Note: Wikis and Microsoft Word do not play well together. Thus, you can download this document in Word by scrolling to the very bottom. You can make changes in the wiki below. Don't worry, you can't harm this document -- we can always scroll back to earlier documents.
Comment from Leo:
Here is what I came up with for the finishing section of the basic book. I wasn’t sure how detailed to go, there is plenty more to put in, but Amos was really stressing leaning more towards ‘basic’. I’m sure there is enough information for an intensive course just on finishes, but for the basic section, we tried to boil it down and get the most important stuff. We did NOT include stainless or copper alloy metal specific finishes. The idea there was that these more exotic metals could stand to have a class of their own, and a basic section would raise more questions than it would answer.
Most of the outline comes from the NOMMA/NAAMM book, the rest from shop experience and a little bit of research.
One thought Amos had about the Platinum level certification: Double-blind review of a shop’s work. As part of the accreditation process, the shop submits 10-12 good photos. The file is then reviewed by someone (perhaps a committee of someones) who assess to ensure that the work being done is of platinum level, perhaps a rating scale, 1-100; 40 being the minimum for basic, and 50-60 being silver, 70-80 being gold and 90-100 being platinum. The photos and work would be evaluated for different areas: complexity, attention to detail, neatness of fabrication, consistency, finish quality, etc. The scores in the categories would be added together and that would be the score for the shop. For instance if a shop scored 75, they could complete modules and testing required and become a silver, then gold shop, and even if they complete all the modules they couldn’t become platinum without being reevaluated.
Amos included his suggested costs: $395 for basic. $195 for each additional level, $880 for platinum. Hopefully we could keep the module cost lower (perhaps $50 including the study guide and 1 session of testing).
I. Introduction to finishing
A. Definition of finishes
B. Types of Finishes
i. Involve the use of no chemical or electrochemical treatment and no additive
ii. Provide a surface texture by mechanical means
iii. Range greatly from mill-finish to polishing
iv. Includes both directional, non-directional and patterned finishes
i. Processed by washing or dipping fabricated product in chemical solutions
ii. Can be an intermediate process to clean without changing appearance
iii. Can give matte textured appearance or as an intermediate finish
iv. Can chemically prepare the metal for later finishing.
v. Can be a final finish with a patina or oxide
i. Applied to the Surface of fabricated product
ii. Many different types and application methods.
C. Importance of selecting the right finish
II. Types of Finishes
A. On Aluminum
a. As Fabricated
i. Also known As Mill finish
ii. Subsequent fabrication operations (forming, sawing, welding, punching, etc) can mar the appearance.
iii. Hot Rolled and heat-treated products typically have a dull and darker surface
iv. Cold-rolled has a brighter and more metallic color, Extruded is similar to cold-rolled but has striations caused by the extrusion die.
v. Castings have a rougher matte finish, die castings being smoothest, and sand castings the roughest.
i. Created by successive processes of grinding, polishing, and buffing.
ii. Top Quality bright appearance, commonly used for entrance doors and framing.
iii. Should NOT be used on wide flat surfaces because of their reflectivity
iv. Smooth Specular is the brightest mechanical finish obtainable and is produced by buffing. Material is ground and polished to a lustrous finish, final stage is buffing with 320 grit.
v. Specular is the finish created by buffing only, with no preliminary grinding or polishing, the resulting finish can show some evidence of surface irregularities
c. Directional Textured Finishes
i. Smooth Satiny sheen, but limited reflectivity, caused by characteristic tiny parallel scratches produced by wheel or belt polishing with fine abrasives, by hand rubbing with stainless wool , or by brushing with abrasive wheels.
ii. Fineness of the finish is controlled by the size of grit used, speed of the belt, hardness of the block or pad used, the pressure exerted on the block and the condition of the belt.
iii. Fine satin, Medium Satin, Coarse Satin: Produced by wheel or belt polishing with grits of varying degrees of fineness
iv. Hand rubbed: produced by rubbing with abrasive cloth or stainless steel wool o increasing degrees of fineness, finishing with No. 0 or No.00. Expensive, only used where the nature of the work being finished makes other methods impractical or to blend in other finished.
v. Brushed: Produced by using power driven stainless steel wire wheel brushes, brush backed sander heads, abrasive impregnated foamed nylon discs or abrasive cloth wheels.
i. Matte finishes of varying degrees of roughness produced by blasting a media (such as sand, aluminum oxide, glass beads or other specialized media) against the metal under constant controlled conditions
ii. Texture of the surface is determined by the size and type of abrasive media used, air pressure and position and movement of the nozzle
1. The Finer the abrasive the smoother the finish.
2. Silica sand is coarse, dust blasting with a very fine abrasive or ‘vapor honing’ with a slurry of extremely fine abrasive and water produces the finest finishes
iii. Not recommended on material less than ¼” thick.
