Fig. 5.55 shows a precentered die, for which, as the name indicates, no additional
centering is required [125]. It is claimed that a further advantage of this die is that
the conductor is already surrounded by a thin layer of melt as it passes through the
inner conductor guide. This reduces the wear of the guide and improves the adhesion
between the conductor and the polymer.
The geometry of the orifice of the outer die ring affects the permissible maximum
coating speeds as well as the surface quality of the extrudate. The latter is positively
affected by less taper and longer die lands [129]. According to [109] die lands of 0.2
to 2 D are suitable for plasticized PVC (PVC-P) and 2 to 5 D for polyethylene. The
product quality is influenced by the size of the die relative to the dimensions of the
product to be coated. If the die is too large, the residence times are too long, if it is
too small, the extrudate dimensional control can be adversely affected, because the die
provides an insufficient damping action between the screw and the die exit. In some
wire coating dies the mandrel or the mandrel tip can be shifted in order to change the
resistance to eliminate flow markings caused by the distributor system. As with pipe
dies and blown film dies, only mandrels of large dies can have a separate temperature
control.
Fig. 5.55 shows a precentered die, for which, as the name indicates, no additionalcentering is required [125]. It is claimed that a further advantage of this die is thatthe conductor is already surrounded by a thin layer of melt as it passes through theinner conductor guide. This reduces the wear of the guide and improves the adhesionbetween the conductor and the polymer.The geometry of the orifice of the outer die ring affects the permissible maximumcoating speeds as well as the surface quality of the extrudate. The latter is positivelyaffected by less taper and longer die lands [129]. According to [109] die lands of 0.2to 2 D are suitable for plasticized PVC (PVC-P) and 2 to 5 D for polyethylene. Theproduct quality is influenced by the size of the die relative to the dimensions of theproduct to be coated. If the die is too large, the residence times are too long, if it istoo small, the extrudate dimensional control can be adversely affected, because the dieprovides an insufficient damping action between the screw and the die exit. In somewire coating dies the mandrel or the mandrel tip can be shifted in order to change theresistance to eliminate flow markings caused by the distributor system. As with pipedies and blown film dies, only mandrels of large dies can have a separate temperaturecontrol.
การแปล กรุณารอสักครู่..
