DE1926138B2 - Process for the production of ceramic-like bearing components with self-lubricating effect - Google Patents

Description

Various types of self-lubricating bearing components are already in use. Such Components consist, for example, of nylon, metals, sintered carbon particles or resin compositions, in which filler particles with lubricating effect, such as graphite or molybdenum disulfide. incorporated are.

However, these known materials show under high stress and under high temperature operating conditions Disadvantage. So tend z. B. Metals and polymeric materials at high temperatures to become soft and lose their load-bearing properties, which are often required. Since no Bearing component that completely prevents friction, there is always the problem of heat dissipation. Due to the lack of strength of many materials, the lubricant content of the component must have a fairly deep cross-section under high loads. But this increases the heat dissipation problem, as it is difficult to dissipate the heat through the bearing components themselves. Also tend to some of the resinous materials currently in use under high temperature service conditions to collapse, resulting in component failure.

This collapse often leads to gas expulsion, which in certain types of application is undesirable.

The present invention is therefore concerned with the manufacture of bearing components incorporating the above Eliminate disadvantages as far as possible.

The bearing components which can be produced according to the invention and have a self-lubricating effect are at high temperatures stable, functional under high loads, can be easily molded and require a minimal space requirement.

The method according to the invention for the production of ceramic-like bearing components with a self-lubricating effect is characterized in that mixtures consisting of

1. 3 to 50 percent by weight of resinous organopolysiloxanes, containing per Si atom in total 1 to 3 substituents linked to hydrogen atoms or to the Si atom via a Si - C bond are organic radicals, in which radicals apart from carbon and hydrogen atoms oxygen or nitrogen atoms can also be included and each organic residue but no more than 18 atoms in total, excluding of hydrogen atoms, are present,

2. 0 to 30 percent by weight of a reinforcing filler and

3. 97 to 50 percent by weight of a finely divided filler with a self-lubricating effect,

4. Optional curing catalysts, 0.5 to 2.5 percent by weight of a mold release agent and other common additives.

cured while shaping, and then the molded bodies obtained in this way are subjected to a firing process at temperatures above 500 ° C are subjected. The moldings obtained in this way with ceramic-like Structure are stable at high temperatures and are only very slightly even under extreme loads deformed. Once the ceramic structure has been reached, the molded bodies no longer tend to Gas expulsion under high temperature operating conditions. Since the ceramic-like material thus obtained is high in strength, the bearing members can made with fairly thin cross-sections compared to the previously known bearing components of this type so that both space requirements and heat dissipation are kept to a minimum can be reduced.

The following detailed explanations serve for a better understanding of the invention Procedure:

ίο In accordance with the claimed method a ceramic-like molded body is produced in the shape of the desired bearing component. Of the The term "ceramic-like" used here means that not only real ceramic structures are included here but any structures that are ceramic-like in nature. In the literature will the ceramic structure is often interpreted in such a way that a phase change has taken place in the material. However, this fact does not play a decisive role in the method according to the invention.

When carrying out the method according to the invention, in the mixtures of resinous Organopolysiloxanes (1) as reinforcing fillers (2), which can be either granular or fibrous, silicon dioxide, aluminum oxide, aluminum, copper, Bronze, talc, silicon carbide, tungsten carbide, carbon, zirconium silicate, mica, potassium carbonate, Sodium carbonate, boron nitride, asbestos, magnesium silicate, aluminum silicate, calcium silicate, lithium aluminum silicate, Magnesium oxide and / or thorium oxide are used. As finely divided fillers with a self-lubricating effect (3) those used, which are at least 50 percent by weight of graphite, boron nitride and Sulphides, selenides and tellurides of molybdenum, tungsten, titanium, zirconium, hafnium, and niobium Must pass thorium. The remaining proportions can be solid lubricant additives such as calcium fluoride. Zinc oxide, potassium titanate, zinc sulfide and antimony trioxide.

The shaping of the mixture can, for example, by compression molding, such as compression in closed Molding under heating, by injection molding and extrusion molding processes or by coating a base body, which is less advisable, however.

In the compression molding process, it is often advantageous, but not essential, to use a curing catalyst for the resinous organopolysiloxanes to be used. By adding the curing catalyst, the molded bearing components can be removed from the mold during the firing process and easier to handle. Mixtures with a very high one Fillers can also be removed from the mold prior to firing, even if they are are not yet hardened, but great care must be taken to avoid damage to avoid these parts. The addition of fillers such as carbon black or graphite. Asbestos or silicon carbide, in fibrous form, gives the bearing components sufficient in both the unfired and the fired state Strength.

