Title of Invention

HIGH-TEMPERATURE LUBRICANT AND ITS USE

Abstract

High-temperature lubricant for the lubrication of two areally touching heated metal objects that execute a relative movement vis-à-vis to one another, in particular steel objects, containing alkali phosphate, wherein the lubricant, based 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.

Full Text

High-temperature lubricant and its use The invention relates to high-temperature lubricants for the lubrication of two areally touching heated metal objects that execute a relative movement vis-à-vis each other. For example, in the production of seamless steel or non-ferrous metal pipes, it is important to intensively lubricate the tools, in particular the mandrel rods in order that they have the highest possible lives. The surfaces of the mandrel rods are to be uniform and smooth in order 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 rods. If the inner surface of the pipes is rough or rippled or even has damage that is attributable to the quality of the mandrels, there is a high discard rate. Efforts have therefore already been made in the past to increase the lives of mandrel rods by applying lubricants to them. Organic lubricants used in the thermoforming of metals, such as fats, oils or soaps, proved unsuitable at high temperatures. To improve the lubricant properties, graphite was therefore used as an essential constituent of the lubricant in DE-PS 4 300 464 or EP-PS 0 554 822. In particular in conjunction with inorganic salts such as for example borates or phosphates, graphite has good separation and lubrication properties. Disadvantageous however is the tendency of graphite to contribute at high temperatures to carbonizations of the workpiece surfaces, here the pipe surfaces. Tool and workpiece can also become welded together pointwise. The result of both effects is a high tool wear and a high discard rate of the workpieces. To avoid this negative effect of graphite, salt mixtures have already been used as high-temperature lubricants which melt at the working temperatures at which they are used as lubricants and ensure good lubricant properties in the liquid state. Such salt mixtures are known from EP-OS 0 829 528, which for improvement also contain a gas-forming additive. According to column 3, lines 41 to 48 of this document, an advantage of these lubricants is that they already begin to melt at 200 to 250°C and are present as clear melts as of 500°C. As a result good lubricant properties are already to be ensured at low temperatures. With such lubricants that are present as melts at working temperatures, scale that has formed and so-called secondary scale is firmly stuck to the tool, as a result of which the surfaces of the tool, such as the mandrel rod, becomes correspondingly rough. As mentioned above, this results for its part in roughness of the inner surfaces of the . pipes. At the same time the flow behaviour of the metallic material on the mandrel rods is disrupted, which manifests itself when measuring the current consumption between the individual roll grooves. The object of the invention is thus to obtain a high-temperature lubricant to which no graphite need be added and which reduces the discard rates compared with a use of known lubricants. In particular, with the help of the new lubricants the services lives of mandrel bars in the production of metal pipes are to be increased and the quality of the inner pipe surfaces improved. This object is achieved according to the invention with high-temperature lubricants for the lubrication of two areally touching heated metal objects that execute a relative movement vis-a-vis each other in that the lubricant comprises at least 80 wt.-% of at least one alkali orthophosphate and has a melting temperature above the maximum working temperature of the heated metal objects. Although it is known to add alkali phosphate to graphite-free mandrel-bar lubricants., the alkali phosphates in such lubricants account for only a relatively small percentage and are mixed with other salts such that the lubricant is present in melted, i.e. liquid, state at the working temperatures. The high-temperature lubricants according to the invention can be used wherever two areally touching metal objects execute a relative movement vis-a-vis each other at high temperatures. These are for example friction bearings with which high temperatures can occur. Preferably however the lubricants according to the invention are used where the areally touching metal objects are a tool on the one hand and a workpiece on the other. .The lubricants are quite particularly suitable for the lubrication of mandrel bars in the production of seamless metal pipes. In principle, the inventive concept is suitable for the lubrication of any metal objects, but is particularly suitable for the machining of steel objects, in particular as mentioned above