MXPA99006706A - Compacting auxiliary agent for producing sinterable shaped parts from a metal powder - Google Patents

Abstract

The invention relates to a method for producing sinterable shaped metallic parts from a metal powder to which a compacting auxiliary agent has been added. Said compacting auxiliary agent contains at least partially components from the family of polyalkylene glycols. The metal powder is placed in the mould and compacted under pressure before being discharged from the mould in the form of a shaped compacted part.

Description

PROCEDURE FOR THE MANUFACTURE OF SINTERED MOLDING PARTS OF METAL POWDER DESCRIPTION OF THE INVENTION: In the manufacture of metal mold parts in the metallurgical process difficulties arise, the mold parts have to be manufactured with a density as high as possi since the metal powder must first be filled in a pressing die and then by means of presses of one or more axes, by hydraulic or mechanical press installations, they must be compressed with high pressure. A mold body thus obtained, generally referred to as a rough mold, is then sintered in a thermal process under a protective atmosphere, so that a rigid and strong metal mold part is produced and also in an exact manner. The density of the finished sintered mold part here essentially depends on the density of the blank or primitive, in the pressing of the metallic powder particles it happens unlike in the pressing of ceramic powders, that the metallic powders in reason of its different crystalline structure and the number with it linked of constructive faults in the structure undergo a plastic deformation. Due to the geometry of the particles - equally different from the ceramic powders - the dusting capacity of the dust particles is reduced in metallic powders.

REF: 30624 individual, so that already the loose shaking in the pressing mold has a volume of pores, which in the pressing only with the application of very high pressure forces can be almost eliminated. However, the high pressures result in high wear on the press tool and also lead to a sliding friction friction of the blank in the pressing die during the pressing process, so that they also have to be applied here. very high ejection forces with also strong wear. High ejection forces also bring about the danger of a new undesiralocal compression and the formation of cracks in the raw part In order to avoid these disadvantages, EP-A-0 375 627 proposed a method in which the metallic powder It is treated by csn by liquefied lubricating agent in a fluid solvent, metallic stearates, especially lithium or zinc stearate, as well as paraffins, waxes derived from natural or synthetic fats are used as a lubricating medium, which firstly for example have been made by mixing fluids. The disadvantages of this process are that the dry metal powder with a two-component lubrication system, properly the stearates and the solvent, must first be mixed, where this pre-mixing must be very homogeneous. This mixing of powder must be carried out before filling the pressing mold firstly into the the softening point of the lubricant used, which must be preheated enough. This also presents the danger of burning or damage to the transport facilities towards the press mold. After finishing the press process and ejecting the raw object, the lubricating agent must be evaporated with a special process, before the hot part can be heated to its own temperature for sintering. Here it can not be avoided, that there remain traces of the lubricant in the sintered body, which according to the purpose of application and according to the class the metallic powder used pure or in alloy, can give pros. From EP 0 559 987 an iron-based metallurgical powder composition is known which contains an organic binder for the iron-based powder fraction and the alloy powder fractions. To improve the pressing behavior, the organic binder contains a fraction of polyalkylene oxide, which has a molecular weight of at least 7000 g / molHowever, substantially higher molecular weights are preferred. The present invention proposes the task of improving the described procedures. This task is solved with a process for the manufacture of metallic sintered molding parts made of a metallic powder which is mixed with a pressing aid, which. it contains at least components of the polyaguylene oxide family and which is filled in the press mold and after the pressurized tablet is expelled from the pressure mold as part of the pressed mold. The use of press aids, especially polyalkylene glycols, preferably polyethylene oxide, especially in the form of polyethylene glycols, has surprisingly shown that in order to achieve high densities and strengths in the entrub- piece. very low pressing forces have to be applied and with other pressing aids, and in order to expel the pressed molded part from the mold the necessary forces are clearly lower, so that the most important disadvantages of the known processes are avoided. A special agglutinator in the powder mixture is not needed, since already due to the "lubrication" of the powder particles moving together in the pressing process, together with a relatively large density, it also produces high mechanical strength of the a rough piece by means of which a very high "pack density" of the powder particles can be achieved and with this an increase in direct contact between the metal particles in the powder. A high mechanical strength of the enki-uto piece always has value, if the ariJ-ruto piece before the sintering has yet to undergo a certain elaboration. The expression "metallic powder" indicates in the meaning of the invention the mixture of powders provided for the manufacture of the mold part with all the alloys, special additions, except the pressing aid. A