Kitchen Mixer Plastic Lid Injection Mould

Analysis of the ABS plastic injection molding process

Injection molding performance of ABS: Generally, the melting point of ABS plastic injection molding is about 170℃ and its decomposition temperature is 260℃, with a wide range of adjustable injection temperatures. During the injection molding process, the temperature often ranges between 180 – 240℃. Due to the existence of rubber, it is able to absorb a small amount of water, so it needs to be dried during production – dried for 1 – 2h in temperatures between 80 – 90℃; at the same time, due to its poor thermal stability caused by the existence of rubber, it tends to decompose, so it is better than the raw material does not stay in the barrel for too long during injection molding; though the viscosity of the molten ABS is higher than that of PS, it is able to completely fill the mold with average gates and sprues; the product often generates static electricity, which tends to attract dust and dirt; shrinkage rage is 5‰, and overflow limit value 0.05mm.

The previous 3 points about the dry process, injection pressure, and injection temperature can see on this page https://www.swymould.com/product/electrical-appliance-mould/more-appliance-mould/kitchen-blender-abs-base-stand-injection-mold.html

4. Injection speed

For the ABS plastic injection molding material, a moderate injection speed will bring about a great effect. If the injection speed is too fast, the plastics will be burnt or decomposed to separate out gasification products, so defects like weld lines, poor glossiness and plastic around the gate turning red, etc. will occur. However, when producing thin-walled or complex products, a high injection speed needs to be ensured, or insufficient filling will be caused.

5. Mold temperature

The injection molding temperature of ABS is relatively higher, and so is the mold temperature. Usually, the mold temperature is adjusted between 75 and 85℃. When manufacturing products with a large projection area, the cavity temperature is required to be between 70 and 80℃, while that of the core is between 50 and 60℃. When injection molding large, complex-structured, or thin-walled products, it should be considered to heat the mold especially. In order to shorten the molding cycle and maintain mold temperature stability, after the product is ejected, a hot bath, cold bath, or other mechanical molding methods need to be applied to compensate for the original cooling and molding time of the cavity.

6. Shot size control

Usually, During the ABS plastic injection molding process, each shot size only reaches 75% of the standard shot size. To improve product quality, as well as dimensional stability, surface glossiness, and even color, the shot size is required to be 50% of the standard size.

7. Selection of injection mold

May select the standard injection machine (screw length-to-diameter ratio is 20:1, compression ratio greater than 2, and injection pressure greater than 150MPa). If a masterbatch is used or the product has a high requirement for appearance, the screw of a smaller-size diameter can be selected. Clamping force should be identified as per 4700 – 6200t/m2, depending on the specific plastic grade and product requirements.

Plastic injection molding gate type

For plastic injection mold design, one of the most important factors is how and where the gate should be located. As the mold opens, the gate is where the molten plastic flows into the final part. It serves as the boundary between the part and the scrap, so its location, size, and shape play an important role in how everything should be constructed, from structural integrity to the exterior appearance of the finished product. Below is the gate type we often choose.

1. Direct gate/sprue gate

Pros:

* Little pressure loss;

* Easy preparation.

Cons: 

* High stress around the gate;

* Gate (runner) needs to be trimmed manually;

* Obvious gate scars will be left on the surface.

Application:

* Suitable for the production of large and deep barrel-shaped plastic parts. However, warping can easily occur due to contractibility and stress when applied on shallow and flat plastic parts.

* For plastic parts that do not allow gate marks on the exterior, the gate can be designed on the inner surface of the parts.

2. Side gate

Pros:

* Simple structure, easy processing;

* Easier to remove the gate.

Cons:

* Automatic separation of the part and the gate is not allowed;

* Gate marks are easily left on the plastic part.

Parameters:

* Gate width W = (1.5~5.0)mm. Usually, W = 2H, which may be appropriately increased for large and transparent plastic parts.

