PE blown film machine traction speed setting

1、 Basic concepts of traction speed

The traction speed of a PE blown film machine refers to the speed at which the film is extruded from the die, stretched, cooled, and coiled by the traction roller. This parameter is one of the core control elements in the blown film process, directly affecting the physical properties, appearance quality, and production efficiency of the film.

The traction speed is usually measured in meters per minute (m/min), and the traction speed range of modern blown film machines is generally between 5-150m/min, depending on equipment specifications and product requirements. The traction speed, extrusion speed, and blowing ratio together constitute the "three major speed parameters" of the blown film process, and accurate coordination between the three is required.

2、 The Influence of Traction Speed on Film Properties

1. Impact on mechanical properties

The increase in traction speed will lead to an enhancement of the molecular orientation of the film in the longitudinal (MD direction) direction, thereby improving the longitudinal tensile strength, but at the same time, it will reduce the transverse (TD direction) strength. When the traction speed is too high, it may cause an imbalance in the longitudinal and transverse strength of the film, affecting its performance.

2. Uniformity of thickness

Appropriate traction speed helps to obtain a thin film with uniform thickness. Low speed may cause the film to sag, resulting in a "curtain effect"; If the speed is too high, it may cause thickness fluctuations, especially when changing specifications.

3. Surface quality

The traction speed affects the surface glossiness and transparency of the film. Generally speaking, increasing traction speed appropriately can improve surface gloss, but excessive increase may lead to surface roughness or the appearance of "shark skin" phenomenon.

4. Crystallinity and heat sealing performance

The change in traction speed will alter the cooling rate of the film, thereby affecting its crystallinity. Higher traction speed usually leads to lower crystallinity, which may have a beneficial effect on heat sealing performance.

3、 Principles for setting traction speed

1. Match with extrusion speed

The traction speed should be maintained in an appropriate ratio to the extrusion speed, which is commonly referred to as the "stretch ratio". For PE film, the recommended stretch ratio is generally between 4:1 and 20:1, depending on the resin type and product requirements.

Calculation formula: Draft ratio=(traction speed)/(extrusion speed)

2. Consider the inflation ratio

There is an interactive relationship between traction speed and inflation ratio. Generally speaking, higher inflation ratios require corresponding adjustments to the traction speed to maintain the balance of film performance. Empirical formula:

Better traction speed ≈ (extrusion speed) × (bubble circumference)/(die diameter × π)

3. Product specification requirements

Thin films of different thicknesses and widths require different traction speed settings:

Thin film (15-50 μ m): usually using higher traction speed (60-120m/min)

Thick film (80-200 μ m): generally using lower traction speed (10-50m/min)

Ultra thin film (<15 μ m): requires high traction speed (100-150m/min) and precise control

4. Material characteristics

The adaptability of different PE resins to traction speed varies:

LDPE: Wide speed range, good adaptability

LLDPE: requires higher traction speed for better performance

HDPE: The traction speed range is narrow and requires accurate control

MLLDPE: requires particularly high traction speed and accurate temperature control

4、 Method for adjusting traction speed

1. Manual adjustment

Traditional blown film machines often use manual adjustment methods:

Set initial speed based on experience

Observing the stability of membrane bubbles

Gradually fine tune to a better state

Record successful parameters as reference

2. Automatic control

Modern blown film machines are often equipped with automatic control systems:

Speed closed-loop control: achieving accurate speed regulation through encoder feedback

Synchronous control: Ensure that the speed of each traction roller is consistent

Tension control: Maintain constant tension through floating rollers or sensors

3. Segmented control

The blown film system adopts segmented traction control:

First traction zone: higher speed, preliminary shaping

Second Traction Zone: Accurate Control, Adjust Final Performance

Third traction zone (optional): Special treatment such as corona discharge, etc

5、 Common problems and solutions

1. Unstable membrane bubbles

Possible reason: mismatched traction speed and extrusion speed

Solution: Adjust the traction speed or extrusion amount to maintain an appropriate stretch ratio

2. Uneven thickness

Possible reasons: Fluctuations in traction speed or uneven cooling

Solution: Check the mechanical components of the traction system to ensure stable speed; Optimize cooling system

3. Surface defects

Possible cause: Excessive traction speed leading to melt fracture

Solution: Reduce traction speed or increase melt temperature

4. Uneven winding

Possible reason: The traction speed and winding speed are not synchronized

Solution: Check the transmission system and adjust the speed matching parameters

6、 Optimization strategy for traction speed

Step by step debugging method: Starting from low speed and gradually increasing by 5-10%, observe the changes in film performance

Response surface methodology: Establish a mathematical model of traction speed and other parameters to find a better combination

DOE Experimental Design: Systematic Investigation of the Influence of Traction Speed on Various Quality Indicators

Historical data analysis: Collect production data and establish a better parameter database

7、 Safety precautions

Speed adjustment should be carried out when the equipment is running at low speed

Avoid rapid speed changes to prevent bubble rupture or equipment damage

Ensure that protective devices are intact during high-speed operation

Regularly check the wear of the traction roller

Prioritize the use of emergency stop devices in emergency situations

The traction speed setting of PE blown film machine is a process technology that combines theoretical knowledge and practical experience. Operators need to have a deep understanding of the relationship between speed parameters and film properties, master scientific adjustment methods, and continuously accumulate production experience. With the development of automation and intelligent technology, the control of traction speed will become more precise and efficient, providing strong support for the production of high-quality PE films.