Common problems and solutions of hollow blow molding products

Hollow blow molding products are widely used in all walks of life, containers, beverage bottles, toys... It can be said that hollow products have been integrated into our lives. Today, let's take a look at the common problems and solutions of hollow blow molding products.

First of all, the first problem encountered with hollow blow molding products is usually a large fluctuation in product weight.

The main reasons for this problem are as follows:

1. The embryo changes suddenly;

2. Uneven mixing of raw materials;

3. The feed section is blocked or bridged, and the extrusion is unstable;

4. The extrusion speed is unstable.

In view of the above problems, we can start from the following aspects:

1. Check and maintain the wall thickness control equipment to ensure the parison is more stable;

2. Use appropriate material mixing equipment, properly extend the material mixing time, so that the raw materials can be fully mixed;

3. Check the entrance for blockages or other foreign matter blocking the entrance;

4. Properly reduce the inlet temperature to avoid "bridge" phenomenon;

5. Check whether the extruder motor is abnormal, whether the motor and gearbox are loose or slipping, and ensure that the screw speed is stable;

6. At the same time, we also need to check the electronic scale regularly to avoid the fluctuation of the measuring instrument from affecting the quality judgment;

When hollow blow molding products are used to hold liquids, they often encounter unqualified capacity.

The main reasons for this problem are as follows:

1. Different grades of raw materials have different shrinkage rates. Mold cooling temperature and blow molding solidification time are the reasons for excessive product shrinkage. We need to analyze and solve problems in a targeted manner so that the product shrinks within a controllable range;

2. In addition, the wall thickness of the product is too thick or the wall thickness is uneven, resulting in deformation and depression. The appearance of the product does not meet the design requirements, and the volume is unqualified.

We can also:

1. To repair and improve the mold, first meet the theoretical volume requirements;

2. Replace the raw materials with smaller shrinkage, prolong the blowing time, reduce the cooling temperature of the mold, and reduce the shrinkage of the finished product as much as possible;

3. Adjust the wall thickness controller to make the wall thickness evenly distributed and solve the concave and deformation problems of individual parts;

4. Properly adjust the blowing time to make the product shape conform to the original design intention;

5. Or solve the problem by increasing the blowing pressure appropriately.

In addition, we found that the effect of weight on capacity is also crucial. It's not a simple linear relationship where 1 kg less weight equals 1 liter more capacity. The specific relationship between weight and volume requires us to conduct a specific analysis of different barrel types.

The size problem can also be said to be a further extension of the volume problem. The size exceeds the standard category. The causes and solutions are basically the same as the volume problem and will not be explained here. If the product control size cannot be directly formed during the hollow blow molding process, it can be solved by adjusting the appropriate process time, product wall thickness, selecting appropriate raw materials, and even using the external mold to control to meet the quality requirements.

In addition, the appearance of the product is the customer's first impression of the quality of the product.

The black spots and black lines on the surface of the product are mainly caused by improper temperature setting and carbonization of the raw materials; the carbide accumulated in the accumulator or the head flow channel is taken out; the foreign matter is caused by foreign matter.

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For the above problems, we can check and solve the following methods:

1. Properly reduce the processing temperature;

2. Clean the runner system or reduce the injection pressure;

3. Purification of raw materials, timely cleaning of filter plates, magnetic frames and other measures can effectively solve such problems;

4. In addition, by analyzing the location and characteristics of black spots, it helps us quickly find out the cause of the problem and improve the processing speed of quality problems.

In addition to the black dots and black lines, the injection pressure is too high; the wall thickness controller is inaccurate in tracking the wall thickness; problems such as the blank mold will cause the parison to encounter resistance during extrusion, resulting in horizontal stripes on the surface of the parison. 

Feasible method:

1. Properly reduce the injection pressure;

2. Check the wall thickness controller or reset the wall thickness of the parison to slow down the fluctuation of wall thickness;

3. Solutions such as cleaning and grinding the mold.

At the same time, there are foreign objects in the mold; there are burrs or gaps on the edge of the mold sleeve or the core; foreign objects in the stocker or the head may cause longitudinal stripes on the surface of the product. We need to clean the mould; repair the core mold sleeve, usually pay attention to protection when using or cleaning the core mold sleeve to avoid personal injury; clean the stocker, machine head or increase the injection pressure, use molten material to remove foreign matter and solve it.

At the same time, product wall thickness is also one of the factors affecting product quality.