The resinous organopolysiloxanes used advantageously have an average of at least contain an organic radical of the defined type per Si atom. These organic residues can be monovalent or be multivalued, d. That is, the organic radical can either have only one Si atom or two or more Si atoms be linked. The inven-

Organopolysiloxanes which can be used according to the method can therefore be built up on units contain the structures of the following types:

ξ Si - R '- Si =

Si
ξ Si - R "- Si ==

where R 'denotes a divalent radical and R "denotes a trivalent radical.

Specific examples of siloxanes which can be used in the process according to the invention are those from the following units are constructed:

Hydrocarbon-substituted siloxane units, such as dimethylsiloxane, monoethylsiloxane, methylhydrogensiloxane, Monophenylsiloxane, phenylmethylsiloxane, monomethylsiloxane, monopropylsiloxane, Dipropylsiloxane, monovinylsiloxane, monocyclohexylsiloxane, or phenyldihydrogensiloxane units; Siloxane units with organic radicals containing oxygen atoms, such as y-hydroxypropylmethylsiloxane, / J-Methoxyäthylmethylsiloxan-, γ-Carboxypropylsiloxan-,

C ₆ H ₅ - OCCH ₂ CH ₂ SiO, ₅ -CH ₃ OOCCH ₂ CH ₂ CH ₂ SiO _1-5 -

CH ₃ CH ₃ OCH ₂ CH ₂ OCH ₂ CH ₂ SiO units

30th

35

and from organic radicals containing nitrogen atoms, such as y-aminopropylsiloxane,

40

45

H ₂ N (CH ₂ CH ₂ NH) ₃ CH ₂ CH ₂ SiO _1-5 -

O CH ₃

H ₂ NC (CH ₂ J ₂ SiO-

y-cyanopropylmethylsiloxane and

CH ₃

cH ₂ CH ₂ Si0 units

Besides these mentioned siloxane units, in which all organic substituents are monovalent, Siloxanes composed of units with the following structures can also be used:

O ₁₅ SiCH ₂ CH ₂ SiO ₁ ^ CH ₃

60

65 CH ₃
OSiCH ₂ CH ₂ (OCH ₂ CH ₂ ) ₂ OCH ₂ CH ₂ SiO ₁₅

5 and CH,

IO OSi (CH ₂ ) ₃ N (CH ₂ ) ₃ SiO _{1 5}

As can be seen from these explanations, is the constitution of the organic substituents on the Si atom incidental, d. that is, these can be linear as well as branched or cyclic in structure exhibit.

It should also be pointed out that the siloxanes which can be used according to the invention can be homopolymers or copolymers or mixtures thereof and that the copolymers can be built up from SiO ₂ , monoorgano, diorgano or triorganosiloxane units, only the total number of organic radicals and hydrogen atoms present must be within of the specified range from 1 to 3 per Si atom.

The term "siloxanes" used here means that there is at least one SiOSi bond per Si atom have to be; this term also includes incompletely hydrolyzed silanes.

It should be noted that when carrying out the process according to the invention, the organopolysiloxanes per se can be mixed with the filler material. Instead, the filler material also with a hydrolyzable organosilicon compound or with a silanol under conditions are mixed, which is the hydrolysis and / or condensation of these products with the formation of the siloxanes assist during the mixing or molding process. The siloxanes can also have Si - Si bonds contain. For example, the fillers can be mixed with methyltrimethoxysilane or with dimethylsiloxane and these products are then hydrolyzed to the SiI-oxanes.

A modified method is to first dissolve a hydrolyzable silane in aqueous solution and then mix the filler with this solution. With this method it is advantageous to use a Condensation catalyst, such as acetic acid, to be used to support hydrolysis and condensation to the corresponding siloxanes. The physical properties of the siloxanes are irrelevant decisive role, these can range from liquids of low viscosity to no longer flowable masses up to resinous solids. The choice is determined by the availability of the materials as well as the ease of giving them the desired shape. To some extent play a role The strength requirements for a particular application also play a role in the selection.

