General information about the silicone compound Molykote and Dow Corning and their application

Provides an overview of silicone compound as a specific category of consumables Molykote and Dow Corning, which combines a lubricating, sealing, insulating and conductive properties when used in mobile and fixed joints.

1. The purpose and the main special features of the compounds as a specific category of the grease-like lubricating materials
2. The components of the Molykote and Dow Corning compounds
3. Molykote and Dow Corning compounds applications to lubricate, seal and electrically insulate the flexible and fixed joints and to increase their heat conductivity


1. The purpose and the main special features of the compounds as a specific category of the grease-like lubricating materials

The flexible and fixed joints lubrication implies a layer of lubricating material to be formed between their mating surfaces. The main functions of this lubricating layer are to reduce friction losses, to prevent seizure and to minimize wear.

Depending on the unit work specifics and its operation conditions, the lubricating materials can fulfill some additional functions, too, including:

  • corrosion protection for metal surfaces;
  • preventing plastic or rubber parts from deformation and destruction;
  • preventing some environmental substances from penetrating into the friction unit;
  • sealing the flexible joints in the hydraulic and pneumatic systems;
  • removing heat and wear debris out of the friction zone;
  • damping noise and vibration during friction unit running;
  • electric insulation or high electric conductivity in electric junctions.


In order to fulfill their prescribed functions, the lubricating material must have a set of certain properties such as  viscosity, adhesion, safe load value, resistance against different environmental factors (including dust, humidity, radiation, etc.), ability to work under low and high temperature conditions, compatibility with the mating parts structural materials. The different operation conditions define such a great variety of the existing lubricating materials kinds.

 

The lubricant matter aggregation state is one of the most important classification criterion for lubricating materials. In addition to the liquid lubricants (oils), grease-like lubricants (greases and compounds) and solid lubricants (powders and anti-friction coatings) there are also the polyphase systems that consist of the components not reacting between each other chemically. These are pastes (solid lubricants dispersed in oil) and dispersions (liquid lubricants with solid anti-friction filler materials).

Where it is impossible or unpractical to use liquid lubricants in the friction units, the grease-like materials are applied for regular or resource lubrication. They differ from the liquid lubricants by the thickeners of the various kinds added to their composition to increase their base oils resistance to squeezing out of the friction zone while exposed to the different loads and temperatures.

When they choose the operating materials for the frictions units of the precision mechanisms, the vacuum systems, the systems operating under pressure, as well as for the components of the electric circuits and other equipment exposed to water and severe weather conditions, a great attention is paid not only to the anti-friction properties of the lubricants but also to their adhesion, sealing, protection, dielectric and heat-conducting features.

All the properties mentioned above are represented the best in the special catergory of the grease-like lubricating materials, that is in the greases and sealants or compounds.

Compounds (as a mixture, composition) are the lubricating materials based on the high viscosity silicone oils and inert fillers (mostly mineral, inoranic).

2. The components of the Molykote and Dow Corning compounds

The grease-like lubricating materials properties primarily depend on the properties of their components including base oil, thickener and additives. The Molykote and Dow Corning compounds unique qualities are achieved by a special combination of the thoroughly selected elements (see Table 1) and their percentage ratio.

Table 1. Compound Components

Compounds

High viscosity silicone base oil
(kinematic viscosity is * x1000 cSt)

Additives

Filler (Thickener)


Silicon dioxide SiO2
Zinc oxide ZnO
Polytetrafluorethylene (C2F4)

The silicone oil, an uncolored organosilicone liquid (oligoorganosyloxan) is used to produce compounds. It is resistant to chemicals, soluble in spirits and aromatic hydrocarbons but insoluble in water.

The silicone liquids are so widely applied due to their following features:

  • wide service temperatures range: low freezing point (below -60°C), resistance to thermal oxidation (up to +250°C at the long-term exposure and up to +300°C during short-term periods);
  • chemical stability;
  • ability not to be wetted by water (water repellency);
  • low flammability;
  • low surface tension what defines high wetting ability;
  • low saturated vapors pressure;
  • low toxicity;
  • high dielectric properties almost independent on the temperature and the electric power parameters;
  • slightly sloping viscosity-temperature characteristic.

The different non-organic chemical compounds such as Silicon dioxide SiO2, Zinc oxides ZnO and other metals are the most often used as thickeners (fillers) to produce silicone compounds. However, the polymer organic thickeners, for example, Polytetrafluorethylene (C2F4), have been recently getting more and more important. The fillers to be used to produce compounds must be finely powdered, have large specific surface and good hydrophobic properties. For instance, Silicon dioxide SiO2 is used as a silicious jelly powdered down to 5…50 µm and specific surface about 150…1000 m2/g. The silicon dioxide high powdered level is achieved during the chemical processes.

The dispersed silicone dioxide produced by different methods consists of the ball-shaped particles which are rolling alone the surface without cutting or scratching it while it gets in contact with the mating parts. Besides, the oxide layer of the metal surfaces change its properties due to the SiO2 fine-dispersed particles  as they refill the existing surface cavities and imperfections and bond it with the surface layer of the parts. Therefore, having been repeatedly exposed to the SiO2 fine-dispersed particles, the rough surface upper layer becomes tightly “packed” with the SiO2 particles what significantly increses the mating surfaces quality and reduces friction coefficient. When heated the silicone oxide doesn’t undergo the phase transformations and doesn’t melt. As a result, the structural viscosity of the compounds based on it hardly depends on temperature and is defined by the viscosity-temperature characteristics of the silicone oil they contain in their composition.

The silicone compounds (silica gel lubricants) consist of the silicone oils blend and the hydrophobic silicious jelly and work well at both high (up to +200...+230°C) and low (down to -40°C and below)  temperatures. They are characterized by good adhesion and low volatility, resistance to chemicals and water. They have good anti-seized, wear-preventive and dielectric properties.

