Bottle Blowing Problem Analysis | How Many Problems Have You Encountered in Bottle Blowing?

Fifteen Common Issues in Blow Moulding (Part II)

Faygo Union & Suzhou Yuda

7 Common Questions in This Issue

01 Moulding line flattening (flat bottle)

Symptoms:

The moulding line on the vertical side of the bottle appears flat, and there is a tendency for the mould to separate under the pressure of bottle blowing.

Factors:

1. Since the bottle is blown from all sides, the applied air pressure will escape through the ventilation holes (exhaust holes) along the moulding line. When excess gas cannot be discharged in time, the pressure gas will tend to separate the moulding. (The thin layer of material on the broken arm is pushed into the exhaust hole by high-pressure air, causing blockage.)
2. Blockage or leakage in the mould compensation air pipe, or wear and tear on the mould shell rubber ring causing air leakage. This results in insufficient compensation pressure.
3. Excessive mould gap.
4. Wear of the mould closing positioning pin and bushing.

Solution:

1. Reduce the high-pressure air supply rate and adjust the high-pressure blowing time, i.e., decrease the high-pressure blowing duration. However, this will reduce the effective cooling time of the mould.
2.  Drill additional ventilation holes along the mould closing line (hole diameter: 0.5–0.7 mm).
3. Inspect and test the size of the mould compensation air and check for leaks; replace if necessary.
4. Adjust the mould clamping gap (gap range: 0.1–0.2 mm). In cases where clamping is slightly easier, minimise the clamping gap as much as possible.
5.  Inspect the wear of the mould clamping locating pins and bushings.

02 Bottom wrinkles (commonly known as ‘volcanoes’)

Symptoms:

Creases are caused by the embryo base and may appear inside or outside the bottle. These bottles are prone to explosion or breakage.

Factors:

1.External wrinkles:

A: External wrinkles are usually caused by insufficient pre-blow pressure, which pushes excess material to the bottom during stretching.

B: The bottom temperature is too low, preventing the material from being stretched and pushing it to the bottom.

2. Internal wrinkles are caused by overheating of the bottom of the preform or delayed pre-blow after stretching begins.

Solution:

1. Adjust the pre-blow pressure to ensure that the pre-blow pressure is adequate at each blow moulding station.
2. Ensure that the bottom temperature of the preform is not too low.
3. Ensure that the bottom temperature of the preform is not too high.
4. Ensure that the delay between the start of self-stretching and the pre-blow air intake is not too long.

03 Neck wrinkles (commonly known as ‘neck bands’)

Symptoms:

Internal folds are commonly found 5–8 mm below the convex ring, forming a distinct ring shape, and there are obvious creases when touched externally.

Factors:

1. This is related to excessive stretching of the thinner end of the cone section of the preform. In severe cases, stretching will begin from the parallel section below the convex ring. During stretching, the preform gradually cools as the stretching rod moves downward, and the material at this point is very thin, so it cools quickly. Natural wrinkles are produced during the blow moulding process.

Solution:

1. Re-adjust the hot spot position to bring it closer to the main body of the bottle blank.
2. Adjust the pre-blow air intake time to ensure it is not too late. Check if the pre-blow solenoid valve is functioning normally.
3. Caused by a blow nozzle malfunction. This requires checking the blow nozzle cylinder seals, distributor, spring, solenoid valve, and whether the upper and lower movements of the mounting sleeve are smooth (these can all cause the blow nozzle to operate slowly).
4. The material in the relevant area is too thin. Increase the material thickness in the relevant area (lower the temperature in the relevant area or raise the temperature in the area where the bottle is thicker).

04 Bottleneck accumulation (commonly known as ‘flower neck’)

Symptoms:

 Bottleneck accumulation commonly occurs 5–8 mm below the convex ring, with wave-like stripes, and the convex ring is irregular or oval in shape.

Factors:

When the preform is transferred to the mould cavity by the transfer arm, it comes into contact with the cooled mould cavity and cools down first. Alternatively, if the preform is pre-inflated too early during stretching, it will form as it is stretched downward by the stretching rod during the stretching process.

Solution:

1. Pre-blowing pressure is too high.
2. Pre-blowing air intake time is too early.
3. Zone 1 temperature is insufficient (increase the heating percentage of Zone 1 or increase the number of lamps).
4. The lamp frame is too high; adjust the lamp frame position.
5. Zone 2 temperature is too high or temperatures in other zones are too high (this requires adjusting the temperatures of each zone based on the actual weight and thickness of the bottle sections to reduce material at the bottle neck).

