DE2503613C3 - lubricant - Google Patents

Description

The invention relates to the lubrication of a cooling or refrigeration system and relates to Lubricant compositions for such lubrication.

It is well known rotary compressor with an inevitable delivery, such as Lubricate the screw compressor. Such compressors that are used in cooling or refrigeration systems and Other devices used are generally characterized by the generation of Compression chambers created by the meshing engagement of the flanks of two intermeshing rotary pistons be formed with a screw profile. The two rotary pistons work with a suitable housing together, which is provided with inlet and outlet openings. The volume of the compression chambers decreases, when the rotary pistons are in a range of rotation between the time of separation of the Chambers from the inlet port and the time of connection of the chambers to the outlet port is so that a fixed pressure ratio is generated in the compressor.

Compressors of the above type can be divided into two classes. To the originally developed Class include the so-called dry compressors. These compressors have compression chambers through a packing, d. H. sealed by a packing that has an extremely small clearance between the meshing rotary piston via the interposition of synchronizing and control devices as well an equally small play between the circumference and the end faces of the rotary piston on the one hand and the surrounding housing on the other hand. With these compressors there is constant leakage from the Compression chambers are present over these small clearance gaps. These compressors are characteristically always operated at high top speeds on the circumference of the rotary lobes to prevent leakage to make this clearance gap as small as possible and the greatest possible volumetric efficiency

ίο for the compressor to reach.

The second class of the above-mentioned compressors include the so-called wet or Oil-flooded compressors that are supplied with a liquid lubricant for two reasons. The first reason is to create a liquid seal to close the clearance gaps and the second reason is the cooling of the gaseous flow medium that occurs during the compression phase of the cycle is compressed directly. The present invention is particularly concerned with the lubrication of Compressors of the last-mentioned type Such compressors are in a considerable number of Patents described, for example in US-PS 30 73 514, 30 84 851, 3088 658, 3138 320, 32 83 99Ö, 33 07 777, 3314 597, 34 23 017, 34 32 089, 34 67 300 and 37 56 753.

In addition to the screw compressors, other types of wet compressors were used, those for refrigeration or Refrigeration systems considered appropriate

jo hen were. For example, rotary vane or Wankel compressor used as a wet compressor The last-mentioned compressors are for the present Purpose designed as a compressor that is lubricated by direct oil injection.

In commercial refrigeration, a liquid coolant is evaporated from a container resulting vapor is compressed to condensation pressure, the vapor is condensed by cooling the gas and the Liquid returned to the container In reality, the liquid container is an evaporator. The steam is compressed in a mechanical compressor and the hot, high-pressure refrigerant becomes converted into a liquid in a condenser. The liquid coolant is collected and in one Reservoir Stored The flow of liquid refrigerant from the reservoir to the evaporator is controlled by an expansion valve. The temperature at which the refrigeration will take place controlled by the pressure at which the evaporated

5 (i fende coolant is held. The pressure on which the steam to be compressed is controlled by the condensate temperature, which is determined by the available Cooling medium is determined.

The lubrication of the compressor cannot be viewed separately from the entire system that the liquid lubricant, such as a commonly used mineral oil, that goes with the refrigerant to the condenser and evaporator is brought, disrupt the heat transfer and the operation of the expansion valve and so that it can influence the overall efficiency of the refrigeration system.

Although mineral oils have so far been used in general for the lubrication of compressors for refrigeration these lubricants have been used

t> 5 properties that help to achieve the best Total performance must be balanced. Mineral oil lubricants can only be used in liquid form Condition to be kept at low temperatures,

when using oils of relatively low viscosity made from selected crude naphthene distillates with special refinery treatment stages. For the lubrication of bearings and cylinders, the designer will generally prefer an oil whose viscosity is slightly higher than the viscosity, which is determined by the requirements for low temperatures. An important The phenomenon of the lubrication of compressors for refrigeration is the decrease in the viscosity of the Lubricant, as the coolant has a tendency to become dissolve in the lubricant.

