Guide for Adjusting Uneven Film Thickness of Blown Film Machines
In the industrial production of plastic film, blown film machines plays a vital role. They process plastic granules by heating, melting, extrusion, blow molding, etc., and form a variety of specifications and applications of thin film products, widely applied in packaging, agriculture, architecture and many other fields. The uniformity of film thickness is one of the important indexes to measure film quality. The uniform thick film not only has good physical properties and appearance quality, but also ensures stability and reliability of subsequent processing and use. On the other hand, uneven film thickness will lead to a series of problems, such as poor packaging sealing, inadequate product protection and dislocation of printing patterns, which will seriously affect the product's market competitiveness. Therefore, timely and effective adjustment of the blown film machine, to solve the problem of film thickness imbalance, in order to improve product quality and production efficiency is essential.
Common Manifestations of membrane Uneven Film Thickness in membrane blowers
Transverse Thickness Unevenness (Left-Right Direction)
In the lateral direction of the film, the thickness of the left and right sides is not the same. This could be one side thicker than the other, the middle thicker than the other, or vice versa. This unevenness will lead to uneven stress on one side of the film when packaging items, affecting the sealing and stability of the packaging.
Longitudinal Thickness Unevenness (Front-to-Back Direction)
Thickness differences occur along the direction of film production, front andback. This manifests that during the tensile process of the film, the film thickness is not uniform due to the different degrees of tensile in some regions. Uneven longitudinal thickness can lead to folds and dislocations in the winding process, affecting subsequent processing and use.
Combined Thickness Unevenness (longitudinal and Transverse Directions)
Thickness heterogeneity was observed in both the transverse and longitudinal directions films. This combined unevenness is the most complex and has the greatest impact on film quality. This results in inconsistent physical properties of the films in different directions, which does not meet the requirements of high quality products.
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Raw Material Factors
Instability of raw material quality:
Molecular weight distribution of raw material may vary from batch to batch. The ultrawide molecular weight distribution results in inconsistent melt index and different flow characteristics during extrusion, which affects film thickness uniformity. For example, the larger molecular weight parts of the melt viscosity is high, slow flow, easy to accumulate in the mold, resulting in the localized film thickening; the smaller molecular weight parts of the flow too fast, resulting in localized film thinning.
Effect of impurities in raw materials
Impurities in raw materials, such as dust and metal particles, clog the flow channels of the mold during extrusion, affecting uniform extrusion. Impurities can also cause defects in the film, leading to variations in local thickness. In addition, impurities will affect the melt and flow characteristics of the raw materials, further increasing the uniformity of film thickness uniformity.
Improper Raw Material Ratio: During production, multiple raw materials are often mixed to meet different membrane properties. If these raw materials mismatch, will alter the physical and chemical properties of the raw materials, affect the uniformity of film thickness uniformity. For example, too high or too low a proportion of a raw material can alter the melting temperature and viscosity of the film, resulting in uneven thickness during extrusion.
Inaccurate Additive Dosage
Additives such as plasticizers, stabilizers and lubricants are often added to improve the properties of the films. Inaccurate additive dosage will affect the processing properties of raw materials and the physical properties of films. For example, excessive plasticizer dosage can soften and increase the fluidity of a film, which tends to lead to thinning during tensile processes; insufficient use can harden the film, reduce its tensile properties and may lead to an increase in local thickness.
Equipment Factors
Screw and barrel issues
In long-term use, the screw will wear out, resulting in the screw and barrel clearance is too large. During the extrusion process, raw materials will flow back, affecting the transport of materials and the quality of the melt, resulting in uneven thickness of the film. In addition, uneven barrel heating will also cause the material melting states is inconsistent, some parts do not melt completely, some parts overheat decomposition, affecting the uniformity of film thickness uniformity.
Die Head Issues
The die head is one of the key components of the blower and its design directly affects the quality of the blower. The improper design of die head, such as unreasonable flow structure or uneven flow size, will lead to uneven flow of die head material, resulting in uneven film thickness. Die head blockage or wear will also cause the change of the extrusion volume, resulting in inconsistent thickness of the film. Improper adjustment of molded lip clearance is also a common cause. If the molded lip clearance is not uniform in different positions, the thickness of the film will also vary during extrusion.
Airring Issuess
The role of the air ring is to cool and mold the freshly extruded film. Inproperly designed air rings, such as poorly designed air ducts or unevenly distributed air vents, can lead to uneven airflow distribution and uneven pressure on the film surface. Where the airflow is large, the film cools quickly, resulting in thinning; where the airflow is small, the film cools slowly, resulting in thickening. In addition, blockage or dust accumulation within the air ring can also affect the uniformity of airflow and pressure, further resulting in uneven film thickness.
Towing and Rewinding Issues
During the tensile process, the tensile ratio of the film will change due to the unstable Unstable traction speed, and the thickness of the film will not be uniform. If the traction speed is too fast, the film will be overstretched and thin; if the traction speed is too slow, the film will be understretched and thickened. Uneven winding tension also affects film thickness uniformity of the film. Too much winding tension will cause the film to be stretched and thinned during winding process, and not enough winding tension will cause wrinkles and affect the film's flatness and thickness uniformity.
Process Parameter Factors
Improper Temperature Settings
The temperature setting of each region of the membrane blower has a great influence on the quality of the membrane. If the temperature in each region is too high or too low, it can affect the melting and flow characteristics of the material. Excessive temperature will lead to overheating and decomposition of raw materials, bubbles and other defects, resulting in uneven film thickness; too low temperature will lead to inadequate melting of raw materials, poor flowability, easy to jam when pressed, uneven thickness. In addition, high temperature fluctuations will also cause the film thickness fluctuation, affecting the film's quality stability.
