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The failure form of plastic gear

by:CSSSLD     2021-01-23
Injection molding products processing rigidity is not sensitive to machining error, develop high machining accuracy is a waste. Due to poor plastic heat resistance properties and thermal conductivity is very low, and other plastic gears of the same reasons in addition to the friction heat generating and viscoelastic hysteresis heating energy consumption, so whether ultra-high molecular weight polyethylene bearings, or other engineering plastic bearings to design the thinner the better as far as possible, to facilitate heat dissipation and improve the bearing capacity.

tooth fracture is mainly due to: plastic modulus low hertzian contact area is big, two gear tooth surface contact stress is small, so don't usually appeared pitting. Plastic is not elastomer is viscoelastic body, in addition to the friction heat production, on the teeth and viscoelastic hysteresis energy consumption. Plastic heat conduction performance is poor, strength decreases with the rise of temperature, and because of the small tooth stiffness, loading engenders big deformation after another gear tooth in advance into the match, the tooth addendum scraping dig plastic gear tooth root contact offset part of the produce crack of heat source and as gear operation, eventually lead to broken gear gear teeth in contact offset part of the plastic.

the plastic heat bilges cold shrink coefficient is generally about 10 times of metal, so the gear tooth backlash to the corresponding bigger, in case the expansion card dead. Due to the rigid plastic, easy to deformation after loading. Therefore, in order to improve the carrying capacity of gear tooth width than metal gear width, corresponding additional plastic hardness, low stiffness is easy to deformation, so machining accuracy can not be set too high, this is due to: develop processors are not high, because the plastic cannot grinding machining.

keyway cracking is due to the plastic bearing capacity is low, the severe stress concentration root grooves, the root is a rectangular keyway maximum stress 2 higher than the rounded keyway. Seven times. The measures to prevent tooth broken methods and measures to prevent tooth surface burn method is basically the same, because burns is a prelude to tooth broken, burns to produce tooth fracture crack source, the broken is due to the tooth surface friction heat, heating energy consumption of viscoelastic hysteresis and mating gear tooth top blowing dig tooth root in hot heat transfer heat, and plastics are poor gathered. Therefore, the measures to prevent tooth broken, the method is mainly about how to reduce the above several kinds of heat generated in order to develop.

in order to reduce the addendum scraping dig heating can by improving the gear tooth of gear tooth stiffness and tooth addendum modification to solve. In order to reduce the friction heat production, viscoelastic hysteresis energy consumption as well as in central tooth surface appear high hotspots, on the teeth along the tooth width direction is modification. In order to improve the carrying capacity of gear, to lower the rise of temperature of the plastic gear tooth, as far as possible on the gear for the axial and radial injection hole, for the tooth surface heat reduce tooth surface burns and tooth broken.

low speed and light load with open, half open transmission, the main wear, tooth fracture and insufficient rigidity, etc. , mainly tooth wear. For high speed load in general are closed at this time of transmission failure modes are: gear wear, tooth broken, keyway cracking and local burn, etc. , which is primarily a broken tooth. Steel gear tooth pastry corrosion failure modes mainly, and the failure form of injection molding processing gear are not appeared pitting.

in order to reduce the stress of the root grooves can adopt the root grooves of the rectangular structure change to round corner or square corner structure. Can be used to prevent the keyway craze, gangsu composite structure, the key doesn't open above the plastic of the low strength, and above the metal of the high strength. In addition, also can use two kinds of common gangsu composite structure, which can prevent the keyway craze, and can improve the stiffness of gear tooth, so as to improve the bearing capacity of the gear.

more excellent articles: plastic gear finite element calculation, click directly.
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