EP1444314B1 - Use of an alkaliphosphate in a high temperature lubricant - Google Patents

Abstract

The invention concerns a high temperature lubricant for lubricating two heated metal objects, in mutual contact through their surfaces, moving relative to each other, in particular steel objects, comprising at least 80 wt. % of an alkaline orthophosphate and having a melting point higher than the maximum working temperature of said heated metal objects. The inventive lubricant is mainly used for lubricating mandrel bars during production of seamless metal tubes.

Description

The invention relates to the use of alkali metal phosphate in a high-temperature lubricant for lubricating two surface-contacting heated metal objects, which perform a relative movement to each other.

For example, in the production of seamless steel or non-ferrous metal pipes, it is important to lubricate the tools, especially the mandrel bars, intensive, so they have the longest possible life. The surfaces of the mandrel bars should be uniform and smooth to ensure a uniform material flow of the metal to be processed.

The quality of the inner pipe surfaces depends on the surface quality of the mandrel bars. If the inner surface of the tubes is rough or wavy, or even has damages due to the quality of the mandrels, a high rejection rate is obtained. It has therefore been tried in the past to increase the service life of the mandrel bars by applying lubricants on them.

Organic lubricants used in the hot forming of metals, such as fats, oils, or soaps, have proven unsuitable at high temperatures. To improve the lubricating properties was therefore used for example in the DE-PS 4 300 464 or the EP-PS 0 554 822 as an essential component of the lubricant graphite. Especially in conjunction with inorganic salts, such as borates or phosphates, graphite has good release and lubricating properties. However, a disadvantage is the tendency of graphite, at high temperatures to carburize the workpiece surfaces, here the tube surfaces contribute. Also spot welds between the tool and the workpiece can occur. The consequence of both effects is a high tool wear and a high reject rate of the workpieces.

In order to avoid this negative effect of graphite, high-temperature lubricants have also been used in batch mixtures which melt at the working temperatures where they are used as lubricants and ensure good lubricating properties in the liquid state. From the EP-OS 0 829 528 Such salt mixtures are known, which additionally contain a gas-forming additive for improvement. According to column 3, lines 41 to 48 of this document, an advantage of these lubricants that they begin to melt at 200 to 250 ° C and present from 500 ° C as a clear melt. This should ensure good lubrication properties even at low temperatures.

The JP-A-10168469 also describes salt mixtures which are in the molten state at the operating temperatures at which they are used. The lubricants described herein contain 75-95 weight percent disodium hydrogen phosphate and / or potassium phosphate and 5-25 weight percent sodium chloride. The sodium chloride is added to lower the melting point. In addition, the lubricants described therein optionally contain 10-50% by weight of graphite.

The GB-A-350275 describes a method of treating wires to be drawn in a cold condition in which the material to be drawn is first treated in an acid bath, then neutralized with a trisodium phosphate solution and cold drawn with mineral oil as a lubricant.

For such lubricants, which are melted at the working temperatures, formed scale and so-called secondary scale are adhered to the tool, causing the surfaces of the tool, such as the mandrel bar, to become correspondingly rough. As mentioned above, this in turn gives roughness to the inner surfaces of the tubes. At the same time, the flow behavior of the metallic material on the mandrel bars is disturbed, as shown by the measurement of the current consumption between the individual roller calibers.

The problem underlying the invention was thus to obtain a process with a high-temperature lubricant to which no graphite must be added and which reduces the reject rates compared to a use of known lubricant. In particular, with the help of the new lubricants, the service life of Domstangen be increased in the metal tube production and the quality of the inner tube surfaces can be improved.

This object is achieved by the use of alkali metal phosphate in high-temperature lubricants for lubricating two surface contacting heated metal objects that perform a relative movement to each other, wherein the lubricant to at least 80 wt .-%, based on its solids content of at least one Alkali orthophosphate and a melting temperature above the maximum working temperature of the heated metal objects, but at least above 600 ° C, has.

