Filling Balance

The increase in the number of requirements made of injection moulded products has made it increasingly necessary to maintain a cavity filling balance in the mould, so that HR systems must match up to the following basic injection moulding principles  

Apart from improving product quality, filling balance makes the injection process easier to carry out (broader range of processing parameters). Achieving a filling balance is dependent on proper organisation of the HR system. 

Sometimes balancing of filling is done by having different nozzle temperatures, but this is not recommended, as it causes varying shrinkage and internal stresses in the moulded pieces. 

It should be emphasised that obtaining 100% filling balance is not easy, since it also depends on other factors, e.g., measurement deviations for individual cavities, local differences in the temperature distribution in the mould, and uneven venting of the cavities. 

It may, however, be assumed (according to Ewikon) that maintaining filling balance is of minor significance when very small moulded items are being produced. 

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Structure. In the case of ZDDP, the role of other additives on film formation and antiwear behaviour has been discussed. Successful control of anti-wear and anti-friction properties of oils requires a care fill balance of the additives in the formulation. 

A unique system which can be described as fluid filled, balanced pressure, heated, floating mold technology was created by Neil Graham, Quickstep Technologies Pty. Ltd., Apple-cross, Western Australia, with the scientific back-up of CSIRO, and patented in 1994. 

Figure 6.3 Orientation of pieces in a mould to improve filling balance a - different flow paths in HR system b - flow paths brought closer together Reproduced with permission from Gunther Heifikanaltechnik GmbH)...

It should be stressed once again, thongh, that the filling balance for this monld will be dependent on use of the same plastic and the given injection time and processing temperature. A change in these parameters will cause a change in the melt viscosity and different pressure drops in the flows to cavities A-D. 

In the event that the manifold is designed by the customer, if filling balance is achieved in a natural way, the channel diameters may be defined using general recommendations (see Chapter 4.2). The correctness of the adopted channel diameter may be checked by calculation using the condition of the admissible pressure loss in the flow path, but one must have the i](y) diagram for the given plastic (see Chapter 6.2). 

The settlement (both total and differential) that occurs in the natural soil underneath the fill and within the fill material itself, as well as the rate of settlement/ excess pore-water dissipation is often one of the most critical elements of the project. It may affect many aspects of project development such as cut/fill balance, ground improvement requirements, construction schedule, pavement design, maintenance, foundation and structural design. Prediction of the magnitude and rate of settlements during the design phase is needed to ensure that hydraulic fill requirements, such as a certain percentage of the total (differential) settlements, are achieved within the time frame allocated for construction in the project schedule. More information about settlement requirements is described in section 8.S.3.4. 

FILLING BALANCE OPTIMIZATION BY BEST GATE LOCATION... 

Baesso, R., Salvador, M., Lucchetta, G., Filling Balance Optimization for Plastics Injection Molding, Proceedings of Advanced Manufacturing Systems and Technology, 617-624 (2005). 

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