What is the cause of plastic injection molding? Analyze with Xiaobian
When the polymer is extruded or injection molded, the die or gate extrudate has a lubricated profile and an average shape at a low fluid shear rate. When the shear rate or shearing should increase the strength of the modified plastic to a certain value, the appearance of the extrudate is fresh and beautiful outside; when the extrusion speed of the plastic is raised, the surface of the extrudate will be voluminous. We define the rules of nodules, misinterpretations or slubs, and even break and break into pieces or columns, which we call "melt fracture." These phenomena indicate that at low shear stresses or velocities, small perturbations caused by various components are threatened by the melt; at high shear stresses or rates, disturbances in the fluid are difficult to suppress and are carried out. Indiscriminate movement; when a critical shear force is reached, it will cause a break in the fluid. 1, material aspects The cracking of the fluid under high shear leads to the peeling of the manufactured product. Taking the PC/aBS raw material as an example, the two-phase mechanism of PC and aBS is more prone to the fluid substrate and the separation of the two phases under high shear. Then there is a layered skinning weather. For PC/aBS raw materials, a small portion of the PC and aBS modified plastic parts are compatible with each other, so a certain amount of compatibilizer can be added during the modification to improve the compatibility. Of course, due to the poor skinning caused by the mixing is the first step to break. Figure plastic peeling 2, mold design The principles of mold design are subject to the goal of reducing shear. Products with dense grain surface are more prone to skinning (higher shear due to melt in the cavity and the inner wall of the cavity during high-speed filling); at the same time, the gate size is too small and will produce This results in high shear forces as the melt passes through the gate, which in turn causes the product surface to peel. Mold design should be done in a direction that minimizes shear. Figure plastic layered peeling 3. Injection molding process High-speed high pressure will cause the melt to produce excessive shear force at the gate position, and the shear of the melt and the inner wall of the cavity and the shear between the core layer and the skin layer will be sharply added; in addition, the injection temperature/die The temperature is too low, the melt fluidity is lowered, and the flow resistance during the filling process is increased, resulting in high shear force. Therefore, reducing the injection speed, injection pressure, injection temperature / mold temperature can effectively reduce the shear force, reduce or eliminate the occurrence of peeling. Trying to avoid high shear forces during the filling process is the best way to improve the phenomenon of injection molding. User a: The material is mixed with miscellaneous materials, and it is easy to layer and peel. Other reasons: too much release agent used in molding; excessive moisture; inconsistent resin temperature.
Product Name: N-propyl bromide ,1-Bromopropane
CAS NO.: 106-94-5
UN NO.: 2344
Hazard Class: 3.2
Molecular Formula: CH3CH2CH2Br
Chemical Formula:
Product Name: N-butyl Bromide ; 1-Bromobutane
CAS NO.: 109-65-9
UN NO.: 1126
Hazard Class: 3
Molecular Formula: C4H9Br
Chemical Formula:
Product Name: Ethyl bromide ; Bromoethane
CAS NO.: 74-96-4
UN NO.: 1891
Hazard Class: 6.1
Molecular Formula: C2H5Br
Chemical Formula:
Product Name: Iso-propyl bromide ,2-Bromopropane
CAS NO.: 75-26-3
UN NO.: 2344
Hazard Class: 3.2
Molecular Formula: C3H7Br
Chemical Formula:
Product Name: P-chlorobenzotrifluoride (PCBTF)
Synonyms: 4-chlorobenzotrifluoride
CAS No: 98-56-6
M.F: C7H4CLF3
Un No: 2234
Imdg Class: 3
Chemical Formula:
Chemical Intermediate & Solvent Iso-Propyl Bromide IPB, N-Propyl Bromide NPB, P-chlorobenzotrifluoride PCBTF Shandong Novista Chemicals Co.,Ltd (Novista Group) , https://www.novistachem.com