While it is known to add alkali phosphate to graphite-free mandrel bar lubricants, the alkali phosphates in such lubricants only make up a relatively small percentage and are so mixed with other salts that the lubricant is in a molten, that is liquid state, at the working temperatures.

The use according to the invention of alkali metal phosphate in a high-temperature lubricant can be used wherever, at high temperatures, two metal objects in contact with each other in a plane make a relative movement relative to one another. These are, for example, bearings in which high temperatures can occur. Preferably, however, the lubricants according to the invention are used where the surface-contacting metal objects are, on the one hand, a tool and, on the other hand, a workpiece. In particular, the lubricants are suitable for lubricating mandrel bars in the manufacture of seamless metal tubes.

In principle, the inventive concept is suitable for lubricating any metal objects, but is particularly suitable for the machining of steel objects, in particular, as mentioned above, for the production of seamless steel tubes in which the dowel bars are lubricated with the lubricant according to the invention. However, this should not exclude the use of lubricants of the invention, for example, for the production of tubes made of non-ferrous metals, aluminum or the like.

When it is referred to maximum working temperatures, this is the highest occurring at the lubricated contact surface temperature, as this, if the melting temperature of the lubricant would be below, the lubricant could melt, which should be avoided. When machining workpieces with a tool, as a rule, the workpiece will have the higher temperature and the tool will have the lower temperature, as in the case of the use of mandrel bars in the manufacture of metal pipes. The maximum operating temperature above which the melting temperature of the lubricant is to be, in this case the temperature of the hotter metal object, i. H. of the workpiece.

Suitably, the high temperature lubricant in the inventive use is in the form of an aqueous solution. This is sprayed or otherwise applied, for example, on the Domstangen in pipe production and forms after evaporation of the water, a fine release and lubricant film, which is extremely resistant to abrasion in use. Since the lubricant does not melt due to its high melting temperature in use, scale is prevented from being fixed by the lubricant on the mandrel bar surface or other tool surface. After drying, the lubricant is in the form of very fine particles, which fill all surface roughness of the tool surface and thus smooth this surface, which is transferred to the workpiece surface. The formed release film also promotes the material flow of the metal to be formed on the tool surface and therefore has the property of an excellent lubricating film.

The use according to the invention of alkali metal phosphate in a high-temperature lubricant is particularly suitable in the atelier rolling process with the technology of the "free dome bar" and in the impact bench process. Even when Kontiwalzen, z. B. on the "semifloating" principle, significant advantages in terms of surface quality, the service life of the mandrels and the force between the rolling stands are achieved.

In the use according to the invention, the lubricants can easily be used to produce clear, high-percentage solutions which are applied to the mandrels by means of an airless pump and nozzles. The atomization is also possible by means of air, so-called two-fluid nozzles or the like. Of course, the lubricant can also be applied in powder form.

The melting temperature of the lubricant is suitably at least 10 ° C above the maximum working temperature, as defined above, in the use according to the invention.

When used, the lubricant should largely consist of one or more alkali orthophosphates; the content of alkali orthophosphate is expediently at least 95% by weight. If several Alkali orthophosphates are used, it is important to ensure that even with such mixtures, the melting temperature is above the maximum operating temperature.

Up to a maximum of 20% by weight, preferably up to a maximum of 5% by weight, of the lubricant may consist of other substances, which may also include small amounts of graphite, which is generally not preferred.

The appropriately used alkali orthophosphates are trisodium orthophosphate having a melting temperature of 1583 ° C, tripotassium orthophosphate having a melting temperature of 1340 ° C and trilithium orthophosphate having a melting temperature of 857 ° C. Trisodium orthophosphate and tripotassium orthophosphate are preferred, especially the latter. As far as the melting temperature of the lubricant remains high enough, other phosphates can be added in small amounts.

It has been shown that with the addition of small amounts of alkali aluminate and / or alkali zincate, the fineness of the lubricant particles and thus the adhesion of the lubricant to the metal surface are improved. It is thus preferred to add to the lubricant in each case in an amount of at most 5% by weight, preferably 0.2 to 3% by weight, at least one alkali aluminate and / or at least one alkali metal zincate. As mentioned, the superfine particles of the lubricant settle in all the recesses of the surface, thereby forming their seal, so that the scale can not settle in these recesses. The lubricating effect can also be explained as smoothing.

