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Notes: Summary The highly regulated expression of zein genes in endosperm tissue suggests that trans-acting factors, by binding to cis-acting sequences, influence the coordinate and developmentally regulated expression of these genes. A 15 55 bp 5′ flanking region of a zein gene was analysed for sites of specific interaction with nuclear proteins from endosperm and seedling tissue. At least four different protein binding sites were mapped to the zein 5′ region by the nitrocellulose filter binding technique and two of these exhibit tissue-specific binding.

Notes: One of the basic prerequisites for rational and high quality production of plastic parts is a tool layout tailored to the production process. To date, both design and construction have generally been based on values acquired by experience. This first, necessitates highly qualified personnel and second, involves what is frequently time consuming and costly finishing work. Experience acquired so far with computer-aided layout of injection molds shows that even a designer with little experience reaches the target more quickly and more reliably. At the same time he is able to draw on the results of intricate calculation and simulation methods which he was unable to apply in the past for reasons of time alone. This paper thus sets out the possibilities currently open and the experience available for computer-aided mold layout. The chief point of focus here is a system for the layout of injection molds. Working on from this system, however, the potentials for computer application are presented for blow mold- and foaming mold-design. After finding the mold principle, mold layout essentially divides up into two major areas, namely dimensioning calculations (CAE) and compilation of production documents (CAD). In dimensioning, the different functional elements of the mold are calculated. The aids that have been developed and the potentials of computer-aided dimensioning are presented with examples from the fields of rheological, thermal, and mechanical mold layout. Computer-aided rheological layout divides up into two steps. The first gives information on qualitative filling behavior (filling picture, flow paths) and the second provides quantitative results (pressures, shear stresses, temperatures). Computer-aided thermal layout similarly divides up into part steps. These are a rough overall energy balance, a rough layout of the tempering system, a segmented layout, and a homogeneity check, which involves simulating the temperature conditions in the mold by means of difference methods. When it comes to mechanical layout of the mold, programs are available for deformation calculations on basic cases and these will frequently be sufficient. For more complex cases of loading and deformation, a finite element program is used. Graphic data processing units can be used to supply extra facilities - first, to provide an aid for the simulation programs in dimensioning and second, to rationalize the compilation of the production documents. An illustration of a CAD workplace is given, incorporating the necessary computer configuration and peripherals. Compiling production documents is essentially a problem of variant design. The variants in this case are the individual components of the mold and a number of standardized accessories that can be called up as “standardized components.” The mold cavity, however, always has to be a free design. All programs are dialogue driven and are in a standardized manner so that even designers with no data processing experience can use the computer as an aid. The CAD/CAE system presented duly fulfils all these requirements. It allows the designer, at a single computer work station, to carry out both simulation and dimensioning calculations, to obtain information on material data, and to compile production documents on the basis of variant and free design. This provides the designer with a readily manageable aid and makes a considerable contribution towards improving the design result. Finally, the capacity of different computer concepts and the CAE/CAD/CAM systems on the market are discussed. For the future it will be possible to establish a computer-aided link between the different areas of design, from development of the molded part, via mold design and production, through setting the processing parameters of the injection molding machine.

Notes: The complexity of the counterflow injection process may be regarded as a prime reason for the reluctance to apply PUR. The fact of several reactions and physical processes taking place along side each other in a very short time causes considerable difficulties and leads to high reject rates or high finishing costs in practical operation. These difficulties include obtaining an adequate mixing quality for high-grade components, transporting the ready-mixed blend into the mold cavity, and maintaining absolutely constant the optimum process parameters for production.The homogenizing effect of high-pressure mixing heads was established by using transparent model liquids. The measuring systems we applied was a chemical decolorizing method and the so-called random sampling method. The findings established with these methods and the model liquids have been summarized in the form of design and setting recommendations for counterflow injection mixers. We also compiled an energy description for the layout and operation of counterflow injection mixers, based on the correlation between energy input and mixing quality. This description is in the form of a dimensioning reference value and allows the user to achieve a rapid layout. We checked the findings obtained on real PUR systems. The dimensioning reference value makes it possible to establish a critical limiting blend.The guarantee of a specific blend quality is an essential, though by no means adequate, criterion for the production of defect-free moldings. While the ready-mixed blend is flowing into or inside the mold cavity, incorrect flow guidance can cause bubbles to be enclosed in the blend, or several flow fronts meeting at an unfavorable point can lead to air pockets being trapped. We were able to observe and record the flow processes visually by using transparent molds. The effects of a series of throttle and gate systems on air bubble enclosure can now be assessed on the basis of these records. We also developed an easy-to-use method for the mold designer, which allows him to describe the flow processes in the mold. By using this method, the designer can establish a visual picture of the filling process right at the design stage. This makes it possible to eliminate serious errors early on, at little expense, by modification of the construction drawing. In the past, these errors could only be rectified by costly alterations to the finished mold, if at all.One of the characteristics of the PUR manufacturing process is that the chemical reaction and the shaping of the reaction melt take place simultaneously within a very short time and mutually influence one another. The process parameters for a given mold geometry must be selected so as to ensure that both the process sequence for the chemical reaction and the flow and filling process are controlled in such a way as to give a defect-free part which can be demolded in the shortest possible time. The trial and error method of process optimization applied today is time-consuming and costly. In addition, it does not permit clear-cut conclusions to be drawn about the machine setting from the molded part, on account of the complex chemical/thermodynamic interactions involved. Objective criteria for machine setting can be found by measuring the decisive process parameters in the mold itself. Automatic process monitoring is possible, or better, essential, for recognizing errors and deviations right at the manufacturing stage and implementing countermeasures automatically.The control parameter is the reaction temperature in the mold. It is this which determines the reaction speed, the viscosity profile, the crosslinking and curing process and hence the flow in the mold, the foaming and filling process, and the attainable demolding time. The level and time profile of the reaction temperature is controlled via the liberated heat of reaction, the starting temperature of the components, and the mold wall temperature, which, in the case of thin-walled parts, constitutes the chief influencing variable.The pressure inside the mold is easy to measure and provides a valuable aid in setup and process monitoring. Its profile indicates the flow resistance, the filling and foaming pressure, and the reaction shrinkage. The pressure measurement can thus be used to monitor the viscosity profile of the reaction, and then the metering time, filling capacity, gas charge, and blowing agent aligned to give optimum mold filling without overinjection.A modular unit concept is described for monitoring and controlling the metering unit. Precise operation of this unit marks a prerequisite for a reliable process sequence. This concept incorporates the potential of present-day microcomputers and personal computers to log and evaluate data. The central feature here is the control of component temperatures and the flow measurement and metering control. It is essential to measure component pressures in the recirculation and mixing phase in order to detect and smooth out pressure differences which could otherwise lead to a change in the blend (dynamic reference value shift).When it comes to the gas charge, the solution of the gas by the conveying pressure is decisive. The dissolution process in the mold is pressure- and time-dependent. It is thus essential to measure the pressure inside the mold in order to check the actual impact of the gas charge for the foaming and holding pressure phase in the mold.