RU2354499C1 - Powder heating device by direct electric current transmission during hot pressing - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention is referred to metal powder industry, particularly, to devices for powders heating by direct electric current transmission during hot pressing. The invention may be used, for example, for hot pressing of diamond-containing segments for cutting wheels in graphite compression molds. The device contains electrode with current lead and, at least, one graphite multi-electrode unit installed on the above current lead. The surface area of the multi-electrode unit contacting with the upper surface of electrode is less than the area of the upper electrode surface. There are crossing grooves on the upper electrode surface where it contacts with the above graphite multi-electrode unit. The groove width makes free deformation possible under temperature loads of electrode surface sections being between grooves without joining. The groove depth is sufficient enough to maintain temperature equal to 0.3-0.5 from temperature measured at the electrode surface where it contacts with graphite multi-electrode unit. The grooves are implemented as parallel lines in two intercrossing directions or in the form of concentric rings and radial lines crossing the above rings.

EFFECT: improving electrode stability and increasing heating device life time.

4 cl, 5 dwg

Description

The invention relates to the field of powder metallurgy, in particular to devices for heating powders by direct transmission of electric current during hot pressing, and can be used, for example, for hot pressing diamond-containing segments for cutting wheels in graphite molds and other diamond tools and materials.

A known installation for hot pressing products from high-resistance composite materials, including a device for heating powders, made in the form of a flat conductive heater installed in the press perpendicular to the direction of pressing and equipped with graphite pads and a current source; a matrix with a punch forming a working cavity filled with sintered powder is placed on a flat heater, while the matrix and punch are made of heat-insulating non-conductive material (RF patent No. 2064367, class B22F 3/14, 1993). The device provides uniform heating to the required temperature of products made in the form of thin plates of high resistance materials. In the manufacture of products from other materials, for example, powder materials in the form of mixtures containing non-conductive particles, such as diamond, as well as products having a sufficiently large thickness (height), it is impossible to achieve a uniform distribution of the required temperatures over the entire volume of the product.

Known hot pressing for the manufacture of direct-current-heated diamond segments designed for brazing on the body of cutting wheels. The hot pressing press includes a device for heating powders containing the upper and lower electrodes, on which are prefabricated in the form of a "sandwich" design, containing the first conductive graphite blocks. On the first conductive blocks are heat-resistant insulating blocks with holes in which graphite conductive rods are installed; on top of the rods are second conductive graphite blocks. In the device for heating between the prefabricated structures, a graphite mold is installed containing a sintered metal powder with diamond grains for the manufacture of diamond segments (US patent No. 3583035, CL 425-78, 1969). The disadvantage of this device is that it is very bulky and material-intensive, it contains many graphite electrically conductive elements that complicate the design of the device for heating, as a result of which there are large energy losses.

The closest is a hot-pressing press of diamond segments heated by direct transmission of electric current through a mass containing metal and diamond powders placed in a graphite mold. The press includes a device for heating the diamond-containing mass, consisting of an electrode with current leads and a graphite block electrode, made in the form of a massive block mounted on the electrode. The press contains two similar devices for heating, located opposite in the direction of pressing. A graphite mold with a diamond-containing mass is located between the graphite block electrodes of the heating device (Operation Manual for Sintering Press Mod. DSP 515. Published in the Industrial Diamond Review, No. 2, 2003, p. 37). To obtain the desired temperature in the mold, the surface area of the graphite block electrode in contact with the surface of the electrode is always less than the total surface area of the electrode. Therefore, the passing electric current, due to differences in the contact areas of the electrode and the graphite block electrode, and therefore the different electrical resistance of these parts, heats the graphite block electrode rather and more strongly than the electrode. Considering also that the electrodes in hot-pressing presses are usually cooled from the bottom side, temperature differences are formed on a part of the electrode surface, especially in contact with the graphite block electrode, causing large internal stresses to arise in this electrode zone. As a result of this, a network of cracks uncontrolled in direction and depth is formed in the electrode, which after a certain amount of sintering breaks the electrode.

The technical result of the invention is to increase the resistance of the electrode and, accordingly, a device for heating powders by direct transmission of current during hot pressing.

To obtain a technical result in a device for heating powders by direct transmission of electric current during hot pressing, containing an electrode with a current supply and installed on it, at least one graphite block electrode having a surface area in contact with the upper surface of the electrode is less than the area the upper surface of the electrode, on the last in the contact zone of the graphite block electrode, intersecting grooves are made with a width that allows free deformation at a pace the structural loads of the electrode surface sections located between the grooves without their closure.

The lip of the grooves is selected from the condition that the temperature at the bottom of the groove is equal to 0.3-0.5 of the temperature on the upper surface of the electrode in the contact zone with the graphite block electrode.

Grooves must be made intersecting. Such grooves located on the electrode surface in the contact zone with a graphite block electrode, which has a higher temperature than the surface outside the block electrode, divide the heated part of the electrode into separate sections, while the grooves create conditions for the free linear expansion of each section in all directions, without distorting the surface of the metal electrode, contribute to the redistribution of internal stresses in the electrode, being barriers to their propagation and significantly reducing the risk ozniknoveniya unregulated cracks.

The grooves can be made in the form of parallel lines in two mutually intersecting directions or in the form of concentric rings intersecting radially directed grooves.

To obtain a specific temperature, a device for heating powders may contain more than one graphite block, with the help of which a gradual increase in temperature to the required value occurs.

