DE1046812B - Lubrication of machines and devices that are exposed to ionizing radiation - Google Patents

Description

GERMAN

With the beginning of the industrial exploitation of nuclear fission, there are new and unexpected lubrication problems popped up. Most common lubricating oils and greases fail because of the chemical Reactions that occur in the components of such lubricating oils and greases if they are used for a long time Exposed to ionizing radiation. They either harden to form insoluble, waxy ones Products as a result of the occurrence of cross-links (cross-links), or they become as a result the destruction of the grease structure or the depolymerization of the molecules into products degraded with a lower viscosity.

It has now been found that these difficulties can be overcome by going to Lubricate machines and devices that are exposed to ionizing radiation Used lubricating grease made from specially selected mineral lubricating oils with a Vis ^ cosity-dichite-cotistatite of at least 0.85 as well made from inorganic gelation agents is.

Such lubricating greases are applicable for the lubrication of any machine or device which one exposed to ionizing radiation. But they are particularly suitable for lubricating systems, which are used in nuclear reactors, such as fission stations for the conversion of atomic energy in electrical energy and systems for propulsion of ships and aircraft in which the Atomic energy is converted into mechanical energy, as well as being used for nuclear reactors for others Purposes are used, e.g. B. for the generation of radiation with high energy for material testing and for the production of radioactive isotopes or for research purposes. These special greases are also particularly suitable for lubricating equipment used for loading and unloading Fuel elements are used, as well as for handling the balancing rods (moderators), regulating the excessive activity of nuclear reactors and for lubricating facilities, which are used in the circulatory system of the heat exchange medium, in particular of pumps or blowers, valve spindles and control instruments.

The term "ionizing radiation" in the present description does not include radioactive radiation Radiation as it is ordinarily present in the atmosphere, or the cosmic rays emitted by extraterrestrial sources.

The requirements for the various components known per se of the lubricating grease are set out below discussed in more detail:

lubrication

of machines and devices,

that of ionizing radiation

are exposed

Applicant:
"Shell" Research Limited, London

Representative: Dr. K. Sdiwarzhans, patent attorney,
Munich 19, Romanplatz 9

Claimed priority:
Great Britain December 18, 1956 and October 10, 1957

John Owen Cliffe, Whitby _r Cheshire (Great Britain), has been named as the inventor

2

The lubricating oil component

It is essential that the lubricating oil component of the lubricating grease be a mineral lubricating oil which has a viscosity-density constant of at least 0.85, and preferably at least 0.88. The viscosity-density constant was first defined by JB Hill and HB Coates in a paper entitled "The Viscosity-Gravity Constant of Petroleum Lubrication Oils" published in Industrial & Engineering Chemistry, Vol. 20, pp. 641-644 ( 1928). The resistance of mineral lubricating oils to radiation seems to be related to the viscosity-density constant. There were z. B. different lubricating oils are subjected to neutron radiation corresponding to 1.0 · ΙΟ ¹⁸ or 1.8 · 10 ¹⁸ neutrons / per cm ² . The results of these experiments are summarized in the table and the graph. From them it can be seen that an increase in the viscosity of the lubricating oils when exposed to the neutron irradiation is closely related to the viscosity-density constant. The oils used in the experiments all came from Venezuelan crude oils. No. 1, 2 and 3 oils were refined by Duosol extraction, No. 4 oil by Edeleanu extraction, and No. 5, 6 and 7 oils by treatment with sulfuric acid, fuller's earth and lime, respectively.

809 699/505

3 Viscosity 4th % Increase in viscosity % Increase in viscosity oil Starting viscosity cSt Density constant at 1.0 · ΙΟ « _n / _cm 2 at 1.8 x 1018 n / cm ^ No. at 37.8 ° C 0.81 537 fixed 1 261 0.81 337 4510 2 108 0.81 313 2620 3 35.1 0.85 281 1080 4th 137 0.88 165 575 5 270 0.89 138 420 6th 117 0.89 118 310 7th 21.7.

From the table and the graph it can be seen that lubricating oils with a viscosity-density constant of less than 0.85 is not suitable for the lubricating greases to be used according to the invention are.

Usually the intensity of the radiation is at the points where such greases are used are, quite low, so that the viscosity increases indicated in the table above only after occur over a long period of time.

The gelling agent

Although various thickening agents have been used in the art of making grease, it has been found that only organic gelling agents can be used to make a grease which is believed to be useful for the purposes of the invention. Lubricating greases made using a sodium soap-nitrite complex or lithium oxide stearate became liquid ^{when exposed to neutrons of 0.5 x 10 18} neutrons per cm ^2. On the other hand, under the same conditions, a grease containing colloidal silica as a gelling agent showed no appreciable softening.

