DE1223108B - Process for the production of casting molds - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

German class:

Number:

File number: N 24907 VI a / 31 c
Filing date: April 30, 1964
Opening day: August 18, 1966

The invention relates to a method for producing casting molds, in particular for casting of metal objects.

It is known that such casting molds, inter alia, from layered walls by a method can be produced in which the first layer of clothing is applied to a model by means of a gellable Suspension of a fine-grain, heat-resistant powder in a solution of a binder, e.g. Am a silica sol or in a solution of polysilicates or polysilicic acids, e.g. B. by Dip, applied, a coarser heat-resistant layer is applied to the still moist layer. Powder applied will, e.g. B. by sprinkling, the applied layer is gelled, onto the resulting layer a second layer is applied by, for example, the whole in a gellable suspension of the The same powder used to make the first layer is immersed in a silica sol the second layer, which is still moist, is sprinkled with a coarser, heat-resistant powder is, the second layer is gelled and then in the same way several layers with one Composition equal to that of the second layer can be applied until a wall (shell) is sufficient Strength is achieved. After the last layer, if necessary after sprinkling the still moist layer with heat-resistant powder that has been gelled, the mold is dried and / or subjected to a heat treatment, whereupon, if after sufficient hardening of the casting mold, the model is removed, then a ready-to-use mold is available.

The layers to be applied to the first layer of clothing are hereinafter referred to as support layers designated.

In the following description and identification of the invention "Silicic acid sol" is also a solution of polysilicates, with more or less alkyl radicals in the polymer molecules, e.g. ethyl residues, and understood as a solution of polysilicic acids. solutions of polysilicates and polysilicic acids are often saponified, ζ. B. with hydrochloric acid, organosilicates, z. B. tetraethyl silicate or polymerized ethyl silicate obtained in alcoholic solution. A silica sol can also be prepared by dialysis of a solution of water glass. In this If desired, the basic solution can be acidified by adding acid.

In the production of casting molds with the historical process for the production of casting molds

Applicant:

N.V. Philips' Gloeilampenfabrieken, Eindhoven

(Netherlands)

Representative:

Dipl.-Ing. H. Zoepke, patent attorney,

Munich 5, Erhardtstr. 11

Named as inventor:

Gerrit Lucas Wiggerink, Emmasingel, Eindhoven (Netherlands)

Claimed priority:

Netherlands May 2, 1963 (292 265)

There are various ways of moving the walls.

In known methods, for. B. dried the first layer of clothing before putting on this one first support layer is applied. This then causes the backing layer to gel brought that they z. B. ammonia vapor is exposed. Further layers of support will be then gelled in the same way. In the case of the molds made in this way arise during drying, which takes place with simultaneous combustion of escaping alcohol vapor can, if an alcoholic suspension is used to apply support layers has been, multiple bubbles on the mold surface. This disadvantage can be caused by very slow Drying of the molds can be suppressed.

A disadvantage of such a longer drying process is that the drying apparatus or the Drying room used for a long time.

The inventor has now come to the knowledge that the occurrence of the above-mentioned. Bubbles with related to the described manner of gelation of the support layers, in which the gelation takes place from the outside of the layer inwards, and has surprisingly found that Even if the molds dry quickly, the appearance of bubbles can be avoided if that Gelling of the first support layer takes place from the inside out.

609 610/336

3 4

Accordingly, the invention relates to an aqueous solution, the 700 g ammonium process for the preparation of a granular acetate or ammonium acetate and acetic acid to mass of bound, heat-resistant material together about 700 g and z. B. 600 g ammonium existing casting mold with layered wall, with acetate and 100 g acetic acid or 125 g ammonium dem on a model a first layer of clothing 5 acetate and 525 g acetic acid contain,
a gellable suspension of a fine-grained, one can also use the buffer solutions mixed with other metal-resistant powders in a solution of a binding solution. Such liquids by means of, in particular in a silica sol, are z. B. water-soluble alcohols and especially brought, if desired to the still moist solutions of binders, eg. B. colloidal silica layer a coarse-grained, heat-resistant powder io acid, polysilicates, polysilicic acid, polytitanates or is applied, the layer is gelled on these polyzirconates. Preferably, a solution of the binding agent powder in a solution of a binding agent is used for mixing by means of a gellable suspension of a heat-heated solution with a buffer solution, which is used in the first supporting layer to be applied, at least one supporting layer. If one is used, the applied support layer or binder in a buffer solution will also gel the support layers or the adhesion of the first clothing layer and the and the shape obtained before or after removal of the first support layer is improved.
Model until the shape example (B) has hardened sufficiently. A buffer solution that is also dried on. This method has according to the binder contains, z. B. by mixing an invention on the peculiarity that at least the 20 of 130 ecm polyethylene silicate (40 percent by weight first support layer by means of a on the SiO ₂ ), 30 ecm water, 13 ecm hydrochloric acid (1 normal) first layer of gelling agent and 14 ecm ethanol existing mixture that is gelled from the inside. Stirred for 20 minutes at room temperature

