DE1458351C3 - Use and method for the production of a sintered material from metallic and oxidic components for surfaces subject to friction - Google Patents

Description

The invention relates to a sintered material for surfaces subject to friction, which Can be used for bearings, piston rings, seals, clutch plates and the like, as well as on a process for its manufacture.

A material has already been proposed whose basic structure consists of a metal powder mixture is formed from a material whose free energy in the formation of the oxide is more positive than that the lead oxide is PbO, so z. B. made of copper or silver; the basic structure is made up of particles interspersed, which are predominantly formed by PbO. This will be a relatively large one Amount of oxide particles caused to penetrate into the basic structure, thus on the sliding surfaces of the materials lying on top of one another, there is always a fairly large amount of particles present consist predominantly of lead oxide. Due to the depth of the basic structure, the sliding surface material resists Over a long period of time an abrasion and also acts to the effect that a bearing material forms on the surfaces lying on top of one another.

Albeit the use of a composite material with a permeated matrix for may be desirable for certain purposes, such an imbued structure is nonetheless in other cases associated with pronounced disadvantages. The penetration is namely a function the viscosity of the material, in this case the molten oxide; a highly viscous, viscous one However, melt does not always properly penetrate into the matrix material. Besides that the binary lead oxide mixture has a certain viscosity range, that of an alloying additive depends. This means that only certain mixtures can easily penetrate. Furthermore, penetration into difficult to influence in some cases, especially if the penetration speed is quite high is low. As far as the molten lead oxide dissolves the copper, a prolonged surface contact can

3 4

to a considerable surface erosion and then one then passes through a chamber in which

structural weakening. A penetrated powder particles on their contact surfaces

The same structure has to be re-sintered together with contiguous areas.

Have lead oxide particles which have a harmful effect on a composite metal body, as it is according to the invention

kung is made on the processing of the composite material with 5 manure, contains a base from

exercise of the machine. Large coherent steel and a bonded, binding

Areas of the lead oxide or its alloys become the intermediate layer of the same circumference that of

which under certain circumstances consists of a metal whose free energy is in the

Machine tool slightly pulled apart, and oxide formation more positive than that of lead oxide (PbO)

it remains in the finished surface and its alloys are. The composite metal body

At least in microscopic dimensions bubbles per also contains a firmly sintered bearing or

or cavities. Support layer that extends as far as the intermediate

From German patents 1 029 571 and schenschicht expands, is bound to this over

1 126 624 are already materials for electrical this lies and from a metal powder mixture

Contacts known, which is formed, inter alia, from lead oxide 15 a basic structural material, the free

and silver or 5 to 20% lead oxide, the remainder copper being more potent than the energy in oxide formation

or silver-copper alloy in which there is lead oxide (PbO); the powder distribution

the lead oxide is finely divided and uniform in its base, which mainly consists of PbO, independent

metal is embedded. and discontinuous areas in the material of the

The subject of the invention is the use of 20 basic structures are embedded.

of a sintered material, consisting of 5 to 20% For a better understanding of the invention are the

an oxidic component consisting of 8 to 28% figures explained in more detail.

SiO ₀ , 4% Al ₂ O ₃ , 28% Bi ₂ O ₃ , 8% CrO ₃ , 13 to Fig. 1 is a 250 times enlarged microphotograph

45 _{% V 2} O ₅ , 5 to 33% As ₂ O ₃ , 18% MoO ₃ , 29% graph, which for the purpose of comparison the metallurgical

WO ₃ , 12%> B ₂ O ₃ , 3% TiO ₂ , 1.5% SnO ₂ , 5 to 25 features of the material already proposed

25% P ₂ O ₅ , 15% Fe ₃ O ₄ or 18% Cu ₂ O, balance shows, and

PbO, which is distributed in non-contiguous areas in Fig. 2, is an equally enlarged photo 80 to 95% of a metallic base alloy and shows the metallurgical characteristics of the whose composition is only provided by the material according to the invention.
The condition is that their affinity for the 30 According to FIG. 1 forms the oxidic proportion of oxygen less than that of lead in the sintered material to be used in the form of PbO, as a material for areas 10 that are generally contiguous with friction. Even if such a connection is not in

