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selecting gates for molding

How to Choose Gates for Plastic Injection Molding

Master the art of selecting gates for plastic injection molding to enhance your part quality and production efficiency.

When selecting gates for plastic injection molding, consider various types like edge gates, submarine gates, cashew gates, and more. Edge gates suit larger parts but leave visible marks; submarine gates work well for small parts with automatic trimming below the parting line. Cashew gates offer discreet injection points but can be tricky to maintain if broken. Direct and sprue gates have different advantages, while diaphragm gates guarantee consistent part shrinkage. Hot runner gates offer precise material flow control, and pin gates are effective for fast-flowing resins. Gate placement is essential for controlling flow dynamics and achieving desired part quality. Understanding these options will help you optimize your molding process.

Edge Gates

Edge gates are commonly selected for filling larger parts with a substantial cross-sectional area in plastic injection molding. They're advantageous for flat parts and sections of medium to thick dimensions.

However, one drawback of edge gates is the visible mark they leave at the parting line, which can impact the overall aesthetics of the part. These gates are often grouped with fan gates and tab gates for their unique characteristics in the injection molding process.

The flow path of the molten plastic in edge gates is straightforward, making them suitable for parts that require uniform distribution of material. When essential, edge gates offer a reliable solution due to their focused injection point.

Understanding the impact of edge gates on part aesthetics is essential when deciding on the gate type for larger parts. By considering both the functional and visual aspects, you can optimize the injection molding process for your specific requirements.

Submarine Gates

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Submarine gates, commonly utilized for small parts or high cavitation molds, are machined below the parting line to facilitate automatic trimming processes. These gates are ideal for applications where aesthetics are important, as they allow for a clean parting line. However, caution must be exercised when using large submarine gates, as they can result in cosmetic issues in the final part. Additionally, using a small gate for a large part may lead to shear heating during injection, potentially affecting the part quality.

It is essential to take into account the limitations of submarine gates, particularly regarding the maximum cross-sectional area they can effectively handle. Due to their design, these gates may not be suitable for parts with extensive cross-sections. Careful evaluation of the part geometry and material flow is necessary to determine the most suitable size and placement of the submarine gate to ensure a successful injection molding process.

Cashew Gates

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Cashew gates, resembling the nut, are strategically placed below the mold parting line to allow for automatic shearing. When selecting cashew gates, consider their benefits, gate size limitations, and compatibility with different materials for best performance.

Understanding the challenges of removing cashew gates during ejection is important, as it may necessitate the use of gate inserts to address any issues that may arise.

Cashew Gate Benefits

Machined below the parting line to enable automatic shearing during injection molding, cashew gates offer the advantage of positioning the injection point discreetly behind the visible surface of the part. These gates help maintain the aesthetics of the part by concealing the gate location from the show surface.

However, maintenance can be tricky as broken cashew gates are challenging to remove during ejection. Addressing this issue, cashew gates require removable gate inserts for repairs. It's crucial to bear in mind that similar to tunnel gates, cashew gates have limitations in size and cross-sectional area, which may restrict their application in certain molding scenarios.

Despite these limitations, the discreet positioning and aesthetic benefits make cashew gates a valuable option for specific injection molding needs.

Gate Size Considerations

Considerations regarding the size of cashew gates in plastic injection molding play a pivotal role in determining their applicability and effectiveness in specific molding scenarios.

Cashew gates, shaped like a tree nut, are ideal for challenging mold areas. Machined below the parting line, these gates allow for automatic shearing. The injection location can be strategically placed behind the show surface using cashew gates.

However, removing cashew gates during ejection can be difficult, often requiring removable gate inserts for broken gates. While cashew gates have size limitations similar to tunnel gates, they offer distinct advantages in certain molding situations. Properly sizing cashew gates is essential for ensuring successful injection molding processes in challenging mold areas.

Material Compatibility Tips

When selecting materials for cashew gates in plastic injection molding, it's important to take into account their compatibility with the specific plastic resin being used. Cashew gates are designed to be machined below the parting line for automatic shearing during injection molding, ensuring the injection location remains hidden behind the show surface of the final molded part.

