LUBRICANT FOR THE HOT FORMING OF METALS

Abstract

A lubricant for the hot forming of metals, with respect to the solid constituents, contains at least the following constituents: 55 to 85 wt % of a solid lubricating agent comprising a mixture of talc and a potassium mica, wherein the ratio of talc to potassium mica in the solid lubricating agent is 2.0 to 5.0, 10 to 30 wt % of an adhesive agent selected from a polyvinyl acetate, sodium water glass and dextrin or a mixture of same, 2 to 10 wt % of a thickener selected from hydroxy cellulose, hydroxyethyl cellulose, hydroxyproply cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose, ethylhydroxymethyl cellulose, carboxymethylhydroxy cellulose, dextrin, starch, organically modified bentonite, smectite and xanthan gum, 0 to 10 wt % of further auxiliary agents, and not more than 10 wt % of graphite.

Claims

1. A lubricant for the hot forming of metals, wherein the lubricant, with respect to the solid constituents, contains at least the following constituents: 55 to 85 wt % of a solid lubricating agent comprising a mixture of talc and a potassium mica, wherein the ratio of talc to potassium mica in the solid lubricating agent is 2.0 to 5.0, 10 to 30 wt % of an adhesive agent selected from a polyvinyl acetate, sodium water glass and dextrin or a mixture of same, 2 to 10 wt % of a thickener selected from hydroxy cellulose, hydroxyethyl cellulose, hydroxyproply cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose, ethylhydroxymethyl cellulose, carboxymethylhydroxy cellulose, dextrin, starch, organically modified bentonite, smectite and xanthan gum, 0 to 10 wt % of further auxiliary agents, and not more than 10 wt % of graphite.

2. The lubricant according to claim 1, wherein the ratio of talc to potassium mica in the solid lubricating agent is 2.5 to 4.5.

3. The lubricant according to one of claim 1, wherein the potassium mica is selected from phlogopite, muscovite and a mixture of both.

4. The lubricant according to claim 1, wherein the potassium mica contains at least 60 wt % phlogopite.

5. The lubricant according to claim 1, wherein the lubricant is an aqueous suspension with 10 to 45 wt % solid constituents.

6. The lubricant according to claim 1, wherein the adhesive agent is or includes ethyl vinylacetate copolymer (EVA).

7. The lubricant according to claim 1, wherein the thickener is or includes xanthan gum.

8. The lubricant according to claim 1, wherein the lubricant as the remainder contains further auxiliary agents, wherein the auxiliary agents are selected from anti-foaming agent, dispersing agent and biocide.

9. The lubricant according to claim 1, wherein the lubricant contains 0 to 5 wt % boron-bearing compounds.

10. A method comprising lubricating with said eta lubricant composition according to claim 1, a mandrel bar and/or a hollow block in the production of seamless tubes by hot forming of metals.

11. The method according to claim 10, wherein the lubricant is sprayed in the form of an aqueous suspension on to the mandrel bar and/or the hollow block in an amount of 30 to 150 g/m.sup.2 sprayed surface area.

Description

DESCRIPTION OF THE INVENTION

[0017] That object is attained by a lubricant for the hot forming of metals, in particular for lubricating the mandrel bar and/or the hollow block in the production of seamless tubes, wherein the lubricant, with respect to the solid constituents, contains at least the following constituents:

[0018] 55 to 85 wt % of a solid lubricating agent comprising a mixture of talc and a potassium mica, preferably phlogopite, muscovite or a mixture of both, particularly preferably phlogopite, wherein the ratio of talc to potassium mica in the solid lubricating agent is 2.0 to 5.0,

[0019] 10 to 30 wt % of an adhesive agent selected from a polyvinyl acetate, sodium water glass and dextrin or a mixture of same, preferably ethylene vinylacetate copolymer (EVA),

[0020] 2 to 10 wt % of a thickener selected from hydroxy cellulose, hydroxyethyl cellulose, hydroxyproply cellulose, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, methylethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, ethylhydroxymethyl cellulose, carboxymethylhydroxy cellulose, dextrin, starch, organically modified bentonite, smectite and xanthan gum, preferably xanthan gum,

[0021] 0 to 10 wt % of further auxiliary agents, preferably selected from anti-foaming agent, dispersing agent and biocide, and

[0022] not more than 10 wt % of graphite, preferably not more than 5 wt % graphite, particularly preferably no graphite.

