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Surface Finishing Tutorial

#217 Metal Cleaning - Grime on Metal Surfaces - 2

Category : Metal cleaning
October16, 2015
(3) Solid material

The surface of metal products is contaminated with various types of grime listed here.The contaminants include organic/inorganic dirt, such as products formed by chemical reaction on the metal surfaces during processing, as well as dirt and dust in the air attached to the surface or onto the oil films, including rust-preventing/lubrication oils.

(1) Oxide/sulfide films formed during molding or heat treatment
(2) Oxidized materials, carbonates, and sulfide films formed during storage
(3) Dirt and dust floating in the air or attached onto oil films
(4) High-viscosity oily films (lubricant oil, etc.) formed during long-term storage
(5) Fingerprints and sweat marks/stains left on the products by touching them with bare hands
(4) The mixture of oil and solid refuse

Surface conditioning on the product surface may be performed by mechanical polishing before the surface treatment process.This is one of the decoration techniques achieved by buff polishing or sandblasting to add the aesthetic product value to metal surfaces, such as matting, satin finish, hairlines, and mirror gloss.
This section introduces details on the methods of buff polishing.The common buffing methods are as follows:

Emery polishing

(Emery polishing smooths out the product surface using a round buff with emery abrasive powder adhered to the glue in the circumferential direction. This buff is made of multi-layered fabric stitched up closely. Common types of abrasive powder for this buffing are #120 and #220 [coarser powder], and #320 and #400 [finer powder], which will be used from the lower number.To reduce friction and avoid grinding burn of the metal, oil-based abrasive paste will be used together.This paste is also called "grinding compound".)

Buffing

(This buffing adds mirror polishing or matte polishing to emery-polished products.The buff used here is called a "cloth buff", a round-shaped buff made of multi-layered fabric stitched up roughly. Apply oil-based abrasive paste onto the circumferential surface for polishing.)

A variety of buffing methods are available including the ones introduced here. Emery polishing may be enough for some products, but some of them require polishing on the glossy surface.

(1) Buffing compound --- A mixture of metal fine particles and compound oil
(2) Carbon and carbonaceous contaminant --- Varnish-like film formed by decomposed oil
(3) Stains from marking or divider materials --- Stains and transfer of print ink or synthetic resin

Grime attached to the metal surfaces is largely divided into the following two types: Oil-based grime, such as lubricants, and metal-based contaminant, such as oxide films formed during processing or heat treatment.To remove these contaminants, "degreasing" is performed on the former type whereas "acid washing" is performed on the latter type.

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