Patent Application
20240399451
The invention relates to a method and a device for producing a foamable, strip-like pressed powder metal sheet blank by means of cold rolling, as well as to a pressed powder metal sheet blank produced by means of this method or this device.
The production of metal workpieces that are foamed during further processing is described in a number of documents. According to U.S. Pat. Nos. 3,087,807 and 5,303,485, for example, a powder mixture is extruded to form the foamable workpiece.
In U.S. Pat. No. 5,151,246, extrusion, hot pressing or hot rolling at temperatures between 350° C. and 400° C. is used to produce the foamable workpiece.
US 2004/0258553 A1 describes hot pressing by means of rollers at a temperature between 43° and 500° C. to produce the foamable workpiece.
In WO 2007/137681, pre-compacting, in particular by means of single-stamp axial pressing, and subsequent final compacting, in particular by means of extrusion pressing, of a mixture of recycled material and foaming agent is described for the production of the foamable workpiece. In this context, only recycled metal chips should be used.
WO 2010/127668 A2 describes a powder metallurgical method for the production of metal foam. In this process, an Al(1-x)Mg(x) alloy is added to the powder mixture both as a gas former and as an alloy component. The powder mixture is then compacted at a temperature in the range of 200° C. to 450° C.
The methods described above are energy-intensive and can only be used to a limited extent with different foaming agents.
The underlying problem of the invention is therefore to provide a method and a device for producing a foamable pressed powder metal sheet blank which can be produced at low cost and is easily foamable.
According to the invention, this problem is solved by a method for producing a foamable, strip-like, in particular elongated, pressed powder metal sheet blank from a powder mixture containing at least one metal powder and a foaming agent powder, wherein the metal powder contains a metal from the group aluminum, copper, zinc, lead, iron, wherein the foaming agent for foaming the pressed powder metal sheet blank contains, in particular consists of a foaming agent, and wherein the powder mixture is cold-rolled between two rotating rollers to form the pressed powder metal sheet blank.
The above problem is further solved according to the invention by the use of a cold rolling machine with two rotating rollers for producing a foamable pressed powder metal sheet blank from a powder mixture containing a metal powder and a foaming agent powder by means of cold rolling, wherein the metal powder contains a metal from the group aluminum, copper, zinc, lead, iron and wherein the foaming agent powder contains a foaming agent or consists of a foaming agent.
The solution according to the invention departs from the above-mentioned common production methods by producing the pressed powder metal sheet blank by cold rolling and not, as in the prior art, by hot pressing. This results in lower energy consumption during production. In addition, the lower temperature during the compaction of the powder prevents outgassing of the foaming agent, so that more foaming agent is available for the subsequent production of the foamed metal. In addition, the reactivity of the outgassing foaming agent is reduced due to the lower temperature, so that there is less risk of the properties of the metal of the metal powder being changed by reaction with the foaming agent. This makes it possible to use a wider range of foaming agents. Finally, the fact that the powder is not additionally heated during compaction prevents the oxide layers of the grains from growing. This means that more non-oxidized material is available at the end of the cold rolling process without the need for compaction in an inert atmosphere.
The foaming agent may contain at least one metal hydride, at least one carbonate, at least one hydrate and/or highly volatile substances. An example of a metal hydride that can be used as a foaming agent is titanium hydride, TiH2. Examples of a carbonate that can be used as a foaming agent are calcium carbonate, potassium carbonate, sodium carbonate and/or sodium bicarbonate. Suitable hydrates include aluminum sulfate hydrate, alum and/or aluminum hydroxide. Highly volatile substances can be, for example, mercury compounds and/or powdered or pulverized organic compounds. Zirconium hydride, ZrH2, can also be used as a foaming agent for a pressed powder containing zinc.
The powder mixture preferably contains between 0.2 and 4 wt.-% foaming agent.
The foaming agent proportion can thus depend on the foaming agent and/or the metal to be foamed and/or the porosity to be achieved. For example, a foam density of 0.5 to 0.8 g/cm3 can be achieved with AlSi10 as the metal powder if 0.7 to 0.9 wt.-% TiH2 is contained in the pressed powder metal sheet blank as the foaming agent. If a foam density of 1 g/cm3 is aimed for, 0.3 to 0.5 wt. % foaming agent, for example TiH2 or another foaming agent specified above, may be sufficient.
