Engineering Properties
Selecting the Right Finish
The tables below will serve as a guide towards the most appropriate casting finishing operation(s) if any
Fettling/Deburring/Smoothing Operations
| Process | Objective | Finish | Limits to effectiveness | Mode |
| Belt Grinding | To remove traces of ingate, parting line, burs, ejector marks and surface defects before bobbing | 60 grit Ra = 1 to 2400 grit Ra = 0,1 | Internal areas | ManualSemi- automatic
(carousel) Automatic |
| Bobbing | Reduce surface roughness and remove grinding marks | Ra 0,01 to 0,25 | Internal areas | ManualSemi- automatic
(carousel) Automatic |
| Vibro Finishing | To reduce roughness and grinding marks. To deburr, radius, polish. |
Ra 0.01 to 0.3 | Internal areas with small dimensions | Semi- automaticAutomatic |
| Shot/Grit Blasting | To reduce surface defects. To deburr | Variable | Areas not exposed to the shot direction | Semi- automaticAutomatic |
Where an applied coating is considered necessary the following table gives an indication of the most suitable type of finish for any given application.
Finishing Processes for Zinc Alloy Diecastings
| Y= Can achieve desired effecty= May achieve effect but not usually specified for that reason | corrosion resistance | aesthetics | colour coding | alter reflectivity | prevent tainting of foodstuff | increase wear resistance | reduce friction | remove sharp edges | increase surface hardness | allow soldering | electrical contact resistance | Improve EMI shielding |
| vibratory finishing | Y | Y | Y | |||||||||
| shot/grit blasting | y | Y | Y | |||||||||
| chemical passivation | Y | y | y | y | Y | |||||||
| electrophoretic paint | Y | Y | Y | Y | ||||||||
| lacquer (dip/barrel) | Y | Y | Y | |||||||||
| zinc plate | Y | Y | ||||||||||
| powder coat | Y | Y | Y | y | Y | |||||||
| wet paint | Y | Y | Y | y | Y | |||||||
| copper plate | y | Y | y | y | Y | y | Y | |||||
| brass plating | y | Y | y | y | ||||||||
| nickel plate | Y | Y | y | Y | Y | y | y | y | ||||
| tin plate | y | y | y | y | y | Y | y | |||||
| satin nickel plate | y | Y | Y | y | y | y | ||||||
| chromium plate | y | Y | Y | Y | Y | Y | y | |||||
| satin chromium plate | y | Y | Y | y | y | y | y | |||||
| black chromium plate | y | Y | Y | y | y | y | y | |||||
| dry film lubricant | y | y | y | y | Y | Y | ||||||
| silver plate | y | Y | Y | y | y | y | y | |||||
| gold plate | y | Y | Y | y | y | Y | y | |||||
| hard chromium plate | y | y | y | y | Y | Y | Y | |||||
| electroless copper | y | y | y | y | Y | y | y | |||||
| electroless nickel/phosphorous | y | y | y | Y | Y | Y | y | y | ||||
| electroless nickel/ptfe | y | y | y | Y | Y | y |
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| Type of Treatment | Maximum class of use advised(See following table) | Properties affected? | Comments | ||
| Protec-tion | Decor-ation | Mech | Phys | ||
| Chemical Conversion Coatings | |||||
| Chromate Passivation | 3-4 | no | no | no | Anticorrosion |
| Chemical Black | 1-2 | 1-2 | no | yes | Antireflective |
| Phosphate | 1 | no | no | yes | Pretreatment, organic finishes |
| Electroless Plating | |||||
| Nickel Phosphorous | 4 | no | yes | yes | Hardness, anti-corrosion, friction, electrical contacts |
| Nickel PTFE | 4 | no | yes | yes | Friction, wear resistance |
| Electroplate | |||||
| Silver | 4 | 1 | no | yes | Food contact, anti-corrosion, electrical contacts, RMI, EFI |
