The issue and solution about HDPE water pipe production

Normal pipe appearance (smooth and symmetrical)

1. The appearance is smooth and evenly proportioned.

2. The appearance is the same color.

Rough surface

①  adjust the process temperature, usually caused by low temperature,

②  Increase cooling water temperature or increase production speed

③  Check the waterway for blockage or uneven water pressure (even unevenness), resulting in a rough water point or excessive water pressure and a too fast cooling rate.

④  Check the barrel, the head and other heating coils for damage, resulting in insufficient processing temperature and the formation of rough outer surface

⑤  Adjust the sizing sleeve into the water flow and③The same reason

⑥  Consult the raw material supplier, the raw material parameters of this batch (melt size, processing temperature, etc.)

⑦  Check the core temperature of the mold. If it is higher than the temperature of the die section, raise or lower the core temperature (for the inner wall roughness)

⑧  Clean the mold (0.5-1CM in the die core mold is particularly prone to produce coke material and cause the surface to be not light)

⑨  Adjust the distance between the sizing sleeve and the die (the closer the smoother, the sizing, the polishing)

⑩  Adjusting the formula, generally caused by poor ratio of low-melting and high-melting materials

2.Groove marks on the outer surface

①  Adjust the outlet pressure of the sizing sleeve, the water output is required to be balanced, and the water volume is too large to cause the ditch

②  Adjust the nozzle angle in the vacuum setting box to make the tube cool evenly

③  Check the hardware such as die, sizing sleeve, cutting machine, etc., burrs, etc.

⑨When the raw materials are replaced, the striped grooves will also be formed, which may take a while to improve. When changing the type of raw materials (such as when the MPP is changed to PE), it is necessary to wash the barrel with a low melting point of about 200KG.

Wash other materials in the barrel and then use the formula to produce

3.Groove marks on the inner surface：

①  Check if the inner tube is filled with water. For example, if the water is in the water, the tube blank of the outlet mold is kneaded to close the inner cavity. Large calibers must be shut down to drain the water before starting, or use a dam to prevent water from pouring into the newly connected pipe.

Note: The groove caused by water (the inner groove is small, the outer groove is water)

②  Reduce the internal temperature of the mold (the higher the temperature, the more sensitive the smoothness of the mold)

③  Clean and repair the polishing mold, such as the mold has a thorn or backlog

④  Excessive downtime causes local temperature of the core mold to be low or fouled.

Rough inner wall：

Α.Check if the mandrel temperature is low or high

Β.Check that the mold gap is too large (or too large) → need to change the mold

C.Check if the raw materials are wet → need to be dried.

D.The downtime is too long, it needs to be cleaned for a while, and the temperature is high. 

4.Jitter ring (or corrugated) inside the pipe

①  Adjust the sizing sleeve to make the water out evenly (when the water pressure is large, it is easy to cause the jitter ring)

②  Adjust the vacuum of the two chambers so that the vacuum in the back chamber is slightly higher than the vacuum in the front chamber (reducing the friction of the seal on the pipe)

③  Check if the vacuum seal is too tight

④  Check the tractor for jitter. There is a jitter ring (or corrugated) inside the pipe.

⑤  Check if the main unit discharges evenly                                                  

⑥  Check the vacuum box or the host for shaking. If the die of the main unit is shaken, add a mold holder to fix the mold. If the vacuum box is shaken, replace the vacuum pump or pump with large jitter, or adjust the support points of the limbs to make the force even. .

⑦Adjust the cutting machine's moving air pressure to reduce the impact on the speed of the pipe when cutting.

⑧Reduces melt temperature and reduces appearance

⑨Pull the distance between the sizing sleeve and the die to reduce the impact of equipment vibration on the tube blank

5.No vacuum：

①  Check the vacuum pump inlet for water or blockage, such as blockage, use a needle to clear, or remove the water pipe joint for cleaning.

②  Check that the vacuum pump is working properly and reversed.

③  Check the vacuum line for leaks

④  Check if the small hole in the middle of the mandrel compression screw is blocked, such as blockage, and the wire is unblocked (causing the pipe to be sucked and cannot be vacuumed)

⑤Check the vacuum box cover and seal for leaks.

.Tube outer diameter (outer diameter) size is out of tolerance：

①  Adjust the degree of vacuum to change the outer circle size

②  Adjust the degree of vacuum to change the outer circle size

③  Correct the inner hole size of the sizing sleeve (such as SDR17--SDR11)

Remarks: The general pipe vacuum control between 0.3-0.4 has the least impact on product quality. The thicker the wall (usually larger than 30mm extrusion ≥700kg), the slower the outer diameter is, the faster the outer diameter is, the larger the outer diameter is, the higher the water temperature is, the larger the outer diameter is, and the lower the temperature is, the smaller the outer diameter is.

7.Tube roundness (ellipse) is large：

①  Adjust the angle of the vacuum setting machine and the nozzle inside the spray box to make the tube cool evenly

②  Check the vacuum setting machine, the water level in the spray box, and the pressure of the water pressure gauge to make the spray volume large and powerful.

③  Check the water temperature of the spray box. If it is >35 °C, the chilled water system should be configured to reduce the water temperature.

④  Adjust the pipe guide clamping device to correct the ellipticity of the pipe

⑤  Check if the position of the roller is at the same level, whether the product specifications are met, or convert the vacuum box bracket into a semi-circular tray.

