General Considerations of Plastic Gearing
Plastic gears are increasingly favored over metal gears due to their evolving material properties and cost-effectiveness. They offer advantages such as lightweight, shock absorption, minimal lubrication needs, and corrosion resistance. However, they have limitations like lower load capacity, dimensional instability, and temperature sensitivity.

Properties of Plastic Gear Materials
Common materials include acetal resins, nylon resins, and acetal copolymers, each with varying strength, rigidity, and moisture absorption. Detailed tables provide physical and mechanical properties, highlighting differences in impact strength and thermal expansion.

Material Properties and Comparisons
Tables present data on tensile strength, flexural strength, and other properties for various plastics, emphasizing differences in impact strength and specific gravity.

Considerations for Combining Plastics with Other Materials
When combining plastics with metals, differences in thermal expansion and elasticity must be considered. Additional tables provide wear and Poisson's ratio information.

Material Properties and Specifications
Specifications for materials like metals and nonmetallics are detailed, focusing on modulus of elasticity and thermal expansion coefficients.

Wear Characteristics and Material Ranking
Plastics are ranked based on wear resistance and water absorption, with acetal, nylon, and polycarbonate noted for their wear resistance.

Plastic Gear Design Considerations
Design considerations include pressure angles and modules, with a 20° pressure angle preferred for strength and noise reduction.

Strength of Plastic Gears
Focus is on the bending and surface strength of plastic spur gears, using the Lewis formula to calculate allowable tangential force.

Application Notes
Designing plastic gears requires consideration of heat and moisture effects, influencing backlash and lubrication needs.

Conclusion
The document provides guidelines for selecting and designing with materials, emphasizing understanding material properties and environmental factors.

Specifications and Calculations
Formulas for calculating parameters related to plastic gears are provided, including allowable tangential force and bending strength.

Bending Strength of Plastic Worm Gears
Calculating worm gear strength is crucial due to its general weakness compared to the worm.

Strength of Plastic Keyway
Equations calculate stress on keyway sides, emphasizing not exceeding maximum allowable surface pressure.

Effect of Part Shrinkage on Plastic Gear Design
Shrinkage affects gear size and shape, with equations provided to calculate post-shrinkage dimensions.

Proper Use of Plastic Gears
Guidelines cover backlash, environmental tolerances, and stress concentration, with methods for attaching gears to shafts.

Lubrication
Discusses lubrication methods and compatibility with plastic materials, including the use of solid-state lubricants.

Molded vs. Cut Plastic Gears
Choice between molded and cut gears depends on production quantity and precision needs, with performance differences due to material and process variations.

Elimination of Gear Noise
Noise reduction can be achieved using resilient materials like urethane, though they require increased face width.

Mold Construction
Mold construction involves components like locating rings and sprue bushings, with advanced techniques for uniform material flow.

Features of Tooth Surface Contact
Improving tooth surface contact involves modifying tooth shape and ensuring accurate assembly, with quality classified by JIS B 1741.