DE1569117B1 - Thermosetting molding compound - Google Patents

Description

1 2

The invention relates to thermosetting mixtures ins- molding material have the disadvantage that solid cores especially for making casting molds for the expansion during casting a crack use in the mass production of casting in the core can lead to a shells and cores for casting metal. Grain of the cast leads.

In the manufacture of metal castings are generally 5 It has now been found that casting shells and Molds and cores from a granular, refractory core can be made in a much shorter time, Material is used, the grains of which are combined with one another by combining a mixture to produce a shape utilizes a thermosetting synthetic resin binder which uses a phenolic novolak as a binder are. According to a known process contains resin with a high proportion of 2,2'-bonds, for the production of such casting shells or cores io Such resins can using soluble is a flowable mixture of a granular metal borate of bivalent metals as catalysts refractory material, usually sand, to be made one

powdered phenolic novolak resin and a hardener to demix a shell molding process

for the Novqlak resin, e.g. B, hexamethylenetetramine, used simple mechanical mixtures dropped onto a stencil, which is based on a powdered phenolic resin and a granular, It is customary to avoid the temperature above the melting point of the Novo refractory material lakarzes is located. By thus melting granules of the refractory material with the resin of the novolak resin in the area of the heated to coat by removing the refractory, granular Surface, the sand particles in this area material are mixed with the resin while this is in tied together. Excess mixture is caused by the liquid state. The liquid state can escape the stencil is removed and the obtained neither by applying a solution of the resin Shell by heating in an oven before removing in a suitable solvent or by removal the stencil hardened. This procedure leads the coating process at increased is commonly referred to as a shell molding process. Temperatures at which the phenolic resin is liquid, To be achieved when using a simple mixture 25. The latter method is preferred, Entities arising from powdered resin and sand, since hot sand is generally easily accessible To avoid mixing, it is customary to remove the grains of sand and those with the recovery of the solvent, to coat with the resin binder and this solvent losses, fire hazard and toxicity To use the mixture in the shell casting process. the disadvantages associated with the solvent avoided

The shell molding process has the advantage that you turn 30. When using a reactive resin of the type described, a relatively small amount of the mixture is required to produce the mold and, furthermore, that its reactivity entails the risk that fine details of the stencil will harden prematurely during the coating process. These can be reproduced. However, the shell has danger can be avoided by 1 to 3 ° / ₀ casting the disadvantage that, to prepare 35 "Water is added to the mixture of sand and resin, each finished shell much an initial coating is achieved relatively solbald. The added water evaporates during the layer of resin-bound sand on the coating and is not part of the heat stencil, only about 15 to 30 seconds required hardenable molding compound.

is a subsequent oven hardening of about 40. The thermosetting molding compound contains the granular, 70 to 90 seconds duration is needed, and during this refractory material, either blended or timed The stencil cannot be used to produce further layers with a phenolic novolak resin. Bowls are used. For mass production Usually and preferably contain

From casting shells it was therefore necessary to use a larger molding composition according to the invention than granular, refractory Number of stencils to use, resulting in a 45 material sand. However, you can also partially consider the sand Increase in operating costs. wise or entirely by another granular, refractory In order to mass-produce cores, a newer material has to be replaced. Suitable such substances are Process under the name "hot box process" z. B. zircon, quartz and aluminum oxide, known. In this process, a flowable die in the thermosetting mold according to the invention

Mixture of a granular, refractory material containing novolak resins consist predominantly and a resin binder, advantageously by means of granular phenol nuclei, which are connected to one another via the 2,2 'positions in the primed air in a ring at elevated temperature. That is, the held box is fed in. With this method, phenol nuclei are in the o-position to the phenolic ones, there is no post-curing in an oven, hydroxyl _{groups are linked to one another via —CH 2} groups and the use of a urea-formaldehyde 55 is linked.

Resin binder enables the core to be cast from the novolak resins previously used in the foundry eject in about 15 to 30 seconds. That turns their bonds between the phenolic nuclei However, the hot box process has the disadvantage that it is p-position to the "phenolic hydroxyl group." previously found necessary for its successful implementation (such novolak resins originated, for example, in was, nitrogen-containing resins of urea-formaldehyde- 60 using oxalic acid as a catalyst) or hyd type to use. When using the bonds connecting the rings into one after this process with these binders her ring in p-position and in another ring in Cores provided for the production of knot-o-position were located (such novolak resins were formed In the form of cast iron, however, pinholes occur. z. B. when using sulfuric acid as a catalyst This process is because of its high strength 65 sator).

of the unfired phenolic novolak resins used to make molds, the cores of which are in o-positions

Mixture for the production of core shells connected to phenolic hydroxyl groups suitable. In addition to the required larger amount, and therefore mostly free p-positions are closed

have the phenolic hydroxyl groups, using catalysts directing in the o-position, z. B. zinc borate. Other useful catalysts in the manufacture of novolak resins with 2,2 'bonds are zinc acetate, zinc benzoate, and cadmium acetate. The making of this Novolak resins are not part of this invention. It takes place in accordance with the usual procedures.