[0023] An essential advantage of the lubricant according to the invention is that, in particular in the production of seamless tubes in continuous processes or push bench processes, it has very good friction values and wetting properties which, with identical or smaller layer thicknesses or amounts used, are comparable to those of graphite-bearing lubricants which are used at the present time in those processes, or are even superior thereto. The lubricant according to the invention can therefore replace the graphite-bearing lubricants used hitherto in continuous processes or push bench processes and at the same time can save on costs, disposal outlay and problems and the expenditure on working protection measures. Preferably the lubricant according to the invention contains not more than 5 wt % boron-bearing compounds, particularly preferably no boron-bearing compounds like boric acid, borax, boric acid salts or borate-containing minerals which are frequently used in known lubricants for the hot forming of metals. The lubricant according to the invention can therefore overcome the disadvantages of graphite-based and boron-bearing lubricants.

Application:

[0024] In the production of seamless tubes in continuous processes or push bench processes the lubricant is sprayed in the form of an aqueous suspension for preparation of the following rolling step on to the cooled mandrel bar, in which case however the mandrel bar is still at a temperature of the order of magnitude of about 100° C. An essential point of view for good lubricating performance of the lubricant in that case is complete continuous wetting of the mandrel bar and in particular the thickness of the layer of lubricant on the wetted mandrel bar. The lubricant according to the invention is distinguished by good adhesion on the mandrel bar and good uniform wetting of the surface of the mandrel bar. At the same time the amount of lubricant used or the layer thickness required for good lubrication in those processes is equal to or even less than graphite-bearing lubricants used in those processes at the present time.

[0025] When reference is made herein to the layer thickness or the use amount of the lubricant this denotes the solid amount of the lubricant on a given surface area of the tool, that is to say the mandrel bar, measured in grams of solid of the lubricant per square metre [g/m.sup.2]. A suitable layer thickness for the lubricant according to the invention is of the order of magnitude of about 30 to 150 g/m.sup.2 surface area of the mandrel bar, preferably 50 to 120 g/m.sup.2, particularly preferably 70 to 100 g/m.sup.2, depending on the respective composition of the lubricant.

[0026] Wetting of the surface of the mandrel bar and the layer thickness can be set by the amount of lubricant suspension sprayed on to the surface of the mandrel bar or the spray duration and by the viscosity and adhesion of the suspension. It has been found that the same or better lubricating effect can be achieved with the lubricant according to the invention in comparison with commercially usual graphite-bearing lubricants for the same purpose of use with the same or even smaller layer thickness or use amount. In that way it is possible to save on considerable costs in the production of seamless tubes in comparison with graphite-bearing lubricants used at the present time. At the same time further disadvantages of graphite-bearing lubricants are overcome like the particular working protection measures required when dealing with graphite-bearing lubricants, point welding of tool and workpiece as well as carburisation and the embrittlement caused thereby of the material at the inside surfaces of the rolled tubes.

[0027] An essential feature of the lubricant according to the invention is the proportion of solid lubricating agent which is a mixture of talc and potassium mica and wherein the ratio of talc to potassium mica is at least 2.0 and does not exceed 5.0.

[0028] In an advantageous embodiment of the invention the ratio of talc to potassium mica in the solid lubricating agent is 2.5 to 4.5, preferably 3.0 to 4.0 and particularly preferably 3.3 to 3.8.

Talc

[0029] Talc which according to the invention is one of the main constituents of the solid lubricating agent in the lubricant according to the invention is the powdered form of the mineral talc, a layered silicate (phyllosilicate), more precisely magnesium silicate hydrate. Depending on the respective modification it crystallises as talc-1A in the triclinic or talc-2M in the monoclinic crystal system.

Potassium Mica

[0030] Potassium micas which according to the invention form the further main constituent of the solid lubricating agent in the lubricant according to the invention but are contained in a smaller amount than talc are also layered silicates (phyllosilicates) which however have a potassium ion.

[0031] Basically the use of layered silicates in lubricants, also those for the hot forming of metals, was known. It was however surprising that it is precisely the combination of talc and potassium mica in the ratio claimed herein that contributes substantially to the improved and particularly advantageous properties of the lubricating agent according to the invention.

