SE515012C2 - Feeding of casting powder - Google Patents

Abstract

A granulated casting powder is used for the continuous casting of molten metals, which powder essentially consists of substantially spherical particles. This is distributed upon the molten metal only by means of gravity from a superjacent container (1), through a valve (3) and a transport tube (5), and out upon the molten metal. The casting powder "flows" with a constant flow independently of the filling height in the container (1), the desired flow being adjusted with the valve (3).

Description

This layer loosens by itself on cooling the string with water sprinkles and falls to the bottom of the cooling tower.

From the above described, it is easy to see the importance of the casting powder supply taking place at a steady pace without any interruptions. Usually, this casting powder feed is done manually in such a way that an operator feeds on casting powder from a tub or a tub with a straight line, the required amount being assessed visually by the operator. In addition to the fact that this is a dusty, monotonous and not completely risk-free work, it requires constant care. Furthermore, it is easy to misjudge the required amount of casting powder, which can mean sudden breaks in the layer between the string and the mold wall. Therefore, for a long time there has been a strong desire for an automation of the casting powder feed. The plant is extremely expensive and complicated; it includes two robot arms and a spreader tube with a built-in, motor-driven screw feeder. Due to the complexity of the plant, it is prone to disturbance and costly downtime becomes inevitable.

Furthermore, JP-A-57-195568 describes the principle of how an IR detector can control a motor-driven feeder device in the inlet pipe for a casting powder during continuous casting. In addition to a very scanty description of details, this construction is also unnecessarily complicated and prone to disturbance.

A first object of the present invention is thus to ensure an even and continuous supply of casting powder on a molten metal, in particular in continuous casting.

A second object of the present invention is to eliminate the safety risks that exist when casting powder is applied manually.

A third object of the present invention is to simplify as far as possible the equipment required for applying casting powder to a molten metal, in particular in continuous casting.

These and further objects have been achieved in a surprisingly simple manner by applying a method which comprises the measures specified in the characterizing part of claim 1.

For illustrative but non-limiting purposes, the invention will now be described in more detail with reference to the accompanying drawings. These are presented herewith: Figure 1 shows a principle drawing of a feeding device according to the invention.

Figure 2 shows a diagram of the powder flow's dependence on the valve area.

Figure 3 shows the grain size distribution for two different commercial, granulated casting powder varieties.

In Fig. 1, a container for casting powder is denoted by 1. This is, for example, suspended with suitable hooks on the casting box itself. At the lower part of the container a pipe 2 connects with a valve 3. To the outlet end of this valve connects a shorter, substantially vertical pipe section 4, which in turn connects to an angled transport pipe 5. This opens above the upper surface of the metal melt 6, whereby the supplied casting powder melts of the heat from the melt and forms in the form of a liquid layer 7 on top of it. The melt itself is supplied from the casting box (not shown) through the tap tube 8 to the water-cooled copper mold 9. The cast strand is passed continuously downwards, surrounded by a slag shell of first melted and then solidified casting powder. This cracks and comes loose when sprayed with cooling water.

If desired, the described equipment can also comprise two separate parts in such a way that the container 1, the pipe part 2 and the valve 3 form a unit, while the pipe part 4 and the transport pipe 5 form a second unit. According to this embodiment, the outlet from the valve 3 opens into the "free air", whereby the casting powder falls freely for a short distance and down into the mouth of the tube 4 placed under said outlet. In this case, the upper mouth part of the tube 5 is designed as a collecting trough or vessel 10 with a widened cross-sectional area, in order to catch all the casting powder.

This embodiment has the advantage that the container with associated valve can be mounted, respectively disassembled, separately, and the transport pipe 5 (with associated collecting trough 10) separately. Furthermore, the transport pipe 5 can be designed as a branched pipe of substantially Y-shape, which enables the two mouths of the pipe to be placed on each side of the tap pipe 8 and thus ensure a more even spread of the casting powder on the surface of the melt.

The transport tube / s can also be made telescopic, which facilitates the achievement of the desired positioning of the mouth of the tube over the molten metal.

An essential feature of the present invention is that the casting powder is granulated.

