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How many common defects do you know about bottle blowing? - Maypak

May 03, 2023
How many common defects do you know about bottle blowing? - Maypak


1. The Bottom Molding is Not Full  (The bottom of the bottle is uneven)  



Symptom: 

The petal bottom profile is not ideal, especially the bottom corners are partially concave. Although the bottom is not fully formed, it has little effect on filling, but it affects the stability of the PET Bottle.


Factor: 

  1. 1). Insufficient high pressure gas.

  2. 2). The temperature in the area where the bottom corner is located is not enough.

  3. 3). The high-pressure blowing time is too short (the pre-blowing time is too long).

  4. 4). The pre-blowing air is too late.

  5. 5). The exhaust hole of the bottom mold is blocked.


Solution:

  1. 1). Check whether the high-pressure air intake is above 28BAR.

  2. 2). Check whether the high-pressure filter on the side of the mold is unblocked.

  3. 3). Check the working conditions of each valve to ensure accurate positioning of stretching during pre-blowing and high-pressure molding.

  4. 4). Check the pre-blowing and high-pressure blowing control components to ensure the correct set value and the interior is unblocked.

  5. 5). Ensure that the pre-blowing is not too late, and the time should not be too long. Otherwise, the high-pressure blowing time is too short, and the effective cooling time of the bottle in the mold is       not enough.

  6. 6). Make sure that the vent holes in the bottom mold are unblocked.

  7. 7). Increase the heating percentage of the area where the bottom corner is located or increase the number of lamp tubes to increase the temperature of the area.

  8. 8). According to the actual situation of the bottle (bottle partition weight, thickness). Decrease the temperature where the thinner areas are located so that the bottom corner material is distributed         to these areas.


2. Bottle Mouth Expansion (Closure Expansion)  



Symptom: 

The closure area swells, and it conducts from the mouth of the bottle to the anti-air groove, which is more serious in hot weather. Due to the high temperature, it will happen when the Plastic Bottle is blown, and the popping sound when the high-pressure gas leaks can be heard.


Factor:

  1. 1). The temperature of the furnace cooling water is too high.

  2. 2). The flow rate of furnace cooling water is not enough.

  3. 3). The position of the furnace cooling plate is incorrect.

  4. 4). The stove is not well ventilated.

  5. 5). The height of the furnace lamp tube frame is not adjusted well.

  6. 6). The temperature in the first zone is too high.


Solution: 

  1. 1).  Check the temperature and flow of the furnace cooling water.

  2. 2). Adjust the position of the cooling plate so that it can protect the threaded area of the bottle mouth. (Make the cooling plate 1.5mm away from the front and back of the preform, and 2mm above the plane of the preform support ring.

  3. 3). The blowing and exhausting of the furnace can be increased to reduce the ambient temperature. Or open the side door of the heating furnace to strengthen the air convection so that the heating furnace can dissipate heat well.

  4. 4). Lower the heating percentage of the first zone or reduce the number of lamp tubes.

  5. 5). The design of the cooling plate is unreasonable.


3. Neck Bending  



Symptom: 

Usually the neck is tilted, curving to one side. The convex ring under the thread of the bottle mouth is deformed and is not perpendicular to the center of the bottle body. This Cosmetic Bottles seriously affects filling and capping.


Factor:

  1. 1). Caused by mechanical reasons.

  2. 2). The mold body temperature is too high.

  3. 3). The flow rate of the mold body is not enough.

  4. 4). The temperature on both sides of the mold body is inconsistent.

  5. 5). The bottle neck is too thick.


Solution:

  1. 1). The convex ring is clamped too tightly in the recess of the mold top plate, the size of the preform must be fixed when it is still hot, and it needs a gap of 0.25mm.

  2. 2). Check the mold body flow rate (insufficient flow rate leads to higher temperature), temperature (cooling water temperature or mold temperature machine temperature). The flow rate on both             sides of the mold body is inconsistent, resulting in different temperatures on both sides. If the temperature is different or too high, when the bottle is shaped after it comes out of the mold, the           neck will be crooked due to different shrinkage.

  3. 3). Mismatch between mouthpiece and mold.

