[Industry knowledge sharing]Common quality defects in blowing process of plastic bottles (Part 2)

Introduction: Blowing bottles are one of the main plastic containers used in cosmetics packaging. The molding methods include injection-blow, stretch-blow, extrusion-blow, etc. Common blowing bottle materials are HDPE, LLDPE, LDPE, PP, EVA, PETG, PETP, etc. Blowing bottles are widely used in skincare and hair care products. This article analyzes common quality defects in the blowing process of plastic bottles, providing reference for Chamsmetic’s customers.

 

VI. Damaged bottle mouth threads:

Symptoms:

Damage to the bottle mouth threads or excessive stretching of the exhaust groove at the thread area.

 

Causes:

1)Mechanical reasons (the bottle blanks are conveyed into the mold cavity by a conveying arm robot. When the robot clamps the bottle blanks, the two sides of the thread area are subjected to force. When the robot picks up the blanks from the blank entry guide rail, it may clamp the bottle mouth threads. The bottle picking robot may also clamp them.)

2)Poor alignment between the blowing nozzle and the mold (The blowing nozzle relies on the force of the spring to determine the position of the bottle blank, which is not sufficient to correct the misalignment between the two. At the beginning of blowing, there is considerable impact force, which can cause thread damage)

3)Excessive temperature in the thread area (When the temperature in the thread area is too high, the exhaust groove in the thread area is subjected to tensile force and deformed.) This situation is generally manifested as the deformation of the support ring.

 

Solutions:

1)Ensure accurate adjustment of the conveying arm robot (synchronize the adjustment between the robot and the main turntable, synchronize the adjustment between the robot and the furnace, and adjust the gap between the mechanical hand and the mold plane [entry: 1mm, bottle exit: 0.7mm])

2)Use a special tool to align the blowing nozzle and mold.

3)Adjust the distance of the cooling plate to protect the thread well or increase ventilation. Reduce the percentage of Zone 1, reduce the number of lamps in Zone 1, and increase the height of the furnace rack. (Some solutions are found in the thread expansion section.)

 

Wheat straw bottles1-Chamsmetic

 

VII. Excessive liquid level drop after filling:

Symptoms:

Once PET containers are filled, the container should preferably change as little as possible. This change is called excessive creep.

 

Causes:

The container should be blown at a low temperature as much as possible during the blowing process. At high temperatures, there is no pearlescent phenomenon on the container, but it needs to be biaxially stretched to the maximum so that the container lacks sufficient strength to resist expansion after filling. Bottles made at high temperatures are prone to burst after swelling.

 

Solutions:

Bottles generally show some visible pearlescent phenomenon at the end of blowing. Therefore, the heating temperature should be correctly set when starting the equipment to avoid overheating or overcooling during startup.

 

VIII. Bursting:

Symptoms:

The bottom or near the bottom of the bottle breaks, and some breaks occur in the transition zone from a thick to a thin bottom.

 

Causes:

There are several possible reasons.

 

1)The material did not reach its natural stretch limit during blowing, causing radial changes (creep) in the container after filling and the bottom cracking due to lack of sufficient strength.

2)Creases formed at the bottom burst during or after filling.

3)The bottom is too thick or too thin.

4)The IV value is too low and the bottle swells after filling, leading to rupture.

5)The bottom transitional zone was damaged by external forces after forming.

6)The alkaline solution concentration of the chain lubricant is too high.

 

Solutions:

Solution 1 of the previous “bottom damage” section solves the above problems.

Solution 2 is found in the following “Bottom Wrinkles” section. When blowing bottles, observe more and if the blank number is fixed, it is related to the quality of the bottle blank.

 

ECO dispenser bottles-Chamsmetic

 

IX. Flat seam line (flat bottle):

Symptoms:

The bottle’s vertical seam line appears flat and has a tendency to separate the mold under blowing pressure.

 

Causes:

1)Because the bottle is blown in all directions, the applied air pressure will flow out through the ventilated hole (exhaust hole) along the seam line, and when excess gas cannot be discharged in time, the pressure gas tends to separate the mold (the thin material in the broken arm is pressed into the exhaust vent during high-pressure blowing, causing blockage).

2)The compensation air duct of the mold is blocked or leaking, or the mold shell sealing ring is worn and air leaks, resulting in insufficient compensation pressure.

3)The gap between the molds is too large.

4)The short positioning pins and liner sleeves of the mold are worn.

 

Solutions:

1)Reduce the high-pressure supply gas rate and adjust the high-pressure blowing time, that is, reduce the blowing time but this will also reduce the effective cooling time of the mold.

2)Drill a few more ventilation holes along the seam line (aperture: 0.5-0.7mm).

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

4)Adjust the mold clamping gap (gap at 0.1-0.2mm). In the case of relatively easy mold clamping, try to minimize the mold clamping gap.

5)Check the wear of the short positioning pins and liner sleeves of the mold.

 

X. Bottom wrinkle (commonly known as “volcano mouth”):

Symptoms:

Wrinkles are brought to the bottle by the bottom. These bottles are prone to bursting or cracking.

 

Causes:

External wrinkles:

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

B: The bottom temperature is too low, so it cannot be stretched and pushed toward the bottom during stretching.

 

Internal wrinkles are caused by the bottom of the bottle being overheated or pre-blowing too late.

 

Solutions:

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

2)Do not let the bottom temperature be too low.

3)Do not let the bottom temperature be too high.

4)Ensure that there is no delay between self-stretching and pre-blowing.

 

Wheat straw bottle finished product display-Chamsmetic

 

As a leading eco-conscious brand, Chamsmetic provides innovative and sustainable solutions for cosmetic packaging. Our wheat straw bottles have become increasingly popular among environmentally conscious consumers. Our commitment to quality ensures that our bottles meet the highest standards in the industry. Our blowing technology is constantly evolving to eliminate common quality defects in plastic bottles. With Chamsmetic, you can trust that your products are packaged in the most ethical and eco-friendly way possible.