special advantage of the pressing aid selected from the polyethylene oxide family, especially used in the form of polyethylene glycol, is that a corresponding selection of the molecular weight can have an influence on the pressing parameter, and precisely as much as Regarding the flow behavior in the mixture as to the filling of the mold. And also with regard to the point of softening and with this to the conduction of the temperature and the flow of the material in the pressing process. Here, it is particularly advantageous that the pressing aid proposed in accordance with the invention has its softening point between 40 and 80 °, so that, for example, in mass production, the presses can reach "as a rule, the temperature of the tool adjusted to cause a problem-free flow of the powder mixture when filling the press mold as well as during the pressing itself Correspondingly the metal powder mixed with the pressing aid is placed in the Press mold at ambient temperature Especially in series production, it may be advisable to heat the pressing tool accordingly, to compensate for some interruptions in the course of series production Conveniently for the intended purpose, it is a regulated heating of the tool of pressing at approximately 55 °, so that the heating by the friction heat as well as the cooling by the work interruptions can be considered and thus constant pressing conditions occur.Thus the handling of the metal powder is greatly simplified, especially the filling process, put dust with "cold" well with At room temperature, it is possible to work baked, the formation of lumps can be avoided, since the heating of the powder mixed with the press auxiliary is carried out up to the press mold. In parts of an extremely large volume, additional heating of the powder may be desirable. The other advantage of the low softening temperature is that, immediately after filling, the fraction of the press auxiliary medium obtains in the amounts of metallic powder in contact with the heated mold walls its softening temperature, so that in the next Pressing process The relative movements between the powder filling and press tool are already done "lubricated" and thus the friction in those areas decreases. In the next step of total application of the pressure all the powder filling due to the pressure force is heated above the softening point, so that also the relative and relatively large movements caused by the geometry of the particles of the metallic powder, in the filling with metallic powder, they are facilitated. Due to the formation of the powder particles and thus the increase in the paging density, a part of the auxiliary pressing means which is already in a creeping state in the edge region is displaced, so that During the ejection of the finished piece, there will be a reduced friction between the piece and the wall of the pressing die. The temperature of softening of the auxiliary pressing means must thus be adjusted, so that observing the working temperature in the pressing process the external surfaces of the piece a? Krub- > do not "moisten" by the auxiliary pressing means, avoiding an adherence of the dust particles. Also with a low molecular weight there are no disadvantages when mixing with the metal powder. By selection of the pressing aid and / or a mixture of pressing auxiliaries with a corresponding molecular weight, it is possible to have an influence between certain margins on the mixing process when mixing the metal powder and on the softening point. Surprisingly it has been presented that polyethylene oxide also with very low molecular weights / is allowed to mix uniformly with metal powders also in low fractions of weight, and in addition a good flow of the powder mixture is achieved when filling the press mold and when compressing The introduction with mixing of the pressing aid in the metallic powder can be performed "cold", that is, at room temperature. The hot mixing of the pressing aid with the metal powder is especially suitable, for example in a heated drum mixer with subsequent simultaneous stirring cooling, where the temperature of the mixer is firstly somewhat higher than the softening temperature intended for the process of pressing. The temperature of the mixture is preferably 50-100 ° C, more preferably 85 ° C. After cooling, a powder mixture capable of running or sliding is available, which guarantees ease of handling in the filling of the mold. Because of the fluid consistency of the pressing aid, it is possible to reduce the pressing aid further by means of an additional solvent in its viscosity, so that the dust particles in a process comparable to the spray drying can still be covered in a thinner manner. csn the pressing aid. Suitable solvents are alcohols, such as ethanol, isopropanol or benzyl alcohol, which evaporate rapidly after spraying, so that the powder mixed with the pressing aid is "dry" and the ability to flow or run is still maintained when filling the press mold. In an advantageous embodiment of the invention, it is provided that the pressing aid is contained in the mixture in an amount of up to 5% by weight, based on the fraction of the metal powder. Agui is advantageously used, since the density of the pressing aid according to the invention is greater than the density of the pressing auxiliaries which have hitherto been common and with this, with the same fraction by weight, a filling of smaller space by the auxiliary is adjusted of pressing and therefore a filling of greater space by the compressed metallic powder. A fraction of the pressing aid of more than 1% by weight is advantageous. The pressing aid in the form of polyalkylene glycols especially in the form of polyethylene glycols is selected such that a softening point is present between 