  4. 4). If the bottle neck is too thick, increase the temperature of the area (increase the heating percentage of the area or increase the number of lamp tubes).


4. The Bottom Line is Blue  


Symptom: 

Pearlescent stripes along the cut line on the bottom, the areas where the pearlescent stripes are thinner on the secondary bottle than on the good bottle.


Factor:

1). The pre-blowing pressure is too high.

2). The extension is too slow.

3). The pre-blowing air is too early.


Solution:

1). During the pre-blowing, the bottle is inflated too quickly (this is often the fault of the pre-blowing solenoid valve, and high-pressure air leaks in during the pre-blowing).

2). The pre-blowing pressure is too high.

3). The control pressure of the extension cylinder is insufficient, the solenoid valve is dirty, the sealing ring of the control valve is worn or the coil reel is broken, resulting in air leakage.

4). There is resistance to the extension mechanical movement (the extension cylinder seal is worn or too dirty, the extension guide rail is not installed correctly or the linear bearing is worn).

5). The exhaust of the extension cylinder is blocked (the exhaust muffler is blocked or the air path is not smooth).

6). Adjust the angle of the pre-blowing air.


5. Bottom Damage  


Symptom:

There is often a small section of fine cracks at the place where the bottom accumulation is too thick, and it always passes through or is close to the pouring point.

Factor:

1). Mechanical reasons.

2). The temperature of the bottom of the preform is not enough (especially the bottle shape with a flat bottom of the mold).


Solution:

1). Check the gap between the stretch rod and the bottom of the mold (the gap is: 2/3 of the bottom thickness of the preform used)

2). Check the extended buffer.

3). Increase the heating percentage of the area where the bottom is located, and increase the number of lamp tubes in the area (the temperature at the bottom of the preform is low. When stretching, the               stretch rod runs against it towards the bottom, and cracks are formed at the bottom. But the temperature at the bottom cannot If it is too high, the bottom will be convex if it is too high).


6. The Threaded Part of The Bottle Mouth is Damaged


Symptom:

The bottle thread is damaged or the vent groove in the thread area is stretched unduely.


Factor:

1). Caused by mechanical reasons (the preform is sent into the mold cavity by the manipulator of the transfer arm. When the manipulator grips, the force on both sides of the preform thread area, and the               position of the manipulator is not accurate. When the manipulator takes the embryo from the embryo guide rail, it will be pinched. The thread of the bottle mouth. The bottle taking robot will also be                 pinched.).

2). The alignment between the mouthpiece and the mold is not good (the mouthpiece depends on the force of the spring to determine the position of the preform, which is not enough to correct the gap             between the two. When the blowing starts, there is a considerable impact. This impact can cause thread damage.).

3). The temperature in the threaded area of the bottle mouth is too high (when the temperature in the threaded area is too high, the exhaust groove in the threaded area is deformed by the tensile force.) In           this case, the support ring is usually deformed and upturned.


Solution:

1). Ensure that the adjustment of the manipulator of the transfer arm is accurate (synchronous adjustment of the manipulator and the main turntable, synchronous adjustment of the manipulator and the               furnace, and adjustment of the gap between the manipulator and the upper plane of the mold [embryo entry: 1mm, bottle exit: 0.7mm])

2). Align the mouthpiece and mold with special tools.

3). Adjust the distance of the cooling plate to protect the thread well or enhance the ventilation. Reduce the percentage of the first area, reduce the number of lamps in the first area, and raise the furnace               frame. (See the thread expansion section for some solutions).


7. The Liquid Level Drops Too Much After Filling  


Symptom:

Once the PET container is filled, the container itself should change as little as possible. And this change is called excessive creep.


Factor:

Containers should use as low a temperature as possible during the blowing process. When the temperature is too high, there is no pearlescent phenomenon on the container, but the maximum bidirectional stretching is required, so that the container lacks sufficient strength to resist expansion after filling. Bottles made at high temperatures are prone to bursting after expansion.


Solution:

The bottle generally has some visible pearlescent phenomenon at the end of the blow bottle. This means that the heating temperature should be set correctly when starting the equipment to avoid overheating or overcooling.


