Manufacturing Process: How Are Plastic Stools Made?

Plastic stools are super lightweight and versatile, making them perfect for families, offices, and outdoor gatherings. So how are plastic stools made? Figuring this out can help retailers get a better understanding of the process, check out their design and quality, and see how they stack up against other brands. In this article, we’ll break down how plastic stools are made step by step, giving you all the juicy details!

1. So How Are Plastic Stools Made?

Plastic stools come in a wide variety of types, including standard plastic stools and bar stools. They also come in many different styles, such as modern, backless, and with or without armrests. They are designed for use in various settings such as classrooms, offices, homes, and outdoor areas. However, despite the different types, they generally have a similar manufacturing process, so we will go through the most common one.

Here are an example of manufacturing process of plastic stools and chairs:

1.1. Raw Material Selection

There are 3 main plastic material often used in manufacturing plastic stools:

• Polypropylene (PP): This is a very popular plastic for making stools. It is durable, flexible, and relatively inexpensive. Polypropylene stools are known for their strength and ability to withstand frequent use.
• Polyethylene (PE): Polyethylene comes in different densities, with high-density polyethylene (HDPE) being a common choice. HDPE is rigid, impact-resistant, and can be molded into sturdy stool frames.
• Acrylonitrile Butadiene Styrene (ABS): ABS is a strong, rigid plastic and has good impact resistance and can be easily molded into various shapes and designs. ABS stools are known for their durability and aesthetic appeal.

Some other materials are also used in the production of plastic chairs: Polythene, nylon, acrylic, PVC and uPVC, polythene, bakelite, melamine, Epoxy resin.

In addition, when selecting a raw material for a manufacturing project, there are several key factors to consider:

• ABS and PP tend to be stronger and more durable than PE.
• PP and ABS generally have better durability than PE.
• ABS and PMMA can provide a high-quality, glossy finish, while PE may have a more utilitarian appearance.

Other factors that may influence material selection include cost, ease of manufacturing, and environmental considerations like recyclability.

Among them, PP is the most commonly used plastic because it is very durable, flexible, inexpensive, safe, and easy to clean.

1.2. Compounding and Pelletizing

Compounding is the process of mixing different materials together to create a new plastic material. This often involves mixing a plastic polymer with various additives like colorants, stabilizers, or other compounds (This is necessary). The goal is to create a new plastic material with specific properties or characteristics.

Before that, the R&D team will need to calculate the material ratios to meet product requirements or specific customizations from customers.

The compounding process typically involves melting and mixing the materials together in an extruder machine (Inochi Global recommends using Werner & Pfleiderer (W&P) ZSK Series or Coperion K-Tron from Germany for this step).

The extruder heats and mixes the materials, then forces the molten mixture through a die to create long strands of the new plastic compound. And the temperature required to melt the plastic pellets is usually very high (around 200 degrees Celsius or higher).

These long strands are then cut into small pellets or “nurdles” as they exit the extruder. This pelletizing process creates small, uniform pieces of the compounded plastic that can be more easily stored, transported, and used in other manufacturing processes like injection molding or extrusion.

The pelletizing is often done using an underwater pelletizer, where the hot plastic strands are cut into pellets and immediately cooled in water to solidify them. The pellets are then dried and packaged for distribution.

This compounding and pelletizing process allows manufacturers to create custom plastic materials tailored to their specific needs by combining polymers and additives in the right formulation.

1.3. Mold Preparation

The mold for an injection-molded part is typically made from metals like aluminum or steel. The mold is designed with two main sections – the cavity and the core. The cavity forms the outside of the part, while the core forms the inside.

To create the mold, the cavity and core are machined, often using CNC (computer numerical control) machines. This allows the mold to be precisely made with the desired features and dimensions.

There are a few key design features that are important for the mold:

• Draft Angles

Draft angles refer to the slight taper or angle applied to the surfaces of the mold. This taper helps the molded part release and eject from the mold easily after it has been formed. Without draft angles, the part could stick to the mold and become damaged during ejection. Typical draft angles range from 0.5 to 5 degrees, depending on the part design and materials used.

• Ejector Pins

Ejector pins are small pins that push against the molded part to help eject it from the mold cavity. They are strategically placed in the mold to apply force evenly and prevent the part from sticking or deforming. The location and size of the ejector pins is an important part of the mold design.

1.4. Injection Molding

This is an important step and also a strategic secret of each factory, including Inochi Global, so I will only cover a few basic steps as follows:

1. Melting the Plastic Pellets: The plastic pellets are fed into the hopper of the injection molding machine. The pellets then move into the barrel, where they are heated and melted by the rotating screw. The screw acts like a corkscrew, pushing the melted plastic forward. 
2. Injecting the Molten Plastic: Once the plastic is fully melted, the screw acts as a piston, pushing the molten plastic through the nozzle and into the mold cavity. The mold is clamped tightly shut to prevent any leaks.
3. Cooling and Ejection: The molten plastic fills the mold cavity, taking the shape of the desired part. The mold is then cooled, allowing the plastic to solidify. Once cooled, the mold opens, and the finished part is ejected.

This continuous process of melting, injecting, cooling, and ejecting allows for the rapid production of plastic parts. The injection molding machine precisely controls the temperature, pressure, and speed to ensure the molten plastic fills the mold cavity completely and the final part has the desired properties.

