Spur gears the simplest types of gears with teeth projecting towards or away from the centre. Spur gears are used in low-speed applications and in situations where noise control is not a problem. They tend to be noisy at high speed.

Helical gears are similar to spur gears except that their teeth are cut in a spiral shape. Helical gears are used in high-speed applications, large power transmission, or where noise control is important.

Some helical gears have just one continous tooth. They are called worms. A worm pairs worm gear, which help reduce speed.

Rack and pinion gears comprise a circular gear engaging a linenear gear, which operate to convert rotatinal motion to linear motion. 

Bevel gear have a conical form and can be used to transmit rotational power through shaft at an angle, typically 90 degress to each other.

 

First step is casting. In this step hot liquid of cast iron is poured into a container and then cooled to make the correct shape

The cast iron is then turned on a lathe to remove ecessive parts

Next, holes are made using a drill

After drilling process, the next step is painting. The surface is covered by paint

The final step, product is checked carefully.

This is when we make sure that the part is made properly.

First of all, one important advantage of plastic is that they are pretty convenient to use. For instance, if you go to supermarket, you will likely use shopping plastic bags to carry home the things you just bought since it is simply the most convenient way. Moreover, Plastic is cheap. Compared to other packaging materials, plastic is also quite cheap. Further more, plastic is durable. Plastic is also quite durable and resistant to all kinds of adverse outside factors. For example, plastic is quite resistant to heavy rain, storms and so on. However, using too much plastic everyday, people may face with different problems. First, plastic hurts the environment. It leads to sorts of pollution and especially poor countries will suffer the most since they are often flooded with plastic waste from all over the world. So, we should reduce plastic waste. Second, Plastic is not biodegradable. Finally, Recycling of plastic may not possible. Some plastic items cannot be recycled and will therefore be either have to burned or disposed into landfills. 100 years ago manufacturers could produce modern synthetic plastic but we couldn’t mould plastic into complex shapes. Nowdays, manufacturers can mould plastic into variety of complex shapes. At present, it is possible to replace components in engine with plastics and Plastic can be used to help designers reduce weight in aircraft. In the future, it will save money and increase efficiency by using smart plastic. Soon it will be possible to use eco-friendly bioplastics in a wide range of applications in electronics, automotive and other fields. In the near future, we will able to make plastics from any kinds of plant materials.

The next type of plastic is LDPE stand for Low Desity Polyethylene. Then, plastic code number five is PP stand for polypropylene. More over, PS is the sixth type of plastic and PS stand for polystyrene. Finally, if plastic cannot be identified in six types above then it will be included in group number 7. PET is the most common type of plastic. It holds the number one because of its widespread utility. It mostly used for food and drink packaging purposes due to its oxygen prevention. Also, PET bottles are the most widely recycled plastic in the world.