Appliance for continuous production of the metal band from the powder

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for the continuous production of metal strips from a precursor web formed by metal powder compression.

It is known that metal strips and other shapes can be made by powder compression. However, in the known processes, cold pressing alone is not sufficient to produce a strip having a densities and strength that is close to the strip rolled from the ingot. The compressed powder should be subjected to sintering, i.e. heated to a temperature at which the powder tends to bond at incipient melting, or solid-state diffusion at high temperatures. The sintering may be followed by further pressing and heat treatment to obtain a tape having suitable mechanical properties and surface treatment. In this way, a strip having a dense density and mechanical properties comparable to those having bars rolled from ingots can be obtained.

The ideal solution is for the sintering to be carried out continuously in a continuous furnace. However, in order to prevent the belt from collapsing, there must be a support in the furnace. It has been proposed that the support be formed in the form of an endless support metal strip moving through the furnace at the same time as being produced; bands.

However, attempts to make a finished belt in this manner have encountered a serious problem. The sintering of the web feedstock while it is supported on the support web does not provide the web with the desired mechanical properties due to such tension caused by the support web that acts on the compressed powder and prevents it from shrinking as it passes through the furnace. In particular, the frictional resistance exerted by the support belt on the sintered belt that it is trying to shrink leads to deficiencies in the sintering process, causing a crack on the surface during subsequent rolling.

Another possible solution is to replace the support belt in the sintering furnace with a gas cushion of inert gas fed to the furnace under pressure, and to provide the displacement of the sintered strip with a separate displacement means. If the furnace belt displacement and the sintered belt displacement from the furnace are not carried out with proper tension control and displacement speed, the tensile stress is transferred to the sintered material and thus to similar failures as in the previous case.

These drawbacks are overcome by an apparatus for the continuous production of a metal strip from powder, including a pressing device, a sintering furnace with inlet openings for¹ a gas connected by a gas source under pressure, a shifting means for shifting the strip blanks made by the press, the sintering furnace, and drawing rollers for shifting the sintered strip from the sintering furnace, which according to the invention is characterized in a sintering furnace, the drive of the drawing rollers being connected to the output of the speed control device, the input of which is connected to a voltage or speed sensor of the belt blank, located in its displacement path between the die and the draw rollers.

According to one embodiment of the invention, the displacement means may be a pair of draw rollers and the sensor is mounted on the pair of draw rollers.

According to another embodiment of the invention, the displacement means may be formed by a rotating drum provided with a friction surface, and the sensor is formed by a sensor for detecting the height coordinate of the belt path located between the pressing device and the rotating drum.

According to a further embodiment, the displacement means is formed by a downwardly inclined chute in the form of a floating table and the sensor is formed by a sensor for sensing the position of the strip relative to the surface of the floating table.

The device thus designed enables the belt to be moved by the sintering furnace so that the tensile stress that is transmitted to the sintered belt during the passage of the furnace is substantially zero. Thus, there are no drawbacks in the sintering process, as in the prior art.

The term & quot; substantially zero stress & quot; as used herein refers to the tensile stress applied to the product as it passes through the furnace, the value of which allows the sintered strip to contract freely. The tensile stress applied to the sintered powder of ferritic and austenitic stainless steel should not be greater than 50 to 70). 10 “³ MPa. However, it is desirable that for both powder materials the tensile stress to be generated is less than 16.10 @ -1³ MPa and preferably below 10. 10r³ MPa. In order to improve sintering, a compressive stress can advantageously be applied to the web blank, unless this tension causes the sintered web to buckle as it passes through the furnace.

The carrier gas can be any gas or gas mixture whose physical and chemical properties are compatible with the system and material used. For example, the gas cushion may consist of argon, nitrogen or a mixture of argon and hydrogen, nitrogen and hydrogen, or argon, nitrogen and hydrogen or argon, hydrogen and methane. The gaseous mixture preferably contains about 80% of a heavy carrier gas such as argon or nitrogen, or both.

