TECHNICAL TERMS USED IN INJECTION MOLDING

GLOSSARY – TECHNICAL TERMS USED IN INJECTION MOLDING

Additives:

A substance adds to a plastic compound to alter its characteristic. Examples are plasticisers, flame retardant.
Alloy: A combination of two or more plastics which form a new plastic.

Amorphous: A plastic material in which the molecular structure is random and become mobile over a wide temperature range.

Anneal: To heat a moulded part up to a temperature just below its melting point and slowly cooling it back down to room temperature. This relieves moulded

Anisotropic Shrinkage: Shrinkage that occurs more in one direction (Usually the direction of flow reinforce material shrink more across the direction of flow), then another.

Automatic Operation: The term used to define the mode in which a moulding machine is operating when they is no need for an operator to start each cycle.

Barrel: A metallic cylinder in which the injection screw (or plunger) resides in the moulding machine.

Blend: A mixture of two or more plastic

Boss: A projection of the plastic part, normally round, which is used to strengthen an area of a part provide a source of fastening or to provide an alignment mechanism during assembly.

Cartridge Heaters: Pencil shape electrical heater device sometime in moulds to raise the temperature level of the mould, as special beneficial when moulding high temperature crystalline materials.

Cavity: A depression or female portion of the mould which creates the external plastic part surface.

Check Ring: A ring shape component that slides back and forth over the tip end of the screw. The check ring eliminated the flow of the molten material backwards over the screw during the injection process.

Clamp Force: The force, in-terms, that the clamp unit of a moulding machine exerts to keep the mould close during the injection process.

Clamp Unit: That section of the moulding machine containing the clamping mechanism this is used to close the mould and keep it close against injection pressure created by the injection process. The clamp unit also contents the injection mechanism.
Cold Slug Well: A depression (normally circular) in the injection half of an injection mould opposite the sprue, design to receive the first front, or cold portion of molten plastic during the injection process.

Compressive ratio:  The factor that determines the amount of shear that is imparted to plastic material as it travels through the barrel. It is determined by dividing the depth of the screw flight in the feed section by the depth of the screw flight in the metering section.

Conditioning: Exposing a moulded part to a set of condition (such as hot oil) Which imparts favourable characteristic to the product.

Cooling Channel: Drill holes or channels machined in to various plates or component of injection moulding providing a flow path for cooling medium (such as water) in order to control the temperature of the mould.

Core: An extended or male portion of the mould which creates the internal plastic part surface, A pin or protrusion design to produce a hole or depression in the plastic part.

Counter bore: A recessed circular area commonly used to fit the head of an ejector pin (return pin, socker pin etc) in the ejector plate.

Crystalline: A plastic material in which the molecular structure becomes mobile only after being fitted above its melting points.

Suchion: A pad of material left in the barrel end of the injection stroke. It is excessive to the amount needed to fill the mould and acts as a focus point for holding pressure against the cooling melt.

Cycle: The total amount of time required for the completion of all operation needed to produce a molded part. Sometime referred to as the gate to gate time. Mining the time when an operator first close the gate until the time the operator close the gate again for starting the next cycle.

Decompression: A method of relieving pressure on the melt after preparing it for injection during the upcoming cycle. These minimize the drooling that occurs when a shut off nozzle is not utilized.

Defects: An imperfection in a moulded part that result in the product not meeting original design specification.  These defects can be visual, physical and hidden.

Draft: An angle (or topper) provided on the mould to facilitated injection of the moulded part.

Injector Half: That half of the moulded which is mounted to the moving platen of the injection machine. Sometime called the live half or the movable half because it moves. This half of the mould usually contents the ejection systems.

Ejector Pin: A pin, normally circular place in either half of the mould, usually the ejector half, which pushes to the finishes molded product or runner system out of a mould. Also referred to as a knock out pin, for obvious reason.

Feed Throat: The area at the rear end of the injection unit that allows fresh plastic to fall from the hopper in to the heating barrel.

Feed Zone: That area of the screw that is at the rear and receive fresh material from the feed throat.

Filler: Specific material added to the basic plastic design to obtain particular chemical, electrical, physical or thermal properties.

Flash: A thin film of plastic that tends to form at parting line area of a mould, may also be found in vent area and around ejector pin. Flash is caused by too great a clearance between mating metal surface which allow plastic material to enter.

Flight: The helical metal thread structure of the injection screw.

Gate: An opening found at the entrance of a cavity (end of the runner system) which allow material to enter.

Granulators: A machine design to grind up rejected pre-moulded plastic (product or runners). The material generated by this process is called regrind.

Guide Pins: A pin (Usually circular) which normally travel bushing in order to provide alignment of two on attached components such as the two halves of an injection mould. Also called leader pin.

Heating Cylinder: That section of the injection moulding machine in which the plastic resin is heatd to the proper moulding temperature prior to injection in to the mould.

Heating Zone: An area of the heating barrel that is controlled by a temperature controller attached to a set up heater bands. There are four major zones rear, centre, front and nozzle.

Heater Band: Bracelet shape electrical heaters that are place around the outside circumference of the heating barrel.