The subject matter of the invention is furthermore a full measure is visible, this still consists in

drive to the production of such sintered materials, 35 another level. Furthermore, Fig. 1 shows bright

which is characterized in that the oxidic areas 12, which are the material of the basic structure

Components with the base alloy in each case in pulse form and of course such spaces

deform intimately mixed, up to green density or have inclusions.

presses and then above the melting point of Aus F i g. 2 are the independent and interrupted

oxidic fraction is sintered. 40 different areas from the oxidic part 14

In the case of the improved workmanship obtained in this way, which is in the metallic base alloy 16

The oxidic powder particles form the substance under which they are embedded.

lead oxide predominates, independent and the reason why the base alloy

interrupted areas, which in the basic structure of the metal powder have a lower affinity for

material are embedded, so that the above 45 must have oxygen than that of the lead

Difficulties in using the material of the formation of PbO is that the material of the

rials are excluded. Basic structure otherwise the lead oxide to metallic

A particular embodiment of the method would reduce lead if both materials are sintered together according to the invention in the manufacture of one. The metals copper and metal lining made of sintered powder on a solid, 50 silver meet this requirement. Silver can be used on top of a reinforcing steel base. In this case, an intermediate layer of the binding material is also used as an alloying element, on which, for example, the copper can be strengthened without any adverse effect on the flat surface of a coherent strip on the PbO. Arsenic can also be applied from steel. Then powder particles alloying element will find application; however, it is made from the material whose free energy is not harmless when the oxide is used as the base metal. All quantity formation is more positive than that of lead oxide PbO, data apply in percent by weight,
with the powder particles of the oxidic component, copper powder of almost any quality can be mixed, and the resulting mixture is useful for carrying out the invention. It has spread the flat surface of the strip on the side of the however a certain powder mixture as a special intermediate layer. According to this, the 60 ders is proven to be suitable, which flows very easily when strips are drawn through a sintering chamber with the fine powdery oxide component in which the powder particles are sintered together. This is an important property that there is merely point contact between the ar particles, especially when at high speed; In addition, the part-working compression presses will be used on the flat surface of the strip metallur- 65, which is generally bound in the powder metal industry. The strip will then be used by two nodes. The analysis of these before-printing rollers, which produce 80 to 90% of the copper mixture supplied with standardized sieves, of the theoretical density of the metal lining; gives the following values:.

percent

22nd

23

38

Sieve size

-100 +150
-150 +200
-200 +250
-250 +325
-325

This copper powder is mixed with the oxidic part. The strength of the composite material is primarily attributable to the base body made of copper, while the oxidic additives are the Abrasion properties result in the friction.

The following table shows the permissible compositions of the oxidic fraction with the associated melting points and viscosity data for the melt are given. In line 1 of the In the table, the data only relate to PbO; they are included for comparison.

PbO base mixtures

Additional oxide Eutectic
at salary
of addition
oxide Enamel
Point Melted
Status (Vo) ( ⁰ C) PbO 51 888 viscous SiO ₂ 8th
15th
28 733
733
733 fluid
viscous
very viscous AlA 4th 865 very viscous Bi ₂ O ₃ 28 581 fluid PbO-CrO ₃ 8th 786 viscous V ₂ O ₅ 13th
45 760
482 fluid
viscous As ₂ O ₅ 5
17th
33 803
815
788 fluid
fluid
fluid PbO-MoO ₃ 18th 788 fluid PbO-WO ₃ 29 724 fluid BA 12th 496 fluid TiO ₂ 3 815 fluid SnO ₂ 1.5 855 very viscous P ₂ O ₅ 5
9
25th 815
843
815 fluid
fluid Cu ₂ O 18th 682 very viscous Fe ₃ O ₄ 15th 733 fluid

In order to produce a sliding material with the best possible combination of sliding properties and mechanical strength, the correct mixing ratio must be selected. In the case of a basic structure made of copper, the addition of z. B. 5 o / o of an oxidic portion of PbO with 8Vo SiO ₂ significantly improves the sliding properties in comparison with unalloyed copper. Above 20%> oxide, the strength of the composite material and also the abrasion resistance during sliding are reduced. The most favorable range for the oxides appears to be between 10 and 15% for most applications.