Inappropriate Blow-Up Ratio and scaling down
The bloating ratio is the ratio of the expansion diameter of the film to the diameter of the die, and the tensile ratio is the tensile ratio of the film in the direction of traction. High and low blowing ratios, as well as mismatched blowing ratios, can affect the film's thickness uniformity. Too high a blowout ratio will lead to the transverse direction stretching, which will lead to thinning of the film; on the contrary, too low a blowout ratio will lead to insufficient lateral stretching, which will lead to thickening of the film. Similarly, too high or too low a tensile ratio can have a similar effect, resulting in uneven thickness of the longitudinal direction.
Poor Cooling Effect;
The cooling effect also has an important effect on the uniformity of film thickness uniformity. Inappropriate cooling air temperature and velocity, or improper cooling roller temperature control, will lead to uneven film cooling speed. Thinner films will appear in areas where cooling is faster, and thicker films in areas where cooling is slower. In addition, uneven cooling will induce stress inside the film and affect the physical properties and appearance quality the film.
Methods for Adjusting Uneven Film Thickness
(I) Raw Material Adjustment
Selecting stable and compliant raw materials is fundamental to ensuring uniform film thickness. When choosing raw materials, select products from reputable manufacturers and test different batches to ensure that their molecular weight distribution, impurity content, and other indicators meet requirements. Simultaneously, strictly control the raw material ratio and accurately add various additives. When mixing raw materials, use appropriate mixing equipment and methods to ensure uniform mixing.
(II) Equipment Maintenance and Adjustment
Screw and Barrel Maintenance
Regularly check the wear of the screw. If severe wear is found, replace it promptly. Simultaneously, ensure uniform heating of the barrel and regularly check the working status of the heating elements. Repair any malfunctions promptly. Temperature sensors can be installed on the barrel to monitor the temperature of each zone in real time, ensuring the temperature is controlled within a reasonable range.
Die Head Treatment
Regularly clean die head blockages using specialized cleaning tools and agents to ensure unobstructed flow in the die head. Repair or replace worn die head components promptly. Precisely adjust the die lip gap using professional adjustment tools to ensure a uniform gap at different positions. When adjusting the die lip gap, follow the principle of coarse adjustment first, then fine adjustment, gradually adjusting to the optimal state.
Air Ring Optimization
Improve the air ring structure, optimize the air duct design and air outlet distribution to ensure uniform distribution of airflow and air pressure on the film surface. Airflow adjustment devices can be installed to adjust the airflow of each air outlet according to actual conditions. Regularly clean the dust and debris inside the air ring to keep it unobstructed.
Traction and Rewinding Adjustment
Check the traction equipment to ensure stable traction speed. Traction speed can be monitored and adjusted in real time by installing speed sensors and controllers. Adjust the winding tension using a tension control device, precisely controlling the winding tension according to the film specifications and requirements to ensure uniform tension.
(III) Process Parameter Optimization
Temperature Control
Set the temperature of each zone reasonably according to the raw material characteristics and film requirements. Before production, conduct sufficient testing and debugging to determine the optimal temperature parameters. Install temperature control devices, such as temperature controllers and thermocouples, to monitor and adjust the temperature of each zone in real time, reducing temperature fluctuations. During production, closely monitor temperature changes and make timely adjustments.
Blow-up Ratio and Draw-out Ratio Adjustment
Determine the optimal blow-up ratio and draw-out ratio through experiments. Multiple tests can be conducted based on factors such as film specifications, application, and raw material properties to find the most suitable production parameters. During production, adjust parameters promptly according to actual conditions, such as changes in raw materials or equipment status, to ensure the blow-up ratio and draw-out ratio remain at their optimal levels.
Improving Cooling Effect
Optimize the cooling air system and adjust air temperature and speed. Install air temperature and speed adjustment devices according to the film's cooling requirements to precisely control cooling air parameters. Control the cooling roller temperature using a cooling water circulation system to ensure uniform and stable cooling roller temperature. Temperature sensors can be installed on the cooling roller surface to monitor temperature changes in real time and adjust cooling water flow and temperature accordingly.,
Precautions measures during Adjustment period
**Pre-Adjustment Equipment Inspection and Safety Measures**
Before adjusting the diaphragm blower, a thorough inspection should be carried out to ensure that all components are working normally and that there are no safety hazards. Wear appropriate personal protective equipment such as safety helmet, safety glasses and gloves to prevent accidents during the adjustment process.
** Gradually adjust parameters to avoid Large Fluctuations**
Process parameters should be adjusted step by step, step by step to avoid large fluctuations. Larger parameter adjustments may lead to greater fluctuation of film quality or even new quality problem. After each parameter adjustment, observe changes in the quality of the film for a period of time before deciding whether to continue.
** Document the Adjustment Process and Parameter Changes for Experience Summarization**
In the adjustment process, carefully record the adjustment time, adjusted parameters, adjustment before and after the change of film quality. These records are valuable for learning from experience, analyzing problems, and optimizing production processes. By analyzing and summarizing the recorded data, the key factors affecting the uniformity of film thickness uniformity can be found, which can provide guidance for future production.
After adjustment, the film should be subjected to comprehensive quality inspection to ensure that it meets requirements. This includes checking parameters such as thickness, tensile strength, fracture elongation and light transmittance. We can use the test method of on-line and offline to ensure that the quality of the film conforms to the product standards and customer requirements. If the test results are not up to scratch, the cause should be investigated and adjusted until the quality of the film meets the requirements.
