Industry Knowledge Sharing: Common Quality Defects in Blow Molding Processed Products (Part 3)

Introduction:

Welcome to Chamsmetic, a leading brand specializing in the creation of eco-friendly and biodegradable containers and packaging. With over 15 years of experience, we are dedicated to providing high-quality solutions for our valued customers. In this article, we will discuss the common quality defects found in blow molding processed products and their respective solutions.

 

In the previous two articles, we shared the top ten common quality defects in blow molding processed products and their solutions. Today, Chamsmetic would like to share the last five quality defects and their solutions in blow molding processed products.

 

Eleven: Neck Wrinkles (Commonly Known as ‘Ring Wrinkles’)

Symptoms:

Internal wrinkles are commonly seen 5-8mm below the convex ring, forming a distinct circular shape, with noticeable creases on the outer surface when touched.

 

Factors:

It is related to excessive stretching of the thinner end of the parison cone. In severe cases, stretching starts from the parallel section below the convex ring. During the stretching process, the parison gradually cools down along with the downward movement of the stretching rod. The material at this location, being thin, cools down quickly, leading to natural wrinkling during blow molding.

 

Solutions:

1)Readjust the position of the hot spot to make it closer to the main body of the parison.

2)Adjust the timing of pre-blowing and ensure it is not too late. Check if the electromagnetic valve of pre-blowing is functioning properly.

3)Check for faults in the blow nozzle. Inspect the seals, diffuser, spring, electromagnetic valve, and smooth operation of the fixing sleeve of the blow nozzle (any of these can cause slow operation of the blow nozzle).

4)The material at that location is too thin. Increase the thickness of the material at that location (lower the temperature or raise the temperature of the thicker section of the bottle).

 

Biodegradable Pump Bottles-Chamsmetic

 

Twelve: Neck Accumulation (Commonly Known as ‘Flower Neck’)

Symptoms:

Neck accumulation is commonly seen in the wave-like stripes 5-8mm below the convex ring, with irregular or elliptical shape of the convex ring.

 

Factors:

When the parison encounters a cooled mold cavity during the transfer from the transfer arm to the mold cavity, it cools down prematurely. Or, if the pre-blowing is done too early during stretching, the parison will stretch downward along with the stretching rod and form neck accumulation.

 

Solutions:

1)Reduce the pressure of pre-blowing.

2)Delay the timing of pre-blowing and ensure it is not done too early.

3)Increase the temperature of Zone 1 (raise the heating percentage or increase the number of lamps).

4)Adjust the position of the lamp holder if it is too high.

5)Excessive temperature in Zone 2 or other zones (adjust the temperature of each zone according to the actual weight and thickness of the bottle, in order to reduce the material at the neck).

 

Thirteen: Eccentricity

Symptoms:

The bottom structure of the bottle is not aligned with the container, and in severe cases, it can cause whitening of the bottom corners. This type of bottle bottom has weaker stress resistance and is prone to cracking or bursting.

 

Factors:

This problem is related to two points. To determine which point is causing the issue, observe the position of the stretching rod’s stretching point. If the stretching point is eccentric to the pouring point at the bottom of the parison, it indicates that the stretching rod is misaligned with the mold. If the stretching point is concentric with the pouring point, it indicates that although the stretching rod is properly positioned, it has shifted during the blow molding process.

 

Solutions:

A. Mechanical Reasons

1)Misalignment between the parison and the mold.

2)Misalignment between the blow nozzle and the mold.

3)Excessive tightness between the parison and the upper mold.

4)Deformation of the stretching rod.

5)Abnormal sliding guide or linear bearing of the stretching rod.

6)Inappropriate adjustment of the buffer pad of the stretching rod, causing slow descent or incomplete lowering.

 

B. Electrical Malfunctions

1)Excessive pressure during pre-blowing.

2)Pre-blowing done too early.

3)Contamination of the electromagnetic valve of the stretching rod, worn-out seals of the control valve, or a broken coil.

4)Blockage in the exhaust of the stretching cylinder (muffler blockage).

5)Low control pressure of the stretching cylinder (air loss due to bends in the air circuit).

 

 

 

Fourteen: Pearlescence – Whitening of Bottom Corners

Symptoms:

Pearlescence can be observed in any part of the bottle but is most commonly seen at the bottom corners. A small amount of blue whitening in the bottom corners is considered normal, indicating maximum biaxial stretching during blow molding.

 

Factors:

Pearlescence is a direct result of exceeding the natural stretching limit. It is caused by the microscopic tearing of the material’s structure due to stretching. The material in this area is significantly thinner.

 

Solutions:

Since the material in this area is thinner, it is best to increase the material in this area. If the material in this area is already sufficient, consider the following reasons:

 

1)Ensure there is no eccentricity.

2)Extend the pre-blowing time and reduce the pre-blowing pressure.

3)Ensure the correct stretching gap (2/3 of the bottom thickness of the parison). Excessive gap can cause whitening.

4)Ensure smooth and flexible stretching operation (slow stretching causes whitening).

5)Insufficient overall temperature of the parison or insufficient heating during the heating process.

 

Fifteen: Whitening (Bottle Body, Bottle Shoulder)

Symptoms:

Whitening is commonly seen in blow molding, most frequently at the bottom corners (which was discussed in the previous section). When dealing with whitening, it is important to differentiate between high-temperature whitening and low-temperature whitening. Low-temperature whitening appears as a hazy, opaque white, while high-temperature whitening appears as reflective iridescence.

 

Factors:

A. Low-temperature whitening – Increase the temperature of the corresponding zone or raise the overall heating percentage and parison temperature.

B. High-temperature whitening – Decrease the temperature of the corresponding zone or decrease the overall heating percentage and parison temperature.

 

C. In some cases, if bottles from other blow molding stations have good quality but individual bottles from a specific station show whitening, consider two aspects:

1)Insufficient pre-blowing pressure.

2)Air leakage from the blow nozzle (either the blow nozzle is too high or there is uneven height on both sides of the mold).

 

This situation usually manifests as a continuous whitening from the waist to the body of the bottle.

 

At Chamsmetic, we understand the importance of delivering flawless products to our customers. By addressing these common quality defects and implementing the recommended solutions, we ensure that our blow molding processed products meet the highest standards. Trust Chamsmetic for all your eco-friendly packaging needs.