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Glossary of Terms
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Powder Coating Terms & Definitions
(A - E)               (F - O)                   P           R             S                  (T - Z)

Part Bring-up Time
- Amount of time required to heat a part to a desired metal temperature.

Part Opening - The opening in the powder booth, ovens, washers and other equipment where parts enter and exit.

Particle Size - The average diameter of an object having irregular boundaries that can be determined to have diameter through various test methods.

Passivation - Conversion of a metal surface to a less reactive state. A process used to reduce the corrosion rate of metal surfaces.

pH Value - Measure of acidity or alkalinity. pH7 is neutral. The pH values of acids are less than 7. The pH values of alkali bases are greater than 7.

Phosphate - Chemical radical (PO4)-3. In coating operations, zinc, iron or manganese phosphate is used as a conversion coating to prepare the part for coating application.

Pigment - Particles in a powder formula that provide color, corrosion resistance and other properties.

Pinholing - Formation of small holes through the entire thickness of a coating. The appearance of fine, pimply defects in a cured film, due to air trapped under the surface of the film or other causes, resulting in small holes in the film.

Plenum - Air chamber used to transition or distribute airflow within a powder spray booth.

Polyester - A resin or powder containing the chemical group R-COOC-R.

Polyethylene - A thermoplastic resin with the formula (CH2CH2)x.

Polymers - Poly means many and mer means units. Polymers are very large molecules built up by the combination of many small molecules, often having many thousands of atoms.

Polymerization - Chemical reaction in which small molecules combine to form very high molecular weight molecules.

Polypropylene - One of the more common polyolefin thermoplastics. An addition polymer from propylene monomers with a crystalline structure (CH2CHCH2)x.

Polyvinyl Chloride - Synthetic resin used in solvent-type coatings; produced by polymerization of vinyl chloride. Also used in vinyl powders.

Porosity - Degree of integrity or continuity.

Post-curing - Heating of a part after powder coating to complete the cure cycle, which completes the cross linking of the components.

Power & Free Conveyor - Two-track chain conveyor system that allows product to be transported at different speeds and through different routes throughout the finishing system.

Powder - A coating blend made of non-volatile ingredients, applied dry and melted into a continuous film.

Powder Booth - An enclosure used for containment of powder during the spray operation.

Powder Coating - Coatings that are protective, decorative, or both, formed by the application of a coating powder to a substrate and fused into continuous films by the application of heat or radiant energy. Coating powders are finely divided particles or organic polymer which generally contain pigments, fillers and additives; and which remain finely divided during storage under suitable conditions.

Powder Room - A room that isolates the powder application process from the general plant environment. Sometimes referred to as Environmental Room.

Pressure - Force per unit area relative to atmospheric pressure. Usually expressed in pounds per square inch.

Pretreatment - The preparation of a part prior to the application of powder coating in order to improve adhesion and corrosion resistance.

Primer - A type of coating, usually paint, applied to a surface to improve adhesion of a top coat and/or improve corrosion resistance.

Primer Surfacer - Coating used to prime a surface as well as fill irregularities in the substrate. Primer surfacers are usually applied over a primer.

Production Rate - Measurement of square foot per day of the surface area cleaned or coated in one working day by one person.

Profile - Surface contour of a blast-cleaned surface as viewed from the edge cross-section of surface.

Profile Depth - Average distance between top of peaks and bottom of valleys on a surface.

PSI - Pounds per square inch, a measure of force above a vacuum.

Pump - Device which converts mechanical force and motion into hydraulic fluid powder.

Pump Screen - A screen that catches large contaminants in a process solution as the solution flows through it to the pump.

Purging - Cleaning one color or powder formulation from all areas that come in contact with the powder before introducing another color or powder.

Radiation Cure - Curing a coating by means of exposure to electromagnetic waves or particles such as infrared, ultraviolet or electron beam.

Reciprocator - Device used to move automatic guns in a vertical plane. Motion is provided by a reversing or reciprocating drive system.

Reclaim - The process used to recycle nondeposited powder through the delivery system for reuse.

Reclaimed Powder - Powder which has been oversprayed and captured for reuse.

Recoat - Process of refinishing parts that have a surface defect from the first coating application by repairing the defect and respraying.