[0032] According to the invention suitable potassium micas include micas:

[0033] muscovite-celadonite series (dioctahedral), specifically muscovite, K Al.sub.2[AlSi.sub.3O.sub.10(OH).sub.2], aluminoceladonite, K Al(Mg, Fe.sup.2+) [Si.sub.4O.sub.10(OH).sub.2], ferro-aluminoceladonite, K Al(Mg, Fe.sup.2+) [Si.sub.4O.sub.10)(OH).sub.2], celadonite, K Fe.sup.3+(Mg, Fe.sup.2+) [Si.sub.4O.sub.10(OH).sub.2] ferroceladonite, K Fe.sup.3+(Mg, Fe.sup.2+) [Si.sub.4O.sub.10(OH).sub.2]

[0034] the phlogopite-annite series (trioctahedral), specifically annite, K Fe.sup.2+.sub.3[AlSi.sub.3O.sub.10(OH).sub.2], phlogopite K Mg.sup.2+.sub.3[AlSi.sub.3O.sub.10(OH).sub.2],

[0035] the siderophylite-polylithionite series (trioctahedral), namely siderophylite, K Fe.sup.2+.sub.2Al [Al.sub.2Si.sub.2O.sub.10(OH).sub.2], polylithionite, K Si.sub.2 Al[Si.sub.4O.sub.10F.sub.2],

[0036] the tainiolite group, tainiolite, K Li Mg.sub.t [Si.sub.4O.sub.10F.sub.2],

[0037] and mixtures of the above-mentioned potassium micas.

[0038] Phlogopite and muscovite, in particular phlogopite, have proven to be particularly advantageous. In a further embodiment of the invention in the solid lubricant of the lubricant according to the invention therefore the potassium mica contains at least 60 wt % phlogopite, preferably at least 80 wt % phlogopite, particularly preferably at least 90 wt % phlogopite. Quite particularly preferably only phlogopite is used as the potassium mica.

[0039] In the hot forming of metals, in particular for the lubrication of the mandrel bar and/or the hollow block in the production of seamless tubes, the lubricant according to the invention is sprayed in the form of a suspension of the solid constituents in water on to the mandrel bar, possibly also the hollow block. An aqueous suspension with 10 to 45 wt % solid constituents, preferably 15 to 35 wt % solid constituents, particularly preferably 20 to 30 wt % solid constituents, is suitable.

[0040] Besides the main constituent of the solid lubricating agent of talc and potassium mica the lubricant according to the invention further includes 10 to 30 wt % of an adhesive agent and 20 to 10 wt % of a thickener. Ethylene vinylacetate copolymer (EVA) has proven to be particularly advantageous as the adhesive agent and xanthan gum has been found to be particularly advantageous as the thickener. Other suitable adhesive agents and thickeners as are referred to herein can however also be used. Within the above-mentioned quantitative ranges, in each case in relation to the solid constituent of the lubricant, the man skilled in the art can easily ascertain the amounts of adhesive agent and thickener which are suitable for the overall composition of the lubricant, in order to achieve for the respective situation of use good processing capability, usability of the lubricant suspension in the respective available spray installation, wetting, adhesion and layer thickness formation on the tool surface.

[0041] The lubricant according to the invention further contains 0 to 10 wt % of further auxiliary agents which can be used in lubricants of the kind referred to herein advantageously and depending on the respective situation of use. Such auxiliary agents include preferably anti-foaming agents, dispersing agents and biocides.

[0042] Anti-foaming agents are intended to prevent or at least reduce disadvantageous foaming when spraying the lubricating suspension on to the tool, for example the mandrel bar. Suitable anti-foaming agents include polyglycols, amorphous and/or hydrophobic silicic acid, polysiloxanes, demethylpolysiloxanes, organically modified polysiloxanes and naphthalene condensates.

[0043] Dispersing agents can advantageously be used to improve the distribution of the solids of the lubricant in the aqueous suspension and to prevent or retard sedimentation of the solids in the suspension. Suitable dispersing agents include C16-C18 alcohols, ethoxylate salts, sodium and potassium tripolyphosphates, polyethylene glycol, and sodium silicate.

[0044] Biocides can advantageously be used to prevent or at least deter the increase of microorganisms like bacteria, fungi and/or yeasts in the lubricant, in particular upon prolonged storage of the lubricant. Suitable biocides include 1,2-benzisothiazol-3(2H)-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-2H-isothiazol-3-one, 2-octyl-2H-isothiazol-3-one, ethylene dioxy dimethanol, tetrahydro-1,3,4,6-tetrakis(hydroxymethyl)imidazo[4,5-d]imidazol-2,5(1H,3H)-dione, 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-2-carbamoylacetonitrile, sodium hypochlorite and sodium chlorite.