For foaming AIMgSi0.5 as metal powder, 0.5 to 0.9 wt.-% TiH2, preferably 0.6 to 0.8 wt.-% TiH2 can be used as foaming agent. In the case of calcium carbonate as foaming agent, larger quantities, for example at least 0.9 wt.-% foaming agent, are required.
The invention can be further improved by the following further embodiments, each of which is preferred in its own right and can be combined with one another as desired.
Thus, the metal powder may comprise metal powder grains comprising a metal or a metal alloy based on the metal specified above. In addition, metal powder grains containing or consisting of different metal alloys, which can also be based on different metals, can also be used. The metal powder can therefore contain different metals and/or metal alloys or several different metal powders. In this way, the physical and chemical properties of the subsequent metal foam can be adapted to the respective application by the composition of the metal powder.
The foaming agent powder can accordingly have foaming agent grains that contain or consist of the foaming agent. Here too, different foaming agent powders, for example containing foaming agent powders from different foaming agents, can be mixed together as required in order to adapt the properties of the metal foam.
In one configuration, at least 50 wt.-%, preferably at least 75 wt.-% of the foaming agent in the pressed powder metal sheet blank is enclosed by the metal powder. This ensures that the foaming agent foams the metal powder reliably and uniformly.
According to another preferred configuration, the powder mixture stands above the rollers. This has the advantage that the powder mixture is less likely to segregate. The powder mixture is preferably positioned directly on the roller surfaces, at least in sections. The rollers or roller surfaces carry the powder mixture. In this way, the rollers themselves can contribute to trans-porting the powder mixture into the gap between the rollers. The powder mixture is then cold pressed into the pressed powder metal sheet blank in this gap.
According to a further configuration, the pressed powder metal sheet blank is moved or conveyed by the rollers in the direction of gravity. The conveying direction parallel to the direction of gravity contributes to a more uniform distribution of the powder mixture over the gap and prevents the just compacted powder structure from taking on an uneven structure under the influence of gravity.
The powder mixture fed to the rollers is preferably not (pre-)compacted, in particular immediately before cold rolling, in order to reduce the energy required and reduce the risk of unevenly compacted pressed powder metal sheet blanks due to pressure fluctuations. For example, the powder mixture is preferably conveyed exclusively by gravity and the rotating rollers into the gap between the rotating rollers. This leads to a very uniform structure in the pressed powder metal sheet blank.
Another measure to obtain a pressed powder metal sheet blank that is as uniform as possible is to keep the level of the powder mixture above the rollers or above the gap constant. This can, for example, be done automatically by a control circuit, which in particular contains a fill level sensor and a control device. For example, the level of the powder mixture above the rollers can be automatically kept constant within predetermined limits. If the powder level falls below a predetermined lower limit, powder mixture is automatically added until the predetermined upper limit is reached. Alternatively, powder mixture can also be continuously fed in the quantity in which powder mixture is discharged through the gap in the form of the pressed powder metal sheet blank.
The powder mixture is not heated immediately before cold rolling. Preferably, the only heat input during cold rolling is provided by the cold rolling itself. In particular, the temperature of the powder mixture is less than 150° C., more preferably less than 100° C. It is even more preferable if the powder mixture is cold-rolled at room temperature. This is the case, for example, if no heating takes place.
The metal powder can be heat-treated, in particular before it is introduced into the powder mixture. In this case, the metal powder is preferably cooled, in particular to room temperature, before it is brought together with the foaming agent powder, but at least until immediately before rolling.
The rollers preferably exert a contact pressure of at least 100 MPa. Irrespective of this, the contact pressure should not exceed 650 MPa.
