what is the injection molding-part1

Firstly,we must know the base structure of the injection molding machine:

Secondly, we learn some basic theoretical knowledge of injection molding (questions were asked by interviewers frequently)

1,what is the runway effect: The runway effect can be called a high movement along the runway and a regular rhythm of movement. Before filling the thinner part, the fluid passes through the thicker part of the cavity quickly, and the runway effect will appear

2, what is the shear rate: The rate of intense movement of molecules produced by the melt during the filling process is called the shear rate, that is called the shear rate, the motion trajectory generated during molecular motion, such as stretching, extrusion, bending, friction, and the like. The intense movement of the molecules produced during the filling process also causes the temperature of the melt itself to heat up again. Therefore, if the speed of injection is too high, the product will burn. This is another explanation of why the product is burnt down and the injection speed is slowed down。

3, what is internal stress：When an object does not have an external factor, the stress inside the object that still maintains its own phase is called the internal force. When the plastic melt enters the rapidly cooled cavity, the temperature drop rate of the surface of the product is much faster than that of the inner layer, and the surface layer is rapidly cooled to solidify. Due to the poor thermal conductivity of the solidified plastic, the internal solidification of the product is very slow. When the gate is closed, it cannot be The center cools and shrinks to feed, then the inner layer is stretched due to shrinkage, while the surface layer is in the opposite state of compressive stress. These stresses are left in the product after the mold is opened and disappeared. We call it residual stress. 

4, what is stress：The resistance experienced when an object flows is called pressure, and the pressure physically refers to the force acting perpendicularly on the surface of the object. The force object is the support surface of the object, and the action point is on the contact surface, and the direction is perpendicular to the contact surface

5, what is traffic：The flow volume that passes through the unit time is called the flow rate, and the flow rate is the speed of the speed. The amount of fluid passing through a cross section of a river, canal or pipe in a unit of time. Generally refers to the volume flow, expressed in cubic meters per second

6, the five major elements of injection molding：（1）Temperature: (forming temperature, cavity temperature, product release temperature, etc.)，（2） Pressure: filling pressure, low pressure, high pressure, etc.（3）Speed: injection speed, storage speed, opening and closing speed, etc. (4) Time: filling time, holding time, cooling time

7，The role of injection pressure：（1）Reduce the surface shrinkage of the product caused by cooling during the molding process；(2) Preventing warpage of the product after demolding；（3）Stabilizing product size；（4）improve the surface quality of the product

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