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Troubleshooting Common Blow Molding Defects in Plastic Production

Views: 7     Author: Site Editor     Publish Time: 18-05-2024      Origin: Site

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Troubleshooting Common Blow Molding Defects in Plastic Production

Extrusion blow molding is the preferred technology for producing various plastic products such as HDPE chemical barrels, edible oil bottles, stacked jerry cans and containers for beverages, chemicals or pharmaceuticals, IBC tanks, etc. The process is favored for its cost-effectiveness and high throughput, resulting in a product that is not only durable but also of high quality. Therefore identifying the source of blow molding defects and knowing the appropriate remedies are essential skills.

This comprehensive blow molding troubleshooting guide will teach you about the most common defects associated with HDPE extrusion blow molding, their possible causes, and provide solutions to help you get the best plastic products on the market.

Common Defects and Their Causes

Blow molding defects can be broadly categorized into issues related to the mold design, material selection, and the blow molding machine settings. Common defects include leakage, rocker bottoms, tearing at pinch-off, and various surface wall defects.

Mastering the nuances of blow molding defects is an important task that cannot be ignored. In this way, when a production failure or problem occurs, an effective solution can be quickly found to ensure the production efficiency of your factory.

1. Plastic product leakage

Reasons for leakage:

1. Poor quality raw materials: Using substandard raw materials may lead to unstable product quality and prone to breakage.

2. Improper extrusion temperature: Extrusion temperature that is too high or too low may lead to uneven internal structure of the product, thus affecting the strength and durability of the product.

3. The extrusion pressure is too high or too low: Improper pressure control during the extrusion process can also lead to uneven wall thickness of the product and even defects such as bubbles, which can lead to rupture.

4. Mold design issues: Unreasonable mold design or mold damage may lead to incomplete product structure and prone to rupture.

5. Improper cooling method: Insufficient cooling or the influence of the external environment during the cooling process may also lead to uneven internal stress in the product, thereby affecting the quality of the product.


1. Strictly control the quality of raw materials: select high-quality raw materials and ensure that the ratio and quality of raw materials meet standards.

2. Precisely control the extrusion temperature and pressure: According to the requirements of the product, accurately control the extrusion temperature and pressure to ensure a uniform internal structure of the product.

3. Optimize mold design: Optimize the mold structure to ensure uniform wall thickness of the product and avoid structural defects.

4. Improve the cooling system: Optimize the cooling system to ensure that the product can be heated and cooled evenly during the cooling process and reduce internal stress.

5. Strengthen production process monitoring: Strengthen the monitoring and management of the blow molding production process, discover problems in a timely manner and take measures to solve them to ensure stable product quality.

2.The bottom of the blow molded product is unstable

1. The preform is too cold or over-stretched: This may cause the bottom to turn white because the preform is unevenly cooled or over-stretched.

The solution is to adjust the pre-blowing time or pre-blowing pressure to ensure that the preform temperature and stretching degree are appropriate.

2. Too much material at the bottom of the bottle or too late pre-blowing: This may cause a magnifying glass phenomenon at the bottom of the bottle, that is, the bottom of the bottle is thicker in the middle and thinner around the edges.

The solution is to reduce the amount of bottle bottom material and/or advance the pre-blowing time and increase the pre-blowing pressure.

3. The bottom temperature is too high or not cooled well: This may cause wrinkles inside the bottom of the bottle.

The solution is to check the cooling system to ensure that the cooling effect is good, and adjust the pre-blow time and pressure.

4. Mold design issues: If the number of vent holes at the bottom of the mold is insufficient, uneven wall thickness of the product may result.

The solution is to modify the mold design, increase the number of vent holes or replace the mold with a better quality one.

5. Unreasonable design of the stretch rod: If the design of the stretch rod head does not match the shape of the bottom of the blank, or the stretch rod does not reach the bottom, it may cause the bottom to be unstable.

The solution is to replace the stretching rod with a suitable one and adjust its position to fit the base of the embryo.

6. Product temperature is too high: During the melting and heating process of raw materials, if the bottom is heated too high, it may cause the bottom to burst.

The solution is to adjust the heating lamp temperature to the appropriate temperature and increase the cooling time.

7. Insufficient air blowing pressure or too short air blowing time: This may cause insufficient force time at the bottom of the embryo and the bottom will not be formed.

The solution is to check whether the high-pressure supply meets the standards and adjust the blowing time and pressure appropriately.

8. Structural design defects of the product itself: If the bottom of the product is improperly designed, it may lead to poor forming.

The solution is to optimize the design structure of the bottom of the product.

9. Uneven cooling: Uneven cooling may lead to problems such as edge warping, bending, and bottleneck skew in the finished product.

The solution is to set the temperature control of the mold and adjust the mold temperature to suit the characteristics of the raw material.

3. Jerry can surface defects

Surface wall defects of blow molded products, such as small black spots, horizontal ring lines, vertical stripes, wall bubbles, rough, corrugated or "orange peel" surfaces, etc., are common problems that affect the appearance and quality of the product. The following are possible causes of these defects and their corresponding solutions:

1. Little black dot:

   - Cause: It may be due to poor exhaust of the mold, resulting in the mixing of air and melt to form black spots; or there may be impurities in the mold cavity.

   - Solution: Sandblast the mold cavity or add vents to ensure the mold is clean.

2. Horizontal circular line:

   - Cause: It may be that the inflation ratio of the parison is too small, causing the parison to fail to fully expand to form a ring line.