With prolonged moderate exposure, a lubricating grease that meets the requirements of the present invention does not correspond, liquid and then hardens to a brittle, waxy product that no longer has any lubricating properties. Inorganic gelling agents suitable for the purposes of the invention are for example the colloidal inorganic oxides, hydroxides, silicates and carbonates, such as silicon dioxide, aluminum oxide, magnesium oxide, calcium oxide and mixtures of these substances, in particular Mixtures of silicon and magnesium oxide, as well as synthetic and natural zeolites Clays like the betonite.

When selecting these gelling agents, which are known per se, care must be taken to ensure that the presence elements are avoided that are subject to the particular type of radiation under consideration, to which the grease is to be exposed will suffer conversion into other elements, in particular into elements that have strong radioactivity. Neutron radiation in particular can be undesirable Bring about changes in the core of the elements contained in the grease. It has has shown that colloidal silica is a preferred gelling agent when the grease is used used to lubricate equipment exposed to neutron radiation.

The greases generally contain the gelling agent in an amount between 2 and 20 percent by weight, calculated on the total grease, preferably between 3 and 10%.

A disadvantage of most inorganic fats is their sensitivity to the

60

mixes

70 Presence of water or contact with water, which often results in rapid destruction of the lubricating grease structure and decomposition into the components. Various methods of treatment are known to improve the water resistance of the grease, for example the incorporation of an anionic, cationic or nonionic surfactant as described in British Patents 672 650, 672 651, 683 969 and 685 146. A preferred group of surfactants, is known from British patent specification 703 169. These cationic surfactants are polyaminohydroxy compounds in which the total number of amino nitrogen atoms and oxy groups is at least 3 and in which preferably 30 to 70% of the amino groups are converted into amide groups by reaction with carboxylic acids having 10 or more carbon atoms. A preferred surfactant of this type is made by reacting ammonia with epichlorohydrin and converting a portion of the amino groups by reacting with higher fatty acids.

However, it is more convenient to use an inorganic gelling agent such as silica, that by coating with a strongly bound additive, preferably chemically bound short-chain hydrocarbon residues, has been made waterproof. Lubricants that have such a modified Containing gelling agents have greater resistance to exposure to radiation on. It is therefore preferred to use greases which contain colloidal silicon dioxide as the gelling agent which has been reacted on the surface with an alcohol to form an ester. These so-called "esters" are described in US Pat. No. 2,676,148. This Estersiis can be made from a silica alcogel heated in an autoclave. To achieve of a high degree of water resistance and good yield, it is common to use alcohols with 3 to 8 Carbon atoms per molecule, generally n-butyl alcohol, to be used. However, since long organic Residues can lead to a reduction in the radiation resistance, it can be more useful be to use methanol or ethanol to esterify the silica.

It is also known that greases which have been gelled with hydrophobic silica, tend to gel excessively when stored at higher temperatures. To prevent this tendency may contain a small amount of a 1,3-diol or a 1,2-diol, generally with 6 or more carbon atoms, such as B. neopentyl glycol, 1,2-heptanediol or 1,2-octanediol, added to the grease will.

Another known method of improving the water resistance of lubricating greases is in that the particles of the gelling agent with

a polymeric compound, e.g. B. a polymeric silicon compound, an aminoplast or a Phenoplast coated. Among these ■ waterproofing Agents are preferred to the polymeric silicon compounds, which z. B. by polymerizing can be obtained from dimethyldichlorosilane or dimethyldiethoxysilane.

The polymerization of the silicon compounds is preferably carried out in the presence of the gelling agent carried out, for example by adding the silicon compound to a dispersion of the gelling agent in a hydrocarbon solvent is added and the mixture is refluxed until polymerization is finished. However, one can also use a previously prepared polymeric silicon compound, such as in British Patent Specification 704,604.

The amount of waterproofing agent used in the greases used in accordance with the invention exists, can vary within wide limits and is z. B. 0.15 to 4 times the amount of Gelling agent. This amount of the waterproofing agent is preferably between the 0.5- and 2.0 times the amount of the gelling agent.

The greases used according to the invention can be made according to any of the usual ones Working methods are produced. Usually the inorganic gelling agent is in the form of a oleophilic gels in a volatile hydrocarbon solvent manufactured. The gelling agent is then made waterproof, followed by the required Amount of lubricating oil added and the volatile hydrocarbon solvent by distillation Will get removed. Finally, the product is worked up to the required grease consistency to obtain.

The production of a radiation-resistant lubricating grease, which is suitable in the context of the present invention is illustrated by the following examples.

example 1

20 kg of a silica gel in isopropyl alcohol were mixed with 4 times the volume of a gasoline special boiling point (boiling range 65 to 95 ° C) mixed and the mixture stirred for 1 hour. To The supernatant liquid was siphoned off after settling. The treatment was repeated four times, until the amount of isopropyl alcohol in the gel was less than 1 percent by weight.

