When considering the hot runner system for the mould customizing of an 1100L plastic garbage bin mould, there are significant differences between using a pin point gate and a needle valve gate:
1. Gate Size and Flow Characteristics
>Pin Point Gate
A pin point gate has a very small diameter, typically in the range of 0.5 - 2mm. This results in a high shear rate when the molten plastic passes through it. For the 1100L plastic garbage bin mould, the small gate size restricts the flow rate of the melt initially. As a result, the filling speed might be relatively slow, which could be a concern for large - volume moldings. However, the high shear rate can also improve the fluidity of some plastics by reducing their viscosity, which is beneficial for complex - shaped parts like the trash can with various curves and details.
The small size of the pin point gate also allows for a more precise control of the melt flow direction to some extent, as the melt is forced through a narrow passage.
>Needle Valve Gate
The needle valve gate doesn't have a fixed small - scale orifice like the pin point gate. Instead, the opening of the gate can be adjusted by moving the needle. When fully open, it can allow a large volume of molten plastic to flow through quickly. This is highly advantageous for the 1100L plastic garbage bin mould as it can speed up the filling process, especially for large - volume cavities. The flow rate can be precisely regulated according to the filling stage, such as starting with a slow flow to prevent air entrapment and then increasing the flow rate for efficient filling.
2. Gate Vestige and Product Appearance
>Pin Point Gate
After the plastic solidifies, the pin point gate leaves a small, almost dot - like mark on the product surface. In the case of an 1100L plastic garbage bin, if the gate is located in a visible area, this small mark might be a minor aesthetic concern. However, it is generally easier to trim off compared to some other gate types.
>Needle Valve Gate
When properly operated, the needle valve gate can leave almost no visible mark on the product surface. Since the needle can be closed tightly after the injection, there is no residual plastic at the gate area, which is highly desirable for products where a clean surface finish is crucial, such as high - end plastic garbage bins.
3. Process Control and Defect Prevention
>Pin Point Gate
With a pin point gate, the injection pressure needs to be carefully controlled. Due to the small gate size, a higher injection pressure is often required to ensure the melt can fill the entire 1100L mould cavity. This high pressure may lead to issues like flash, excessive packing pressure, and increased internal stress in the product. Also, the small gate is more prone to clogging if there are impurities in the plastic material.
>Needle Valve Gate
The needle valve gate offers better control over the injection process. The ability to adjust the opening and closing time of the needle allows for precise control of the packing and holding pressure. This can effectively prevent defects such as over - packing, sink marks, and air entrapment in the 1100L plastic garbage bin. It also reduces the risk of gate freezing during the injection cycle, which is a common problem with fixed - size gates like the pin point gate.