40 and 80 ° C. The use of polyethylene glycols with molecular weights between 100 g / mol and 6500 g / kg is considered advantageous. mol, preferably 3000 to 6000 g / mol. It is advantageous for the purpose pursued, mixtures of polyethylene glycol on different molecular weights, which however in the mixture correspond approximately to the existing combined molecular weight. The hydroxyl number of the pressing aid can be between 500 to 700, while the density between 0.9 to 1.25 g / cm3. By the mixture of polyethylene glycols with different molecular weights, a pressing aid can be achieved, which can be determined as far as the mixing properties, softening point and lubricating properties of the compression process used are concerned. The pressing auxiliary proposed here can be characterized by the following given addition formula: H-i-0-CH2-CH -] n-OH The increase obtained in the pressing density by the given auxiliary pressing aid is not caused by by a major change in the temperature-dependent variation of the physical properties of the metal powder, as in the process described in EP-A-0 375 627, but essentially by an improvement of the lubrication behavior therein. powder to be compressed, especially between the wall of the matrix and the powder filling with a corresponding temperature conduction to the pressing tools. Another advantage of the auxiliary pressing agent proposed is that it is easy to remove before sintering, for example by diffusion processes, capillary forces, sublimation, evaporation or the like. According to the invention, the pressing aid according to the invention is indicated by a possibility of ecologically good removal, since by pyrolysis it can be decomposed into water vapor and carbon dioxide. Surprisingly, it has been reported that a mixture of the amide wax which has hitherto been usual, which is a very hard powder, also with a polyethylene glycol having a molecular weight of more than 7000 g / mol with outstanding results of compression and good ease of ejection of the piece aitrutodesde press mold. The wetting of the outer surface is safely avoided. The fraction of the polyethylene glycol in the mixture of the auxiliary pressing agent can be clearly below 40%. As the amide wax, ethylene-stearoarylamide can be used. As a lubricating agent to decrease the friction between the wall of the matrix and the dust particles on the one hand as well as between the dust particles on the other hand, metal stearates, especially lithium or zinc stearates as well as paraffins, waxes, natural or synthetic fats, have been used up to now. In the new developments, lubrication means are used for many components resistant to high temperatures (this is about 130 ° C), which cause a reduction in the stretch limit of the metal to be pressed and then lead to high pressure densities such as is described in EP-A-0 375 627. A comparison of the pressing capacity according to the different procedures, conventional presses at room temperature, called hot presses, as described in EP-AO 375 627, with the procedure of the invention, is presented in the following diagram. In one trial an iron powder sprayed in water with 2% copper and 0.6% carbon, both in the form of powder, was used. The curves show schematically the dependence of the density of the pressure force. The curve 1 shows as a reference curve the result in the application of the cold-pressing process with a lubricant hitherto usual in the form of an amide wax or micro-thread, for example ethylene-p-stearoyl amide. Curve 2 shows the result in the application of the hot pressing process according to the given state of the art. Here already a clear improvement can be recognized. However, the disadvantages already mentioned must be considered. Curve 3 finally shows the result of the application of the process according to the invention, which still produces a clear elevation of the final density. The dependence of the apparent densities obtainable by the pressure force and the resistances of the Agui enta-uto piece are presented in the following Tables. The opposite results are presented, which are produced by the different mixing procedures for the metallic powder with the auxiliary pressing and different pressure forces.

Table 1 Tab a 2 Ta a 3 Ta a 4 Table 5 Table 1 shows for the given metal powder with a content of 0.% wt% of polyethylene glycol with a mole weight in the range of about 6000 g / mol, which was cold, mixed and pressed at room temperature. The table shows a proportional increase in the density of the piece in ---- utr > and the resistance of the piece eib-ut-o in relation to lu pressure force. Table 2 shows the results for a starting material with the same composition, but mixed hot but cold pressed. Agui shows, together with an increase in density, a clear increase in mechanical strength with respect to the values of a cold-pressed and mixed powder. By mixing at a temperature in the upper limit margin of the softening temperature of the pre-blanking aid, or also somewhat higher, there is evidently a better distribution in the powder matrix and with this a thinner lubricating film, which favors the sliding movement of the dust particles and with this the contact density of the metal particles and their possible grip. Table 3 shows the values for a cold-mixed powder that is hot-pressed. The values reached for the bulk density correspond to the abovementioned values, while the retesting results in a clear increase, which allows to recognize the changing effect between the class of polyethylene glycol used with low molecular weight and the supply of temperature to the press. In Table 4 is for a hot-mixed metallic powder that has been hot-pressed, where there is a further growth of the density of the blank where, with a pressure