DE2236992A1 - MOLDING AND MOLDING PROCESS - Google Patents

Description

Casting mold and casting process

The invention "relates to molds for the casting of Objects, in particular a coating for casting molds, such as those used for forming battery plates (grids), as well as a casting process.

The molding of battery plates is generally carried out in a semi-continuous manner. One is desirable Casting process that involves molding a plate in one As short a period as possible allowed, in particular during the cooling or solidification of the metal during the Plate formation. A working time of 1 minute can be used to manufacture a plate for a large industrial battery are needed, while 10 to 15 plates in one minute can be made for car batteries. The molded plate must come out of the mold easily and quickly can be removed.

Cast iron is the common material for suitable molds, but it does not meet all of the requirements of any one suitable casting process. In practice one tries therefore, casting molds for battery plates with coatings

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of various kinds to make more suitable. A coating agent that is widely used consists of cork flour and clay, suspended in water and sodium silicate. While such substances are equally effective, they tend to decompose or separate from the mold surface in the course of a continuous casting process. The coating has to be renewed every J or 4 hours, which of course interrupts the casting process and means a severe loss of production .

The invention relates to a coating for a casting mold which has a long service life. The invention also relates to a casting method for battery plates which greatly increases the production rate by reducing the working time.

Another object of the invention is a casting mold with a coating with good flow properties between the molten metal and the casting wall, which makes it easy to remove the allows shaped plate out of the mold.

A further object of the invention is a coating for battery plate casting molds with optimal insulating properties against heat, which enables the plate to be completed in a relatively short time during the cooling and solidification of the molten metal or alloy.

Another object of the invention is a coating for casting molds for battery plates, which makes it possible that the displaced Air can quickly escape from the mold during the casting process.

1 of the drawing is a plan view from above of a section of a battery plate mold with the coating according to the invention, the sprue area for the casting metal and the cavity for the plate being visible;

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Figure 2 is a cross-section through a portion of the mold Fig. 1 .and shows "schematically the inventive Cover in greatly enlarged form;

3 is a photomicrograph of a portion of a mold surface with the coating according to the invention and shows its rough texture, which allows the Air allows during the filling of the mold cavity.

The invention is capable of various modifications of the claims feasible and not limited to the forms described in detail. While the invention can be used advantageously for the casting of battery plates, it is in the same way for the casting suitable for other objects, the casting process corresponding to that for casting battery plates. In the same Way the invention can be used for the pressing of plastics, e.g. B. in the injection process can be used.

The invention accordingly relates to a casting mold with a uniform, firmly adhering coating of a perfluorocarbon resin film, preferably of relatively uniform thickness with a certain amount of heat insulating suspended therein shine. The amount and size of these particles are within certain limits in order to have a mold surface with the to ensure the desired heat-insulating properties and a certain roughness, which makes it possible the displaced air can escape and still not have an unfavorable effect on the surface within acceptable limits Invention is particularly suitable for plate casting processes at relatively low temperatures. During such procedures generally in the range of 37Ί - 482 ° C depending on the type of alloy or other casting material be carried out, it has surprisingly been shown that perfluorocarbon resins such as polytetrafluoroethylene on one for a long time represented a stable and durable coating for casting molds, although such resins are generally not used for

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Purposes at temperatures above 250 ° C are recommended and also are considered unstable at temperatures above about 315 C.

When using perfluorocarbon resin with heat insulating Particles for the mold, it is desirable to clean the mold surface first. This increases the adhesiveness of the coating on the mold surface is improved, especially with cast iron. The surface can be cleaned with suitable solvents and known degreasing agents. The mold is advantageously heated to a sufficiently high temperature beforehand, so that the surface is free of oils, greases and other dirt particles. Suitable temperatures are 585 to 427 ° G with a heating time of about 5 minutes and more.

After the mold has cooled down to room temperature, another preparatory stage can be carried out, namely roughening the surface of the mold by mechanical or chemical treatment exists to further improve the adhesiveness of the coating. This can be done by blowing sand for the purpose of formation take place on a uniform matt surface, z. B. using a sand with a fineness of 60 to 80. After the treatment, the sand is removed by blowing off the treated The surface can then be cleaned further with a solvent such as trichlorethylene.

A coating mixture according to the invention is then made up Perfluorocarbon resin and certain amounts of heat insulating Particles made. A polytetrafluoroethylene resin is preferably used for this purpose is used because such resins are particularly suitable for the present purpose. Are also suitable Mixtures of polytetrafluoroethylene and polymonochlorotrifluoroethylene, Polymonochlorotrifluoroethylene, copolymers of tetrafluoroethylene with hexafluoropropylene, mixtures of polytetrafluoroethylene and polytetrafluoropropylene and equivalents thereof. The perfluorocarbon component must not be adhesive be so that the molded article, e.g. B. a battery plate, can be easily removed from the mold. It must also be inert

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in relation to molten metal, it must also be sufficiently stable versus the melting temperatures.