Any of those known for curing organosilicon compounds can be used as catalysts be used. Examples for this are:

Metal salts of carboxylic acids, such as lead stearate, lead 2-ethylhexoate, dibutyltin diacetate, stannous octoate or zinc octoate; quaternary ammonium compounds, such as benzyltrimethylammonium-2-ethylhexoate, Tetramethylammonium acetate or ß-hydroxyethyltrimethylammonium hydroxide; organic peroxides, such as benzoyl peroxides, tert-butyl perbenzoate or di-

cumyl peroxide; Vulcanizing agents containing chloroplatinic acid or sulfur.

When using the two last-mentioned catalysts, it is necessary that Sig-bonded in the siloxane to be hardened Alkenyl radicals and / or hydrogen atoms are present.

If molybdenum disulphide is used as a filler with a self-lubricating effect is used, some of the catalysts mentioned are used due to the acidic nature of the Mixture poisoned. In these circumstances, triethylenediamine is an excellent catalyst for the Gel formation of the resins containing silanol groups. In the case of steric hindrance, under these conditions 2-ethyl-4-methylimidazole can also be used.

The addition of the fillers defined as component (2) leads to a reinforcement of the structure high strength. Some of these fillers can be used in fiber form, resulting in an additional one Tensile strength leads. In general, however, the addition of these fillers is slightly disadvantageous Measure the lubricating properties of the finished bearing component, the addition of the same should therefore be in accordance are kept as low as possible with the required strength properties. It was found that with reinforcing filler loadings up to 30%, based on the weight of the mixture, Structures with sufficient strength can be achieved. However, the amounts of fillers should preferably from the group defined as component (2) are below 20%.

Likewise, should the amount of lubricant additives, such as calcium fluoride, potassium titanate, zinc oxide, zinc sulfide and antimony trioxide, do not exceed the amount of solid lubricants with self-lubricating properties, so as not to impair the lubricating properties.

According to the definition, the resin content of the mixture is in the range from 3 to 50 percent by weight, preferably but in the range from 10 to 25 percent by weight.

The mixture can be fired at temperatures as low as 500 ° C. Due to the unusual long burning times, which are required at low temperatures, are considered to be the lower limit for however, the firing temperatures are preferably 750 ° C. The heating is carried out until there is no further Weight loss is more noticeable. It is assumed that during the heating process the Filler particles with the remaining ingredients, which consist mainly of silicon dioxide, which after the heat decomposition of the organopolysiloxanes remains, are cemented together. The upper temperature limit for the firing process is determined by the filler material used, as some of the Fillers can also be decomposed by heat. It is also advantageous, especially if it is also used of molybdenum disulphide that the burning process takes place in a non-oxidizing atmosphere such as helium, Nitrogen or argon, in order to minimize the oxidation of the filler. The lack of oxygen in the atmosphere does not prevent the formation of fragments, since it is made up of the SiI-oxanes there is sufficient oxygen present in the formation of the cemented silica.

In addition to the resins, catalysts and fillers mentioned, further constituents can optionally be used are also used, which allow easier handling of the mixture. For example Mold release agents such as metal stearates and waxes are incorporated into the mixture, with Calcium stearate and zinc stearate are preferred.

5 Although the method according to the invention has been explained in detail with regard to bearing components, it should be noted that this expression is to be understood so broadly that not only components for rotating and sliding machine parts, but also any other types of application which two parts need to be moved relative to each other. An example of such an application is cited the area of piston rings.

_1S Example 1

The resin used in this example is a phenylmethylsiloxane resin with an average total of 1.15 methyl and phenyl radicals per Si atom and a ratio of phenyl to methyl radicals such as 1.13 to 1.0. 10 parts by weight of the resin, 89 parts by weight of molybdenum disulfide (Molykote type Z) and 1 part by weight of calcium stearate as a mold release agent were mixed for 6 minutes on a two-roll mill. After a good mixture had been obtained, 0.1 part by weight of triethylenediamine was added as a curing catalyst for the resin and vigorously worked into the mixture. Then, test strips were molded under pressure in a helium atmosphere in a lOstündigen firing cycle at temperatures were slowly raised from room temperature to 396 ° C after 1 hour and up to 115o C to ⁰ 7V ₂ hours fired. Once this temperature was reached, the oven was turned off and the test strips were cooled to 425 ° C before being removed from the oven.

These samples were then weighed, reheated and weighed again. There was no weight loss found, indicating that the cullet had formed during the firing process.