In a refrigeration system with a compressor lubricated by direct oil injection the lubricant is in intimate contact with the coolant. In addition to lubricating the compressor, the lubricant also acts as a sealant between the Low and high pressure sides of the system. When the refrigerant from the compressor through the condenser and Evaporator and flows back to the inlet side of the compressor, the refrigerant takes some lubricant with it The lubricant therefore runs through the entire system, although the lubricant only runs in the compressor is required

Difficulties have so far occurred with compressors that are part of a cycle for the Form refrigeration, in which a coolant from a halogenated alkane, such as a Commonly used alkane called "Freon", which to some extent in lubricants i < > The lubricant ajs is soluble in mineral oils Mineral oil that is used in the chambers for bearing lubrication, sealing, load compensation and the like Purposes, usually has a pressure which exceeds the pressure on the high pressure side of the compressor. The amount of Freon refrigerant that dissolves in the lubricant is considerable. This dissolved freon coolant causes the viscosity of the mineral oil lubricant to decrease, thereby causing the disadvantage inherent in the lubricant is reinforced, which is attributable to the relatively low viscosity of the lubricant to the Achieving a low StoikpMiktes and Freon flock point is required. The flock point relates to a temperature at which a heavy precipitate of wax in a mixture of freon and 10 wt% oil occurs. The reduced viscosity of the oil film can lead to an extremely thin film lubrication, which increases the wear and tear. The toughness and strength of this oil film with its lower viscosity is also lowered so that the oil is no longer able to withstand the disintegration effect of the liquid droplets of the coolant, which are carried along with the gas flow under certain conditions and the rupture of the oil film cause, which leads to increased wear. The lower viscosity of the oil film also leads to a lower sealing effect, which results in a great loss of the efficiency of the compressor.

In addition to lubricants made from mineral oils, e> o synthetic hydrocarbon lubricants such as alkylated aromatic hydrocarbons for Refrigeration systems have been proposed in which a refrigerant such as the freon is used. However, these synthetic lubricants are compatible with the preferred halogenated alkane coolants, such as chlorofluoromethane, fully miscible as described in U.S. Patents 3,092,981 and 3,169,928 These synthetic lubricants therefore have some of the same difficulties mentioned above in connection with the lubricants made from mineral oils. Another Prior art is described in US Patents 3,642,634 and 3,733,850, according to which in Combination with coolants made from halogenated alkanes. Cold generating lubricators made from an alkylbenzene can be used which has one or more side chains with one to 25 carbon atoms and a total of between 10 and 25 carbon atoms in the alkyl groups and approximately between 2 and 50% by weight Polyisobutylene contains These blends have the additional disadvantage of careful control the proportions in the mixture of the lubricant is necessary

According to the invention is in combination with a coolant based on a halogenated alkane Lubricant is provided which is a hydrogenated polyalkylene whose monomeric alkylene units contain between about 6 and about 12 carbon atoms.

In comparison with a mineral oil-based refrigerator lubricant composition, the use of a lubricant based on a hydrogenated polyalkylenes have the advantages of higher viscosity index, lower volatility and greater thermal and chemical stability Because lubricants are based on hydrogenated Polyalkylenes do not contain waxy materials, their pour or pour points are naturally low. Furthermore, the viscosity of the hydrogenated polyalkylene lubricants can be higher than for mineral oils because none There is a »natural« connection with the flow point. In addition, the "Freon" coolant is not to the same extent as is the case with mineral oil, so the The dilution effect is noticeably lower. It has been found that these properties make hydrogenated polyalkylene-based lubricants extremely good suitable for compressors that handle refrigerants of the "Freon" type. In systems where the As with screw compressors, viscosity has a pronounced effect on efficiency where the lubricant has a primary function in terms of sealing, the lubricants supply the basis of hydrogenated polyalkylene a very substantial improvement in compressor efficiency or performance.

The coolants used here are the halogenated alkanes, particularly containing fluorine, preferably having 1 or 2 carbon atoms, and usually Are called "freons". Typical coolants include

Trifluorochloromethane (R 13), Trifluorobromomethane (R 13 Bl), Trichlorofluoromethane (R 11), Dichlorodifluoromethane (R 12), Dichlorofluoromethane (R 21), Chlorodifluoromethane (R 22), Trichloitrifluoroethane (R 113), Hexafluoroethane (R 116), Dichlorotetrafluoroethane (R 114), an azeotropic mixture of Dichlorodifluoromethane and Difluoroethane (R500), an azeotropic mixture of Monochlorodifluoromethane and

Monochloropentafluoroethane (R 502) and Chlorofluoromethane (R 31).