The pressed powder metal sheet blank can be cooled. The cooling preferably takes place after leaving the gap between the rolling and before any cutting to length of the pressed powder metal sheet blank. In this context, it is preferred that the pressed powder metal sheet blank is cooled transversely to the rolling direction, in particular in its width direction, differently or with a different heat dissipation. In particular, the heat dissipation in a center area of the pressed powder metal sheet blank should be greater than at the edges of the pressed powder metal sheet blank. The greater heat dissipation in the center of the metal blank leads to more uniform cooling across its cross-section. As a result, stress cracks and deformations due to temperature gradients in the pressed powder metal sheet blank can be avoided.
The pressed powder metal sheet blank can be cooled immediately after leaving the rollers.
Preferably, however, a heat-insulated area is provided between the rollers and the cooling system. The heat-insulated area can have heat insulation that reduces the heat dissipation from the pressed powder metal sheet blank. The heat-insulated area can be directly adjacent to the rollers. The heat-insulated area slightly reduces the cooling of the pressed powder metal sheet blank immediately after compaction, so that the compacted material can settle slightly before it is cooled. This reduces the risk of buckling and warping, especially in the edge area. The heat insulation preferably surrounds the pressed powder metal sheet blank transported past the heat insulation on all sides, however at least on its flat sides. In an alternative configuration, however, the heat insulation can also cover only an edge area of the pressed powder metal sheet blank transported past and, for example, cover the center area, or the center area of the pressed powder metal sheet blank transported past is less heat insulated than the edge area. This should lead to a more even heat distribution across the cross-section of the pressed powder metal sheet blank.
At least one of the rollers, preferably both rollers, can be cooled during cold rolling. Thus, according to a preferred configuration, a cooling device can be provided which is configured to cool at least one of the rollers, preferably both rollers, during cold rolling.
The cooling device can have an internal roller cooling system that extends into the interior of one or both rollers. The internal roller cooling system can, for example, have one or more cooling fluid lines that extend at least in sections into the interior of one of the two rollers or both rollers. The one or more cooling fluid lines can be configured to conduct a cooling fluid, for example a fluid containing water, oil or air, into and/or out of the interior of at least one roller.
Alternatively or additionally to an internal roller cooling system, the cooling device can also have a surface cooling system. The surface cooling system can have a blower device that is configured to direct a cooling fluid flow, for example a gaseous, liquid or aerosol-type cooling fluid, onto the rollers. In a simple configuration, the cooling fluid directed onto the rollers is air.
The cooling fluid flow can be directed to a surface and/or along a surface of the rollers. The cooling fluid flow can be generated by blowing and/or suction. A suction device can be provided for suction.
The surface cooling can be combined with a dust extraction system. For example, the cooling device can be configured to generate an air flow along the roller surface(s) by suction, which removes not only heat but also fine dust.
In a preferred configuration, the narrowest point of the gap between the rollers is no wider than 5 mm, however, in a further configuration it can be no wider than 4 mm. According to a further configuration, the narrowest point between the rollers is at least 0.1 mm. In particular, the narrowest point of the gap can be between approximately 0.008 times and 0.12 times the roller diameter, preferably approximately 0.01 times the roller diameter.
The diameter of the rollers can be between 50 mm and 500 mm, preferably between around 200 mm and 300 mm.
The material thickness of the pressed powder metal sheet blank is preferably at least 0.3 mm and at most around 6 mm. The material thickness is primarily determined by the width of the narrowest point of the gap.
The level of the powder mixture above the rollers is no more than 400 mm. It can be at least 50 mm. Preferably, the level of the powder mixture is around 200 to 300 mm. In order to prevent the powder mixture from no longer being uniformly drawn in due to an excessively high powder level, the level of the powder mixture is automatically maintained in a predetermined range, for example between 200 mm and 300 mm, during cold rolling.
A feed angle, which is measured from the center of one of the rollers and via which the powder mixture is in contact with the surface of the roller, is at most 35° according to a preferred configuration. Preferably, the feed angle is at least 15°, more preferably at least 20°.
The metal powder can consist of pure substances and/or alloys of such pure substances. The metal powder can result in a wrought aluminum alloy such as AlMg1Si.05 and/or a cast aluminum alloy such as AlSi12 and/or consist of such an alloy. The main alloy components are preferably silicon and/or magnesium. The silicon content of the metal powder can be between 0 wt.-% and 15 wt.-%. The magnesium content of the metal powder can be between 0 wt.-% and 15 wt.-%. In addition, the metal powder may contain at least one metal from the group Cu, Fe, Zn, Mn with 0 wt.-% to 1 wt.-%.
