Fan gates of Plastic Injection Molding

Fan gates of Plastic Injection Molding are modified of edge gates, just out at an angle from the runner system to the plastic injected parts where in the edge gate. The width of chisel-type gate is from 6mm to 1/4 width of the plastic injected parts and shallow is from 0.25mm to 1mm.

Fig 1 shows fan gate design. Fan gates provide reduced pressures and clamp tonnage over other conventional gate designs and are excellent for plastic injection molding. Flat the plastic injected parts such as automotive trim objects and electronics covers and enclosures. Fan gates allow for a wide process window and reduce overpacking issues since the pressure is lower than in pinpoint gates and submarine gates. The disadvantages are that the gates must be trimmed by special fixture and there is an obvious gate vestige and increased scrap due to the difficulty of trimming off fan gates. 

                                                        Fig 1 Fan gate design

Fig 2 are cross section of fan gate. To reduce the vestige and alleviate the trim issue, a chisel cross section can be used for the fan gate. This chisel type allows the waste to break off from the plastic injected parts cleanly and evenly as show in Fig 3. The fan gate thickness of the export and import are calculated as follows:

                                            Fig 3 Chisel cross section of fan gate

                                                 Fig 3 Chisel cross section of fan gate

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production of Plastic Injection Parts with Injection Machine 1000 Ton

Blush at the Gate of Plastic Injection Parts

Blush is hazy surface imperfection which is found at the gate of the workpiece. It appears as a visual difference in color and gloss surrounding the gate and is usually in the direction of flow. Here are some causes and solutions below.

The high pressures and velocity going through a gate, a phenomenon called melt fracture occurs. The material is squeezed through the small gate opening, and as this takes place, the polymer chain is extended. The material expands rapidly as it hits the cavity wall, the polymer material will cool, and the polymer chains will contact. Due to this cooling and contraction, a haze or discoloration will appear at the gate area, referred to as gate blush. The higher the injection speed, the more pronounced the gate blush. At the same time, lack of a cold slug well can force this colder material into the gate and into the part showing up as gate blush.

Reducing the injection speed so that the polymer chain do not extend as much as with higher speeds. This will lay down a clean skin of material without gate blush. Velocity profiling of the process can be used to start with a slow injection speed, building to a higher injection speed as the cavity is filled. Increasing the melt temperature to provide easier flow to the material. An increase in nozzle temperature can produce a higher melt temperature as it enters through the gate.

Setting a cold slug well at the ends of runner. The purpose of a cold slug well is to receive the first slug of material from the nozzle and keep it from interfering with the flow path of the hotter material behind. Increasing the mold surface temperature so that the cooling rate at the gate will be slowed and will be closer to the cooling rate of the rest of the part. Gate size can be increased to provide less resistance from the material in entering the cavity.

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Edge Gate of Plastic Injection Molding

Edge gate characteristic of injection mold are gate and runner on parting surfaces, the mold two-platen (single parting surface) structure. When molten material from the sides of the cavity filling mould, adjusting the edge gate of the section thickness and width can adjust filling the melt shear rate and the curing time of the gate.

The cross-sectional shape of the edge gate is simple, easy processing, mainly for small and medium sized plastic injected parts of the multiple-cavity mould, which have good adaptability to all kinds of plastic injection molding. But the side of the products left traces, which will affect the appearance of products, injection pressure losses and Deep type plastic molding process exhaust inconvenience. The edge gate size can be calculated according to the experience formula:

 

b—The width of the edge gate

A—Plastic parts surface area

h-—The thickness of the edge gate

Here are some edge gates design (Fig1 and Fig2). Edge gates (rectangular inlets) are used most often in a variety of injected plastic parts. The gate comes out in a straight line from the runner to the nest. The gate is placed along the side or width of plastic injection parts, and the width can range anywhere from 1.5 to 5.0mm, the height from 0.5 to 1.5mm and the length is 1.5 to 2.5mm. For large and complex object, the width of gate is 7.0 to 10.0mm, the height is from 2.0 to 2.5mm that is approximately 0.7 to 0.8 times the nominal wall thickness of plastic parts, and the length if from 2.0 to 3.0mm.

                                                                                           Fig 1 Edge gate design

                                                                                                     Fig 2 Edge gate design

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Direct Gate of Plastic Injection Molding

Direct gate of Plastic Injection Molding is the simplest of the gate, which is also the most original.
It is a vertical sprue as shown in the Fig 1.

                    Fig 1 Vertical Sprue

d—the small end diameter of sprue
L—the length of sprue
α—the taper of sprue

Direct gate is a nonrestrictive gate, because of the molten plastic directly into the cavity by direct gate, so the pressure loss is small, filling more easily and can apply all kinds of plastics. The section size of direct gate is usually large and sprue fixed need a long time, so there is plenty of time to fill material, but the large stress produced at the gate.
Direct gate is typically used for large, deep barrel-shaped products. For shallow rectangular products, because of stress and shrinkage, products are prone to warping deformation. At the same time, we need to add fill material process at the gate.
We can set up direct gate at the outer surface of the products as shown in the Fig 2. Should be noted that the big end of the direct gate should not be too large, otherwise can bring difficult to remove gate, also will left a larger mark on the products.

                                                   Fig 2 Outer Surface Direct Gate

We can also set up direct gate at the inner surface of the products as shown in the Fig 3. Some products, in order to ensure the quality of appearance, don't allow the gate directly design on its outer surface, so the gate design must be on the inner surface. This design approach, the product in cover half. When opening the mold, puller hook drive stripper plate, the products will demould from the cover half.

                                               Fig 3 Inner Surface Direct Gate

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