[0045] A further advantage of the lubricant according to the invention is that it can replace graphite-based lubricants used at the present time in continuous processes and push bench processes for the production of seamless tubes and can thus overcome the disadvantages in using graphite. Nonetheless graphite is an excellent lubricant and is particularly suitable in the hot forming of metals by virtue of its heat resistance. The graphite-based lubricants used hitherto for those applications therefore usually contain high proportions of graphite.

[0046] Even if the lubricant according to the invention is intended to overcome the disadvantages of graphite-bearing lubricants and to replace same it can be advantageous in embodiments of the lubricant according to the invention to add a certain amount of graphite to adjust the properties of the lubricant and further improve them. According to the invention however the proportion of graphite in the lubricant may not be more than 10 wt % graphite, preferably not more than 5 wt % graphite. Such a proportion of graphite in the lubricant according to the invention however is markedly less than the high graphite proportion in graphite-bearing lubricants used hitherto and therefore also does not involve the disadvantages of graphite to the known extent. Particularly preferably however the lubricant according to the invention does not contain any graphite.

[0047] The invention further concerns the use of the lubricant composition according to the invention for lubrication of the mandrel bar and/or the hollow block in the production of seamless tubes by hot forming of metals, preferably using the continuous process or the push bench process. In that respect the lubricant is desirably in the form of an aqueous suspension sprayed on to the mandrel bar which is at a temperature of about 100° C. before it is introduced into the hollow block.

[0048] Depending on the respective composition the lubricant according to the invention is sprayed in a layer thickness (use amount) of 30 to 150 g/m.sup.2 surface area of the mandrel bar. Preferably the layer thickness (use amount) is 50 to 120 g/m.sup.2 sprayed surface area, particularly preferably 70 to 100 g/m.sup.2 sprayed surface area.

[0049] The invention is further described hereinafter by means of examples and the description of methods and materials used. The examples however are not to be interpreted as restrictive on the scope of protection of the invention.

Material and Methods

Viscosity Measurement

[0050] Viscosity measurements were carried out with a rotational rheometer R/S Plus from Brookfield (AMETEK GmbH-BU Brookfield, Lorch, Germany) with a coaxial cylinder (40 mm spindle) in accordance with DIN 53019 and in accordance with the manufacturer instructions and using the software Rheo3000 at a sample temperature of 20° C.+/−0.4° C.

[0051] Friction value measurements Friction value measurements were carried out with the tribometer “HT-Tribometer Prüfstand 564” from Lohrentz GmbH Prüftechnik, Nidda-Harb, Germany. The tribometer comprises an inductively heatable rotating disc of Thermudur 2342 EFS steel of a diameter of 280 mm and a table which is displaceable hydraulically in the direction of the rotating disc and on which a test body of S355MC steel heatable by means of resistance heating is mounted.

[0052] For the friction value measurements the rotating disc was heated to 100° C. (±10° C.) and sprayed with the lubricant to the desired layer thickness. The spacing of the spray nozzle from the disc surface was 10 mm. Unless something different is expressly stated the lubricant was applied in a layer thickness of 80 g/m.sup.2 and was allowed to act prior to measurement for about 5 seconds.

[0053] In the subsequent measurement the disc was rotated at 10 rpm. The test body was heated to 1230° C. (±20° C.), pressed by means of the hydraulically displaceable table with a pressing force (FN) of 32,000 N (±2,000 N) against the rotating disc and the radial force (FR) acting at the disc perpendicularly to the pressing force was measured over a period of several seconds. The friction value (μ) is the quotiant of the radial force (FR) and the pressing force (FN), μ=FR/FN. Six measurements were performed with each sample (6 fold determination). In each case the mean value of the detected friction values in the period of 2 to 6 seconds after contact of the workpiece with the rotating disc was viewed as the friction value of a measurement. The friction value specified herein is in turn the mean value from the six measurements carried out with each sample.

Layer Thickness Inspection

[0054] The layer thickness of a lubricant applied to the disc of the tribometer under the spray conditions (spray duration) was inspected by a procedure whereby, prior to spraying the lubricant, a magnetic strip foil was applied to the surface of the disc and the lubricant was then sprayed on. The magnetic strip foil was removed, weighed with the lubricant applied thereto, and the layer thickness was determined from the difference in relation to the weight of the foil not bearing the lubricant.

