Causes of wire drawing in the injection molding process

In the injection molding process, the phenomenon of wire drawing is a relatively common defect. It not only affects the appearance of the product quality, but also reflects some deficiencies in the injection molding process. In order to ensure the quality of the product, it is important to understand the causes of wire drawing.

Drawing usually refers to the process of mold opening and ejection, due to the role of adhesion between the plastic and the mold, so that part of the already cured plastic material is stretched, thus forming a thin filament.

The reasons for the generation of wire drawing can be analyzed from the following aspects:

1. Material properties: the viscosity of different plastics, fluidity, and compatibility with the mold material will affect the generation of wire drawing. For example, the higher viscosity of the material in the mold surface fluidity is poor, more likely to form wire drawing; and certain additives such as slippery agent, release agent is not used properly, may also increase the adhesion between the material and the mold, resulting in wire drawing.

2. Mold design: The surface finish of the mold, the design of the exhaust system, and the cooling efficiency of the mold may all be triggers of wire drawing. If the surface of the mold is not polished in place or there is damage, the flow of plastic on it will be impeded, increasing the risk of drawing; poor exhaust design will lead to the accumulation of gas in the mold cavity, forming a vacuum effect, increasing the contact area between the plastic and the mold, which will in turn cause drawing; non-uniform cooling will make part of the area of the material is not cured in a timely manner, increasing the likelihood of adhesion.

3. Injection parameter settings: Inappropriate settings of parameters such as injection speed, pressure, holding time and back pressure will affect the filling and curing process of the plastic. Too fast injection speed may cause a large shear force between the plastic and the mold wall, resulting in pulling; while too high a pressure or insufficient holding time may result in the plastic failing to completely fill the mold cavity in advance of the curing, will also increase the chance of pulling.

4. Machine conditions: the stability and precision of the injection molding machine is also an important factor affecting wire drawing. If the clamping force of the injection molding machine is not stable or the response speed of the injection system is not precise, it will introduce instability in the production process, which will induce wire drawing.

5. Environmental factors: Changes in temperature and humidity have a direct impact on the performance of plastic materials. In some cases, fluctuations in the environment may lead to changes in material properties, which can affect its interaction with the mold and produce wire drawing.