When the wall thickness of the product is uneven or the wall thickness is too thin, the following reasons should be analyzed in time:

1. Improper adjustment of the die clearance of the machine head, and the parison is skewed during extrusion;

2. The mold is inconsistent with the center of the machine head;

3. When the parison is extruded, it sags;

4. The length of the extrusion parison is large and the fluctuation is large;

5. The blowing ratio of the parison is too large;

6. The mold design is unreasonable;

7. The temperature distribution of the mold is uneven.

So we should:

1. Adjust the mold gap according to the wall thickness distribution;

2. Adjust the position of the machine head or adjust the installation position of the mold;

3. Properly increase the extrusion speed or clamping speed, and choose raw materials with low melt flow;

4. Check whether the hopper is blocked or bridged. If different grades of mixture are used, they should be mixed as evenly as possible;

5. Appropriately reduce the inflation rate;

6. Re-improving the mold;

7. According to the product characteristics, properly adjust the mold cooling temperature of different parts to solve the problem.

In addition, the ductility of raw materials in the molten state is also a problem that must be considered. Before the problem is completely solved, mass production should be avoided to avoid the expansion of quality problems.

Another problem is that the sealing performance of the product is one of the important quality control points of the product. The compatibility of the sealing material with the contents and the fit between the sealer and the bottle finish are important considerations.

Sealing is just a matter of degree.

At present, the sealing methods mainly include inner cover sealing, sealing sealing and gasket sealing.

All three have their pros and cons:

The sealing effect of the inner cover is slightly poor, but it is stable and durable; the gasket is well sealed, but the reuse rate is slightly poor; the sealing ring has good sealing performance, but the design should pay attention to interference and friction.

When choosing a sealing method, various issues such as material, sealing ability, and sealing aging must be considered comprehensively.

The reasons for the failure of ordinary seals are as follows:

1. The plane or inner wall difference of the product seal;

2. There is a deviation between the front and back of the product seal;

3. The chemical reaction between the sealing material and the contents;

4. Mismatch between sealant and mouth.

We can:

1. Adjust the plane or inner wall of the seal to make it flat;

2. Adjust the height deviation to make the contact surface height consistent;

3. Select the appropriate sealing material to avoid corrosion of the contents;

4. Adjust the cooperation between the sealing machine and the mouth to solve the problem.

By studying the sealing state, it is helpful to improve the prevention of seal failure. In the research process, we need to pay attention to practice is the way to test the theory. Too much belief in theory will make it difficult to produce qualified products, and too much reliance on experience will make it difficult to find potential problems.

During the transportation process, the product will encounter stacking and transportation problems.

During transportation, if the product accidentally falls from a high place, it is easy to break.

The usual reasons for rupture are:

1. Improper wall thickness adjustment;

2. The molding temperature setting is not appropriate;

3. The selection of raw material grades is unreasonable;

4. Unreasonable mold design and other reasons.

We should

1. By readjusting the wall thickness of the product, the wall thickness control of the force is strengthened. It should be noted that the wall thickness is not as thick as possible, and sometimes the wall thickness of some parts is reduced to improve drop performance;

2. Reset the molding temperature, if it is too high, it will lead to the decomposition of raw materials, if it is too low, it will lead to poor plasticization;

3. Reselect the applicable raw material grade. The emphasis on raw materials for each grade is also different. There are no good raw materials, only suitable raw materials;

4. The method of improving the product structure can solve the problem of poor drop performance.

At the same time, if the wall thickness is not adjusted properly, the choice of raw material grade is unreasonable, and the mold design is unreasonable, it will lead to poor product stacking performance and affect product transportation.

By readjusting the wall thickness of the product, the control of the wall thickness of the force has been strengthened, the applicable material grade has been reselected, the mold has been improved, and reinforcing ribs have been added as needed to further improve the stacking performance of the product.

Studying the hollow container as a shell structure simplifies the research process while improving the stacking performance. Generally speaking, when determining the product structure, drop performance and accumulation performance are complementary and opposite to each other. We need to find the right balance point to meet the requirements of good stacking performance and good drop performance.

Finally, with the different service conditions of products, the environmental stress crack resistance of products has been paid more and more attention. Improper selection of raw material grades; inappropriate mold design temperature, resulting in stress concentration and other reasons, will lead to poor environmental stress cracking performance of the product.

Method:

1. Select the appropriate raw material grade;

2. Improve the mold, especially at the sharp corners;

3. Problems such as setting an appropriate molding temperature, adjusting wall thickness, and avoiding stress concentration can be solved. Due to the particularity of environmental stress cracking, it is difficult to detect environmental stress cracking problems in time during the production process, which may cause losses during the test. Therefore, this issue must be considered at the beginning of production.

When selecting materials, try to use materials with wide molecular weight distribution and high branching degree. When designing the mold, try to avoid structures that are easy to bear force such as sharp corners. Set appropriate temperature and cooling rate during process setting.

The F50 time of raw materials provided by most raw material manufacturers can effectively reflect the environmental stress cracking resistance of raw materials. However, in actual production, the data can be used as a reference and cannot be overly relied upon.

Various situations may arise during the production of blow molded products. This time, you only need to choose a few finished products that are prone to problems for discussion, and propose a few solutions for your reference. All aspects and details of the production of blow molded products, such as raw materials, equipment, plasticization and molding, are worthy of further study.