It is a section of the mold that connects the nozzle of the injection molding machine to the runner or cavity. The top of the main flow channel is concave for engagement with the nozzle. The main channel inlet diameter should be slightly larger than the nozzle diameter (O.8mm) to avoid spiking and prevent the two from being blocked due to inaccurate convergence. The diameter of the inlet depends on the size of the product, usually 4-8mm. The diameter of the main flow path should be enlarged inwards at an angle of 3° to 5° to facilitate the stripping of runners.

 

Gate

 

The gate, also known as the feed port, is a narrow passage between the runner and the mold cavity, and it is also the shortest part of the meat. Its role is to use the tight flow surface to accelerate the effect of plastic, high shear rate can make the plastic fluidity (because of the plastic thinning thinning properties); viscosity heating effect of temperature rise also has to increase the temperature, reduce viscosity effect. ?

 

After the molding is completed, the gate first solidifies the seal, preventing the plastic from flowing back, and avoiding the mold cavity pressure dropping too quickly, so that the molded product has a function of shrinkage and depression. After molding, it is easy to cut off to separate the runner system and plastic parts.

 

Cold material hole

 

It is a hole located at the end of the main channel to trap the cold material produced between the two shots at the tip of the nozzle, thereby preventing the clogging of the runner or the gate. If the cold material is mixed into the cavity, the internal stress is likely to occur in the manufactured product. The cold material hole has a diameter of about 8 to 10 mm and a depth of 6 mm. In order to facilitate demoulding, the bottom is often borne by the stripper. The top of the stripping bar should be designed as a zigzag hook or a depressed groove so that the strip can be smoothly pulled out during demoulding.

 

Split channel

 

It is the channel connecting the main channel and each cavity in the multi-slot die. In order to make the molten material fill the cavity at equal speed, the arrangement of the runners on the mold should be symmetrical and equidistantly distributed. The shape and size of the runner section affect the flow of the plastic melt, the release of the product and the ease of mold making. If an equal amount of flow is used, the flow path resistance with a circular cross section is minimized. However, due to the small surface area of ​​the cylindrical flow path, the cooling of the diversion channel material is unfavorable, and the diversion path must be opened on the two mold halves, which is both labor-intensive and easy-to-align. Therefore, trapezoidal or semi-circular cross-section runners are often used, and they are opened on half of the mold with a stripper rod. The surface of the runner must be polished to reduce the flow resistance to provide a faster filling rate. The size of the runner depends on the type of plastic, the size and thickness of the product. For most thermoplastics, the cross-sectional width of the runner is not more than 8m, the extraordinarily large 10-12m, and extremely small 2-3m. To meet the needs of the premise should minimize cross-sectional area, so as not to increase the shunt material and extend the cooling time.

 

The basic principles of gating system design

 

1. Cavity layout considerations

 

1) Use Balances Layout as much as possible;

 

2) The symmetry of the mold cavity arrangement and the gate opening are symmetrical to prevent the mold from uneven loading and the mold overflowing occurs.

 

3) The mold cavity arrangement is as compact as possible to reduce the size of the mold.

 

2. Flow guidance considerations

 

1) It can guide the molten plastic to fill the mold cavity smoothly, without eddy current, and can be smoothly exhausted;

 

2) Minimize the impact of small diameter cores and metal inserts on the front side of the plastic melt to avoid core shift or deformation.

 

3. Heat loss and pressure drop considerations

 

1) The smaller the heat loss and pressure drop, the better;

 

2) The process should be short;

 

3) The cross-sectional area of ​​the flow path should be large enough;

 

4) Try to avoid bending the flow path and suddenly change the flow direction (change the direction with the arc angle);

 

5) The surface roughness of the runner is low;

 

6) Multi-point pouring can reduce pressure drop and required injection pressure, but there will be suture problems.

 

4. Consideration of flow balance

 

1) When Multi-Cavity is filled, the runners must be balanced. Plastics must be filled in at the same time to ensure the consistency of the quality of the molded parts.

 

2) Naturally-Balanced Layout is adopted for the runners as much as possible;

 

3) When it is impossible to balance naturally, the artificial balance method is used to balance the flow channel.

 

5. Waste considerations

 

Under the premise of smoothly filling without affecting the flow and pressure loss, the flow channel volume (length or cross-sectional area size) is reduced to reduce waste flow generation and recovery costs.

 

6. Consideration of cold material

 

Design suitable cold slug wells and overflow troughs on the runner system so as to fill the plastic wave fronts that are relatively cold in the initial stage to prevent the cold materials from directly entering the mold cavity and affecting the filling quality.

 

7. Exhaust considerations

 

The plastic should be successfully guided to fill the mold cavity and allow the air in the mold cavity to escape smoothly so as to avoid the problem of enveloping the scorch.

 

8. Consideration of the quality of molded products

 

1) Avoid short shots, burrs, wraps, sutures, flow marks, jets, residual stresses, warpage, mold deflection, and other issues;

 

2) When the flow system has a long flow or multiple gating, the warpage of the finished product due to unbalanced flow, insufficient pressure or uneven shrinkage should be prevented.

 

3) The appearance of the product is good, and it is easy to remove the trimming gate. The gate mark does not damage the appearance and application of the plastic part.

 

9. Consideration of production efficiency

 

Minimize the post-processing required to shorten the molding cycle and increase production efficiency.

 

10. Top-out considerations

 

Need to take into account the appropriate ejection position to avoid the mold release deformation.

 

11. Considerations for using plastics

 

Plastics with higher viscosity or shorter L/t, avoid use of flow channels that are too long or too small.

 

A set of high-quality molds not only needs good processing equipment and skilled mold manufacturing workers, but also a very important factor is to have a good mold design, especially for complex molds, mold design quality accounted for the quality of the mold 80 %the above. An excellent mold design is: to meet the requirements of the customer, the processing cost is low, the processing is difficult, and the processing time is short. To achieve this, it is necessary not only to fully digest the requirements of the guests, but also to understand the injection molding machine, mold structure, processing technology and the processing capability of the injection mold factory itself.