Injection plastique : Polimer properties descriptions

Kit décorations pièces plastiques

Kit décorations pièces plastiques

In the injection molding process, thousands of thermoplastic and thermosetting materials are used. Each of them has their own individual qualities. We can therefore classify our materials based on:

Indicates the family that a material belongs to. Every material in the database will have one generic name.

Often called commercial name, this is the name given to a material by a manufacturer.

Indicates the organization that manufactures or sup­plies the material.

Uniquely identifies a material and is associated with a particular tradename.

The type of substance added to a plastic material; often used to make a resin less costly. Fillers are used to enhance materials strength, stiffness, or other charac­teristics. Numbers following the abbreviation in the tables represent the percent of reinforcement or filler.

The ratio of the density of the material to the density of water where density is defined as the mass divided by the volume of the material at standard temperature and pressure. A specific gravity value of 1 is equal to 0.9975 g/cm3.

The ratio of the difference between the molded plastic part dimension and the mold dimension. Shrink is tested by obtaining a measurement of the length of the cavity of a standard bar mold, or the diameter of the cavity of a standard disk mold, or the length or width of a standard plaque mold, to the nearest 0.001 inch. Measurements of the molded test specimens are then taken and the shrink value is the difference between the two.

For injection molding materials the test specimens con­sist of three types:

  • Bars, 1/2 by 1/8 by 5 inches gated at the end to provide flow throughout the entire length. These are usually used to determine shrinkage in the direction of flow.
  • Disks, 1/8 inch thick and 4 inches in diameter gated radially at a single point in the edge. These are usually used for measurements of shrinkage of diameters parallel and perpendicular to the flow.
  • Plaques, 2.36 by 0.79 by 2.36 inches gated along the length of one edge. These are usually used for mea­surements of shrinkage parallel and perpendicular to the flow.

Mold shrink can vary due to wall thickness, flow direc­tion, and molding conditions. Generally rigid amor­phous and thermoset materials have lower mold shrink than semi-crystalline thermoplastics. Reinforced or filled materials tend to have lower shrink than unfilled materials.

Rate of extrusion of molten resin through a die of a specified length and diameter under prescribed condi­tions of temperature and pressure.

An extrusion plastometer is used for this test. The test material is placed in the cylinder and the piston is loaded as prescribed by the test conditions. The extrudate issuing from the orifice is cut off flush and dis­carded at 5 minutes and again 1 minute later. Cuts for the test are taken at 1, 2, 3, or 6 minutes, depending on the material or its flow rate. The results are strongly dependent on temperature. Therefore, values of melt flow are reported at prescribed test conditions.

Any material form that can be introduced into the cylinder bore may be used. For example, powder, granules, strips of film, or molded slugs are common material forms. Reported values of melt flow help dis­tinguish between the flow characteristics of different grades of material. Generally, high molecular weight materials are more resistant to flow than low molecu­lar weight materials. In addition, melt flow results are useful to the manufacturer as a method of controlling material uniformity.

The recommended temperature for drying the materi­al before molding.

The recommended time for drying the material before molding.

The recommended level of dryness to avoid material degradation during processing. It is expressed as a percentage of the total weight.

The recommended maximum percentage regrind that can be used without a significant drop in properties.

The recommended pressure range to achieve proper mold filling without degrading the material. The value may be expressed as either hydraulic (gauge) pressure or actual pressure on the material, which is roughly a factor of 10 greater than hydraulic pressure. A typical range would fall within 500 to 2000 psi hydraulic pres­sure (.5 to 2.0 ksi), which corresponds to 5000 to 20,000 psi actual pressure (5.0 to 20.0 ksi).

The recommended temperature setting for the rear portion of the barrel of the injection molding machine.

The recommended temperature setting for the middle portion of the barrel of the injection molding machine.

The recommended temperature setting for the front portion of the barrel of the injection molding machine.

The recommended temperature setting for the nozzle of the injection molding machine.

The recommended overall processing temperature for a material, usually expressed as a range.

The recommended temperature of the mold during molding.