Surface Preparation for Coatings 120

abrasive blasting

A mechanical preparation method that involves spraying a surface with dry particulate media at high velocity. Abrasive blasting is also called blast finishing.

acid cleaning

A solvent cleaning process that removes surface contaminants with hydrochloric and sulphuric acids.

acid pickling

An aggressive form of acid cleaning intended to remove tough deposits of scale and oxides. Acid pickling is harsh enough to etch metal surfaces.

acidity

The ability of a substance to neutralize bases. Acids have a pH value below 7.

alkali

A non-acidic substance that dissolves in water and increases the pH of a solution. Alkalis are opposite acids on the pH scale.

alkaline cleaning

A chemical surface preparation method involving alkalines, substances that have a pH value above 7. Alkaline solutions displace particles, emulsify oils, and dissolve oxides.

alkalinity

The ability of a substance to neutralize acids. Alkalines have a pH value above 7.

anodic electrocleaning

A type of electrolytic cleaning in which the part is positively charged and the cleaning action is derived from the release of oxygen.

anodizing

A conversion coating method used to make a surface passive and to increase the thickness of an oxide layer on the surface of metal. The metal part forms the anode electrode of an electrical circuit, and experiences better corrosion and wear resistance and and better coating adhesion than if left untreated.

belt sanding

A manual mechanical surface preparation process that involves contacting a part with a rotating abrasive belt. Belt sanding is ideal for flat surfaces in small quantities.

blast finishing

A mechanical preparation method that involves spraying a surface with dry particulate media at high velocity. Blast finishing is also called abrasive blasting.

boronizing

A metallurgical surface preparation method by which metal is heated within a boron-rich environment in order to increase wear resistance.

boundary layer

A layer of contamination that covers a surface. Coatings tend to adhere to the boundary layer instead of the surface, rendering the coating ineffective.

buffing

A manual mechanical surface preparation process that involves contacting the part with a rotating, slightly abrasive wheel.

carbonitriding

A metallurgical surface preparation method by which a metal is heated within a carbon- and nitrogen-rich environment in order to increase hardness.

carburizing

A metallurgical surface preparation method by which metal is heated within a carbon-rich environment in order to increase carbon levels on the metal surface for added hardness.

cathodic electrocleaning

A type of electrolytic cleaning in which the part is negatively charged and the cleaning action is derived from the release of hydrogen.

chemical preparation

A surface preparation method that involves the use of chemicals like alkalines and solvents.

chromating

A conversion coating method used to make a surface passive through the deposition of an oxide layer. Chromating is used to prevent corrosion, to retain conductivity, and as a primer and decorative finish.

chromizing

A metallurgical surface preparation method by which metal is heated within a chromium-rich environment in order to increase wear resistance and corrosion resistance.

coating

A finish used for protective and decorative purposes. Coatings like paint or varnish are applied to products in an industrial manufacturing setting as a component of the part creation process.

cold trap

A cooling component used within a vapor degreasing system that causes the solvent to condense and collect in liquid form for later reuse.

cold working

The shaping of metal at temperatures much lower than the metal's molten state, often at room temperature. Cold working adds certain properties to the metal, such as increased strength and improved surface finish.

conversion coating

A surface preparation method that converts a surface into a thin layer with advantageous qualities. Phosphating, anodizing, and chromating are conversion coating methods.

corona

A type of energized spark that generates ozone, which in turn can be used to energize surfaces.

corona discharge treatment

A surface preparation method used to energize low energy surfaces like plastics and glass. During corona discharge treatment, electric current ionizes air and creates an ozone-generating spark that raises the surface energy of some surfaces.

curing

The process during which a liquid coating becomes a dry, hard film. Ample curing is crucial to the successful performance of a coating.

deionized water

A form of purified water that has mineral ions removed.

dielectric

An electrical insulator that can be polarized by an electric field. A basic corona discharge treatment system consists of an electrode, a dielectric that includes the surface and an air gap, and a grounded base.

diffusion

A type of metallurgical surface preparation during which an element is diffused into the surface of a part to achieve a particular quality. Diffusion processes like carburizing and nitriding are named after the element being diffused into the part.

electrolytic cleaning

A modified type of alkaline cleaning in which electricity is applied to the solution and the surface. Anodic and cathodic electrocleaning are types of electrolytic cleaning.

flame etching

A surface preparation method used to energize low energy surfaces like plastics and glass. During flame etching, a flame from propane gas is passed over a surface causing hydrogen atoms to react with the burning gas, thus raising its energy level.

