FI58082C - FOERFARANDE FOER FRAMSTAELLNING AV METALLREMSA AV PULVER - Google Patents

Description

2 58082

A support formed by an endless metal belt that would pass through the furnace has been proposed.

Efforts to make metal strip in this way present difficult problems. The sintering of the strip, when supported by a metal belt, does not form a strip having the desired mechanical properties because of the tensile stresses on the compressed powder during sintering, as the belt prevents the strip from shrinking as it passes through the sintering furnace. In particular, the friction applied to the strap by the • •. . '* stress as it tends to shrink leads to unsatisfactory sintering, which causes cracks in the strip surface during subsequent rolling.

The invention is mainly characterized in that the raw strip is isolated from the stresses on the strip before sintering during sintering and that the removal rate of the sintered strip from the furnace is adapted to the strip feed rate so that the strip can shrink during sintering. which corresponds substantially to the linear shortening of the strip as it shrinks as it passes through the furnace.

The metal powder can be fed to the contact surface of two rolls rotating in opposite directions in a pressing device to form a green strip, and the raw strip can be supported by a support table before it enters the sintering furnace. The raw strip is conveyed through the sintering furnace by means of two cooperating receiving rollers located at the outlet of the sintering furnace. The green strip can be fed to the furnace by means of gripping rollers, and the relative thread speeds of the gripping rollers and receiving rollers are adjusted so that the tensile stress on the strip as it passes through the sintering furnace remains substantially zero.

The term "substantially zero stress" as used in this brochure means the tensile stress on a compressed strip that, when the strip is in the furnace, allows it to shrink freely. The tensile stresses applied to the compressed ferritic and austenitic stainless steel powders are preferably less than 50 and TO per kilonevton per square meter, respectively. The tensile stresses applied to each powder material are suitably less than 15 kilonevtons per square meter and preferably less than 10 kilonevtons per square meter. Compression stresses can be advantageously used to improve sintering, as long as the use of such stresses does not cause the green strip to warp as it passes through the furnace.

The support gas can be any gas or gas mixture whose physical and chemical properties are compatible with the support system and the material to be treated. For example, the gas cushion may consist of argon, nitrogen or a mixture of argon and nitrogen, nitrogen and hydrogen, or argon, nitrogen and hydrogen or argon, hydrogen and methane. The gas mixture preferably contains about 80% by weight of a support gas (e.g. argon and / or nitrogen).

After leaving the sintering furnace, the sintered strip can be cold-rolled to reduce its thickness by about 20%. The sintered, rolled 5 58082 strip can then be passed through a reheating furnace before it is Vals to its final dimension. The reheating furnace may be a sintering furnace as described above »in which the strip is supported by a gas cushion as it passes through the furnace. Alternatively, the sintered and rolled strip may be re-passed through the aforementioned sintering furnace before being rolled to its dimensions. After each sintering, cold rolling and reheating step, the strip can be wound before being directed to the next step. Alternatively, one or more of these steps may follow each other without an intermediate winding step.

According to another object of the present invention, there is provided an apparatus for continuously producing a metal strip, the apparatus comprising means for compressing powder to form a green strip, means for conveying the compressed strip through a sintering furnace, means for feeding gas to a sintering furnace. that the tensile stress on the strip as it passes through the furnace is substantially zero.

The invention will now be described with reference to the accompanying diagrams, in which Figure 1 is a side view of a partially cut device for producing a metal strip according to the invention; Fig. 2 is a sectional view of the sintering furnace shown in Fig. 1; Fig. 3 is a side view of an apparatus for cold rolling a strip made with the apparatus shown in Fig. 1; Fig. 4 is a side view of an apparatus for reheating a rolled strip by means of the apparatus of Fig. 3; Fig. 5 is a side view of a Sendzimir rolling apparatus for making a strip made by means of the apparatus of Fig. 4, and Figs. 6 and 7 are side views of another partially cut apparatus for making a metal strip according to the invention.