Of these, the lower boiling freons are preferred. These include

Chiordifluoromethane (R 22), Dichlorofluoromethane (R 21), Trichlorofluoromethane (R 11) and Dichlorodifluoromethane (R 12)

The hydrogenated polyalkyl chloride used can be obtained by means known in the art Process (see e.g. US-PS 3199178) will. In short, these include a polymerization of normal alpha monoolefins (Ce to C12) either thermally or catalytically, in the presence of a di-tert-alkyl peroxide or a Friedel-Crafts catalyst such as aluminum chloride or boron trifluoride. Normal alpha-monoolefins with between 6 and 12 carbon atoms are applied. It is generally preferred that the mean value be the Olefin chain length is about 10 carbon atoms Representative examples of olefins are 1-hexene, 1-octene, 1-nonene, 1-decene and 1-dodecene. Of these 1-octene and 1-decene or olefin mixtures rich in one or both of these olefins, preferred

In general, the relative amounts of the halogenated alkane refrigerant and the hydrogenated one are Polyalkylene lubricant such that the resulting mixture in contact with the compressor of the refrigeration system is a major portion and especially from 60 to 90% by weight of hydrogenated polyalkylene and a minor proportion, and especially from about 10 to 40% by weight, of halogenated Contains alkane coolants.

The invention is explained in more detail below with reference to the drawing

F i g. 1 illustrates the miscibility behavior of blends of hydrogenated polydecene and Chlorodifluoromethane when the temperature changes;

F i g. 2 shows the miscibility behavior of mixtures of different mineral oil lubricants and synthetic lubricants and chlorodifluoromethane as the temperature changes.

To illustrate the physical properties of mixtures of a typical hydrogenated Polyalkylene and a halogenated alkane coolant, a determination of the density, viscosity, Solubility and miscibility properties performed density measurements on mixtures of (1) one synthetic oil made from hydrogenated polydecene, which is an antioxidant and an anti-wear additive Contains and (2) chlorodifluoromethane were carried out These measurements are for the conversion of the dynamic viscosity in kinematic viscosity useful. These measurements are also for the Flow rate calculation useful when such mixtures are mechanically pumped. the The composition with the synthetic oil based on hydrogenated polydecene was as follows Characteristics:

25 03 613
6th 37.6 50.0 ° CcSt 9.3 98.9 ° C (210 ⁰ F) ₁ CSt 149 Viscosity index -60 -reon's pour point, "C 240 5 flash point, "C <0.01 Ash (oxide), wt .-% specific heat (50 ° C) -0.48 calg -'- C- '

in The method used to determine the density was similar to that used by HJ L ö ff! ε r in refrigeration technology, 11 (1959), 70/4 has been described. This procedure involved the use of spherical glass vials with graduated capillaries (0.02 ml / division) and a total volume of about 25 ml. The vials were volumetrically calibrated with bromobenzene at i = 20 ° C prior to the experiments. The required amount of synthetic oil composed of hydrogenated polydecene is in the test vessel through a metal capillary is filled, the test tube is weighed mg to ± 0.1 and the test coolant is under vacuum distilled over the test mixtures are frozen in liquid nitrogen and after pumping down to P <10 ^-2 Torr, the vessels are sealed with a propane-oxygen flame. The exact amount of coolant in the mixture is determined by reweighing the test vessel plus the removed capillary pieces. Pipes or vessels with different mixture concentrations are produced and placed in a desilvered Dewar vessel.This is coupled to a circulating thermostat and regulated to ± 0.01 ° C The volume changes are determined over a range of temperatures, thereby reducing the

Calculation of the density of the mixture is made possible.

The density of the mixture was in the temperature range - 20 to 70 ° C for mixtures with concentration of 70, 80 and 90% by weight for the synthetic oil The results are determined from hydrogenated polydecene

4 (i are shown in Table I below:

Tabel

45

Temperature density g / ml

temperature mixture concentration wt .-%, synthetic
Hydrogenated polydecene oil

l'L 70.0

80.0

90.0

100.0

50
-20 0.9573 0.9223 0.8867 0.8535 -10 0.9492 03146 0.8806 0.8480 ± 0 0.9413 0.9075 03743 0.8422 10 03335 03009 0.8680 0.8364 55 20 03262 0.8935 03617 0.8307 30th 0.9188 03865 Ο3553 0.8249 40 0.9117 0.8796 0.8490 0.8191 50 03046 0.8727 0.8426 0.8133 60 0.8979 0.8663 0.8364 0.8076 60 70 0.8906 0.8598 03302 0.8018

Density (15 ° q, gml- 'kinematic viscosity at 373 ⁰ C (100 ⁰ F) ₁ CSt

There were viscosity measurements with the above-mentioned mixtures of synthetic oil from hydrogen tem polydecene and chlorodifluoromethane

A falling ball viscometer similar to the type 61.0 as pointed out by H. J. Löffler. In "Kältetechnik", 12 (1960),

