tailieunhanh - THE SURFACE COATING OF CAR BODIES

The potential benefits are large and greatly exceed the expected costs of improved fuel economy. Cutting global average automotive fuel consumption (L/100 km) by 50% (. doubling MPG) would reduce emis- sions of CO2 by over 1 gigatonne (Gt) a year by 2025 and over 2 gigatonnes (Gt) by 2050, and result in savings in annual oil import bills alone worth over USD 300 billion in 2025 and 600 billion in 2050 (based on an oil price of USD 100/bbl). The Initiative proposes several steps and actions to work towards the 50:50 overall goal and each step will achieve some of. | THE SURFACE COATING OF CAR BODIES Cars need a surface coating to prevent them from rusting excessively. Currently this surface coating is an electrocoat paint . a paint that is applied using an electrochemical reaction rather than simply by dipping the car body into a vat of paint. The whole electrocoat process consists of five steps. Step 1 - Precleaning The car body is assembled from imported metal panels and cleaned with kerosene to remove dirt and grease. Step 2 - Phosphating The metal is treated with phosphoric acid leading to the following two reactions occuring in the zinc-rich surface of the steel 2H3PO4 3Zn 3H2 Zn3 PO4 2 2H3PO4 Fe 2Zn 3H2 FeZn2 PO4 2 This gives a mixture of zinc phosphates. The electrocoat paint binds better to these zinc phosphates than to the steel alone and the zinc phosphates corrode much slower than the pure steel. Step 3 - Electrocoating A mixture of resin and binder and a paste containing the pigments are fed into a tank. The vehicle is then lowered into the tank from an overhead conveyor and an electric current applied. This car body becomes the cathode and the tank the anode in an electrocoating reaction that results in a resin polymer being very tightly and evenly bound to the metal surface of the car body. Step 4 - Rinsing The vehicle is rinsed several times both with water and with a weak paint solution to remove a thin coat of paint that clings to the surface but hasn t bonded to the metal. If this wasn t removed then the car would have an uneven messy coat of paint. Step 5 - Baking The car body is then baked to 170 - 180oC in an oven. This causes the different polymer chains to crosslink . bind to each other in many places forming a very strong flexible interconnected network of polymer over the whole surface of the car. New types of paint are continually being designed which are more environmentally friendly longer lasting and more tolerant of steel defects such as oil being left on the steel. INTRODUCTION Vehicles .

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