for the production of seamless steel pipes in which the mandrel bars are lubricated with the lubricant according to the invention. However this is not intended to exclude the use of the lubricants according to the invention for example for the production of pipes from non-ferrous metals, aluminium or similar. Here, by maximum working temperatures is meant the highest temperature occurring on the lubricated contact surface, as this could melt the lubricant if the melting temperature of the lubricant were lower than it, which is to be avoided. When machining workpieces with a tool, as a rule the workpiece will have the higher temperature and the tool the lower temperature, as in the case of the use of mandrel bars in the production of metal pipes. The maximum working temperature above which the melting temperature of the lubricant is to lie is in this case the temperature of the hotter metal object, i.e. the workpiece. Expediently the high-temperature lubricant according to the invention is present in the form of an aqucous solution. This is applied for example to the mandrel bars during pipe production or elsewhere and, after the water has evaporated, forms a fine separation and lubricant film that is extremely abrasion-resistant when used. As the lubricant does not melt due to its high melting temperature when used, scale is prevented by the lubricant from becoming fixed on the mandrel bar surface or other tool surface. After drying, the lubricant is present in the form of very fine particles that fill all the surface roughnesses of the tool surface and thus smooth this surface, which is transmitted to the workpiece surface. The separation film formed also promotes the material flow on the workpiece surface of the metal to be formed and therefore has the character of an excellent lubricating film. The high-temperature lubricant according to the invention is particularly suitable in the case of the Assel rolling process with the "free mandrel bar" technique and in the case of the rotary forge process. Clear advantages with regard to the surface quality, the life of the mandrels and the exertion of force between the roll stands are also achieved with continuous rolling, e.g. according to the "semi-floating" principle. With the lubricants according to the invention, clear, high-percentage solutions can be easily prepared that are to be applied to the mandrels by means of airless pumps and nozzles. Atomization is also possible using air, so-called binary nozzles, or similar. Naturally, the lubricant can also be applied in powder form. The melting temperature of the lubricant according to the invention is expediently at least 10°C above the maximum working temperature that was defined above. The lubricant is to consist largely of one or more alkali orthophosphates, the alkali orthophosphale content being expediently at least 95 wt.-%. If several alkali orthophosphates are used, care is to be taken that the melting temperature is above the maximum working temperature with such mixtures also. Up to a maximum 20 wt.-%, preferably up to a maximum 5 wt.-% of the lubricant can consist of other substances, which can optionally also include small quantities of graphite, which as a rule however is not preferred. The expediently used alkali orthophosphates are trisodium orthophosphatc with a melting temperature of 1583°C, tripotassium orthophosphatc with a melting temperature of 1340°C and trilithium orthophosphale with a melting temperature of 857°C. Trisodium orthophosphatc and tripotassium orthophosphatc are preferred, in particular the latter. Provided the melting temperature of the lubricant remains high enough, other phosphates can also be added in smaller quantities. It has been shown that with the addition of small quantities of alkali aluminate and/or alkali zincate, the fineness of the lubricant particles, and thus the adhesion of the lubricant to the metal surface, is improved. It is thus preferred to add to the lubricant, in each case in a quantity of at most 5 wt.-%. preferably 0.2 to 3 wt.-%, at least one alkali aluminate and/or at least one alkali zincate. As mentioned, the superfine particles of the lubricant settle in all depressions of the surface and in so doing seal them, with the result that the scale cannot settle in these depressions. The lubricating action can therefore also be described as smoothing. The actual melting temperature of the lubricant according to the invention depends on the maximum working temperature when using the lubricant and thus on the condition of the areally touching heated metal objects. Thus the melting temperature of the lubricant can be relatively low if it is to he used to produce pipes from non-ferrous metal or aluminium, as relatively low working temperatures are employed with these metallic materials. When machining steel, a lubricant with much higher melting temperatures must be used, these