Injection Molding is a manufacturing process for producing parts by injecting material into a mold. Injection molding can be performed with a host of materials, including metals, (for which the process is called casting), glasses, elastomers, confections, and most commonly thermoplastic and thermo-setting polymers. Material for the part is fed into a heated barrel, mixed, and forced into a mold cavity, where it cools and hardens to the configuration of the cavity.
How Injection Molding Works:
Thermoplastic materials are commonly fed into the heated barrel of the machine in the form of pellets, where a screw conveys them forward creating shear heat to melt the material thoroughly. Once the desired amount of plastic has been plasticized it is injected into a mold under high pressure. As the material shrinks during cooling, a so called holding pressure is applied to counteract this volume contraction (shrinkage) for some time. After applying the holding pressure, the molded part further cools down to the de-molding temperature.
After a product is designed, usually by an industrial designer or an engineer, molds are made by a mold maker, usually out of either steel or aluminum, and precision machined to form the features of the desired part.
Animated View of an Injection Molding Process:
Injection molding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photo-polymers which do not melt during the injection molding of some lower temperature thermoplastics, can be used for some simple injection molds.
Parts to be injection molded must be very carefully designed to facilitate the molding process; the material used for the part, the desired shape and features of the part, the material of the mold and the properties of the molding machine, must all be taken into consideration. The versatility of injection molding is facilitated by this breadth of design considerations and possibilities.
Injection molding uses a ram or screw-type plunger to force molten plastic material into a mold cavity; this solidifies into a shape that has conformed to the contour of the mold. It is most commonly used to process both thermoplastic and thermosetting polymers. Thermoplastics are prevalent due to characteristics which make them highly suitable for injection molding, such as the ease with which they may be recycled, their versatility allowing them to be used in a wide variety of applications and their ability to soften and flow upon heating.
Injection molding consists of high pressure injection of the raw material into a mold which shapes the polymer into the desired shape. Molds can be of a single cavity or multiple cavities. In multiple cavity molds, each cavity can be identical and form the same parts or can be unique and form multiple different geometries during a single cycle. Molds are generally made from tool steels, but stainless steels and aluminum molds are suitable for certain applications. Aluminum molds typically are ill-suited for high volume production or parts with narrow dimensional tolerances, as they have inferior mechanical properties and are more prone to wear, damage, and deformation during the injection and clamping cycles. However, aluminum molds are cost-effective in low-volume applications, as mold fabrication costs and time are considerably reduced. Many steel molds are designed to process well over a million parts during their lifetime and can cost tens of thousands of dollars to fabricate.
Thermoplastics also have an element of safety over thermosets; if a thermosetting polymer is not ejected from the injection barrel in a timely manner, chemical cross-linking may occur causing the screw and check valves to seize and potentially damaging the injection molding machine.
CPVC:
Chlorinated Poly (Vinyl Chloride) (CPVC) is a thermoplastic pipe and fitting material made with CPVC compounds meeting the requirements of ASTM Class 23447 as defined in ASTM Specification D1784.CPVC applications are for potable water distribution, corrosive fluid handling in industry, and fire suppression systems.
CPVC piping systems are:
Environmentally friendly.
Provide long service life.
Easy to install and handle.
Corrosion resistant.
Cost effective.
Widely accepted by codes.
Examples of CPVC Components:
Industrial CPVC pipe is manufactured by extrusion in sizes from ¼” to 12″ diameter to Sch 40, Sch 80, and SDR (Standard Dimension Ratio) dimensions.
CPVC pipe for plumbing systems is manufactured by extrusion in sizes ¼” through 2″ copper tube size (CTS) dimensions. The CTS plumbing products are made to copper tube outside diameter dimensions, in accordance with ASTM D-2846 specifications, and have an SDR 11 wall thickness. The pressure ratings of the CTS SDR 11 systems are 400 psi (pounds per square inch) at 73 F and 100 psi at 180 F. CPVC plumbing pipe is sold in both straight lengths and (in small diameters) coils.
USES/APPLICATIONS:
CPVC piping which is suitable for hot and cold water distribution has a 400 psi pressure rating at room temperature, and a 100 psi pressure rating at 180 F. CPVC materials are resistant to many everyday household chemicals. Since CPVC materials do not support combustion, they cannot burn without an external fuel source. This property makes CPVC pipe an attractive alternative to steel and copper pipe for fire sprinkler applications. CPVC fire sprinkler piping systems are approved for light hazard applications and for use in single and multifamily dwellings. Installation shall be in accordance with the NFPA Section 13, 13D, and 13R.
Plastic:
Any of numerous organic synthetic or processed materials that are mostly thermoplastic or thermosetting polymers of high molecular weight and that can be made into objects, films, or filaments, primarily by Injection Molding.
Examples of Injection Molded Plastic Components:
Plastics are macromolecular connections from the elements Oxygen, Nitrogen, Hydrogen and Carbon. They consist of connected molecules called macromolecules, chainmolecules or polymers.
There are 3 main categories of plastics that can be molded into a variety of parts. The characteristics of the plastics depend on the inter-connections of their macromolecules.
- Thermoplastic (amorphous and semi-crystalline thermoplastic)
- Thermoset
- Elastomer
The injection molding process using thermoplastic or thermoset plastics is fundamentally different. Thermoplastic in pellet form is melted and then injected into a cool mold. After cooling the mold opens and the part drops out. In thermoset plastic molding the cold material is injected into a heated mold to make the part. Through this process the part cures.
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