Injection clamp force

Semibatch Reactors. Semibatch reactors are the most versatile of reactor types. Thermoplastic injection molds are semibatch reactors in which shaped plastic articles are produced from melts. In mol ding thermoplastics, large clamping forces of up to 5000 metric tons are needed to keep molds together, while highly viscous polymers are forced into their cavities. Heat transfer is critical. If the molds are too cold, polymers soHdify before filling is completed if they are too hot, the time required for cooling delays production. 

Wall sections in foam moulding are thicker than in solid material. Longer cycle times can therefore be expected due to both the wall thickness and the low thermal conductivity of the cellular material. In contrast, however, the injection pressures in foam moulding are low when compared with conventional injection moulding. This means that less clamping force is needed per unit area of moulding and mould costs are less because lower strength mould materials may be used. 

Since the reactants have a low viscosity, the injection pressures are relatively low in the RIM process. Thus, comparing a conventional injection moulding machine with a RIM machine having the same clamp force, the RIM machine could produce a moulding with a much greater projected area (typically about 10 times greater). Therefore the RIM process is particularly suitable for large... 

The container shown at the top of p. 341 is injection moulded using a gate at point A. If the injection pressure at the nozzle is 140 MN/m and the pressure loss coefficient, m, is 0.5, estimate (i) the flow ratio and (ii) the clamping force needed. 

It may be seen from the above analysis and that in Chapter 4 for the calculation of clamping force on an injection moulding machine the Mean Effective pressure (MEP) across the cavity may be obtained from... 

Fig. 5.27 shows the variation of MEP with flow ratio (R/H) for spreading flow in discs of different depths. The material is polypropylene and the constant injection rate is 3.4 x 10 m /s. This is a high injection rate but has been chosen because the clamp forces predicted by this diagram are representative of those occurring in real moulding situations (even though it is based... 

Mold temperature = 90°C maximum clamping force = 700 kN maximum injection pressure 225 MPa. 

Accuracy and repeatability of temperature/time/velocity/pressure controls of injection unit, accuracy and repeatability of clamping force, flatness and parallelism of platens, even distribution of clamping on all tie rods, repeatability of controlling pressure and temperature of oil, oil temperature variation minimized, no oil contamination (by the time you see oil contamination damage to the hydraulic system could have already occurred), machine properly leveled. 

Though its production, e.g. in an injection moulding machine, requires special tricks, the injection pressures and the mould clamping forces required are much lower than with a solid product. 

Figures 8.44, 8.45, 8.46 and 8.47 present the dimensionless injection pressures and clamping forces. Values from these graphs can be used to estimate injection pressure and...

Sample application of the radial flow method. In this sample application, we are to determine the maximum clamping force and injection pressure required to mold an ABS suitcase shell with a filling time, tf=2.5 s. For the calculation we will use the dimensions and geometry schematically depicted in Fig. 8.49, an injection temperature of 227°C (500 K), a mold temperature of 27°C (300 K) and the material properties given in Table 8.8. 

The isothermal injection pressure and clamping force are computed next,... 

Rework Example 8.10 to find clamping forces that are more realistic. Use an injection temperature of 240°C and a mold temprature of 90°C. Are your results reasonable ... 

This process—injection compression moulding—offers other advantages besides lower clamping forces compression of the hot melt gives excellent surface finish and lower pressure at injection reduces orientation in the melt, so improving dimensional stability. The method is used currently to make compact discs of high quality from polycarbonate. 

The preceding discussion has shown that a significant portion of the electrical energy In injection molding is used in the operation of the clamping system. The amount of clamping force is determined by the projected area of the parts and runners. The relationship is ... 

In creating a process window for the combination of material, machine and heater used in this study, the first consideration was the moldability, which was dictated by the maximum injection pressure and the maximum clamp force. No changes in melt and mold temperature, injection velocity, or gate size could remedy this situation. Thus, an injection molding machine with higher injection speeds, pressures and clamp force was required to mold thin-walled syndiotactic polystyrene. 

With the pressures in the mixing head at between 1,500 to 3,000 psi (10.3 to 20.6 MPa), the in-mold pressures are significantly lower than in many of the other molding processes. When comparing a typical RIM in-mold pressure of 50 to 150 psi (0.4 to 1.1 MPa) with the 5000 to 30,000 psi (34.5 to 206.7 MPa) required for thermoplastic injection molding (Chapter 4), it becomes apparent why RIM is particularly suitable for larger parts. Automotive bumpers are routinely produced on RIM presses with 100 to 150 tons of clamping force, while comparable injection molded parts require presses of 3500 tons or more. 

Flash Excessive injection pressure Excessive melt temperature Mold parting face faulty Insufiticient clamp force Foreign matter on mold parting face Flow restriction in one or more cavities of multicavity mold... 

The clamping force depends on the injection pressure and speed, dimension of parts and runners, precision and tolerances. Typical clamping force varies from 48 to 69 MPa. Thin parts with restricted flow may require pressures up to 100 MPa. 

From the perspective of a life cycle analysis (LCA), the RIM process presents two winning cards with respect to thermoplastic injection molding the use of liquids instead of thermoplastic granules and the necessity to use much less clamping force during the molding process. 

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