The sintered strip may be subjected to cold rolling after leaving the sintering furnace to reduce the thickness by about 20%. The sintered and rolled strip can then be conveyed again by a reheating furnace and subjected to further calibration rolling. The reheating furnace may consist of the above-described sintering furnace in which the strip is supported by a gas cushion. After each sintering, rolling and reheating the strip can be rolled into a roll before further processes. Alternatively, one or more of these processes may be performed in succession without the belt being rolled between them.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is explained in more detail below with reference to the accompanying drawings, in which: Figure 1 is a side view, partly in section, of a metal strip manufacturing apparatus according to the invention; Fig. 3 is a side view of the cold strip rolling apparatus produced by the apparatus of Fig. 1; Fig. 4 is a side view of a device for subsequently heating a rolled strip rolled by the apparatus shown in Fig. 3; 5 a side view of a Sendzimir rolling mill for rolling a strip processed on the apparatus shown in Figures 4 and 6 and 7 - side views, partly in section, of an alternative embodiment of the apparatus according to the invention.

The apparatus shown in FIGS. 1 and 2 comprises a powder feed hopper 1. The powder may be made of a ferrous material, for example a ferritic or austenitic stainless steel, a non-ferrous material. materials such as aluminum, ores containing bearing metals or metal oxides. Immediately adjacent to the hopper 1 is a pair of press rollers 2, which are arranged so that the powder leaving the lower opening of the hopper 1 is drawn into the gap between the rollers of the presser 2. they rotate in opposite directions to each other.

Behind the press mechanism¹ 2, a pair of interlocking pulling rollers 4 of the displacement means 40 are arranged to further advance the strip-shaped sintering furnace -6. In front of the sintering furnace 6 a floating table 5 is placed. After the sintering furnace 6 a pair of drawing rolls 7 and a winding device 8 of the finished strip into the coil 9 are placed. As can be seen from the figures, the web blank exiting the press device 2 is conveyed above the floating table 5 and the sintering furnace 6 as a result of its movement by the pulling rollers 4 and the exit pulling rollers 7. and the output draw rollers 4 are controlled such that the tensile stress applied to the web S as it passes through the sintering furnace 6 is substantially zero. For a strip pressed from austenitic-stainless steel powder, the tensile stress is adjusted to a value less than 70. 10³MPa of cross-section and for ferritic powder to less than 50 .. Ю “³ MPa of cross-section. For this purpose, the rotational speeds of the draw rollers 4 and 7 are synchronized by the speed control device 10 such that the rotational speed of the output draw rollers 7 is less than the rotational speed of the draw rollers 4 of the feed means 40 by a value corresponding to - shrinkage when passing through the sintering furnace 6. For this purpose, the input of the speed control device 10 is connected to a voltage or speed sensor 50 of the belt blank S located in its displacement path between the press device 2 and the sintering furnace 6, in this case the draw rollers 4 of the displacement means 40.

The value of the expected shrinkage can be determined by knowing the composition of the web to be produced, the metal powder morphology and the conditions in the sintering furnace 6. For the web made of stainless steel powder, the linear shrinkage is up to 5%. Normally, this linear shrinkage is about 1 to 2%. For a strip molded from materials such as metal oxides, the linear reduction is at most 30-40%. The adjustment of the speed control device 10 may be automatic or manual, following the quality control, by means of a feedback circuit. Alternatively, the tensile stress sensor 50 may be located at any other location between the pulling rollers 4 of the displacement means 40 and the output pulling rollers 7, for example in a sintering furnace -6.

The floating table 5 is provided with a horizontal surface and is positioned to occupy as much space as possible between the draw rollers 4 and the sintering furnace 6. The floating table 5 has a gas inlet 11 and a series of small outlet inlet openings (not shown) on its upper surface. -for the gas to lighten the sheet stock before it enters the sintering. pece- 6.

In an alternative embodiment, the float table 5 is replaced by a pneumatic chamber with bevelled sidewalls similar to the walls¹ the sintering furnace 6 shown in Figure 2.

