All
| Term | Definition |
|---|---|
| Tensile Strength |
The maximum tensile stress sustained by the specimen before failure in a tension test. Usually expressed in pounds per square inch or megapascals. The cross-sectional area used is that of the original specimen, not at the point of rupture. |
| Terpolymer |
The product of copolymerization of three different monomers, or of the grafting of one monomer to the copolymer of two different monomers. An example of a terpolymer is ABS resin, derived from acrylonitrile, butadiene, and styrene. |
| Thermal Conductivity |
The rate at which heat is transferred by conduction through a unit cross-sectional area of material when a temperature gradient exists perpendicular to the area. |
| Thermal Decompsition |
Decomposition resulting from action by heat. It occurs at a temperature at which some components of the material are separating or reacting together, with a modification of the macro or microstructure. |
| Thermal Stability |
Ability of a polymer to maintain its initial physical and chemical properties at elevated temperature. |
| Thermocouple |
A device which uses a circuit of two wires of dissimilar metals or alloys, the two junctions of which are at different temperatures. A net electromotive force (emf) occurs as a result of differences in conductivity. The minute electromotive force or current, is sufficient to drive a galvanometer or potentiometer. |
| Thermoforming |
The process of forming a thermoplastic sheet into a three dimensional shape by clamping the sheet in a frame, heating it to render it soft, then applying differential pressure to make the sheet conform to the shape of the mold or die positioned below the frame. |
| Thermogravimetric Analysis |
The measurement of changes in weight of a specimen as it is heated. Some tests are conducted in air and some in other atmospheres. The resulting data reveals information about the materials thermal stability and polymerization processes. |
| Thermoplastics |
Resins or plastic compounds which, in their final state as finished articles, are capable of being repeatedly softened by an increase of temperature and hardened by a decrease of temperature. |
| Thermosets |
Resins or plastic compounds which in the final state as finished articles are substantially infusible and insoluble. Thermosetting resins are often liquids at some stage in their manufacture or processing, and are cured by heat, catalysis, or other chemical means. After being fully cured, thermosets cannot be resoftened by heating. |
| Thinning |
This refers to the finished wall of a blow molded container or the corners of a thermoformed part. The wall thickness has thinned out in some areas due to improper blowing or excessive stretching. |
| Tie Bars |
Bars which provide structural rigidity to the clamping mechanism often used to guide platen movement. |
| Titanium Dioxide |
A white powder available in tow crystalline forms, the anatase and rutile types. Both are widely used as opacifying pigments in thermosets and thermoplastics. |
| Toggle |
A mechanism that exerts pressure developed by applying force on a knee joint. It is used to close and exert pressure on a mold in a press. |
| Torpedo |
A streamlined metal block placed in the path of flow of the plastic material in the heating cylinder of extruders and injection molding machines, to spread it into thin layers, thus forcing it into intimate contact with the heating areas. |
| Toxicity |
The degree of which a substance is poisonous. Although most pure resins and polymers are relatively nontoxic, compounding additives such as stabilizers, colorants, and plasticizers must be carefully selected when products are to be used for food packaging or other applications involving body contact. |
| Transition Section |
In an extruder, the section of the screw that contains material in both the solid and molten state. |
| Transition Temperature |
The temperature at which a polymer changes from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one. |
| Treater |
Equipment used for preparing resin-impregnated reinforcements including means for the delivery of a continuous web or strand to a resin tank, controlling the amount of resin pickup, drying, or partially curing the resin, and rewinding the impregnated reinforcement. Term also used to refer to equipment and process used to render a surface of inert plastics, such as polyethylene more receptive to inks, adhesives, or coatings. |
| Two-Stage Injection |
The two-stage plasticator injector unit utilizes two separate stages to perform its function. The first, or plasticating stage, is devoted to the melting and mixing of the plastic melt by utilizing long, rotating screws. This screw conveys the processed plastic forward where, by means of a diverter valve, it is transferred into the injection or holding cylinder. When a sufficient quantity of melt has been plasticated and transferred into the injection cylinder, the diverter valve shifts to create a flow path from the injection cylinder to the mold runner system, and the second stage or injection stage, now begins. The melted plastic is forced out of the injection cylinder by a hydraulically driven piston or plunger. After injecting the melt into the mold, the diverter valve again shifts to connect the flow path from the rotating screw to the injection cylinder to transfer more plasticated material into the cylinder for the next cycle. During injection the plasticating screw continues to rotate and reciprocate to build up a change in front of it for the next cycle. |
| Ultimate Strength |
The maximum stress developed in a tensile-compression specimen. |
| Ultraviolet (Uv) Stabilizer |
Chemical agents which absorb or screen out radiation beyond the violet end of the spectrum of electromagnetic radiation. Such radiation has sufficient energy to initiate reactions leading to the degradation of many plastics. These agents are often combined with other additives, e.g. heat stabilizers and antioxidants, with which they act in synergistic fashion. UV stabilizers can be UV absorbers or radical scavengers. |
| Undercut |
An indentation or protuberance in a mold that tends to impede withdrawal of a molded part from the mold. Articles of soft materials such as flexible vinyls can be removed from molds with severe undercuts, but undercuts must be avoided in molds for rigid materials. Slight undercuts are sometimes deliberately formed in one half of a mold to cause the article to remain in a desired half until ejected. |
| Van Der Waals Forces |
Forces that exist between molecules of a substance after all of the primary valences within covalent molecules are saturated. Also called secondary valence forces or intermolecular forces. |
| Vapor |
As most frequently used, the term vapor describes a substance which, although present in the gaseous phase, generally exists as a liquid or solid at room temperature. |
| Vapor Barrier |
A layer of material through which water vapor will not pass readily or at all. |
| Vent |
A small hole or shallow channel in a mold which allows air or gas to exit as the stock enters. |
| Vented Barrel |
Port in extruder barrel through which volatiles can be removed. |
| Vented Screw |
Two-stage screw with vent in second stage to remove volatiles from the screw core. |
| Verolite® |
Verolite is a multiwall polycarbonate sheet. Verolite offers high quality glazing for greenhouses, conservatories, stadiums, walkways, canopies, and overhead glazing. Verolite sheet offers high impact strength, high light transmission, and thermal insulation. It is virtually unbreakable in a range of applications, and offers excellent UV protection. Verolite is a registered trade mark of SABIC Innovative Plastics (formerly GE Plastics). |
| Vibratory Feeders |
Devices for conveying dry materials from storage hoppers to processing machines, comprising a tray or tube vibrated by mechanical or electrical pulses. The frequency or amplitude of the vibrations controls the rate of flow. |
| Vicat Softening Point |
The temperature at which a flat-ended needle of 1 square millimeter circular or square cross section will penetrate a thermoplastic specimen to a depth of 1mm under a specified load using a uniform rate of temperature rise. (ASTM D-1525-58T). |
| Vinyl Acetate |
A colorless liquid obtained by the reaction of ethylene and acetic anhydride in the presence of a catalyst. It is the monomer for polyvinyl acetate, and a comonomer and intermediate for many members of the vinyl plastics family. |
| Virgin Material |
Any plastic compound or resin that has not been subjected to use or processing other than that required for its original manufacture. |
| Viscoelasticty |
The tendency of plastics to respond to stress as if they were a combination of elastic solids and viscous fluids. This property possessed by all plastics to some degree, dictates that while plastics have solid-like characteristics such as elasticity, strength, and form-stability, they also have liquid-like characteristics such as flow depending upon time, temperature, rate, and amount of loading. |