In carrying out the new process according to the (ethyl silicate is saponified), with 12 ecm

Invention, the gelling agent is applied to the first 25 of an aqueous solution containing 125 g of ammonia per liter

the layer of clothing is applied before it contains the sodium acetate and 575 g of acetic acid,

first support layer is applied. The similar solutions that 10 to 40 ecm of the usual

Application is preferably carried out after drying. Buffer solutions contained in the product provided good ones

the first layer of clothing. Results.

The gelling agent can be applied in a manner known per se. B. by immersion, layer is applied if this has already getrock-basting or splashing. net, this can be done in a more dilute solution

The gelling agent to be used has worn off a bit.

Depending on the composition of the suspension which is to be applied by the method according to the invention, the first support layer can be used to gel the first support layer. Is proficient as a binder in the sus- table. This can be done for a factory pension by hydrolysis, e.g. B. of ethyl silicate implementation of the process of importance. mit_ acid, e.g. B. hydrochloric acid, obtained silica sol Of further importance is that when used, one will use a gelling agent, turning of buffer solutions can achieve that the gelling is only able to reduce the acidity of the suspension a few time after the application of the. Preferably, the method begins after the layer to be gelled. This time is used from the invention of such a suspension. It depends on the composition, the concentration in the suspension in question as a binder and the amount of buffer solution used.
If silica sol is used, which is obtained by dialysis of So was in the example described below, in water glass, a gelling agent will be used as a buffer, 175 g of ammonium acetate and the aqueous level containing 525 g of acetic acid per liter to increase the acidity of the suspension can. It is also possible to use a solution obtained in this way to gel the first supporting silica sol by adding acid in 10 minutes. The acid was thereby applied, whereby the measure of the first case is applied to the outside of the layer by spraying with one. 50 buffer solution gelled.

A buffer is preferably used as the gelling agent. When using solutions that have the same

solution used. For this purpose, a special buffer amount of electrolyte comes in, but a larger amount

Solutions in question that only contain compounds that contained ammonium acetate was the time mentioned

those in the case of heat treatment by evaporation, are significantly shorter. It was 6 minutes for one

optionally after previous decomposition, from 55 solution, the 200 g of ammonium acetate and 480 g

removed from the mold. Suitable buffers are acetic acid contained per liter,

especially those who are affected by an acid. The gelling of the outside of the support

a degree of dissociation of about 10 ~ ^5, z. B. vinegar layer can be brought about in a manner known per se

acid, propionic acid or butyric acid, and ammonia, e.g. B. by means of ammonia vapor and special

are derived. 60 or by spraying the applied layer

If the support layer to be gelled is made with a buffer solution. This also applies to the wide

an acidic suspension is formed, the support layers to be applied are preferred,

wise a solution of ammonium acetate or am- The drying of the prepared according to known methods

monium acetate and acetic acid are used. 'Casting molds made must be relatively slow

Preferably, buffer solutions with a high 65 are made to prevent bubbles from forming on the mold surface

Concentration used, especially those to be avoided as much as possible.

which contains more than 500 g of electrolyte per liter

th. Examples of very suitable buffer solutions are present invention is that the drying of the form

men can take place much faster than with the known methods. So were z. B. with the procedure Molds obtained according to the invention, which consisted of five layers, dried in 5 minutes. This resulted in molds with regularly smooth mold surfaces. To be made of the same materials Molds produced according to the known method give shape surfaces of comparable quality the permissible drying time is 120 minutes.

The method according to the invention is applicable to the production of casting molds which are used for production of castings are suitable by various processes. The procedure is special for the production of molds used for precision casting, e.g. B. according to the lost model method. This process uses a melt-out model used, the one made of wax, plastic, a low-melting metal or a low-melting Alloy. The method can be used particularly advantageously in the production of casting molds, which are used in casting processes in which there are several, at least two Share existing, detachable molds are used.

For the first layer of clothing, for. B. a known mixture of a fine-grained, heat-resistant Powder and a gellable silica sol are used to apply a first layer of clothing to a model in the manufacture of casting molds is usable. Such a mixture consists essentially of a fine-grained powder heat-resistant material, such as. B. aluminum oxide, sillimanite, chamotte, zirconium silicate or quartz, suspended in a silica sol, which can change into the solid state by gelling. Farther the mixture can e.g. B. one or more plastics, surfactants, emulsifiers and / or contain defoaming agents.