The metal powder can also consist partly or completely of recycled material. In this case, the recycled material may comprise:
The contact pressure of the rollers during cold rolling is preferably lower for a wrought aluminum alloy than for a cast aluminum alloy. In the case of a wrought aluminum alloy, the contact pressure of the rollers is preferably below 400 MPa, preferably around 350 MPa±20%, in the case of a cast aluminum alloy preferably above 450 MPa, in particular around 500 MPa±15%.
The feed angle is preferably greater for a cast aluminum alloy than for a wrought aluminum alloy. For a wrought aluminum alloy, the feed angle is around 20°, for a cast aluminum alloy between 20° and 25°.
The density of the pressed powder metal sheet blank is preferably between about 70% and about 99% of the density of the starting materials of the powder mixture in their mixing ratio present in the powder mixture. Preferably, the density is between about 95% and about 99% of the corresponding solid material.
A circumferential speed of the rotating rollers can be between 0.1 m/min and 6 m/min, preferably between about 1.4 and 5 m/min. At circumferential speeds of more than 1 m/min, the rollers are preferably cooled during cold rolling.
In a preferred configuration, the pressed powder metal sheet blank has a width of between 20 cm and 50 cm.
To prevent the powder from sticking to the rollers, a coating firmly bonded to the rollers, for example tungsten carbide or diamond-like substances such as Diamor® and/or an applied separating agent, for example boron manganese, graphite or molybdenum sulphide, can be used.
For the continuous application of a separating agent, an application device can be provided which is configured to spray, wipe or apply the separating agent to the surface of one or both rollers by means of contact wetting.
In the following, the invention is explained by means of an embodiment and by means of experimental examples with reference to the accompanying drawings and tables. In the drawings, the same reference signs are used for elements which correspond to one another in terms of structure and/or function.
In accordance with the above observations, individual features of the embodiment can be omitted if their technical effect is not important. Conversely, further features as described above can be added to the embodiment if the technical effect associated with this feature is important for a particular application.
It is shown by:
First of all, the method and the device 1 are described by means of the Figures, with which a foamable, strip-like pressed powder metal sheet blank 2 is produced from a powder mixture 4 by means of cold rolling 6. The powder mixture 4 contains at least one metal powder 8 and one foaming agent powder 10. The powders 4, 8, 10 are transported through the device 1 along the arrows 11.
The metal powder 8 has metal powder grains 12 that contain at least one metal. The metal is, for example, a metal from the group comprising aluminum, copper, zinc, lead and iron. Preferably, the metal is provided in the form of a powdered metal alloy. In particular, the metal alloy can be a cast aluminum alloy such as AlSi12 and/or a wrought aluminum alloy such as AlMg1Si.05.
The foaming agent powder 10 has foaming agent powder grains 14 that are suitable for foaming the metal or metal alloy. For example, the foaming agent powder 10 has a metal hydride, in particular TiH2, as foaming agent. Alternatively or additionally, the foaming agent powder 10 may also use as foaming agent a carbonate, for example calcium carbonate, potassium carbonate, sodium carbonate and/or sodium bicarbonate; a hydrate, for example aluminum sulfate hydrate, aluminum hydroxide, and/or alum; and/or another highly volatile substance such as a mercury compound and/or a powdered or pulverized organic substance.
The pressed powder metal sheet blank 2 serves to produce a metal foam 16, for example a sandwich panel (
The powder mixture 4 is pressed between two rotating rollers 18 without additional heating, preferably at room temperature, thus at about 16° C. to about 25° C., so that the pressed powder metal sheet blank 2 is formed directly by this cold rolling process. The rollers 18 are aligned parallel to each other. Preferably, both rollers 18 are driven. Cold rolling 6 is of course also possible at a wider temperature range, for example below 100° C. The pressed powder metal sheet blank should not heat up above 120° C. during cold rolling. In particular, neither the powder mixture 4 nor the pressed powder metal sheet blank 2 heat up to over 150° C. in the course of cold rolling.
