Solutions to abnormal problems in TPE extrusion and granulation!

TPE extrusion line and granulation is the most common production way for many manufacturers,  extrusion and granulation will cause various problems. In fact, these problems are not only faced by us, but also by our customers when they are injection molding. so how to quickly solve these common problems?

1. Long strip

Generally, any length greater than 2 times that of normal pellets is considered long strips.The main reasons are: the strip is stretched or broken when the machine is turned on, the direction of the strip is not straight, the strip is not properly soaked in water, the pelletizer tool is worn or has chips, etc.Main solutions:
1)During normal production, adjust the direction in which the material strip enters the pelletizer and adjust the immersion length;
2)Severe strip breakage during production requires adjustment of the extrusion process;
3)Pay attention to the inspection of the granulating motor knife and replace the damaged knife in time;
4)The long strips that appear can be screened using a suitable vibrating screen.

2. Connecting pellets

Two or more pellets connected side by side are called continuous pellets.The main reasons for the continuous granulation of modified materials include failure to separate or break the strips in time when driving, insufficient water immersion length, and excessive temperature of the machine head, etc.Main solutions:
1)When extruding the strips, use a guide nylon wheel with appropriate width to separate the strips that are stuck together in time;
2)Adjust the appropriate length of cooling water immersion to prevent overheating of the material strips and reduce continuous graining;
3)Appropriately lower the temperature of the machine head and adjust the temperature of the material strip;
4)For the continuous grains that appear, a vibrating screen with appropriate mesh openings can be used to sieve.

3. Centipede strips

The cross sections of two or more pellets are not all cut and are connected together called centipede strips. In fact, they belong to the category of connecting pellets.The main reasons include the speed when driving the strip is fast and slow, the discharge port of the twin-screw extruder is ejected, the length of water immersion is not enough, the cutting tool of the pelletizer is worn, or the gap between the fixed knife and the movable knife is too large, etc.Main solutions:
1)The operator should pull the strip at a constant speed to avoid the strip being too thick;
2)Adjust the appropriate extrusion process to avoid material coming out of the discharge port;
3)Adjust the appropriate cooling immersion length to avoid overheating of the material strips;
4)Adjust the gap between the fixed knife and the movable knife, and replace the tool with a new one if it is not possible.

4. Black spots

There are black speck granules on or inside the granules.The main causes of black spots are:the pumping screw is not clean when put into the truck;there are black spots in the raw materials;screw carbonization；environmental pollution;brought in artificially.Main solutions:
1)During the process of converting the product, the screw was not cleaned. Just pump the screw again;Cleaning points: "Three ports", the mesh plate behind the filter and the large machine head;
2)Strengthen inspection of incoming materials, especially black spots and impurities that are more likely to appear in filled mineral powders or flame retardants;For example, Z30S or T30S pellets containing wood chips, low-level filling mineral powder or flame retardants in the package;None of these can be used to produce modified plastics with strict black point requirements;
3)Pay attention to controlling and adjusting the barrel temperature and the residence time of materials in the barrel to prevent the processing temperature from being too high;That is to say, the corresponding extrusion process should be designed according to the formula of each product;
4)It is necessary to pay attention to surrounding environmental hygiene and keep the ground moist. It is necessary to isolate and protect the machines that produce products of different colors;
5)Auxiliary equipment of extrusion equipment such as sinks, pelletizers, etc. should be cleaned regularly;
6)Every time you change the screen, the remaining material on the moving screen and template must be cleaned to prevent carbonization over time;
7)Note that floor-standing material strips are strictly prohibited from entering the pelletizer to prevent dust from being introduced;
8)Prevent the generation of plastic static electricity, which can easily attract dust.