The silicon dioxide gasoline gel obtained was made waterproof in individual batches by heating under reflux with dimethyldichlorosilane in an amount equal to 250% of the amount of silicon dioxide present mattered. After about 10 hours, 98% of the dimethyldichlorosilane had been consumed.

The waterproof petrol gel was made from Venezuelan crude oil with such an amount manufactured lubricating oil with a viscosity of 117 cSt at 37.8 ° C (oil no.6 in the table), that the amount of silica in the finished grease was 4.5 weight percent.

This was followed by the volatile hydrocarbon solvent and the unreacted dichlorosilane removed by scraping, whereupon the product was ground to the desired grease consistency to obtain.

The lubricating grease produced in this way had an initial worked penetration value of 159. After irradiation with 0.5 · 10 ¹⁸ neutrons per cm ² , the worked penetration was 164 and after irradiation with 1.3 · 10 ¹⁸ neutrons per cm ^{2 it} was 159. A lubricating grease containing lithium oxystearate as a gelling agent and a grease containing a sodium soap-nitrite complex as a gelling agent showed ^{considerable softening when irradiated with 0.3 x 10 18} neutrons per cm ² , and they were softened at a dose of 0. 5 · 10 ¹⁸ neutrons per cm ² liquid.

Example 2

A grease was made using the same base oil as in the previous example manufactured. The gelling agent was colloidal silicon dioxide, which was formed with a condensation product Epichlorohydrin and ammonia had been waterproofed, in which about a third of the amino groups were converted into amide groups by reaction with tall oil acid. The composition of the finished grease was 5% silica, 1.2% waterproofing agent and 93.8% Lubricating oil.

The original worked penetration of this grease was 112. After irradiation with 0.5 x 10 ¹⁸ neutrons per cm ^2, the penetration 172, after irradiation with 0.8 x 10 ¹⁸ or 1.3 x IO ¹⁸ neutrons per cm ² 182 or 167.

Example 3

Another grease that can be used in accordance with the invention was prepared as follows:

6 parts by weight of methyltriethoxysilane were added to 82 parts by weight of the same hydrocarbon lubricating oil, as used in Example 1, solved. Then 12 parts by weight became dry colloidal Silica and the calculated amount of water were added to the solution to hydrolyze the silane. The mixture was heated to 120 ° C. for half an hour in order to reduce that of the hydrolysis of the silane to remove any alcohol formed and some excess water. Then it was stirred vigorously while the resulting grease mixture cooled to room temperature. The initial walk penetration of the grease so obtained was 169.

Lubricating greases with similar properties were introduced by the introduction of trimethylethoxysilane resp. Dimethyl diethoxysilane obtained in place of methyltriethoxysilane. The initial walk penetration of this Greases was 136 and 163, respectively.

Example 4

Other greases suitable for use in the invention included a commercially available one Estersil as a gelling agent. 12 percent by weight of the ester was in a mineral Dispersed lubricating oil, which had a low viscosity index, made from a Venezuelan crude oil had a viscosity of 117 SUS at 37.8 ° C and a viscosity-density constant of 0.89. The resulting sludge was ground to a grease consistency. Walk penetration of the grease obtained was 295. Three other suitable greases were prepared in a similar manner with the change that 15.2 weight percent Estersil was used and the three greases additionally contained 4.8 percent by weight neopentyl glycol or 1,2-heptanediol or 1,2-octanediol. These three greases had a worked penetration of 268 and 268 and 262, respectively, and all showed improved

Gelling properties compared to the non-diol containing grease described above.

Claims (4)

Patent claims: 1. Use of a lubricating grease based on a mineral lubricating oil with a Viscosity-density constant of at least 0.85, preferably 0.88 and above, as well as per se known inorganic gelling agents for the lubrication of machines and devices, exposed to ionizing radiation. 2. Embodiment of the invention according to claim 1, characterized by the use of a grease with colloidal silicon dioxide as a gelling agent in plants that use the Are exposed to neutron radiation. 3. Embodiment of the invention according to claim 2, characterized by the use a lubricating grease, which in a known manner by treatment with a low aliphatic alcohol, such as methanol, ethanol or n-butanol, made waterproof with formation of estersil has been. 4. Embodiment of the invention according to claim 1 to 3, characterized by the use a lubricating grease, which additionally contains minor amounts of a 1,2- or 1,3-diol with 6 or contains more carbon atoms in the molecule. Considered publications:
U.S. Patent No. 2,657,149; French patent specification No. 1 096 774. 1 sheet of drawings