Hopper: A funnel shape container mounted over the feed through of a moulding machine. It holds fresh material to the gravity feed zone in to the heating barrel. Hoppers are normally designed to hold an average of two hours worth of material for a given machine size.

Hydraulic Clamp: A term used to describe the use and large hydraulic cylinder to open and close the clamp unit of a moulding machine.

Hygroscopic: A term applied to those plastics materials such as (ABS, Nylon) which observe moisture from the atmosphere.

Injection Capacity: A rating of the maximum amount of plastic material, in ounces, a machine is capable of injecting a single stroke of the injection screw or plunger. It is based on the specific gravity of polystyrene as a standard.

Injection Moulding: The process of pushing a molten plastic material in to a relatively cooled mould in order to produce a finish product.

Injection Pressure: That pressure which performs the initial filing of the mould. It is supplied by the injection screw or plunger as it pushes material out of the heating barrel and in to the mould.

Injection Unit: That section of the moulding machine which content the injection component, including the hopper, heating cylinder, screw, nozzle and heater bands.

Isotropic Shrinkage: Shrinkage that occurs equally in all direction.

Land: A term used to describe the area in which the gate or vent resides. It can also be though of as the length dimension in the L,W,H. Terminology used for describing the dimension of the gate or vent.

L/D Ratio: The reason of a calculation which divides the entire length of flighted area on a screw by its nominal diameter.

Manual Operation: The term used to define the mode in which a moulding machine is operating when there is a need for an operator to start and finish each phase of the total cycle.

Melt: A term given to describe the condition of molten plastic prior to injection in to mould. A proper melt has the consistency of warm honey.

Metering Zone: That area of the screw at the front and which content properly melted plastic that is ready to inject.

Mould: The term given to the entire tool (cavity, core, injectors etc) needed to produce moulded parts from molten plastic material.

Monomer: A molecular unit of an organic substance usually in the form of a liquid or gas.

Moving Platen: The platen of a moulding machine that travels (open & closes). It is connected to the clamp unit and is the mounting location for the V or travelling, half of the mould.

Non-Return Valve: A mechanism mounted in the nozzle of the injection machine which operates to shut up injection flow at the end of the injection cycle. This eliminates material from the upcoming shot from drooling out of the nozzle when the mould open to eject part from the previous shot.

Nozzle: A device mounted at the end of the heating barrel which focus plastic material to flow from the machine in to the mould.

Parting Line: A plane at which two halves of a mould meet. Also apply to any other plane where two moving section come together and from a surface of a moulded part.

Plunger: The injecting member of a non screw design moulding machine. Plungers do not rotate to bring material forward in preparation for the next cycle. Nor do they blend the material as a screw dose.

Purging: A process of a injecting unwanted plastic material from the injection cylinder in to the atmosphere for the purpose of changing materials, changing colors, or removing degrade material. Also the name given to the mass of material that is purged.

Reciprocating Screw: A helical flighted metal shape which rotates with in the heating cylinder of a moulding machine, shearing, blending and advancing the plastic material. After rotating the screw is pushed forward which injects the plastic in to the mould, also simply referred to as the screw.

Runner: Grooves or channel cut in to either one or both halves of the injection mould to provide a path for the molten plastic material to be carried from the sprue to the gate of the cavity.

Screw Speed: The rotating speed of the screw as it augers new material towards the metering zone it is expressed in RPM (revolution per minute).

Semi automatic operation: The term used to define the mode in which a moulding machine is operating when there is a need for an operator to start each cycle.

Shot: A term given to the total amount of plastic material that is injected in to a mould in a single cycle.

Shut up land: A raised area of the mould surface surrounding the cavity image. This area usually between 0.002 & 0.003 inch high. Approximately ½ inch wide and is used to focus clamping pressure on the mould. The use of a shut up land reduces the amount of tonnage required to keep a mould closed against injection pressure.

Slide: A section of the mould which is made to travel at an angle to the normal movement of the mould. Used for proving under cuts, recesses etc.

Sprue: The plastic material that connects the runner system to the nozzle of the heating cylinder of the moulding machine. It is formed by the internal surface of a bushing that joints the mould to the machine nozzle.

Screw Bushing: A hardened bushing that connects mould to the moulding machine nozzle and allows molten plastic to enter to the runner system.

Stress: A resistance to deformation from a applied force. Moulded plastic product tend to contain stresses moulded in as a result of force applied during the injection forces. These stresses may result in fractures, cracks and brakage. If they are released during use of the product.

Thermocouple: A device made of two dissimilar metals which are used to measure the temperature of a heated area such as a barrel or nozzle. It sends a signal to a controller which then turns off or on to control the temperature of that area.

Tie bars: Large diameter rods that connect stationery pattern A to a stationary pattern B. The moving pattern contains bushing which are used for sliding over the tie bars. Allowing the moving pattern to travel between the two stationery patterns.

Transaction Zone: That area in the center of the screw (between the feed zone & metering zone) this section has a tapering flight depth condition which compresses the plastic material in preparation for injection.

Vent: A shallow groove machined in to the parting line surface of a mould in order to allow air and gases to escape from the cavity or runner as the molten plastic is filling the mould. Sometime also located on ejected or core pin.