Analysis of the Extrusion Blow Molding Process

The extrusion process in blow-molding machinery, particularly the extrusion blow-molding process, is an important technique for shaping polymer materials. Below is a detailed analysis of this process:

### I. Process Steps

The extrusion blow molding process primarily involves the following steps:

1. **Parison Extrusion**: A semi-molten tubular preform is extruded by an extrusion device.

2. **Mold Closure**: When the parison reaches a certain length, the mold moves beneath the die head to close, gripping the tube blank, and a cutting blade severs the tube blank from the parison.

3. **Air Blowing**: The mold is moved to the blow-molding station, where an air-blowing rod enters the mold and inflates it with compressed air, causing the parison to tightly adhere to the inner walls of the mold as it cools and sets into shape.

4. **Cooling, Shaping, and Trimming/De-molding**: After being blown into shape, the parison cools and sets within the mold. The mold is then opened, the finished product is removed, and trimming operations are performed.

### II. Process Characteristics

1. **Advantages**:

* High production efficiency, ideal for mass manufacturing.

* The equipment has low costs and requires less investment compared to other forming processes.

* A wide range of molds and machinery is available, allowing adaptation to the production of products in various sizes and shapes.

2. **Drawbacks**:

* The scrap rate is relatively high, requiring strict control over both raw materials and manufacturing processes.

* Waste recycling and utilization are inadequate, highlighting the need to prioritize environmental protection and sustainable development.

* The thickness control of the product and the dispersibility of the raw materials are limited, which may affect product quality.

### III. Influencing Factors and Control

1. **Screw Speed**: This affects the extrusion rate and parison quality. Higher screw speeds can increase production output and reduce parison sagging, but may lead to a decline in the surface quality of the parison. Therefore, it’s essential to select an appropriate screw speed that strikes a balance between productivity and quality.

2. **Temperature Control**: The extrusion temperature depends on the properties of the resin. If the temperature is too low, it results in a rough surface on the parison; if it’s too high, it leads to uneven wall thickness in the parison. Precise temperature control is essential to ensure high-quality parisons.

3. **Die Dimensions and Quality**: The die dimensions determine the shape of the parison, requiring a smooth inner surface on the die to ensure a uniformly smooth parison for the final product. Additionally, it’s necessary to carefully control the die gap to precisely adjust the wall thickness of the parison.

4. **Raw Material Selection**: The performance and processability of the raw materials must meet the requirements of both the final product and the blow-molding process. Commonly used materials include HDPE, PP, PET, and others, each with distinct characteristics and application ranges. For instance, HDPE offers excellent tensile strength, high moldability, and is completely non-toxic; PP has a semi-transparent texture, high rigidity, and low density; while PET boasts superior physical and mechanical properties as well as outstanding transparency.

### IV. Applications

The extrusion blow molding process is primarily used to produce daily chemical, food, and pharmaceutical packaging containers, as well as large industrial drums and tanks. These products must exhibit excellent mechanical properties, transparency, and barrier performance.

In summary, the extrusion process in blow molding machinery is an important technique for shaping polymer materials, offering advantages such as high production efficiency and low equipment costs. However, this process also has drawbacks, including a relatively high defect rate and poor recyclability of waste materials. Therefore, in practical applications, it is essential to carefully control process parameters and select raw materials meticulously, ensuring improved product quality while reducing overall production costs.