Omar Khalid
Injection molding gates are designed openings that control the flow of molten plastic into a mold cavity. Tunnel gates are a type of injection molding gate that is used to fill the cavities in a two-plate mold. The curved tunnel gate is a variation of the tunnel gate, also known as a cashew gate, that provides gating in regions that cannot be reached by the standard tunnel gate. The curved tunnel gate has a shape that is curved from the parting line towards the inside of the movable core. The four most common types of tunnel gate designs are elliptical gates, D-gates, ball-gates, and chisel gates.
| Characteristics | Values |
|---|---|
| Definition | A curved tunnel gate is a type of tunnel gate with a curved structure. |
| Use Cases | Curved tunnel gates are suitable for smaller parts and can be used to gate non-visible locations, improving the appearance of the final product. They are also useful for reaching areas that cannot be accessed by standard tunnel gates. |
| Advantages | Curved tunnel gates reduce time and cost during injection molding, taking up less space in a tool than a two-part gate. They can also prevent defects caused by uneven cooling and untimely hardening of molten plastic. |
| Common Types | Cashew gates, a variation of tunnel gates with a curved structure, are commonly used and can reach areas that standard tunnel gates cannot. |
| Gate Mark | The gate mark left by a tunnel gate depends on its design. For example, a full conical gate leaves an elliptical mark, while a truncated cone or D-gate leaves a "D"-shaped mark. |
| Plastic Resins | Some suitable plastic resins for tunnel gates include ABS, polypropylene, low-density polyethylene, and high-density polyethylene. |
| Gate Location | Tunnel gates are usually placed below the mold parting line, facilitating automatic trimming during component ejection. |
| Gate Size | The size of tunnel gates can vary, with gate inserts available in sizes ranging from 0.1 to 0.47 sq mm. |
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What You'll Learn
Tunnel gates are used to cut moulded items automatically
Tunnel gates, also known as submarine gates, are used in injection moulding to automatically cut moulded items. They are placed below the mould parting line, facilitating automatic trimming during component ejection. This is achieved through a narrow channel that joins the cavity near the parting line, filling the cavity from below.
The tunnel gate is a high-shear gate, allowing only a small amount of molten plastic into the mould cavity. This makes it ideal for moulding small components. Using tunnel gates for larger parts can lead to long cycle periods and poor surface finishes due to shear heating. The curved tunnel gate is a variation of the standard tunnel gate, with a curved shape that allows gating in areas that are inaccessible to the standard gate. The curved structure makes it challenging to extract moulded parts without damaging them.
There are four common types of tunnel gate designs: the full conical gate, the truncated cone or D-gate, the spherical or ball-gate, and the chisel gate. All four designs have a knife-edge section of steel on the side nearest the parting line, which is used for shearing. The D-gate and ball-gate also have a knife edge on the opposing side. These edges can wear out quickly during injection, especially with filled or abrasive materials.
Tunnel gates can be machined at almost any angle, which is convenient for reaching locations that would be inaccessible with other gate types. However, they have a reputation for being temperamental and can freeze off too early, fail to fill or pack out a part, or generate excessive shear. These issues are often due to an undersized tunnel gate.
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The curved tunnel gate has a unique structure
The curved tunnel gate, also known as a cashew gate, is a unique structure with distinct characteristics and applications. Its design and functionality set it apart from other types of tunnel gates used in injection moulding processes.
The curved tunnel gate is characterised by its curved structure, which distinguishes it from typical tunnel gates that are often conical or elliptical in shape. This curvature allows the cashew gate to access areas that standard tunnel gates cannot reach. It can navigate challenging regions within a mould, making it particularly useful for complex product designs.
One of the key advantages of the curved tunnel gate is its ability to prevent deformation during the ejection process. The curved shape ensures that the material within the gate undergoes significant distortion, enabling the removal of moulded parts without causing damage or distortion. This feature is especially valuable when manufacturing intricate or delicate components.
In terms of its structure, the curved tunnel gate is positioned with the gate opening part at the top surface of the core. It incorporates an ejector pin placed near the gate and a boss provided above the pin for support. The length of the boss, denoted by H, is carefully selected to ensure that the gate remains supported until the moulded product is completely removed from the mould, allowing for smooth cutting of the gate.
The curved tunnel gate is known to be temperamental, sometimes presenting challenges during the moulding process. One common issue is the gate not releasing properly, which can be addressed by increasing the length of the boss or adjusting the amount of undercut formed on the boss. Additionally, the curvature of the gate is often determined through trial and error, making it a complex design process that requires careful consideration.
Overall, the curved tunnel gate, or cashew gate, offers a unique structure that expands the capabilities of injection moulding. Its ability to access hard-to-reach areas and prevent deformation during ejection makes it a valuable tool for creating small, detailed components with complex designs.