* Height H = (0.5~1.5)mm. Specifically speaking, usually, H = (0.4~0.6)d for commonly seen ABS and HIPS. Among them, d refers to the basic wall thickness of the plastic part; H = (0.6~0.8)d for materials with poor fluidity, like PC and PMMA; the suggested gate height for POM and PA is H = (0.6~0.8)d, so as to help avoid shrink marks and wrinkles by guaranteeing sufficient pressure holding because though these materials possess good fluidity, they become solid very fast with larger contractibility; for materials like PE and PP, gate height H = (0.4~  0.5)d, because the small-sized gate is helpful for molten plastic shear thinning, thus reducing stickiness.

Application:

Suitable for the production of plastic parts of various shapes, but it is will not be selected for slender barrel-shaped parts.

3. Tab gate

Pros:

* It is a form evolved from the side gate, so it shares the various advantages of the side gate;

* It is a typical impingement gate that can effectively prevent molten plastic jetting.

Cons:

* Automatic separation of the part and the gate is not  allowed;

* Obvious gate scars are easily left on the surface.

Parameters:

Refer to the side gate parameters for the application.

Application:

Suitable for flat plastic parts that impose requirements on surface finish.

4. Fan gate

Pros:

* The horizontal distribution of the molten plastic is more uniform when passing through the gate, helpful for reduction of plastic part stress;

* Lower the possibility of air getting into the cavity, to avoid the occurrence of defects, like silver lines and bubbles, etc.

Cons:

* Automatic separation of the part and the gate is not allowed;

* Long gate marks are left on the edge of the plastic part, which needs to be flattened by a tool.

Parameters:

* The commonly used height H = (0.25~1.60) mm;

* Width W = 8.00 mm to ¼ of the cavity width at the gate end.

* The section area of the gate should be larger than that of the sub-runner.

Application:

Usually used for the production of wide but thin plastic parts, as well as transparent plastic parts and those with poor fluidity, like PC and PMMA, etc.

5. Submarine gate

Pros:

* Flexible choices of gate location;

* Automatic separation of the part and the gate is allowed;

* Smaller gate marks;

* Applicable for both 2-plate and 3-plate molds.

Cons:

* Plastic powder is easily dragged at the gate position;

* Stress mark is easily created at water entry;

* Plastic films need to be sheared manually;

* Great pressure loss from the gate to the cavity.

Parameters:

* Gate diameter d = 0.8~1.5mm;

* The plastic flow direction and the vertical direction form an angle between 30°and 60°;

* The taper b is between 15° and 25°;

* Distance to the cavity A = (1.5~3.0)mm.

Application:

Suitable for plastic parts that do not allow exposed gate marks on the exterior. For a multi-cavity mold, the resistances from the gate to each cavity should be kept as close as possible, so as to avoid viscous flow and obtain better flow balance.

6. Banana gate

Pros:

* Automatic separation of the part and the gate is allowed;

* The gate area does not need additional processing;

* No gate marks will be left on the exterior of the plastic parts.

Cons:

* Stress marks may show on the surface;

* Complicated processing;

* Easily broken and thus blocking the gate if not appropriately designed.

Parameters:

* A = approx. 2.5D;

* Φ2.5min* refers to the gradual transition from the large end 0.8D to the small end Φ2.5.

Application:

Normally used for ABS and HIPS, suitable for neither crystalline materials like POM and PBT nor high-rigidity materials like PC and PMMA, so as to avoid the curvy runner from being broken and thus blocking the gate.

7. Point gate

Pros:

* Flexible choices of gate location;

* Automatic separation of the part and the gate is allowed;

* Smaller gate marks;

* Low stress around the gate.

Cons:

* High injection pressure;

* Complicated structure, usually employing the 3-plate structure.

Parameters:

* Usually the gate diameter d = (0.8~1.5) mm;

* The gate length L = (0.8~1.2) mm;

* To help pull the gate broken from the root, a taper should be set for the gate, a = approx. 15°~20°;

* The gate and the runner are joined by arc R1 to ensure that the plastic part is not damaged when pulling the point gate broken; R2 = (1.5~2.0) mm; R3 = (2.5~3.0) mm; height h = (0.6~0.8) mm.

Application:

Usually used for the production of large plates and bottom cases. The proper distribution of gate can help reduce the flow distance of molten plastic and thus guarantee satisfactory distribution of melting marks; also able to be used for the production of long barrel-shaped plastic parts to improve ventilation.