The device is illustrated by drawings:

figure 1 conventionally shows a device for heating powders by direct transmission of electric current during hot pressing;

figure 2 shows a top view of a device for heating powders by direct transmission of electric current during hot pressing;

figure 3 shows the surface of the electrode with a zone in which intersecting grooves are made in the form of parallel lines in two mutually intersecting directions;

figure 4 shows the electrode in section along one of the grooves;

figure 5 shows another variant of the location on the surface of the electrode of the grooves made in the form of concentric rings intersecting radial grooves.

A device for heating powders includes an electrode 1 provided with an electric bus 2 for supplying electric current to the electrode. A graphite block electrode 4 is installed on the upper surface 3 of the electrode. The electrode 3 and the graphite block electrode 4 in the plane perpendicular to the axis of the devices can have any shape, for example, a square, rectangle, circle, etc. For the device to work effectively, the surface area of the graphite block the electrode in contact with the electrode, as a rule, is smaller than the area of the upper surface 3 of the electrode, as a result of which a zone 5 is formed on the upper surface 3 of the electrode, which is subject to high thermal loads. In addition, the heating temperature of this zone varies along the height of the electrode, i.e. to the lower surface of the electrode, opposite the upper surface, most often cooled, it decreases. In this zone 5, intersecting grooves 6, 7 are made on the upper surface 3 of the electrode 1. The depth h and width b of the grooves depend on the dimensions of the electrode 1 and the graphite block electrode 4, on the temperature that must be obtained in the mold for sintering products, from material from which electrodes are made, etc. In particular, the depth h of the grooves must be such that the bottom of the 8 grooves is in the area of the electrode, where the temperature is significantly lower than the temperature of the upper surface of the electrode, while the significantly lower temperature in this area of the electrode will no longer cause large internal stresses affecting the integrity of the electrode . To fulfill the above conditions, the depth of the grooves is chosen so that the temperature at the bottom of the groove is 0.3-0.5 of the temperature on the upper surface of the electrode in the contact zone of the graphite block electrode. Performing grooves deeper will not lead to additional positive results, but will reduce the strength of the electrode. Making the grooves smaller will not lead to a significant increase in the resistance of the electrode.

The width b of the grooves should allow free deformation from the temperature loads of the electrode surface sections 9 located between the grooves, preventing them from closing. Therefore, for specific conditions, the dimensions of the grooves will be different.

The grooves should preferably be evenly distributed in zone 5 of the upper surface of the electrode 1 and with the intersection of some grooves with others. In one embodiment, the grooves can be made in the form of parallel lines in two mutually intersecting directions. For example, the grooves 6 are located horizontally, and the grooves 7 are vertically on the surface 3 of the electrode (figure 3). In another embodiment, concentric annular grooves 10 intersecting radially directed grooves 11 are made on the electrode surface (FIG. 5). However, the claimed options for the location of the grooves of the invention is not limited.

A device for heating powders is preferably used in hot pressing presses, in which two devices for heating powders are usually installed: one (usually fixed) - at the bottom of the press table having a cooling device, and the second (movable) - at the top on the crosshead.

The electrode 1 can be made of various electrically conductive heat-resistant materials, such as alloy steels and alloys, graphite, etc.

Using a device for heating powders by direct transmission of electric current during hot pressing on a hot pressing machine of the DSP 515 mod, diamond segments were made consisting of a diamond-containing mass, including diamond powders and metal binder powders. A multi-seat graphite mold was filled with a diamond-containing mass and placed between two (upper and lower) graphite block electrodes. Then, the diamond-containing mass was pressed at a force of ~ 500 kg / cm ² while an electric current was passed through it. An electric current was supplied by a current supply to the cooled electrodes and, passing through graphite block electrodes, the current passed to a graphite mold with extruded segments. As a result, the temperature necessary for sintering the segments was reached in the mold, which was ~ 1200 ° C. The electrode was made of alloy steel, 70 mm thick and had a circular cross section with a diameter of 330 mm. On the upper surface of the electrode in a zone with a diameter of 180 mm, parallel grooves 1.5 mm wide and 12 mm deep were made in two mutually perpendicular directions (Fig. 3). The graphite block electrode had dimensions 140 × 140 mm. On the surface of the electrode in the contact zone of the block electrode, the temperature was 800-900 ° C, inside the electrode at the bottom of the groove - 300-350 ° C. Using an electrode with intersecting grooves of a given depth, the number of press sintering with one electrode increased up to 100 times, compared with an electrode without grooves.

Claims (4)

1. A device for heating powders by direct transmission of electric current during hot pressing, comprising an electrode with a current supply and installed on it, at least one graphite block electrode having a surface area in contact with the upper surface of the electrode less than the area of the upper surface of the electrode characterized in that on the upper surface of the electrode in the zone of contact with the graphite block electrode, intersecting grooves are made with a width that allows free deformation when emperaturnyh loads the electrode surface portions located between the grooves without clamping. 2. The device according to claim 1, characterized in that the intersecting grooves are made with a depth that provides at the bottom of the groove a temperature equal to 0.3-0.5 of the temperature on the surface of the electrode in the contact zone with the graphite block electrode. 3. The device according to claim 1, characterized in that the grooves are made in the form of parallel lines in two mutually intersecting directions. 4. The device according to claim 1, characterized in that the grooves are made in the form of concentric rings and radially intersecting lines intersecting them.

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