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Fasteners lubrication

2016-07-20 18:00:00

Lubrication fastener connection is a common technique, this article briefly describes the role of lubrication of fasteners and common lubricating materials.

(one) Lubricates fastener connections

In the general machinery products, lubrication is often used to reduce friction, improve mechanical efficiency. For fasteners, particularly threaded aerospace fasteners, lubrication can significantly improve its performance, ensure the quality and reliability of aerospace products structure connection. Lubricates fastener connections include the following aspects.

(1)Reduce the friction coefficient, give full play to the carrying capacity of threaded connections

The tightening of threaded fastener will affect the carrying capacity of the threaded connection, the preload over the General Assembly to reduce the external load bearing capacity, preload is too small will lead to screw loosening, slotted, leaking seal. Therefore, people working for different states a lot of research to find a reasonable preload.

Use a torque wrench to control the fastener preload method is widely used at home and abroad, so-called "torque method." Under normal circumstances, to overcome friction (or under the bolt head) nut bearing surface and the friction between the threads The torque required to account for some 90% of the tightening torque. Therefore, the friction coefficient of the twist-Latin American relations a great impact, the highest can preload error of ± 35%. In order to avoid the bolt appears in the assembly because preload is too large Damage caused had the desired preload to a lower level. Some companies preload applied only up to the bolt yield load of 30% to 40%, although this can be avoided when the preload screwed assembly Damage, but significantly reduced the carrying capacity and anti-loose screw connections.

Lubrication can be significantly less coefficient of friction, improve the friction bearing surface and thread status, improve twist - Latin American relations curve consistency, reduce the dispersion curve. After lubrication of threaded fasteners links, can be applied to a larger tightening torque to obtain a reasonable preload, thus effectively improving the carrying capacity and performance of threaded fasteners.

(2) help prevent thread "killed"

Some material threaded fasteners (such as titanium bolt / nut titanium alloy) and a number of threaded fasteners used in high temperature environments, will happen after tightening adhesion and "killed", can not use the normal method for disassembly, Cause great difficulties for assembly and maintenance. Tu lubricating film lubrication or take other measures, can significantly improve the situation with the screw pair, effectively prevent adhesion threaded connection and "killed."

(3) self-locking and stable performance of the self-locking nut

Self-locking nuts, especially all-metal self-locking nut, when screwed into the male screw bolt and nut portion serious interference. Threaded surface dry friction, so that the bolt screwing torque when screwing the extremely unstable, difficult To control the self-locking nut locking performance. Lubricated self-locking nut is screwed into the self-locking torque becomes smaller and stable, wring out repeatedly screwing torque increases and stable power, significantly improved the performance of the locking self-locking nuts. Therefore, domestic and international air Aerospace all-metal self-locking nut, without exception, require lubrication process.

(4) stripping rivets require lubrication

Some specific aerospace rivets, rivet ring groove and as blind rivets, nails required by the sleeve (or other parts) deformed during the riveting process to form a rivet head. These parts are often required in the forming process of forming a Mold or similar parts, forcing the nail set (or other parts) deformation. Lubrication nail sets can greatly reduce the friction coefficient between the forming die and nail sleeve, and the forming mold can be more uniformly transfer molding force to put the nail to make nail sleeve material Uniform deformation, uniform flow to the locking groove shank, materials and nail sets full lock grooves, so as to ensure the quality of riveting, rivet ring groove so that the pull-off force and clamping force up to standard requirements. So, for the lubrication ring groove Rivets, blind rivets riveting is essential.

(B) aerospace fastener commonly used lubricants

Commonly used lubricants are molybdenum disulfide, cetyl alcohol (polar wax), neutral grease and ointment.

(1) molybdenum disulfide

Molybdenum disulfide (MoS2) is a kind of silver gray glossy black powder, hexagonal crystals. Melting point 185 ℃, 450 ℃ sublimation. Generally, the coefficient of friction of 0.05 to 0.09. In large Gas, at a temperature of about 400 ℃ gradually oxidized oxide is molybdenum trioxide. MoS2 good chemical and thermal stability, high temperature, low temperature, high load, high speed, chemical corrosion, and ultra-vacuum conditions By having excellent lubricating properties, is the aerospace industry's most commonly used lubricating material. The MoS2 Add oil, grease can play to improve lubrication and friction reduction effect. In the use of fasteners, often MoS2 Mixed with an epoxy-based thermosetting resin, curing agent, diluent, etc., by spraying or soaking it attached to the fastener surface. After heating cured to form a thin film strongly adhered to the fastener products, this is a thin film layer Often say "dry lubricating layer of molybdenum disulfide," coefficient of friction than MoS2 Powder to a large coefficient of friction. Molybdenum disulfide dry lubricant layer fastener having to add additional lubricant during assembly, commonly used in the self-locking nut lubrication.

Common dry lubricant grades are:

HM-102 Dry Film Lubricant: strong adhesion to the metal substrate, good overall physical and chemical properties and friction and wear properties, is a medium class oil for each lubricated, fasteners surface species can be at a temperature of -55 ℃ ~ 220 ℃ use.

GM-2 dry lubricant: high load carrying capacity and longer wear life, and good resistance to liquids and metal adhesion capacity, and generally do not use grease and can be at a temperature of -55 ℃ ~ 220 ℃ use.

GM-45 dry film lubricants: lubrication performance, in the salt spray of steel, aluminum and non-corrosive, low temperature does not crack under the pressure force than other molybdenum disulfide dry lubricant , little better performance than ten inositol molybdenum disulfide lubricants and other dry film lubricant.

GM-71 dry film lubricants: excellent heat resistance, long-term working temperature up to 300 ℃, short-term up to 400 ℃. Suitable for the harsh conditions of friction, the load is not too high working temperature is high sliding friction parts, grease and generally does not use.

FM-510 Dry Film Lubricant: long-term use at high loads, with lower coefficient of friction, fretting wear resistance, corrosion resistance, and other characteristics of a variety of grease, operating temperature -55 ℃ ~ 220 ℃, short-term up to 300 ℃.

(2) cetyl alcohol

Cetyl alcohol is a polar wax-based lubricant. Because of its polarity can be in the form of a dry film adhered to the fastener excellent lubricating function. Cetyl alcohol phrasebook annular groove rivets, blind rivets and high lock fasteners Run slip. And black molybdenum disulfide different kind of dry film lubricant is transparent, it does not affect the fastener's logo and due to security and other requirements necessary for the colored fasteners. The relative density of 0.8176 cetyl alcohol, Melting point of about 49 ℃ ~ 50 ℃, therefore, it only applies to room temperature. Octadecanol also a polar wax-based lubricant is sometimes used instead of stearyl alcohol cetyl alcohol.

(3) the anointing oil or grease ZTE

Neutral grease and lubricant ointment is widely used in the aerospace industry, low temperature grease No. 2 (ie 201 aviation grease) is the most commonly used therein. It is the most common thread lubricant, lubricating and anti Rot aspects have good results. It is mostly used to control preload bolt lubrication, dry lubrication and no self-locking nut, prior to assembly coated on the threads. Such lubricant temperature generally does not exceed 120 ℃, otherwise the grease will melt and evaporate. Neutral grease or ointment not be used in a vacuum environment.

(4) silver coating lubrication

Silver surface protection layer can, but also be used as a dry lubricant can be used at 870 ℃ of environment, it is a good high-temperature lubricant. The high temperature environment of aerospace products, need to be bolted connections Silver (usually nuts silver), can play a good lubrication, prevent sticking and "killed" after mating thread high temperatures. Some silver wire Lo sets standard requirements, but also for high temperature lubrication, not surface protection.