The second Factory Study Tour for this semester was held at Bridgestone Corporation on November 10th, 2009. It was located at 10-1, Kyobashi 1-chome, Chuo-ku, Tokyo. Bridgestone Corporation has many facilities all around the world, it has 192 plants in 26 nations, 5 technical centers in 4 nations, 11 proving grounds in 8 nations.
Bridgestone Corporation is a tire and rubber company that produces tires for many kinds of vehicles and other kinds of rubber related products with advanced technology. Tires account for about 80% of Bridgestone Group sales. The other 20% are diversified products such as antivibration rubber, air springs, conveyor belts, bicycles, electronic paper which was released in summer 2009, seismic isolator for buildings, etc.
In this factory study tour, first we heard some explanation about Bridgestone company and about the process of making a tire. Tires have four main functions:
- Supporting the weight of a car
- Transmitting driving and braking force
- Maintaining and changing direction force
- Absorbing shocks from road surface
In order to fulfill those functions, tires are consisted of several components:
- Tread: outer part of the tire which has direct contact with road surface
- Carcass ply and belt: forming the cord of a tire
- Bead: firmly grasp tire to a wheel
There are several processes for making tires:
1. Mixing process
Tire materials (natural/synthetic rubber, carbon black, sulfur and chemical agents) are mixed together and then formed into sheet strips and cooled.
2. Tread extruding process
Rubber sheets are heated to make them elastic, then they are extruded and cooled. The extruded rubber sheets are cut to tire length.
3. Manufacturing process
- Cord manufacturing process
Nylon, polyester and other materials are mixed to make tire cord and weaved into cord fabric. The cord fabric is dipped into a solution to improve its strength, then it is coated with rubber and cut at proper angle into specific length and width.
- Steel belt manufacturing process
Steel cord is coated with rubber and cut at proper angle into specific length and width.
- Bead making process
Bead wires are aligned and coated with rubber, and then coiled to form bead.
4. Building process
Body ply is formed into the proper shape of a green tire, and the bead is attached to the body ply. After that, sidewall steel belt, and tread are applied to form green tire.
5. Vulcanizing process
Heat and pressure are applied to green tire to form it into an end product tire.
6. Inspection process
The tires are trimmed and inspected to check the appearance and balance/uniformity.
After getting some explanations about Bridgestone company and tire-making process, we were brought to the tire museum and the factory to see the tire manufacturing. In the museum, there are many kinds of tires produced by Bridgestone displayed, including the tires for F1 and the biggest tire in the world for 400-ton dump truck. There was even environmental friendly product like prosthetic dolphin fin which could be used to replace the tail fin of a dolphin. We also got to see the foundations of the technical center building which had seismic isolators applied in them in order to absorb earthquake vibration. In the factory, we were shown about the tire making process, like the building process, vulcanizing process, and inspection process. There were several rules that should be obeyed in the factory, like we may not touch the machines, we had to walk on the blue area because the green area was only for factory vehicles. The factory had a very strong smell of rubber in it, so there was some devices applied in the factory to reduce the smell of rubber inside the factory. But still, the rubber smell was so strong inside the factory.