A powder quantity 19 of the powder mixture 4 is located above the rollers 18. The powder mixture 4 is conveyed preferably exclusively by gravity 20 and the rotating rollers 18 into the gap 22 between the two rollers 18. In the gap 22, the direction of rotation 23 of the rollers 18 points in the direction of gravity 20. Heating of the powder mixture 4 or the powder quantity 19 above the rollers 18 does not take place. For example, a container-shaped powder reservoir 25 can be arranged above the rollers 18, the bottom of which is formed by the rollers 18.
The level 24 of the powder quantity 19 standing above the rollers 18, the gap 22 or the narrowest point 26 of the gap 22 is preferably kept constant, or at least approximately constant, within predetermined limits during cold rolling 6. The narrowest point 26 of the gap 22 has a gap width 27 which is preferably not wider than 10 mm, according to a further configuration not wider than 5 mm. According to another configuration, the gap width 27 is at least 1 mm. During start-up, the gap 22 is closed and is then opened to the desired gap width 27.
In order to set the gap width 27, at least one of the rollers 18 can be moved towards or away from the other roller 18, as indicated by the arrow 28.
The level 24 of the powder mixture above the rollers, in particular above the narrowest point 26, is at most 400 mm in one configuration and at least 100 mm according to another configuration. According to another configuration, the level is regulated to about 200 mm. Deviations of ±20% from a level 24 specified as a set value are still to be regarded as constant.
For example, the device 1 may have a fill level sensor 29 which is connected to a control device 30, for example a computer. The control device 30 is connected to systems of the device 1 via at least one data transmission path 31, which is configured for wireless and/or wired, unidirectional and/or bidirectional transmission of data.
For example, a conveyor 32 can be controlled by the control device 30. The conveyor 32 is configured to convey the powder mixture 4 to the powder reservoir 25. The control device 30 is configured to automatically keep the level of the powder mixture 4 constant, for example by setting a quantity 34 of powder mixture 4 conveyed by the conveyor 32 to the powder reservoir 25 per unit time as a function of the level 24, in particular the current level 24. Alternatively, the quantity 34 conveyed into the powder reservoir by the conveyor 32 can also simply be kept constant at a value which corresponds to the discharge of the powder mixture 4 from the powder reservoir 25 through the gap 22.
For the production of the powder mixture 4, the metal powder 8 and the foaming agent powder 10 are mixed. The aim is to achieve as uniform a distribution as possible of the two components in the powder mixture. The powder mixture 4 contains between 0.2 and 4 wt.-%, preferably between 0.5 and 1.0 wt.-%, and particularly preferably about 0.8 wt.-% foaming agent, wherein the foaming agent proportion may depend on the foaming agent and/or the metal to be foamed and/or the porosity to be achieved. The remainder is preferably metal powder 8, wherein different metal powders can also be mixed together. Preferably, the metal powder 8 and/or the foaming agent powder 10 have each been mixed in order to ensure a uniform size distribution over the volume.
For mixing 35 the metal powder 8 and the foaming agent powder 10, the device 1 may have a mixer 36. In order to avoid clumping, the mixing time during which the metal powder 8 and the foaming agent powder 10 are mixed can be between 10 minutes and two hours, preferably around one hour. The mixer 36 is preferably also controlled by the control device 30. The mixer 36 produces the powder mixture 4.
A buffer container 38 may be provided between the mixer 36 and the conveyor 32, in which the powder mixture 4 is temporarily stored. In this case, a further conveyor 40 may be present between the mixer 36 and the buffer container 38, which conveys the powder mixture 4 from the mixer 36 into the buffer container 38. The conveyor 32 is then configured to convey the powder mixture 4 from the buffer container 38 into the powder reservoir.
Alternatively, the powder mixture 4 can also be conveyed directly from the mixer 36 to the rollers 18 without a buffer container 38 being provided. In this case, for example, the conveyor 32 can be configured to convey the powder mixture 4 from the mixer 36 into the powder reservoir 25.