The device shown in Figures 1 and 2 comprises a vibrator 1 containing a powder "P". The powder may be made of an ferrous material, for example ferritic or austenitic stainless steel, a non-ferrous material such as aluminum, a metal-containing ore or a metal oxide. Immediately below the vibrator 1, two pressure rollers 2-2 are mounted so that the powder exiting the open lower end of the vibrator 1 enters the junction between the rollers 2-2. As shown, the rollers 2-2 are forced to rotate in opposite directions, and the entire structure of the rollers 2-2 and the vibrator 1 forms a pressing device which produces a green belt "S". After the pressing device, two co-operating gripping rolls 4-4 »support table 5» sintering furnace 6, two co-operating 4 58082 receiving-pressing rolls 7-7 and a tape winding device 8 are installed in sequence 8. The coiled tape is indicated by the number 9. the strip "S" is fed over the floating table 5 And through the oven 6, whereby the pairs of gripping rollers 4-4 and 7-7 pass it through the oven. The respective rotational speeds of the feed gripping rolls 4-4 and the receiving gripping rollers 7-7 are adjusted so that the tensile stress on the green strip passes substantially zero through the sintering furnace 6, whereby the tensile stress of to a strip of powder up to a maximum of 50 kilonewtons per square meter of cross-section. In this case, in order to allow the strip to shrink as it passes through the sintering furnace 6, the respective speeds of the gripping rollers are adjusted by the adjusting device 10 so that the speed of the rollers 7-7 is lower than the number of rollers 4-4.

The expected shrinkage can be determined based on the composition of the raw strip, the morphology of the metal powder and the knowledge of the conditions prevailing in the sintering furnace. A strip made of stainless steel powder can always show a shortening of $ 5. Usually, this linear shortening is of the order of 1-2. The linear shrinkage of a raw strip made of materials such as metal oxides can be as large as 50-40 fo. The setting of the controller 10 can be made automatically or manually, depending on the quality control, by means of a feedback circuit. Alternatively, the tensile stress of the strip can be determined at some point between the gripping rollers 4-4 and 7 "7, and thus the determined tension value is fed back to the controller 10 to perform the differential adjustment of the speeds of the gripping rollers. Preferably, the tensile stress is determined at some point in the furnace.

The support table 5 has a flat horizontal surface and is positioned so as to cover as much as possible of the area between the gripping rollers 4-4 and the oven 6. The table 5 has a gas inlet 11 and several small gas outlets (not shown) on its upper surface so that the raw strip is supported before it enters the oven.

In an alternative embodiment, the support table is replaced by a pneumatic chamber with sloping side walls corresponding to that used in the furnace 6 shown in Fig. 2.

As can be seen more clearly from Figure 2, the sintering furnace 6 has a refractory cladding 12 and includes an inlet opening 15 and an outlet opening 14 at each end of the furnace. The gas inlet 15 is located at the bottom of the furnace. Alternatively, the gas inlet may be located on each of the furnaces 6 and 5 58082

Sideways. At least a portion of the gas contained in the furnace 6 can be removed through line 19 and returned to inlet 15 through condenser 19A, compressor 19B, and gas treatment chamber 19C where contaminants such as oxygen are removed. Additional gas of required composition from source 19D is added to circulating gas before entering the furnace. Before returning to the furnace, the circulating gas and additional gas are heated to a predetermined temperature.

The electric heating elements 16 are arranged inside the furnace 6 together with one or more temperature controllers (not shown). Horizontal edge strips are installed on each vertical wall of the oven 17 · In an alternative design, they can be tilted downwards by as much as a row.

After leaving the sintering furnace 6, the strip is cooled, transferred; through the receiving gripping rollers 7-7 and wound in a tape winder 9 to obtain a tape reel 9.

The coil is then transferred to a rolling station as shown in Fig. 3. As shown therein, the strip passes through the rolls 20 through the cold rolling apparatus 21 and is rewound by means of a strip winder 22 to obtain a strip roll 23.

In an alternative embodiment, the strip is hot rolled before cooling and winding. In this alternative arrangement, the hot rolling rolls replace the receiving rollers 7-7 and their rotational speed is adjusted so that the tension in the strip remains substantially zero as it passes through the furnace.

As can be seen in Figure 4, after rewinding, the spool 23 is transferred to a reheating station where it passes through the furnace 24 and is wound once more to obtain a strip spool 25. The strip is transferred into and through the oven 24 by means of gripping rollers 26 and receiving gripping rollers 27. The furnace 24 may be similar to that 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 may include a continuously advancing belt that supports the strip as it passes through the furnace 24.

Finally, the strip coil 25 is moved to the last rolling station, as shown in Fig. 5, where the strip is rolled to the final thickness by means of a Sendzimir device ("Z" rolling machine) and rewound to obtain a finished coil 29.

