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Hot runner refueling or bad color change
May 30, 2018

Problem: Bad refueling or color change

main reason

 Inappropriate method of refueling or changing color; the unreasonable design or processing of the flow channel leads to the presence of more stagnant material inside.

solutions

(1) Improve the flow channel structure design and processing methods. When designing the flow channel, the dead point of the flow channel should be avoided as much as possible, and the transition of arcs should be made at each corner. Within the allowable range, the size of the flow channel is as small as possible, so that less material is retained in the flow channel and the flow rate of the new material is larger, which facilitates quick cleaning. When processing the flow channel, no matter how long the flow channel is, it must be processed from one end. If it is processed from both ends at the same time, the center of the hole may be misaligned, which will inevitably result in the formation of a stagnant material part. Generally, the external heating nozzle can clean the flow passage easily because the heating device does not affect the flow of the melt, and the internal heating nozzle easily forms a condensation layer on the outer wall of the flow passage, which is not conducive to quick refueling.


(2) Select the correct refueling method. In the hot runner system refueling and color changing process, all the remaining material in the flow path is generally pushed out directly by the new material, and the retained material in the flow path wall is moved forward as a whole, so the cleaning is relatively easy. On the contrary, if the new material has a low viscosity, it will easily enter the center of the retentate and separate the retained material layer by layer, which makes cleaning more troublesome. If the viscosity of the old and new materials is similar, rapid refueling can be achieved by accelerating the injection rate of the new material. If the viscosity of the retentate is more sensitive to temperature, the material temperature may be increased to reduce the viscosity to speed up the reloading process.


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