Thury and H. Sagmeister, Gießerei-Praxis 22 (1978), S. 359).

Since it has been shown that the problem is usually from Binder cannot be dissolved alone, comes the Ver of additives is of increasing importance. The stake iron oxide as an additive to foundry sand mixtures is far spread and the effectiveness of this measure was established examined. For example, B. K.H. Caspers 1971 in Gießerei (1971) 21, pp. 652-658 results from Untersu Research on the influence of iron oxide on the shape fabric structure and properties of furan resin-bonded Molding sand for cold hardening in terms of appearance or avoid casting errors. It was found that the Thickness of the oxide binder sheath that reverses the grains of sand ben, basic sand properties necessary for the emergence  of casting defects are decisive; under consideration The stress can be viewed together addition of sand mixtures over the level of iron oxide set can be controlled.

Also described for. B. Berndt et al. in foundry (1972) 3, pp. 61-71 the effect of various iron oxides the formation of leaf veins in the hot box process put castings. It was found that for good Effectiveness an iron oxide with at least 95% Fe₂O₃ + FeO or a specific surface area of at least 10 m² / g is necessary; however, these are usually too high for cost reasons Requirements for an application in practice.

S. Hasse and G. Pokorny describe in Gießerei-Rundschau (1995) 1/2, pp. 8-12 the addition of natural iron oxide "MIOX" (natural iron mica, mined and prepared by the Kärntner Montanindustrie GmbH, Klagen ford) to bentonite-bound molding material. The same authors provide more in Gießerei-Rundschau (1995) 3/4, pp. 5-12 Insights into the effects of natural iron oxide in form and core molding materials on the surface quality of castings pieces.

However, iron oxide also has disadvantages: Due to its Ba it reduces the processing time of cold box bin on the other hand, it contributes greatly to the contamination of the core manufacturing tools at. The latter applies above all to finely ground, synthetic iron oxide.

Nevertheless, iron oxide is often part of kommer currently available additives. Other effective substances are e.g. B. wood flour, minerals, carbohydrates, carbon, natural Liche oils, mineral oils, waxes, natural and synthetic resins etc.

DM. Gilson et al. report in Modern Casting (May 1995), P. 38 about casting results with combination additives on mine  base. The authors put 5% additive in the sand to, but they also mention the possibility of a 10% Use of the additive.

Although the additives on the market are available in many Reduce the occurrence of leaf veins still a significant need for improved additives, to ensure the highest possible production security most.

It is therefore the object of the present invention to create new ones To provide additives for foundry sands that Occurrence of casting defects such. B. leaf veins still effekti ver reduce.

According to the present invention, it has now been found that the Addition of cryolite or cryolite-containing additives to the Foundry sand does the job.

The high effectiveness of cryolite enables a reduction amount of additive. This leads to an improvement in Cast surface, as conventional, especially wood flour-like ad ditics due to gas formation during pyrolytic decomposition can cause increased surface roughness.

The additive according to the invention is used in an amount of 0.1 to 10 wt .-% based on the sand added. Preferably who who uses 0.1 to 7.5% by weight; is particularly preferred the range of 0.1 to 5% by weight.

According to the invention, cryolite can be used alone as an additive are or mixed with at least one component from Mi minerals, wood flour, organic fiber material carbohydrates carbon, natural oils, mineral oils, waxes, Natural and synthetic resins. Suitable minerals are e.g. B. Colemanite, mica and iron oxide. A suitable wood flour is z. B. beech wood flour. Polyethylene fibers are an example for suitable organic fiber material and as coals  hydrate can e.g. B. Starch can be used. Suitable natural Che oils are castor oil and linseed oil, while petroleum one Example of suitable mineral oils is. Come as waxes e.g. B. polyethylene wax and petroleum jelly in question. As a natural resin component in the additive can e.g. B. balsam resin can be used while as synthetic resins e.g. B. phenolic resin solutions come into question men. Carbon is used as an additive component in addition to cryolite used, he can e.g. B. in the form of coke and / or graphite and / or coal dust are used.

