How to Change the Mold on PPR Pipe Extrusion Line?

PPR Pipe Mold Replacement Procedure

The essential requirements for replacing PPR pipe molds involve ensuring concentricity between the die core and sleeve, maintaining airtight sealing between the mold and machine head, and achieving parameter compatibility post-installation. These factors directly influence the outer diameter, wall thickness accuracy, and surface quality of the pipe. 

The following sections outline standardized operational procedures and precautions:

I. Preparations Before Replacement

1. Shut down and cool down, then cut off the power supply. Stop the extruder following the standard shutdown procedure, turn off the heating system while keeping the cooling water circuit running, and wait until the die head temperature drops below 100°C before proceeding (to prevent scalding and material sticking to the die).

1. Disconnect the power supply to the extruder and die head, and display an 'Equipment Maintenance-Do Not Close Switch' warning sign to ensure operational safety.

2. Tools and Materials Preparation

1. Special tools: torque wrench, hex key, screwdriver, dedicated mold removal puller, and dial indicator (for concentricity calibration).

2. Auxiliary materials: heat-resistant sealing gasket (compatible with machine head flange), copper rod (to prevent mold damage from hammering), cleaning material/PPR recycled material (for subsequent residual material removal), dust-free cloth, high-temperature grease.

3. Inspection and Cleaning of New Dies

1. Verify that the new mold's specifications match the target pipe dimensions (inner diameter determined by die core, outer diameter by die sleeve).

2. Inspect the inner walls of the die core and die sleeve for smoothness, scratches, corrosion, or deformation; check the mold runner for patency and absence of impurity blockage.

3. Wipe the mold surface with a dust-free cloth dipped in a specialized cleaner to remove rust preventive oil or dust. After drying, apply a small amount of high-temperature grease to the mating surfaces of the mold.

II. Disassembly Steps of Old Mold

1. Remove the head accessory. First, remove the vacuum shaping box and cooling water pipes connected to the machine head. Then, move the shaping box backward to a safe distance to avoid hindering the mold disassembly.

4. Remove the heating ring, thermocouple, and other temperature control components from the machine head, and store them properly to prevent cable damage.

2. Dismantling the Mold Flange and the Old Mold

3. Use a hex key to symmetrically loosen the flange bolts connecting the machine head and mold (loosen symmetrically to prevent uneven force distribution that may cause flange deformation).

4. Gently tap the tail of the mold with a copper rod to remove the entire old mold from the machine head. If the mold is stuck and difficult to remove, a dedicated puller may be used to assist in disassembly. Do not violently strike the working surfaces of the mold core or sleeve.

5. Disassemble components of the old mold, including the core, sleeve, and clamping nut. Use cleaning material to extrude at low speed through the extruder, removing residual PPR melt from the flow channel of the head until the discharged material is free of impurities and uniformly colored.

III. Installation of New Die and Concentricity Calibration

1. Installation of die core and die sleeve

6. Insert the new die core into the die core holder of the machine head, ensuring the core positioning step fits tightly against the holder, and secure it with a compression nut (initially tightened, not locked).

7. Fit the die sleeve over the die core and insert it into the machine head flange, ensuring the feed end faces inward. Place the high-temperature resistant sealing gasket to prevent material leakage during extrusion.

2. Concentricity calibration (core step)

8. Concentricity deviation may cause uneven wall thickness in pipes, requiring precise calibration with a dial indicator.

1. The dial indicator is fixed on the head flange, and the measuring probe of the dial indicator is vertically attached to the outer surface of the die sleeve.

2. Gently rotate the die sleeve to observe the oscillation range of the dial indicator, ensuring the oscillation is ≤0.05mm. If the deviation is excessive, make fine adjustments by adjusting the clamping bolts of the die sleeve or the position of the die core.

3. Similarly, for the concentricity of the calibration die core: place the dial indicator probe against the die core's outer circumference, rotate the die core to verify that the runout meets the specified tolerance.

9. After calibration, symmetrically tighten the die sleeve clamping nut and flange bolts using torque values specified in the equipment manual (typically 25–35 N·m) to prevent over-tightening-induced die deformation.

3. Reduction accessory

10. Reinstall the heating ring and thermocouple, ensuring the heating ring is tightly fitted against the machine head and the thermocouple is inserted to the required depth for accurate temperature measurement.

11. Move the vacuum setting box forward to adjust the coaxiality between the setting sleeve and the new mold. The distance between the front end of the setting sleeve and the mold outlet should be controlled at 5–10mm (excessive distance may cause tube collapse, while insufficient distance may scratch the tube surface).

IV. Preheating and Trial Production After Installation

1. Mold preheating and holding

12. Connect the heating power supply and raise the temperature to the preset value (205–210°C) of the PPR extrusion die. Maintain the temperature at the set level for 30–40 minutes to ensure uniform mold temperature and prevent uneven melting of the material in the flow channel.

2. Test Extrusion and Parameter Adjustment

13. Start the extruder at low speed (screw speed 5–10 rpm), feed clean material or PPR raw material, and observe the material flow after it is uniformly extruded from the die opening: the material flow should be cylindrical, with no eccentricity or burrs.

14. The material flow is introduced into the vacuum shaping box, the vacuum and cooling systems are activated, the pipe is drawn at low speed, and samples are taken to measure the outer diameter and wall thickness.

15. If uneven wall thickness is observed, the position of the die sleeve can be fine-tuned (loosen the clamping bolts on one side and slightly adjust the eccentricity of the die sleeve). If the outer diameter is excessively large/small, the corresponding specification die sleeve/die core must be replaced.

3. Production confirmation

16. After the pipe dimensions and surface quality meet the standards, gradually increase the screw speed and traction speed to normal production parameters. After stable operation for 10–15 minutes, take another sample for testing. If no abnormalities are detected, proceed to formal production.

V. Precautions for Replacement

1. During disassembly and assembly, hard objects must not scratch the working surfaces of the die core or die sleeve to prevent compromising the surface finish of the tubing.

2. Seal gaskets require regular replacement. If they become aged or damaged, material leakage may occur during extrusion, resulting in raw material waste and production accidents.

3. The runner design of different molds is different, and the temperature of the machine head must be reset after replacement; the temperature parameters of the old mold cannot be used.

4. The removed old mold must be thoroughly cleaned of residual materials, coated with rust preventive oil, and stored properly to prevent corrosion or damage.