Hardener - A substance or
mixture of substances added to plastic composition,
or an adhesive to promote or control the curing reaction
by taking part in it. The term is also used to designate
a substance added to control the degree of hardness
of the cured film. See also Catalyst.
Hardness - The resistance
of a plastic material to compression and indentation.
Among the most important methods of testing this property
are Brinell hardness, Rockwell hardness and Shore hardness.
Haze - The degree of cloudiness
in a plastic material.
Head - The end section of
a blow molding machine (in a general extruder) in which
the melt is transformed into a hollow parison.
Head Space - The space between
the fill level of a container and the sealing plane.
Heat Chamber - In injection
molding, that part of the machine in which the cold
feed is reduced to a hot melt. Also Heating Cylinder.
Heat Deflection Temperature - The temperature at which a standard test bar (ASTM
D648) deflects 0.010 in. under a stated load of either
66 or 264 psi.
Heat Sealing - A method
of joining plastic films by simultaneous application
of heat and pressure to areas in contact. Heat may be
supplied conductively or dielectrically.
Heat-Distortion Point -
The temperature at which a standard test bar (ASTM D648)
deflects 0.010 in. under a stated load of either 66
or 264 psi.
Hob - A master model in
hardened steel used to sink the shape of a mold into
a steel block.
Hobbing - Forming multiple
mold cavities by forcing a hob into soft steel (for
beryllium-copper) cavity blanks.
Homopolymer - A polymer,
consisting of (neglecting the ends, branch junctions,
and other minor irregularities) a single type of repeating
unit.
Honeycomb - Manufactured
product consisting of sheet metal or a resin impregnated
sheet material (paper, fibrous, glass, etc.) which has
been formed into hexagonal-shaped cells. Used as core
material for sandwich constructions.
Hoop Stress - The force
per unit area in the wall of the pipe in the circumferential
orientation due to internal hydrostatic pressure.
Hopper - Conical feed reservoir
into which molding powder is loaded and from which it
falls into a molding machine or extruder, sometimes
through a metering device.
Hopper Dryer - A combination
feeding and drying device for extrusion and injection
molding of thermoplastics. Hot air flows upward through
the hopper containing the feed pellets.
Hopper Loader - A curved
pipe through which molding powders are pneumatically
conveyed from shipping drums to machine hoppers.
Hot Gas Welding - A technique
of joining thermoplastic materials (usually sheet) whereby
the materials are softened by a jet of hot air from
a welding torch, and joined together at the softened
points. Generally a thin rod of the same material is
used to fill and consolidate the gap.
Hot-runner mold - A mold
in which the runners are insulated from the chilled
cavities and are kept hot. Parting line is at gate of
cavity, runners are in separate plate(s), so they are
not, as is the case usually, ejected with the piece.
Hot-stamping - Engraving
operation for marketing plastics in which roll leaf
is stamped with heated metal dies onto the face of the
plastics. Ink compounds can also be used. By means of
felt rolls, ink is applied to type and by means of heat
and pressure, type is impressed into the material, leaving
the marking compound in the indentation.
Hydraulic - A system in
which energy is transferred from one place to another
by means of compression and flow of a fluid (e.g., water,
oil).
Hydrocarbon Plastics - Plastics
based on resins made by the polymerization of monomers
composed of carbon and hydrogen only.
Hydrogenation - Chemical
process whereby hydrogen is introduced into a compound.
Hydrolysis - Chemical decomposition
of a substance involving the addition of water.
Hygroscopic - Tending to
absorb moisture. |