The composite metal body is only compressed to an extent well below the theoretical density, so that it can be soaked in the usual way with a lubricant through which the sliding body itself lubricates when these properties are desired. How to find out

ίο has, with a lO% porosity of a compact Basic structure retained some oil and a certain degree of uniformity within the Materials can be achieved.

The method for producing the above-mentioned composite material as a compact sintered body is described in detail in two parts. The first part refers to the sintered, solid Composite structure as such, while the second part deals with the metal lining that results from this Material is formed and bound to a steel body as a base. Basic for the In both processes, the basic structure material is sintered in the presence of PbO alloys. This Factor is of the utmost importance.

To produce the composite structure, the basic structural materials are first thoroughly mixed with a lubricant in order to coat the copper particles and to reduce the frictional forces that develop between the particles and the wall of a mold during pressing. These powders can of course also be pressed without the addition of a lubricant. However, in order to extend the life of the tool and to increase the pressing speed, the lubricant should be added to the mixture. The copper particles were ^{found to be mixed with stearic acid for 1} hour prior to the addition of the base oxide mixture, and the mixing was continued for ³ hours. Because the copper

particles are mixed with the lubricant first, this can coat the copper powder better, so that the tendency of the oxide to agglomerate with the lubricant is greatly reduced will.

The mixture is then compacted with the aid of conventional, automatic pressing devices. The green" The density (when wet) to which the materials are compressed has some meaning. As one found out is such a density of

so 7.3 g / cm ³ in the moist state is best. This roughly corresponds to about 83% of the theoretical density of the composite material. If the density exceeds 7.3 g / cm ³ , there is a risk that the oxide will leak out during the sintering process. This is because the oxides melt and expand; if this expansion cannot be compensated for by the inner pores, the oxide emerges from the compacted mass. In order to achieve this “green” density in the moist state, a pressure of around 3500 kp / cm ^{3 is} required.

The compact mixture of powder particles is then sintered in a two-step process.

The first step of the two-step sintering process is a pre-oxidation, in which a film of copper oxide around the copper particles. In general, this treatment is carried out at a temperature between 371 and 538 ° C, preferably at 426 ° C, at which a controlled oxidation to be possible

appears without the materials needing to be exposed to this temperature for a long time. Depending on the mass of the treated piece, a period of time on the order of 10 to 15 minutes is used at this temperature. The time can of course be reduced at higher temperatures; at temperatures above 426 ° C., cuprous oxide (Cu ₂ O) is essentially formed. However, this coating is not as break-proof and tough as that of cuprioxide (CuO), and in all cases it easily separates from the copper. This pre-oxidation pre-sintering is desirable for two main reasons:

1. Free lead, which is formed by the breakdown of the powdered lubricant, is eliminated has, and

2. A surface structure is formed with the most favorable frictional properties.

When Cu ₂ O is added, the melting point of PbO is lowered from 888 to 682 ° C. Apparently a similar relationship must also exist for the PbO-CuO system. If a film of CuO is present on all copper parts, sintering above 682 ° C leads to wetting of the entire copper surface with the mixture rich in PbO. As a result of this behavior, the oxide can be located on the interfaces of the part in question after sintering. Therefore, after a subsequent embossing or press smoothing, the part can be completely usable without the need to machine it.

The presence of a film of CuO also serves another function during the sintering process. Any metallic lead that forms as a result of the powdered lubricant burning off, reacts in the molten state with CuO, whereby a thermite reaction takes place, in the case of the metallic Cu and PbO is generated. This allows the presence of Pb in the composite body can be almost completely avoided.

