Hybrid grease with low friction coefficients and high wearing protection

Abstract

A hybrid grease is provided having low coefficients of friction and high wear protection which is employable over a wide temperature range. The hybrid grease includes a combination of a grease based on a silicone oil in conjunction with a grease based on synthetic hydrocarbon oils, mineral oils or polyglycols. The hybrid grease may especially be used to lubricate joints in vehicle parts based on plastic-steel pairings.

Claims

1. A hybrid grease consisting of: (A) 10% to 20% by weight of a grease based on a synthetic hydrocarbon oil, mineral oil or polyglycol containing 70% to 80% by weight of a base oil selected from synthetic hydrocarbon oil, PAO, mineral oil and polyglycol, 10% to 20% by weight of thickener, 1% to 7% by weight of additives, and (B) 80 to 90% by weight of a silicone grease containing 70% to 80% by weight of a silicone oil selected from the group consisting of polydimethylsiloxane, polyphenylmethylsiloxane and mixtures thereof, 10% to 30% by weight of thickener and 1% to 10% by weight of additives.

2. A method of using the hybrid grease as claimed in claim 1, comprising applying the hybrid grease to a joint in the vehicle sector for the lubrication of the joint.

3. The method of using the hybrid grease as claimed in claim 2 wherein the joint being lubricated is based on plastic and steel pairings.

4. A method of using the hybrid grease as claimed in claim 1, comprising applying the hybrid grease to an actuator for the lubrication of the actuator.

5. A method of producing the hybrid grease as claimed in claim 1, comprising: mixing the component (A) grease and the component (B) grease, and subsequent homogenization of the mixture.

6. The method of claim 4, wherein the actuator being lubricated is selected from the group consisting of: vehicle power steering systems (EPS), brake actuators, brake boosters, and power windows.

7. The hybrid grease as claimed in claim 1, wherein the synthetic hydrocarbon oil is an oil selected from the group consisting of PAO, mixtures of PAO and olefin copolymers, mixtures of PAO and polyisobutylene.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the setup of an apparatus for determining the coefficients of friction by means of a torque test in a ball joint.

(2) FIG. 2 shows by way of example the course over time of the measurement from the apparatus in FIG. 1.

(3) FIG. 3 shows the apparatus for determining wear protection using a wear protection test in a ball joint.

DETAILED DESCRIPTION

(4) The invention is now more particularly elucidated by the following examples.

EXAMPLES

(5) Production:

(6) A standard production process according to the prior art for lubricating greases was employed.

(7) The base oil/a portion of the base oil or oil mixture is initially charged in a suitable heatable container comprising a stirrer such as is used in the prior art for the production of lubricating greases. Production of the thickener is carried out therein, for example neutralization of stearic acid or 12-OH-stearic acid with lithium hydroxide and a subsequent heating phase for removing the water and for forming the thickener structure. Peak temperatures of up to 210° C. may be achieved to completely melt the soap thickener and subsequently adjust the morphology of the thickener by targeted cooling. The additives are added and homogeneously distributed in the subsequent cooling phase. It is also possible to produce a batch comprising silicone oil as the base oil and a thickener and add the synthetic hydrocarbon oil as the mixing component analogously to an additive. It is likewise possible to produce a batch comprising synthetic hydrocarbon oil as the base oil and a thickener and only add the silicone oil as the mixing component analogously to an additive. This is followed by a homogenization process, for example using a roller apparatus or a colloid mill or a high-pressure homogenizer such as is customary according to the prior art for the production of lubricating greases.

(8) The grease components (A) and (B) shown in Table 1 were produced according to the procedure described above. All reported amounts are in % by weight.

