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Sheet Extrusion
Sheet extrusion is melting hot plastic granules and then extruding the molten material through a narrow flat die onto rolls that calm and solidify the material into a continuous sheet used for packaging and manufacturing container lids. It most often overcomes difficulties that can affect the quality of the extruded product. Here is an elaborate analysis of the 11 common issues with the extrusion process, their causes, and some relative solutions.
Applesauce Texture
This texture is rough and uneven; it usually results from very high melt temperatures. In this regard, the temperature in the extruder can be reduced, and the screw speed can be adjusted so that the melt flow will be stabilized. Also, there is a need for further investigation into the properties of the materials themselves since some formulations may be more sensitive to this defect under high-heat conditions.
Black Specks
These defects usually arise due to thermal degradation of polymers or extraneous impurities. It is also important to adhere to an extremely rigid lubrication schedule and avoid all contaminations in a material-handling environment. The use of high-purity resins and the addition of better filtration systems can also lower the occurrence of black specks.
Gels
Gels originating from undissolved particles remain sticky due to insufficient mixing or low processing temperatures. An enhanced design of the mixer and optimization of the temperature profiles can correct this. Quality evaluation of raw materials is also helpful since impurities can aggravate this problem.
Fish Eyes
These are fish eyes: small, round voids from moisture entrapment or poor mixing. Fish eyes can often be eliminated with better drying of the polymer and improved mixing techniques. Some of the new drying technologies may be worth investigating to deliver a moisture-free resin ahead of extrusion.
High Clarity Issues
Problems of clarity may result from a high cooling rate or from using low-quality resin. To improve the product’s transparency, it is essential to reduce the cooling rate and simultaneously use higher-quality resins containing better optical properties. Furthermore, continuously monitoring the cooling process can ensure the required clarity level is achieved.
Bubbles in Sheet
Bubble formation due to air entrapment and entrainment may be contained considerably by adjusting the die temperatures and increasing the number of vents. Secondly, the die design should be considered to ensure adequate provisions for the maximum escape of trapped air during extrusion. This should be combined with checking for any changes in processing conditions likely to further worsen the air entrapment situation.
Milky Areas in Sheet
Milky spots are common due to the moisture impurity within the polymer. As a result, the most critical processes are proper drying of the polymer and ideal extrusion conditions. Advanced high-performance drying systems should be used to lower the residual moisture content.
Poor Gloss
Losing a glossy finish due to roll surface defects or incorrect roll temperatures can be problematic. To obtain gloss, the rolls must be polished and temperature-controlled. Maintenance and inspection of the roll surfaces must be done regularly to allow the treatment of any defect that might arise.
Edge Curling
Frequently, edge curling is caused by an unbalanced cooling system or an insufficient balance flow at the edges of the sheet. Balanced chill rolls and balanced material flows will take care of this. The machine must be appropriately calibrated to provide balanced temperature and flow distribution.
Uneven Sheet Thickness
The hiccups in sheet thickness are mainly due to irregular material flow and improper die adjustments. Periodical die calibrations and uninterrupted material feeding would bring about uniformity in thickness. Automated thickness measurement systems that make real-time adjustments in the process should also be installed.
Surface Scratches
Scratches generally arise supported by particles inside the die or upon the surface of the roll. To minimize surface defects, cleaning and inspection for wear should be carried out much more frequently. Correctly applying good quality dies and rolls with improved resistance to abrasion will also minimize the number of scratches.
These problems can only be resolved effectively with technical corrections but with full knowledge of the materials and conditions of the process—particularly extrusion—while delivering high-quality results. Obtaining that singular objective must also be pursued with an efficient production flow.
Granuwel Extrusion – Your Trusted Extrusion Machine Manufacturer & Supplier
Since our establishment in 2015, Granuwel Extrusion has been committed to researching and innovating Sheet Extrusion Lines. We deliver Sheet Extrusion solutions to customers globally. With years of experience, we have honed our technology in this field, if you have any other questions about sheet extrusion, feel free to contact us.
We can provide our customers with the most suitable solutions at the most competitive prices. Contact Granuwel Extrusion to get your competitive edge.