CS253482B1 - Compound for foundry molds and cores - Google Patents

Abstract

The solution relates to a mixture for the production of foundry molds and cores, where the primer is bonded with an alkyd resin. The essence of the solution is a mixture containing a foundry primer, a sicculated alkyd binder and a hardener, where the sicculated alkyd binder is a resin with an acid number of 5 to 20 mg/KOH/g, a hydroxyl number of ?5 to 40 mg KOH/g and the hardener is boric acid and/or sodium tetraborate and/or their combination with polyisocyanate.

Description

The invention relates to a composition for the production of foundry molds and cores, wherein the grit is bonded with an alkyd resin.

At present, the use of self-setting mixtures with alkyd resin, grit and hardener is widely used in the manufacture of molds and cores. Alkyd resins are generally siccated or added separately to the curing accelerator compositions and have a hydroxyl number in the range of 50-140. Polyisocyanate or, more rarely, boric acid / inorganic oxidizer mixtures are used as hardeners. These curing methods have some drawbacks that limit their use. In the case of the isocyanate, it is especially impossible to effectively control the course of curing by changing its content and using a mixture of boric acid with oxidizing additives, in addition to the mixing problem, especially the very low compressive strength - max. 2 to 3 MPa.

These disadvantages are overcome by the foundry mold and core composition according to the invention, consisting of an abrasive, a binder and a hardener. The principle of the invention consists in that the mixture contains per 100 wt. 0.7 to 5 wt. parts of a siccated alkyd binder which is an alkyd resin having an acid number of 5 to 20 mg KOH / g and a hydroxyl number of 25 to 40 mg KOH / g, and 0.1 to 3 wt. parts of a hardener consisting of boric acid or sodium tetraborate or a combination thereof with a polyisocyanate, for example hexamethylene diisocyanate or diphenylmethyldiisocyanate or diphenylmethane diisocyanate.

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The advantage of this system is that the use of sodium tetraborate alone achieves a fast curing process without adverse environmental temperature. binders · The cured mixture reaches the highest values of cold strength even after thermal exposure.

The composition for the manufacture of foundry molds and cores according to the invention can be prepared on both continuous (continuous) mixers and batch mixers, i.e. in the foundry of conventional wheeled, ram vertical or horizontal · For mixing in general, the dosing procedure is as follows:

1 · dry foundry sanding

2. powder additives (boric hardeners, iron oxide etc.)

Binder - alkyd resin

Hardener - polyisocyanate

Example 1

Sand quartz sand Provodin 036 · .. 100 wtct «parts alkyd binder ........«. ···· ........... 1.6 mass «parts polyisocyanate .. ......................... 0,4 parts by weight of boric acid ................. ........ 0.32 parts by weight

Mixing procedure:

grist, boric acid, binder, polyisocyanate ·

The mixture prepared in this way achieves a compressive strength of up to 12 MPa after 24 hours curing and is suitable for medium steel castings and heavy gray cast iron castings.

Example 2

Crushed chromite ...... ···· alkyd binder ....... ·········· polyisocyanate .................. ........

boric acid .............................

Mixing procedure: see Example 1.

100 parts by weight 0.9 parts by weight 0.13 parts by weight 0.23 parts by weight

The mixture according to example 2 is suitable for demanding steel castings. Its workability is 40 to 60 min.

Example 3,253,482

Quartz sand grit Shaid.Humence W 27 ····· 100 hmet * parts alkyd binder ······························ 1 , 7 parts by weight of sodium tetraborate .................. ··· ··· · · 0.45 parts by weight

Mixing procedure:

grit, sodium tetraborate, binder.

This mixture is suitable for mass castings with gray cast iron and all types of non-ferrous metal castings. · Workability of this mixture is 20 to 30 min.

Example 4

Sand quartz sand Šajd.Humence Š 27 ..... 100 wt. Parts iron oxide (POgO ^) ············· · ··········· 1 wt. part alkyd binder ...................... · ······ · · · 1.2% by weight «parts boric acid ......... ..................... 0.18 parts by weight

Mixing procedure:

grist, iron oxide, boric acid, alkyd binder ·

So the prepared mixture is suitable for all cores dried at temperatures of 200 to 250 ° C for castings of gray cast iron and non-ferrous metals, its workability is more than 120 min ·

Claims (1)

Mixture for the production of foundry molds and cores, consisting of grit, binder and hardener, characterized in that the mixture contains per 100 wt. · parts of a siccated alkyd binder which is an alkyd resin having an acid number of 5 to 20 mg KOH / g and a hydroxyl number of 25 to 40 mg KOH / g and 0.1 to 3 wt. parts of a hardener consisting of boric acid or sodium tetraborate or a combination thereof with a polyisocyanate, for example hexamethylenediisocyanate or diphenylmethyldiisocyanate or diphenylmethane diisocyanate