In the above statement it is implicit that the pre-oxidation is not a strict requirement for is creating a composite of Cu and PbO. With that, however, a fabrication with the usual ones Powder metal devices is possible and an end product with the most favorable possible strength and sliding properties arise, this pretreatment offers considerable advantages.

the pre-oxidized compact is then sintered in order to strengthen the bond between the copper particles and to obtain a bond between the oxidic fraction and the copper particles. While the temperature required for sintering is not critical, it has been found that sintering above the melting point of the oxide additive is most beneficial. A temperature range from 760 to 927 ° C. generally leads to the compositions which can be used according to the invention. For PbO, which melts at 888 ° C, sintering can take place between 900 and 955 ° C. On the other hand, z. B. the binary PbO-8% -SiO ₂ alloy, which melts between 677 and 733 ° C, can be sintered at 815 to 843 ° C. The preferred length of time that the compositions should be held at the sintering temperature in order to obtain reproducible strength properties appears to be about 15 minutes, although this is not overly critical. Since PbO is easily reduced to metallic Pb, the sintering must not be carried out in a reducing atmosphere, e.g. B. hydrogen, endothermic, exothermic or dissociated ammonia gases without post-oxidation, as noted below, take place.

> 5 For this purpose, a non-reactive gas is preferably used, z. B. argon or nitrogen applied. Even if the sintering of the unalloyed copper in one An unreactive atmosphere is usually not nearly as effective as using one

If there is a reducing gas, the difficulty is overcome by adding PbO alloys to the Cu powder, insofar as some PbO evaporates during sintering and combined with any Cu or Cu ₂ O present, so that a clean copper

surface remains. The lead particles can also be post-oxidized to convert them into lead oxide by means of a thermite reaction with the copper oxide particles. In the above-described sintering or post-oxidation of the material, it is desirable to press or emboss the compact again. This can be done with the same tool that was used to compact the original "green" compact, since the sintering process brings about very little change in dimensions. Normally, the same pressure that is applied during the compaction process can also be used to emboss the sintered compact. The prescribed density of the final composition will depend on the type of application for which the article is intended. When hydrodynamic lubrication conditions exist and a thin film of lubricant must be maintained, a material close to full density is desired. A composition with about 90% density, based on theoretical density (7.93 g / cm ³ ), appears to be best for these conditions. The 10% porosity remaining in this material allows some oil to be absorbed. The lubricant is introduced into the composite material, in particular into its porous sections, with the aid of conventional vacuum impregnation processes. If the final density is decreased, the internal oil hold-up can be increased to produce a self-lubricating composite material. The process of making a metal liner from sintered powder on a solid, reinforcing metal base generally follows the principles already outlined. In order to facilitate the bonding of the composite material to the steel base and to eliminate an undesirable reaction between the oxidic component and the steel base, the latter is electrolytically coated or plated with a binding material which has the same properties with regard to oxide formation as the metallic base alloy. In general, the steel body is plated with a copper or silver layer or with an alloy of these metals; a copper film in the thickness range from 0.0125 to 0.05 mm appears sufficient for most of the compositions listed above. However, a greater thickness may be necessary when materials with higher melting temperatures are used.

The powder mixtures of copper and the oxide are prepared according to the processes already explained. However, no lubricant is added since there are no process steps involved

309 584/91

which require lubrication. The powder mixture is then placed on the flat surface of the strip spread on the side of the intermediate layer. The strip runs through a sintering chamber, whose conditions are chosen so that the powder particles sinter together, a point contact with limited Cohesion is created between the particles and the particles adhere to the flat surface of the strip be metallurgically bound. The temperature for sintering the strip is normally intended for the various compositions already explained are between 760 and 927 ° C. For one Cu-PbO-SiOg mixture seems z. B. a temperature of about 815 ° C to be most suitable.

In the manufacture of known bearings with a steel body made of lead copper, bearing white metal or aluminum as a running layer, the final dimensions are achieved by precision drilling. Therewith the surface condition of the cast or sintered strip is irrelevant. In some cases however, if you want to create a bearing from a strip and the final bore by means of dimensioning and roll polishing processes. In this case it is desirable to have an area with a to have the most favorable oxide distribution possible. For this reason, the freely sintered composition oxidized in advance by a treatment similar to that of the method described above applied treatment is comparable. This pre-oxidation should preferably take place before the rolling process take place.

