Plastic Home For Eng Mohamed Bayoumi

 Preforms can be divided into four sections.  Figure 1 To better tailor the injection profile to the preform it is cut into sections. Gate area covering the hemispherical portion, also called end cap. Body area Transition area where the thicker body merges into the thinner neck. Neck area To keep shear constant and achieve a uniform preform temperature, the melt should move at a constant speed inside the cavity. However, the amount of material that fills each cavity section is not uniform because of the differences in wall thickness and diameter. Therefore, the fill speed should be adjusted to account for these differences. Here is how this is done. The first step is to cut the preform at the three places indicated in the drawing and weigh each piece, also noting its wall thickness. For the end cap and the transition zone, the wall thickness in the middle of each part should be noted. If only three speed and position settings are available, only two cuts are made, cap and body...

  The parameters operators can control are: Injection pressure Injection speed Transition point Hold time. Hold pressure. Material “cushion” Most modern machines allow the operator to set all relevant values on the screen, whereas older machines may feature manual hydraulic and position controls. For this discussion it has no relevance how the pertinent values are controlled. It is important that readers understand the concepts. 1- Injection Pressure Many operators are under the misconception that the injection pressure can be dialed in because there is a field on the screen with this name. However, this is not the case. Injection pressure is the result of how hard the machine pushes the resin and how hard the resin resists this pressure. The value on the screen merely determines the pressure at which the machine hydraulics will stop pushing and drain oil to the tank instead of sending it to the injection cylinder. The factors that determine injection pressure are: • Injection spee...

How does plastic flow؟ Study the behavior of the substance during  injection. 1- Material  behavior Molten thermoplastic exhibits viscoelastic behaviors, which combines flow characteristics of both viscous liquids and elastic solids. When a viscous liquid flows, the energy that causes the deformation is dissipated and becomes viscous heat. On the other hand, when an elastic solid is deformed, the driving energy is stored. For example, the flow of water is a typical viscous flow, whereas the deformation of a rubber cube falls into the elastic category. Deformation Deformation In addition to the two types of material flow behavior, there are two types of deformation: simple shear and simple extension (elongation), as shown in (a) and (b) below. The flow of molten thermoplastics during injection Moulding filling is predominantly shear flow, as shown in (c), in which layers of material elements "slide" over each other. The extensional flow, however, becomes significant as the mat...

Designing the wall thickness of a PET preform  involves considering various factors such as required bottle strength, size, material properties, and processing conditions. I can give you an overview of the mathematical equations for this. 1-     Taper Thickness Equations            1-1           Linear Taper Equation:                                                 Tt = Tb - (Tb - Te) * (L - Lt) / L Where: Tt = taper thickness Tb = bottom/maximum thickness Te = top/minimum thickness L = total length Lt = length of taper section           1-2           Exponent...