Definition

Short note, short shot, insufficient filling and dissatisfied parts commonly referred to as owe note (as shown below). It refers to the material imperfection phenomenon appears at the end of the first mock exam or multi cavity part filling, especially at the end of the flow path of the thin area or region. 

 

The main cause of this phenomenon is that the melt is condensed without filling the cavity, or the melt enters the mold cavity but does not fill completely.

 

 

Reason:

1) Material temperature or the mould temperature is too low. In the suitable range of molding, the material temperature and the filling length close to the direct proportion, and the flow properties of low temperature melt decline, shortening the filling length.

 

2) The feed capacity is not enough. Common method of controlling feed is the constant volume feeding method.

 

3) Feed viscosity is too large. Generally, raising the feed temperature can solve this problem.

 

4) Poor liquidity of material. Viscous flow defect of mold casting system should be improved, such as setting up reasonable sprue position, expand gate runner and sprue size, and the larger nozzle.

 

5) Insufficient injection pressure or the packing pressure is, the injection pressure and the mold length close to the direct proportion, the injection pressure is too small, the mold filling length is short and the cavity filling is not satisfied.

 

6) The injection speed is too slow, and the injection speed is directly related to the mold filling speed. If the injection rate is too slow, the melt is filled slowly, while the melt at low velocity is easy to cool down, resulting in a further decrease in its flow performance.

 

7) Unreasonable design of the gating system. In actual production, the design of sprue is often unreasonable, which results in the defects of plastic parts. The gating balance shall be noted when designing the gating system. The weight of the plastic parts in each cavity should be proportional to the size of the gate so that the cavities can be filled at the same time. And the sprue position shall be located on the thick wall.

 

If the sprue or the runner is small, thin, long, the melt pressure will be too large in the flow process, and the flow will be blocked, which is prone to poor filling. So, the runner section and gate area shall be enlarged, and multi-point feeding method may be adopted if necessary.