Comparative Lubricant

[0055] As a comparative lubricant, use was made of the graphite-based mandrel bar lubricant PHOSPHATHERM® 120 GLW 30 (hereinafter “PH120”) which is industrially used inter alia in the continuous process for the production of seamless tubes, from Chemische Fabrik Budenheim KG, which is in the form of a 30% suspension.

Lubricant Formulations and Raw Materials

[0056] Unless otherwise specified raw materials stated hereinafter were used in the lubricant formulations. All percentages are percents by weight and correspond to the details from the manufacturer. [0057] Talc: chemical composition: SiO.sub.2: 61.0%, MgO: 31.0%, Al.sub.2O.sub.3: 0.1%, Fe.sub.2O.sub.3: 1.8% and CaO: 0.6%; mean particle size (D50): 5 μm [0058] Phlogopite: chemical composition: SiO.sub.2: 41%, Al.sub.2O.sub.3: 10%, MgO: 26%, CaO: 2%, K.sub.2O: 10%, Fe.sub.2O.sub.3: 8%; mean particle size (D50): 44 μm [0059] Muscovite 1: chemical composition: SiO.sub.2: 44%, Al.sub.2O.sub.3: 31%, K.sub.2O: 9%, Fe.sub.2O.sub.3: 3%; mean particle size (D50): 45 μm [0060] Muscovite 2: chemical composition SiO.sub.2: 51.5%, Al.sub.2O.sub.3: 27.0%, K.sub.2O: 10.0%, Fe.sub.2O.sub.3: 2.9%, MgO: 2.8%; mean particle size (D50): 5 μm [0061] Graphite: natural graphite, carbon content: 95%, mean particle size (D50): 21 μm [0062] Adhesive: vinylacetate ethylene copolyer (EVA) [0063] Thickener: xanthan gum (E415)

EXAMPLES

[0064]

TABLE-US-00001 Optimum talc/layered silicate ratio Formulation PH120 A B C D E F G H Water in % 75 75 75 75 75 75 75 75 Talc in % 12 13 15 15.45 17 10.5 Phlogopite in % 7.5 6.5 4.5 4.05 2.5 19.5 Muscovite 1 in % 19.5 Adhesive in % 5 5 5 5 5 5 5 5 Thickener in % 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Talc/mica ratio — 1.6 2 3.3 3.8 6.8 — — — Friction value 73 57 49 44 45 51 49 55 63 (×1000) in μ

[0065] FIG. 1 shows the friction values of the compositions investigated. Formulations C and D with a ratio of talc to phlogopite of 3.3 and 3.8 respectively presented the best results. Formulations B and E with a ratio of talc to phlogopite below 3.3 and above 3.8 respectively presented similar results to formulation F with phlogopite alone. Formulation A presented similar results to formulation G with talc alone. Formulation H, in which in comparison with formulation F the mica moscovite (moscovite 1) was used instead of phlogopite, presented markedly worse results than formulation F with phlogopite alone.

[0066] The friction values of al formulations A to H however were markedly lower than the comparative formulation PH120 with the graphite-based product in accordance with the state of the art.

TABLE-US-00002 Various amounts of solid lubricant of talc plus phlogopite Formulation R C S U D T Water in % 70.1 75 80.6 70.6 75 81 Talc in % 18.8 15 10.7 18.9 15.45 10.7 Phlogopite in % 5.6 4.5 3.2 5 4.05 2.8 Adhesive in % 5 5 5 5 5 5 Thickener in % 0.5 0.5 0.5 0.5 0.5 0.5 Talc/mica ratio 3.3 3.3 3.3 3.8 3.8 3.8 Friction value 56 44 42 56 45 42 (×1000) in μ

[0067] FIG. 2 shows the friction values of the compositions investigated. With the ratio of talc to phlogopite in the range of 3.3 to 3.8 which was found to be particularly advantageous in respect of the achievable friction value, with about 13% talc plus phlogopite (formulations S and T), comparably good friction values as with 19.5% talc plus phlogopite (formulations C and D) were achieved. When using 26% and 25.24% talc respectively plus phlogopite (formulations R and U) the friction values were higher, but still always markedly lower than the comparative formulation PH120 with the product according to the state of the art on a graphite basis.

