Product dimension

It is the prediction of performance in its broadest sense, including all the characteristics and properties of materials that are essential and relate to the processing of the plastic. To the designer, an example of a strict definition of a design property could be one that permits calculating product dimensions from a stress analysis. Such properties obviously are the most desirable upon which to base material selections. 

An allowance must also be made for postforming shrinkage. Molds should be designed oversize so that when shrinkage is complete the product dimensions will be correct to within the design tolerances. 

In conclusion regarding creep testing, it can be stated that creep data and a stress-strain diagram indicate whether plain plastic properties can lead to practical product dimensions or whether a RP has to be substituted to keep the design within the desired proportions. For long-term product use under continuous load, plastic materials have to consider creep with much greater care than would be the case with metals. 

To predict product dimensions and the fluctuation of dimensions (tolerances) during a... 

The required land length depends not only on the type and temperature of the TP melt, but also on the flow rate. The deformation of the melt in the entry section of the die invariably causes strains that only gradually decrease with time (relaxation). Usually the target is to allow the melt to relax before leaving the die. Otherwise the product dimensions and the mechanical properties may vary, particularly with rapid cooling. 

Profile forming is achieved by passing the extrudate through a series of calibration dies, which cool the material through contact with the metallic walls of the calibrators. Vacuum holes or slots are used with the water cooled walls to improve and maintain final product dimensions. Alternatively, for pipe extrudate, the... 

The hypothesis indicates that energy consumption per unit area of new surface produced increases faster than the linear ratio of feed and product dimensions, a phenomenon already noted and explained. The proportionality of net energy input and new surface produced has been confirmed in some grinding operations. 

Profile extrusions are the most difficult to make because changes in take-up speed or screw rotational speed alone are not enough to compensate for deficient product dimensions. In the case of sheet and film, if the edges of the sheet are not at the target thickness, they can be trimmed off and sent back to the extruder... 

As stated above, extrusion die design is a complex task because the extrudate product dimensions depend not only on the die design (die shape), but also on the polymer properties and extrusion process parameters. The following are general recommendations for extrusion die design ... 

Table III. Average Product Dimension and Growth Rate for All Synthetic Runs (The suffix A in the sample number indicates runs made using Ludox AS-40 as the silica source ) ...

The measurement framework in Figure 16 provides an example of the product dimensions that should be continuously monitored and improved. 

The rheological properties of molten polymers influence many aspects of processing. In injection molding and extrusion they affect screw pumping efficiency, generation of mechanical heat, and die pressure (and hence output rate). They also influence die and mold weld lines, surface finish, product dimensions, etc. 

Extruded products, such as pipe, sheet or complex profiles for window frames, have a constant cross section. Figure 5.8 shows part of a pipe extrusion line the continuous output must either be coiled, if it is sufficiently flexible, or cut into lengths and stacked for distribution. All parts of the line must be carefully controlled to keep the product dimensions within the acceptable limits. We will concentrate on the analysis of the extruder output. 

The mould cavity must be filled completely without any flash occurring. The simplest control for mould filling uses limit switches on the screw travel. These actuate after the correct volume of melt has been injected, reducing the injection pressure to a lower holding value. However, any melt leakage past the screw non-return valve, or at the nozzle, causes the part mass to vary, with a consequent variation in the product dimensions. A better, more direct, control method uses a melt pressure transducer in the mould, which detects the rapid pressure rise, once the mould is full the... 

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