Glossary

Plastics Glossary - B

Back pressure The hydraulic pressure developed in the injection cylinder of an injection molding machine during plasticating to cause more shear heating and mixing of the material. The pressure generated on the plastic as the screw rotates and pumps the plastic into the front of the barrel.

Baffle Partition or plate that changes the direction or restricts the cross section of a fluid, thus increasing velocity or turbulence.

Baffles Used to divert coolant from the straight sections of the circuit to cool deep draw areas, pins, and cores.

Balanced Runner In injection molding, a runner system designed to place all cavities at the same distance from the sprue.

Band heater Electrical heaters used as the primary source of heat on barrels and nozzles of injection molding machines and extruders.

Barcol hardness The hardness value obtained by measuring the resistance to penetration of a steel point into the surface of the test material. The instrument, called the Barcol Impressor, gives a direct reading on a 0-100 scale.

Barrel capacity The maximum weight of material a machine can produce from one forward motion of the ram, screw, or plunger.

Barrel Cylinder portion of the plasticating chamber of an extruder or injection molding machine. The cylinder forms the chamber within which the plastic resin is converted from a solid form into a viscous melt. The barrel also contains the plasticating screw or plunger.

Base Stock Blend of materials that makes up the bulk of a product.

Batch The quantity of resin made in one operation. Sometimes referred to as a “lot”.

Bentonite A colloidal clay used as an adsorbent.

Benzin (Petroleum Benzin) A refined light naphtha meeting USP specifications.

Binder to bind the pigment particles together.

Bingham Plastic A substance that will not flow until its yield value is reached; thereafter, it flows like a normal liquid.

Binodal Curve Curve in a triangular isothermal equilibrium plot that connects miscibility points.

Biocolloid Lyophilic colloidal system found in living organisms.

Biodegradability Susceptibility of a chemical compound to depolymerization by the action of biological agents.

Birefringence Difference between any two refractive indexes. When the refractive indexes measured along three mutually perpendicular axes are identical, the plastic is classified as optically isotropic. When the plastic is stretched (molecular reorientation) and the refractive index parallel to the direction of stretching is altered so that it is no longer identical to that which is perpendicular to this direction, the material displays birefringence.

Bisphenol A A condensation product formed by reaction of two (bi) molecules of phenol with acetone (A). This phenol with carbonyl chloride make up polycarbonate. Bisphenol A and epichlorohydrin produce many epoxy resins.

Bitumen Mixture of natural and pyrogenous hydrocarbons that is soluble in carbon disulfide.

Black Specks or Streaks Small dark particles or streaks on the surface of the part.

Black Specks A specific kind of inclusion/contamination often associated with degraded materials.

Blast Finishing The process of removing flash from molded objects and/or dulling their surfaces, by impinging media such as crushed apricot pits, walnut shells or plastic pellets upon them with sufficient force to fracture the flash.

Bleed hole/vent Hole in the mold that serves to release excess pressure (material, gases) during molding.

Bleed Escape of material or gases through a passage in the mold; migration of additives to the surface of an article or to an adjacent article; release of color in an article in contact with water or solvent.

Bleeding Separation of the oil constituent of a grease from the base.

Blend Technically, a blend is a physical mixture of different polymers. However, in practice, some blends involve copolymers and there are cases where some chemical interaction occurs between components.

Blending Mixing of several components to obtain a homogeneous material.

Blind hole Hole molded or drilled into a part but not entirely through the part.

Blister An imperfection, a rounded elevation of the surface of the plastic, with boundaries that may be more or less sharply defined. Often caused by trapped gas from moisture, air, degraded polymer or degraded additives.

Blisters Bubbles on the surface of the part caused by trapped gases.

Bloom An undesirable cloudy effect or whitish powdery deposit on the surface of a plastic article caused by the exudation of a compounding ingredient such as a lubricant, stabilizer pigment, plasticizer, etc.

Blow Mold See Mold, Blow

Blow mold.Tool used to form hollow plastic products, such as bottles and cans. Generally aluminum, molds can have either water jackets, cast in tubing, or drilled cooling lines. Isolated areas, such as threads or pinched edges, can be inserted in steel for longetivity. Molds are equipped with method for injecting air into the cavities.

Blow molding A method of processing in which a parison (hollow tube) is forced into the shape of the mold cavity by internal air pressure. Extrusion blow molding. Extruder is operating continuously and the output either feeds an accumulator or flows through the die as an endless parison. Basic equipment consists of an extruder, crosshead die (and accumulator), clamping arrangement, and mold. Injection blow molding. Suited for containers that have very close tolerance threaded necks, wide mouth openings, and highly styled shapes. In the basic process, plastic melt is injected as a parison to a preform cavity forming the preform around a core rod. A completely finished injection molded neck is formed at this station. The preform is indexed to the blow station where it is blown through an opening in the core rod into the final shape. Reheat blow molding For critical containers for foods, cosmetics, carbonated beverages, etc., this process gives many resins improved physical properties. In biaxial orientation, parisons are stretched lengthwise by an external gripper, or by an internal stretch rod, and then stretched radically by blow air to form the finished container against the walls of the mold. This aligns the molecules along two planes – a configuration that gives substantially better barrier properties.

