Black wash for producing mould coatings

Details Black wash for producing mould coatings Black wash for producing mould coatings

1995-01-05

1996-11-12

Bell, Mark L.

Compositions: coating or plastic

Coating or plastic compositions

Molds and mold coating compositions

106 3822, 501 80, 501 87, 501 88, 501 95, 501 96, 501 99, B28B 736

Patent

active

055735800

DESCRIPTION:

BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION

This is a 371 of international application No. PCT/DE94/00555, filed May 17, 1994.
The invention relates to a refractory wash or generally to a mould coating material which is used in foundry work for coating shaped foundry parts such as moulds, cores and patterns.
Ready-to-use refractory washes are suspensions of finely divided refractory to highly refractory inorganic materials in a carrier liquid, which are applied to the shaped parts by an application method matched to the particular case, for example by painting, spraying, casting or dipping, dry there and thus form the desired coating.
The finely divided refractory to highly refractory inorganic materials are the components of a refractory wash which determine its function in foundry work. They are also described as "base materials" and are suspended in the carrier liquid with the aid of suspension agents. The carrier liquid also contains dissolved binders which serve to fix the base-material particles on the surface of the shaped part after removal of the liquid. If necessary, wetting agents, antifoaming agents and bactericides can also be included.
Typical examples of base materials include (individually or in admixture with another) mineral oxides such as corundum, magnesite, mullite, quartz and chromite, furthermore silicates such as zirconium silicate, olivine and chamotte and also coke and graphite. The suspension agents used are swellable sheet silicates or cellulose derivatives which are capable of incorporating water. The carrier liquid can be water or a solvent such as petroleum ether, methanol, ethanol, isopropanol or isobutanol, and suitable binders are starch derivatives such as dextrins, lignin derivatives such as lignosulphonates, natural resins, synthetic resins or synthetic polymers such as PVA, the binders being selected according to their solubility in the carrier liquid.
The refractory washes are supposed to fulfil the following functions in foundry work: ribs, scabs, penetration or burning-in. materials.
The functions 1 and 2 can generally be fulfilled well by the combination of various suitable base materials, and the function 4 is only a fringe area since metallurgically active refractory washes, for example containing sulphur, are only sometimes used. However, the function 3 still requires action.
The function 3 is of increasing importance, today and in the future, because all sand moulds and cores bonded with synthetic resin tear open at high temperature as a result of the expansion of the sand, and the melt then penetrates into the mould or the core. The removal of the resulting surface flaws from the casting is very difficult and time-consuming.
Mould coating materials which counteract these defects have already been developed and used, and are described, for example, in the references J. Levelink, Gie.beta.erei, volume 66, 1979, pp. 456-458 and D. Bartsch, Report of Technical Forums, 58th World Foundry Congress, Krakow 1991.
The mode of action of such coatings is based on the use as base material of platelet-shaped sheet silicates, such as kaolinite, pyrophyllite, talc and mica, which can be more readily deformed under the action of a tensile stress. In addition, the mineral materials are combined in such a way that temporary softening phases are formed, which likewise improves the ductility of the coating.
However, a disadvantage which has been found is that these coatings have a very dense texture and thus do not have sufficient permeability for gases which are formed in the thermal decomposition of the binders of the sand moulds. This results in a high gas pressure being built up in the mould and/or in the core, which pressure, as soon as it exceeds the metallostatic counterpressure, leads to boiling of the metal and to gas bubbles. In addition, the pressure rise can also make parts of the coating flake off, which pieces then again occur as inclusions in the casting.


BRIEF DESCRIPTION OF THE DRAWING

The attached figure shows the gas pressure curve of a coldbox core coated with

REFERENCES:
patent: 3804701 (1974-04-01), Bognar
patent: 4012262 (1977-03-01), Patterson et al.
patent: 4174331 (1979-11-01), Myles
patent: 4332618 (1982-06-01), Ballard
patent: 4950627 (1990-08-01), Tokarz et al.

Affiliated with

Also associated with

Rating

Black wash for producing mould coatings does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Black wash for producing mould coatings, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Black wash for producing mould coatings will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-559353