Three-tier co-extrusion blown film machineRelated technical terms:
Three-tier co-extrusion blown film machine, also known as frost dew point line, refers to the plastic by the viscous flow state into the high elastic state line.In the process of blown film, low density polyethylene (LDPE) from mold squeeze in molten state, good transparency.When, after leaving the die by cooling ring on membrane bubble of wind blowing area for cooling, cooling air blowing at certain Angle and speed just out from the plastic bubble, high temperature membrane bubble with cooling air contact, membrane bubble of heat will be taken away by the cold air, clear the decrease of the temperature to the low density polyethylene (LDPE), the viscous flow of temperature the following, so that the cooling and solidification and become blurred.In blown film bubble is a transparent and we can see on the dividing line between fuzzy. This is dew point (or called frost line).In the process of blown film, the dew point height has a certain influence on film performance.If high dew point, located above the film after blowing bubble of, is the film blowing in liquid, huff just make film thinning, and molecules from stretching orientation, then the blowing film performance is close to the stretch film.On the contrary, if the dew point is lower, is blowing in the solid state, the plastic under high elastic state, blowing like transverse tensile, the molecular orientation effect, thus make blown film machine blowing film performance close to the oriented film.
Three-tier co-extrusion blown film machine blowing ratio is one of the control points of blown film production process, is refers to the film after blowing bubble diameter and not blowing the ratio between the pipe ring diameter.Blowing ratio of thin films of lateral expansion ratio, is actually to transverse tensile membrane, will have a certain degree of orientation effect of plastic molecules, blowing ratio increases, thus increase the lateral strength of thin film.However, blowing ratio also cannot too big, otherwise easy to cause membrane bubble is not stable, and film prone to buckling.The blowing ratio, therefore, should work with traction than appropriate, in general, low density polyethylene (LDPE) film blowing ratio should be controlled in 2.5 ~ 3.0 is advisable.
Traction traction than refers to the film speed and the ratio between the pipe ring extrusion speed.Drawing ratio is longitudinal draw ratio, make the film has a directional role in the leading direction.Traction ratio increases, the longitudinal strength will increase, and the thickness of the thin film thinning, but if excessive traction than, the thickness of the thin film is hard to control, and may even film break, broken film phenomenon.Low density polyethylene (LDPE) film of traction control than normal between 4 ~ 6 is advisable.
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