When engaging in plastics injection-molding, the greatest single cause of wastage is the malformation of products. Putting to one side wastage resulting from mold failures and injection-molding machinery performance issues, the incidence rate of product malformations tends to increase in accordance with the complexity of the product being molded. Two examples of such difficulties can be seen in those requirements set forth for precision components, examples being thin-wall moldings and moldings with transfer functionality.

Considering such problems, the prime cause of malformations can be traced to issues related to the gas-venting performance of molds being deficient. Leveraging the flow pressure of the resins being deployed in the forming process, the "natural ventilation" method of gas-venting pushes any gases present within the mold (invariably air) via the gas-vent to outside the mold cavity. In accordance with this practice, the cross-sectionals of gas-vents are designed to be so small as to limit gas volumes. This is done in order that resins are prevented from penetrating into mold gaps, which results in burring to injection-molded products. Because of this, with regard to the injection-pressure utilized in the case of "natural ventilation," 30% - 50% of set pressures exerted are used for the purpose of gas-venting. Moreover, in the first instance, it is impossible from a design perspective to develop a gas-vent cross-sectional that is commensurate with injection speeds.
Gases that cannot be smoothly vented are compressed due to the flow pressures exerted by resins, this phenomenon results in an increasing of internal pressures within the formation molds. If gases are compressed, it could be argued that their cubic volume would decline, however, this does not equate to the volume of gases present declining to an effective zero. If the internal pressures present within formation molds increase rapidly, the temperature of any gases present can rise to hundreds of degrees due to the phenomenon of adiabatic compressive heating. This in turn can result in injected resins being singed by hot gases.
Furthermore, because compressed gases can expand in volume, such expansions can act as a form of counter-pressure to the flow pressure of molding resins. This in itself can act as a brake on injection speeds. To wit, injection speeds therefore become uncontrollable. Unfortunately, there is no injection-molding technology that can resolve such a turn of events.
The essence of injection–molding technologies lies in an ability to smoothly inject resins into molds as they are required, with all other molding criteria being attendant to this issue. Because of this, the premise that is proposed by this company is that, as a means by which molder units can control the injection speeds of resins, a decisive factor is the ability to gas-vent molds in a situation that is equivalent to that of an atmospheric vacuum.
Placing operations in state of atmospheric vacuum means that gases could be vented from molds and absorbed by the vacuum with only the tiniest of clearances required. Furthermore, there is also the method of performing injection-molding within molds after a vacuum has been initiated within the mold. Generally speaking, gas-venting practices that combine these two methods in a surplus-redundancy format are widely used within industry, with the final decision regarding which gas-venting method to use being based on the structure of the molds being employed. This company has called its method of decompressing molds prior to injection-molding the "Zero Air Injection-Molding System."

1

|

2