PET Strapping Band Extrusion Production Line: Common "Question-Answer" Technical Guide

PET Strapping Band Extrusion Production Line: Common "Question-Answer" Technical Guide

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Why must PET strapping bands undergo "dehumidification and drying + crystallization" pretreatment?

The PET molecular chain is highly prone to hydrolysis. When the moisture content is greater than 50 ppm, the melt viscosity will drop sharply in the extrusion section, resulting in brittle cracking of the strip and insufficient tensile strength. The production line usually first crystallizes the loose bottle flakes with a 170 ℃ hot air crystallizer, and then passes them through a 160 ℃ honeycomb rotor dryer with a dew point of -40 ℃ to reduce the moisture content to below 30 ppm before they can enter the extruder.

What is the most appropriate length-to-diameter ratio for an extruder screw?

For recycled materials or high-viscosity slices, it is recommended that the L/D ratio be 32:1 to 36:1, in combination with a barrier and a mixing section. For new materials or low-viscosity slices, an L/D ratio of 30:1 can be used to reduce energy consumption. The model with a screw diameter of 65mm can achieve a production capacity of 120 kg/h at 260 ℃ and a rotational speed of 25 rpm, and the melt pressure remains stable at 8 to 10 MPa.

How often should the screen of a melt filter be replaced?

A 100-mesh + 150-mesh double-layer filter screen is used. If the raw material contains powder impurities, the screen needs to be replaced when the pressure difference rises to 8 MPa within 2 to 3 hours. The non-stop dual-station screen changer can reduce the downtime from 20 minutes to less than 1 minute.

Why is it necessary to do "two longitudinal and one transverse" during the stretching process?

The strength is determined by the first longitudinal stretching (80 ℃ hot roller, stretching ratio 4.5). The second longitudinal stretching (110 ℃, stretching ratio 1.2) increases the modulus. Subsequently, transverse heat setting (120 ℃, tensile ratio 1.05) was carried out to eliminate internal stress, ensuring the dimensional stability of the tape from -50 ℃ to 120 ℃.

Can 100% recycled bottle flakes be used to make qualified packing straps?

Sure, but a "viscosity increase" step needs to be added. Typical process Crushing → material sorting (PET purity ≥95%) → Vacuum drying → forced feeding and extrusion → vacuum reactor (vacuum degree 10 Pa, 270 ℃, 10 min) to increase the melt viscosity from 0.5 dl/g to 0.8 dl/g, then stretching and forming, the final tensile strength ≥380 MPa, elongation at break ≤15%.

How can the production line quickly switch between different widths and thicknesses?

Replace the die lip gasket and perform closed-loop regulation with an online thickness gauge. Taking the JZX/65-2 model as an example, the switch from 9.5mm to 15.5mm specifications only requires a 25-minute shutdown: loosen the die head bolts → insert new gaskets → readjust the bolts → the laser thickness gauge automatically corrects the traction speed with an accuracy of ± 0.02mm.

How to eliminate the common surface defect "bamboo joint pattern"?

Cause: The melt temperature fluctuates by more than 3 ℃ or the water temperature of the cold roller is uneven. Countermeasures: ① Add a static mixer at the die head outlet; ② The water temperature of the cold roller is controlled within ±1 ℃. ③ Before stretching, the temperature gradient of the preheating oven was changed to 90 ℃→110 ℃→90 ℃, which made the inner and outer layers of the strip soften simultaneously and the bamboo joint pattern basically disappear.

How to calculate the energy consumption of the entire line?

Take an annual output of 3,000 tons (three-shift system) as an example:

Dehumidification and drying: 45 kW

The extrusion host is 110 kW

• Stretching oven 55 kW

Auxiliary fan/pump: 30 kW

The total installed power is approximately 240 kW, the actual operating load rate is 70%, and the power consumption per ton of product is approximately 580 kWh/t.

How can environmental protection emission standards be met?

The non-methane total hydrocarbons produced in the extrusion and stretching sections are processed by the "low-temperature plasma + secondary activated carbon" process. The inlet concentration is 120 mg/m³, and the outlet concentration can be reduced to 8 mg/m³, which is lower than the special emission limit (60 mg/m³) stipulated in the "Emission Standard of Pollutants for Synthetic Resin Industry" (GB 31572-2015).

How to determine whether a production line is "easy to operate and maintain"?

You can use the "Five-minute Rule" to self-test on the spot

Change the filter screen within 5 minutes (without stopping the screen changer)

Cleaning the screw mold removal ≤5 minutes (quick-opening mold head + electric hoist)

All daily lubrication points are external and there is no need to remove the guard cover

Meeting the above three points can significantly reduce the reliance on highly skilled operators