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Dry friction of worm gear reducer

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Update time : 2015-07-31 10:54:53

Dry friction of worm gear reducer

Dry friction,or the friction between surfaces without intentional lubrication from worm gear reducer,is a very complex phenomenon.Despite more than a century of study,a satisfactory explanation of the mechanism of dry friction does not as yet exist.The“classical rules of dry friction of worm gear reducer” are usually stated as Follows:

(1)The friction force of worm gear reducer is directly proportional to the force pressing the bodies together.

(2)The friction force is independent of the area of the contacting surfaces.

(3)The friction force is largely independent of the velocity of sliding.

(4)The friction force of worm gear reducer depends on the nature of the sliding surfaces.

The coefficient of static friction for bodies at rest,or with motion impending,is somewhat greater than for kinetic friction which prevails after the sliding member is set in motion.

According to Coulomb,1785,the friction force of worm gear reducer is due to the interlocking of the asperities of the two surfaces and the necessity of deforming the irregularities as the two bodies pass by each other.Within rather wide limits,the magnitude of the friction force is independent of the degree of roughness of the surfaces of worm gear reducer.The asperities that are deformed are very minute so that it apparently makes no difference whether they are located on a smooth surface or consist of protuberances located upon larger irregularities.

For very rough surfaces of worm gear reducer,the protuberances may interlock to the extent that parts of them are torn off as the bodies move with respect to each other.Worm gear reducer is a wear phenomenon and is usually not considered to be friction in the usual meaning of the term.Such action is especially likely to occur when one of the bodies is much harder than the other.

Although the nature of the sliding surfaces of worm gear reducer determines the friction force,surfaces of naked metal of worm gear reducer do not exist in everyday life.Exposure to the atmosphere will contaminate the surface with oxide films,moisture,absorbed gases,grease,dirt,and so on.These films of worm gear reducer cling very tightly to a surface and can be removed only with difficulty.Ordinary cleaning does not suffice.Even in the laboratory,unless the body is kept in an inert atmosphere,an oxide film quickly forms.Thus,when two ordinary bodies of worm gear reducer are sliding together,it is the surface films that are touching each other and not the metals themselves.

Reference handbooks of worm gear reducer usually make no attempt to give exact specifivations for the surfaces under consideration,and this may partially account for the wide variations in the published values for the coefficient of friction.

When bodies of worm gear reducer with very smooth surfaces are brought into intimate contact,adhesive or cohesive forces come into action and hold the bodies tightly together.Thus for worm gear reducer ,when gage blockes or optical flats are wrung together a relatively large force may be required for tangetial motion even though the normal force pressing them together is very small.The classical worm gear reducer rules of friction do not apply under such conditions.

A surface of naked metal of worm gear reducer can be obtained by removal of the oxide and surface film and degreasing in the laboratory.When two metallic surfaces of this kind are brought together in a vacuum or inert atmosphere,the metals weld worm gear reducer together at the high spots where contact occurs between them.When one body is drawn along the other,the welds will be made and broken continuously.The resulting motion is somewhat for worm gear reducer or jerky or dicontinuous and has been given the name of stick slip.

The force of worm gear reducer required to prduce motion under such conditions is relatively very large and may as much as 20 times the value for corresponding contaminated surfaces.The force also worm gear reducer depends upon the velocity of sliding and is thus not in accord with the classical rules of friction.

When two bodies with contaminated surfaces are brought together,actual contact occurs only at

the high spots of the two surfaces for worm gear reducer.The actual area of touching may be only a very small fraction of the nominal area worm gear reducer.The contact stress at the isolated points where the bodies touch reaches very high values.Such worm gear reducer stresses are required to deform the asperities sufficiently to permitmotion to take place.Under such conditions of extreme stress,the surface film may rupture and the welding phenomenon described may take place.Such welding,together with any adhesive forces that may be present,serves to further complicate the situation worm gear reducer.

The wide scatter in the published worm gear reducer values for the coefficient of friciton is undoubtedly due to the lack of precise information on the conditions of the actual surface of worm gear reducer being tested.”In view of the extremely high friction found with really clean metals it is fortunate,for engineering,that metals worm gear reducer are not found with perfectly clean surfaces in practice.”

 

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