Short Shot

Views: 0 Author: Site Editor Publish Time: 2020-07-25 Origin: Site

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A short shots or insuficient workpiece fill is a molded part that is underfilled or not filled

completely. Visually, this can be seen as sections, such as the last areas of the part to fill, or

projections of the part that are missing. The lists causes and solutions for short shot

Cause:

1. If the melt temperature is too low, material cannot flow easily to fill out a part completely

2. Insufficient packing pressure also prevents the mat from filling out the cavity, creating short shots

3. Injecting material at a slow speed causes the viscosity of the material to increase, restricting flow

4. A worn check ring in the nozzle creates inconsistent cushion, causing shot-to-shot variation of material entering the cavity; some parts are filled completely and others are short. If shot size or feed setting is also set to low, the part will not fill out completely

5. As a blocked nozzle can cause a blockage inhibiting material from flowing into the cavity, a blocked gate can also restrict flow into the cavity, producing short shots

6. Too small a gate size can freeze off before the mold is resulting in incomplete fills

7. Low mold temperatures are a common cause of short shots since this causes the melt front to cool too soon before the part is full

8. If not enough vents are used in a mold cavity or if no vents are used, air can be trapped and acts like a cushion, halting material flow

9. Long part lengths can cause the molten material to cool fast, before filling out the cavity

Solutions:

1. Raising the melt temperature will permit easier flow to fill out more sections of the part

2. Increasing the packing pressure exerts more pressure on the melt to flow farther and pack out the part

3. Increasing the injection speed provides more shear heat to the material, reducing its viscosity and increasing flow

4. Enough shot size needs to be provided to assure that enough material enters the cavity and fills it completely

5. One of the more common blockages is cold material breaking off from the runner or stuck in the gate from a previous shot. Also contamination such as metal can block a gate as well. It is recommended to remove these blockages in the gate and also to locate the source or

sources of these blockages

6. Enlarging the gate size. A larger gate size will allow more material into the cavity

7. Increasing the mold temperature can keep the melt front from cooling prematurely, before the cavity is full

8. The addition of vents will force trapped air out of the mold, facilitating material flow into the cavity

9 .(1) A number of options to filling long-length parts is to use flow leaders, which are concentrated areas of increased thickness in the part that guide flow to a specific area of the part.(2) Additional gates also can be added to supply more entry areas for the molten material to enter the part

10. Using a material with a higher viscosity, or a high melt flow rate, will fill the part easier and faster and reduce the chance of short shots