FR2622131A1 - Foundry liquid die dressing, especially for continuous centrifugal casting - Google Patents

Abstract

Process for the preparation of a liquid foundry die dressing of the type consisting of bentonite gel, sodium silicate, silica and optionally a red ochre dye, which consists, on the one hand, in mixing in the following proportions: - 40 to 50 % of water, - 25 to 30 % of bentonite gel, - 10 to 15 % of silica, - less than 1 % of red ochre, - and 10 to 15 % of sodium metasilicate solution and then, on the other hand, in filtering, if necessary, this so-called "base die dressing". Application: especially to continuous centrifugal casting of engine liners.

Description

LIQUID FOUNDRY POTTING, ESPECIALLY FOR CASTING
CONTINUOUS CENTRIFUGAL.

The present invention relates to a process for the preparation of a liquid coating used in foundries in the case of a centrifugal process in particular. This coating allows one to obtain a heat-insulating layer between the mold and the centrifuged cast iron.

This coating has been used since 1954 by the applicant for the manufacture of tubes, for example engine liners according to a process known as centrifugation;
The Applicant thus uses a liquid "poteyage" coating which is made from various products - bentonite gel, - sodium silicate, - silica, - a red ocher dye (for basic poteyage).

These various elements are added with water and mixed together according to a certain percentage and a well defined process. The elements are all characterized, in particular, by a very precise purity and particle size. The so-called "poteyage" product thus used, also used under very specific conditions, must be constantly stirred.

The deposition of this coating is carried out by spraying with pressure type guns, the coating is brought in by pressure piping, from the storage pot to the spray guns. This deposit, prolific inside a tool (shell) brought to a temperature of 4000c, loses its water, hardens and gives a thin layer of bound silica. This layer provides and protection of the tool (improvement of the tool's resistance from 1000 to 1500 castings), and a thermal function thus giving the conditions for a correct metallurgical quality of the product (structure and hardness).

This does not preclude compliance with the manufacturing processes (quality of the basic materials, quality of the metal, casting temperature, inoculation, correct and regular thermal regime, etc.).

The invention therefore provides a process for preparing such a liquid coating which makes it possible to significantly improve the behavior of the tools and to obtain optimum product quality by reducing foundry and machining waste.

According to an essential characteristic, this process consists on the one hand, in mixing in the following proportions - 40 to 50% of water, - 25 to 30% of bentonil gel, - 10 to 15% of silica, - less than 1% of red ocher, - and 10 to 1596 of sodium metasilicate solution then, on the other hand, to filter if necessary this so-called "base coating" mixture.

According to another particularity, it consists, in order to obtain a so-called "cleaning-maintenance" mixture to be applied to the base layer, to mix - 60 to 7% of water, - 25 to 30% of silica, - and less than 10 % bentonil gel.

 Other features and advantages of the invention will emerge more clearly from the description which follows of a preferred embodiment, given by way of nonlimiting example, with reference to the appended drawings in which - FIG. 1 represents a section d 'a tool showing the distribution of a coating layer; - Figure 2 shows a top view of a centrifuge installation comprising a potage station - and Figure 3 shows a view of products obtained at the outlet of this centrifuge installation.

According to the centrifugal casting process implemented by the applicant by means of an installation shown in FIG. 2, the shells 20 used and illustrated in FIG. 1 comprise two poteyages - one of which is basic, placed on a new shell ; this operation is carried out outside the centrifuge site (item 7); some repairs may be necessary during this lifetime at station 8 for opening the shells - the other for maintenance, carried out before each casting at
Production equipment (item 2).

The base coating is applied to the half-shells preheated to around 4000C. Several layers are deposited using a gun on the problem areas of the tooling (rounded), special care is given to the removal of this poteyage. The thickness of the final base layer is around a few tenths of a millimeter.

The maintenance coating is applied to the existing base layer before each casting (item 2 in Figure 2) in one tool. This application is made using a lance in the spinning centrifuge head. This lance is calibrated. The temperature of the tools is also around 4000C at this point. This maintenance layer is around 1/10 mm.

To prepare this basic soup, the following products are mixed in the following proportions - 40 to 509 Ó of water, - 25 to 30, ó of bentonil gel (this gel is prepared beforehand with a small amount of bentonil less than 30XI, and water leaving to swell for a few hours), - 10 to 15% of silica, - less than 1% of red ocher; - 10 to 159; of sodium metasilicate solution (this solution is prepared beforehand with water and sodium metasilicate at around 10%).

This preparation made, it is sometimes necessary to filter it.

The maintenance product which is applied before each pouring is composed as follows - 60 to 70% of water, - 25 to 30% of silica, - and less than 10% of bentonil gel.

These various preparations for obtaining the base and maintenance poteyae must undergo a certain mixing time.

As can be seen from FIG. 3, a raw pouring tube 20 obtained with this liquid coating according to this contrifugation process has an optimal quality, essential for reducing the number of foundry and machining rejects. In this example, the tube 20 provides four factory shirts 30;

Claims (4)

CLAIMS 1. Process for the preparation of a liquid foundry coating of the type consisting of bentonite gel, sodium silicate, silica and optionally a red ocher dye, characterized in that it consists of a hand, to be mixed in the following proportions - 40 to 50% of water, - 25 to 30% of bentonil gel, - 10 to 15% of silica, - less than 1% of red ocher, - and 10 to 15 % of sodium metasilicate solution then, on the other hand, to filter if necessary this mixture known as "base coating". 2. Method according to claim 1, characterized in that it consists, in order to obtain a mixture called "maintenance coating" to be applied on the base layer, to be mixed - 60 to 70 zó of water, - 25 to 30 % silica, - and less than 10% bentonil gel. 3. Method according to claim 1, characterized in that this rel of bentonil is prepared beforehand with less than 3% of bentonil and I water, leaving to swell for a few hours. 4. Method according to claim 1 or 3, characterized in that this sodium metasilicate solution is prepared beforehand with water and approximately 10% sodium metasilicate.