(9) TABLE-US-00001 TABLE 1 Synth. Synth. HC/PAO HC/PAO Silicone grease A grease B grease Polydimethylsiloxane — — 75% Viscosity at 40° C. 10000 mm.sup.2/s Synth. HC/PAO — 80.5% — Viscosity at 40° C. 3500 mm.sup.2/s Synth. HC/PAO 74% — — Viscosity at 40° C. 350 mm.sup.2/s Thickener: 20%   13% 24% lithium 12-OH- stearate/lithium stearate Antioxidant  1%  0.5% — Anticorrosion agent  5%   1%  1% Solid lubricant —   5% —
Hybrid Greases:

(10) The mixture of the two greases may be manufactured using stirrers such as are prior art in the production of lubricating greases. It is also possible to produce a batch comprising silicone oil as the base oil and a thickener and add the synthetic hydrocarbon oil as the mixing component analogously to an additive. It is likewise possible to produce a batch comprising synthetic hydrocarbon oil as the base oil and a thickener and only add the silicone oil as the mixing component analogously to an additive. Mixing may be followed by a subsequent homogenization process step, for example using a milling apparatus (colloid mill), roller apparatus or high-pressure homogenizer.

(11) The hybrid greases according to the invention were produced from the components (A) and (B) shown in Table 2 by this process. All reported amounts are in % by weight.

(12) TABLE-US-00002 TABLE 2 Hybrid grease A Hybrid grease B Hybrid grease C Synth. HC/PAO 20% — — grease A Synth. HC/PAO — 20% 10% grease B Silicone grease 80% 80% 90%
Determination of Coefficients of Friction

(13) To determine the coefficients of friction by means of a torque test in a ball joint the test method described hereinbelow was used. The setup of the test apparatus is shown in FIG. 1.

(14) Ball joints such as are standard-fit in the running gear of vehicles were used. The balls are made of steel with a diameter of 23 mm. The steel ball is enclosed by a plastic cup made of POM (polyoxymethylene). The lubricant is introduced between the plastic cup and the steel ball. The POM cup with the ball is then introduced into a housing by positive attachment. The housing is compressed such that a certain force is exerted on the system composed of the cup and ball. In the present example the pressure is about 1 N/mm.sup.2.

(15) Table 3 shows the results of the determination of the coefficients of friction by means of a torque test.

(16) TABLE-US-00003 TABLE 3 Synth. Synth. HC/PAO HC/PAO Silicone Hybrid Hybrid Hybrid Sample grease A grease B grease grease A grease B grease C Loosening torque 6 Nm 5.8 Nm 3.2 Nm 5 Nm 3.2 Nm 3.1 Nm at +25° C. Loosening torque 3.9 Nm 3.2 Nm 2.7 Nm 3.6 Nm 2.7 Nm 2.6 Nm at −40° C. Loosening torque 5.5 Nm 5.7 Nm 3.2 Nm 5.4 Nm 3.2 Nm 3.1 Nm at +80° C. Running torque 2.5 Nm 1.6 Nm 1.8 Nm 1.8 Nm 1.6 Nm 1.6 Nm at +25° C. Running torque 2.7 Nm 2.0 Nm 0.9 Nm 0.6 Nm 0.8 Nm 0.8 Nm at −40° C. Running torque 3 Nm 2.5 Nm 2.3 Nm 2.6 Nm 2.3 Nm 2.2 Nm at +80° C. (stick slip)

(17) Compared to the greases based on synthetic hydrocarbons hybridization had a positive effect on loosening and running torque. The low loosening torques and running torques of silicone grease over the entire temperature range were particularly advantageously achieved and in some cases even exceeded, i.e. lowered, with hybrid greases B and C in particular.

(18) Determination of Wear Protection

(19) The wear test was performed in a ball joint.

(20) The described ball joint is subjected using an apparatus to a load of 3240 N. The apparatus is movably mounted so that the ball may be tilted in the POM cup. The tilting motion is performed with a deflection of 3° and a frequency of 15 Hz. The motion is halted at regular intervals and the play resulting from wear was determined by unloading and reversal of the load.

(21) The setup of the apparatus for wear protection testing is shown in FIG. 3.

(22) The result of the wear test is shown in Table 4.

(23) The wear distance of the joint was evaluated after 1.1 million load cycles

(24) TABLE-US-00004 TABLE 4 Synth. Synth. HC/PAO HC/PAO Silicone Hybrid Hybrid Hybrid Sample grease A grease B grease grease A grease B grease C Wear distance 0.25 mm 0.15 mm >0.65 mm 0.4 mm 0.2 mm 0.3 mm (mm)

(25) Hybridization had a positive effect on wear values compared to silicone grease Hybrid grease B in particular achieved a very good wear level.