The freely sintered strip is now rolled until its thickness is reduced to at least 75%, so that it condenses and its bond strength is increased. The preferred area for compaction of the sintered powder mixture is between 80 and 95% theoretical density. the The strip is then re-sintered at a temperature between 759 and 926 ° C to make the contact points to sinter and melt the particles together, thereby strengthening the bond and improve. When the strip is re-sintered, the powder mixture can be used in a vacuum impregnated with a lubricant that fills the remaining pores. The finished strip is then processed with a machine or with the desired coating using conventional methods and provided the desired final structure.

1 sheet of drawings

Claims (11)

Patent claims: 1. Use of a sintered material, consisting of 5 to 20% of an oxidic component, consisting of 8 to 28% SiO. ,, 4% Al ₀ O ₃ , 28% Bi ₀ O. ,, 8% CrO ₃ , 13 to 45% V., O ₃ , 5 "to 33% As ₀ O ₃ , 18% MoO ₁ , 29% WO ₃ , 12% B ₂ O ₃ , 3% TiO. ,, 1.5% SnO. ,, 5 to 25 % P., O ₅ , 15% Fe ₃ O ₄ or 18% Cu ₂ O, remainder PbO, which is distributed in non-contiguous areas in 80 to 95% of a metallic base alloy, the composition of which is only restricted by the condition, that their affinity for oxygen is less than that of lead in the formation of PbO, as a material for surfaces subject to friction. 2. Material according to claim 1, characterized in that the material containing lead oxide PbO- 8% SiO. ao 3. Material according to claim 1 or 2, characterized in that the finished mixture is a Has a density of at least 75% of the theoretical density and that the pores of this porous are filled with a lubricant in the usual way. 4. Material according to one or more of claims 1 to 3, characterized in that the entire extent of the material rests on an intermediate layer and is bound to it is, the intermediate layer, which in its entire extent to a steel base is bound, consists of a metal whose free energy is more positive than the oxide formation of lead oxide is. 5. Material according to claim 4, wherein the basic structure consists essentially of copper or Silver consists, characterized in that the intermediate layer consists of copper, silver or a Alloy consists of it. 6. Material according to claim 4 or 5, characterized in that the intermediate layer has a thickness of 0.0125 to 0.05 mm. 7. A process for the preparation of according to claims 1 to 6 composite and to sintered materials used, characterized in that powder particles, which are predominantly consist of lead oxide, with metal particles whose free energy is more positive than the oxide formation is of lead oxide, are intimately mixed, pressed to green density and then above the melting point of the oxidic component is sintered. 8. The method according to claim 7, characterized in that made of Cu, Ag or their alloy existing base alloy mixed at least with an organic lubricant and that the particles provided with the protective layer are then mixed with the powder particles containing predominantly lead oxide. 9. The method according to claim 7 or 8 for producing one designed according to claim 4 and to be used sintered material, characterized in that the sintered metal as Lining is applied to a solid, stiffening steel base by placing an intermediate layer of a material serving as a binder onto a substantially smooth surface of a continuous strip of non-porous material is applied to which the Powder mixture spreads, the powder particles sintered at their points of contact and attached to the flat surface of the strip to be metallurgically bonded to manufacture the strip a predetermined density of the metal powder is then passed through two pressure rollers and the powder particles are re-sintered at their points of contact. 10. The method according to claim 9, characterized in that the predominantly lead oxide containing material of PbO-SiO., and the temperature used to sinter the mixture is between 760 and 930 ° C. 11. The method according to claim 9 or 10, characterized in that the metal lining of the Stripes when passing through the pressure rollers to 80 to 95% of the theoretical Density is compressed and that subsequent to the renewed sintering, the pores by impregnation be filled in a vacuum with a lubricant.