However, these gates have limitations in size similar to tunnel gates and may lead to cosmetic issues if too large. Cashew gates are particularly suited for challenging mold areas where maintaining the show surface appearance is essential.

It's imperative to contemplate the properties of both the gate material and the plastic resin to ensure proper functioning and best results in the molding process.

Direct or Sprue Gates

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For plastic injection molding, choosing between direct gates and sprue gates depends on the part's design requirements and production considerations.

Direct gates are simple and common, suitable for shell molds, and boxed molds. They require less injection pressure, resulting in a short feeding time. However, direct gates may not be suitable for parts that require high aesthetic considerations due to the visible marks they leave at the parting line.

On the other hand, sprue gates are located at the thickest section of the parting line, ensuring uniform filling. While they're ideal for parts with specific design requirements, they may require higher injection pressures compared to direct gates.

Understanding the trade-offs between direct and sprue gates is important in achieving the desired results for your plastic injection molding project. Make your choice based on the specific needs of your part to optimize production efficiency and final product quality.

Diaphragm Gates

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Diaphragm gates offer the advantage of ensuring consistent part shrinkage by allowing an even flow of plastic. These gates are particularly suitable for parts with large open diameters.

When used, diaphragm gates permit a significant volume of plastic to enter the cavity, commonly seen in open-ended cylindrical parts.

Diaphragm Gate Benefits

Using diaphragm gates in plastic injection molding processes guarantees consistent part shrinkage and uniform filling for top-quality production. Diaphragm gates are designed to secure even plastic flow, particularly beneficial for parts with large open diameters where maintaining uniform filling is critical.

These gates aid in managing the distribution of plastic within the mold cavity, resulting in precise part shrinkage. By facilitating a continuous and controlled flow of plastic, diaphragm gates contribute to the production of high-quality parts.

Their ability to control the plastic flow and guarantee consistent filling makes them an essential component in achieving the desired part characteristics. Diaphragm gates are essential for maintaining quality standards in injection molding processes.

Diaphragm Gate Limitations

When contemplating diaphragm gates in plastic injection molding, it's important to be mindful of their limitations to guarantee excellent production outcomes. Diaphragm gates, while ensuring even plastic flow for consistent part shrinkage, aren't suitable for all types of parts. They're best suited for components with a large open diameter, as they allow a significant amount of plastic to flow into the cavity.

However, diaphragm gates are less effective for parts that aren't open-ended or cylindrical in shape. Additionally, one limitation is that diaphragm gates need to be sheared off in a secondary operation for part separation, which can add complexity to the manufacturing process.

Hot Runner Valve Gates

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Hot Runner Valve Gates play a vital role in maintaining ideal pressure and temperature conditions during the plastic injection molding process, ensuring precise control over material flow and part quality. As part of a hot runner system, these gates help retain molten plastic in a liquid state, enhancing efficiency compared to cold runner systems.

The gate design in Hot Runner Valve Gates leaves a vestige on the part where the gate breaks from the hot runner tip. This design feature contributes to material savings and improved process control. By utilizing Hot Runner Valve Gates, manufacturers can achieve better part quality and reduced waste, optimizing the injection molding process.

These gates are instrumental in minimizing inconsistencies and ensuring that the molten plastic reaches the mold cavity in a controlled manner, ultimately leading to higher-quality finished products with reduced material wastage.

Hot Runner Thermal Gates

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Maintaining material in a liquid state between the machine barrel and the part, hot runner thermal gates utilize controlled temperature and pressure conditions to act as temporary stoppers during the molding process.

These gates play an important role in ensuring consistent thickness and quality of the final product by facilitating the flow of molten material into the cavity.

Proper gate placement is essential in injection molding design to optimize the filling process and prevent defects.

Hot runner thermal gates offer advantages such as improved process control and material savings compared to other gate types.

However, one common issue with this gate type is the occurrence of gate vestiges resulting from material breaking off at the hot runner tip.

Understanding the dynamics of material pressure and flow is key to leveraging the benefits of hot runner thermal gates effectively in plastic injection molding.

