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Plastic injection molding is one of the popular techniques utilized in producing plastic products, from toys to automotive parts. Thanks to its fast, repeatable, and incredibly scalable capabilities, it’s widely used in different industries. 

Injection molding sprue is one of the important components in the process. It acts like a connector for the passage of molten plastic between the machine and the mold. This channel is in charge of transferring the molten plastic to its proper desired location. 

Besides, what else should we know about this detail? Let’s find out in the article below!

1. What is a Sprue In Injection Molding?

An injection molding sprue is a channel allowing molten plastics to transfer into the mold. The component is the vertical passage whose widest end connects to a system of runners. The sprue is the entrance for the molten plastic to reach its ultimate destination, the mold cavity, which is the empty space between the two halves of the mold. 

2. Why is it Important?

Without the properly located injection molding sprue, the molten plastic cannot flow evenly into the mold cavity to fill up all part’s details and features. Once the component is settled too close to the thickest section of the part, it will lead to fast cooling plastic, which is the main reason for warpage and other problems. On the other hand, if the sprue’s location is too far, the plastic does not likely flow evenly; thus, you will have a potential incomplete filling, such as sink marks or voids.

The injection molding sprue should be installed at the thickest section of the part to fill the cavity effectively and avoid creating defects. The position should be proper enough for the plastic flows to go evenly throughout the part without any potential for excessive shear and high stress.

3. Common Injection Molding Sprue Options  

3.1. Cold Runners

Cold runners or cold sprue is the conventional sprue system used in plastic injection molding. It consists of a vertical passage allowing the molten to flow to the mold. However, due to the high potential defective points and high maintenance requirements, this option is not preferred anymore.

3.2. Hot Runners

It is an alternative format for the cold runners. Hot runners heat the plastic in a way that makes it unsolidified inside the operating runners. Therefore you will gain high efficiency and fast production.

3.3. Hot Sprue Bushings

These heated bushings help keep the plastic molten hot. Unlike the hot runners, they don’t maintain the molten state of the runners. Depending on how long it takes the sprue to cool down, this format can reduce cycle times and waste. Sometimes, it can be used as a mediator between cold and hot runners.

4. Choose The Proper Sprue

4.1. Design

One crucial factor affecting the effectiveness of injection molding sprue is its design. The channel’s shape and design should be suitable for the molten material to move evenly and smoothly into the mold cavity. It should not cause any defects to the finished part and should make it easy for the excessive material to be removed. You might need to adjust the shape of the channel according to the specific geometry of the product you are making.

You also should choose the diameter of the injection molding sprue suitable for the viscosity of the material you are processing. It should be large enough for the molten material to flow with ease. However, it should not be too large; otherwise, you might need to face turbulence and other flow-related matters.

4.2. Materials

One of the most common materials for injection molding sprue is aluminum or steel. They are tough, resistant to wear and tear, and can tolerate high temperatures and pressures during the process of molding and trimming. 

5. Methods of Using Sprue in Injection Molding

5.1. Prepare The Mold

The mold should be clean and free of debris. It should be set in the correct position. Then, attach the sprue in the proper place.

5.2. Injection Molding Process

Start the process by injecting the molten material into the mold cavity through the sprue. The material then will be pushed under high temperature and pressure to fill the mold cavity, forming the shape of the part you are making.

5.3. Cooling

How long it takes for the system to cool down depends on the device’s complexity and size. It can be from a few seconds to several minutes. After that, the material will be solidified and will form the desired shape.

5.4. Ejection

The next step is to open the mold, eject the finished part, and trim off the excess material, including the sprue, with a cutting tool before using.

5.5. Clean Up

After finishing, clean the mold and prepare for the next injection molding cycle. You should remove excessive material and debris and ensure the correct position of the injection molding sprue.

6. Abbey – A Professional Manufacturer of Black Masterbatch for Injection Molding

Abbey Vietnam is the result of the long-term cooperation of Abbey Masterbatch Ltd. UK and European Plastic Co. Vietnam. Located in the seaside country, Abbey has access to high-quality raw material resources and an advantage in shipping our products to many countries in the world at a cost-effective price.

Our black masterbatch is the perfect combination of black carbon pigment, virgin resin, and other additives that are suitable for various applications. We provide a wide range of options with high gloss, brightness, and shine to help you achieve a colorful and eye-catching appearance for plastic products and cover aesthetic requirements. Besides various choices of particle size, Abbey’s black masterbatch is dust-free in the producing process, has weather-ability properties and excellent dispersion.  

Moreover, our product is specified for injection molding. It contains a high color of carbon black and a wide range of pigment loading choices. Abbey’s black masterbatch grades possess outstanding features that are ideal for the injection molding process, such as great dispersion, compatibility, temperature stability, and diluted ability. 

In addition, Abbey has seasoned technicians and the most pleasant sales consultants to bring you the best service, guaranteeing you increased productivity and a satisfying experience.