During the commissioning and production of PPR pipe production line, dimensional fluctuations in outer diameter (i.e., dimensional jump) emerged as the most typical and relatively straightforward troubleshooting issue. As a professional PPR pipe production line manufacturer, Yongte provides a comprehensive, efficient troubleshooting methodology with prioritized solutions to assist clients in swiftly and accurately identifying and resolving this problem.
Failure characteristics: The outer diameter of the pipe exhibits synchronous fluctuations in response to variations in vacuum pressure, with intermittent increases and decreases.
Rx ：
Observe whether there are obvious and persistent fluctuations in the pointer or numerical display of the vacuum pressure gauge.
Inspect and thoroughly clean the sealing strip of the vacuum setting box. If aging, damage, or deformation is detected, replace it immediately.
Inspect and clean the entire vacuum pipeline, filter, and impeller of the vacuum pump. Any blockage may cause unstable vacuum pressure.
Verify that the water level in the vacuum setting chamber is within the normal range to prevent air from being drawn into the vacuum system.
Key stability parameters: For PPR pipes with specifications ranging from 20 to 63 mm, the vacuum pressure must be maintained stably within the range of-0.04 to-0.06 MPa.
Failure manifestation: The pipe material experiences varying speeds of traction, leading to accumulation of extruded material or uneven stretching, thereby causing changes in outer diameter.
Rx ：
Appropriately increase the clamping pressure of the traction machine's tracks on the pipe material, ensuring uniform pressure distribution on both sides.
Inspect the traction rubber blocks (caterpillar blocks) for severe wear or surface contaminants that may cause insufficient friction or slippage.
Monitor the stability of the output current from the traction frequency converter. If current fluctuations occur, prioritize inspecting the traction encoder for looseness or damage, as these are common causes of inaccurate speed feedback and outer diameter variations.
Ensure synchronization between traction speed and extruder screw rotation speed for optimal control, eliminating the need for manual fine-tuning during production.
Failure manifestation: The extruded melt material from the die exhibits inconsistent output, directly causing fluctuations in the tube blank's outer diameter.
Rx ：
Check the temperature control accuracy of each heating zone (particularly the homogenization section and die head section), with the fluctuation range controlled within ±2°C. If exceeded, inspect the heating coil, thermocouple, and temperature control module.
Inspect the hopper discharge port for any bridging or material interruption phenomena, promptly break the arch, and verify the unobstructed operation of the feeding system.
For the new production line: Note that the new screw needs sufficient break-in. It is recommended to run it at low speeds (e.g., 60-70% of normal production speed) for approximately 1 hour under no-load or low-load conditions until plasticization stabilizes, after which normal production can be resumed.
Monitor the operating current of the host machine (extrusion motor) for stability. Significant current fluctuations typically indicate potential issues such as poor plasticization, material feeding obstruction, or transmission system malfunctions.
Failure characteristics: During cooling, the pipe material exhibits localized fluctuations in hardness, resulting in uneven cooling shrinkage and subsequent outer diameter dimensional variations.
Rx ：
Inspect and clear all spray nozzles inside the vacuum setting box or spray cooling box to ensure uniform water distribution along the pipe circumference without blockages.
Ensure stable supply pressure for cooling water, recommended range: 0.25-0.35 MPa.
The temperature of cooling water should not be excessively high, generally recommended to remain below 30°C to ensure adequate cooling efficiency.
Failure characteristics: In addition to outer diameter runout, it is often accompanied by uneven wall thickness (wall deviation) or elliptical shape in the pipe material.
Rx ：
Re-adjust the adjustment bolts around the die head to ensure uniform melt flow rate and thickness distribution from all points along the die circumference through fine-tuning.
Check whether the flange bolts connecting the die head to the extruder are diagonally and evenly tightened to prevent eccentricity caused by loose connections.
After disassembly and reassembly of new machines or die heads, strict concentricity calibration between the die head and sizing sleeve must be performed again.
1. Step 1: Check the vacuum gauge. If the pointer or reading keeps fluctuating, the issue is likely related to the vacuum system. Proceed with maintenance as outlined in Section 1, Point 1.
2. Step 2: Check the traction speed display. If the set traction speed value remains stable but the actual feedback value or inverter frequency fluctuates → The issue is likely in the traction system or encoder. Refer to Section 1, Point 2 for troubleshooting.
3. Step 3: Check the main motor current meter. If the extruder's main motor current shows abnormal fluctuations, the issue may lie in material discharge, temperature control, or screw plasticization. Refer to Section 1, Point 3 for troubleshooting.
4. Step 4: Observe die ejection. If the extruded melt shows significant thickness variations in all circumferential directions of the die → the issue lies in die head concentricity or ejection uniformity, and address it according to Point 5 in Part 1.
5. Step 5: Inspect the cooling spray system. If the spray flow is noticeably uneven or the water pressure is unstable → the issue lies in the cooling system. Resolve it according to Point 4 in Part 1.
III. Recommended stable process parameters for producing 20-63mm PPR pipes using your SJ65/33 model
Vacuum pressure: It is recommended to set and maintain it at approximately-0.05 MPa, as this value typically demonstrates the highest stability within the specified range.
Cooling water pressure: Set to 0.3 MPa and maintain stability.
Heating temperature: The temperature must be strictly set and controlled according to the previously provided temperature process table. Temperature in each zone must remain stable, and significant fluctuations are strictly prohibited.
Extrusion speed matching traction:
For producing 20-32mm pipes, the extruder rotational speed should be adjusted within the range of 8-12 Hz.
For producing 40-63mm pipes, the extruder rotational speed should be adjusted within the range of 12-18 Hz.
Core principle: The traction speed must be set to synchronize with the extrusion rotational speed (proportional control). Independent manual fine-tuning of traction during production is strictly prohibited to avoid disrupting speed matching.
PPR pipe production experiences erratic variations in outer diameter, with over 99% of cases stemming from one of three root causes: pressure instability in vacuum shaping systems, operational slippage or speed fluctuations in traction devices, or inconsistent extruder discharge volume. By applying this prioritized troubleshooting methodology, issues can be efficiently identified and resolved.
