Molding flow chart

Problems and Troubleshooting - Injection Molding Flow chart 5.2.1 - Part sticking In cavities... 

Fra. 15-27. Flow chart of production of molding compound from caprolactam. 

FIGURE 2.49 Flow chart showing key stages in the fabrication of composite structures from raw materials by prepreg molding. (After Lee, W. J., Seferis, J. C., and Bonner, D. C. 1986. SAMPE Q., 17, 2, 58.)... 

In troubleshooting of molded part defects, it is important to look at the shot size, injection speed, injection pressure, cushion, decompression, and nozzle tip. The following troubleshooting flow charts will help to resolve a majority of the problems. The forming of weld lines wherever polymer flow fronts meet is one of them [1]. 

Mold to be properly fit in the machine and to be checked for substrate sinks and substrate support. Cut the tool to obtain complete shut off with interference into substrate. Thickness of the vents has to be checked and in some cases this has to be reduced to avoid the flash. Flow chart 5.2.10 shows the way to solve problem of flash over substrate or on periphery of part. 

Either relocating the gate to the thickest section or avoiding gating to the thinnest wall area of the substrate may resolve the problem. Mold parts should be fully supported and substrate may need to be changed to resolve. Flow chart 5.2.13 shows a schematic approach to the problem of overmold breaks/impinges through hollow substrate. 

Optimizing or equalizing the mold temperature and uniformity of ejection or handling of parts after ejection from mold will help to resolve the problem. In case of counteract warp, trying differential mold temperatures may resolve the problem. Increase or design the substrate stiffness by the addition of glass reinforcement or thickness of ribs on substrate part structure. Flow chart 5.2.14 shows the schematic approach to the problem of warpage or warped parts. 

The first thing to understand about sink marks is a sink or a pull. It can be eliminated or decreased with some simple practices. Study of part weight when the gate freezes and packing of material into the mold is also important. A gate that is too far away or too small may also be a cause of the sink marks. Enlarging the gate or runner may solve the problem of sink marks. Flow chart 5.2.18 shows the way to solve the problem of sink marks. 

Shrinkage is a complex parameter and can be influenced by many interrelated factors, such as machinery, mold design, part geometry and direction of flow, processing conditions, and molding system. Shrinkage is critical to control the dimensions of the finished part. Flow chart 5.2.19 shows the way to approach and solve the problem of shrinkage. 

Tool When processing plastics some type of tooling is required. Tools include molds, dies, mandrels, jigs, fixtures, punch dies, perforated forms, etc. These tools febricate or shape products. They fit into the overall flow chart in fabricating plastic products. The terms for tools are virtually... 

We now have to thank Stanton and PanneU, and also Moody for their studies of flow using numerous fluids in pipes of various diameters and surface roughness and for the evolution of a very useful chart (see Fig. 48.6). This chart enables us to calculate the frictional pressure loss in a variety of circular cross-section pipes. The chart plots Re)molds numbers (Re), in terms of two more dimensionless groups a friction factor < ), which represents the resistance to flow per unit area of pipe surface with respect to fluid density and velocity and a roughness factor e/ID, which represents the length or height of surface prelections relative to pipe diameter. 

There is also a friction factor chart drawn by Dodge and Metzner plotting the Fanning friction factor versus the Metzner-Reed Re molds number (although this has been subsequently redrawn for convenience with ( ), see ret 4). This chart shows that the friction factor decreases with n in turbulent flow— that is, it decreases as shear-thinning character increases. If you are studying this chart, be aware that the only experimentally verified data for turbulent flow is that given for n = 1.0 to w = 0.4. 

The selected resins were polypropylene injection molding grades supplied by SABIC, with flow indexes of 5.7 19 and 47 g/lOmin. The flow curves of these materials, at the processing temperature, are presented in Figure 1. Values of the viscosity for the typical injection molding shear rates are displayed in the top right comer of the chart. 

Table I displays the heat resistance, % haze, and mechanical properties of blends consisting of PEC and PC-PDMS. When PEC and PC-PDMS were blended and extruded, the plastic pellets were hazy and white (Examples 4-6). Upon injection-molding of the pellets into plastic articles, the molded disks were pearlescent, showed streaking, and were nearly opaque. However, when the TE catalyst was used in the formulation, the two polymers became more transparent and did not show any pearlescence or flow lines after injection molding. Examples 1-3 each had the TE catalyst in the formulation, which made the blends more miscible and less hazy. The heat resistance of the products was varied by changing the PEC to PC-PDMS ratio in the formulation, and the heat resistance was not significantly affected by the addition of the TE catalyst. The notched-izod impact strength was not decreased by the addition of TE catalyst, and all materials were 100% ductile at 23 °C. Chart 1 shows the optical characteristics of Examples 1-6. The chart shows that the percent haze is decreased dramatically by the addition of TE catalyst to the blend.

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