 

3. Molykote and Dow Corning compounds applications to lubricate, seal and electrically insulate the flexible and fixed joints and to increase their heat conductivity

Molykote и Dow Corning silicone compounds consistency resembles thick greases (NLGI Class 2 or 3 usually).


Initially they were designed as release agents that is as the chemical substances which don’t conduct electricity and don’t cure when exposed to the environment in order to create an anti-adhesion barrier on the lubricated surfaces. However, the unique set of the compound properties enabled to use them to lubricate and to seal the flexible and fixed joints.


Molykote and Dow Corning compounds applications in different technical fields are defined by their following features:

 

 

Molykote and Dow Corning compounds represented on the Russian market as well as their primary purpose and typical characteristics are shown in Table 2.

Table 2. Molykote and Dow Corning Silicone Compounds Characteristics

Compound Function Color Service Temperatures Range, °C NLGI Class Oil Bleeding after 24 hours at 200° C, % Oil Evaporation after 24 hours at 200° C, % Increased Dielectric Proerties Food Grade Approval
Molykote 111 Lubrication, Sealing, Insulation White or light-gray, transparent  -40…+204 3 0,5 2 + +
Dow Corning 4 Lubrication, Sealing, Insulation White, translucent -57…+204 2 4,5 1,4 + +
Dow Corning High Vacuum Grease Lubrication, Sealing White to gray, translucent -45…+200 ~2 0,5 2,0 - +
Dow Corning 7 Protective coating, release agent White, translucent -40…+204 1 6,5 0,8 + +
Dow Corning 340 Effective heat sink White -45…+200 2 0 0,35 - -
Molykote G-807 Effective lubrication for metal/plastic and metal/rubber friction pairs combined with protective functions White -40…+150 - 0,5 1,0  - -

The Molykote and Dow Corning silicone compounds characteristics shown above define to a considerable degree the specific character of their applications.

So, in 1942 Dow Corning 4 Compound became the first silicone material in the world which was implemented into scale production – the fact later secured the “Organosilicone Pioneer” status to the Dow Corning company. High dielectric properties and arc resistance of the Dow Corning 4 Silicone Compound make it the most effective as an insulating agent. That’s why the very first application of Dow Corning 4 was a solution for the problem of the aviation equipment electric systems failures. Nowadays the dielectric properties of this compound are also used in the automotive ignition systems, in the electrical circuit plug-type connections, etc. The high lubricating and sealing properties of Dow Corning 4 enable the manufacturers to recommend it for the valves, rubber and plastic gaskets lubrication and their leak resistance increase.

Molykote 111 and Dow Corning High Vacuum Grease compounds are characterized by thick consistency, little oil bleeding and evaporation. Such properties of these materials allow to use them for lubrication and sealing on the elements of both vacuum systems and systems under pressure. The mentioned products are recommended by the manufacturers for the control valves, seals, gaskets and stuffing boxes lubrication.

Molykote 111 and Dow Corning High Vacuum Grease compounds are suitable sealants for the equipment (including the marine one) exposed to water and severe weather conditions. In addition, they are used as chemical barrier coatings. The good dielectric properties and quite thick consistence of the Molykote 111 compound enable to use it for high-voltage electric contacts sealing.

Dow Corning 7 Compound has имеет high thermal stability and resistance to oxidation, it is unreactive towards metals and the most kinds of polymers. It is insoluble in water, in spirits or in mineral oils. These properties enable to apply Dow Corning 7 widely as a release agent, lubricant and protective coating for the polymer and elastomer products production equipment, in mold and smelting production, for continuous welded seams formation, in ceramic tiles production, etc.

Because of its good adhesion and high heat-conductivity coefficient, Dow Corning 340 compound is the effective medium between any combinations of metal, ceramic and plastic surfaces when it is required to provide efficient heat-transfer (see the   Dow Corning 340 Heat-Conductive Compound article). The high stability of the physic and mechanical characteristics in the wide temperature range allows to use this compound in the especially important units, for example, in the aircraft engine cooling systems.

The modified polytetrafluorethylene in the Molykote G-807 compound composition gives it high anti-friction properties, resistance to corrosion, wide service temperatures range and make it compatible with many plastics and elastomers. This allows to use it as high performance lubricant on plastic/metal and metal/rubber friction pairs in various electro-mechanical devices.


The Molykote and Dow Corning compounds take on special significance when they are used for operating the drinking water supply systems and the food production equipment. The accidental contact between the conventional lubricating materials and food or drinking water causes not only their taste change but also makes them dangerous for human health. Molykote 111Dow Corning 4Dow Corning 7 and Dow Corning High Vacuum Grease silicone compounds are absolutely safe for human health, have NSF/ANSI 51 (the materials approved to be used in the food production equipment) and NSF/ANSI 61 (the materials approved to be used in the drinking water supply systems) food grade approvals. In addition, Molykote 111Dow Corning 4 and Dow Corning 7 compounds meet the FDA 21 CFR 175.300 (for the materials with the possibility of the accidental contact with food) standard requirements. Molykote 111 compound is approved by Water Regulations Advisory Scheme (WRAS) organization to be used in the drinking water supply systems.

So, the expansion of the operation conditions range for the modern technical units and the growth of the requirements towards them dictate the necessity to design new lubricating materials that combine the best highly specialized products’ samples’ characteristics. The physic and chemical properties of the components in the composition of the Molykote and Dow Corning compounds, included in the thoroughly selected ratio, enable to achieve the unique combination of releasing, lubricating, sealing, dielectric and heat-conductive features. The set of the characteristics this category operating materials have provide their efficient work in various technical fields including the most crucial and un-to-date ones.

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