Assume that you are manufacturing a product in which all of the gears are made o
ID: 2074684 • Letter: A
Question
Assume that you are manufacturing a product in which all of the gears are made of metal. A salesperson visit you and asks you to consider replacing some of these metal gears with plastic ones. Consider and answer these following list of questions that you would raise before making a decision.
a.) What are the advantages and drawbacks of using plastics for gears?
b.) What are the design requirements?
c.) What class of polymers (thermoplastics, thermosets, elastomers) might be most appropriate?
d.) What particular polymer might you first consider?
Explanation / Answer
Advantages of using plastic gear:
1. Reduced total weight of the system
2. It can absorb more shock and vibration due to its elastic nature
3. Low frictional losses due to low co-efficient of friction
Drawbacks of plastic gears
1. Less load carrying capcity
2. Incresed cost of production due to high material cost
3. High tolerance can't be achieved.
Design requirments
1. Generally pressure angle of 14.50, 200, and 250 is used in production.
2. Provide larger pitch for large and strong teeth and smaller pitch for small but sensitive teeth.
3. Provider greater amount of backlash for higher thermal expansion.
4. Avoid stress concentration
The most common plastics that are used in plastic gears are Thermoplastics as acetal and nylon. Generally type 6 nylons are used but type 12 nylons are also used. Nylon gears are also fail safe in nature. Acetal is also used in these cases. Using acetal can provide high resistance to moisture, resitance to chemicals and high dimensional accuracy.