One of reasons for surface problems of TPE injection parts is poor quality of raw materials, which is also related to uneven dispersion of formula, and it is also related to setting of some parameters of injection moulding process.
In injection production process, products often have various quality defects, such as cracking, warping deformation, poor size, shrink marks, weld lines, color difference, flash, insufficient strength, gas traps and black spots. For a long time, designers have lacked scientific system analysis for causes of these problems, resulting in long blind adjustments and large waste of raw materials, but they cannot solve these problems, affecting quality and delivery time of products. In severe cases, it will cause large-volume returns and reduce competitiveness of enterprise.
Injection moulding is an engineering technique that involves transforming plastic into a product that is useful and maintains its original properties. Important process conditions for injection moulding are temperature, pressure and corresponding individual time of action that affect plasticizing flow and cooling.
First, appearance, size, and fit of molded products 1. Defects are not allowed on the surface of product: lack of material, charring, whitening, white line, peaking, foaming, whitening (or cracking, breaking), baking, wrinkles. 2. Welding marks: Generally, length of circular perforated weld line is not more than 5 mm, length of shaped perforated weld line is less than 15 mm, and weld line strength can be tested by functional safety. 3. Shrinkage: shrinkage is not allowed in apparent surface, inconspicuous areas allow for slight shrinkage (not feeling dents).
Injection moulding process is a complex process involving plastic engineering materials, molds, injection molding machines, molding process and many other aspects. Appearance of defects in injection molded products is inevitable. Therefore, it is particularly important to find inherent mechanism of defects, location and types of defects that may be generated to guide project development. Today, we will talk to everyone about common appearance defects - flow marks.
Double shot injection molding can make two different characteristics of resin and color into a single two-color product, which can reduce assembly and post-processing of molded products, save cost of dissolution and printing, increase aesthetic appearance of product, and enhance grade and added value of product. Below I will introduce difference between advantages of double shot injection molding, molding principle, structural form, technology and overmolding.
"Gate" has a large influence on formability and internal stress of injection molding mold. Usually, appropriate form is determined according to shape of molded products, and it can be classified into two types: "restricted gate" and "unrestricted gate". The former is made into a narrow part at the entrance of runner and cavity, is easy to process and easy to cut molded article from runner, which can reduce residual stress. Gates of most of plurality of shaped products are easily formed at one time, cavity is easily balanced. Plastics are not easy to countercurrent, and this form is generally used. It can also be divided into Side Gate, Overlap Gate, Tab Gate, Fan Gate, Film Gate, Ring Gate, Disk Gate, Point Gate, Submarine Gate and so on. The latter is a gate that directly injects plastic into cavity from down sprue as a representative of unrestricted gate. Type, position, size, and number of gates directly affect appearance, deformation, forming shrinkage, and strength of molded products. Therefore following items should be considered in design.