Industry Terms & Definitions

AUTOCLAVE: Same as pressure cast but has the addition of heat.

CASTING: The pouring of a liquid material into a form or mold.


  • ‘A’ Stage – Original state.
  • ‘B’ Stage – Partial cure, may be in a thermoplastic or thermoset state.
  • ‘C’ Stage – Final cure, all cross-linking has taken place.

COMPRESSION MOLDING: Material usually in a gum or solid state is placed in a mold and compressed. The material is maintained under pressure until the part is formed either by Cooling(Thermoplastics), or heating(Thermosets).

COMPRESSIVE STRENGTH: The amount of resistance a product has to a force pushing down or compressing a test sample. The compressive strength is expressed in pounds per square inch of area. Two results are reported; compressive yield, the point under load where the resistance substantially reduces and ultimate compressive strength, the resistance recorded at break.

DROP FORGE HAMMER DIE: A metal forming process where the metal is formed by attaching a heavy weight to the male side of a mold and then dropping it from a specified height. This process is used to instantly form metals, usually aluminum, eliminating stress cracks associated with slower forming methods.

ELECTRO FORMING MANDRELS: Shapes made from Thermoset systems used to deposit metal (i.e. nickel, copper) around the system. A shell .100 – .300 inches thick is formed. After plating, the mandrel is removed and usually destroyed in the process.

ELONGATION: The amount of stretch in a specified area that takes place during a tensile test. The elongation can be reported at yield or ultimate.

EXOTHERMIC: Gives off heat.

ENDOTHERMIC: Absorbs heat.

FLEXURAL STRENGTH AND FLEXURAL MODULUS: Similar to tension in theory but the sample size, shape, and method of force are different. The sample is laid on its side and supported only at the 2 ends. A downward force is applied to the center, unsupported area and the resultant resistance to the downward compression pressure is recorded in PSI. This test measures resistance to a flexing load.

FOUNDRY BLOW TUBES: A nozzle at the end of a machine that blows sand into a foundry tool, usually made of Hapflex.

FOUNDRY CORE BOX: The tool used to make the sand shapes that are placed in a sand mold for metal casting. The cores, or sand shapes, become holes or areas where there is no metal.

FOUNDRY PATTERNS: The tool used to make a female sand mold in which metal is cast.

FOUNDRY SPRUES, RISERS AND GATING: Processing aids that are mounted as part of the foundry pattern to make shapes used to aid in the metal pouring process.

HARDNESS/DUROMETER: The resistance to penetration of a point on a meter having numerical values of 0 – 100. The Shore Instrument Company manufactures the instrument most commonly used in our Industry. The most common scales used are the A scale for softer products and the D scale for harder products. There is no exact conversion from A to D scale; it depends on the properties of the product. A general rule is: add 50 points to the A scale for a D scale estimate.

HEAT CURE SYSTEM: A system that requires heat to cure. The system may ‘B’ stage but cross-linking takes place with heat. An endothermic system, although some heat cure systems give off a slight exotherm, initially.

HOLDING FIXTURES: A tool with the reverse shape of a portion of the geometry of a part. It holds the part in a particular orientation while another operation is being performed. Drilling fixtures, gluing fixtures, painting fixtures, assembling fixtures, robotic fixtures, machining fixtures, sandblasting fixtures, sonic welding fixtures, bending fixtures, trimming fixtures, checking fixtures, quality control fixtures, curing fixtures, cooling fixtures, and secondary operations fixtures are just some of the fixture applications.)

INJECTION MOLDING: A molding process using a thermoplastic system. The plastic is heated until liquified and then high pressure injected into a mold. The mold cools the plastic, forming a shape. The molded, solidified, part is ejected or pushed out of the mold.

LAMINATING: The wetting out of layers of fiberglass cloth, layer by layer, into a form or mold. The cloth is laid in place and coated or wetted with a Haprez Laminating System until the proper thickness is desired. This can be done by brushing the fiberglass, or it can applied by hand. After the laminate is complete, a support structure made of wood, metal, or tube stock is put in place and laminated to secure the support structure. This system adds strength, rigidity, and prevents flexing of the laminate structure.

LIQUID MOLDING COMPOUNDS: Hapco materials that are liquid thermoset systems. They are injected into molds to form parts. These products look and act like injection molded parts. A major advantage of using LMC is that they do not require expensive tooling. Tooling is cheap and fast!

LIQUID MOLDING/LOW PRESSURE INJECTION MOLDING: A molding process where Liquid Molding Compounds, liquid thermosets, are injected or poured into a mold and cured. Liquid Molding is ideal for part volumes from 1 – 10,000 parts per year.

MIXING RATIO: The exact proportions of the ingredients, allowing a total reaction between all components. Can be shown by weight or by volume, usually by weight.

MODEL: The original, or master, prototype. A model can be made by hand, machine, CNC, or rapid prototyping (computer modeling). The model has the exact part dimensions.

MODULUS AT ELASTICITY IN TENSION: A relationship between stress and strain expressed in PSI. A simple way of understanding modulus is the relationship between tensile and elongation. The stiffer the material, the higher the modulus number.

OPEN CAST MOLDING: A Thermoset material is poured into an open mold and cured. Curing may be at room temperature or with heat.

PATTERN: The pattern is a model dimensioned for the process (shrinkage) and may contain process engineering geometry (gates, etc.).

(PPH) PARTS PER HUNDRED: A method of expressing the mixing ratio. The parts of B added to 100 Parts of A (i.e. 50 pph means to 100 Parts A, add 50 Part B by weight, for a total of 150 parts).