The novolak resin is preferably finely ground beforehand, e.g. B. so far that there is a sieve of about 0.053 mm clear mesh size happened. Then it is mixed with the refractory in a suitable manner granular material, together with one which is at least sufficient to harden the resin when heated Amount of hexamethylenetetramine.

However, the granular, refractory material can also be coated with the resin by known methods. For example, the solid resin can be fed into a mixing device containing the refractory material previously heated to a temperature above the melting point of the resin and mixed. Then you can add water and then ψ hexamethylenetetramine and continue mixing until the viscous mass begins to become crumbly, whereby no hardening reaction occurs.

The mixtures so produced are free flowing, but combine quickly when in contact with brought to a heated surface. They are therefore known for the production of core shells Process suitable, after which the refractory, coated with the resinous binder or mixed Material is fed into a heated box and remains in it until the refractory material is up is fused to the required depth, whereupon the excess, d. H. the non-fused material, can flow out of a cavity in the box.

The amount of resin contained in the molding compounds is about 2 to about 6 percent by weight, based on the refractory Material related. Before making the molds, the granular, refractory material was mixed with the phenolic If the novolak preparation is coated, the amount of novolak resin used may be less than if a simple mixture of refractory material

»And powdered novolak resin is used. Is therefore carried out a pre-coating, so are preferably used about 3 percent by weight and of a simple mixture is about 4.5 ° / ₀ novolac resin, based upon application to the refractory material.

The hexamethylenetetramine is preferably used in an amount of about 10 to about 15 percent by weight, based on the resin, used. However, amounts from about 7 to about 20 percent by weight can be used will. The mixture used to make the molds can also contain other additives, e.g. B. wax, Bright ore, graphite and the like, which act as mold release agents, contain.

example

4000 g of clay free quartz sand was placed in a high power mixer, heated to 130 ° C and at that temperature, with mixing, 120 grams of a phenolic novolak resin with a predominant one ο, ο structure together with 3 g of a waxy mold release agent (reaction product of stearic acid and polyamide) were added and mixed for 1.5 minutes. The novolak resin was made of phenol and formaldehyde in the ratio of 1 mole of phenol to 0.66 mole

Formaldehyde has been produced in the presence of zinc borate. 48 g of water were then added and mixed for another 3 minutes. 14.5 g of hexamethylenetetramine and a further 2 g of des were then added Mold release agent added. After an additional 2 minutes of mixing, the mixture began to become crumbly and was then emptied, sieved through a sieve with a mesh size of 0.776 mm and in a pan mill Mill for 1 minute, a fine, free-flowing product being obtained.

The product was tested by looking at the mixture brought to a surface located at 200 ° C and determined the curing time of a 6.35 mm thick dish.

Comparative examples

For comparison, other comparable mixtures were tested under the same conditions, but these Contained novolak resins produced under catalysis with oxalic acid and predominantly one ρ, ρ-structure or those under catalysis were made with sulfuric acid and predominantly had an ο, ρ structure. The results showed that the coated sand produced according to the invention, as described in the example, is approximately 25 seconds hardened, while those with novolak resins, those under catalysis with oxalic acid or with sulfuric acid coated sands hardened in about 80 and about 70 seconds, respectively.

In contrast to the molding compositions customary to date, the compositions according to the invention require significant amounts less hardener to harden them. The molds and cores made therefrom are also essential higher temperature resistant, and finally the corresponding iron castings have almost none Pin holes on their surface.

To prove the first two advantages mentioned, the following experiments are given:

40
% Hexamine
to 3.5%
Resin-resistant
fabrics Tensile strength
examination at a
Temperature of
Specimen from tensile strenght
ortho-linked
Phenolic resin (6.3 mm
strong)
Usual
phenol
resin 45
12.0
12.0
8.0
6.9 20 ° C
200 ° C
200 ° C
200 ° C 131
126
118
84 120
97
61
38

The table shows that significantly less when using ortho-linked phenolic resin Hardener is required than a normal phenolic resin. It also shows that the tensile strength of the material produced from the molding compositions according to the invention significantly at elevated temperature is better and ultimately also decreases significantly less depending on the temperature.

Claims (2)

Patent claims: 1. Thermosetting molding compound for the production of casting molds and cores from a refractory Filler and a novolak binder, characterized in that the molding compound as a binder a novolak resin, the phenol nuclei of which are predominantly in the o-position to the phe- Molic hydroxyl groups are linked together in an amount of about 2 to 6 percent by weight, based on the filler, and hexamethylenetetramine as a hardener for the novolak resin in an amount between about 7 and 20 percent by weight, based on the resin, the filler optionally being coated with the novolak resin. 2. Thermosetting molding compound according to claim !, characterized in that this compound is a mixture in which the novolak resin contained therein has a particle size of at most 0.053 mm , 3, thermosetting molding compound according to one of claims 1 and 2, characterized in that the Molding compound additionally contains a mold release agent.