1.5. Cooling and Ejection

The cooling and ejection of stools in injection molding is a critical part of the manufacturing process. During the injection molding of plastic stools, proper cooling and ejection techniques are essential to ensure the successful removal of the part from the mold without deformation.

Firstly, the cooling system of the stool mold needs to be carefully designed to ensure even and efficient cooling of the plastic material. This typically involves incorporating cooling channels or water jackets within the mold to circulate coolant and remove heat from the part as it solidifies. Proper cooling is crucial to prevent warping or distortion of the stool’s shape.

Secondly, the ejector system of the stool mold must be designed to effectively eject the part from the mold. Since stools are generally tall and have a relatively high profile, the mold will require long ejector pins to push the part out of the cavity. These ejector pins are often on the underside of the stool, to avoid leaving visible marks on the top surface.

Additionally, the mold design should incorporate appropriate draft angles on the stool’s surfaces to facilitate the ejection process. Draft angles, which are slight tapers on the walls of the part, help reduce the force required to remove the stool from the mold, preventing deformation or damage.

Finally, the parting line of the mold, where the two halves of the mold come together, should be carefully positioned on non-critical areas of the stool to minimize any visible seams or parting line marks on the final product.

1.6. Trimming and Finishing

After the stool components have been molded, there may be some excess plastic or “flash” along the edges and joints. This flash should be carefully trimmed away using a sharp utility knife or chisel. Take care not to damage the underlying surface of the stool pieces during this trimming process. Any rough or uneven edges can then be sanded smooth.

Once the stool components have been trimmed, additional finishing techniques can be applied to achieve the desired surface texture and appearance.

• Sanding: The stool surfaces should be sanded in progressive grits, starting with a coarser 80-100 grit paper to remove any remaining imperfections, and then moving up to finer 120, 150, and 220 grit papers to achieve a smooth, uniform finish.
• Polishing: After the final sanding, the stool can be polished to enhance the sheen and luster of the surface. This can be done using a buffing wheel or soft cloths along with a furniture polish or wax.
• Surface textures: Depending on the desired aesthetic, additional surface textures can be applied to the stool. This could include lightly distressing the surface with a wire brush to create a weathered, rustic look, or embossing a pattern into the plastic using a texture plate or stamp.

1.7. Assembly

Usually, common types of plastic stools are almost finished products when they are pushed out, and they often just lack rubber pads at the bottom of the legs to increase friction.

And that is also the final stage of the production – assembly of sub-parts.

This is the final step in our production process, representing the high standards upheld by Inochi Global. We take pride in our meticulous approach, which results in products with minimal defects and maximum customer satisfaction.

 

Whether you’re an individual buyer or a distributor seeking top-quality plastic stool supplies at competitive prices, Inochi is your go-to source. Don’t miss out on the opportunity to partner with us! Contact us via WhatsApp at +84 83 214 8855 for a detailed quote and discover the quality and value we offer.

 

1.8. Packaging and Shipping

Once the finished stools have been produced, it’s important to inspect the packaging and prepare them for shipping and distribution. Here are the main steps:

1.8.1. Packaging Inspection

• Check that the packaging materials (boxes, cushioning, etc.) are the correct size and in good condition to protect the stools during shipping.
• Ensure the packaging is securely sealed to prevent damage or contamination.
• Verify that any required labeling, barcodes, or other markings are properly applied to the packaging.

1.8.2. Stool Inspection

• Carefully inspect each stool to make sure there are no defects, damage, or issues with the final product.
• Check that the stools match the design specifications and quality standards.
• Confirm the stools are clean and free of any debris or residue.

For plastic stools, the most common symbol found on plastic stools is the recycling symbol (a triangle with a number inside) and the plastic identification code is #5 (PP) – Polypropylene (due to its strength and durability)

1.8.3. Packing and Stacking

• Carefully place the inspected stools into the packaging, using any necessary cushioning or dividers to prevent shifting or damage.
• Stack the packaged stools in a way that maximizes space and protects the contents during shipping.
• Ensure the stacked packages are stable and secure for transportation.

1.8.4. Labeling and Documentation

• Apply clear shipping labels with the destination address, tracking information, and any handling instructions.
• Include any required documentation, such as packing slips, invoices, quality certificates and community compliance certificates or customs forms.
• Keep detailed records of the packaging, inspection, and shipping process.

1.8.5. Shipping Preparation

• Schedule the shipment with the carrier and provide them with all necessary information.
• Arrange for the packaged stools to be loaded onto the shipping vehicle carefully to avoid damage.
• Monitor the shipment’s progress and be prepared to address any issues that may arise during transit.

By following these quality control steps for packaging and shipping, you can help ensure the finished stools arrive at their destination in perfect condition, ready for distribution to customers.

2. Environmental Considerations

Meeting environmental and community compliance standards is essential for any factory. These standards help protect our planet and ensure that manufacturing processes are safe for everyone.

Inochi Global has also been awarded the BSCI (Business Social Compliance Initiative) certification, demonstrating that the business takes this responsibility seriously and complies with all necessary regulations. We prioritize sustainable practices in our operations, ensuring that our manufacturing methods minimize waste and reduce environmental impact.

In short, we have explored how are plastic stools made, from the selection of raw materials to the final production steps. These steps will contain very important information, especially for those who are new to manufacturing or distributors. They will be able to know which steps are indispensable and which steps require what machinery.