1. What is injection molding?
Injection molding is a method to obtain molded products by injecting plastic materials molten by heat into a mold, and then cooling and solidifying them.
The method is suitable for the mass production of products with complicated shapes, and takes a large part in the area of plastic processing.
The process of injection molding is divided into 6 major steps as shown below.
1. Clamping
2. Injection
3. Dwelling
4. Cooling
5. Mold opening
6. Removal of products
The process is proceeded as shown above and products can be made successively by repeating the cycle.
2. Injection molding machine
Injection molding machine is divided into 2 units i.e. a clamping unit and an injection unit.
The functions of the clamping unit are opening and closing a die, and the ejection of products. There are 2 types of clamping methods, namely the toggle type shown in the figure below and the straight-hydraulic type in which a mold is directly opened and closed with a hydraulic cylinder.
The functions of the injection unit are to melt plastic by heat and then to inject molten plastic into a mold.
The screw is rotated to melt plastic introduced from the hopper and to accumulate molten plastic in front of the screw ( to be called metering ) . After the required amount of molten plastic is accumulated, injection process is stared.
While molten plastic is flowing in a mold, the machine controls the moving speed of the screw, or injection speed. On the other hand, it controls dwell pressure after molten plastic fills out cavities.
The position of change from speed control to pressure control is set at the point where either screw position or injection pressure reaches a certain fixed value.
3. Mold
A mold is a hollow metal block into which molten plastic is injected to from a certain fixed shape. Although they are not illustrated in the figure shown below, actually there are many holes drilled in the block for temperature control by means of hot water, oil or heaters.
Molten plastic flows into a mold through a sprue and fills cavities by way of runners and gates. Then, the mold is opened after cooling process and the ejector rod of the injection molding machine pushes the ejector plate of the mold to further eject moldings.
4. Molding
A molding consists of a sprue to introduce molten resin, a runner to lead it to cavities, and products. Since obtaining only one product by one shot is very inefficient, a mold is usually designed to have multiple cavities connected with a runner so that many products can be made by one shot.
If the length of the runner to each cavity is different in this case, the cavities may not be filled simultaneously, so that dimensions, appearances or properties of the moldings are often different cavity by cavity. Therefore the runner is usually designed so as to have the same length from the sprue to each cavity.
5. Use of reprocessed materials
Sprues and runners among moldings are not products. These portions are sometimes discarded, but in other cases they are finely reground and reused as materials for molding. These materials are called reprocessed materials.
Reprocessed materials are not solely used as materials for molding but usually used after blending with virgin pellets, since there is possibility of deterioration in various characteristics of the plastics because of the initial molding process. The maximum allowable limit for the ratio of reprocessed materials is about 30 %, because too high ratio of reprocessed materials may spoil the original properties of the plastics used.
For the properties when reprocessed materials are used, please refer to "reprocessing capability" in the plastic data base.
6. Molding condition
Molding condition means cylinder temperature, injection speed, mold temperature etc. set in a molding machine to obtain required moldings, and the number of combinations of conditions is innumerable. Depending on the conditions selected, the appearances, dimensions, and mechanical properties of the molded products change considerably.
Therefore, well-tried technology and experience are required to select the most suitable molding conditions.
The standard molding conditions for our materials are shown below. Please click the mouse at the following names of plastics.
Main Features：
One.The Lock Section
1.Arch template, effectively protects the mould, especially suitable for big template with small mold.
2.The electric ruler is installed on the crosshead, the position is more precise.
3.The front connecting rod uses connected structure, increases the rod strength, and easy for assembly
4.The connected tail-board stills itself with big lock shaft, improves tail-board strength, and ensures zero abrasion of the tail-board, easy for maintenance.
5.Connected movable plate, improves its rigidity and reduces deformation
6.Connected thrust bearing, improves its strength and stills itself with small lock shaft, ensures zero abrasion.
7.Arch template fully complies with mechanical property, largely improves template strength.
8.More reasonable toggle design, speeds and stabilizes mold opening and closing.
9.Adjustable movable plate mounting plate, makes the installation easier.
10.Mixed design of T-shape groove and die hole, increases universality of the mold.
Two.The Injection Section.
1.Bridge type support, improves injection smoothness.
2.Longer length-diameter ratio screw design, improves plasticizing effect.
3.Double seal structure, ensures no oil leakage.
4.Withhold type press plate, easy for debugging and assembly.
5.Bijection structure, improves stability.