Recovery - The process of removing nondeposited powder from the air prior to recirculating the powder through the delivery system.

Recovery System - A filtration system that separates powder from the airstrip with a fan that captures oversprayed powder and maintains negative air pressure inside a powder booth. Most common type of recovery systems are the cyclone system and the cartridge module system.

Resin - Any class of solid or semi-solid organic material of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.

Resistivity - The resistance to the flow of electrical current afforded by a substance.

Reverse Osmosis - Method of removing metal ions from an aqueous solution via semi-permeable membranes.

Rework - Procedures to correct powder coating imperfections or defects.

Runs - Sags in the coating.

Rust - Corroded iron. Red iron oxide deposited on metal. Also other metal oxides formed by corrosion.

Salt Spray Test - Corrosion test using salt (NaCl) solution sprayed as a mist in a heated humidity chamber to simulate seashore conditions, or to accelerate corrosion at a controlled rate. (ASTM Test B117)

Sand Blast - Blast cleaning using sand as an abrasive.

Sanitary Pan - A trough that is mounted under a conveyor chain to catch debris and keep it from falling on work in progress.

Scale - Rust occurring in layers, commonly found on hot-rolled steel.

Screen Mesh Size - The mesh number of a screen designates the openings per square inch using standard wire. Screens are used to classify the size of the coating powders.

Seal Rinse - A final rinse in a spray washer that passivates the pretreated surface to prevent oxidation and provide corrosion resistance in the field.

Seeding - Formation of small agglomerates or gel particles. Seeds in coating powders can form when the material is overheated during the extrusion process.

Shelf Life - Maximum amount of time a material may be stored and still be in usable condition.

Shot Blasting - Blast cleaning using steel shot as the abrasive.

Side-draft Booth - A powder booth where the air extraction opening is on the side of the booth.

Sieve - Powder particle classifier which utilizes wire mesh of various sizes to screen out oversized powder particulate and foreign material or dirt. (Rotary Sieve - Cylindrical screen equipped with an electrically driven paddle used to classify powders, or remove undesirable particulate from powder materials. Vibratory Sieve - Electrically or pneumatically driven screen utilizing vibration to classify powders, or remove undesirable particulate from the powder materials.)

Silicone - One of a family of polymeric materials in which the recurring chemical group contains silicone and oxygen atoms as links in the main chain. These compounds are derived from silica, i.e., sand, and methyl chloride. The various forms obtainable are characterized by their resistance to heat. Uses for silicone include: greases for lubrication; rubber-like sheeting for gaskets; heat-stable fluids; compounds for waterproofing and insulation; thermosetting insulation varnishes; and resins for both coating and lamination. [Silicone lubricants should not be used around a finishing system because it will cause defects in the finished surface.]

Sintering - The tendency of some powders and powder coating materials to agglomerate during storage.

Soils - Foreign matter on a part's substrate prior to being cleaned in a pretreatment system. Can be organic or inorganic.

Solvent - Liquid or blend of liquids used to dissolve or disperse a paint. A true solvent is a single liquid which can dissolve a paint.

Solvent-borne Coating - Coating containing only organic solvents. (Non-water-borne)

Specific Gravity - An expression of density of a material relative to water. Examples: water - 1.000; ammonia - .587; propane - 1.550; natural gas - .665. Ration of the weight of a given volume of liquid or solid to the wight of an equal volume of water. (ASTM Test D3451)

Specular Gloss - Mirror-like reflectance. Gloss measured at a specific specular angle. (ASTM Test D523)

Spray Pattern - Configuration of spray with a powder gun. See Diffuser and Fan Spray Nozzle.

Spray-to-waste Operation - Utilizing virgin powder only. All overspray powder is discarded and not recycled. 

Storage Life - Period of time that a powder material will remain usable in storage.

Storage Stability - The ability of coating powders to maintain uniform physical and chemical properties after being subjected to the manufacturer's specified storage conditions.

Substrate - The part to be powder coated.

Surface Defects - Flaws in the surface of a coated part.

Surface Preparation - Operations necessary to prepare the surface of a part prior to the application of a coating.

Surfactant - Chemical used to adjust surface tension of a material.

Surge - (1) A rise of pressure in an electrical circuit. (2) A sudden burst of powder from the spray gun.