6 STAGES OF THE MOLDING PROCESS SIMPLIFIED

MOLD CLOSING

The Press closes the mold and applies clamp pressure and monitors as a safety check.

MATERIAL INJECTION

The Screw moves forward pushing molten plastic into the mold cavity at precise speed and velocity.

PACK AND HOLD

After the cavirty is filled, the screw assembly packs the plastic and holds material pressure until the gate freezes enough to cap the cavity.

COOLING / SOLIDIFING

Extra time after pack that is allotted for cooling to absorb heat from the part ensuring quality

MOLD OPENING

After cooling stage is complete the mold is opened and any actions and slides activate and release undercuts

PART EJECTION

After the mold is open the ejection pin system is activated to push the finished part off core side of the mold

Polyethylene can be classified into three ranges of density. Low density polyethylene (aka LDPE) has a density of .910 to .925 g/cc; whereas the medium density grade has a density of .926 to .940 g/cc. The high density grade (HDPE) has a density of .941 to .960 g/cc. As a general rule, the higher the density, the harder, the more rigid and more heat resistant the plastic. Low and medium density polyethylene’s, for example, have melting points of about 230 -240°F whereas the high density material has a melting point about 25°F higher. Higher density resins show improved tensile and flexural strength, chemical resistance, surface hardness and abrasion resistance but poorer elongation and brittleness at low temperatures. Various polyethylene copolymers are also available that show much different characteristics than the parent monomer.

PHYSICAL MATERIAL PROPERTIES

Property used to define the hardness or softness of a plastic

ASTM D2240  Test Method based on indentation of specimen when force is applied.

Property used to define the how heavy or light a plastic is based on volume

ASTM D792  Test Method based on the ratio of mass of a given volume of material usually reported relative to water

Property used to define the plastics ability to withstand tensile stress while being pulled or stretched without failure

ASTM D638  Method based on pulling a dog bone specimen and reading the rate at which the material yields or breaks

Property used to define the materials ability to resist a force applied in an instantaneous implementation of a load

ASTM D2240  Method based on swing pendulum with a defined weight. Testing can be performed as Notched Izod with and without low temp definitions.

Property used to define the ability to stretch the material of a plastic

ASTM D638  Method based on indentation of specimen when force is applied.

Property used to define the length of recovery of a material after it has been stretched

ASTM D790  Method is based on measuring % of a specimen original length

ASTM D395  Method based on geometric recovery of specimen after force is applied for 24 hours.

Method based on measuring deformation at time intervals from 1 to 1000 hours

Property used to define the amount of growth or shrink a specimen exhibits during temperature change

ASTM D696  Method based on measuring the % coefficient of linear change in length of a material relative to each degree of temperature change

Property used to define a slow deformation phenomena while under constant strain (also known as “Cold Flow”)

ASTM D2990  Method based on measuring deformation at time intervals from 1 to 1000 hours

ISO27 Property used to define a material deflection perpendicular to force applied

Method based on indentation of specimen when force is applied.

ENVIRONMENTAL MATERIAL PROPERTIES

Property used to define the hardness or softness of a plastic

ASTM D2240  Test Method based on indentation of specimen when force is applied.

Property used to define the how heavy or light a plastic is based on volume

ASTM D792  Test Method based on the ratio of mass of a given volume of material usually reported relative to water

Property used to define the plastics ability to withstand tensile stress while being pulled or stretched without failure

ASTM D638  Method based on pulling a dog bone specimen and reading the rate at which the material yields or breaks

Property used to define the plastics ability to withstand tensile stress while being pulled or stretched without failure

ASTM D638  Method based on pulling a dog bone specimen and reading the rate at which the material yields or breaks

Property used to define the plastics ability to withstand tensile stress while being pulled or stretched without failure

ASTM D638  Method based on pulling a dog bone specimen and reading the rate at which the material yields or breaks

MATERIAL IDENTIFICATION CHART:

This chart is used to reverse engineer any material. Although it is not a perfect science, you can learn a lot about your material with a few simple procedures.