The samples obtained in this way were then tested using a lubricant tester Alpha LFW-I according to US Pat. No. 3,028,746 using a load of 40.8 kg. At 400 revolutions per minute the coefficient of friction was 0.06 and the temperature was constant ^{at 68 ° C.} When the speed was increased to 1000 rpm, the coefficient of friction decreased to 0.04 and the temperature rose to 85 ° C and remained constant. The abrasion was low in both cases.

Example 2

The process steps according to Example 1 were repeated, but the resin content between 3 and 50 percent by weight varies and the content of molybdenum disulfide adjusted accordingly. With a content of 50% resin, 400 revolutions / Min. A coefficient of friction of 0.1 was determined and a temperature rise to 93 ° C. In addition, a very strong abrasion noted. If the resin content was 3%, the sample became too soft for the test, which indicated indicated that the amount of binder was insufficient for a uniform structure.

Example 3

An organopolysiloxane copolymer made from 25 mol percent monomethylsiloxane and 25 mol percent Monovinylsiloxane, 10 mole percent diphenylsiloxane and 40 mole percent monoethylsiloxane units was

mixed with molybdenum disulfide and calcium stearate. The ratio of the individual components was: 20 parts by weight of copolymer, 79 parts by weight of molybdenum disulfide and 1 part by weight of calcium stearate. Then 0.2 percent by weight of dicumyl peroxide was added to the mixture as a catalyst.

After the mixture was compression molded and fired according to Example 1, the samples became tested on the Alpha LFW-I lubricant tester with a load of 40.8 kg. At 400 revolutions / min, the coefficient of friction was 0.065, and the temperature remained constant at 60 ° C, at 1000 revolutions / Min. The coefficient of friction decreased to 0.055 and the temperature remained constant at 82 ° C. In both cases the abrasion was low.

Example 4

Molding compositions were produced, compression molded and fired from the amounts given in Table I appended to the examples. Each sample was then tested for friction and abrasion on the Alpha LFW-I tester at a load of 38.0 kg / cm ² . The abrasion is given in units of 10 ~ ⁹ cm abrasion of the test strips per 30.5 cm sliding contact.

In order to obtain comparative data, commercially available storage materials were tested on the Alpha LFW-I tester with a load of ^{38.0 kg / cm 2.} The results are compiled in Table II which follows the examples.

Example 5

Molding compositions were produced, compression molded and fired from the amounts given in Table III. Friction and abrasion were measured on a Hohman tester. The percentages are based on that Based on weight. The abrasion is given in g / 304.8 m and the speed in m / minute. As resin a phenylmethylpolysiloxane was used.

Example 6

Was copper, bronze, silicon carbide, tungsten carbide, Silicon dioxide, aluminum oxide, aluminum, zirconium silicate, Mica, potash, asbestos, magnesium silicate, aluminum silicate, magnesium oxide and thorium oxide used either alone or in combination with up to 30 percent by weight molybdenum disulfide, practically the same results as in Examples 1 to 5 were obtained.

Example 7

Was in the molding compositions according to Examples 1 ίο and 2 calcium fluoride, zinc oxide and antimony trioxide either alone or in combination with up to 50 weight percent molybdenum disulfide were used practically 'the same results as in Examples 1 to 5 achieved.

Example 8

If any amount of molybdenum disulfide was replaced by tungsten disulfide in the molding compound according to Example 3, Replacing boron nitride, graphite and molybdenum diselenide, practically the same results were obtained.

Example 9

If the resins in Examples 1 to 5 by

1. a methyl hydrogen siloxane,

2. a copolymer of monomethyl, dimethyl and trimethylsiloxanes with an average 1.26 methyl groups per Si atom,

3. a copolymer of 10 mol percent monocyclohexylsiloxane, 50 mol percent monomethylsiloxane, 20 mol percent monopropylsiloxane, 15 mol percent diphenylsiloxane and 5 mol percent H ₂ SiO units,

4. a siloxane composed of units of the formula

30th

35 QH ₅

40

45 and
5. a siloxane composed of units of the formula

CH ₃ CH ₃

OSiCH ₂ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ SiO

were replaced, practically the same results were obtained.

