Mechanical Clamping Units

The toggle lever clamping unit is now the predominant mechanical system for injection molding machines. It is not a purely mechanical system in the strictest sense, because hydraulics are also used for the movement of the toggle lever in this system. In principle, however, it is a mechanical system. 

As the name suggests, the toggle lever clamping unit is based on the use of levers. Levers offer two great advantages  

Note that attainable speed and transmittable force exist in a direct, mutually dependent relationship. As transmittable force increases, speed decreases. 

The opposite applies to the forees being transmitted. When the mold is wide open, it is only necessary to transmit enough force to displace the movable mold half. However, when the mold is elosed, it is necessary to transmit a very large amount of force in order to hold the mold shut in opposition to the injeetion pressure. Both eonditions ean be fiilfilled quite effectively with the toggle lever. 

To move the lever, a comparatively small hydraulic piston is sufficient in all cases. Once the mold is closed and the lever has been fully extended, it is not necessary to apply any additional force with the hydraulic piston. 

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Figure 3.46 Clamping unit with a toggle mechanism.

The permeability is also affected by stress the induced change decays logarithmically with time as a form of disaccommodation. Inductors are usually made in two parts so that the winding can be introduced on a bobbin the parts must then be joined closely together to prevent the permeability from being affected by an uncontrolled air gap. If a mechanical clamp is used, the force must not be excessive and must be the same in similar units. Its effect must be allowed to decay before the inductance value is finally adjusted. 

For movement of the hand/arm, two hands are better than one. Using two hands takes more time and effort, but more is produced so cost/unit is lower. When one hand (generally the left) is acting as a clamp, consider it as idle and use a mechanical clamp instead. 

Several techniques can be used for the clamping unit (1) hydraulic clamps, in which the hydraulic cylinder operates on the movable parts of the mold to open and close it (2) toggle or mechanical clamps, in which the hydraulic cylinder operates through a toggle linkage to open and close the mold and (3) various types of hydraulic mechanical clamps that combine features of (1) and (2). 

The sprayed anodes are widely used in the United States for impressed current cathodic protection. Originally, the mesh anodes were mechanically clamped to the pile. In later versions, a GRP jacket containing the zinc mesh is attached to the pile and filled with gront after connecting the zinc to the reinforcement (Figure 7.6). All these systems and their performance in Florida are discussed in Kessler et al. (1995, 2002). 

To perform the mold movements, the clamping unit needs a drive mechanism. Two fundamentally different systems are used as drives. There is thus a basic distinction between mechanical clamping xmits and hydraulic clamping units. 

Besides the two main types of clamping units (mechanical and hydraulic), there are also combinations of both systems. All systems have advantages and disadvantages. In other words, there is no universal optimum design of clamping unit. The choice of system employed in the injection molding of plastics articles is ultimately determined by the the most cost-effective production method, e.g. single- or multi cavity mold and machine suitabdity. 

Clamping units support the mold, hold the mold closed during injection, open and close the mold as rapidly as possible, provide for part ejection, and provide mold close protection. The four types of clamps are hydraulic, hydraulically actuated toggle (mechanical), electrically actuated toggle, and hydromechanical. 

The mould is mechanically fastened (e.g. bolted) in the clamp unit, but is interchangeable to allow different products to be moulded. The essential features of a mould are listed below. 

FIGURE 1.141 Clamp unit with a barrel mold the mechanism to change the extrusion slot, using hydraulic actuators with an adjustable mandrel, is visible on the extrusion die... 

The force requirements ensure that the clamp unit must be engineered very robustly, but this conflicts with the need to open and close the mold rapidly to minimize production time. A variety of clamp mechanisms has evolved in the search for a suitable compromise. The two most common types are the direct hydraulic clamp (Fig. 7.2) and the toggle clamp (Fig. 7.3). Other variants include hybrid toggle/hydraulic types, lock-and-block systems, and electromechanical systems. 

Ejects the moulded parts from the tool. The mechanism is activated through the clamping unit. The ejection force may be hydraulic, pneumatic or mechanical. 

The inner face of the clamping unit that moves during mould closing. The moving half of the mould is bolted onto this platen. This platen also contains the ejection mechanism and mould mounting holes. 

Approaches to artificial ion channels have, for instance, made use of macrocyclic units [6.72,6.74] (see also below), of peptide [8.183-8.185] and cyclic peptide [8.186] components, of non-peptidic polymers [8.187] and of various amphiphilic molecules [6.11, 8.188, 8.189]. The properties of such molecules incorporated in bilayer membranes may be studied by techniques such as ion conductance [6.69], patch-clamp [8.190] or NMR [8.191, 8.192] measurements. However, the nature of the superstructure formed and the mechanism of ion passage (carrier, channel, pore, defect) are difficult to determine and often remain a matter of conjecture. 

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