Recycled foundry sand can also be used here as sand be used. The additives according to the invention can both in the gas-hardening process (e.g. cold box Process) as well as in the warm box process, the hot box Process, the croning process or the cold curing Processes (e.g. polyurethane cold resin) can be used. There the cold box process is particularly susceptible to leaf ribs education, the experiments below were based on this Procedure concentrated.

Examples

So-called step wells were used to carry out all tests Gel made from quartz sand and a han using the cold box process standard cold box binder (Isocure 300 OS4 / Isocure 600 OS4) manufactured by Ashland-Südchemie-Kernfest GmbH. The additive was 0.5% by weight and 2.4% by weight, respectively on sand, depending on the composition of the additive.

The step cones were also covered with a synthetic resin (Pep Set 1505 / Pep Set 602 from Ashland-Südchemie Kernfest GmbH) bound forms inserted and with cast iron with ball cast graphite (GGG 50) at 1398 to 1430 ° C.

The step cone is a well-known test specimen with which Help the thermal load when casting on a core can be examined (see also D.M. Gilson et al., Modern Casting, May 1995, pages 38-40). The thermal The burden is lowest at level 1 and at level 6  against it the strongest. The number of leaf ribs decreases half from level 1 to level 6.

example 1

3000 g quartz sand F33 (Quarzwerke GmbH, Frechen) are in a laboratory wing mixer (from Vogel & Schemmann). 15 g (0.5% by weight) of cryolite (synthe table cryolite powder, ABR Handel GmbH, Bottrop) added and mixed homogeneously (mixing time: 2 minutes). Subsequently become 21 g with further stirring within 15 seconds (0.7% by weight) Isocure 300 OS4 (binder component I) was added and mixed for another 45 seconds (total mixing time with bin component I: 1 minute). After that, among others Stirring within approx. 15 seconds 21 g (0.7% by weight) Isocure 600 054 (binder component II) added and others 45 seconds mixed (total mixing time with binder component I and II: 2 minutes).

After removal from the mixer, the so produced Molding material mixture in the so-called shooting cylinder one Core shooter (Röper H5) transferred and from there by dry compressed air (approx. 4 bar) into the tapered cone stuff shot. By gassing with a triethylamine air Mixture (2 ml amine, 2 bar compressed air; fumigation time: 1 minute) the binder is cured.

The step cone is inserted into an outer mold for casting. The cavity between the core and the outer shape is filled with the river filled with metal.

After cooling, the casting of adhering sand is ge cleans and to assess the effectiveness of the additive Leaf veins counted on the individual stages of the Have formed the casting.

The result is shown in Table I.  

Example 2 Production of the additive:

1000 g cryolite and colemanite (Portabor B 250; NV Mineral treatment Uikhoven, Belgium) are consecutively filled with stirring in a laboratory wing mixer and to the Ho Mogenization of the two components for about 10 minutes long mixed.

15 g (0.5 wt .-%) of this additive are used in the manufacture of the step cone used as described in Example 1 ben, is done.

The result is shown in Table I.

Example 3 Production of the additive:

1100 g beech wood flour (55% by weight; HBS 150/500; Rettenmaier & Sons, wooden mill) and 520 g cryolite (26% by weight) successively with stirring in a laboratory wing mixer fills. To do this, continue stirring within approx. 2 minutes 120 g castor oil (6% by weight; Alberdingk Boley, Krefeld) and then 260 g within approx. 10 minutes a commercially available synthetic resin solution (Novathen 180) from Ashland-Südchemie-Kernfest GmbH (13% by weight). For homogeneous distribution of the individual components is still approx. Mixed for 20 minutes.

72 g (2.4 wt .-%) of this additive are used in the manufacture of the step cone used, otherwise as in Example 1 described.