Using the apparatus shown, the steel powder "P" is conveyed from the vibrator 1 to the point of contact between the press rolls 2-2, from where it exits as a raw belt "S". The strip is then guided by means of gripping rollers 4-4 over the horizontal surface of the support table 5 into the oven 6 through the inlet opening 13 and exits the oven through the outlet opening 14. The strip "S" passes from the oven to the receiving gripping rollers 7-7 and. is wound by means of a tape winder 8.

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While in the furnace 6, the strip is supported by a gas obtained under pressure from the gas inlet 15. Contact between the runner strips 17 and the strip on the side walls of the oven is minimized or prevented by a gas allowed to flow between the strip edges and the sloping surfaces 17, as shown by arrows 18. . The gas exits the furnace via line 19, the cool is compressed and reheated before being returned to the furnace through inlet 15. The gas losses at the inlets and outlets 13 and 14 are compensated by adding gas from the tank 19D.

The gas fed through the inlet 15 may consist of a mixture of 20 volumes of hydrogen and 80 volumes of argon. Alternatively, the gas mixture may contain argon and a gas that chemically reacts with the strip to increase the nitrogen or carbon content of the metal powder used to make the strip, the mixture may contain argon and nitrogen or argon and a hydrocarbon gas such as methane, respectively. Thus, to increase the nitrogen content of an austenitic stainless steel strip by $ 0.2, the gas mixture may contain $ 25 nitrogen, 55 ° C argon, and $ 20 hydrogen.

When making a strip from stainless steel powder, the furnace temperature is maintained at approximately 1350 ° C by heating elements 16 so that the strip "S" sintered at the correct temperature. While in the swim 6, the tensile stress on the belt is kept substantially zero by the gas cushion supporting the belt and by the rotational speeds 4-4 and 7-7 of the aforementioned synchronized coordinated gripping rollers.

The sintered strip is removed from the furnace 6 by means of recovery gripping rollers 7-7 and a strip winder 8. The formed coil 9 is then transferred to a cold rolling apparatus 21, where the strip is unwound from the coil, transferred through rollers 2Θ-20 and then rewound by means of a strip winder 2.2. With rollers 20-20, a reduction in the thickness of the strip is achieved.

The spool 23 is then transferred to a reheating line, as shown in Figure 4, the strip is unwound from the spool, guided through the oven 24 by the gripping rollers 26-26 and 27-27, and rewound to obtain the spool 25.

Finally, the coil 25 is transferred to a "Z" rolling mill 28 where it is rolled to a final thickness and rewound. The thickness reduction achieved in a "Z" rolling mill is usually of the order of 35, but can be significantly more determined by the final thickness and properties.

In an embodiment not shown, the sintered strip exiting the gripping rollers 7-7 is fed directly to the rolling device 21 without an intermediate winding step. Additionally or alternatively, the rolled strip exiting the rolling apparatus 21 may be directed directly to the furnace 24 without a winding step between the rolling station shown in Figure 3 and the reheating station shown in Figure 4.

7 58082

The devices used to heat the furnaces 6 and 24 need not be electrical, but may preferably be high frequency induction or electron spray devices.

Figure 6 shows an alternative way of providing a substantially zero tensile stress to the raw "S" strip as it is passed through the sintering furnace 6 by the gas cushion. In this alternative arrangement, in which the same numbers as in Fig. 1 denote the corresponding ones by reference numeral, a rotating kit drum 30 is placed between the press rolls 2-2 and the support table 5.

The motor-driven friction drum 30 has its outer circumference coated with a friction material 31 »which is preferably a cellular elastomer such as foamed polyurethane. Such a material, in addition to creating a frictional force between its surface and the green strip passing over it, also prevents powder from accumulating on its surface. Loose powder on the surface of the honeycomb material 31 passes over its open pores and exits gravity as the drum 30 unwinds.

In use, the raw strip "S" leaving the pressing device is passed over a part of the material on the outer circumference of the friction drum 30, over the surface of the support table 5, through the furnace 6 and through the opposing rotating receiving rollers 32-32 to the winding device Θ. As in Fig. 1, while in the furnace 6, the raw strip is supported by a gas cushion fed through the gas inlet 15.

As before. mentioned, it is important that the tensile stress on the strip "S" is kept substantially zero. In the arrangement shown in Fig. 6, the raw belt forms a short hanging bend HL "between the pressing device and the friction drum 30, and the rotational speed of the friction drum 30 is determined by the speeds of the pressing rollers 2-2, receiving rollers 32-32 and winding device 8 at a substantially zero level from the friction drum 30 as the belt passes through the support table 5 and the furnace 6.