in turn depending on whether chrome nickel steels with working temperatures of approximately 1050 to 1100°C or steels with higher working temperatures are used. When lubricating tools for steel workpieces, such as for example when lubricating mandrel rods for producing steel pipes, the melting temperature is expediently above 1100°C, preferably above 1200°C. When lubricating tools for the machining of non-ferrous metals, the melting temperatures can be for example 600 or 650°C. Taking account of the technical teaching according to the invention, lubricants with different melting temperatures are expediently prepared, which is to be easily achieved by varying the ingredients and the quantities of the mixture. The appropriate lubricant, the melting temperature of which is known, can then be selected for each work process. The following examples serve to further explain the invention. Example 1 On an Assel rolling mill with free mandrel rod, a mixture of 99 wt.-% tripotassium orthophosphate and 1 wt.-% sodium zincate (each relative to the solids content of the lubricant) was poured as 10% aqueous solution into the tank that served to cool the rods alter the rolling process had ended. The temperature of the bath and mandrel rod was 80 to 90°C. After the Assel mandrel was dried, it was coated with a white lubricant film. Light- to medium-alloyed steels were rolled with the Assel rolling mill. The lives of the Assel mandrels were able to be increased by 25% compared with Assel mandrels lubricated with a known lubricant. The surface-roughness measurements of the inner surface of the finished pipes that were used for antifriction bearings showed a reduction from 22 µm to 10 µm. Example 2 In a tube-piercing bench unit, the mandrels with a diameter of 130 mm were treated by spraying-on of a 20% lubricant solution comprising 98 wt.-% tripotassium orthophosphate and 2 wt.-% sodium aluminate (both relative to the solids content of the lubricant). The mandrels had a temperature of 450°C. A white coherent lubricant layer was produced. Medium- to high-alloyed steels were rolled. The impact force between the roll stands was reduced by 35% compared with conventional lubricants. The durability of the mandrels increased by 20%. The inner surface of the pipes was clearly smoother than when using the known lubricants. The quality test showed a reduction in the discard rate from 4 to less than 1 %. We Claim: 1. High-temperature lubricant for the lubrication of two areally touching heated metal objects that execute a relative movement vis-a-vis to one another, in particular steel objects, containing alkali phosphate, wherein the lubricant , based 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. High-temperature lubricant as claimed in claim 1, wherein it has a melting temperature at least 10°C above the maximum working temperature. 3. High-temperature lubricant as claimed in claim 1 or 2, wherein at least 95 wt-% of the lubricant consists of at least one alkali orthophosphate. 4. High-temperature lubricant as claimed in one of claims 1 to 3, wherein it has a melting temperature above 1100°C, preferably above 1200°C. 5. High-temperature lubricant as claimed in one of claims 1 to 4, wherein as alkali orthophosphate, it contains at least one trialkali phosphate, preferably trisodium, tripotassium or trilithium orthophosphate, in particular trialuminium orthophosphate. 6. High-temperature lubricant as claimed in one of claims 1 to 5, wherein it 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. High-temperature lubricant as claimed in one of claims 1 to 6, wherein it is present in the form of an aqueous solution. 8. Method for the lubrication of mandrel rods in the production of seamless metal pipes, wherein a high-temperature lubricant as claimed in one of the claims 1 to 7 is applied. High-temperature lubricant for the lubrication of two areally touching heated metal objects that execute a relative movement vis-à-vis to one another, in particular steel objects, containing alkali phosphate, wherein the lubricant, based 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.

Documents:

723-KOLNP-2004-(29-03-2012)-CORRESPONDENCE.pdf

723-KOLNP-2004-(29-03-2012)-FORM-27.pdf

723-KOLNP-2004-(29-03-2012)-OTHERS.pdf

723-KOLNP-2004-FORM 27.pdf

723-kolnp-2004-granted-abstract.pdf

723-kolnp-2004-granted-assignment.pdf

723-kolnp-2004-granted-claims.pdf

723-kolnp-2004-granted-correspondence.pdf

723-kolnp-2004-granted-description (complete).pdf

723-kolnp-2004-granted-examination report.pdf

723-kolnp-2004-granted-form 1.pdf

723-kolnp-2004-granted-form 18.pdf

723-kolnp-2004-granted-form 2.pdf

723-kolnp-2004-granted-form 26.pdf

723-kolnp-2004-granted-form 3.pdf

723-kolnp-2004-granted-form 5.pdf

723-kolnp-2004-granted-reply to examination report.pdf

723-kolnp-2004-granted-specification.pdf

723-kolnp-2004-granted-translated copy of priority document.pdf