5. Discoloration

It is manifested by sudden changes in product color during the production process and obvious color differences.The main reason for discoloration is uneven mixing or incorrect mixing;unclear machine cleaning;temperature too high;cut too strong;impurities in the back material.Main solutions:
1)Strictly follow the mixing process to ensure the uniformity and accuracy of the mixing;
2)After the machine is cleaned, a dedicated person will inspect it to ensure it is clean;
3)Control the extrusion temperature to prevent toner decomposition caused by excessive temperature;
4)Choose the right screw combination to avoid too strong shear;
5)Make sure there are no impurities in the remixed material.

6. Bad vacuum

There are two or more vacuum holes or foaming on the cut surface of the pellet.The main reasons for poor vacuum include insufficient vacuum, vacuum return, bad vacuum system, poor sealing, etc.Main solutions:
1)Regularly inspect and maintain vacuum pumps and vacuum pressure gauges;
2)Clean vacuum tanks, vacuum chambers, and vacuum pipes promptly;
3)Properly control the flow of circulating water of the vacuum pump;
4)Solve the problem of vacuum return and ensure that the vacuum cover is sealed well.

7. Iron filings/metal particles

There are iron filings or other metal particles on the surface or in the middle of the plastic pellets.The main reasons include screw wear, broken movable knife, and iron filings or other metal particles in the raw materials.Main solutions:
1)Check whether the screw, moving knife, vibrating screen, etc. are damaged;
2)Check whether there are corresponding metal particles in the raw materials;
3)For defective products, strong magnetic or other metal separators can be used to screen out metal particles;
4)Non-enhanced cars add filters.

8. Poor plasticization

From the cross-section of the particles, there are refractory substances, or the surface is black and looks like toad skin.Reasons for poor plasticization include too low heating temperature, impurities in raw materials, excessive feeding speed, too weak screw shear, and too much lubricant in the formula.Main solutions:
1)Control the temperature according to the process regulations, and increase the temperature appropriately when poor plasticization is found；
2)Check whether there are impurities and insoluble matter mixed in the raw materials or during the process；
3)Properly control the feeding speed to increase the time for the plastic to be heated and plasticized in the screw；
4)Choose a screw combination with moderate shear capacity；
5)Adjust the recipe appropriately.

9. Moisture is too high

Can see shiny water on the surface of the material strip, or you can feel the moisture in the material pellets with your hands, or there is water dripping from under the pelletizer, and other similar phenomena.The reasons for excessive moisture content include excessive immersion of the material strips in water, failure to separate the strips in time when driving, too fast pelletizer, too small wind force of the air knife, and too close distance between the pelletizer and the air knife.Main solutions:
1)Appropriately adjust the length of the material strip soaked in water;
2)When drawing strips, the strips are immediately divided into strips after entering the pelletizer;
3)Properly adjust the speed of the granulator and the height of the strip support;
4)Make sure the wind force of the air knife is strong enough. If necessary, use two air knives;
5)Properly adjust the distance between the granulator and the air knife.

10. Minced

After the material strips are cut by the granulator, many tiny powder-like particles are produced. Due to the static electricity of the plastic, they are adsorbed at the lower opening of the vibrating screen.The main reasons for the formation of broken pieces include too much water immersion in the material strips, wear and tear of the cutting tools of the granulator, too much filler and too hard material strips, etc.Main solutions:
1)Properly adjust the amount of water soaked in the material strips;
2)Replace the cutting tool with a new one;
3)Adjust the formula appropriately to reduce the distance between the granulator and the air knife.

11. Carbonization

The leakage material at the die head charred into black matter, and granular charred matter appeared on the surface of the plastic.The main reason for carbonization is that the heating temperature is too high, causing the melt to burn;The screw has been used for a long time without cleaning, and charred matter accumulates;The shutdown time was too long and the machine head and screw were not cleaned.Main solutions:
1)Always check whether the heating system is normal, and if there are any problems with the heating system, solve them promptly;
2)Periodically pump out the screw or clean the machine head and clean it thoroughly;
3)Screens, filters, and die heads must be cleaned promptly and cleanly to prevent carbonization. If carbonization is found, the machine head and screw should be cleaned immediately.Clean to prevent carbonization. If carbonization is found, clean the machine head and screw immediately.