The result is shown in Table I.

Example 4

The additive is prepared analogously to Example 3, but in this example it has the following composition:
Beech wood flour (45% by weight), cryolite (19.5% by weight), mica (19.5% by weight; Suzorite Mica, Suzorite Mica Products, Canada) castor oil (6% by weight) and one commercially Resin solution available from Ashland-Südchemie-Kernfest GmbH (13% by weight).

The preparation using 72 g (2.4 wt .-%) Addi tiv and evaluation of the step cone takes place as above described; the result is shown in Table I.

Example 5

The additive is prepared analogously to Example 3, but in this example it has the following composition:
Beech wood flour (55% by weight), cryolite (13% by weight), mica (13% by weight), castor oil (6% by weight) and a commercially available synthetic resin solution from Ashland-Südchemie-Kernfest GmbH (13 % By weight).

The preparation using 72 g (2.4 wt .-% Addi tiv and evaluation of the step cone takes place as above described; the result of the evaluation is Table I too remove.

Comparative Example 1

The step cone is produced as in Example 1 described.

However, 72 g (2.4% by weight) of BR additive are used as additives 028/1, a commercially available additive free of iron oxide from Ashland-Südchemie-Kernfest GmbH.

The result of the assessment of the casting is shown in Table I. remove.

Comparative Example 2

The step cone is produced analogously to the example 1, but 72 g (2.4% by weight) of additive BR 85 are used as additives  R, a commercially available additive containing iron oxide from Ashland-Südchemie-Kernfest GmbH.

The number of leaf veins that have occurred is shown in Table I. remove.

Comparative Example 3

The step cone is produced analogously to the example 1, but 15 g (0.5% by weight) of colemanite are used as additives used.

The number of leaf veins that have occurred is shown in Table I. remove.

Comparative Example 4

72 g (2.4% by weight) of the following mixture are used as an additive:
Beech wood flour (55% by weight), colemanite (26% by weight), castor oil (6% by weight) and a commercially available synthetic resin solution from Ashland-Südchemie-Kernfest GmbH (13% by weight).

The additive and the step cone are produced analogous to the procedures described in Example 3. The result is shown in Table I.

Comparative Example 5

72 g (2.4% by weight) of the following mixture are used as an additive:
Beech wood flour (55% by weight), mica (26% by weight), castor oil (6% by weight) and a commercially available synthetic resin solution from Ashland-Südchemie-Kernfest GmbH (13% by weight).

The additive and the step cone are produced analogous to the procedures described in Example 3. The result is shown in Table I.  

Table I

Casting results

From Table I it is clear that in the comparison try d. H. when using cryolite-free additives, from a thermal load of level 2 sheet trip pen occur while using Ad ditive ver at a thermal load of level 6 isolated leaf veins occur.

Claims (8)

1. Composition containing foundry sand and additive, characterized in that the additive comprises cryolite. 2. Composition according to claim 1, wherein the additive min at least one component selected from minerals, wood flours, organic fiber material, carbohydrates, Koh lenstoff, natural oils, mineral oils, waxes, nature contains resins and synthetic resins. 3. The composition of claim 2, wherein the carbon in the form of coke and / or graphite and / or hard coal dust is present. 4. Composition according to one of claims 1 to 3, wherein the additive in an amount of 0.1 to 10 wt .-% based on the sand. 5. Additive containing cryolite and at least one compo selected from minerals, wood flour, organic Fiber material, carbohydrates, carbon, natural Oils, mineral oils, waxes, natural resins and synthetic resins. 6. Use of cryolite as an additive in the manufacture of foundry cores and molds. 7. Use according to claim 6, wherein the additive is an ad ditive according to claim 5. 8. Use according to claim 6 or 7, wherein the manufacturer development of the foundry cores or molds by means of gas hardening the process, the warm box process, the hot box Process, the croning process or by means of cold tender procedure takes place.