Blow molding pressure is an important factor affecting the wall thickness and shape of hollow products. The blow molding pressure is determined based on the size, material, and thickness requirements of the product. Usually, the blow molding pressure is between 0.2-0.8MPa. Excessive pressure may lead to thin or even broken product walls, while insufficient pressure may result in uneven wall thickness or incomplete molding of the product. For example, when manufacturing small plastic bottles, the blow molding pressure may be around 0.3-0.5MPa.

The shape and size of the mold cavity should be precisely designed according to the design requirements of the product. The surface roughness of the cavity will affect the appearance quality of the product, and it is generally required that the surface roughness of the cavity reach Ra0.8-Ra1.6 μ m. When designing the cavity, the shrinkage rate of the product should also be considered. Different plastic materials have different shrinkage rates, and the appropriate cavity size should be selected according to the actual material to ensure that the product size meets the requirements. For example, for PE materials, their shrinkage rate is generally between 1.5% and 3.6%, and the mold cavity size should be correspondingly enlarged.

What are the requirements for material thickness in Dalian hollow forming process?

The relationship between material thickness and product performance

Strength requirements:

For hollow molded products, the material thickness directly affects their strength. Thicker materials generally provide higher strength, allowing the product to withstand greater pressure, weight, or external impact. For example, when manufacturing large industrial hollow containers (such as chemical raw material storage tanks), sufficient thickness of material is required to ensure the strength of the container in order to withstand the pressure of internal liquid and possible external collisions. If the material thickness is insufficient, the container may deform or even rupture under pressure, leading to chemical leakage and causing safety accidents.

However, thickness is not necessarily better. Excessive increase in thickness can increase material costs and product weight, and in some cases may affect other properties of the product. For example, for some hollow containers that require easy handling or transportation, overweight products will increase transportation costs and operational difficulties.

Barrier performance impact:

The thickness of the material is also crucial for the barrier performance of hollow products. For packaging hollow products such as food, drug, or cosmetic packaging bottles, appropriate material thickness can help prevent the permeation of substances such as oxygen, water vapor, and carbon dioxide. A thicker material layer can extend the shelf life of the products inside the packaging. Taking PET beverage bottles as an example, a certain wall thickness can effectively prevent the escape of carbon dioxide, maintain the carbonated content of the beverage, and make the beverage taste better.

In terms of appearance and touch:

The thickness of the material will affect the appearance and texture of hollow products. Appropriate thickness can make the surface of the product smoother and firmer. For some products with appearance requirements, such as cosmetic bottles or high-end gift packaging containers, a suitable thickness can present a better texture. At the same time, thickness can also affect the tactile feel of the product, and thicker materials may make users feel stronger and heavier.

Differences in material thickness requirements for different molding methods

Extrusion blow molding hollow forming:

The wall thickness uniformity of products produced by this process is relatively poor. In the design and production process, the range of material thickness variation is relatively large. Generally speaking, for large extruded blow molded hollow products (such as garbage bins and large water storage tanks), the wall thickness can be between 1-5mm. The specific thickness is determined based on factors such as the size, purpose, and pressure that the product can withstand. For example, the wall thickness of a regular household garbage bin may be around 1-2mm, while the wall thickness of a large industrial water storage bin may reach 3-5mm.

Due to the complex expansion and stretching of the billet during extrusion blow molding, it is necessary to consider how to minimize the unevenness of wall thickness in mold design and process parameter control. For example, by optimizing the blow molding pressure distribution and adjusting the extrusion speed of the billet, it is ensured that the product has sufficient thickness in key areas such as the bottom and side areas that are subjected to high pressure.

Injection blow molding hollow forming:

The injection blow molding process can accurately control the shape and size of the billet, so the wall thickness uniformity of the product is good. This process is commonly used to manufacture small, high-precision hollow plastic products, with relatively thin material thickness and high precision requirements. For example, for small plastic medicine bottles, the wall thickness is generally between 0.5-2mm. During the injection molding process, the basic wall thickness of the preform is determined during the injection molding stage, and uniform expansion is mainly carried out on this basis during the blow molding process, so the thickness change is relatively small.

Stretch blow molding hollow forming:

The stretch blow molding process can first stretch the preform axially before blow molding, which allows the material molecular chains to be oriented in both axial and radial directions. Under this process, the thickness of the material can be relatively thin, but it can still ensure that the product has high strength and good performance. For some beverage bottles manufactured using stretch blow molding technology (such as PET beverage bottles), the wall thickness is usually between 0.2-0.5mm. The stretching process improves the performance of the material, allowing it to meet usage requirements even with thin thickness, while also saving material costs and reducing product weight.

Hollow molding is a popular plastic processing method that can be used to produce various hollow shaped products, such as bottles, containers, pipes, etc. The principle of hollow molding is to inject high-pressure gas or liquid into the mold to fill the hollow part of the mold with plastic material, thereby forming the desired hollow shape. This processing method has the advantages of speed, efficiency, and low cost, and is therefore widely used in industrial production.

The temperature of the mold affects the cooling rate and appearance quality of the product. During the blow molding process, appropriate mold temperature helps the billet to better adhere to the inner wall of the mold and achieve better surface quality. The general mold temperature is controlled between 20-50 ℃. For some products with high transparency requirements, such as PET beverage bottles, lower mold temperatures can quickly cool the product and improve transparency.