alloys such as tzm 120 w mk copper and beryllium alloys 120 300 w mk aluminium 260 w mk electrolytic copper 300 390 w mk and also graphite 60 400 w mk as already said the choice and the combination of the first and second materials are applied according to the type of plastic material to be injected and the configuration of the injection point u201c gate u201d for example regarding the characteristics of the plastic material crystalline materials generally have a u201c cold cap u201d problem or freezing at the point of injection which sometimes prevents molding or may require an increase of the temperature for the restarts the crystalline materials therefore generally require a high temperature of the tip 11 and a highly conductive material for the radially outer element 13 is therefore preferable instead amorphous plastic material often behaves in a different way according to the type of configuration of the tip or the u201c gate u201d for example in the case of valve nozzles these amorphous materials require high temperature to flow better and to avoid filaments particularly in the case of direct injection of the figures while in the case of free flow a lower temperature of the tip is required to avoid problems of u201c stringing u201d the formation of a plastic thread that remains between the molded part and the nozzle when the mold is open during extraction of the piece which is difficult to remove completely and may remain trapped in the mold during the successive injection cycle or of u201c drooling u201d from the u201c gate u201d or rather of dripping of plastic material.