8. Burst  


Symptom:

Cracks occur at or near the bottom of the bottle, and some cracks are in the transition zone where the bottom of the bottle changes from thick to thin.


Factor:

There are several possibilities:

1). The material fails to reach its natural stretch limit during the blowing process, which will cause the container to undergo radial changes (creep) after filling, causing the bottom to crack. 

2). Wrinkles generated at the bottom burst during filling or within a period of time after filling.

3). The bottom of the bottle is too thin or too thick.

4). The IV value is low, and the bottle expands after filling, resulting in rupture.

5). The bottom transition zone should be damaged by external force after forming.

6). The concentration of lye in the chain lubricant is too high.


Solution:

The above factors:

1). See the previous section 'Bottom damage' for solution.

2). See the section 'Bottom creases' below.

     Observe more when blowing the bottle. If it is a fixed preform number, it is related to the quality of the preform.


9. Mold Line Flat (Flat Bottle)  


Symptom:

The parting line of the bottle in the vertical direction is flat, and there is a tendency to separate the mold under the blowing pressure.


Factor:

1). Since the bottle is blown in all directions, the applied air pressure will run outward along the ventilation hole (vent hole) of the clamping line. When the excess gas cannot be discharged in time, the 

     pressure gas will tend to separate the clamping mold. (The thin-layer material of the broken arm pushes into the exhaust hole during high-pressure blowing, causing blockage.)                              

2). The mold compensation air pipe is blocked or leaked, or the rubber ring of the mold shell is worn and leaked. As a result, the compensation pressure is too small.

3). The mold gap is too large

4). The positioning short pin and bushing of the mold clamping are worn.


Solution:

1). Slow down the high-pressure air supply, adjust the high-pressure blowing time, that is, reduce the high-pressure blowing time, but this will reduce the effective cooling time of the mold.

2). Drill several ventilation holes along the mold line (aperture: 0.5-0.7mm).

3). Check the size of the test mold compensation gas and whether there is any leakage, and replace it if necessary.

4). Adjust the mold closing gap (the gap is: 0.1-0.2mm). In the case of easy mold closing, minimize the mold clamping gap.

5). Check the wear of the clamping pin and bushing of the mold.


10. Wrinkles at The Bottom



Symptom:

The wrinkles are brought to the bottle by the bottom of the embryo, and the wrinkles may be inside or outside the bottle. This bottle may burst or break.


Factor:

1). External wrinkles:

A: The formation of external wrinkles is usually due to insufficient pre-blowing pressure, which pushes too much material to the bottom when stretching. 

B: The temperature at the bottom is too low, so that the material cannot be pulled apart during stretching and the material is pushed to the bottom.

2). Internal wrinkles are caused by overheating at the bottom of the preform or too late pre-blowing after stretching begins.


Solution:

1). Adjust the pre-blowing pressure to ensure that the pre-blowing pressure is good at each blowing station.

2). The temperature at the bottom of the preform should not be too low.

3). The temperature at the bottom of the preform should not be too high.

4). Make sure that the delay between the start of stretching and the pre-blowing air is not too long.


11. Wrinkles in The Bottleneck  


Symptom:

Inner folds are often found at 5-8 mm below the convex ring, showing an obvious ring shape, and there are obvious creases on the outside when touched by hand


Factor:

Both are related to the fact that the preform is stretched too easily from the thinner end of the cone segment. In severe cases, the stretching will start from the parallel segment below the convex ring. When the preform is stretched, it will gradually become colder as the stretch rod goes down. , and the second part of the material is very thin, it will be cold quickly. Natural wrinkles are produced during the blowing process.


Solution:

1). Readjust the position of the hot spot so that it is close to the main body of the preform.

2). Adjust the pre-blowing time to make sure it is not too late. Check whether the pre-blowing solenoid valve is normal.

3). Mouthpiece malfunction. This is to check whether the blowing nozzle cylinder seals, diffusers, springs, solenoid valves and fixing sleeves are running smoothly up and down (these will cause the blowing             nozzle to run slowly).

4). The material in the area is very thin. Increase the material thickness in the zone (decrease the temperature in the zone or increase the temperature in the zone where the bottle is thicker).