Of course, it is also possible that a ready-mixed powder mixture 4 is used, so that a mixer 36 can be omitted and the ready-mixed powder mixture 4 can be introduced directly into the powder container 38. Nevertheless, even in this case it is advisable to use a mixer 36 in order to ensure uniform mixing, since segregation can occur during transportation of a ready-mixed powder mixture 4.
The device 1 may further comprise a metal powder container 42 and a foaming agent powder container 44. In the foaming agent powder container 44, the foaming agent powder 10 is stored separately from the metal powder 8. In the metal powder container 42, the metal powder 8 is stored separately from the foaming agent powder 10.
Before cold rolling 6 and in particular before mixing 35 with the foaming agent powder 10, the metal powder 8 can be heat treated. A furnace 46 may be provided for the heat treatment 45.
Of course, the powder mixture 4 can also or additionally be heat-treated. However, as this can lead to outgassing of the foaming agent, for example hydrogen, this is not preferred.
The heat treatment 45 can be annealing, for example. For the heat treatment 45, a system 47 for cooling may be provided in addition to the furnace 46. Alternatively, cooling can simply take place in still air or in the furnace 46.
Heat treatment 45 is particularly preferred for a metal powder 8 containing or consisting of an aluminum alloy. In such a case, the metal powder 8 can be heat-treated for at least three hours at a temperature of at least 400° C., but in particular below 577° C. Preferably, the heat treatment 45 takes place in an inert atmosphere in order to avoid oxide formation on the grains of the metal powder.
After the heat treatment 45, the metal powder 8 is conveyed from the furnace 46 or system 47 to the metal powder container 42 for cooling.
A conveyor system 48 can pass through the furnace 46 and—if present—the system 47 and convey the metal powder 8 from a delivery container 49 to the metal powder container 42. If no heat treatment 45 is provided, the delivery container 49, the conveyor system 48, the furnace 46 and the system 47 can of course be dispensed with. The device 1 may have a further mixer 50 arranged downstream of the furnace 46 or the system 47 and upstream of the metal powder container 42. The mixer 50 is used to mix the heat-treated metal powder 8.
The rollers 18 can be part of a cold rolling machine 51 for vertical powder rolling, which is used to produce the foamable, strip-like pressed powder metal sheet blank 2.
After leaving the gap 22, it is advantageous if the pressed powder metal sheet blank 2 is cooled in a cooling process 53. A cooling device 52, for example a blower device 54, may be provided for this purpose. The blower device 54 can also be used for blowing off and/or extracting dust. For example, the blower device 54 can be configured to direct a cooling air flow 55 onto the pressed powder metal sheet blank 2 during cold rolling.
In an alternative or cumulative configuration, which is shown in
Instead of or in addition to the blower device 54 and/or 54a and/or the suction device 54b, the cooling device 52 can also cool one or both rollers 18 from the inside. Thus, the cooling device 52 may have one or more fluid lines 54c which extend into the interior of the rollers 18 or are located inside the rollers, and in which a cooling fluid flows. The cooling fluid can be gaseous, liquid or an aerosol and can remove the heat transported by the cold rolling.
Between the cooling device 52 and the gap 22, there may be a heat insulated area 57 through which the pressed powder metal sheet blank 2 extends or is moved during its production. The heat insulated area 57 has a heat insulation 58, which extends along at least the flat sides of the pressed powder metal sheet blank 2 and preferably encloses the pressed powder metal sheet blank 2 transversely to the rolling direction 56. The heat insulated area 57 reduces the heat dissipation from the pressed powder metal sheet blank 2 immediately after the pressing process, so that setting processes can take place, driven by the heat energy from the pressing process. The length of the heat-insulated area 57 in the rolling direction 56 is dimensioned such that the pressed powder metal sheet blank 2 does not heat up by more than 100° C. during operation, that is, the difference between the temperature of the pressed powder metal sheet blank 2 and the temperature of the powder quantity 19 is not more than 100° C.
