Glossary of VPI and Porosity Terms
What Is Porosity?
In metal castings and other parts, porosity consists of tiny holes and open spaces in the parts that air and water can get through. These cavities cause leaking, plating issues, and performance problems when pressure is applied. Castings are often porous due to issues with the design, tooling, or pouring.
What Is Impregnation?
Impregnation is the penetration of resin in a porous or absorbent substrate to permanently seal it.
What Does VPI Stand For?
VPI is vacuum pressure impregnation, an impregnation method that ensures castings and components are fully penetrated by resin to fill every void. Steps in the VPI process include vacuum treating the component, introducing resin to seal porosity, applying pressure, draining, and curing.
What Is Air Decay Leak Testing?
Air decay leak testing is a leak testing method where an object is subjected to a measured amount of air and a leak is indicated by the loss of air pressure.
What Is Capillary Action?
Capillary action is the movement of liquids within the spaces of a porous material due to the forces of adhesion, cohesion and surface tension. It is the ability of a liquid to flow in narrow spaces without the assistance of, and sometimes in opposition to, external forces like gravity.
What Are Castings?
Castings are a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting.
What Is Discontinuity?
Discontinuity is an interruption in the normal physical structure or configuration of an object, such as cracks, forging laps, seams, inclusions and porosity.
What Is Immersion Leak Testing?
Immersion leak testing is a leak test method where an object is immersed in a fluid and leak is indicated by the escape of air in the form of bubbles.
What Are Resins?
Resins are any of a class of nonvolatile, solid or semisolid organic substances, as copal or mastic, that consist of amorphous mixtures of carboxylic acids and are obtained directly from certain plants as exudations or prepared by polymerization of simple molecules: used in medicine and in the making of varnishes and plastics.
What Is Anaerobic Resin Impregnation?
This is a process involving methacrylate sealants with a more sophisticated curing system. Once impregnated into the porosity of the parts, anaerobic sealants will automatically self-cure to a fully polymerized state.
What Is Viscosity?
Viscosity is the property of a fluid that resists the force tending to cause the fluid to flow.
What Is a Vacuum Chamber?
A vacuum chamber is a rigid enclosure from which air and other gases are removed by a vacuum pump, resulting in a low-pressure environment within the chamber. A vacuum environment allows for processes such as vacuum drying or vacuum coating. Chambers are typically made of metals, which may or may not shield applied external magnetic fields depending on wall thickness, frequency, resistivity, and permeability of the material used.
What Is Wet Vacuum (WV) Impregnation?
Parts or components are submerged in resin and a vacuum is drawn to remove air from resin and parts. This is the second stage of a Dry Vacuum Process, but can be performed independently.
What Is Wet Vacuum Pressure (WVP) Impregnation?
A vacuum is drawn to remove air from resin and parts. The vacuum is then vented and pressure is applied. Pressure cycle is the third stage in the Dry Vacuum Pressure process.