A mixture (A) to be used for applying a first layer of clothing can e.g. B. can be obtained by stirring a mixture of 1300 ecm of polyethylene silicate (about 40 percent by weight SiO ₂ ), 300 ecm of hydrochloric acid (1 normal) and 1800 ecm of ethanol for 20 minutes at room temperature and the resulting mixture 70 ecm of a 20 percent by weight dodecylnaphthylsulfonate sodium Solution, 10 ecm octanol, 3500 ecm water, 300 ecm hydrochloric acid (4 normal) and 25 kg fine-grain, heat-resistant powder, e.g. B. zirconium silicate (particle size 10 to 60 μ) are added.

The mixture to be used for the first layer of clothing can be used in a known manner, e.g. B. by Immersion, pouring or spraying, can be applied to a model.

If this is done using split, detachable casting molds, the model and the model plate advantageously with a thin layer of a solvent, e.g. B. Vaseline or silicone oil, be provided.

For the heat-resistant powder that is applied to the still damp first layer of clothing, z. B. by scattering, z. B. an aluminum silicate (particle size 250 to 600 μ) can be used.

The drying of the first layer of clothing sprinkled with heat-resistant powder can be carried out in a known manner Way. When using a wax model, it is preferable to work slowly and in relatively moist air (ζ. Β. 80 to 90% relative humidity) dried at room temperature. In the case of a model made of metal or wood, as is the case when using the split, from Molds that can be detached from one another can be dried at a higher temperature.

Applying the first support layer and sprinkling it with heat-resistant material when it is damp Powder can be done in a manner similar to the first layer of clothing.

The method according to the invention is explained in more detail below using an example.
A metal model attached to a model plate was immersed in a mixture similar to the mixture (A) given above and then, while still moist, sprinkled with aluminum silicate (particle size 250 to 600 μ). The first layer of clothing thus applied was air-dried. The dried layer was wetted by immersing it in a buffer solution according to Example (B) given above. The first support layer was applied to this by immersing in a suspension of 7 kg of zirconium silicate (particle size 10 to 60 μ) in a mixture that was stirred for 20 minutes at room temperature from 2600 ecm of polyethylene silicate (40 percent by weight SiO ₂ ), 600 ecm of water, 260 ecm hydrochloric acid (1 normal) and 280 ecm ethanol was obtained.

The still moist support layer was sprinkled with aluminum silicate powder as above. Thereon it was sprayed with a buffer solution containing 600 g of ammonium acetate and 100 g of acetic acid per liter contained. Five further support layers with the same composition as the first one were applied in the manner described. After sprinkling with aluminum silicate, as above and the subsequent gelling of the final support layer was the result Form with simultaneous combustion of escaping alcohol vapor in the warmth (oven temperature 1000 ° C) dried.

Claims (10)

Patent claims: 1. Process for the preparation of a from a granular mass of bound, heat-resistant Material existing casting mold with a layered wall, in which on a model a first clothing layer of a gellable suspension of a fine-grained, heat-resistant Powder applied in a solution of a binder, in particular in a silica sol If desired, a coarse-grained, heat-resistant powder is applied to the still moist layer is applied, the layer is gelled, on this by means of a gellable suspension of a At least one support layer is applied to heat-resistant powder in a solution of a binder, the applied support layer or support layers is / are gelled and the shape obtained before or after removal of the model up to sufficient hardening is dried, characterized in that at least the first layer of support from within is gelled by means of a gelling agent applied to the first layer of clothing. 2. The method according to claim 1, characterized in that that the gelling agent is applied to the dried first layer of clothing. 3. The method according to claims 1 and / or 2, characterized in that as a gelling agent a buffer solution is used. 4. The method according to claim 3, characterized denotes overall ίο that a buffer solution is used which has been obtained using an acid with a degree of dissociation of about 10 ~. ⁵ 5. The method according to claims 3 and 4, characterized in that a buffer solution is used, which only contains compounds that are removed from the mold during heat treatment removed. 6. The method according to claims 4 and 5, characterized in that a buffer solution is used which contains at least 500 g of electrolyte per liter. 7. The method according to claims 3 to 6, characterized in that as a buffer solution a solution of ammonium acetate or of ammonium acetate and acetic acid is used. 8. The method according to claims 1 to 7, characterized in that with the gelling agent a binder is applied at the same time. 9. The method according to claim 8, characterized in that the binder in the The binder used in the first backing layer is used. 10. The method according to claims 3 to 9, characterized in that the binder in the buffer solution is dissolved.