Blow mold | Eight common blow molding problems and analysis

Introduction:

Blow molding is a versatile manufacturing process used to create a wide range of products. However, like any production method, it comes with its own set of challenges. In this article, we will explore eight common blow molding problems and provide insightful analyses to help you understand the root causes of these issues. Whether you're an experienced professional or new to blow molding, this information will be valuable in troubleshooting and improving your production processes.

Problem 1. Black spots or black lines: There are black substances or short black lines on the surface of the product.

problem analysis:

1. The raw materials stay in the blow molding barrel or flow channel for too long, and the material properties change.

2. There is foreign matter in the blow molding barrel.

3. The heating wire is loose and the heating temperature is unstable, resulting in material degradation.

4. The temperature difference of the die mouth is large.

5. Hydraulic oil leaks inside the die head and contacts the material causing performance changes.

6. The blow molding screw and barrel are severely worn and the raw materials cannot be melted evenly.

7. The cooling water of the mold is poor, causing a large temperature deviation in the overall mold.

8. The mold is poorly vented and air accumulates inside the mold cavity, causing burnt material.

9. Residual grease or lubricant inside the mold contacts high-temperature raw materials, causing the material to burn.

10. The quality of raw materials is too poor and contains many impurities.

11． The machine parameters are confusing and the temperature setting range is incorrect.

Problem 2. Surface bubbles: Gas that has not had time to escape during the blow molding process enters the surface of the product.

problem analysis:

1. The blow molding material is moist and water vapor evaporates into the surface of the material.

2. The mold exhaust air is blocked or the exhaust is poor, and the gas cannot be discharged smoothly.

3. The blow molding cycle time is too short and the cavity gas cannot be discharged quickly.

4. The machine production air pressure parameter setting is wrong.

5. The blow screw rotates too fast.

6. Screw back pressure is too low.

7. There are volatile additives in the raw materials.

Problem 3. Matte: The surface finish of the product is low

problem analysis

1. The blow molding pressure is not enough and the raw materials are not fully compacted.

2. The temperature of the barrel is too low and the raw materials are not completely melted.

3. Blow molding cycle time is too short.

4. Mold temperature is too low.

5. The mold is insufficiently vented and the product cannot adhere to the inner surface of the mold.

6. The mold surface is dirty and rough.

7. The raw materials are too moist and the production process has poor fluidity.

Question 4. Jet lines: Snake-like lines formed on the surface of the blow molded product when the melt flows into the front mold.

problem analysis:

1. The barrel temperature setting is wrong, the temperature is too high or too low.

2. The nozzle is too small.

3. The material temperature at the nozzle is not enough.

4. Mold temperature is too low.

5. Injection speed is too fast

6. The nozzle position is wrong.

7. The outlet channel is too long.

8. The raw materials are of poor quality and have performance issues.

Problem 5. Water lines: During the blow molding process, the two material flows cannot merge into one place.

problem analysis:

1. The mold temperature is too low and the product cools before it is formed.

2. The clamping pressure is insufficient and the product expands.

3. Injection pressure or injection speed is too low.

4. The water outlet is too small.

5. The spout is in the wrong position.

6. The nozzle joint area is too long.

Question 6. Cracking: The product has a tendency to crack under normal environmental conditions.

problem analysis:

1. Incorrect blow screw design.

2. The blow molding cycle is too short.

3. The rubber material condenses in the flow channel.

4. The injection pressure is too high, the screw speed or the blowing speed is too fast.

5. The melt temperature at the nozzle is too high.

6. Blow molding pressure is too low.

7. Raw materials are too moist and performance degrades.

Problem 7. Delamination: The surface of the blow molded parts is delaminated and appears like fish scales.

problem analysis:

1. The injection speed is too slow.

2. Not enough blow molding filler.

3. When injecting glue, the holding time is too short.

4. The barrel melt temperature is too low.

5. Mold temperature is too low.

6. The sharp corner of the spout.

7. Mold runners and gates are too large,

8. The nozzle material is contaminated.

9. Influence of external materials or auxiliary materials.

10. The blow molding material is too moist.

Problem 8. Dirty: The surface of the product is dirty

problem analysis:

1. Oil leakage or lubricant dripping onto the product.

2. Unreasonable packaging and transportation, and careless operation may cause pollution.

3. The blow molding material is too moist.

Conclusion:

Achieving high-quality blow-molded products requires a keen understanding of potential issues and their underlying causes. By addressing problems like black spots, surface bubbles, matte finishes, jet lines, water lines, cracking, delamination, and dirt, manufacturers can enhance their production processes and produce top-notch results. Regular maintenance, careful material selection, and meticulous attention to process parameters are essential for success in blow molding.

FAQs

Q1: How can I address the issue of black spots or black lines on blow-molded products?

A1: Black spots can result from various factors, such as material degradation, foreign matter, or temperature instability. Investigate each potential cause and take appropriate corrective actions.

Q2: What should I do to prevent surface bubbles in blow-molded products?

A2: Surface bubbles can be caused by moisture in materials or poor gas discharge. Ensure material dryness, optimize mold exhaust, and adjust process parameters to address this issue.

Q3: How can I improve the surface finish of blow-molded products if they appear matte?

A3: A matte finish may result from insufficient pressure, low barrel temperature, or inadequate mold venting. Adjust these factors and enhance mold cleanliness for smoother surfaces.

Q4: What causes jet lines on blow-molded products, and how can I prevent them?

A4: Jet lines can be linked to incorrect barrel temperatures, small nozzles, or high injection speeds. Analyze these factors and make necessary adjustments for jet-free products.

Q5: How can I avoid water lines in blow-molded products?

A5: Water lines form due to inadequate cooling or low injection pressure. Ensure proper cooling, optimize clamping pressure, and adjust injection parameters to eliminate water lines.