force of 800Mpa, one approaches the maximum possible theoretical density close to the density of massive iron, it is especially important here the growth of the resistance of the piece eakruto. This was determined by a 3-point bending test. The value of the dice indicates each time the maximum specific load, in which a break of the raw pressed part occurs. The improvement seen in the Tables of the apparent density, especially also the mechanical strength, can be attributed to the use of a polyethylene glycol with a molecular weight of less than 7000 g / mol. Here it is decisive that the hot mixing produces the increase in the mechanical strength of the solid part that can be attributed, since in the hot mixing process the iron powder particles, the copper particles and the carbon particles are covered with a thin layer of the pressing aid. Thus by reading it follows that in a hot-mixed powder the given composition of the mixed coal powder is not powdery and in a "finger test" as compared to cold-blended powder, it does not stick to the finger. A test of the distribution of copper and carbon alloy parts produces a homogeneity, which corresponds to the homogeneity of a metal powder made by diffusion alloy, as a metallic powder in which first the iron powder and the constitutive parts of the alloy they are mixed and the mixture is previously thermally treated, to place the alloy powder next to the iron powder. So that intermingling is avoided. Only then is mixing of the pressing aid carried out in another working step. As the tests show, it is possible, according to the method of the invention, to dispense with the energy-expensive thermal pre-treatment of the powder mixture, since especially in the hot mixing process it is achieved that the constituent parts of the alloy In powder form, the pressing aid is bonded to the iron particles with good homogeneity. Also, the advantage of the invention is presented. The growth of the re-emergence can be attributed to the better deluxe behavior of the pressing aid with the relatively low molecular weight in the metallic powder matrix under pressure and temperatureThis can happen, on the one hand, due to the very homogeneous mixing of the presetting aid and "on the other hand because of the very thin film of lubricant already reached during the mixing, which by the hot preheating reduces even more, which gives between the metal particles a high frequency immediate contact between the metal surfaces and thus the plastic deformation described at the beginning and the hooking of the metal dust particles, compared to the somewhat elevated values of Table 2 are also surprisingly presented for a mixture of the metal particles. auxiliary pressing agent from the amide wax and with a fraction of approximately 40% of a polyethylene glycol with a molecular weight of less than 6000 g / 1, which was hot mixed in the metallic powder, which was then pressed hot. 5 repeat, as a reference, the values for the metallic powder, to which a cold amide wax was added as a pressing aid and that cold pressed It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (12)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property:
2. Method for the production of molding parts made of metal powder, characterized by being mixed with an auxiliary pressing agent, which has at least components of the polyalkylene oxide family that is filled in a press mold and after being compressed at a pressure as part of pressed molding is ejected from the press mold. 2. Process according to claim 1, characterized in that the auxiliary pressing agent contains at least one polyethylene oxide, especially at least one polyethylene glycol.
3. 3. Process according to claim 1 and 2, characterized in that the auxiliary pressing agent is contained in the mixture in an amount of up to 5% by weight, preferably less than 1% by weight, based on the metal powder fraction.
4. 4. - Method according to claim 1 to 3, characterized in that the auxiliary pressing agent has a softening point between 40 and 80 ° C.
5. 5. - Method according to one of claims 1-4, characterized in that the auxiliary pressing has a molecular weight of less than 7000 g / mol.
6. 6. - Method according to one of claims 1 to 5, characterized by, the auxiliary thought has a molecular weight between 100 and 6500 g / mol, preferably 3000 to 6000 g / mol.
7. 7. Process according to one of claims 1 to 6, characterized in that in a fraction less than 40% in polyethylene oxide in the auxiliary pressing agent the polyethylene oxide has a molecular weight of more than 6500 g / mol.
8. 8. - Method according to one of claims 7, characterized in that the auxiliary pressing agent has a hydroxy number of 5 to 700.
9. 9. - Method according to one of the claims 8, characterized in that, the auxiliary pressed has a density of 0.9 to 1.25 g / cm3.
10. 10. Method according to claim 1, characterized in that the metallic powder mixed with the auxiliary pressing agent in the press mold is filled at a temperature below the softening point of the pressing aid used, so that a softening of the pressing agent is produced by the energy applied in the pressing mold, preferably during compression, that is to say hot-pressed.
11. 11. - Method according to one of claims 1-9, characterized in that the metal powder mixed with the pre-filling aid is filled in the press mold at a temperature below the softening point of the used press auxiliary and without supplying energy, when pressing is compressed, that is, it is cold pressed.
12. 12. - Method according to one of claims 1-11, characterized in that the auxiliary pressing agent is mixed at a temperature in the metallic powder, which at least remains in the area of the softening point of the pressing aid, that is to say a hot mix.