Transverse to the rolling direction 56, thus to the direction in which the pressed powder metal sheet blank 2 is conveyed by the rollers 18, the heat dissipation generated by the cooling device 52 does not have to be constant. For example, it can be advantageous if the heat dissipation, that is, the cooling of the pressed powder metal sheet blank 2, is greater in a center area 59, which is remote from the two edges 60 located transverse to the rolling direction 56, than at the edges 60. For example, the heat dissipation can be increased in the direction from the edges 60 towards the center area 59 transverse to the rolling direction 56. This allows the pressed powder metal sheet blank 2 to cool down uniformly.
In one configuration, the contact pressure 62 of the rollers 18 is between 200 and 500 MPa, in another configuration between 250 and 400 MPa. The device 1 or the control device 30 is preferably configured to keep the contact pressure constant, wherein deviations of less than ±20% from a contact pressure specified as a set value are still to be regarded as a constant contact pressure 62. However, the more precisely the contact pressure 62 can be maintained, the better the quality of the pressed powder metal sheet blank 2.
In one configuration, a feed angle 64 is at most 35° and/or at least 15°. According to a further configuration, the feed angle may be around 20°. The feed angle 64 is measured from the center 68 of the rollers and is the angle through which the powder mixture 4 is in contact with the surface 66 of a roller 18.
The circumferential speeds of the rotating rollers 18 are between 0.1 m/min and 6 m/min, preferably between 1.4 and 5.0 m/min. At circumferential speeds of more than 1 m/min, the rollers are preferably cooled during cold rolling.
The pressed powder metal sheet blank 2 may have a width 70 of between 5 cm and 50 cm. The width 70 is constant over a length 72 of the pressed powder metal sheet blank extending in the rolling direction 56. Here, a deviation of ±10% from the width 70 in the direction of the length 72 is still to be regarded as constant. The length 72 of a pressed powder metal sheet blank is at least one meter. Preferably, the length 72 is several meters.
The device 1 may have a cutting device 73, by means of which the pressed powder metal sheet blank 2 leaving the gap 22 is cut to length in a cutting step 74, preferably after cooling.
A material thickness 75 of the pressed powder metal sheet blank 2 can be greater than 0.3 mm and/or less than 10 mm.
A foaming rate of the pressed powder metal sheet blank is at least 4.7, preferably at least 5. The foaming rate is the quotient of the volume of the foamed pressed powder metal sheet blank and the volume of the non-foamed pressed powder metal sheet blank.
In order to test the basic suitability of cold rolling for the production of foamable pressed powder metal sheet blanks in a single compaction step, experiments were carried out, the results of which are shown in Table 1.
TiH2 was used as the foaming agent in the experiments and the proportion of TiH2 in the powder mixture was about 0.8 wt.-%. The metal powder 8 was heat treated and mixed for about one hour after heat treatment 45 and cooling before it was brought together with the foaming agent powder 10.
For the production of the powder mixture 4, the metal powder 8 and the foaming agent powder 10 were mixed in the mixer 36 for at least one hour.
For each experiment, a pressed powder metal sheet blank 2 was produced, the length of which was approximately 3 meters. An evaluation was carried out on the basis of an examination of the pressed powder metal sheet blank 2 at the last two meters. Foamable pressed powder metal sheet blanks 2 could be produced with all experiments.
In order to assess the quality of the pressed powder metal sheet blank produced with the respective experimental constellation, the foaming rate and the strip quality were determined. Both are shown in the Table below. Here, “o” denotes a foaming rate or strip quality that is acceptable in practice, “+” denotes a value that can be used well in practice and “++” denotes a value that is excellent in practice.
The foaming rate was evaluated as follows. A foaming rate below 4.7 results in the value “o”, a foaming rate between 4.7 and 5.75 leads to the value “+” and a foaming rate of over 5.75 to the value “++”.
A strip quality of “++” characterizes a pressed powder metal sheet blank 2 that has no cracks and is completely usable for foaming. A strip quality of “+” denotes a pressed powder metal sheet blank that has isolated cracks, however is still usable and manageable as precursor material. However, use may be impaired, particularly at the edges. A strip quality of “o” characterizes a pressed powder metal sheet blank 2 with many cracks, which can only be used for foaming to a limited extent.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 126 310.7 | Oct 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/077843 | 10/6/2022 | WO |