POST CURE: A standard operating procedure for many Liquid Molding applications in which the cure requires 2 or more steps; a room cure followed by a heat cure. As with tempering steel, raising the temperature of a thermoset material will properly align the the molecules while they are crosslinking to form a stronger finished part. Heat Distortion Temperature, Impact, Flexural and Tensile Strengths can all be raised with a postcure. This procedure may require fixturing during post cure to insure dimensional stability.

POT LIFE, GEL TIME, WORKING LIFE: Used synonymously but actually are different. Pot Life and Gel Time are the same. The amount of time for a given mass (usually 100 grams) to gel at a given temperature (usually 25 0C). Working life is usually defined as one half the Gel Time.

PRESSURE CAST: The mold is cast or poured and then placed in a pressure tank under 60 – 80 psi pressure while curing. This process compacts bubbles, gains intricate detail, and, in the casting of urethanes, prevents carbon dioxide bubble formation. This process is necessary with certain products such as Ultralloy, but is a great advantage with all products.

PRESSURE FORMING: Same as vacuum forming, but with pressure (50-100 psi) applied to the non-tool side to ‘push’ the hot plastic sheet down into the tool while the vacuum is applied. This method achieves a higher degree of part detail.

(RIM) REACTION INJECTION MOLDING: A molding process where a very fast cure, thermoset, urethane microcellular foam is injected into a mold where it expands and cures. The mold is tilted to direct air and the part is usually flashed at the parting line to let air out.

ROOM CURE SYSTEM: A thermoset system in which the total cure takes place at room temperature, normally 700F. Room curing systems are exothermic.

SHRINKAGE: The dimensional change that occurs between the original state and the cured state. ASTM has 4 mold sizes; all half round molds 10″ long with varying heights – 3/4″, 1¼”, 2½”, 4½”. Shrinkage is measured in inches per inch. Shrinkage, or dimensional variation, is largely influenced by 5 factors:

  • 1. Mass ( total volume and thickness)
  • 2. The temperature of the material
  • 3. Maximum temperature reached during the exotherm (reaction). The faster the material, the higher the exotherm, the greater the shrinkage.
  • 4. The temperature of the mold.
  • 5. The thermal properties of the mold material.(Insulator vs. Conductive)

The stability of the mold material and geometry, thickness, and total volume of the part vary in each design, therefore, the customer responsible to test and determine the shrinkage factor to be used. The values in the brochures are for comparative reference only.

SPECIFIC GRAVITY: The density or weight of the material as compared to water. Water weights 8.33 lbs. per gallon. Therefore, a gallon of a material with a specific gravity of 1 weights 8.33 pounds; a material with a specific gravity of 2 weights 16.66 pounds per gallon.

SPLASH/FEMALE MOLD/THROW AWAY MOLD: A reverse shape of a positive pattern whose purpose is to aid in duplicating or replicating the original. Multiples can be made in materials with different physical properties.

STRETCH DIES: A metal forming process where metal sheets are pulled over a die and stretched into a shape (i.e. the leading edge of an airplane wing).

SURFACE CAST MOLDS: A mold where the surface material, usually 1/4’’ -1/2’’ thick, is different than the backup and is not permanently bonded to the backup or core. The core or backup is fabricated first.

SURFACE CAST TOOL: A tool in which the surface thickness 1/8”-1/2’’ (normally 1/4’’) is cast and bonded to the structural backup or core. The core is cast or fabricated first and then the surface is cast. Surface cast tooling gives the best dimensional accuracy, the toughest tools, and the longest run tooling.

SURFACE COAT: A brush or spray applied system having specific properties desired by the user. Surface coats are usually backed up by a structural component (i.e. fiberglass layup, casting, etc.). By using a surface coat, the physical properties of the surface can be different than the structural system used in back of the surface coat.

TENSILE STRENGTH: A sample shaped like a dog bone is placed between to jaws and is pulled apart at a given speed. The resistance to the force is recorded in pounds per square inch (psi). Again, there is a yield and ultimate.

THERMOPLASTIC: A product that can be heated and it will liquify. Subsequently it can be cooled and it will solidify (i.e. injection molded, plastics, chocolate, ice, metal, etc.).

THERMOSET: A product formed by the reaction of 2 or more components and the resultant product is completely different that any of the components. A + B = C where C is completely different than A or B.

THERMAL EXPANSION/CONTRACTION: The amount of dimensional change, per degree, in temperature measured in inches per inch per degree F or C.

THERMOFORMING: The forming of heated Thermoplastic sheet stock into a shape. The two most popular types of Thermoforming are vacuum forming and pressure forming.

TRACING MASTER: A shape with a hard surface used as guide for cutting metal.

UL 94V RATING: Underwriters Laboratories has an internationally recognized test for flammability or the resistance of a material to support a flame. The UL test number is 94 and the most severe situation is ‘V’ or vertical. A carefully dimensioned sample is put in a fixture and a specific temperature flame is applied and then removed. The length of time it takes for the flame to go out is recorded. Depending on the rating sought, this may be repeated. The final results are reviewed and a rating is given by UL (i.e. 94V-0, 94V-1, 94V-2, etc.). UL 94V-0 is the best V rating.

VACUUM DEGAS: A method of removing entrapped air. The liquid material is placed in a sealed container and a vacuum is applied. The negative pressure (the absence of air) pulls the air out of the liquid.

VACUUM FORMING: A one sided tool, male or female, which when placed in contact with a heated sheet of plastic and vacuum or suction is applied through the mold, a part is formed.

VISCOSITY: The measure of the thickness of a liquid. Viscosity numbers range from 1 (water) to millions of centipoise. The equipment generally used in our Industry is a Brookfield Viscometer. The apparatus has several size spindles with a round disc of varying diameters near the bottom. The spindle is emerged into the liquid until the disc is covered and the motor is switched on turning the spindle. The drag, or resistance, created on the combination spindle/disc torques a spring and reads out on a gauge. The liquid is normally measured at 250 C.

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