05 Eccentricity

Symptoms:

The bottom structure of the bottle is not concentric with the container, and in severe cases, white discolouration may form at the bottom corners. This type of bottle bottom has poor stress resistance and is prone to cracking or bursting.

Factors:

This issue is related to two points. To identify which point is relevant, observe the position of the stretch rod’s stretching point. If the stretching point is offset from the sprue point at the bottom of the preform, it indicates that the stretch rod is not aligned with the mould. If the stretching point is concentric with the sprue point, it indicates that although the stretch rod is correctly positioned, it has shifted during the blow moulding process.

Solution:

1. Mechanical causes
2. The preform is not aligned with the mould.
3. The blow nozzle is not aligned with the mould.
4. The preform is too tight against the upper part of the mould.
5. The stretching rod is bowed.
6. The stretching rod sliding guide or linear bearing is abnormal.
7. The stretching rod buffer pad is not adjusted properly, causing the stretching to slow down or fail to descend completely to the bottom.

• Electrical faults
• Pre-blow pressure too high.
• Pre-blow intake time too early.
• Stretching rod solenoid valve dirty, control valve seal worn or coil shaft broken.
• Stretching cylinder exhaust blocked (silencer blocked).
• Stretching cylinder control pressure too low (air path turning loss).

06 Pearlescent — White Base Angle

Symptoms:

Pearlescence occurs anywhere on the bottle, but is most common at the corners of the bottom. A slight blue tint at the corners of the bottom is normal and indicates that the bottle blowing process achieved maximum bidirectional stretching.

Factors:

Pearlescence is a direct result of stretching beyond the natural stretching limit. It is actually caused by the microstructure of the material being stretched and torn. The material in this area is significantly thinner.

Solution:

Since the material in this area is relatively thin, it is advisable to increase the material in this area. If the material in this area is already sufficient, consider the following reasons:

1. Ensure that there is no eccentricity.
2. Extend the pre-blowing time and pre-blowing air intake time. Reduce the pre-blowing pressure.
3. Ensure the extension gap is correct (two-thirds of the thickness of the blown bottle preform bottom). A gap that is too large can cause whitening.
4. Ensure the extension operation is smooth and flexible (slow up/down movement of the extension can cause whitening).
5. Caused by low bottle preform temperature or overall low temperature during heating.

07 Bleaching (Bottle Body, Bottle Shoulder)

Symptoms:

Whitening is commonly seen in blow moulding, with the most common type being bottom corner whitening (as mentioned in the previous section). When dealing with whitening, it is important to first distinguish between high-temperature whitening and low-temperature whitening. Low-temperature whitening appears foggy and opaque, while high-temperature whitening appears reflective and pearlescent, with transparency.

Factors:

1. Low-temperature whitening — Increase the temperature of the area or increase the overall heating percentage and bottle preform temperature.
2. High-temperature whitening — Decrease the temperature of the area or decrease the overall heating percentage and bottle preform temperature.
3. In addition, if the bottles from other blowing stations are of good quality, but bottles from individual blowing stations are whitening, two aspects should be considered.

1. Adjust the heating process for low-temperature whitening treatment:

Increase the heating furnace temperature (especially in the bottom corner area) to ensure the material reaches the uniform temperature required for blow moulding (PET bottles typically need to reach above the glass transition temperature of 95-110°C). Inspect the infrared heating lamps for ageing or uneven power distribution, and replace or rearrange them as necessary. Optimise pre-blow parameters: increase pre-blow pressure (0.8-1.2 MPa) or extend pre-blow time to ensure the preform is fully stretched. Ensure that the pre-blowing timing aligns with the preform temperature to avoid insufficient stretching due to premature blowing. Mould temperature control: Appropriately increase the temperature in the bottom corner area of the mould (e.g., by increasing the flow rate of cooling water channels or adjusting the water temperature to 10–25°C) to prevent sudden cooling of the material. Inspect the mould cooling channels for blockages and ensure uniform heat dissipation.

• High-temperature whitening treatment Reduce heating temperature: Lower the heating furnace temperature (especially in the bottom corner area) to prevent material overheating and degradation. Use a thermocouple to monitor the actual temperature of the blank material and ensure it does not exceed the recommended range for the material (PET typically does not exceed 120°C). Shorten heating time: Reduce the dwell time of the blank material in the heating zone, or adjust the rotation speed to avoid local overheating. Optimise high-pressure blowing: Advance the timing of high-pressure blowing to avoid prolonged exposure of the material to high temperatures. Check Whether the blowing pressure (typically 25–40 bar) is too high, which could cause molecular chain rupture.