hydrated oxide

An oxide surface layer that has reacted with water. Hydrated oxide layers are very difficult to remove.

ion implantation

A metallurgical surface preparation method during which atoms of an element are added to a surface with a beam of ionized particles. Ion implantation can be performed at lower temps than diffusion methods.

ionized water

Water that retains naturally occuring mineral ions.

mechanical preparation

A surface preparation method involving physically removing layers. The largest category of physical surface preparation involves cleaning with abrasives.

mold release agent

A chemical used to help release a molded part from a mold cavity. Mold release agents can prevent adhesion of a coating on a plastic surface.

nitriding

A metallurgical surface preparation method by which metal is heated within a nitrogen-rich environment. Metals that are nitrided typically contain aluminum or chromium.

oxide

A chemical compound containing oxygen and one other element. The oxide layer is the main factor in determining the surface treatment for a metal surface.

ozone

A powerful oxidizing agent that, when harnessed and exposed to low-energy surfaces, can energize low energy surfaces. Corona discharge treatment is designed to generate ozone.

pH

A measure of the relative acidity or alkalinity of a substance.

phosphating

A conversion coating method in which phosphoric acid and phosphate salts react with the surface to form a layer of insoluble phosphates. Phosphating imparts lubricity and corrosion resistance and generally is a foundation for a coating.

plasma

A state of matter created by energizing a gas. Next to solid, liquid, and gas, plasma is the fourth state of matter.

plasma treatment

A surface preparation method used to energize low energy surfaces like plastics and glass. During plasma treatment, pressurized gas is energized by an electrode and then directed at high velocity at a surface.

polarity

The attractive forces that exist between two opposites like a coating and a surface. Some surfaces have low polarity and thus do not attract coatings.

pressure washing

The process of removing surface material and contaminants by spraying pressurized water onto a surface. Pressure washing is also called water blasting.

primer

A preparatory coating used to prepare surfaces for other coatings. Primers encourage adhesion, durability, and longevity.

reactivity

The tendency of a surface to react with other elements and substances. Low energy surfaces have low reactivity and thus repel interaction.

rust

A general term for iron oxide. Rust is a reddish-brown substance caused by ferrous metal's reaction with moisture and oxygen.

shot peening

A variation of abrasive blasting involving the streaming of cast steel pellets at a surface. Shot peening cleans and strengthens the surface.

slurry

A thick mixture of liquid and suspended solids. Wet abrasive blasting involves a slurry.

solvent

A chemical used to dissolve another material. Solvents are often used to dissolve surface contaminants.

substrate

The material onto which a coating is applied. The surface is the top portion of the substrate that directly interacts with the coating.

surface energy

A measure of the tendency of a surface to repel a coating. Low surface energy indicates a tendency to repel, while high surface energy indicates a tendency to attract.

surface preparation

The process of treating a surface in order to increase its attraction to coatings. Surface preparation can be mechanical or chemical and is crucial to the success of a coating.

tumbling

A relatively slow mass finishing process during which several small parts are placed in an enclosed container full of abrasive media. Surface preparation occurs as the container is agitated and the parts rub against the abrasive media.

ultrasonic cleaning

A modified type of alkaline cleaning in which high-frequency vibrations are introduced in the solution. Ultrasonic cleaning produces vapor bubbles that shock contaminants off surfaces.

vapor degreasing

A solvent cleaning process that uses vaporized fluorinated or chlorinated solvents to remove contaminants. The process has fallen out of favor because of environmental concerns.

vapor honing

A combination of several types of mechanical preparation, a process similar to glass bead blasting, but instead using a fine abrasive suspended in a slurry. Vapor honing cleans and aids surface wettability.

vibratory finishing

A relatively fast mass finishing process during which parts are placed in an open barrel and agitated. Process times are faster because more part area is exposed to the abrasive action of the vibrating process.

water blasting

The process of removing surface material and contaminants by spraying pressurized water onto a surface. Water blasting is also called pressure washing.

water break test

The process of pouring water onto a surface to determine the presence of oil on the surface. If the surface is oily, the water forms into beads.

wettability

The ability of a coating or surface to interact with each other. Cleaning or energizing a surface increases its wettability.

wetting angle

Also called contact angle, the angle formed where a drop of a coating meets the surface. Smaller angles indicate high wettability, while large angles indicate low wettability.

wetting angle test

The process of measuring the wetting ability of a surface by comparing the wetting angle with a reference liquid.

wire brushing

A manual mechanical surface preparation process that involves contacting a part with a rotating wire brush. Wire brushing imparts fine scratches on the surface of parts.