Uneven adjustment of gap between wire drawing film mouth
Uneven die gap may be due to improper adjustment. If the detection is uniform after cold state adjustment, but the deformation of die lip is uneven after heating, hot state adjustment shall be carried out again. Do not try to reduce the die gap in order to make the extruded molten film thinner, because forcibly reducing the die gap will produce "aging" deformation in the long-term heating process, and the die gap is more difficult to adjust. The extrusion amount should be reduced and the molten film should be thinned by increasing the traction speed (one traction).
Material and machining accuracy of wire drawing film mouth
The die material shall be heat-resistant steel. The non heat-resistant steel will produce thermal deformation and difficult to recover during repeated heating, and it is difficult to adjust the die gap after use for a period of time; The runner of the die should be processed smoothly with high precision to reduce the melt flow resistance to small.
Channel shape of drawing film port
The shape of the die channel is very important. In the design, the resistance drop of different resins flowing to the far and near parts of the die lip shall be equal as far as possible, and the extruded molten film can be uniform, such as clothes hanger flat die head.
Temperature of each part of wire drawing film mouth
The heating temperature at each part of the die mouth has a great influence on the flow velocity of the melt in viscous flow state over the whole width of the die mouth. The melt at the part with high temperature flows quickly and the molten film may be thick. Therefore, it is very important to reasonably design the distribution and power of heating elements on the whole width of die.
Rheological behavior of raw materials
The rheological behavior of raw materials, including melt index, molecular weight distribution and melt flow viscosity, has a considerable influence on the thickness of each part of the flat die after melt film extrusion. The resin suitable for wire drawing extrusion can be drawn only with wire drawing grade material. The powder material is not as uniform as the granular material extruded film, and the recycled material is not as uniform as the powder material extruded film.
The gap of drawing film mouth is too narrow
The designed die gap is too narrow, or the adjusted die gap is too narrow, which will reduce the resistance of melt flow. As the temperature is inevitably very uniform, the flow channel resistance is inevitably very uniform, and the extrusion expansion is also unequal, resulting in uneven extrusion resistance of molten film and uneven thickness. If the die gap is slightly larger, these influencing factors are relatively weakened.
Insufficient head pressure, etc
Insufficient head pressure, uneven screw mixing, semi blocked filter screen, etc. may also make the extruded diaphragm uneven in thickness.