In use, the friction drum 30 rotates at such a speed that its circumferential speed is slightly higher than the speed at which the green belt "S" exits the press rolls 2-2. The tensile stress on the belt as it enters the furnace 6 can be adjusted to the desired zero level by adjusting the hanging bend height ML ". This adjustment is achieved by adjusting the rotational speeds of the receiving rollers 32-32 and the coil 8 at the end of the furnace 6. These speed adjustments can be made automatically according to the appropriate readings. The MitCapää can, for example, measure the tension of the strip as it passes over the support table 5

Figure 7 shows another device for applying a substantially zero tensile stress to the green strip "S" as it passes through the sintering furnace 6.

8 58082 In this alternative arrangement, a curved, downwardly tilting support table 35 is placed between the press rolls 2-2 and the inlet 41 of the furnace 6. The gas is led to the support table 35 via line 36. The oven 6 is inclined by a small angle deviating from the horizontal so that the strip passes through the oven by gravity. The angle of inclination from the horizontal is such that the traction caused by the friction on the strip as it passes through the furnace 6 is compensated for by the gravity applied to the strip. The angle is 0.3-5 ° and is obtained by placing the inlet 41 in the oven higher than the outlet 42. The measuring head 39 determines the distance between the table 35 and the strip "S".

The bucket is moved through the oven by two counter-rotating receiving rollers 37, and the rotational speed of these rollers is adjusted by a controller 40 to keep the tensile tension of the strip substantially zero by means of signals from the probe 39 corresponding to the "S" tension of the strip. In this way, the tensile stress of the strip can be kept at the desired value.

Although the invention has been described with reference to the manufacture of metaculose from a raw strip by passing a metal powder through a press apparatus, it is to be understood that other methods may be used to make the raw strip from a powdered starting material. One such alternative method comprises the steps of applying a slurry coating containing a suspension of powdered material in a binder composition to the support, drying the slurry to form a dry self-supporting film, removing the dried film from the surface of the support, and rolling the dried film to form a press.

Claims (9)

9 58082 A method of continuously producing a metal strip from a powder, wherein the powder is continuously compressed to form a continuous green strip, the green strip is continuously conveyed to a sintering furnace inlet, the strip is passed through a furnace and supported on a gas cushion as it passes through the furnace. and that the rate of removal of the sintered strip from the furnace is adapted to the rate of entry of the strip into the furnace so that the strip can shrink during sintering, the rate of removal of the sintered strip from the bath being less than its rate of entry into the furnace. Method according to Claim 1, characterized in that the raw strip is supported by means of a support table (5) before it enters the sintering furnace (6). Method according to Claims 1 to 2, characterized in that the raw strip is conveyed through a sintering furnace by means of two cooperating receiving rollers (7, T) located at the outlet of the sintering furnace. Method according to Claim 3, characterized in that the raw strip is guided into the sintering furnace by means of two cooperating gripping rollers (U, U) and that the respective rotational speeds of the gripping rollers and receiving rollers (7, T) are such that the tensile stress on the strip passes substantially zero. through. A method according to claim 3, characterized in that the green belt is conveyed over at least the circumferential part of the rotating friction drum (30), the rotational speeds of the receiving rollers (32, 32) and the friction drum being such that the tensile stress on the belt remains substantially zero as it passes through the furnace. Method according to claims 2 and 3, characterized in that the surface of the support table (35) is curved and inclined downwards and that the rotation speed of the take-up rollers (37,37) is adjusted as a wire tension as it passes over the support table to keep the tensile stress on the strip substantially zero as it passes. through the oven. Method according to one of the preceding claims, characterized in that the path of the green strip through the sintering furnace is inclined downwards with respect to the horizontal. Method according to one of Claims U to 6, characterized in that the tensile stress on the strip as it passes through the furnace is less than 70 kilonevtons per square meter of cross-section, preferably less than 10 kilonevtons per square meter of cross-section. '0 58082 Apparatus for carrying out a method according to any one of the preceding claims, comprising means (2,2) for compressing the powder to form a raw strip (5), means (7> T) for conveying the compressed raw strip through a sintering furnace (6), and means (15) for feeding gas an iron cushion (6) for forming a gas cushion thereon for supporting the strip as it passes through the oven, characterized in that the device has means (10jU0) for adjusting the strip transfer means (1U, 7; 37) so that the tensile stress on the strip passes substantially zero.