By this expression is meant that the casting powder grains consist mainly of spherical particles with a certain grain size distribution. The chemical composition of a granulated casting powder can vary between different brands available on the market. A group of casting powders is marketed under the registered 515 012 5 trademark "Scørialit", of which the type designation SPH 107-77 II may serve as an example (stated percentages refer to weight percent) of a representative composition of a casting powder: 10 l5 20 25 30 Basicity: 1.43 sioz 23.7% CaO 33.0% Mgo 0.82 ° <111203 7.29% Na2O 8.04% Kao 0.13% Tioz 0.35% MnO 6.25% Fe2o3 1.12% Cfriu 4fo% coz 9.3% cum 6.58% F 6.71% H 2 O (60 ° C) 0.52% S 0.05% Softening point: 1060 ° C Melting point: 1140 ° C Pour point: 1180 ° C Bulk density: 0 , 64 kg / dm3 Sieve analysis: Remaining 500 pm: 19.0% Return code 125 pm; 97.2% Residue 63 μm: 99.6 Viscosity (1300 ° C) 0.7 dPa 10 These are manufactured in a manner known per se by means of a spray-drying process. Thanks to this geometric configuration, even and continuous feeding of the casting powder has been achieved in an extremely simple and reliable manner. Thus, an even and continuous outflow from the casting powder container can be achieved by means of a conventional ball valve, e.g. a 9.5 mm (3/8 ") brass ball valve. When the granulometry is suitably such that the average particle diameter is between 100 and 700 μm, preferably between 150 and 400 μm, and in principle no particle is larger than 1.0 mm, flows or "flows" the powder in a manner not heretofore assumed to be possible, provided that the transport tube 5 does not slope towards the horizontal plane at an angle α which is less than the inherent race angle of the casting powder. SPH A-72 (incl. The additional variety SPH A-72 / S) and SPH 107-77 (I and II) are this angle of inclination 31.2 °, which means that the angle of inclination a of the conveyor tube 5 towards the wave line should be equal to or greater more than this value when these casting powders are used. Preferably the angle of inclination a should not be less than 30 ° for any casting powder. powder out of the container, through the valve and out onto the melt with constant flow and independent of the filling height in the container 1. This flow is linearly dependent on the valve area, which is illustrated in the diagram in Fig. 2. In this the upper line (A) corresponds to the powder quality SPH A-72 and the bottom line (B) 10 15 20 25 30 515 012 7 powder quality SPH 107-77. On the x-axis the size of the valve opening is stated in mmz and on the y-axis the flow of casting powder is stated in kg / min.

The grain size distribution of two commercial "Scorialite" varieties is shown in the diagram in Figure 3. On the X-axis the grain diameter is given in pm and on the y-axis 0 the occurrence in 6. As can be seen, the diameter distribution of the substantially spherical particles essentially corresponds to a normal distribution. As the granule size affects the flow, the desire for a certain flow interval can influence the choice of granulometry, thus giving a smaller average diameter a larger flow. If a narrower grain size distribution is desired, certain fractions can be removed by sieving.

As long as there is casting powder left in the container, the preset setpoint of the flow is substantially constant. However, if for some reason some of the casting powder becomes moist, the grains may agglomerate and a disturbance of the flow may result. For this reason, an alarm sensor or a flow sensor can be mounted. This can, for example, be fixed at the transition between the pipe part 4 and the transport pipe 5. Different sensors can be selected. A suitable, tested type is a flow sensor which measures the sound frequency from the casting powder which collapses through the bend between the tubes 4 and 5, this frequency being converted into an electrical signal in mA or mV. Should for some reason the casting powder stop flowing, the signal drops below a certain minimum value in mV or mA and an alarm is triggered.

Claims (8)

10 20 25 30 515 012 8 PATENT REQUIREMENTS 1. A process for feeding casting powder to a metal melting surface, in particular in continuous casting, characterized in that the casting powder is granulated so that it consists essentially of substantially spherical particles, which are allowed to flow by means of only (1), and a threat to the horizontal plane angled (5), flow is adjusted only with the valve (3) gravity from an overlying container through a valve (3) transport pipe and out onto the metal melting surface, the desired and the opening of the transport pipe (5) being located at a certain distance from the top surface of the cast powder layer on the molten metal. 2. A method according to claim 1, characterized in that the angle of the transport tube (5) towards the horizontal plane is equal to or greater than the inherent, material-specific race angle of the granulated casting powder. 3. A method according to claim 1 or 2, characterized in that the grain size distribution of the casting powder is such that the particle average diameter is between 10 and 700 μm. 4. A method according to any one of the preceding claims, characterized in that the amount of casting powder applied corresponds to a flow of between 0.1 and 1.0 kg / min, preferably between 0.1 and 0.7 kg / min. Device for carrying out the method according to any one of the preceding claims, characterized in that it comprises a container (1) for receiving casting powder, a valve (3) attached to an outlet nozzle or outlet pipe at the lowest point of the container. and a transport pipe (5) at the outlet end of the valve, the transport pipe being angled towards the horizontal plane. Device according to claim 5, characterized in that the transport tube (5) is angled towards the horizontal plane at an angle of at least 30 °. Device according to claim 5 or 6, characterized in that the transport tube (5) is branched in the form of a Y-tube, in order to improve the spread of the casting powder on the metal melting surface. Device according to claims 5-7, characterized in that the transport tube (5) is telescopic.