Spur Gears

The most common type of gears are spur gears, also known as straight-cut gears, and can be found in a multitude of applications. They have been specifically designed to transmit large amounts of power by placing them on parallel shafts which rotate in opposite directions.
Spur gears have an involute profile with straight teeth which project radially and are parallel to the rotation of the axis. This allows for a smoother operation between each gear and permits greater mounting distances. Spur gears can have a central hub or be hubless.
The standard pressure angles in spur gears are 14.5, 20 and 25 degrees, and refer to the angle that force is transmitted between the meshing gears.
Spur gears are capable of meshing with other gears, with many gears being used to create large gear reductions. When they are meshed the gear with the most teeth is referred to as the “gear”, whereas the one with smaller teeth is referred to as the “pinion”.
So what are the advantages?
• High transmission efficiency
• Compact and very easy to install
• Constant velocity ratio
• No slippage – unlike belt drives
• Highly reliable
• Can transmit large amounts of power
Types of spur gears
Plastic spur gears are commonly made from acetal or nylon and have many positive characteristics including being lightweight, non-rusting and quiet. They enable low cost and large production capabilities, and are also able to operate without lubrication. For hygiene reasons, plastic spur gears are an excellent choice for use in industries dealing with food production and medical equipment.
Metal spur gears have more strength, load-carrying capacity and heat resilience than their plastic counterpart. They are more dimensionally stable compared to plastic and can be made from many metals such as aluminium, brass and stainless steel.
Common applications
• Metal cutting machines
• Power plants
• Marine engines
• Mechanical clocks and watches
• Fuel pumps
• Washing machines
• Gear motors and gear pumps
• Rack and pinion mechanisms
• Material handling equipment
• Automobile gear boxes
• Steel mills
• Rolling mills
Spur gears are however very loud and so will not be found in vehicles. When the teeth collide with each other there is an impact noise which is really loud compared to the helical gears found in cars.