08-17-2017, 12:34 AM
PROPERTIES OF GEAR MATERIAL AND THEIR ADVANTAGES
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Introduction
In order for gears to achieve their intended performance, life and reliability, the selection of a suitable gear material is very important. High load capacity requires a tough, hard material that is difficult to machine; whereas high precision favors materials that are easy to machine and therefore have lower strength and hardness ratings. Gears are made of variety of materials depending on the requirement of the machine. They are made of plastic, steel, wood, cast iron, aluminum, brass, powdered metal, magnetic alloys and many others. The gear designer and user face a myriad of choices. The final selection should be based upon an understanding of material properties and application requirements.
Plastic Gears
Plastic gear first emerged into large-scale use in the 1950s and soon became economical and functional alternatives to metal gears. Plastic gears are made of inexpensive commodity plastics for use in low power drives in products like clocks, motorized toys and lawn sprinklers.
Properties Plastic gears have greater consistency and are easily molded to various shapes. They are less expensive and are lighter in weight. Plastic gear is chemical and corrosion resistant and have quieter and smoother operation. They deflect to compensate for inaccuracies by absorbing tiny impacts of small tooth errors and gear misalignment. They offer more efficient drive geometry. Plastic gear ratios are feasible to allow for wider gears that transfer more power in single stage, thereby increasing load capacity. The dimension and properties of plastic gears change with temperature, moisture absorption and chemical exposure. The plastic material can withstand high tangential force with acceptable tooth deflection. They have high strength to withstand shock loads during sudden stops and overloads. They are creep resistant and maintain contact ratio, tip clearance and overall gear geometry.
Steel Gears
Steels are divided into carbon steel and alloy steel. Carbon steel offers low cost and can be hardened. A major disadvantage is the lack of resistance to corrosion. Alloy steel is elements like stainless steel, and elements other than carbon. They offer high strength and a wide range of heat treatment properties. They provide highest strength and durability. Stainless steel may be stainless steel (austenitic) that is non-magnetic and has good corrosion resistance; they may be of stainless steel (martensitic) that can be easily hardened by heat, is magnetic and have reasonable corrosion resistance. Stainless steel (aust) can be used where low power ratings are there and the other stainless steel is used where low to medium power ratings is there. Alloy steels are used in industrial field. While making gears many times few minerals are added to steel. These minerals are nickel, chromium, vanadium, manganese, molybdenum, and chrome-nickel.