Water injection assisted

Process > Injection

What is water assisted injection molding?
The technology of water-assisted injection (WIT or WAIM, for its acronym in English) was born with the scope to replace the gas used (nitrogen) in gas assisted injection (GIT) technology for water to reduce cooling times . Initially the injection system with water presented some problems, difficulty to generate high pressures and high flow rates, as well as obtaining a hollow section. Overcoming these problems, WAIM technology has become a liquid injection technique (WIT), for its acronym in English) of increasing commercial interest.
Four process approaches
Short shot
Also called bubble process or explosion, the water is injected into the mold before the end of the melt injection, pushing the material to the end of the cavity for the final packing. The valves close from the injection unit and the water from the pin. A release valve for water A valve mounted on or near the end of the fill can be facilitated by the evacuation of water using compressed air. This method is considered good for very thick parts. It does not imply wasting material or shredding. The entry and exit points for water (and air) can be in / near the same point. Disadvantages related to the strict control required. Too little material can lead to water breaking through melting in the mold. The water injection pressure must be greater than that of the melting. The point of change of the surface of the piece, I know that the Class A finish may not be feasible. In addition, material at the end of a short blow.
Pushback
El fuso llena por completo la cavidad. Al abrir un pasador de agua cerca del final de la masa fundida se llena el exceso de masa fundida Las ventajas de este enfoque incluyen la ausencia de material de desecho y la capacidad de lograr el acabado Clase A. Es para una boquilla especial y compruebe que el material vuelva a la unidad de inyección. Los usuarios deben tener cuidado de regar el espacio libre (podría ser un gran problema con los materiales higroscópicos como el nylon). Una parte del proceso debe ser subrayada. Proceso de cambio en el barril, creando un proceso que puede influir en el siguiente tiro. Se requieren sistemas separados de entrega de aire y agua.
Overflow
The mold cavity is completely filled with melt and closed by a valve. Next, a pin is opened in the mold for water injection, while at the same time, a valve at the end of the filling of the cavity opens a path from the main cavity to a secondary or overflow cavity. The incoming water displaces the molten mass, which is pushed into the secondary cavity. The secondary valve is closed for holding and packing. Water can be expelled by gravity or by evaporation. It is reported that this approach provides a class A surface. It is the closest thing to conventional molding, offering a wider processing window. It also requires a lower water pressure than the short firing method. On the negative side, the material displaced from the core must be recycled. A secondary trimming is needed to separate the finished product from the excess material in the secondary cavity.
Flow process
A combination of short-shot and overflow methods The mold cavity is partially filled, then the water is introduced, pushing the material until the end of the filling. A special valve opens at the end of the filling, and the water breaks through the melt and flows through the valve into a water recirculation circuit. The advantages are material savings and a high cooling rate. Disadvantages includes a spot on the tip of the piece. In addition, low pressure can cause water to seep between the inner surface and the outer surface. A common factor in WIT is the need to purge water. Define the WIT sequence with gas-assist. Alliance Gas Systems says that its WIT systems include a pressurized gas purge. For sensitive materials, Alliance can supply a gas assistance system with a secondary water injection, followed by a gas purge. The suppliers indicate that the entire process of injection and evacuation of water takes only a few seconds.