12. Bottleneck Accumulation  


Symptom:

Bottleneck accumulation is often found in wavy stripes at 5-8mm below the convex ring, and the convex ring is irregular or ova


Factor:

When the preform is sent from the conveying arm to the mold cavity, it will be cooled first when it meets the cooled mold cavity, or the pre-blown air is too early during stretching, and the preform will be stretched downward with the stretching rod during stretching. form.


Solution:

1). The pre-blowing pressure is too high.

2). The pre-blowing time is too early.

3). The temperature in the first zone is not enough (increase the heating percentage of the first zone or increase the number of its lamp tubes).

4). The light stand is too high, adjust the position of the light stand.

5). The temperature in the second zone is too high or the temperature in other zones is too high (this is to adjust the temperature of each zone according to the actual partition weight and thickness of the             bottle to reduce the bottleneck material).


13. Off-Center  


Symptom:

The bottom structure of the bottle is not concentric with the container, and in severe cases, the bottom corner will be whitened. The bottom of this bottle has poor stress and is prone to cracks or bursts.


Factor:

This problem is related to two points. To recognize which point needs to observe the position of the stretching point of the stretch rod. If the position of the stretch point is off-center from the pour point on the bottom of the preform, the stretch rod is not aligned with the mold. If the position of the stretch point is concentric with the pouring point of the preform, it means that the stretch rod, although positioned correctly, has shifted during the blowing process


Solution:

A. Mechanical reasons:

1). The preform is not aligned with the mold.

2). Mismatch between mouthpiece and mold.

3). The preform and the upper part of the mold are too tight.

4). The stretch rod is bow-shaped.

5). The sliding guide rail or linear bearing of the stretch rod is abnormal.

6). The adjustment of the buffer pad of the stretching rod is not suitable, resulting in a slow down of the stretching or the inability to completely drop to the end.


B. Electrical failure:

1). The pre-blowing pressure is too high.

2). The pre-blowing time is too early

3). The stretch rod solenoid valve is dirty, the control valve seal is worn or the coil reel is broken.

4). Stretching cylinder exhaust blockage (muffler blockage).

5). The control pressure of the stretching cylinder is low (gas circuit turning loss)


14. Pearlescent - Whitish Bottom Corner  


Symptom:

Pearlescence can occur anywhere on the bottle, but is most common at the bottom corners. A small amount of bluishness in the corners of the bottom of the bottle is normal and indicates that the blowing process has achieved maximum biaxial stretching.

Factor:

Pearlescence is a direct result of stretching beyond the natural stretching limit. In fact, the microstructure of the material is stretched and torn. The material in this area is significantly thinner.


Solution:

Because the material in this area is relatively thin, it is better to increase the material in this area. If the material in this area is sufficient, consider the reasons:

1). Make sure not to be biased.

2). Extend the pre-blowing time and pre-blowing air time. Reduce pre-blowing pressure.

3). Make sure that the extension gap is correct (2/3 of the bottom thickness of the blown preform). Too much gap can cause whitishness.

4). Ensure that the extension runs flexibly and smoothly (if the extension runs slowly up and down, it will produce whitishness).

5). The temperature of the preform is low or the overall temperature of the preform is low during heating.


15. Albinism (Bottle Body, Bottle Shoulder)  



Symptom:

Blooming is common in bottle blowing, the most common being whitening of the bottom corner (this has been mentioned in the previous section). For whitening, it is first necessary to be able to distinguish whether it is high-temperature whitening or low-temperature whitening. Low-temperature whitening is foggy and opaque. High temperature whitening is reflective pearlescent color, transparent.


Factor:

A. Low temperature whitening - increase the temperature of the area or increase the overall heating percentage and preform temperature.

B. High temperature whitening - reduce the temperature of the area or the overall heating percentage and preform temperature.

C. Another situation is that if the quality of the bottles in other blowing stations is good, but the bottles in individual blowing stations are white, two aspects should be considered:

1). The pre-blowing pressure is small.

2). Mouthpiece leaks. (The mouthpiece is higher or the heights on both sides of the mold are different)

     In this case, the albinism usually occurs at the waist of the bottle or the body of the bottle is bleached from top to bottom.


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