Blown film forming process
DATE：2022/5/11 8:35:56 / READ： / SOURCE：This station
Blown film forming process
1. Process flowThe film produced by blow molding method is commonly known as blow molding film, which is referred to as blow film for short. The blow molding process flow of blow molding film. Introduction to packaging and processing technology of old and new plastics: raw material molding, one euro molding - film winding. Process flow diagram of blown film forming: the production mode of blown film is divided into three types: flat extrusion up blowing method, flat extrusion flat blowing method and flat extrusion down blowing method according to the different blowing and traction directions of film tube. The three film blowing processes have their own advantages and disadvantages. Table 34 compares them. The production mode can be selected according to product specifications, raw materials, production conditions, quality requirements and economic accounting. EVA film production line www.handern.com com
Blow molding process comparison process advantages and disadvantages 1 The shape of bubble tube is stable 1 2. The plant is on the high side, and the flat extrusion and upward blowing method is required Small floor area 2 Not suitable for raw materials with low viscosity Easy to produce, folding diameter can be large or small 1 Large floor area flat extrusion and flat blowing method 2 Simple auxiliary structure 1 Easy film introduction, easy operation, uneven thickness 2 The membrane tube sags due to its own weight, and the membrane 3 Not suitable for the production of film with wide folding diameter 1 Conducive to film cooling 1 It is not suitable for producing thin flat extrusion and down blowing method 2 Suitable for raw materials with low viscosity 3 High production line speed 2 Inconvenient feeding 2 Expansion ratio and traction ratio EVA film production line www.handern.com com
2. The ratio of the pipe diameter of the blown film to the diameter of the die mouth is called the blowing ratio. For the convenience of calculation, the relationship between film folding diameter and die diameter is commonly used to express the expansion ratio: D = 2bnd = 0.637 BD, where: λ-- Expansion ratio B -- film folding diameter, mm D -- die diameter, mm
Blow up ratio is the key point of blow molding film production process control. Large blow up ratio and high transverse strength of film. If the expansion ratio is not properly controlled, the stability of membrane tube is poor. Traction ratio is the ratio of film traction speed to tube extrusion speed. The traction ratio makes the film directional in the drawing direction, and the longitudinal strength of the film increases with the increase of the traction ratio. If the traction ratio is too large, the film thickness is difficult to control, and even the film may be broken. Generally, the traction ratio is 4 ~ 6, which is more suitable for the traction speed, that is, the circumferential linear speed of the film passing through the traction roller. The extrusion speed of the tube blank can be obtained by dividing the weight of the resin extruded per unit time (film yield) by the cross-sectional area of the die gap. The formula is as follows: v = nd-b-p, where: V -- extrusion speed of tube blank, cm / minm -- film yield, g / min, D -- die diameter, CM B -- die gap, CMP -- density of molten resin, g / cm expansion ratio and traction ratio are transverse expansion multiple and longitudinal drafting multiple of film respectively. If both increase at the same time, the film thickness will become thinner, but the film folding diameter will become wider. The expansion ratio of LDPE film is applicable in the range of 1.5 ~ 30 and the traction ratio is in the range of 4 ~ 6. The expansion ratio of HDPE film is generally 3 ~ 6. The allowable expansion ratio range when producing films with different folding diameters with dies of different diameters is shown in table 3-5, and the traction ratio is in the range of 4 ~ 6. The expansion of polypropylene blown film is smaller than that of polyethylene, usually in the range of 1 ~ 2, up to 2.5, and the traction ratio is also in the range of 4 ~ 6. High density polyethylene film expansion ratio range die diameter / mm appropriate expansion ratio film folding diameter / mm introduction to packaging bag processing technology of new and old plastics film folding diameter / mm die diameter / mm appropriate expansion ratio continued table
3. Die size EVA film production line www.handern.com com
The die size is determined by the film specification (film folding diameter) and expansion ratio. After the film specification requirements are determined, the die size can be determined according to the expansion ratio and application range of various films. In order to adapt to the changes of film width and thickness specifications, the same head is often used. The films with different thickness can only be obtained by changing the traction ratio, and the films with different folding diameters can be obtained by changing the expansion ratio, so as to fully improve the utilization of the head. Nevertheless, because the traction ratio has a certain limit and the expansion ratio has a certain scope of application, the die gap required for films with different thickness can be obtained according to the specific relationship between film thickness and die gap. It can be seen from the above example that the die gap is 6 ~ 18 times of the film thickness. The die gap required for the production of thick film takes the lower limit value, and vice versa, takes the upper limit value. There are the following relationships among them: die diameter, expansion ratio and traction ratio are interrelated and restricted each other EVA film production line www.handern.com com
Author：admin