Heat Generation in Thermoplastic Spur Gears

Abstract

Since thermoplastics are temperature-sensitive materials, heat generation in running spur gears is an important parameter. This paper presents two models for its evaluation, an exact one which considers all the parameters but needs a computer to solve the equations; then a simplified model. Both models take into account the contact outside the theoretical line of action which is the usual case with thermoplastic gears. Results for the simplified model are within reasonable agreement with the exact one.

Life and damage mode modeling applied to plastic gears

“…Surface thermal surface: Localized softening of the tooth profile as a result of excessive heat, resulting in the melting of the material, material tears and deterioration of the profile [11,15,18]. Root fatigue: A stress concentration in the teeth roots initiates microcracking that propagates, causing the gear to fail later in the gear life.…”

“…Generalized thermal failure: Softening of the entire tooth due to the loss of mechanical properties of the material under the effect of heat hysteresis and friction [2,15,16]. Brutal rupture: The contact stress does not damage the surface, but stress is concentrated in the tooth root due to the contact position and tooth shape [17].…”

Optimized use of cooling holes to decrease the amount of thermal damage on a plastic gear tooth

“…To do this, tooth c 2 is assumed to always make contact at its tip corner for the duration of the contact outside the line of action in the approach phase. 18 As shown in Figure 4, we write the following equation for the approach phase…”

The Use of Cooling Holes to Decrease the Amount of Thermal Damage on a Plastic Gear Tooth

“…The surface temperatures of the teeth of plastic gear are very high and result in local softening and increased surface wear [14][15][16][17][18]. The mechanical resistances of plastic gears is temperature dependent [19,20] and if the plastic gears make contact with the steel gears, then the metal gears quickly transfer the generated heat to the plastic gears because of the high thermal conductivity of the metallic gear. Mao and coworkers [5,20] studied both the measured gear tooth surface temperature and predicted the gear flash or maximum temperature at the gear surface.…”