As can be seen more clearly from Figure -2, the sintering furnace 6 has a refractory lining 12 and is provided with an inlet seal 13 and an outlet seal 14 located at respective ends of the sintering furnace 6. Gas inlets 15 are located at the bottom of the sintering furnace. Alternatively, the gas inlets may be located on one or both side walls of the sintering furnace 6.

At least a portion of the gas contained in the sintering furnace -6 can be removed via line 19 and returned to the inlets 15 via a cooler 19A, a compressor 196 and a treatment chamber 19C in which undesirable elements such as oxygen are removed from the gas. Additional gas is supplied to the recirculated gas from source -19D prior to re-entering the sintering furnace. Before re-entering the sintering furnace 9, the recirculated gas and the auxiliary gas are preheated to a predetermined temperature. - Auxiliary gas - is replaced by losses of the gaseous atmosphere due to leaks at the inlet and outlet of the sintering furnace 6.

Inside the sintering furnace 6 are placed electric heating elements 16 with one or more temperature controllers (not shown). A pair of guide blades 17 are disposed along the vertical walls of the sintering furnace 6. In an alternative embodiment, the guide blades 17 may be inclined downwards at a small angle.

After leaving the sintering furnace 6, the web is cooled, passing between the drawing inlet rollers

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7, which pulls it out of the sintering furnace 6 and winds in the winding device 8 into the coil 9.

The coil is then conveyed to the rolling unit shown in Figure 3. As can be seen from the figure, the strip passes between the rolls 20 of the cold rolling mill 21 and is rewound by another winding device 22 into the coil 23.

In an alternative arrangement, the strip is subjected to hot rolling before it is cooled and coiled. In this alternative arrangement, the hot-rolling rolls replace the draw rolls 7 by the sintering furnace 6 and their speed of rotation is controlled to achieve a substantially zero tensile stress in the web as it passes through the sintering furnace 6, similarly to the previous embodiments.

As can be seen from Figure 4, after rewinding, the coil 23 is conveyed to a reheat unit in which the strip is conveyed by the heating furnace 24 and rewound to the coil 25. The belt is conveyed through the furnace 24 via the inlet rollers 26 and the outlet rollers. The furnace 24 may be the same as shown in Figures 1 and 2. In an alternative embodiment, the coil 25 is returned to the sintering furnace 6 for reheating. Alternatively, the furnace 24 may be provided with an endless conveyor belt supporting the belt as it passes through the furnace.

Finally, the strip of coil 25 is conveyed to the finishing mill shown in Figure 5, in which it is - rolled to a final thickness on a Senderzimir rolling mill ("Z" - rolling mill) 28 and rewound into the coil 29 of the strip in final form.

In the apparatus shown, the steel powder P from the feed conveyor 1 is drawn between the rollers of the press device 2 and emerges as a belt blank S. The belt blank S is then guided through the tension rollers 4 of the shifting means 40 above the horizontal surface of the floating table. 5 into the sintering furnace 6 via the inlet seal 13 and exits the sintering furnace -6 through the outlet seal 14. The strip blank 6 is pulled out of the sintering furnace by the exit drawing rollers 7 and is wound by the winding device 8 of the roll 9.

In the sintering furnace 6, the preform S is supported by the gas supplied under pressure by the inlets 15. Contact between the strip edges and the guide edges 17 located along the side walls of the furnace is minimized or eliminated by - gas flowing between the strip edges and The gas leaves the sintering furnace 6 through line 19, cools, compresses and cleans, and re-heats the feed lines 15 before returning to the furnace. The gas losses that occur at the inlet seal 13 'and the outlet seal 14 are compensated by adding gas from source 19D.

The gas supplied by the inlets 15 may consist of a mixture containing 20% ​​by volume of hydrogen and 80% by volume of argon. Alternatively, the mixture may comprise argon and a gas chemically reactive with the belt to increase the nitrogen or carbon content of the metal material from which the belt is made. The mixture may consist, for example, of argon and nitrogen or of argon and a hydrocarbon gas such as methane. For example, in order to increase the nitrogen content of the austenitic stainless steel strip - 0-0.2%, the gas mixture contains 25% nitrogen, 55% argon and 20% hydrogen.

