Question

Question 3. a) Select an appropriate coating for TWO of the following applications. Justify your selections by referring to the required properties of the material, and briefly discuss the likely deposition process. I. Aluminium mountain bike handlebar. ii. Steel handrail on an oilrig. iii. Electrical contact on a Printed Circuit Board (PCB). iv. Telescope lens. (2x5) (2x5) b) Discuss TWO methods of protecting steel from failing due to corrosion. c) Select a suitable composite material for ONE of the following applications. In each case, state the names of the matrix and reinforcement and give the main reason for your choice of each composite. i. Mountain bike frame; ii. Cutting tool tip. (5) Total Marks [25]

Answer 1

3.) (c). Printed circuit boards:- The components used in PCB are sensitive to host of enviromental conditions that can have a far reaching consequences. So to avoid contact with these harsh environment we apply conformal coating which electrically insualte the component and save it from harsh environment. they form a thin polymeric film and can be applied easily by spray, brushing or dip coating. It prevents the PCB from extereme tempreatures

(d). Telescope lens:-

We can apply a standard coating of aluminiium with silicon monoxide protective coat. The avearge reflectivity of this coat in the visible region is 90% and can be easily cleaned using normal leaning procedures

(4). Protection of steel from corrossion:-1.passive barrier protection works by coating the steel with a protective coating system that forms a tight barrier to prevent exposure to oxygen,water and salt(ions).The lower the permeability of the coating systemto water,better the protection provided.

Electrocoat(E-coat):-electrophoretic deposition is a process in which electrically charged particles are deposited out of a water suspension to coat a conductive part.The process is more commonly known as electrocoating or E-coating.

The process requires a coating tank in which to immerse the part,as well as temperature control,filtering and circulation equipment.Electrocoating systems are known as anodic or cathodic depending upon whether the part is the anode or cathode in the electrochemical process.Cathodic systems are more common since they require less surface preparation and provide better corrosion resistance.Electrocoating requires that the coating binder,pigmrnt and additives be given an electric charge.These charged materials,under the influence of an electric field,migrate through water to the part surface.

5.Firstly,composite cutting tools come in one of three different material types.Carbide, coated carbide or PCD.Each has its advantages.

Carbide can be easily fashioned into any required geometry and will produce a keen cutting edge but will also be expected to wear quickly.

Coated carbide similarly offers flexibility in that it can be ground into a variety of geometries ,but has an additional(CVD)coating applied that can dramatically increase tool life.The disadvantage of these tools is that it is generally considered uneconomical to resharpen them.