Cosmetic defects often forewarn a part’s ability to do its job as it was designed. Improper drying can not only ruin a part’s looks but make it fail in use.

• Aging: The change of a plastic part or piece with time under defined environmental conditions, leading to the continuation or deterioration of properties.
• Crazing: Fine cracks that may extend in a network on or under the surface or through a layer of a plastic part.
• Creep: The dimensional change with time of a plastic part under load, following the initial instantaneous elastic deformation. Creep at room temperature is sometimes called Cold Flow.
• Ductility: The extent to which a solid plastic part can be drawn into a thinner cross-section.
• Environmental Stress Cracking: The susceptibility of a thermoplastic article to crack or suffer craze formation under the influence of certain chemicals and stress.
• Hardness: The resistance of a plastic article to compression and indentation. Among the most common methods of testing this property is the Brinell hardness test procedure.
• Hydrolysis: Chemical decomposition of a plastic article through the addition of water.
• Impact Strength: The ability of a part to withstand shock loading or the work done in fracturing, under shock loading, a specified test specimen in a specified manner.
• Intrinsic Viscosity: The intrinsic viscosity of a polymer is the limiting value of infinite dilution of the ratio at the specific viscosity of the polymer solution to its concentrate on moles per liter.
• Melt Flow: The flow rate obtained from the extrusion of a molten resin through a die of specified length and diameter under prescribed conditions of time, temperature and load as set forth in ASTM D1238.
• Moisture Vapor Transmission: The rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity.
• Notch Sensitivity: The extent to which the sensitivity to fracture of a part is increased by the presence of a surface in homogeneity such as a face notch, a sudden change in section, a crack, or a scratch. Low-notch sensitivity is usually associated with ductile materials, and high-notch sensitivity with brittle materials. This is an important element in complex part design.
• Oxidation: The change occurring in a part by the addition of oxygen or the reduction of hydrogen.
• Permeability: The passage or diffusion of a gas, vapor, liquid, or solid through a barrier without physically or chemically affecting it and the rate of such passage.
• Resiliency: Ability to quickly regain an original shape after being strained or distorted.
• Voids: In a solid plastic, an unfilled space of such size that it scatters radiant energy such as light or more importantly, a cavity unintentionally formed in a molding.

Tolerance/Size Issues in Plastics Part Processing

Poor drying can often compromise a part’s physical characteristics, typically defeating its ultimate benefit in final use or application.

• Concentricity: For a round container part for instance, the shape in which various cross sections have a common center.
• Tolerance: A specified allowance for deviations in weight, dimensions measuring, etc.
• Warpage: Dimensional distortion in a plastic object after molding, particularly common and critical on flat surfaces.
• Wrinkle: An imperfection in reinforced plastics that has the appearance of a wave molded into one or more plies of fabric or other reinforcing material.