Blow pressure Air pressure used to expand the parison within a blow mold.

Blow rate The speed at which the air enters and expands the parison during blow molding.

Blowing agent An additive ingredient used to produce gas by chemical or thermal action, or both, which results in hollow or cellular voids within the plastic article. Also called foaming agent.

Blowing Injection of compressed air into tanks to agitate and mix the contents; the act of foaming a system.

Blush Discoloration on the part at the gates or other obstructions in the flow path.

Blushing The tendency of a plastic article to turn white or chalky in areas that are highly stressed.

Bond Linkage between atoms in a molecule.

Bonding Joining securely through the use of adhesives.

Boost pressure Another name for first stage pressure. Boost pressure is used to inject and fill the cavity with plastic.

Boost timer Another name for the first stage timer that controls the high volume pump that is used to inject plastic into the mold cavity.

Booster ram The hydraulic cylinder used for rapid clamp movement in a hydraulic clamp system.

Boss Small projection from part's surface designed to add strength, facilitate alignment with another part during assembly, or permit attachment to another part. May result in sink if not designed properly. Raised projection in a molded part that usually has a hole in it to accommodate a mechanical fastener.

Bottom plate A steel plate fixed to the lower section of a mold. It is often used to join the lower section of the mold to the platen of the press.

B-Plate A mold plate used to house the cores or core blocks. Located on the moving half of an injection molding machine.

Branched Condition in the structure of molecules polymers where the molecule has side chains attached to the main chain.

Branched polymers Polymer chain with additional monomer chains growing off the primary chain.

Branched Chemistry term referring to side chains attached to original chain (in a direction different from that of the original chain) in molecular structure of polymers.

Branching The growth of a new polymer chain from an active site on an established chain, in a direction different from that of the original chain.

Breakdown Time ( gasoline ) Time elapsed before gasoline forms gums in storage.

Breakdown voltage The voltage at which plastic insulation between two conductors will break down. Breathing Opening and closing the mold to let gases escape. Usually employed in compression molding. Brinell Indentation hardness test using calibrated machine to force a hard ball into the surface of material under test. The diameter of the resulting impression is measured.

Breathing Opening and closing the mold to let gases escape. Usually employed in compression molding.

Brinell Indentation hardness test using calibrated machine to force a hard ball into the surface of material under test. The diameter of the resulting impression is measured.

Brittleness Temperature The temperature at which plastics and elastomers rupture by impact under specified conditions.

Brookfield Viscometer Instrument that measures the viscosity of a liquid as a function of the torque produced by rotating a spindle at fixed rpm in a liquid.

Brownian Movement Random movement of colloidal-size particles that arises from collisions between the particles and molecules of the fluid medium in which they are suspended.

Bubble A spherical, internal void; globule of air or other gas trapped within a molded plastic product. Differs from a blister in that the bubble is contained within the part with no surface protrusion. Also differs from a void, which is developed by formation of a second vacuum during cooling.

Bubblers Method of cooling the mold where coolant is pumped continuously into a tube in the mold.

Buffer Action Property of certain solutions of resisting changes in pH upon the addition of acid or alkali.

Buffer Substance that causes a resistance to change in pH when added to a solution.

Bulk density Mass per unit volume of a molding powder as determined in a reasonably large volume. ASTM D1182-54 test method.

Bulk Factor The ratio of the volume of any given mass of loose plastic material to the volume of the same mass of the material after molding.

Bulk molding compound (BMC) Thermosetting resins mixed with stranded reinforcement, fillers, etc., into a viscous compound for injection or compression molding.

Bunker Fuel Fuel for marine boiler.

Burn marks Small black sections on the part surface caused by burning plastic or ignited air.

Burned Showing evidence of excessive heating during processing or use of a plastic, as evidenced by blistering, discoloration, distortion or destruction of the surface.

Burrs Tiny slivers of metal that have been raised up on a corner or edge of steel. They may cause difficulty in part ejection, and thus damage the mold.

Butadiene styrene, thermoplastic See high impact polystyrene.

Butadiene styrene, thermoset Co-polymers used in bulk molding compounds, wet and dry friction materials, air drying enamels, baked coatings, laminates for circuit boards, randomes, and other electromagnetic applications. Can be formulated for injection, compression, and transfer molding.