Plastic Molding

About Plastic Moldings and Plastic Molding Suppliers Including: Injection Molding, Molded Plastic, Plastic Injection Molding, Plastic Manufacturers, Plastic Molders & Reaction Injection Molding.

Injection plastic molding is the most common method used by plastic suppliers in the plastic processing industry, with 32% of all plastics processed by plastic injection molding. Plastic molders fabricate parts with a range of complexities, from simple shapes to close tolerance precision parts. From medical equipment, computer and automotive parts to office supplies, toys and tools, molded plastic parts are found in almost every sector of industrial and consumer industries. A few common examples include screwdriver handles, catheters, contact lens containers, monitors, mop buckets and video game cartridges. Plastic manufacturers primarily fabricate injection molding with thermoplastics. However, a small amount of thermosets and elastomers are also subjected to this process. Biodegradable plastics are also injection molded. Products such as biodegradable cutlery and plastic pots are now being produced using this molding process.

An injection plastic molding machine has a barrel section which is heated first. Plastic pellets or granules are fed into a hopper where a screw pushes them to the heated barrel. In the barrel, the pellets or granules are heated to the melting point. The molten plastic material is then injected into the cavity of a split die chamber/mold, which is then clamped shut. The plastic resin cools as water or other fluids circulate through the cooling system of the mold, extracting the heat. The molded plastic part is held in the mold under high pressure until the part solidifies. The plastic part is finally ejected from the plastic mold, and the process begins again.

Most commonly, a hydraulic oil injection molding machine is used to produce molded parts. Hydraulic oil machines use the force of hydraulic fluids to move the mold through the machine. Next in popularity is the toggle plastic molding machine. Toggle machines use mechanical links to advance the mold in the machine. Hybrid hydraulic/toggle machines are beginning to emerge in the plastic molding industries. Hybrid machines are used to eliminate some of the problems of other injection plastic molding machines, such as slow processing rates of parts and rapid wear and tear of machines. All injection molding machines inject molten plastic material into a mold, but they may use various methods to move the mold, move un-melted plastic pellets and accomplish other parts of the process.

There are many advantages to the injection plastic molding process. Some advantages of injection molding include high production rates and a wide range of plastic material which can be used. Normally there is little need to finish parts after the molding is complete. The cost per part is very low despite the high cost of tooling. Injection plastic molding can produce very complex parts, and often parts for which no other process is available. Other advantages of the injection molding process include the efficient use of materials and energy, precision-formed parts and a negligible amount of waste produced.

Types of Plastic Molding

• Double-shot molding is a two-step process in which either the color or the material is injected first. Upon the hardening of the material, a second color or material is injected into or around the first shape.
  
• Gas-assisted injection molding is a process in which inert gas, such as nitrogen, is forced into the melt while it is entering the mold, packing the plastic into the cavities. Gas-assisted injection molding reduces cycle time, part weight, warpage and stress to the cooled parts, as well as minimizing other problems.
  
• Injection blow molding is the process in which plastic is injected into a mold to form a plastic tube. The tube is then blown into a cavity mold to form a hollow part.
  
• Injection molding is a process by which plastics parts and products are formed.
• Molded plastic pieces are parts that are formed by pouring heated plastic into molds.
• Plastic injection molding is a process by which plastic is heated into a malleable form and pressed into molds.
• Plastic insert molding is an injection molding process in which plastic gets injected into a cavity surrounding an insert piece just prior to molding. Plastic insert molding results in a single piece encapsulated by the plastic.
  
• Plastic manufacturers make a variety of plastic goods.
• Plastic molders are the tools and dies used to mold molten plastic.
• Push-pull molding is a process that involves multiple layers with different orientations, providing more uniform properties to the parts than if they were molded from a single direction

Plastic Molding Terms

Backing Plate - A plate that provides support for the mold cavity block, guide pins, bushings and so forth.
 
Cavity - The space inside a mold into which the material is injected.
 
Charge - The amount of material needed to fill a mold during a single cycle.
 
Cooling Channels - Channel through which a cooling medium flows to control the temperature of the surface of the mold. Cooling channels are located within the body of the mold.
 
High Density Polyethylene (HDPE) - Plastic used to package products with short shelf lives, such as bottles for milk, juice, water and laundry products. Unpigmented HDPE bottles are translucent and have good stiffness.
 
Hydraulic Units - Devices that use the force of fluids to move the mold in the injection molding process.
 
Linear Low Density Polyethylene (LLDPE) - A plastic that is used predominantly in film applications due to its toughness and flexibility. LLDPE is the preferred resin for injection molding because of its superior toughness and is used in items such as grocery bags, garbage bags and landfill liners.
 
Mold - A series of steel plates, which contain cavities into which plastic resin is injected to form a part.
 
Monomer - A relatively simple compound that can react to form a polymer.
 
Melt Index - A test that measures the ability of molten plastic to flow.
 
Melting Point (Tm) - The temperature at which crystalline portions of polymers melt. A material becomes soft and completely amorphous once it reaches the Tm.
 
Melt Viscosity - A term that refers to the measure of resistance to flow. For all materials, the viscosity decreases as the temperature increases.
 
Polymer - A term that means many units. These units are linked together to form chain-like structures that give polymers unique properties.
 
Polypropylene (PP) - A very strong substance that has the lowest density of the plastics used in packaging. PP has a high melting point, making it ideal for hot-fill liquids.
 
Polystyrene (PS) - A very versatile plastic that can be rigid or foamed and has a relatively low melting point. General purpose polystyrene is clear, hard and brittle.
 
Resin - Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.
 
Thermoplastics - Materials that can be melted by heating and then re-solidified by cooling. Blends of thermoplastics can be prepared by melt-mixing.
 
Thermosets - Materials that "cure" to form solids when heated. Unlike thermoplastics, solid thermosets do not melt when heated, so they are very useful for high heat applications.
 
Toggle Unit - Device that uses mechanical links to move the mold during the formation of injection molded plastics.