Core Reasons and Precautions for Heating Preforms Before Blow Molding

Why is it necessary to heat preforms before blow molding? The core purpose is to endow preforms with stretchable and formable properties, ensuring that the blow-molded plastic bottles have uniform wall thickness, regular shape, and no damage, while guaranteeing stable product quality.

This is an indispensable key step in the blow molding process, and its principle is closely related to the physical properties of plastics and the requirements of the blow molding process. It is also a key link focused on by pet preform manufacturers, plastic preform manufacturers and preform bottle manufacturers in the production process.

I. Core Reasons for Heating

1. Soften Plastics and Endow Stretchable Forming Ability

Preforms are hard and brittle at room temperature and cannot be directly stretched or blow-molded. This applies to all preforms produced by pet preform suppliers, bottle preform suppliers and pet preform hersteller. After heating, the movement of plastic molecular chains intensifies, and the preforms will gradually soften and become flexible and elastic.

At this time, under the action of high-pressure air flow from the blow molding machine, they can be smoothly stretched, blown up, and fit the inner wall of the mold to form the required bottle types (such as shampoo bottles).

 If not heated or insufficiently heated, the preforms will be too hard, and they are prone to cracking and deformation during blow molding, making it impossible to form, which will directly affect the production efficiency and product qualification rate of manufacturer of pet bottles.

2. Ensure Uniform Wall Thickness of Bottle Bodies and Improve Product Qualification Rate

The core requirement of blow molding is that the wall thickness of each part of the bottle body is consistent, avoiding uneven thickness and local weakness (easy to break), which is crucial to the safety and practicality of plastic packaging for products. 

During the heating process, by precisely controlling the temperature, the softening degree of each part of the preform can be uniform. During subsequent stretching and blowing, the plastic will be evenly distributed in the mold, thus ensuring the uniform wall thickness of the formed bottle body and reducing the defective rate.

On the contrary, if the heating is uneven and the softening degree is inconsistent, the thick parts are difficult to stretch, and the thin parts are easy to be blown broken, leading to product scrapping. This is also a problem that pet preform manufacturers in china focus on avoiding in production.

3. Optimize Bottle Texture and Ensure Service Performance

An appropriate heating temperature can make the blow-molded preforms have a smooth surface without wrinkles and bubbles, improving the visual texture and hand feel of the bottle body. It is especially suitable for the shampoo packaging bottles produced by plastic shampoo pump bottles and body lotion bottle manufacturers, which can enhance the market competitiveness of products.

At the same time, the stretching process after heating will make the arrangement of plastic molecular chains more regular, enhance the mechanical strength of the bottle body (such as impact resistance and pressure resistance), extend the service life of plastic bottles, avoid problems such as easy damage in subsequent use, and meet the needs of various packaging scenarios.

II. Supplementary Precautions (Avoid Affecting Products Due to Improper Heating)

Heating is crucial, but the temperature control must be precise, otherwise it will be counterproductive and affect the blow molding effect:

• Excessively high temperature: The preforms will be over-softened, prone to deformation and collapse during blow molding, and even adhere to the mold, leading to product scrapping; at the same time, it may affect the performance of plastics, resulting in yellowing, aging and other problems,damaging the product reputation of pet preform manufacturers, manufacturer of pet bottles and other manufacturers.

• Excessively low temperature: The preforms are insufficiently softened, prone to cracking and incomplete forming during blow molding, or uneven wall thickness of the bottle body, leading to a sharp increase in the defective rate and increasing the production cost of pet preform suppliers and bottle preform suppliers.

• Uniformity of heating: It is necessary to ensure uniform heating in the circumferential direction and upper and lower parts of the preform, which can be achieved by adjusting the position and power of the heating lamp tubes, avoiding local overheating or insufficient heating. This requirement is also applicable to pet preform hersteller and pet preform manufacturers in china.

• Material adaptation: Preforms of different materials require different heating temperatures (for example, the heating temperature of PET preforms is usually 90-120℃, and that of HDPE preforms is slightly lower).

It is necessary to adjust according to the material of the preform to fit the material characteristics, which is also a key detail for plastic preform manufacturers and preform bottle manufacturers to ensure product quality.

In summary, the heating of preforms before blow molding essentially provides a foundation for blow molding by softening plastics and ensuring uniform heating. It not only ensures the smooth forming of products, but also guarantees the quality, strength and texture of the bottle body.

It is a core process link connecting preforms and finished plastic bottles, directly related to the production efficiency and product competitiveness of various related manufacturers such as pet preform manufacturers, plastic shampoo pump bottles and body lotion bottle manufacturers.