71/5 is used. The dynamic viscosity of the mixture is calculated from the time Calibration constant, the falling sphere and the densities of the sphere and the mixture are calculated. the Viscosities were measured in the temperature range from -20 to + 70 ° C at mixture concentrations of 70, 80 and 90% by weight of synthetic oil measured from hydrogenated polydecene. After knowing the mix density the measured dynamic viscosity was converted into the kinematic viscosity. The experimental Results are shown in Table U below:

Table II

Temperature Kinematic Viscosity cSt rature wt .-%, synthetic oil from hydrogenated Polydecene

t, "C 70.0 80.0 90.0 100.0

Table III

51.5 31.3 20.2 13.8 9.90 7.41 5.77 4.60 3.60 2.88

142.5 78.5 47.5 30.9 20.9 15.0 11.1 8.53 6.69 5.42

510

250

138 82.0 51.8 34.4 24.2
17.5
13.3 10.4

2950
1010
482
253
143
86.0
55.0
37.6
26.5
19.4

Temperature Absolute vapor pressure P, at

Mixture concentration

% By weight, synthetic oil from hydrogenated

Vapor pressure measurements were made on the above mixtures of synthetic oil from hydrogenated Polydecene and chlorodifluoromethane run around the solubility of the latter in the synthetic determine oil.

The method of operation and the device used in the determination of such measurements was that described by K-MaII in "Kältetechnik-Klimatisierung", 22 (1970), 257/9. There were vapor pressure measurements at intervals of 10 ⁰ C in the temperature range of -20 to + 70 ° C for mixtures with concentrations of 70,80 and 90 wt .-% executed on synthetic oil composed of hydrogenated polydecene The results are shown in Table III below :

40

45

50 polydecene
0.0

70.0

80.0

90.0

2.50

3.62

5.08

6.94

9.26

12.11

15.57

19.71

24, t2

30.42

2.44

3.56

4.95

6.72

8.81

11.25

13.99

17.25

21.05

24.96

2.18

3.07

4.21

5.56

7.10

8.94

11.08

13.50

16.27

19.25

1.60
2.11
2.88
3.62
4.53
5.61
6.80
8.12
9.57
11.05

A qualitative representation of the miscibility behavior of the above-mentioned mixtures of hydrogenated Polydecene and chlorodifluoromethane is shown in FIG. 1 showing the relationship between temperature and Mixture concentration is shown. It can be seen from this figure that below that shown Temperature range, d. H. the normal temperatures at which the mixture of hydrogenated polyalkylene and halogenated alkane refrigerant is subjected to the Components that make up such a blend at concentrations of hydrogenated polydecene from approximately 1 to 50% by weight are partially miscible. When the temperature is lowered, it grows Range of partial immiscibility up to a concentration of approximately 75% by weight.

The complicated miscibility behavior of the halogenated alkane coolant with various oils is shown in FIG. 2 for chlorodifluoromethane with fine naphthenic mineral oil, (B) a combination of naphthenic mineral oil and alkyl aromatic hydrocarbon, (C) an alkyl aromatic hydrocarbon, (D) hydrogenated polydecene and (E) polyglycol shown. From Figure 2 it can be seen that the miscibility characteristics for the Hydrogenated polydecene lubricants (D) are completely different from comparable characteristics of the other substances shown (mineral oil and synthetic lubricating oils). Thus, the miscibility of the halogenated alkane coolant is lower in the hydrogenated polydecene lubricant than in other available lubricants for refrigeration machine systems.

For this purpose 2 sheets of drawings

Claims (7)

Patent claims: ! .Lubricant, characterized that it consists of a mixture of a minor proportion of a halogenated alkane coolant and a major part of a hydrogenated polyalkylene consists of its monomeric alkylene units Contain 6 and 12 carbon atoms. 2. Lubricant according to claim 1, characterized in that it consists of 10 to 40 wt .-% halogenated) alkane coolants and 60 to 90 Wt .-% hydrogenated polyalkylene 3. Lubricant according to claim 1 or 2, characterized in that it is a hydrogenated polyalkylene contains that consists of hydrogenated polyoctene, hydrogenated polydecene or mixtures that are rich in one or both of these hydrogenated polyalkylenes. 4. Lubricant according to claim 1, characterized in that it is a hydrogenated polyalkylene contains a hydrogenated polydecene 5. Lubricant according to one of claims 1 to 4, characterized in that it is halogenated Alkane coolant contains chlorodifluoromethane and, as hydrogenated polyalkylene, hydrogenated polydecene 6. Use of a mixture according to claims 1, 3 and 4 as a lubricant for Lubricating a compressor of a refrigeration system. 7. Use of a mixture according to claim 1 as a lubricant for lubricating a refrigeration system.