Melt-front-dependent controls

Regardless of the individual application, melt-front-dependent controls are able to significantly improve the quality of molded parts while considerably simplifying management of the process. A method, which is ultimately reflected in cost savings. 

Intelligent control systems are not just available for thermoplastics, but also for thermosets and elastomers. Other control systems are used for example for the automatic and melt front-dependent opening and closing of valve gates in liquid silicone injection molding. 

In injection molding control, along with cavity pressure, nozzle pressure, melt temperature, melt viscosity, and mold separation are widely employed. Process variables are dependent upon the collective effect of the machine setting. Process variables are melt temperature, melt pressure, melt front advancement, shear stress, and the rate of heat dissipation and cooling. 

During the injection phase, the plastic melt flows are speed-controlled and fill the cavity. This means, depending on the set injection speed and the set profile of the machine control, the cavity is filled under different conditions. These settings determine how the thickness of the boundary layer is formed in different areas of the molded part, that is whether the melt front is stagnant in certain areas or whether it continues to move continuously at a constant melt front velocity. 

Tungsten and carbon can form two carbides, namely WC and WjC. It is impossible to crystallize WC as a continuous deposit, because WC is formed at a certain excess of carbon, which is known to passivate the electrodeposition front [11, 12], Hence, the crystallization of tungsten carbide as a continuous deposit requires a finer control over the electrosynthesis process and should be carried out under conditions of W2C formation. Experiments at 1173 K showed that tungsten carbide coatings can be deposited from a melt containing 5 wt% Na2 WO4. When the Na2C03 content does not exceed 0.2 wt%, continuous deposits of W-W2C alloys (the composition of which also depends on the carbonate concenfiation) are deposited on the cathode. Continuous W2C deposits appear at a concentration of 0.2-0.5 wt%, continuous W2C-WC deposits appear at 0.5-1.0 wt% poorly adhered deposits of W2C-WC are formed at still higher concentrations. 

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