GB2241658A - Drying used sand, before cleaning by attrition - Google Patents

Abstract

A process is described for the recovery treatment of predominantly clay-bonded used foundry sand to allow its re-use in place of new sand. In such processes the sand grains are repeatedly accelerated and decelerated and are rubbed against one another by a combined impact stress and shearing stress so as to free the adherent shell from the sand cores and the shell material thus freed is removed pneumatically. According to the invention the process further comprises the step of setting the water content of the old sand before the stress treatment at most one per cent by weight. The low water content avoids the formation of lumps during the recovery process.

Description

- t L E> =1 C> S RECLAMTION The present invention concerns a process for

the reclamation by a regeneration treatment of predominantly clay-bonded casting old sand for its reuse instead of new sand.

Used foundry sand consists of re-u le cores or grains coated with a shell formed during the casting process. This shell consists generally of binding substances and additives. In order to separate the shell from the core processes are known in which the sand grains are repeatedly accelerated and decelerated and are rubbed against one another by combined impact stress and shearing stress and are thereby freed from the shell adhering to the core of the sand grains. A pneumatic dust-removal device leading to the outside is used to remove the pulverized shell material.

For the complete release of the sand grains from the casing it is absolutely necessary for this pulverised shell to be drawn off. If the dust is not removed the effect of the impact stress and shearing stress on the remaining grains is damped and the regeneration treatment is greatly impaired.

It has been found that, in spite of an intensive drawing-off of the dust formed, efficient processing is not achieved if small lumps form. These lumps can be crushed and comminuted by means of a beater or stirrer, but this only succeeds after a certain time. Hence the through-put capacity of such a regeneration installation is reduced. 30 It is therefore desirable to provide a process of the type described above which allows efficient regeneration of old sand and keeps constant the capacity of the sand regeneration installation. According to the invention there is provided a process for the treatment of predominantly clay-bonded used foundry sand to allow its re-use in place of new p sand, in which the sand grains are repeatedly accelerated and decelerated and are rubbed against one another by a combined impact stress and shearing stress so as to free the adherent shell from the sand cores, and the shell material thus freed is removed pneumatically, further comprising the step of setting the water content of the old sand before the stress treatment at at most one per cent by weight.

The fact that the sand lumps or the dust lumps are crushed by a stirrer after a certain time indicates that the mechanical action of the stirrer is being gradually converted into a thermal action, eventually causing the breakup of clumps of sand. However, it is not economical to supply heat to the sand or dust lumps in this way because it is a waste of the electrical energy used to drive the plant.

It is therefore more sand before the start of treatment. This drying efficient process in a should reduce the water regeneration treatment cent by weight. Under formation results and installation maintains i advantageous to dry the old the impact and shear stress step can be done by a more separate plant. This process content so that before the it lies at the most at one per these circumstances no lump the used sand regeneration its full capacity.

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Claims (2)

Claims

1. Process for the treatment of predominantly clay-bonded used foundry sand to allow its re-use in place of new sand, in which the sand grains are repeatedly accelerated and decelerated and are rubbed against one another by a combined impact stress and shearing stress so as to free the adherent shell from the sand cores, and the shell material thus fr is removed pneumatically, further comprising the step of setting the water content of the old sand before the stress treatment at at most one per cent by weight.

2. Process according to claim 1, in which the step of setting the water content of the sand Is carried out in a separate container from the stress treatment container.

Published 1991 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 I RH. Further copies may be obutined from Sales Branch. Unit 6. Nine Mile Point. Cumfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques lid. St Mary Cray. KerA.