   - Solution: Replace the mold sleeve and mold core to increase the parison inflation ratio.

3. Vertical stripes:

   - Cause: The die opening is dirty or there are burrs or chips on the edges of the die sleeve and core, causing material to deposit and form stripes.

   - Solution: Use a copper knife to clean the die mouth and trim the die.

4. Wall Bubbles:

   - Cause: It may be that the inflation air pressure is insufficient or the inflation speed is slow, resulting in poor plasticization of the parison and melt rupture.

   - Solution: Increase the blowing air pressure, clean the compressed air channel, and check whether the blowing rod is leaking.

5. Rough:

   - Cause: The surface of the mold is dirty or condensation occurs in the mold cavity.

   - Solution: Repair the mold, adjust the mold cooling temperature to above the "dew point", and ensure that the mold surface is clean.

6. Ripple:

   - Cause: It may be that the volume of the blow molded product is reduced and the wall thickness of the parison is increased, resulting in thickening of the wall of the product.

   - Solution: Adjust the program control device to reduce the parison wall thickness; increase the parison melt temperature and reduce the parison mold-leaving expansion ratio.

7. “Orange peel” surface:

   - Cause: Poor exhaust of the mold or insufficient inflation pressure, resulting in orange peel-like patterns or pitting on the surface.

   - Solution: Sandblast the mold parison, add vents, and increase the inflation pressure.

4.Uneven wall thickness

1. Mold design issues:

   - Reason: The design of the mold cooling system is unreasonable, resulting in inconsistent cooling rates.

   - Solution: Redesign the mold cooling system to ensure uniform distribution of cooling medium and improve cooling efficiency.

2. Improper control of parison thickness:

   - Reason: The melt distribution of the extruder is uneven, resulting in inconsistent parison thickness.

   - Solution: Adjust extruder parameters such as melt temperature, pressure and speed to ensure even melt distribution.

3. Raw material quality issues:

   - Reason: The raw materials used have inconsistent fluidity or contain impurities, which affects the uniformity of the parison.

   - Solution: Use high-quality raw materials and remove impurities through screening and filtration systems.

4. Uneven cooling of the parison:

   - Reason: Insufficient cooling system efficiency or uneven distribution of cooling medium.

   - Solution: Optimize the cooling system design to improve the distribution uniformity and cooling efficiency of the cooling medium.

5.Product deflash problem

In the blow molding process, removing burrs (also known as "flash" or "flash") from oil drums and bottles should be as simple as possible to improve efficiency and safety. If the deburring process does not work well, this may be due to insufficient clamping force in the flashed areas of the mold. The following is a rewrite and addition to the original content:

1. Matching problem between mold and machine:

   - Problem: When a small mold is run on a blow molding machine designed for larger volume products, such as a 1L or 5L oil drum mold being used on a machine designed for 10L to 25L oil drums, uneven distribution of the clamping force may occur. The problem. This results in the mold not being able to cut accurately around the flash area, which affects the deburring effect.

   - Recommendation: Avoid production on a blow molding machine that is not suitable for the mold size. Choose a blow molding machine that matches the mold size to ensure even distribution of clamping force and improve the quality and efficiency of deburring.

2. Mold cooling and parison thickness issues:

   - Problem: If the deburring effect of the mold is not ideal during operation, this may be due to improper design of the cooling system of the mold or insufficient cooling medium flow, resulting in insufficient cooling of the flash area. In addition, if the thickness of the parison in the flash area is too large, the mold may not be completely closed, further affecting the cooling and deburring effects of the flash area.

   - Solution: Check and optimize the cooling system of the mold to ensure that the cooling medium can flow through the mold evenly and fully. At the same time, adjust the thickness of the parison and reduce the thickness of the flash area to promote mold closing and cooling effects, thereby improving the quality of deburring.

Through these improvement measures, the deburring effect of blow molded products can be improved, the labor intensity of operators can be reduced, and production efficiency can be improved.

Which is the point?

Blow molding defects are critical for manufacturers of plastic products, not only can they impair production capabilities, they can also destroy the trust relationships established with customers. It is undesirable for consumers to purchase defective blow molded products because these products cannot meet the expected quality requirements. Therefore, careful quality review is essential for blow molded products such as bottles, jerry cans or IBC tanks, etc. Once any blow molding defects are discovered, manufacturers should immediately identify their sources and take effective measures to prevent or repair these problems to ensure product quality and maintain customer satisfaction.

How to purchase the right HDPE extrusion blow molding machine?

Choosing high-quality machinery is an effective preventive measure to avoid production problems, especially when purchasing an extrusion blow molding machine. Producing consistent quality containers is very important to customers.Our jerry can blow molding machine is well received by customers in Europe and other parts of the world, and they help customers produce high-standard products suitable for packaging of edible oils and other liquid storage.

Purchasing a suitable blow molding machine can not only meet the production volume needs, but also meet the quality requirements of the market. So, keep in mind that choosing a top blow molding machine manufacturer can provide you with numerous advantages including quality consistency, high output, excellent after-sales service, cutting-edge technology, and reasonable prices.

When you choose a blow molding machine from HUAN Machinery, you can rest assured that our equipment will operate at the highest efficiency to fully meet your production needs. As our valued customer, you will also enjoy the lifetime after-sales support we provide, as well as our online customer service team, who promise to respond quickly to your inquiries within 24 hours.

In just one step, you can achieve a leap in factory productivity and profitability with the blow molding machine we tailor-make for you. Huan Machinery, as your long-term partner and strong backing, will accompany your every step of growth.

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