This issue summarises seven common issues with blow moulding. Combined with the eight common issues from the previous issue, has this been helpful to you?

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Note: The information is sourced from the internet. Different machine models may have slightly different causes and solutions. This sharing is for reference only.

Jiangsu Faygo Union Machinery Co., Ltd.

COMPANY INTRODUXTION

Jiangsu Faygo Union Machinery Co., Ltd. is a high-tech enterprise specializing in the research, manufacturing, production, and sales of plastic machinery equipment. It is a private science and technology enterprise in Jiangsu Province, a specialized and sophisticated enterprise in Jiangsu Province, and a gazelle enterprise. The subsidiaries of Faygo Union Group, Suzhou Yuda Robot Co., Ltd. and Suzhou Dayu Intelligent Equipment Co., Ltd., specialize in manufacturing blow molding machines, filling production lines, blow-fill-capping integrated machines, robotic automation, AGV, and other equipment. The company holds 15 national invention patents and 10 utility model patents.

● Plastic extrusion equipment: plastic pipe extrusion production lines, plastic profile extrusion production lines, plastic sheet and plate production lines, as well as various auxiliary equipment supporting them; PE film, PET bottle recycling production lines and granulation production lines; biodegradable granulators.

● Blow molding machines: linear high-speed blow molding machines, turnover and transfer blow molding machines, semi-automatic blow molding machines, linear blow-fill-crimp integrated machines, rotary blow-fill-crimp integrated machines.

● Bottled water filling lines: Provide comprehensive bottled water filling line solutions and services to customers in countries around the world.

NEW INDUSTRIES, NEW FACTORIES

●Linear blow – fill – capping integrated machine

It is an automated production line equipment integrating three major functions of bottle blowing, filling and capping.

● Rotary blow-fill-capping all-in-one machine

 It features high output. The servo synchronous control technology ensures seamless connection of each unit, greatly improving the overall line efficiency.

Suzhou Yuda Robotics Co., Ltd.

COMPANY INTRODUCTION

Suzhou Yuda Robot Co., Ltd. is a professional factory engaged in the research, manufacture and production of intelligent automation system, automatic and semi-automatic blowing machine production line. We have all kinds of speed models of automatic blowing machine, semi-automatic blowing machine production line and PET, PE, PC material of various types of bottles supporting the cutting machine, to and AGV robots, intelligent robotic arm, to meet the diverse needs of customers.

The company has always insisted on the concept of “good machine and good people”, attaching importance to the research and development of new technologies, and constantly improving and upgrading the level of quality management, “high quality products, favourable price, excellent after-sales service” is the company’s consistent commitment to our customers.

ENTERPRISE REAL SCENE

● Yuda Bottle Blowing Machine
Professional PET Bottle Blowing Machine Manufacturer

High-speed blow molding machines, semi-automatic blow molding machines, and fully automatic blow molding machines.

● Yuda Robot Provides one-stop intelligent robot solutions

Industrial Internet of Things, centralized control and management of workshops and factories, MES system, AGV; system integration of industrial robot welding, loading and unloading, grinding, etc.; intelligent welding production lines, intelligent warehousing and logistics transportation.

 AGV can realize the automatic receiving, sending, transfer, stacking, storage, etc. of raw materials, parts, and finished products. It is applicable to end users in industries such as new energy, manufacturing, e-commerce, 3C, pharmaceuticals, food packaging, printing, and agriculture.

Suzhou Dayu Intelligent Equipment Co., Ltd.

COMPANY INTRODUCTION

Suzhou Dayu Intelligent Equipment Co., Ltd. was established in 2024. It is a manufacturing plant focusing on the research, development and production of high-end packaging machines. The company is located in Zhangjiagang Development Zone Industrial Park. The factory covers an area of more than 5,000m³ and integrates R&D center, production workshop and testing base. It is committed to providing global customers with intelligent and efficient liquid packaging overall solutions.

ENTERPRISE REAL SCENE

●Blow – fill – capping integrated machine

1. Full 3D design, dynamic simulation testing
2. Fast image recognition and detection technology
3.  High – efficiency and energy – saving preform heating system
4.  High – speed and high – precision bottle blowing process
5. Newly designed small and medium – sized mold base bottle blowing station
6. User – friendly human – machine operation interface

●PET bottled water production line

High-quality equipment, comprehensive services, and a strong turnkey service capability for the entire factory. Dayu Intelligent Equipment helps customers achieve efficient equipment operation, technological innovation and upgrading, easy bottle type replacement, and low-cost maintenance. So far, it has closely cooperated with well-known enterprises in more than 50 countries and regions around the world, working hand in hand.