The gate is the vertical channel through which the molten material flows into the mold. It is the first entrance for the molten metal to enter the cavity and the main pressure transmission channel. Therefore, the size of the gate affects the flow rate and filling time of the molten metal.

The design of the die casting mold enables manufacturers to obtain a finished product without assembly. However, the gate may also leave some excess material that needs to be removed from the casting.

It often regulates the amount of material flowing into the mold. The material in the gate connects the runner to the pouring base and usually tapers downward to reduce turbulence and the generation of bubbles.

Casting also depends on the gate and runner design of the gate. There are both bottom gate options and vertical gate options in the design. In the case of equal casting material and gate height, the formula can be adjusted accordingly.

Equation

The path through which liquid material (such as polystyrene or polyvinyl chloride) flows into the mold, where the material hardens into a block, is called a gate in injection molding. The gate is another name for the substance that solidifies in these channels, forming a framework that holds the components together in a roughly flat structure.

Types of Injection Sprue Molding

Cold sprue bushings in injection molding

To provide a passage between the molding machine's injector and the mold cavity, cold sprue bushings are placed in the mold. If appearance is important, they are heated, ultimately leaving a sprue that must be eliminated, which is usually achieved by further operations. The "O" size hole entrance and the circular radius are two critical dimensions of the bushing hose end.

Hot sprue bushings in injection molding

To create a heat path between the molding equipment's nozzle and the mold cavity, hot sprue bushings are placed in the mold. The resin melt is kept hot inside the brush using a heat exchanger located inside the brush.

Sprue bushing design

However, there are also flat-type brushes, whose surface is flat instead of the nozzle radius. The circular radius of the sprue bushing is usually half an inch or three-quarters of an inch. The buyer must select some other size in addition.

You can make the sprue bushing based on the calculation results, or you can buy the sprue bushing. Small molds use sprue bushings with two bolts, which can be used for injection molding machines weighing less than 350 tons. Large molds use sprue bushings with four bolts for use on injection molding machines weighing more than 200 tons.

When making or selecting a sprue bushing, the sprue ball radius must be larger than the nozzle radius. If the radius is smaller, there will be a gap between the gate and the nozzle, the resin will overflow, and the tension of the injection molding machine will be lost. If the radius is larger, the tension can be maintained.

The inner hole diameter must be larger than the nozzle hole diameter. If the inner hole diameter is smaller than the nozzle hole diameter, it prevents the migration of molten plastic material. The diameter of the nozzle is usually 25 mm. Be sure to check the injection molding machine catalog when selecting a gate to ensure that it is 0.5 m or larger in diameter.

Typically, the inner hole angle is about 26 degrees. For best results, inject at a 35-degree angle. Verify the size of the template; the length of the gate must match the thickness of the template. If the gate thickness is larger, the sprue bushing may need to be cooled to speed up the injection process.