Glossary

Plastics Glossary - T

Tailstock Another name for the rear stationary platen.

Talc Refined mineral product (hydrated magnesium silicate) that is a reinforcing filler-extender. Because of its platy configuration, it tends to add stiffness to the resin, while its low cost categorizes it as an extender.

T_c Abbreviation for crystallization temperature.

Tensile bar Used to test tensile strength of a material. Material is molded into a tensile bar. As the bar is pulled, the material shows deformation until it finally yields and is no longer able to recover. The material will then continue to deform under the applied stress until it finally breaks. Ultimate elongation measures how far the material will extend before breaking as a percentage beyond its original length. ASTM D638.

Tensile elongation The maximum tensile stress sustained by the specimen before failure in a tension test. Usually expressed in psi. The cross section area is that of the original specimen at the point of rupture, not reduced by the break.

TG º Abbreviation for glass transition temperature.

TGA Thermogravimetric analysis.

Thermal conductivity Measures the rate at which heat is transferred.

Thermal endurance The time at a selected temperature for a material or system of materials to deteriorate to some predetermined level of electrical, mechanical or chemical performance under prescribed condition of test.

Thermal expansion (CTE) The tendency of a plastic to expand in the heat and contract in the cold.

Thermal pin See Heat pipe

Thermal properties Thermal properties that are important when selecting and processing a material are heat deflection temperature (HDT), thermal conductivity, coefficient of thermal expansion (CTE), dynamic mechanical analysis curves, differential thermal analysis (DTA) and TGA.

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 this temperature difference. The minute electromotive force, or current, is sufficient to drive a galvanometer or amplifier. A temperature sensing device used to measure the temperature of the barrel and nozzle zones.

Thermoelasticity Rubber-like elasticity exhibited by a rigid plastic resulting from an increase in temperature.

Thermoforming mold see Mold, Thermoforming

Thermoforming The process of forming a thermoplastic sheet into a three-dimensional shape by clamping the sheet in a frame, heating it to tender it soft and flowable. Then applying differential pressure to make the sheet conform to the shape of a mold or die positioned below the frame.

Thermogravimetric Analysis (TGA) 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 reveal information about thermal stability and polymerization processes.

Thermoplastic Elastomers The family of polymers that resemble elastomers in that they can be repeatedly stretched without distortion of the unstressed part shape, but are true thermoplastics and thus do not require curing.

Thermoplastics Materials that become soft when heated and solid when cooled to room temperature. This softening and setting may be repeated many times.

Thermosets Materials that may not be reheated and softened again. Once the structural framework is set, these plastics cannot be reformed.

Thick Phase Increase in viscosity found in an emulsion before inversion. The close packing of the internal phase results in a high viscosity. The thick phase is often used to maximize the shear on an emulsion by mixing the emulsion into a thick phase or causing inversion by mixing the thick phase.

Thickner Device that produces separation of solids from liquids by sedimentation; material that increases the viscosity of a fluid.

Thixotropy Reversible gel-sol-gel transition that is characterized by a reduction in viscosity upon the application of shearing stress.

Three-plate mold A mold that has four or five distinct plates and numerous parting lines.

Tie bar In molding machines, the bars that tie the stationary platen and the hydraulic clamping mechanism together. During mold clamp-up, the tie bars resist the strain created by the hydraulic cylinder clamping and moveable against the stationary mold. Also called strain rods. Large, steel bars used on the clamp end of the machine to connect and support the platens.

Time-Measuring Viscometer Instrument measuring the time needed for efflux of a liquid through an opening, rise of an air bubble, fall of a steel ball, revolution of a paddle driven by a constant torque, or slide of a plate.

Titer The re-solidification point of the melted oil, fat, butter or wax.

TM º Abbreviation for melting point.

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.

Toggle clamp A clamping mechanism in which a series of linkages and knuckle joints are mechanically straightened to move and lock up the mold.

Tool In injection molding, the term sometimes used to describe the mold.

Torpedo A streamlined metal block in the path of the flow of stock within an extruder or molder heating cylinder that spreads the melt into the thin layers that can be heated more efficiently. Also called spreader.

Torr Unit of pressure, same as millimeter of mercury.

Transducer force A force measuring device. It has the characteristics of providing an output, usually electrical, which serves as the measurement of load, force, compression, pressure, etc., when placed along the sensitive axis of the force cell.

Transducer A component that measures pressures and can send the information to a control unit.

Transition point The time or stroke point where the injection process is switched over from the high volume to low volume pump.

Transition section of screw The section of a plasticating screw between the feed and metering sections in which the plastic resin is in both a solid state and molten state.

Transition Temperature The temperature at which a polymer changes from (or to) a viscous or rubbery condition (or from) a hard and relatively brittle one.

Translucent Descriptive term for a material or substance capable of transmitting some light but not clear enough to see through.

Transparent A descriptive term for a material or substance capable of transmitting a high degree of light. (e.g., glass)

Trapezoidal runner A runner cut into one mold half with five degree straight side walls and a flat bottom.

Trimming The process of removing all excess plastic, such as flash, gates and runners, from the part after it has been ejected from the mold.

TTC º Abbreviation for crystallization temperature.

Tunnel gate (submarine gate) A type of edge gate in which the opening from the runner into the part is located below the mold parting line.

Turbidimeter Instrument that measures the reduction in light transmission caused by interposing a suspension between light source and observer.

Turbulence Flow caused by superimposing irregular currents on a uniform flow.

Turbulent Flow Motion of a fluid in which its velocity at a fixed point fluctuates randomly with time.

Two-plate mold A mold that consists of two separate mold halves and one parting line.

Two-shot molding The technique of molding parts in two colors or two materials in a single mold or set of molds. This process is accomplished by injecting the thermoplastic into a closed mold, transferring half of the mold to mate with another mold half of different cavity shape, and injecting the second color or material around the first part.

Tyndall Effect Light-scattering that is visible when a beam of coherent light passes through a colloidal system.