The particle component of the coating agent must have a certain size in order to give the casting mold surface the necessary roughness to lend the air out of the mold when flowing in of the molten metal or alloy can escape, so that a flawless plate without damaging the structure is shaped. Furthermore, the particles must be thermally insulating in order to melt the metal flow until the mold is filled to keep. The particles must also be chemically inert to the perfluorocarbon component and the treatment temperatures to be stable towards. Talc and cork flour are popular because of their good heat insulating properties and other properties preferred means. Other materials are also suitable such as silica, alumina and diatomaceous earth. One Particle size of about 10 to 80 microns should be applied to ensure uniform roughness of the surface of the mold to obtain, especially taking into account the filling of the mold with the metal, the adhesion of the coating to the mold surface and the life of the coating.

The perfluorocarbon resin and the heat insulating particles must be combined with each other so that one, as short as possible Filling time for the molten metal is reached before it cools and solidifies. The thickness of the coating should be kept as low as possible in accordance with their function. It should be in the range from about 0.038 to 0.0889 mm (1.5 to 3.5 mils) and about 10 to 40 volume percent of the heat insulating particles. The amount of insulating particles, and to some extent also that Thickness of the film depends on the thickness and size of the one to be molded Object. For example, a common industrial battery plate with a thickness of about 5) 08mm use about 10 vol.% Particles while going for a Ordinary size automotive battery plate about 1.52 mm (0.06 inch) thick used about 40% by volume of the particles.

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The coating is expediently sprayed onto the surface of the casting mold. The spraying of slurries of Perfliiorcarbon & arzen is known. The heat insulating particles can be added to a solution of perfluorocarbon resin to form a uniform dispersion. The mixture can then be passed through a stainless steel screen of e.g. §. 0.147 mm hash must be sieved so that no coagulated perfluorocarbon heat-insulating particles get to the spray device. Conventional spraying by suction (without air) or with compressed air can be used. The spraying should be done in such a way that a coating of relatively uniform thickness is created on the mold surface. After spraying, the coating should air dry for a few minutes (about up to 5 minutes) to improve the adhesiveness. B. 93 ° 0 »dries. Curing then takes place at temperatures and dwell times which correspond to the curing of the perfluorocarbon component. Any known type of furnace with direct or indirect gas heating or electrical resistances can be used. The curing temperatures and times are known and can, for. B. for polytetrafluoroethylene at 232 ° C for at least about 20 minutes.

Figures 1 and 2 show a typical mold for battery plates with a coating according to the invention. Stationary mold part 10 has a sprue from above, double cavities with sprue 12 through which the molten metal or alloy flows. Sprue 12 charges the cavities 14, 14 *, two of such stationary mold parts are during casting matched to limit the cavities in between and are separated again after the casting material has solidified, so that the molded panels can be removed from the cavities. The coating 16 (Fig. 2) consists of a continuous film 18 of the perfluorocarbon component and the particles 20 uniformly dispersed therein.

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The photomicrograph according to FIG. 3 of part of a mold surface with. The coating according to the invention at a magnification of jpO shows a relatively uniformly rough surface which enables the air to escape while the mold cavities are being filled. Obviously it is not necessary that the roughness of the surface is absolutely uniform. However, the heat-insulating lights must be distributed sufficiently evenly in the film in order to avoid the formation of "heat spots ¹¹ , which can lead to uneven degrees of solidification, and to prevent uneven escape of the air.

Therefore, according to the invention, the coating is only on the mold surface and applied to the cavities and not to the gate region. The non-isolated injection point acts in this way to lower the temperature of the molten and cast metal or alloy, so that the temperature of the Material is as low as possible when it comes into contact with the coating. This is not only used to extend the Lifespan of the coating, but also shortens the pouring time.

The inventive train can also be in the form of several layers be applied. The first layer can be a perfluorocarbon resin coating exist, which is treated according to the invention in order to improve the adhesiveness to the iron mold. The second layer can then be a glaze coating, which easily adheres to the first layer. In this embodiment, the first layer can expediently have a thickness in Range from 0.0127 to 0.0254 mm and the glaze layer of . 0.038 to 0.0635 mm (0.5 to i mil). In each layer, heat insulating particles may be dispersed in the first layer 5 to 30% by volume and in the second layer 10 to 40% by volume.

Using the following examples, the invention for .die Use in the manufacture of battery plates explained in more detail.

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example 1

An iron mold for making battery plates (139j7 x 127 x 1 »63 mm) was initially used in an electric Oven heated to 399 ° C for 15 minutes. The mold then cooled down Room temperature, then the surface was treated with a sandblasting fan using silica sand with 60 to 80 grain size and cleaned with trichlorethylene.

9 volume percent talc with an average particle size of 30 microns was sieved through a 230 Tyler mesh sieve. The fraction collected on a +400 mesh sieve was dispersed in a 39 complete polytetrafluoro ^{resin solution (11} TFE Primergreen No. 85O - 204- from Du Pont de Nemours & Co), then the solution was heated to about 22 to 27 ° C. The mixture was further homogenized by treatment with a roller in a container. The solution mixture was then sprayed directly onto the surface of the mold with compressed air using a De Vilbiss # 502 device. The coating was air dried for a few minutes and then cured in an electric oven at 34-3 ° C for 2 hours. The thickness of the finished coating layer was about 0.0127 mm.

