M

 

MALE MOLD

A convex mold where the concave surface of the part is precisely defined by the mold surface.

 

MASTER (plug)

A full scale representation of the intended part, usually retained as a reference and the part from which production molds are made.

 

MAT

See Chapped Strand Mat.

 

MATCHED DIE MOLDING

Technique for producing long runs of identical parts with two finished sides.

 

MATCHED MOLDS

Two or more tools arranged in a set as a male and female mold. Normally used in a press.

 

MATRIX

The polymer liquid component of a composite or laminate.

 

MATCHED-METAL MOLDING

A high volume molding method that uses two machined metal molds in a hydraulic press. Generally the process uses sheet molding compound or bulk molding compound.

 

MEK PEROXIDE (MEKP)

A peroxide initiator often referred to as catalyst and used initiate polymerization of a resin.

 

METHYL ETHYL KETONE PEROXIDE

(See above)

 

MEK SOLVENT

Methyl Ethyl Ketone; a colorless, flammable liquid sometimes used in clean up procedures. It is not a peroxide initiator.

 

MICRO CRACKING

Cracks formed in composites when thermal stresses locally exceed strength of the matrix.

 

MICROSPHERES

Microscopic bubbles of glass, ceramic or phenolic, used as filler or to create syntactic foam or putty mixtures.

 

MIL THICKNESS – MILS

The unit used in measuring film thickness. One mil equals one thousandth of an inch (1 mil = .001”).

 

MILLED FIBERS

Glass fiber processed by a hammer mill into lengths of 1/32” to 1/8”. Commonly used as reinforcement in polyester putty.

 

MODULUS OF ELASTICITY

An engineering term used to describe a material’s ability to bend without losing its ability to return to its original physical properties.

 

MOLD

The tool used to fabricate the desired part shape. Also used to describe the process of making a part in a mold.

 

MOLDING

The process of using a mold to form a part.

 

MOLD RELEASE

A wax or polymer compound that is applied to the mold surfaces acts as a barrier between the mold and the part, thus preventing the part from bonding to the mold.

 

MONOMER

A constituent of polyester or vinyl ester resin. Styrene monomer is most commonly used.

 

N 

 

NET SHAPE

A fabricated part that comes out of the mold and does not require cutting, trimming or machining.

 

NON-DESTRUCTIVE TESTING

Methods of testing materials that involve tests that do not alter the properties of the material.

 

NPG GEL COAT

Neopentyl glycol gel coat has enhanced weatherability compared to non-NPG gel coat.

 

O

 

ONE-OFF

A custom fabrication process in which a single part is fabricated.

 

ORIFICE

An opening, generally referred to regarding spray tip size.

 

ORANGE PEEL

A gel coated or painted finish that is not smooth and is patterned similar to an orange’s skin;

 

ORTHOPHTHALIC OR ORTHO RESIN

A polyester resin based on orhtophthalic acid, also known as a general purpose resin (GP).

 

P

PARTING AGENT

See Mold Release and PVA.

 

PARTING LINE

The location on a mold product between different segments of the mold used to produce the product.

 

PATTERN

The initial model for making fiberglass molds. See Plug.

 

PEEL PLY

A removable non-stick fabric applied to a lay-up surface that is removed from the cured laminate prior to bonding operations, in order to leave clean, resin-rich surface ready for bonding.

 

PEEL STRENGTH

The strength of the bond between laminate plies obtained by stress that is applied in a peeling mode.

 

PEROXIDES

Category of compounds containing oxygen groups that are used as initiators. (see MEK Peroxide)

 

PHENOLIC RESIN

Thermosetting resin produced by condensation of an aromatic alcohol with an aldehyde, particularly phenol with formaldehyde.

 

PIGMENT

A colorant added to gel coat or resin.

 

PIGMENT SEPARATION

Occurs when the pigment is not thoroughly mixed into the gel coat during formulation or the gel coat is improperly mixed prior to use. It is characterized by a non-homogeneous surface color.

 

PINHOLES

Small holes on the exposed gel coated surface. They are about the diameter of common pins and may be easily counted.

 

PLASTICS

Organic chemical compounds called polymers that can be formulated to produce a wide range of properties.

 

PLUG

A composite industry term for a pattern of model.

 

PLY

A single layer within a laminate.

 

POLYESTER RESIN (Unsaturated)

The product of an acid-glycol reaction commonly blended with a monomer to create a polymer resin. In its thermosetting form it is the most common resin used in the FRP industry.

 

POLYMER

A chain molecule composed of many identical groups, commonly found in plastics.

 

POLYMERIZATION

The chemical bonding of molecules during the curing reaction.

 

POLYVINYL ALCOHOL (PVA)

A parting film applied to a mold for part releasing.

 

POROSITY

Entrapped gas bubbles or voids in a gel coat film

 

POST-CURE

To cure by application of heat after the chemical exothermic reaction has subsided.

 

POT LIFE

The time during which the catalyzed resin remains liquid or “workable” See Gel Time.

 

PRE-FORM

A fiber reinforcement reshaped to match the shape of the mold. There are several methods of making pre-forms including the directed fiber method and the use of thermo-formable mat.

 

PREMIX

Reinforcing material mixed with resin and usually with pigment, filler and catalyst, before placing in the mold.

 

PRE-PREG

Reinforcing material impregnated with resin prior to the molding process and cured by the application of heat.

 

PRE-RELEASE

The premature release of the gel coat or laminate from the mold. Pre-release causes cosmetic or dimensional problems.

 

PRESSURE BAG

A membrane that conforms to the inside of a laminate laid up on a mold. The membrane or bag is then inflated by applying pressure that consolidates and densifies the laminate.

 

PRINT THROUGH

A distortion in the surface of a part that allows the pattern of the core or fiberglass reinforcement to be visible through the surface. Also known as print out, telegraphing or read through.

 

PROMOTER

An additive to speed up the cure. This additive is required for room temperature resin cure. See Accelerator.

 

PROTOTYPE

The initial fabrication of a product that is used to develop and refine product specifications, design and process methods.

 

PULTRUSION

A continuous molding process for manufacturing composite profile shapes such as rods, tubes and structural shapes having a constant cross section. Roving and other reinforcements are saturated with rein and continuously pulled through a heated die, where the part is formed and cured.

 

PUTTY

A thickened mixture of resin made by adding fillers, thixotophs and reinforcing fibers.

 

PVA

See Polyvinyl Alcohol