TABLE-US-00003 Comparison of various micas and addition of graphite PH Formulation 120 C I L M O P Q Water in % 75 75 75 75 75 75 75 Talc in % 15 15 15 14.2 11.1 7.3 Phlogopite in % 4.5 4.3 3.4 2.2 Muscovite 1 in % 4.5 Muscovite 2 in % 4.5 Graphite in % 19.5 1 5 10 Adhesive in % 5 5 5 5 5 5 5 Thickener in % 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Talc/mica ratio — 3.3 — 3.3 3.3 3.3 3.3 3.3 Friction value 73 44 47 48 51 45 40 46 (×1000) in μ

[0068] FIG. 3 shows the friction values of the compositions investigated. In the formulations L and M alternative micas muscovite 1 and muscovite 2 with phlogopite in formulation C and with the same use amount of pure graphite instead of talc plus mica in formulation I were compared. While with the same amount of phlogopite (formulation C) the best friction values were achieved, the micas muscovite 1 and muscovite 2 (formulations L and M) also presented good friction values which were only slightly above the use of the same amount of pure graphite instead of talc plus mica (formulation I).

[0069] In the formulations O, P and Q, in comparison with formulation C, a part of the amount of talc plus phlogopite was replaced while retaining the talc/phlogopite ratio=3.3 by 1%, 5% and 10% respectively of graphite.

[0070] The results show overall that with the lubricant according to the invention in comparison with commercially usual graphite-bearing lubricant and when using pure graphite or a proportion of graphite instead of talc plus mica, with the same use amount and the same layer thickness, the same or even markedly better lubricating effect can be achieved. With the lubricant according to the invention therefore considerable cost savings can be achieved in the production of seamless tubes in comparison with graphite-bearing lubricants used at the present time, and further disadvantages of graphite-bearing lubricants were overcome.

TABLE-US-00004 Comparison of various layer thicknesses Formulation PH120 PH120 PH120 C C C Water in % 75 75 75 Talc in % 15 15 15 Phlogopite in % 4.5 4.5 4.5 Graphite in % Adhesive in % 5 5 5 Thickener in % 0.5 0.5 0.5 Talc/mica ratio — — — 3.3 3.3 3.3 Layer thickness 60 80 100 30 50 80 in g/m.sup.2 Friction value 86 73 88 69 59 44 (×1000) in μ

[0071] FIG. 4 shows the friction values of PH120 and the composition C with different layer thicknesses. The comparison of various layer thicknesses of formulation C with the comparative lubricant PH120 shows again that the formulation C according to the invention, even with the smallest use amount, with a layer thickness of only 30 g/m.sup.2 still gives better or at least comparable friction values, in comparison with the comparative lubricant PH120 with double to more than three times the use amount.

[0072] The composition “C” used in the preceding comparisons contains 25% (wt %) of solid constituent and 75% water. In a further test higher levels of dilution of the same solid composition were produced with a lower solid proportion and friction value measurements were carried out as above (20% to 10% solid constituent; hereinafter “C20”, “C17.5”, . . . “C10”)). With increasing dilution (increasing amount of water) and with the same application time the use amount (layer thickness) decreased in the test.

TABLE-US-00005 Comparison of various concentrations and layer thicknesses of the solid composition in accordance with “C” Formulation PH120 C(FS) C20 C17.5 C15 C12.5 C10 Water in % — 80 82.5 85 87.5 90 Talc in % 60 12 10.5 9 7.5 6 Phlogopite in % 18 3.6 3.15 2.7 2.25 1.8 Graphite in % 0 0 0 0 0 0 Adhesive in % 20 4 3.5 3 2.5 2 Thickener in % — 2 0.4 0.35 0.3 0.25 0.2 Talc/mica ratio — 3.3 3.3 3.3 3.3 3.3 3.3 Layer thickness 60 — 58 51 43 36 29 in g/m.sup.2 Friction value 86 — 38 52 65 64 60 (×1000) in μ C(FS) = percentage proportions related to the solid in composition “C” without water.

[0073] The results demonstrate that even with the sample “C10” with the highest level of dilution and the smallest amount of use, of only about half the amount with the lubricant according to the invention, considerably better friction values were still achieved than with the commercially usual graphite-bearing lubricant. A comparison of the results of this test with those of the preceding test shows that, for the solid composition “C” according to the invention, with a dilution of the order of magnitude of 20 to 25% and a use amount of about 50 to 80 g/m.sup.2, particularly advantageous friction value results are achieved.