Fan Gates

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Fan gates, also known as spreader gates, facilitate efficient filling of larger parts in plastic injection molding by widening to promote uniform plastic flow and distribution. They're particularly useful for parts that require a larger cross-sectional area during the molding process.

When compared to other gate types like tab gates and edge gates, fan gates stand out for their ability to guarantee even distribution of plastic within the mold cavities. By widening as the plastic material flows through them, fan gates help reduce flow resistance, leading to a smoother and more consistent filling process.

Additionally, fan gates play a significant role in minimizing shear stress on thin parts, contributing to the overall quality of the final product. When selecting gates for your injection molding project, consider the advantages that fan gates offer in terms of flow control, uniform distribution of plastic, and efficient filling of mold cavities.

Pin Gates

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Pin gates, commonly positioned on the B-side of molds in plastic injection molding, are known for their suitability with fast-flowing resins and their ability to reduce cycle times. When considering the use of pin gates in your injection molding process, keep the following key points in mind:

  1. Gate Vestiges: Pin gates leave small nubs on the parts where the gates were located. If your parts can tolerate these gate vestiges without affecting the final product quality, pin gates can be a suitable choice.
  2. Mold Cavity Introduction: Pin gates offer a simple and effective way to introduce molten plastic into the mold cavity. This direct method can help maintain the integrity of the mold cavity design and reduce the chances of flow-related defects.
  3. Cycle Time Reduction: Due to their ability to quickly fill the mold cavity with fast-flowing resins, pin gates can contribute to reducing cycle times. This efficiency can enhance productivity and lower manufacturing costs.

Gate Placement Considerations

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Strategically positioning gates in plastic injection molding is essential for controlling the flow dynamics of molten plastic into the mold cavity. The gate type and location have a substantial impact on the filling of the cavity and the quality of finished parts. Placing gates appropriately helps in managing high tensile stress around the gate area, ensuring uniform plastic distribution. Here are some key considerations for gate placement:

Types of Gates Gate Location Impact on Finished Parts
Edge Gate Near the edge of parts Minimal vestige, good for small parts
Sub Gate Below the part Reduces visible gate marks, suitable for aesthetic parts
Tab Gate On a flat surface Leaves a small witness mark, ideal for flat parts

Selecting the right gate type and location is vital for achieving desired part quality in plastic injection molding. Proper gate placement minimizes imperfections and enhances the overall appearance of the molded components.

Frequently Asked Questions

How to Determine Gate Size Injection Molding?

When determining gate size in injection molding, you need to take into account factors like material properties, part design, and mold setup. Material viscosity, injection pressure, and part geometry play important roles in gate size selection.

Proper gate sizing guarantees efficient material flow, minimal shear stress, and consistent part quality. By assessing gate type, location, diameter, and design, you can enhance injection molding outcomes for your plastic parts.

What Type of Gate Is Used in Injection Molding?

When deciding on the type of gate for injection molding, consider:

  • Edge gates for larger parts
  • Tunnel gates for small parts
  • Cashew gates for hiding injection points
  • Direct sprue gates for standard designs
  • Diaphragm gates for even flow in cylindrical parts

Each gate type serves a specific purpose in ensuring efficient plastic flow and best part quality. Understanding these variations can help you choose the most suitable gate for your injection molding needs.

Why Is a Small Gate Size Preferred in Injection Molds?

When choosing gates for plastic injection molding, opt for a smaller gate size to reduce material waste, enhance precision, and accelerate cycle times.

Small gates are essential for intricate parts, preventing cosmetic flaws and improving surface finish.

What Is the Gate Mark in Injection Molding?

Imagine the gate mark in injection molding as a tiny door where the plastic gains entry into the mold cavity. It's like a subtle signature left on the final part, indicating where the plastic was injected.

These marks can impact the appearance of the part, potentially requiring additional finishing touches. The gate location and design play an essential role in determining the size and visibility of this mark on the finished product.


When choosing gates for plastic injection molding, consider factors such as part design, material, and production requirements.

For example, if you're producing a complex part with thin walls, a hot runner thermal gate may be the most appropriate option to guarantee uniform filling and reduce cycle times.

By carefully evaluating your options and selecting the right gate design, you can optimize the molding process and achieve high-quality results.

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