| Bronze (on Cu+Ni) | 3 | no | no | Appearance, (protect with lacquer from acid attack) | |
| White Bronze (on Cu+Ni) | 3 | no | no | Jewellery in contact with the skin | |
| Cadmium (on Cu+Ni) | no | yes | yes | Amelioration of corrosion couples | |
| Gunmetal (on Cu+Ni) | 3 | no | no | Appearance, (protect with lacquer from acid attack) | |
| Chromium (on Cu+Ni) | 4 | 1 to 4 | yes | yes | Appearance, anticorrosion |
| Bright | 3 to 4 | 4 | yes | yes | Appearance, anticorrosion |
| Satin | 4 | yes | yes | Appearance, anticorrosion | |
| Black | 3 | yes | yes | Appearance, anticorrosion | |
| Copper | 3 | no | yes | Soldering, food contact | |
| Tin Alloys (Sn,Sn-Pb,Sn-Ni) | 4 | no | no | yes | Soldering, wear, friction, food contact |
| Brass (on Cu+Ni) | 2 to 3 | no | no | Appearance, (protect with lacquer from acid attack) | |
| Nickel (on Cu) | 1 to 4 | 1 to 3 | no | no | Appearance, wear resistance |
| Bright, matt, multicoat | 3 | 1 to 4 | no | no | Appearance, wear resistance |
| Gold(on Cu+Ni) | 4 | 1 | yes | yes | Appearance, electrical contact |
| Palladium (on Cu+Ni) | No | no | yes | Electrical contact | |
| Rhodium (on Cu+Ni) | 4 | no | yes | Appearance, stabilisation of brilliance(gold and silver) | |
| Zinc+chromate | 4 | no | yes | Appearance, anticorrosion | |
| Zinc | 3 | 3 | no | no | Appearance, anticorrosion |
| Vacuum Metallizing | |||||
| Aluminium | 2 | 1 to 2 | no | yes | Reflectivity, wave guides |
| Silver | 2 | 1 to 2 | no | yes | Electrical conductivity |
| Gold | 2 | 1 to 2 | no | yes | Infra red reflectivity |
| Carbon | 2 | 1 to 2 | yes | yes | Wear, anticorrosion |
| Organic Finishes | |||||
| Electropaint | 4 | 4 | yes | yes | Anticorrosion |
| Wet Paint | |||||
| Epoxy | 1 to 2 | 1 to 2 | no | no | Decoration |
| Polyurethane | 4 | 4 | yes | no | Decoration, anticorrosion |
| Acrylic/Polyurethane | 1 | 1 | no | no | Decoration |
| Powder Coating | |||||
| Epoxy | 1 to 2 | 1 to 2 | no | no | Decoration |
| Epoxy-Polyester | 3 | 3 | yes | no | Decoration, good anticorrosion |
| Polyester | 4 | 4 | yes | no | Decoration, good UV resistance, best anticorrosion |
| Special Finishes | |||||
| Dry Film Lubricants | 4 | no | Low friction, , good dielectric | ||
| Plastic Coating | 4 | 4 | Noise and vibration reduction | ||
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Exposure Classes
| Condition of Use | Class |
| Decoration only. Any protection regarded as a bonus | 0 – 1 |
| Dry interior: without condensation, interior of dwellings | 0 – 1 |
| Damp interior: condensation, kitchens, bathrooms, cellars and workshops, unheated warehouses. | 2 |
| Moderate rural outside: Outside in the countryside in moderate climates | 3 |
| Moderate outside city: Outside in industrial towns in moderate climates | 3 (4) |
| Tropical: Heat and condensation experienced in tropical areas | 4 |
| Industrial: Factories and their vicinity. Strong content in the atmosphere of various compounds including SO2 | 4 |
| Marine: Coastal atmospheres and on the sea, without being directly in contact with seawater. Corrosion resulting from high relative humidity and salt in the air. | 4 |
| Occasional splashing with corrosive materialsVariations in temperature (-40C to +120C): variation in the corrosive conditions
Corrosion by various aggressive gases, liquids and solids: |
TestsObligatory |