Table IA

Parts by weight of resin

15 (C ₆ H ₅ ) CH ₃ SiO

20 (C ₆ H ₅ ) CH ₃ SiO
20 (C ₆ H ₅ ) CH ₃ SiO

20 (C ₆ H ₅ ) CH ₃ SiO

% Catalyst based on resin

2 benzoic acid,
1.8 PbCO ₃

0.5 triethylenediamine 1 triethylenediamine

1.8 PbCO ₃
2 benzoic acid

Parts by weight Parts by weight Weight lean MoS, Mold release agents other components 34.5 1 CaStearate 34.5 ZnS, 5 K ₂ TiO ₃ 10 talc 39.5 1 CaStearate 39.5 ZnS 36.8 1 CaStearate 2 B ₂ O ₃ , 3.4 Na ₉ CO ₃ , 36.8 ZnS 37.0 1 CaStearate 37 ZnS, 5 K ₂ TiO ₃

109 547/437

friction

21.95 ni minute

Temp. C

0.100
0.1200
0.1145
0.1166

58
63
61
60

Table IB ALPHA LFW-I results

10

87.78 m minute friction Temp. C Abrasion 1 friction .11.67 m minute Abrasion 0.0611 100 130.0 Temp. C " 45.72 0.0611 100 83.57 0.0300 48.77 0.0500 104 182.03 117 69.62 0.0389 93 69.11 43.18

Abrasion

67.27

material

Polytetrafluoroethylene filled with graphite Delrin + 15% polytetrafluoroethylene

Sintered graphite

Table II

speed

21.95 m / min. 43.89 m / min. 21.95 m / min. 43.89 m / min. 98.76 m / min. 21.95 m / min. 43.89 m / min. 98.76 m / min.

0.13
0.11

friction Temperature. C. 0.21 77 0.22 132 0.11 60 0.16 110

unstable

unstable

38
99

Test cycles Table III friction Temp. C Abrasion speed Pressure, kg / cm ' Molding compound 1 million 0.02 to 0.08 127 3.12 X 10 ~ ⁴ 1.508 20th 65% MoS ₂ 1 million 0.088 116 4.0 χ 10 " ⁴ 0.603 20th 15% resin 20% SiO ₂ 1 million 0.11 77 1.4 χ 10 " ⁴ 1.508 12th 75% MoS ₂ 1 million 0.030 113 1.32 χ ΙΟ " ⁴ 1.508 31.6 15% resin 1 million 0.067 104 0.63 χ 10 ~ ⁴ 0.603 40.4 10% aluminum

Claims (5)

Patent claims: 1. A method for the production of ceramic-like bearing components with self-lubricating effect, characterized in that mixtures, consisting of 1. 3 to 50 percent by weight of resinous organopolysiloxanes, containing a total of 1 to 3 substituents per Si atom. the hydrous atoms or organic radicals linked to the Si atom via a Si - C bond, in which radicals apart from carbon and hydrogen atoms can also contain oxygen or nitrogen atoms, but with each organic radical no more than 18 atoms in total, excluding the hydrogen atoms. available are. 2. 0 to 30 percent by weight of a reinforcing filler and 3. 97 to 50 percent by weight of a finely divided filler with a self-lubricating effect. 4. optionally curing catalysts. 0.5 to 2.5 percent by weight of a mold release agent and other common additives. cured while shaping and then the shaped bodies obtained in this way are subjected to a firing process be subjected at temperatures above 500 C. 2. The method according to claim 1, characterized in that mixtures are used as reinforcing fillers (2) silicon dioxide, aluminum oxide, aluminum, copper, bronze, talc, Silicon carbide, tungsten carbide. Carbon. Zirconium silicate. Mica, potassium carbonate. Sodium, Boron nitride, asbestos, magnesium silicate, aluminum silicate. Calcium silicate, lithium aluminum silicate. Contain magnesium oxide and / or thorium oxide. 3. Process according to Claims 1 and 2, characterized in that mixtures are used as finely divided fillers with self-lubricating properties (3) graphite, boron nitride. Calcium fluoride. Zinc oxide, zinc sulfide, potassium titanate, antimony trioxide. Sulphides, selenides and tellurides of Molybdenum, tungsten. Titanium. Contain zirconium, hafnium, niobium and thorium, with the proportion of Calcium fluoride. No more than zinc oxide, potassium titanate, zinc sulfide and or antimony trioxide 50% of the total amount of filler with self-lubricating effect amounts to. 4. Process according to Claims 1 and 2, characterized in that mixtures are used used as fillers with self-lubricating properties (3) molybdenum disulfide and as hardening catalyst for the resinous organopolysiloxanes Contain triethylenediamine. 5. Process according to claims 1, 2 and 4, characterized in that mixtures are used containing 10 to 25 percent by weight of the resinous organopolysiloxanes (1).