In the manufacture of the stainless steel strip, the temperature in the furnace is maintained by the heating elements 16 at about 1350 ° C so that the strip blank S sinters at the correct temperature. In the sintering furnace 6, the tensile stress in the web is maintained at substantially zero due to the presence of a gas cushion which makes it more light, and due to the aforementioned synchronization of the rotational speed of the pulling rollers 4 of the shifting device 40 and the pulling rollers 7.

The sintered strip is pulled out of the sintering furnace by 6 pulling rolls 7 and is wound up by the winding device 8 of the roll 9. This roll 9 is then conveyed to the rolling-cold rolling table in which the roll is unfolded. it passes through the rollers 20 and is then rewound by the winding device 22 into a further coil 29. The rollers 20 cause a 20% reduction in the thickness of the passport.

The coil 23 is then conveyed to the heating line shown in FIG. 4, the belt unwinds, passes through the furnace 24 and the driving rollers 26 and 27, and then rewound the roll 25.

Finally, the dawn is conveyed to the "Z" rolling mill 28 in which the strip is rolled to - the final thickness and - rewound. The reduction in thickness achieved in the "Z" rolling mill is usually about 35%, but may be greater depending on the desired thickness and properties of the strip.

In one embodiment (not shown), the sintered strip leaving the exit tension rollers 7 is conveyed directly to the roll stand without being wound into the coil. In addition, or alternatively, the rolled strip leaving the grinding stand 21 may pass directly to the oven 24, without winding-up to the dawn as shown in Figure 3 and reheating shown in Figure 4.

The means for heating furnaces -6 and 24 need not operate on the principle of electrical resistance, but may be, for example, high-frequency devices or electron-beam devices.

Giant. 6 shows an alternative solution which achieves virtually zero stress in the belt blank S during its conveyance through the sintering furnace 6 on the gas cushion. In this alternative arrangement, in which the same reference numerals as in Figure 1 are used to denote the individual parts, a rotating drum 30 is positioned between the rollers of the press assembly 2 and the floating table 5, forming the shifting means 40 to advance the strip blanks 6 .

The motor-driven rotary drum 30 is provided on the outer periphery with a friction surface 31 of a suitable material, preferably a foamed elastomeric material, for example foamed polyurethane. Such a material makes it possible to frictionally engage the sheet blank, and at the same time is resistant to powder take-up from the extruded sheet blank. The powder that may fall from the sheet blank onto the friction surface 31 fits into the pores of the elastomeric material from which the friction surface is made and falls off under its own weight when the friction surface 31 of the rotating drum 30 is not in contact with the sheet blank.

The web S extending from the die 2 extends around a portion of the friction surface 31 of the rotating drum 30, through the surface of the floating table 5, further through the sintering furnace 6 and between a pair of counter-rotating outlet draw rolls 7 to the winding device

8. As in Figure 1, the belt blank S in the sintering furnace 6 is supported by a gas cushion powered by inlets 15.

As already mentioned, it is important that the tensile stress in the sheet blank S is substantially zero.

In the configuration of FIG. 6, the web S between the die 2 and the rotating spindle 30 is sutured in a slight loop L. In order to synchronize the rotation speed of the drum 30 and the output draw rollers 7 as well as the winding device 8, between the die 2 and the rotary drum 30, a sensor 50 formed by a sensor 51 for detecting the height coordinate of the respective point of the loop L. The output of this sensor 50 is similar to that of FIG. 1 coupled to the input of the speed control device 10, the output of which is coupled to the drive mechanism of the draw rollers 7.

During operation, the friction drum 30 is driven so that its peripheral speed is slightly greater than the speed at which the web S exits from the rollers of the die 2. The tension occurring in the web at the entrance to the sintering furnace 6 is controlled to the desired zero value. , and it