The nylon five-star bases of office chairs are mainly made of nylon material and glass fiber injection molding, connecting with the gas cylinder, and the production process for this plastic product is injection molding.
After nylon PA is reinforced and modified with glass fiber (GF), its strength, hardness, fatigue resistance, dimensional stability, creep resistance, etc. are greatly improved. And it makes the chair bases more wear-resistant and durable.
However, in the actual production process, the dispersion and bonding strength of the glass fiber in the PA resin matrix have a great influence on the product performance. Glass fiber reinforced PA injection molded products often have various defects.
We have decades experience in the injection molding field and as the manufacturer, we would like to share our idea:
We will divide this topic into 2 parts including the injection molding process of glass fiber reinforced PA and the reasons and solutions for the defects. And in this post, we will introduce the injection molding process.
Glass fiber reinforced nylon injection molding process
After the plastic raw materials, injection molding machine and mold are determined, the selection and control of injection molding process parameters are the key to ensuring the quality of the parts. The complete injection molding process should include preparation before molding, injection process, post-processing of parts, etc. according to the sequence.
1. Preparation before molding
In order to make the injection process go smoothly and ensure the quality of the plastic nylon office chair bases, some necessary preparations should be made before molding.
(1) Confirmation of raw material performance
The performance and quality of plastic raw materials will directly affect the quality of plastic nylon office chair bases.
(2) Preheating and drying of raw materials
In the plastic molding process, the residual moisture in the raw material will vaporize into water vapor, which will remain in the interior or surface of the base.
Then, that may form silver wire, markings, bubbles, pitting and other defects.
In addition, moisture and other volatile low-molecular compounds will also play a catalytic role in a high-heat and high-pressure processing environment. And it will cause PA to cross-link or degrade, affecting surface quality and severely degrading performance.
Commonly used drying methods mainly include hot air circulation drying, vacuum drying, infrared drying and so on.
2. Injection process
The injection process generally includes these several steps: feeding, plasticizing, injection, cooling and demoulding.
Since injection molding is a batch process, quantitative (constant volume) feeding is required to ensure stable operation and uniform plasticization.
The added plastic is heated in the barrel, and the process of transforming solid particles into a viscous fluid state and with good plasticity is called plasticization.
Regardless of the type of injection molding machine used, the injection molding process can be divided into several stages, such as mold filling, pressure holding, and backflow.
(4) Cooling after the gate is frozen
When the melt of the gate system has been frozen, it is no longer necessary to continue to hold the pressure. Therefore, the plunger or screw can be returned and the pressure of the plastic in the barrel can be relieved. Besides, new material can be added, and cooling medium such as cooling water, oil or air can be introduced at the same time.
The mold can be opened when the part is cooled to a certain temperature, and the part is pushed out of the mold under the action of the ejection mechanism.
3. Post-processing of parts
Post-treatment refers to the process of further stabilizing or improving the performance of the parts obtained by injection molding. That usually includes heat treatment, humidity conditioning, post-processing, etc.
The other chair base
Except the nylon material, there are some other, aluminum and chrome-metal one, whose have their own advantage and disadvantage.
And it is no doubt that the nylon chair base is the most used in the market.