Clamp tonnage

The clamp tonnage of a machine must have sufficient locking force not to cause the parting of mold halves it resists the force of melted plastic moving at high pressures into the mold halves. If the mating surfaces of the mold are forced apart, even a few thousands of an inch (depending on type plastic), fluid plastic will flow out and produce flash (Chapter 17). 

In the construction of molds for RIM processing, it must be kept in mind that part quality and finish are roughly equivalent to the quality and finish of the mold surface itself. A common misconception is that because the clamp tonnage for a RIM setup is relatively low, low-quality tools can be used. This, however, is true only insofar as the pressure requirements for the mold are concerned. 

Other developments have not been as dramatic, but they have nevertheless contributed significantly to the process efficiency. The electric screw drives were replaced by hydraulic motors with a gear box on the reciprocating screw unit. In the future the hydraulic motor may in turn be replaced by a direct hydraulic drive (19). The Introduction of stack molds has also increased productivity. In a stack mold, two cavity plates are placed on top of each other so that the projected area is the same and twice as many parts can be formed with the same clamping tonnage. This technique works best with thin wall, flat parts with short cycle times. 

Sizing of the plastication unit should consider the weight of the part and the mnner, melt density (Table 6.24), and clamp tonnage. A tonnage of 5 T/in should be sufficient for molding all fluoropolymers. 

IMM with an oil hydrauUc system provides the power to turn the screw to plasticate the plastic, inject the melt into the mold cavity, close the mold clamp, hold clamp tonnage, release the clamp, and eject the molded part. A number of hydraulic components are required to provide this power, including motors, pumps, directional valves, fittings, tubings, and oil reservoirs/tanks. See drive-system control hydraulic fluid influenced by heat, injection molding machine hydromechanical clamp See clamping, hydromechanical. 

MOLD AND CLAMP Clamp Tonnage Mold Temperature Cavity Pressure... 

Parts can be molded by gas injection using injection molding machines (Chapter 2). This process is most effective and economical when used for large parts. It offers a way to mold parts with only 10 to 50 percent of the clamp tonnage that would be necessary in conventional IM (1). 

Extruder motors are usually electric, but some systems utilize hydraulic motors. For example, injection molding machines use hydraulics to develop clamp tonnage. Electric motors may be of the direct current (DC) or alternating current (AC) types. Traditionally, DC motors, which regulate speed through voltage control, have been more popular because they could provide the necessary power at a lower cost. However, recent advances in frequency control - the technique used to regulate speed in AC motors - have caused this type of motor to become more widely used. 

While a hydraulic clamp machine requires a very large cylinder in the center of the platen to apply full clamp tonnage with hydraulic pressure, hydraulically actuated toggle clamps (Fig. 5.62i ) use a small cylinder and a mechanical toggle. To close the clamp, the cylinder moves forward, extending the toggle links (Fig. 5.6261" ). Clamp... 

Structural foam is generally made in a low-pressmre process where the cavity is not completely filled with the initial injection of the mixture. This low-pressure process featiures the ability to provide a large part molded with an internal cellular structure and a tough external skin while enjoying the economics of reduced clamp tonnage. 

Clamp tonnage Minimum 6, recommend 12 tons/in of projected part area... 

Can the clamp tonnage be adjusted for large or small blow molds ... 

The required clamp tonnage is the sum of the blow pressure tonnage and pinch-off tonnage required with a 25% safety factor calculated as follows ... 

Units. There is no uniform rating by the machinery manufacturers for clamp tonnage units nor is there a uniform use of nomenclature. One might see US. tons listed followed by KN and both are listed. Sometimes the multiplier is 10, so a 42 ton clamp will also show as 420KN. Other times a clamp will show 67 tons and 600KN which means a multiplier of 8.95 was used. Also, sometimes the US. tons are also given in metric eg, Cincinnati Milacron does this. The best conversion would be to rate in US. and metric tons with the US. tons being divided by 1.1 to yield metric tons. 

Clamp tonnage required = 2-5 tons clamp per square in. of part projected surface area... 

Clamp tonnage is determined by the addition of the air blow pressure in pounds per square inch times the product s projected area in square inches, plus the pinch-off area in pounds per square inch. A safety factor of 25% is used. 

Thus, the required clamp tonnage is the addition of the above two forces. 

This calculation will indicate if your blow molding clamp tonnage is sufficient to blow the product with a specific air pressure and not have the clamp blow open during the process. 

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