CS272833B1 - Foundry mixture for moulds and cores production - Google Patents

Abstract

The mixture, suitable mainly for slightly complicated moulds and cores consists of 100 weight parts of opening material, 0.01 to 0.25 weight parts of naphthalene or octoate of cobalt, vanadium, or manganese and of organic binding agent, and eventually of 0.2 to 1.8 weight parts of iron oxide. It also contains from 0.1 to 2.6 weight parts of liquid polybutadiene with average number molar weight of 1,500 to 10,000 g.moles<-1> containing at least 35 percent by weight of 1.2 addition, which has all the chains terminated with hydroxyl groups. The mixture can also contain methyl-tertiary butyl ether for coating the grains of the opening material and in cores with large width it can contain also sulphur, zinc diethyldithiocarbamate and stearin.

Description

Foundry composition for making molds and cores The composition, especially suitable for more complex molds and cores, consists of 100 wt. parts of grit, 0.01 to 0.25 wt. parts of cobalt, vanadium, or manganese naphthenate or octoate; and an organic binder; 0.2 to 1.8 wt. % of iron oxide. It further contains 0.1 to 2.6 wt. % of liquid polybutadiene having a number average molar mass of 1500 to 1500

10000 g.moi ¹ with a content of at least 35% by weight 1,2 addition having all the hydroxyl-terminated chains. The blend may further comprise methyl tertiary butyl ether to coat the kernel grains and additionally sulfur for the core wall thickness, zinc diethyldithiocarbamate and stearin.

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CS 272 833 Bl

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to foundry compositions for the production of molds and cores formed on the basis of grog and organic binder.

They are still. various types of self-hardening mixtures with organic binders are used for the production of foundry molds and cores. Self-curing mixtures with urea-formaldehyde resin, cured by an acid catalyst, require a high content of binder and hardener in the mixture and the achieved level of strength after curing is not high. A great disadvantage of these mixtures is their short workability in the range of 3 to 10 minutes, since the curing reaction takes place almost immediately after mixing the binder with the hardener. This disadvantage causes great difficulties especially in the production of more complex and complicated cores. The self-curing, acid-cured mixtures with furan resin have a lower binder content in the mixture, but their processability is also short. Another limitation of the use for thermally stressed castings is the impossibility of combining this binder with some non-quartz sands. Another type of blend, an alkyd self-curing mixture can also be prepared with non-quartz sinters, but requires high hardener dosage, has higher hygienic defects and is difficult to access. The regeneration of these mixtures is difficult.

The above-mentioned drawbacks are overcome by a foundry mixture for the production of molds and cores, consisting of 100% by weight. parts of grit, 0.01 to 0.25 wt. % by weight of cobalt, vanadium or manganese naphthenate or octoate; and an organic binder and optionally 0.2 to 1.8 wt. % of iron oxide. The composition of the invention further comprises 0.1 to 2.6 wt. % by weight of liquid polybutadiene having a number average molecular weight of 1,500 to 10,000 g.aol ^-1 , containing at least 35 wt. 1,2 addition having all the hydroxyl-terminated chains. In another aspect, the mixture comprises methyl tertiary butyl ether in an amount of from 0.01 to 12.0 wt. parts, based on 100 wt. parts of polybutadiene. Furthermore, the composition according to the invention may contain from 0.003 to 0.018 wt. 0.003 to 0.018 parts by weight of zinc diethyldithiocarbamate and 0.006 to 0.012 parts by weight of sulfur; % of stearin.

The basic advantage of the foundry composition according to the invention lies in the achievement of a high strength characteristic at a very low binder content consisting of liquid polybutadiene in the composition. When using a quartz slag with a mean grain size of 0.25 mm, a strength of 2 to 4 MPa can be achieved even at a content of 0.2 to 0.4 wt. 5 to 1 Heat a lower binder content than other types of organic binder mixtures. Due to these high bonding properties, the mixture has excellent abrasion resistance, which significantly affects the quality of the castings. The very low binder content guarantees exceptionally good disintegration of the mixture after casting, which greatly reduces the casting cleaning effort and reduces or even eliminates the strenuous physical work of casting. The low binder content makes the mixture much easier to regenerate and greatly contributes to creating the possibility of using low-waste or waste-free technology, thus significantly improving the working and environment. Another advantageous property of the composition is the long pot life of the composition. The mixture can be processed for 1 to 6 hours, which is at least 10 times longer than with known mixtures. This makes it possible to produce complex molds and cores, avoids compound losses, and facilitates the organization of work in the manufacture of molds or cores.