30% by volume of talc with an average particle size of about 60 microns (obtained by sieving de * talks through a 200-mesh Tyler sieve) were dissolved in a polytetrafluoroethylene resin solution (TFE-enamal black and clear finish No. 351 245 from Du Pont, 4- 1% by volume of resin solids components) and treated as described above. The glaze layer was sprayed on the first layer. After air drying and curing for JO minutes in an electric oven at 399 *
keep.

at 399 ° C a film with a thickness of 0.0635 mm was

A molten one was used to manufacture the battery plate Lead-antimony alloy with about 4 1/2 wt.% Antimony for one temperature fluctuating between 371 and 454 ° C into the mold

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poured. The finished panels had a perfect shape and surface. The mold was used in a 24 hour period There were no signs of peeling of the coating.

Example 2

An iron mold for the production of battery plates with a size of 254 χ 152 χ 2.57 rom was initially used Trichlorethylene cleaned with sandblasting (aluminum oxide grains 80-150 sizes), washed to remove dust and heated as in Example 1 at 399 ° C for 15 minutes.

210 ml "Teflon S 953 - 100" -Polytetrafluoroäthylenharzlösung (Du Pont) with about 33 volume percent resin solids, 7 g cork flour and 50 ml of a common diluent ("1-874-8" from Du Pont) were vigorously about 5 minutes in a slow running "Lightnin Mixer" mixed. The particle size distribution (Tyler) of the cork flour was as follows: +80 meshes - 0.5 % \ -80 + 140-1.4% j -140 + 200 - 36.5 % ', -200 + 325 - ^ 9.0 % and -325 - 12.5 %>

The solution mixture was sprayed onto the mold surface with a device from De Vilbiss TGA No. 502 with compressed air. The coating was allowed to air dry for about 10 minutes and then placed in an electric heater preheated to 316 ° C Oven heated until the metal temperature inside the mold block reached 204 ° C and then 10 minutes at air temperature of 316 ° C heated. The film was about 0.038 mm thick.

Battery plates were then shaped as in Example 1 using a lead-antimony alloy. The panels were both re Form, appearance and surface impeccable. The mold was made used in a 24 hour period, no peeling of the coating was observed.

The life of the coating according to the invention is relative

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long, the heat-insulating properties in accordance with the cooling and plaguing of the molten metal or the alloy are optimal, so that a very short working time with the formation of plates with perfect »shape and Surface is achieved. The finished panels can be easily removed from the mold.

Claims: 309808/0818

Claims (13)

Expectations 1. Casting mold for the production of objects from one Melt flow with mating sections that form an internal cavity corresponding to the object to be molded delimit, with sprue and channel for melt flow to the 3-form cavity, with the mating sections can be separated to take out the molded article, characterized by a coating of perfluorocarbon resin having a thickness of about 0.0581 to 0.0889 mm (1 x 5 - 3 x 5 mils) including at least the inner Cavity of the mold covered and in which about 10 - 40 % By volume. heat insulating particles with a size of 10 to 80 microns are dispersed, which have sufficient heat insulating properties to solidify the To prevent melt until it has at least completely filled the mold cavity. 2. Casting mold according to claim 1, characterized by a first Coating of perfluorocarbon having a thickness of about 0.0127 to about 0.0254 mm, (0.5-1 mil) the at least covers the inner cavity and in which about 5 to 30 Volume percentage of heat insulating particles with a Large from about 10 to 80 microns are dispersed, and a second perfluorocarbon coating with a thickness of 0.0381 to 0.0635 mm (I.5 - 2.5 mils), the first Coating covered and in which about 10 to 40% by volume of heat-insulating particles with a size of about 10 to 80 Micron dispersed. 3. Casting mold according to claim 1, characterized in that the perfluorocarbon consists of polytetrafluoroethylene. 4. Casting mold according to claim 1, characterized in that the heat-insulating particles made of talc, silica, aluminum »- nium oxide, dietetic earth and cork flour. 309808/0818 5 · casting mold according to claim 1, characterized in that the heat insulating particles are present in an amount of at least 25% by volume. 6. A method of forming an article by pouring a melt flow into one through a pair of adjacent ones Surface cavity formed, solidification of the melt and removal of the molded article from the Cavity, characterized in that before the casting of the Melt flow into the cavity on the surfaces a coating of a perfluorocarbon resin with a thickness of 0.0581 to 0.0889 mm is applied, in which about 10 to 40% by volume of heat insulating particles are dispersed, wherein the particles are sufficiently thermally insulating to prevent the melt from solidifying before it enters the cavity at least completely filled out. 7. The method according to claim 6, characterized in that the Perfluorocarbon is polytetrafluoroethylene. 8. The method according to claim 6, characterized in that the thermal insulating particles of talc, silica, aluminum oxide, Diatomaceous earth and cork flour are made. 9 · The method according to claim 6, characterized in that the coating is sprayed onto the surface « The patent attorney 309808/081 8 , 13. Blank page