⑥  Adjustment process

⑦  Check and correct the roundness of the sizing sleeve

⑧  Lengthen the length of the vacuum box

⑨  Check the waterway and clean the filter

8.Uneven wall thickness：Adjust the wall thickness on the mold, adjust the size of the mold gap around, the small diameter is four weeks, and the large diameter is always up and down.

①  Adjust the wall thickness on the mold, adjust the size of the mold gap around, the small diameter is four weeks, and the large diameter is always up and down.

②  Adjust the angle of the nozzle in the vacuum setting machine and the spray box to make the tube cool evenly

③  Adjust the sizing sleeve (groove water hole) to make the water uniform

④  Open the mold, check if the screws inside the mold are loose, and retighten

⑤  Large diameter can adjust the wall thickness draw ratio to reduce the impact of the hammer on the wall thickness of the pipe

⑥Adjust the temperature around the die and change the flow speed of the melt to achieve a change in wall thickness (usually used for production lines above dn630-en25, and at the same time require the die heating ring to be divided into at least two upper and lower blocks)

 ⑦Adjust the concentricity of the sizing sleeve and the die mandre

⑨Leakage of vacuum, the surface of the vacuum leak must be thin, check the cause of vacuum leakage

⑩Check if the temperature of the lower floor is stable (generally stable at 65 °C - better). The hand feel is not hot, and the water in and out is enough (uneven before and after a pipe) 

9.The plasticizing temperature is too high: (appearance or matt state)

①  Adjustment process

② Adjust the mold core heating temperature and ventilate the mold inside

③  The gap between the screw and the barrel is too large, causing the raw material to repeatedly shear the material and return to the barrel screw.

④  The gap between the screw and the barrel is too large, causing the raw material to repeatedly shear the material and return to the barrel screw.

     δ Large gap, low production efficiency, small shearing effect, not conducive to heat conduction, not conducive to melting and mixing of materials, small δ gap, large shearing effect, easy to cause thermal degradation of materials

     Small diameter screw δ＝0.005 DS

     Large diameter screw δ＝0.002 DS

     δ＝0.1～0.65mm

10.Cutting gauge length is not accurate：

①  Check if the gauge wheel is tight。

②  Check if the gauge wheel is swinging and tighten the gauge wheel fixing bolt

③  Check the cutter travel switch for damage

④  Check if the rotary encoder is damaged

⑤  Whether the rotary encoder wiring is desoldered (air contact is good)

⑥  Each single-machine casing (PE terminal) should be grounded to a common grounding point by a grounding wire, and the grounding point should have a grounding pile that meets the requirements of electrical grounding. The single-machine casing (PE terminal) is not allowed to be grounded in series, otherwise interference will be introduced. Pulse, causing the cutting length is not allowed

11.Coextrusion labeling problem：

①  Coextrusion of marker strips: Generally, due to improper selection of co-extruded materials used by users, special materials such as PE or the same grade of raw materials should be used. If necessary, the temperature of the extrusion section can be lowered.。 

②  The co-extruded label strip can not be squeezed out: if there is no co-extrusion label strip after 2 hours of starting, it is generally caused by the screw retraction of the co-extruder, the screw is removed, the screw is re-tightened, or the screw is broken, and the screw needs to be replaced.

③  Coextrusion marking strip is too thin or too wide: generally due to the mismatch between the extrusion volume of the coextrusion machine and the drawing speed of the pipe, the frequency of the co-extrusion machine frequency converter should be adjusted or the traction speed should be changed so that the speeds of the two can be matched, followed by coextrusion. The reason why the cooling water jacket of the machine lower section does not pass the cooling water is to adjust the raw material melting index to match the pipe material.

④  Coextrusion machine marking strips sometimes do not: generally due to uneven feeding of the co-extruded material in the co-extruding machine, the water passing condition of the cooling water jacket of the lower feeding port should be checked and the appropriate co-extruded particle size should be selected (generally required particles < Φ3Χ3mm)

⑤  The large-diameter pipe has just started the colorless standard or the color code is squeezed into the wall: the speed of the color-coded machine should be reduced when the pipe is stopped at a slow speed. When the machine is started, the color-coder should be extruded at a low speed, and the switch should be synchronized with the host. . Do not squeeze in advance, nor can it be the same as the normal boot speed, and do not squeeze at high speed. 

⑥  PE color standard 4 thickness unevenness: Generally, the co-extrusion ring hole is caused by impurities causing blockage, and the shutdown and co-extrusion color standard ring can be solved. In addition, the size of the co-extrusion ring hole is not uniform, and it is necessary to disassemble the co-extrusion ring to evenly grind the hole.

12.External surface leakage vacuum

①Check if the die and the sizing sleeve are concentric。

②Check whether the sizing sleeve is leaking or lacking water. It is necessary to seal the leaking gap with silicone sealant.。

③Check that the mold meets the pipe requirements. (The die core mode is too large)

13.Appearance

There are three types of surface pitting (water point, impurity point, crystal point)。

Water point: water pressure is too large or too small。

Impurity point: impurities in the raw material, foreign matter in the mixing process or in the raw material。

Crystal point: the raw material is not plasticized. Change the recipe or replace the screw and barrel with good plasticizing effect。

14.Relationship between pipe and sizing water