Production statistics extruded

Pore diameters and their distribution. Small pores limit accessibility of internal surface because of increased resistance to diffusion of reactants inwards. Diffusion of products outward also is slowed down and may result in degradation of those products. When the catalyst is expensive, the inaccessible internal surface is a liability. A more or less uniform pore diameter is desirable, but the distribution usually is statistical and only molecular sieves have nearly uniform pores. Those catalyst granules that are extrudates of compacted masses of smaller particles have tamodal pore size distribution, between the particles and within them. Clearly a compromise between large specific surface and its accessibility as measured by pore diameter is required in some situations. 

The formulation exercise is complicated by the fact that the detailed aspects of the process can have a very strong influence on the outcome. This makes statistically designed experiments difficult, as it is quite easy to provide a combination of variables that do not function at all, which restricts the analysis. I have seen formulations which will function well with one set of conditions on a given set of equipment, but be unsuccessful if the process conditions, e.g., extrusion rate, are changed. I have also seen several examples where a change in the type of extruder can result in effects ranging from toss of yield to total loss of product. This certainly makes the formulation exercise difficult, especially if there is only a small quantity of the active material to work with, as... 

In the manufacture of color master batches, the current industry practice is to perform eritieal color measurements off-line. Typically, a sample of the pelletized color concentrate is diluted with natural resin at a standard ratio and milled, extruded or injection molded into a physieal form suitable for visual and instrumental evaluation. These methods are slow and labor intensive. Furthermore, they do not lend themselves well to statistical process eontrol strategies because of the time lag between production and testing. Since relatively few samples can be examined, laboratory measurements may not give a true indication of the consistency of the concentrate product over the entire manufacturing process. 

Statistical design of experiments (DOE) is often used in the early stages of process optimization. This is followed by a validation of the predictive model using actual plant production data. The response surface model described below captures the process performance window and shows the effect of changing composition and extruder screw speed on blend properties. A validation step can be easily implemented. 

Suppose that 2% carbon black is mixed with PE in a melt extruder and that the product is pelletized and shipped in 25 kg bags. We randomly select 10 bags, extract a number of pellets, and fracture and analyze them in a microscope for carbon black particle statistics. The weight fraction of carbon black is calculated from the number of particles, and their size and density, and it was found to vary as follows in the 10 bags ... 

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