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Ejector pins and bosses support the gate
In the context of curved tunnel gate plastics, ejector pins and bosses play a crucial role in supporting the gate and ensuring the successful removal of the moulded product. Here's a detailed explanation:
Ejector pins are essential components in the injection moulding process. They act as "bouncers", applying force to eject the moulded part from the mould or mold. In the case of curved tunnel gates, an ejector pin is strategically placed near the gate, specifically in the runner, to facilitate the removal of the moulded product. The placement of ejector pins is critical to their function and is determined by experts, taking into account various factors.
Bosses, on the other hand, are structural features that provide additional support. In the context of curved tunnel gates, a boss is positioned above the ejector pin to support the gate effectively. The length of the boss, denoted as "H", is a critical factor. It is carefully selected to ensure that the gate remains supported until the moulded product is completely removed from the mould. This careful consideration of boss length helps achieve smooth cutting of the gate.
The combination of ejector pins and bosses ensures that the curved tunnel gate can be successfully opened and closed, allowing for the efficient production of moulded items. The curved structure of the gate, which curves from the parting line towards the inside of the movable core, requires precise positioning of these components to ensure optimal functionality.
Ejector pins come in various sizes and designs, including center-cut, shortest, and longest options. The selection of the appropriate pin size and type is critical to preventing issues such as sink marks on the back side of the moulded part or holes caused by the pin punching through the surface. Ejector pins can also be utilised within a jump gate design, where the pin is often referred to as a "split pin".
Optimising the design of the ejector pins and bosses is crucial to ensuring a smooth and efficient production process. By selecting the appropriate length for the boss and the right size and type of ejector pin, manufacturers can avoid common issues such as gate vestige and surface marks on the moulded products. This optimisation process contributes to achieving higher-quality parts and improving the overall efficiency of the injection moulding process.
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Tunnel gates are ideal for small components
Tunnel gates, also known as submarine gates, are used to automatically cut the molded item and gate during the opening and closing of the parting surface. They are placed below the mold parting line, facilitating automatic trimming during component ejection. This type of gate is ideal for small components as it allows little molten plastic into the mold cavity. Using tunnel gates for larger parts can lead to unnecessarily long cycle periods and poor surface finishes caused by shear heating.
The basic design of a tunnel gate requires knowledge of its shape and size. The tunnel gate is typically conical in shape, with the smallest end of the cone attached to the part. The gate is cut in the mold, creating a tunnel from the runner to the cavity below the parting line of the mold. The gate opening must be small to ensure that it breaks away from the part during ejection without causing damage or leaving an excessive gate vestige.
Tunnel gates can be machined at almost any angle, making them convenient for reaching locations that would be inaccessible with other gate types. They are also useful for multi-cavity molds or parts with multiple tunnel gates. However, they can be temperamental and may present challenges during processing. Common issues include one gate coming out while another stays put, which can be resolved by extending the length of the bosses formed by the ejector pins.
To prevent flakes, it is important to understand that as the tunnel gate is withdrawn from its bore, it flexes and tries to spring back to its original shape. This spring force can cause a fracture at the tip of the tunnel gate. Converting the elliptical gate to a chisel gate can help keep the boss engaged with the pin, even when it is beyond the parting line of the mold. Additionally, increasing the length of the boss near the tunnel gate or the amount of undercut formed on that boss can address issues with gate removal.
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Common tunnel gate designs include elliptical, D-gate, and ball-gate
Tunnel gates are a type of gate with a structure that automatically cuts the moulded item and gate when the parting surface is opened and closed. The four most common tunnel gate designs are the elliptical gate, D-gate, ball-gate, and chisel gate.
The elliptical tunnel gate leaves an elliptical gate mark. This type of gate is the biggest culprit for flaking, especially if the gate is long and the angle from the parting line is over 45°. This is due to the major diameter of the ellipse being the largest and the structural integrity of the tip being the weakest.
The D-gate, or truncated cone, leaves a "D"-shaped gate mark. D-gates are good at not flaking and are better for gating into shallow parts than elliptical gates.
The ball-gate, or spherical or ball-nosed gate, leaves a perfectly round gate mark.
Chisel gates, also called flare gates, leave a rectangular gate mark. They are the best at not flaking due to their wide structural integrity. They also leave the least amount of gate vestige as they are the shallowest of any tunnel gate type.
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Frequently asked questions
A curved tunnel gate, also known as a cashew gate, is a variation of the tunnel gate with a curved structure that allows gating in regions that cannot be reached by a standard tunnel gate.
A tunnel gate is a type of injection molding gate design used to control the flow of molten plastic into a mold cavity.
The four most common types of tunnel gate designs are the elliptical gate, D-gate, ball-gate, and chisel gate.
Curved tunnel gates can reach areas of the mold that cannot be joined by a regular tunnel gate, making them ideal for molding small components.
Tunnel gates can be temperamental and may present issues such as freezing off too early, not being able to fill or pack out a part, or generating excessive shear. These issues often arise when the tunnel gate is undersized.
