Jetting, also known as jet, worm track, or snake-like pattern, refers to the snake-like curves on a plastic injection molded part along the flow direction from the gate, as shown in Figure    1. Under normal circumstances, the molten plastic fills the mold cavity in a “fountain flow” manner, as shown in Figure  2, which depicts the “fountain flow” in detail. However, when the molten plastic flows at a high speed through narrow areas, such as the nozzle, the runner and the gate, and then suddenly enters an open and relatively wider area, the plastic melt will be injected from one end to the other of the cavity in the form of jet streams, creating folded strips. The melt that enters the cavity later fills the remaining space in the mold cavity with a normal fountain flow and is welded to the jetted streams. Since the melt is immediately cooled the moment it makes contact with the cavity wall (mold surface) which has a relatively low temperatu...

  The shrinkage rates of different plastic materials are different. Usually, the raw materials that are prone to sink marks are crystalline, such as nylon. During the injection molding process, the crystalline plastic is heated to a fluid state, with the molecules randomly arranged; when filled into the cold cavity, the plastic molecules are slowly arranged neatly to crystallize. As a result, the volume is shrunk to be smaller than the specified dimensional range, which is referred to as the “sink mark”.   The shrinkage rates of various plastic materials(mold shrinkage rate) are shown below:   Injection processing: Regarding control of the injection technology, the causes of sink marks include: insufficient pressure, excessively slow injection speed, small gate or long runner. Therefore, when using the injection molding machine, it is necessary to pay attention to the molding conditions and whether the holding pressure is enough to prevent the appearance of s...

How the Hot Runner Systems Works The cold runner of a plastic injection mold refers to the section between the mold inlet and the gate. The molten plastic maintains its fluidity inside the runner by virtue of the injection pressure and its own heat. However, as a part of the molding material, the runner is not a product. As a result, when designing a mold, we need to consider not only the filling effects, but also the material-saving effect produced by shortening or downsizing the runner; but in actuality, it is not easy for us to have the best of both worlds. Types & Application of Hot Runners When applying the hot runner technology, the proper selection of gate type is of critical importance, because gate type directly determines the selection of hot runner components as well as manufacturing and application of molds. Therefore, the hot runner system can be classified into 3 types based on the gate type, i.e. (1) hot tip hot runner system, (2) sprue gating hot runner system and (...

The injection mold cooling system purpose is to ensure uniform cooling of the molded product and then eject the product out within a short period of time. The layout of the cooling channel plays an important role in the injection molding quality as well as the production cycle (cost) of a product. Influence on Quality: During the injection molding process, the cooling channel is used to control mold temperature, of which the fluctuation has a direct influence on product shrinkage, deformation, dimensional stability, mechanical strength, residue cracks and surface quality, etc. Mainly include: surface glossiness, residue stress, crystallinity and thermal flexure. Influence on Production Cycle: An injection molding cycle is mainly composed of the following steps. Reducing the cooling time means an improvement in the injection molding efficiency.   Injection Molding Cooling Types and Layout: 1,Cooling line in core /cavity inserts       2,Connecting cooling line between...

The Runner Design Concept The runner refers to the melt flow passageway between the end of the main runner and the gate, which is used to change melt flow direction and allocate it to each cavity in a stable and balanced way. The basic design principle of the branch runner is little pressure/heat loss, with the minimum quantity of plastic retained in the runner. Sectional Shapes of the Branch Runner:   –Circular, with the minimum specific surface area (runner surface area/runner volume), but during production, both sides of the mold plate need to be aligned. –The commonly applied forms, trapezoid and U-shape are easy to process. –Semicircle. –Rectangle, larger specific surface area and high resistance to flow, thus seldom applied.   The Principle of the Runner Design The runner is usually designed on either half of the plastic injection mold. When considering the layout of the cavity and the branch runner, it is better to ensure that when projected on ...

Mold sprue bush,The main runner refers to the melt flow passageway from the joint between the injection molding machine nozzle and the mold sprue bushing to the starting point of the branch runner. –The design has to minimize melt temperature drop/pressure loss.   –Adopt the cone shape design, to facilitate removal of the condensed material   Forms of The Mold Sprue Bush   Fixing Methods of the Mold Sprue Bushing   The main runner is usually located along the center line of the plastic injection mold, overlapping with the axle of the injection molding machine nozzle. In horizontal and vertical injection molding machines, the runner axle should be perpendicular to the parting surface. To facilitate removal of condensed materials from the main runner, the main runner should be designed into the cone shape, with a cone angle of 2 – 6º; the diameter of the smaller end D ＞ d + (0.5~1mm), d refers to the diameter of the injection molding machine noz...