Engineering Properties

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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

Reference 24

 

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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Reference 2

 

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

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

Reference 24