If desired, the mixture can be modified to include methyl tertiary butyl ether, thereby providing excellent coating of the kernel grains, which is important, for example, when preparing the mixture on continuous mixers. In the manufacture of solid cores or molds with a large wall thickness or large volume, a perfect and rapid cure throughout the cross-section of the mixture is provided by a mixture containing additionally sulfur, zinc oxide, zinc diethyldithiocarbamate and stearin.

The advantages of the composition according to the invention can be illustrated by the following examples:

Example 1

A mixture was prepared with the following composition:

k '5 CS 272 833 B1 2 Polybutadiene quartz sand of 5 000 g.mol ^-1 with a number average molecular weight of 45%

1,2 addition, terminated with hydroxyl groups

100 wt. parts

0.4 wt. % of cobalt naphthenate

0.04 wt. part

The mixture was prepared in a wheel mixer by adding polybutadiene to the quartz sand and dispensing the naphthenate after mixing. The mixture thus prepared had the following properties;

workability of the mixture ........... 3h, the strength of 0.6 MPa needed for disassembly was achieved in another 2h, the strength of the mixture after curing was 5.0 MPa in compression.

After curing the cores had a high quality surface, completely free of abrasion. The mixture had excellent disintegration upon topping up. The shelf life of the cores is very long.

Example 2

A mixture was prepared: corundum polybutadiene with an average number molar mass of 2,000 g.mol ^-1 , containing 37%

1,2 addition, terminated with hydroxyl groups, manganese octoate

100 wt. parts

2.5 wt. 0.18 wt. part

The mixture was prepared by adding polybutadiene along with the octoate to the corundum, and then mixing the mixture. The properties of this mixture were as follows: workability of the mixture ............. 5 to 6 h, disassembly is possible according to the size of the mold or core in 10 to 24 h, the strength after spontaneous curing was 9.8 MPa in pressure.

The composition had exceptionally high strength after curing, the surface of the cured composition being completely abrasion-free.

Example 3

A mixture was prepared: quartz sand of polybutadiene with an average number molar mass of 9,000 g.mol ^-1 , containing 36%

1,2 addition, terminated with hydroxyl groups, vanadium naphthenate methyl tertiary butyl ether iron oxide

100 wt. parts

0.8 wt. 0.09 wt. 0.08 wt. 0.5 wt. dilu

The mixture was prepared in a high speed mixer and had a workability of 1.5 h. After a further 1 h, it already had a strength of 0.8 MPa suitable for disassembly. The strength of the mixture after self-curing is high, at 9 MPa in compression.

Example 4

Mixtures with different grogs (quantity in parts by weight) were prepared:

and

CS 272 833 B1 3

chromite 100 - - - zircon 100 - - magnesite -, 00 - - lupek - 100 - flakes and quartz. sand (1: 1) - - 100 ALIGN! polybutadiene of average number molar mass. 4000 g.mol ^-1 containing 40% 1.2 additions with OH-terminated chains 1.0 0.5 1.2 1.8 0.9 Cobalt octoate 0.12 0.05 0.12 0.18 , 0.09 All these mixtures showed a workability of 2 to 3 hours, possibility of disassembly after 4 h and curing strengths of 5 to 8 MPa. Example 5 A mixture was prepared: quartz sand 100 parts by weight polybutadiene with an average number molar mass of 3 000 g.mol ^-1 containing 36% 1,2 addition, terminated with OH groups 0.6 wt. part zinc diethyldithiocarbamate 0.018 wt. part sulfur 0.012 wt. part zinc oxide 0.018 wt. part stearin 0.006 wt. part Cobalt naphthenate 0.050 wt. part

Sulfur, ZnO, stearin, and zinc diethyldithiocarbamate were first dispersed in the polybutadiene terminated by the OH groups. Finally, cobalt naphthenate was added to the dispersion.

The mixture is suitable for cores with a large wall thickness or a large volume, respectively.

Claims (3)

SUBJECT V ϊ N X L E Z U A foundry composition for the production of molds and cores, consisting of 100 wt. parts of grit, 0.01 to 0.25 wt. % by weight of cobalt, vanadium or manganese naphthenate or octoate; and an organic binder, and optionally 0.2 to 1.8 wt. % of iron oxide, characterized in that it contains 0.1 to 2.6 wt. % by weight of liquid polybutadiene having an average number molar mass of 1 500 to 10 000 g.mol ^-1 containing at least 35 # wt. 1,2 addition having all the hydroxyl-terminated chains. 2. A foundry composition according to claim 1, comprising methyl tertiary butyl ether in an amount of from 0.01 to 12 wt. % by weight, based on. parts of polybutadiene. 3. A foundry composition according to claim 1, comprising from 0.003 to 0.018 wt. % of zinc diethyldithiocarbamate and 0.006 to 0.012 wt. % of stearin.