Unit R014 - Engineering Manufacture - Topic Area 1 - Retrieval G

Finishing Processes -

Many engineered products are painted, why?

• To protect the bare material from the environment.

• To improve aesthetic appearance.

• To aid with safety and visibility.

• To make the product no longer conduct electricity.

Finishing Processes -

A significant amount of engineered products are made from ​ (a)   . This contains high ​ (b)   content. This will lead to the material ​ (c)   , especially if exposed to the ​ (d)   . ​ (e)   provides a layer of protection between the base steel and the atmosphere preventing the corrosion process.

• steel
• iron
• corroding
• environment
• Painting
• cotton
• aluminium
• warping
• wind
• polishing

Finishing Processes -

In mass production the paint process is usually via a spray and automated. What principle is used to help?

• Principal of common sense.

• Electrostatic principles.

• Principal of evolution.

• Ohms principal.

Answer explanation

Electrostatic is the process of opposites attract.

The paint spray will be positively charged and the product grounded (or negatively charged).

The paint particles will therefore be attracted to the product allowing for good, even coverage, reduced waste, faster drying times and reduced overspray.

Finishing Processes -

Where possible automated spray robots will be used however the use of a brush is still often used. Why?

• Spray equipment can be expensive for smaller industries and businesses.

• Automated spray robots are uneconomical if the product is regularly changing.

• Spray robots are large and may struggle to get into all places.

• Some products require painting once installed on site.

• Brushes give a smoother finish

Answer explanation

Automated spray robots are costly and timely to program. If the product is regularly changing they may be un-productive to use.

Also when a product is installed there may be sections of touch up that need to be performed o simply the product cannot be painted until fully installed due to the engineering activities that are still to be performed on it. This is where conventional brush techniques would be used.

Finishing Processes -

Put these basic spray painting steps into order.

• Prep the surface. Tape sections that are not to be painted and degrease/clean/roughen the surface.

• Spray the product with an appropriate primer.

• Spray the product with adequate amount of layers of paint.

• Apply a top coat or lacquer to give a shine if required.

• Removing masking and allow to dry.

Answer explanation

Surfaces to be painted have to be clean. Any dust or dirt will show underneath and affect the quality of adhesion.

Primer has many benefits. It can smooth out any imperfections on the surface before final paint is applied, provide an additional layer of protection and significantly increase the durability of the final coats.

The drying time is crucial until the paint is properly cured it will be soft. Production lines will bake or heat the products to speed up the dry time.

Finishing Processes -

Select the PPE you would expect a paint sprayer to wear.

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Answer explanation

Often the mask and breathing equipment will be built into the same piece of PPE.

The overalls need to protect exposed skin form irritation from the paint.

Gloves also need to protect exposed skin. They should be tight fitting to allow good dexterity and the ability to manipulate the spray gun

Finishing Processes -

Powder coat is becoming increasingly preferred to paint, why?

• The ability to use a variety of plastics and to take advantage of the specific features of these plastics.

• Increased thickness of coating.

• Powder coating can improve the functionality such as: sound deadening, electrical resistance and changes to friction levels.

• Multiple surface finishes available including grit, textured and veined.

• Cheaper than spray painting.

Answer explanation

Some of the finishes with powder coat are simply not available when spray painting.

Finishing Processes -

Put the basic powder coating steps into order.

• Prep the surface.

• Apply the powder

• Cure the surface treatment.

Answer explanation

Prep: The surface must be stripped down and be 100% free of rust, dust, oil and grease. Shot blasting or sand blasting is the recommended treatment for preparing most metals and to remove old paint or rust. Grease and oils are best removed in solvent, either liquid baths or vapour booths.

Applying the powder: A special electrostatic gun gives the powder a positive charge. As long as the target is properly earthed, it means the powder adheres to the surface. The gun has a power socket, usually for a DC connection, an inlet for a compressed air supply, and either a tube to a powder reservoir or an attached receptacle of powder. A spray booth is customary so that the powder discharge area is suitably contained and also to recover and recycle excess sprayed powder.

Curing: To melt the polymers and make them flow, coated objects need to be heated to between 160° C and 200° C for about 15-20 minutes. Thicker steel parts may need to be pre-heated first before allowing them the 20 minutes curing time. Smaller parts may be cured in a non-gas oven while infra-red or halogen lamps are commonly used to cure larger objects.

Finishing Processes -

Which of the images below would you expect to be powder coated?

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Answer explanation

Venders, Outdoor gym equipment and hand rails are high use components. They come under serious abuse at times with high volumes of contact and potential abrasion. The durability and thickness of the powder coat would help maintain a better performance for longer.

Car bodies at different points may need repair therefore powder coat would not be entirely appropriate. With powder coat it is difficult to complete an isolated repair and whole panels would need to be re-covered, potentially the whole vehicle as matching the previous finish is not as easy to achieve as it is with paint.