The actual melting temperature of the lubricant in the use according to the invention depends on the maximum working temperature in the use of the lubricant and thus on the nature of the surface touching heated metal objects. Thus, the melting temperature of the lubricant may be relatively low, if it is to be used to produce pipes of non-ferrous metal or aluminum, since relatively low operating temperatures are used for these metallic materials. When machining steels, one must use a lubricant with significantly higher melting temperatures, which in turn depend on whether chromium-nickel steels with working temperatures of about 1050 to 1100 ° C or steels with higher working temperatures are used. Suitably, the melting temperature for lubricating tools for steel workpieces, such as when lubricating mandrel bars for the production of steel pipes above 1100 ° C, preferably above 1200 ° C. For example, when lubricating tools for processing non-ferrous metals, the melting temperatures may be 600 or 650 ° C.

It is expedient to prepare lubricants having different melting temperatures, taking into account the technical teaching according to the invention, which can be achieved simply by varying the mixture constituents and mixing amounts. It is then easy to choose the right lubricant for each work process, whose melting temperature is known.

The following examples serve to further illustrate the invention.

example 1

On an Assel mill with free mandrel bar, a mixture of 99% by weight of tripotassium orthophosphate and 1% by weight of sodium zincate (based on the solids content of the lubricant in each case) was introduced into the tank as a 10% strength aqueous solution which, after completion of the rolling process to cool the bars. The temperature of the bath and mandrel was 80 to 90 ° C. After drying the Assel bar this was coated with a white lubricant film. The Assel mill rolled mild to medium sized steels.

The service life of the Asseldome could be increased by 25% compared to known lubricant smeared Asseldornen. The roughness measurements of the inner surface of the finished tubes, which were used for rolling bearings, resulted in a reduction of 22 microns to 10 microns.

Example 2

In a billet bank, mandrels with a diameter of 130 mm were treated by spraying a 20% lubricant solution of 98% by weight of tripotassium orthophosphate and 2% by weight of sodium aluminate (both based on the solids content of the lubricant). The spines had a temperature of 450 ° C. A white coherent lubricant layer was produced. Medium to high alloy steels were rolled. The impact force between the rolling stands has been reduced by 35% compared to conventional lubricants. The durability of the spikes increased by 20%. The inner surface of the tubes was much smoother than when using the known lubricants. The quality control resulted in a reduction of the reject rate from 4 to less than 1%.

Claims (8)

1. Use of alkali phosphate in a high-temperature lubricant for the lubrication of two areally touching heated metal objects that execute a relative movement vis-à-vis one another, in particular steel objects, characterized in that the lubricant, bsed on its solids content, consists of at least 80 wt.-% of at least one alkali orthophosphate wherein the lubricant has a melting temperature above the maximum working temperature of the heated metal objects, but at least above 600°C.
2. Use of claim 1, characterized in that the lubricant has a melting temperature at least 10°C above the maximum working temperature.
3. Use of claim 1 or 2, characterized in that at least 95 wt.-% of the lubricant consists of at least one alkali orthophosphate.
4. Use of any of claims 1 to 3, characterized in that the lubricant has a melting temperature above 1100°C, preferably above 1200°C.
5. Use of any of claims 1 to 4, characterized in that, the lubricant as alkali orthophosphate, it contains at least one trialkali phosphate, preferably trisodium, tripotassium or trilithium orthophosphate, in particular trialuminium orthophosphate.
6. Use of any of claims 1 to 5, characterized in that the lubricant also contains, in each case in a quantity of at most 5 wt.-%, preferably in a quantity of 0.2 to 3 wt.-%, at least one alkali aluminate and/or at least one alkali zincate.
7. Use of any of claims 1 to 6, characterized in that the lubricant is present in the form of an aqueous solution.
8. Use of any of claims 1 to 7 for the lubrication of mandrel rods in the production of seamless metal pipes