What is the effect of the injection barrel screw with temperature?


An injection moulding barrel screw is used to transfer […]

An injection moulding barrel screw is used to transfer material between barrel and mold during the general injection molding cycle. This cycle includes filling the barrel with material, plasticizing the material, and then holding the cushion while the material solidifies. The barrel is then closed and the screw is retracted. This cycle repeats itself for each part.

The impact of temperature on melt homogeneity in an injection moulding barrel screw can be quantified using the following flow model. The flow model shows that the solids bed temperature is related to the axial velocity in the melt pool. Initially, the solids bed temperature is lower than the target temperature. As the temperature increases, the solids bed temperature becomes higher, and a fountain flow is observed. The model shows that the temperature difference between the axial and vertical axes is large enough to produce this fountain flow behavior.

The process of plastic injection moulding is characterized by temperature variations that affect the flow of material in the dies. Increasing the temperature of polymer causes the melt pressure to fluctuate and this can affect the viscosity of the material. Moreover, these differences will be observed even with a constant volumetric output.

Compression ratio
The compression ratio of an injection moulding barrel screw is a key factor when selecting the right screw for your moulding machine. This number is the ratio of the flighted length of the screw divided by the screw's nominal outside diameter. Some manufacturers offer a variety of different injection units, but the most common ratio is 20:1. The compression ratio is important because it can reduce the degradation of plastic in the moulding process, improve the mixing of the plastic melt, and speed up the cycle times for larger shots.

The compression ratio of an injection moulding barrel screw determines how much material is injected into the mould. The screw must be able to handle the amount of material that needs to be injected. Injection moulding barrel screws must be able to handle the material's density and temperature, as well as its viscoelastic properties.

Length to diameter ratio
The screw and barrel length-to-diameter ratio are important considerations in the selection process. They determine the process parameters and can affect part quality and consistency. If a screw's length is too long or too short, this can have negative effects on the part and the processor. Considering these factors will make the selection process much faster and easier.

A large length-to-diameter ratio causes the screw to undergo high back pressure, which leads to a distorted working state. This distorted screw then scrapes the inner wall of the barrel. Furthermore, a larger L/D ratio increases contact wear between the screw and the barrel.