Injection Gates

For components of irregular shape the flow path may have to divide and then re-join. It is at the meeting of two flow fronts that air traps and weld lines can be formed. If flow fronts are bound to meet, the gates should be positioned so that the fronts are pushed to the part of the component that is likely to be the least stressed in service. If possible a vacuum gate should be sited at the point where the fronts meet so that the initial weld front and associated gases can purge from the cavity into the vacuum runner (see Section 5.4). 

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Like gated EK injection, gated FID injection was achieved (see Figure 4.23). Sample injection volumes from 0.5 to 10 nL were made in real-time [569]. FID injection conducted in the pinched and gated modes was achieved on a PET chip using three syringe pumps and an eight-port rotary valve [570]. 

A resin injection gun was developed to interface with the injection gate valves, with an anti-dripping system. Molds are opened automatically when the sensors measure a preset degree of polymerization, reducing cycle times. Five hydraulic hoists on the five parallel molding fines... 

Figure 4.6 Dichroic ratio, R, of the 1016 cm absorption band on the opposite face with respect to the injection gate vs. position. The letters a-j and numbers 1-6 represent the positions from the gate and from the mold axis respectively. (Reprinted with permission from [17], copyright 1993 Butterworth-Heinemann Ltd.)...

Figure 4.7 (a) Depth profiles of order parameter s in the center of the width and 20 mm from the injection gate of a 2 mm thick Vectra A950 plate with injection speed of 10cms and 1 cms (b) Lateral profile of s in the core of the Vectra A950 plate with injection speed of 1 cm s (location 0 represents the sample edge). (Reprinted with permission from [18], copyright 1994 Butterworth-Heinemann Ltd.)... 

Reproducible injection for capillary electrophoresis on a microdevice/Lab-on-Chip is not easy to achieve. Different injection designs (e.g., T type, double-T type, and cross type) and different injection techniques have been applied (pinched injection, gated injection, double-L injection) within microfluidic devices. The volume and the concentration of the dispensed sample are the key parameters of this dispensing process, and they depend on the applied electrical field, the flow field, and the concentration field during the injection and separation processes. The problems and properties of the different modes are described below. 

Blocked injection gate Check rubber for contamination Check rubber at nozzle for nibs... 

Trials are therefore an essential precursor to selection of the cleaning method. Dry blasting with fine glass beads produces a polished surface with minimal environmental impact. However, care needs to be taken with injection gates, vacuum ports and sprues, since they can become easily blocked or not be cleaned at all ... 

For injection-moulded TPU the injection gate must be significantly larger than for other thermoplastic materials. 

No back flow should be allowed. That means the resin should flow from the injector s outlet to the mold inlets (gates), but not in the opposite direction. This is especially important when multiple injection gates are used with constant flow rate injection boundary conditions. If the resin pressure inside the mold exceeds the instantaneous injection pressure at any of the gates, an injector with a one-way flow feature does not allow the resin to flow backward by closing the valve at the exit of the injector. 

Along line injection gates Although the above racetracking channels are formed unintentionally, racetracking channels may be formed intentionally... 

Trial-and-error injections are still commonly used to achieve these goals in the industry. The locations of the injection gates and ventilation ports and injection boundary conditions are decided after these time-consuming trials. These injections require experience for iterating the boundary locations and conditions, and may not result in the optimal design. 

Specified flow-rate injection gate with an inlet cross-sectional area of A and with an outward unit normal vector, n... 

Top view of the mold Line injection gate / Flow front... 

Design of the mold Be able to determine the locations of the injection gates and ventilation ports such that no dry regions (voids) remain at the end of the mold filling. The ventilation ports are placed where resin arrives last when the mold is perfectly vacuumed. 

Mold with additional injection gates and vent ports that can be activated if necessary. 

Ability to turn the valves on and off which are connected with injection gates and vents as dictated by the control design formulated with the simulations. 

Fiber preform compaction and fiber volume fraction control the fiber preform compaction is very important for the part thickness control. To have a more uniform part thickness, it is preferred to close all injection gates and leave the vents on after filling the mold. The pressure gradient as well as the non-uniformity of fiber preform compaction will gradually relax as the liquid resin redistributes itself inside the fiber preform. The relaxation process is related to the resin viscosity, the mold temperature, the pressures and locations of vents, the flow distribution medium and the fiber preform. 

Henz, B. J., Mohan, R. V. and Shires, D. R., 2007. A hybrid global-local approach for optimisation of injection gate locations in liquid composite molding process simulations , Composites Part A Applied Science and Manufacturing, 38, 1932-1946. 

Gokce, A., Hsiao, K.-T. and Advani, S. G., 2002. Branch and bound search to optimise injection gate locations in liquid composite molding processes . Composites Part A Applied Science and Manifacturing, 33,1263-1272. 

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