iv. Can have difficulty in maintaining a uniform appearance without special equipment
v. Even the finest finishes are rough, show fingerprints easily, and collects and retains dirt
1. Some type of protective treatment is necessary to retain a clear appearance, such as clear lacquers or anodizing
vi. Common variations obtained from washed silica sand or aluminum oxide:
1. Extra fine matte, Fine Matte, Medium Matte, Coarse Matte
vii. Shot blasting is used to provide peened finishes, using steel shot of different sizes. Can produce the following finishes:
1. Fine shot blast, Medium shot blast, Coarse Shot Blast
i. Available in thin sheet
1. Created by passing the sheet between two machined matching design rolls, aka embossing; or between a solid roll and a design roll aka coining.
a. Non-Etch Cleaning
1. Vapor Degreasing, done in special degreasing machines
2. Solvent or solvent emulsion cleaning with hydrocarbon solvents to remove oil and grease from the metal surface
3. Should be followed by chemical cleaning
4. Can be subject to EPA regulations
ii. Chemical Cleaning
1. Method used when animal fats and oils must be removed
2. Metal is sprayed or immersed in any number of proprietary or non-proprietary solutions, usually at elevated temperatures, then rinsed with water.
3. Inhibited chemicals should be used on aluminum to prevent etching of the surface.
b. Matte Finishes
i. Referred to as Etched finishes or ‘frosted’ finishes
ii. Can be used to prepare for anodizing, or can simply be followed by the application of a clear lacquer
iii. Change the surface texture of the metal from a metallic shine to a stain or dull sheen and are regulated to give varying degrees of roughness.
1. Done using various solutions of acid or alkali and sometimes additives
2. For Production quantities, this can be cheaper than mechanical means
iv. Wide variety of acid and alkaline etches are used
v. Bright Finishes
1. Range from Mirror bright to diffuse bright
2. Chemical brightening, obtained by immersing the metal in certain acid solutions or Electrolytic brightening
a. Minute irregularities in the metal surface are removed by making the piece to be brightened the anode in an electrolyte
b. Produces pieces free from mechanical stresses and embedded abrasive particles
c. Different appearance than mechanical buffing.
4. Highly Specular: This finish is the result of preliminary buffing, followed by electro-polishing or chemical brightening and produces a mirror like surface on certain alloys, can be used for reflectors
5. Diffuse Bright: A finish generally produced by first applying a caustic etch (Medium matte) followed by chemical brightening.
c. Conversion Coatings
i. Generally used for preparing the surface for paint
1. However, can be used as final finish
ii. Natural oxide layer on aluminum does not provide a good bond for paints, or other coatings, it can be ‘converted’ to improve adhesion.
3. Anodic Coatings
a. Consists of immersing the aluminum to be anodized in an appropriate acid solution, referred to as the electrolyte and passing a direct electric current between the aluminum and the electrolyte, with the aluminum acting as the anode.
b. Results in the controlled formation of a durable oxide layer or coating on the surface of the aluminum.
i. Coating is many time thicker than naturally formed oxide film
ii. Can be transparent, translucent or opaque, depending on the alloys and/or processes used
iii. This coating does not affect the surface texture of the aluminum, however fine this texture is, but they greatly increase resistance to corrosion and provide increased resistance to abrasion
c. Proper surface pretreatment
i. Chemical cleaning and finishing is paramount
1. Degreasing or inhibited chemical cleaner is the first requirement
ii. Metal residue from finishing or grinding must be removed
iii. Chemical etching or brightening can be used following the cleaning where the final appearance requires such pre-anodizing treatments.
iv. Can receive one of the buffed, directional, non-direction or patterned finishes.
1. However As-Fabricated finishes are of a quality that eliminates the need for subsequent mechanical finishing operation
2. Most architectural products today are simply etched and anodized.
d. Several different anodizing processes are presently used for architectural aluminum products. They differ in solution used for electrolyte, voltages and current densities required, and the temperature at which the electrolyte is maintained.
e. For exterior applications thickness should be at least .7 mil and minimum coating weight of 27mg per square inch.
i. For resistance to extreme exposure conditions such as sea water or abrasive actions, integral color anodic coatings or ‘hardcoats’ up to 3.0 mils thick.
f. Sealing of the pores in the oxide coatings is essential.
i. Most methods are sealed in a deionized boiling water bath or metal salt sealant.
ii. Surfactants and wetting agents can be used but should be controlled so as not to cause poor adhesion of any organic over-coating.
g. Architectural Class 1 Coatings
i. .07 Mil or more in thickness and weighing not less than 27 mg per sq. in. or a density not less than 38 g per sq in.
ii. Appropriate for interior architectural items subject to normal wear, and for exterior items that receive a minimal amount of cleaning and maintenance.
iii. It is possible to produce hard coat Class 1 finishes in thicknesses ranging from 1 to 3 mils.
h. Architectural Class 2 Coatings
i. Thickness ranging from .4 to .7 mils with corresponding weights of from 15.5 to 27 mg per sq. in. or a density ranging from 22 to 38 g per sq in. The lower figures being the minimums recommended for architectural uses
ii. Suitable for interior items not subject to excessive wear or abrasion or exterior items such as storefronts and entrances which are regularly cleaned and maintained.
