Sprues and runners play a vital role in the die casting process by directing molten metal through the mold. The sprue is the vertical channel that introduces the metal, while the runner system ensures the metal is evenly distributed to all cavities. These components are carefully designed to optimize flow, minimize defects, and enhance the quality of the final casting1
In this article, we’ll discuss the design and classification of sprues and runners, how to prevent die casting defects through proper design, and share the expertise of CEX Casting. Let’s dive into the importance of sprues and runners in die casting production.
Sprue
What Is a Sprue?
The sprue is a key component in the die casting process, serving as the primary vertical channel through which molten metal enters the mold.
Its primary function is to guide the molten metal into the runner system, which then distributes it to the various cavities of the mold.
Sprue Design
Shape and Size: Sprues are typically designed with a conical shape, which helps guide the metal flow and control its rate.
The size and shape of the sprue are determined by the size of the mold, the number of castings, and the shape of the part being produced.
Number of Gates: A single gate may be sufficient for small molds.
However, for larger or more complex molds, multiple gates may be necessary to ensure even metal distribution across all cavities.
Gate Location: The placement of the gate is essential for ensuring consistent metal flow.
It is usually positioned at the top or bottom of the mold to ensure steady, defect-free metal flow without air bubbles.
Flow Rate Control: Adjusting the gate size can help control the metal’s flow rate.
A too-rapid flow can trap gas in the mold, causing pores, while a slow flow may lead to incomplete filling of the mold.
Types of Gates
There are several types of gates commonly used in die casting:
Sprue Gate: The most common type, where molten metal enters the mold cavity directly from the runner. Ideal for simple castings.
Parting Line Gate: Located along the mold’s parting surface, this gate ensures a smooth seam and reduces defects like cracks and porosity.
It’s used for larger or more complex castings.
Subgate: A smaller, auxiliary gate typically positioned near the main gate. It helps control metal flow into smaller cavities and reduces turbulence.
Hot Runner Gate: This system uses a heated runner to maintain the metal at the optimal temperature, ensuring smooth and consistent flow into the mold.
It’s ideal for high-volume, complex castings.
Runner
What Is a Runner?
The runner is a horizontal channel that connects the gate to the cavities of the mold.
Its main function is to evenly distribute the molten metal to each cavity, ensuring uniform filling.
Runner Design
Effective runner design improves casting efficiency, reduces material waste, and shortens cycle times. Consider the following when designing a runner system:
Length and Diameter: The length and diameter of the runner should be tailored to the mold size, metal flow characteristics, and the number of castings.
A poorly designed runner may cause metal flow issues and waste material.
Material Selection: The runner material must withstand high temperatures and be compatible with the mold material.
Common materials include hot-working die steel, copper alloy, and stainless steel.
Runner Layout: A well-designed runner layout ensures even distribution of molten metal across all cavities, reducing the risk of defects caused by uneven flow.
Reducing Resistance: Minimizing resistance in the runner system helps optimize the metal flow rate.
This can be achieved by ensuring smooth surfaces, minimizing sharp angles, and avoiding unnecessary bends.
Types of Runners
Main Runner: The primary channel connecting the gate to the mold cavities.
It is the main path for metal flow and is designed according to the mold and casting specifications.
Branch Runner: A secondary channel that branches off the main runner to distribute metal to each cavity evenly.
This type of runner is used in molds with multiple cavities.
Hot Runner: A heated runner system that keeps the metal molten throughout the process, preventing cooling and solidification.
It is ideal for high-precision castings and mass production.
Cold Runner: An unheated runner where the metal gradually cools.
Cold runners are used for smaller or medium-scale production runs and are typically not suitable for precision applications.
Multi-Branch Runner: This design is used for multi-cavity molds and ensures that each cavity is filled at the same rate, improving production efficiency.
Common Die Casting Defects and Gate & Runner Optimization
Die casting defects such as porosity, cold shuts, shrinkage, flashes, and cracks can occur if the gate and runner system is not properly optimized.
By fine-tuning the gate and runner design, these defects can be minimized.
Porosity: Caused by trapped gas or air during the die casting process.
Optimizing the ventilation design of the runner system and adding exhaust channels can effectively reduce the occurrence of pores.
Cold Shut: This occurs when the metal fails to completely fill the mold due to slow flow rates.
Optimizing the gate size and position, ensuring the appropriate molten metal flow rate, and avoiding premature cooling of the molten metal, can prevent cold shuts.
Shrinkage Cavities: Usually caused by the shrinkage of the metal during the solidification process.
Properly adjusting the metal flow direction and runner path to ensure the uniformity of filling can effectively reduce the occurrence of shrinkage cavities.
Flashing: Caused by molten metal leaking into gaps in the mold.
Optimizing the mold design and gate position to ensure complete metal filling and reduce unnecessary pressure can effectively reduce the flashing phenomenon.
Cracks: Result from excessive stress or uneven metal flow during cooling.
Proper design of the flow rate of the gate and the flow direction of the runner can help reduce local stress and avoid cracks.
Expertise of CEX Casting
At CEX Casting, we specialize in providing comprehensive, in-house die casting mold design and manufacturing services.
Using the mold flow analysis software, we simulate metal flow to predict potential defects, including porosity, shrinkage, cold shuts, etc., before production begins.
This enables us to optimize gate and runner designs in a targeted manner to achieve high-quality aluminum die casting parts.
Each gate system is tailored to the customer according to the structure of the mold and the flow requirements of the product, ensuring that the molten metal can enter the mold under the best conditions.
We also pay special attention to the optimization design of the runner, including the reasonable selection of the length, diameter, and material of the runner to ensure smoother metal flow and reduce the risk of overcooling or too fast filling.
Conclusion
In conclusion, optimizing the gate and runner system is crucial to producing high-quality aluminium die casting parts.
Proper designs optimize flow, minimize defects, and achieve excellent die casting products.
At CEX Casting, we offer tailored, in-house die casting mold development services to help you achieve the best possible die casting effects.
Contact us today to learn how we can elevate your die casting project to a next level with our expertise.