CS213460B1 - Coated mixture for making the shell moulds and cores - Google Patents

Abstract

The invention relates to the use of methylolfenols in the manufacture of coated foundry based blends sands, phenol formaldehyde resins novolac type, hexamethylentetrarain and separators for foundry production shell molds or cores. Using of methylolfenols increases the reactivity of the resinous po.iiva, thereby avoiding declining blends in the manufacture of shell molds or cores, uniform curing is achieved and improving the strength of the shells or kernels. A higher effect is achieved by addition a solution of methylolfenols, which is preferably mixes with sand before adding binder and others component. Per 100 parts by weight Novolak is dosed at a maximum of 10 weight parts of a 40% solution of methylolfenols.

Description

(54) Coated mixture for the production of shell molds and cores

The invention relates to the use of methylphenols in the production of coated foundry sands, novolak type phenol-formaldehyde resin, hexamethylenetetrarain and separators for the production of foundry shell molds or cores. The use of methylphenols increases the reactivity of the resin binder, thereby preventing the mixture from falling off during the manufacture of shell molds or cores, achieving uniform cure and improving the strength of the shells or cores. A higher effect is obtained by adding a solution of methylphenol, which is preferably mixed with sand before the addition of a binder and other components. A maximum of 10 parts by weight of a 40% solution of a mixture of methylolphenols is dosed per 100 parts by weight of novolak.

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The present invention relates to a coated composition for the production of shell molds and cores and its purpose is to eliminate scrap in the manufacture of molds and cores.

Non-coating phenolfermaldehyde resins are used to produce the coated composition.

Woven resins. These resins are thermofusible and, without the addition of a hardener, which is generally haxamethylenetetramine, are not capable of polycondensation reactions leading to crosslinking. In terms of further processing, i.e. the production of shells or cores, considerable demands are placed on the quality of the coated compositions. The coated mixture must melt on contact with a metal mold heated to approx. 270 ° C and form a shell without surface defects in a short time. The shell must have sufficient strength to withstand the casting pressure of the cast metal.

The strength of the shell is influenced by the amount of resin binder, but for economic reasons it is advantageous to use as little binder as possible. In the manufacture of shells, especially if they are of a larger size, the mixture often falls off, one of the causes of this defect, which is to weaken a portion of the shell with the risk that the metal will flow through the wall, is usually insufficient reactivity of the binder system. To produce the shell, the coated mixture is heated to the heat of the core or model plate. This results in a gradual melting and curing of the resin. If the melted binder has insufficient viscosity and reactivity, it will not retain the weight of the melted composition 4 before it can cure the mixture.

Waste solutions are looking for ways to increase the reactivity and viscosity of the binder system. ⁶ often obtained by the addition of various substances ovliviujících viscosity and reactivity of the resin, improvement is sought by selecting a shape and grain size and odtřiva below. In general, it is desirable to have a binder layer on the surface of the grog grain having a high viscosity and a high reactivity under the conditions to which it is exposed in contact with the pattern plate. Such a task is quite demanding, since at the same time a low viscosity of the binder is required to form binder bridges between the grains of the coated composition.

The aforementioned disadvantages are overcome by a coated composition for the production of shell farms and cores consisting of 100 wt. grit parts, 2.5 to 5 wt. parts of phenolfermaldehyde novolak resin. %, 0.3 to 0.75 wt. % of hexamethylontetramine, 0.1 to 0.2 wt. parts of calcium stearate according to the invention, the principle of which consists in

0.01 to 1 part by weight of methylolfenols.

Methylolfenels-phenolalkohels are low molecular weight compounds resulting from the addition of phenol and formaldehyde in an alkaline environment. The mixture according to the invention utilizes a mixture thereof in an aqueous solution which is low viscous, which allows it to completely encapsulate the individual grit blades better than the viscous resin binder, or even penetrate into the capillary depressions on the grit burr surface. Due to the increased coating temperature, a chemical reaction occurs between the methylphenols and the phenel-formaldehyde resin to increase the molecular weight of the resin binder. This results in an increase in viscosity, a shortening of the flow length and an increase in the binding point of the coated composition. During the production of shells, the mixture thus prepared does not fall off. The dosage of methylphenol is chosen with respect to the desired properties of the shell, usually within the range of 1-3% on the phenol-formaldehyde resin.

The effect of methylphenols in the production of the coated mixture was verified using the lily spacing of phenolfermaldehyde novolak resin, quartz sand with an average grain size of 0.17 mm,

213 460 hexamethylenetetramine and calcium stearate, in the preparation of several mixtures with the addition of methylolphenol solution according to Example 1, an average hot flexural strength of 5.0 MPa and a cold flexural strength of 7.84 MPa were found. In the preparation of the mixture under the same conditions, but without the addition of a solution of methylphenols, an average flexural strength of 4.22 MPa and a cold 7.45 MPa were found.

In tests with a mixture with the addition of a solution of methylolphenols, it was confirmed that this mixture had better reactivity. This resulted mainly in complete removal of the drop and better curing of the entire cross-section of the shell. In the case of shells prepared without the use of methylphenol, about 10% of the amount produced was eliminated; There were no cases of shell rupture in the tests and no changes in surface quality or dimensional accuracy. The use of methylphenol did not lead to increased laboriousness or deterioration of hygiene conditions.

Bringing the coated composition of the invention is to eliminate scrap in the manufacture of the cores due to the drop of the composition. Also improved mechanical properties are achieved, which allows to reduce the amount of binder in the composition while achieving the same mechanical properties.

Examples of embodiments of the coated composition according to the invention:

Example 1

To prepare the coated mixture, the ingredients are metered in the following order:

330 parts of quartz sand, 0.5 parts by weight of a 40% aqueous solution of methylphenol, 1.6 parts by weight of hexamethylenetetramine, 0.5 parts by weight of calcium stearate, 19 parts by weight of a 65% alcohol solution of phenol-formaldehyde novolak resin.

By blowing hot air, the solvent is evaporated, the lumps are broken and the coated mixture is sieved and cooled.

Example 2 In order to prepare the coated mixture in a mixer, the raw materials are metered in the following order:

330 parts by weight of quartz sand, a preformed mixture of 19 parts by weight of a 65% strength alcohol solution of phenol-formaldehyde novolac resin with 0.5 parts by weight of a 40% aqueous solution of methylphenols, 1.6 parts by weight of hexamethylenetetramine, 0.5 parts by weight of calcium stearate.

The procedure is the same as in Example 1.

Claims (1)

SUBJECT OF THE INVENTION Coated mixture for the manufacture of shell molds and cores consisting of 100 parts by weight of grog, 2.5 to 5 parts by weight of phenol-formaldehyde novolak resin, 0.3 to 0.75 parts by weight of hexamethylenetetramine and 0.1 to 0.2 parts by weight of calcium stearate, characterized by The composition of claim 1, wherein the additive comprises from 0.01 to 1 part by weight of methylphenol.