4. Finish Considerations for Aluminum
a. See Cleaning and Maintenance Guide for Architecturally Finished Aluminum AAMA 609/610-02
i. Cleaning should begin as soon after installation as possible
ii. Use water at moderate pressure, starting at the top working downwards.
iii. If heavier cleaning is needed scrubbing with brushes or sponges and a mild detergent can be used.
iv. Do NOT use aggressive alkaline or acid cleaners.
B. On Copper and Copper Alloys (OMITTED FOR BASIC)
3. Concerns when finishing Copper and Copper Alloys
C. On Stainless Steel (OMITTED FOR BASIC)
d. Electopolished Finishes
e. Maintenance and Cleaning
D. On Carbon-Steel and Iron
a. Mechanical Surface Treatments
i. Mill Finish
1. Hot-rolled mill finish: Tight mill scale and rust powder
2. Cold-Rolled Mill finish: Should be properly degreased before painting, may need roughening to insure good adherence
1. Hand Cleaning: wire brushes, abrasive paper or cloth, scrapers, chisels, or chipping hammers. Be used for spot cleaning
2. Power tool cleaning: power driven brushes, grinders and sanders, used for removing scale, rust and dirty from material. Less appropriate for thin metal
3. Shot-blasting and Sandblasting: Excellent for obtaining a clean surface suitable for painting may be done either wet or dry, use with caution on thin metal. Also ensures the surface is sufficiently roughened to ensure good paint adhesion.
b. Chemical Treatments
i. Cleaning Processes
1. Pickling: Removes scale and oxide coatings; consists of immersing the metal in a dilute acid solution followed by rinsing in water, then in other solutions and a thorough drying.
2. Vapor Degreasing: uses vapors from chlorinated solvents in special degreasing machines. Can be toxic and comparatively expensive.
3. Alkaline Cleaning: Sprayed with or immersed in any number of solutions, usually at elevated temperatures, after which it is rinsed with water, Caustic soda, soda ash and alkaline silicates and phosphates are common cleaning agents.
c. Conversion Coatings
i. Converts the chemical nature of the surface layer to improving the bond for applied coatings.
d. Applied Coatings
i. Almost all iron and steel products receive some type of applied coatings.
ii. Organic and metallic are most common, but also used are vitreous, and laminated coatings.
iii. Metallic Coatings
1. Common Metals include Aluminum, Nickel Cadmium, Terne metal, Chromium, Copper, Tin, Lead and Zinc
2. Protects against corrosion, permitting the mechanical properties of steel to be used with the assurance of durability.
3. Some Metallic coatings provide unique protective value through electrolytic action.
a. If the coating metal is less noble than the base metal, it protects by acting as a sacrificial metal
b. If the coating metal is more noble, it has its own relative chemical stability to protect the steel beneath.
c. Hot Dip
i. Commonly used for Zinc Galvanizing, but also used for tin, lead, and aluminum.
ii. Steel item is cleaned and immersed in molten metal
iii. Drainage points to allow molten zinc to flow into all cavities are essential, be sure to prevent puddling areas.
iv. Tubular fabrications and hollow structural must be properly vented. Good galvanizing covers the inside and out. After galvanizing vents and drain holes can be plugged with zinc plugs
v. Some assemblies may distort at galvanizing temperature.
vi. Talk to your galvanizer about special procedures including bracing, venting and differing alloys used in assemblies.
vii. Untreated galvanized surfaces generally do not bond well with paint.
1. Zinc dust-zinc oxide and cement-in-oil paints or specially designed paints can have good results.
2. Weathering can increase the adhesion of paints.
d. Thermal Spraying, AKA Metallizing.
i. Uses heat and pressurized air to melt the coating metal and spray it onto the steel item to be coated.
ii. Can be used in the field
iii. Coating metals include zinc, aluminum and copper.
i. Zinc and Cadmium are common anodic coatings. Nickel, Chromium, and copper and cathodic coatings.
i. Produces metal products consisting of a steel core, covered with a thin layer of coating metal.
Documents and slides related to credentialing.