GB2048143A

GB2048143A - A method for hardening foundry moulds and cores

Info

Publication number: GB2048143A
Application number: GB8012535A
Authority: GB
Original assignee: Instytut Odlewnictwa
Current assignee: Instytut Odlewnictwa
Priority date: 1979-04-28
Filing date: 1980-04-16
Publication date: 1980-12-10
Also published as: DE3014631A1; GB2048143B; IT1143140B; PL215279A1; IT8048428A0; FR2454859A1

Abstract

A method for hardening foundry moulds and cores comprises hardening a sand layer by freezing its liquid components as a result of the contact of the sand mixture with the pattern of a moulding box or with a core box cooled to a temperature lower than that of the solidification temperature of the liquid sand components.

Description

SPECIFICATION A method for hardening foundry moulds and cores This invention relates to a method for hardening foundry moulds and cores used for casting cast iron, steel and non-ferrous metal alloys.

There are known methods for hardening foundry moulds and cores which comprise mechanical packing of sand, or chemical, possibly also thermal, treatment of the sand components.

A method is also known, among others, from the International Modern Foundry 1 977 No. 4, p.5, which refers to making foundry moulds and cores and comprises hardening the sand by freezing it through with a liquid gas passed through the moulds made of a mixture of sand, water and binder. Thus prepared moulds are stacked and kept frozen until molten metal is poured therein.

There is also known from Polish Patent Application No. P-201 140 a method of hardening a foundry mould or core by blowing it with a liquid, or with a freezing gas, or by placing the mould or core in an appropriate freezing device at a temperature up to 223 K.

In each of the methods known at present, the hardened-through sand contains large quantities of the binder which is quite often toxic, and if it is to be re-used, an expensive and laborious process of reclamation is required.

The present invention provides a method for hardening foundry moulds and cores by freezing the liquid components contained in a sand mixture, wherein the sand composition is introduced into a moulding box wherein a metallic pattern is placed or into a metallic core box, the said pattern or core box being cooled to a temperature below the solidification temperature of the sand liquid components.

Thus there is provided a method for hardening foundry moulds and cores by hardening a layer of sand mixture by freezing its liquid components as a result of contact of the sand with a pattern or with a core box cooled to a temperature lower than that of the solidification temperature of the sand liquid components.

A metallic pattern is cooled to a temperature lower than that of the solidification temperature of the sand liquid components, and then it is placed inside a moulding box whereinto the sand is introduced by means of a commonly applied method. In the case of making cores, a core box is also cooled to a temperature lower than that of the solidification temperature of the sand liquid components, and then the sand is introduced thereinto by means of a commonly applied method.

After a determined lapse of time, a hardened sand layer of required thickness is obtained. The thickness of the hardened sand layer is controlled by the temperature of the core box or of the pattern, or sometimes by the time during which the sand remains on the cold pattern or inside the core box.

A layer of frozen sand of a thickness amounting to as little as only 20-30 mm provides a strength sufficient to withstand the metallostatic pressure which occurs when pouring small and medium size castings.

Patterns and core boxes are cooled either constantly, or periodically, for example by immersing the pattern in a cooling medium, while the inside of a core box is cooled by pouring a liquid medium thereinto. Such a medium is characterized by a temperature lower than that of the solidifcation temperature of the sand liquid components. It is preferable to use liquid nitrogen as the cooling medium.

Application of the method according to the present invention for hardening foundry moulds and cores enables savings to be obtained in the amount of the cooling medium used in comparison with other methods used so far. A sand composition of a lower initial strength may be used, and the time of moulding may be shortened in comparison with the methods applied so far. Also, a sand composition hardened by the method according to this invention is re usable without necessity for its further reclamation. Moulds and cores hardened by the method according to the present invention are characterized by very good knocking-out properties.

The invention will be further described with reference to the following illustrative Examples.

EXAMPLE I A brass pattern weighing 2 kg was cooled by immersing it in liquid nitrogen at a temperature of 770K for a time of 3 minutes. During this time the pattern reached a temperature of 1730K. Next, each part of the pattern was placed in a separate moulding box and a sand mixture was shot thereinto, the sand mixture having the following composition: zircon sand - 100 parts by weight; H20 -3 parts by weight. After a lapse of 3 minutes from the moment of filling the box with the sand mixture, the pattern was removed therefrom. The thickness of the hardened sand layer was 30 mm. After assembling the boxes, a mould was obtained into which was then poured cast steel.

EXAMPLE II A core box was cooled to a temperature of 1 730 K by pouring into the core box liquid nitrogen at a temperature of 770K for a time of 3 minutes. Next, the cooled core box was filled with a core sand mixture of the following composition: zircon sand - 100 parts by weight; H2O-3 parts by weight. After a lapse of time of 3 minutes the core box was disassembled and ready cores were obtained wherein the thickness of the hardened layer was 50 mm. Next, thus prepared cores are placed in a mould and cast iron was poured therein.

The method for hardening foundry moulds and cores described in this invention is applicable to both batch and piece production of castings.

Claims

1. A method for hardening foundry moulds and cores by freezing the liquid components contained in a sand mixture, wherein the sand composition is introduced into a moulding box wherein a metallic pattern is placed or into a metallic core box, the said pattern or core box being cooled to a temperature below the solidification temperature of the sand liquid components.

2. A method as claimed in Claim 1, wherein the said pattern is cooled to a temperature below the solidification temperature of the sand liquid components by previously immersing the pattern in liquid nitrogen.

3. A method as claimed in Claim 1 , wherein the said core box is cooled to a temperature below the solidification temperature of the sand liquid components by pouring liquid nitrogen into the working cavity of the core box.

4. A method for hardening foundry moulds and cores by freezing the liquid components contained in a sand mixture, wherein the sand composition is introduced into a moulding box wherein a metallic pattern is placed, the said pattern being cooled, preferably by immersing it previously in liquid nitrogen, to a temperature below that of the solidification of the sand liquid components, the time of the pattern remaining in the mould being dependent on the required thickness of the hardened sand layer, while in the case of hardening foundry cores, the sand composition is introduced into a metallic core box cooled most preferably by pouring into the working cavity of the said core box liquid nitrogen, the time of the sand composition remaining in the cavity being dependent on the required thickness of the hardened sand layer.

5. A method according to Claim 1, substantially as herein described in either of the foregoing Examples.