Actual Process Conditions Research Articles

Rheotens‐mastercurves and drawability of polymer melts

AbstractIn a Rheotens experiment, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio. For thermo‐rheologically simple polymer melts, the existence of Rheotens‐mastercurves is proven. Rheotens‐mastercurves are invariant with respect to changes in melt temperature. Also, for polymer melts with different average molar masses, but similar molar mass distribution and branching structure, Rheotens‐mastercurves are invariant to changes in the average molar mass. It is shown, by testing several polyethylenes with different molar mass distribution and different long‐chain branching, that Rheotens‐mastercurves allow a direct and quantitative assessment of the drawability of polymer melts under actual processing conditions, i.e. under the action of a constant tensile force and including the effects of the rheological prehistory in the extrusion die.

Metal-related castability effects in aluminium foundry alloys

Many foundries have intermittently experienced a major outbreak of casting rejects in which the alloy, although clearly within specification, nevertheless appears to be the primary cause of the problem. Minor changes in metal composition or metal quality can be sufficient to facilitate the formation of casting defects, within normally castable products, even when normal process conditions prevail. In the Al-Si based foundry alloys, the formation of porosity and shrinkage defects is sensitive to both metal composition and metal quality. However, the casting design and the actual processing conditions used can alter the sensitivity of the response to variations occurring within the metal. A number of metal-dependent factors of particular relevance to the castability of aluminium foundry alloys are discussed in this review. These include hydrogen level, oxidation tendency, the presence of inclusions, total volumetric shrinkage, alloy freezing range, dendritic growth conditions (dendrite arm spacing, coherency and grain size), formation of intermetallic phases, interdendritic feedability and the mode of eutectic solidification. The review also considers the sources of impurities found in aluminium alloys.

In-line characterization of polymer deformation in melt and solid phase processing

Constitutive relationships obtained from in-process measurements on polymers that have been subjected to typical solid or melt phase processing strain-temperature-time histories can be used for enhanced modelling of deformation and flow (e.g. finite element analysis/computer aided design), or to provide new information on shear and extensional flows. In some circumstances in-line measurement may be the only practical route to reliable constitutive data. In the case of melts, such measurements may also be used for real time assessment of polymer state and for process control. The in-process measurements discussed in this paper are specifically concerned with ‘in-line’ rheometry, where pressure, temperature, stress, strain and strain rate measurements are made upon polymers in actual process geometries, under actual process conditions. Examples of accurate in-line measurements of polymer rheometry in an injection moulding nozzle and in a model solid phase forming process—uniaxial drawing of polymers—are discussed.

Effect of viscosity ratio and processing conditions on the morphology of blends of liquid crystalline polymer and polypropylene

AbstractThe effect of viscosity ratio and processing conditions on LCP/PP blend morphology was studied. The viscosity ratio (ηLCP/ηPP) was varied from 0.1 to 3.6 by using five different polypropylene grades as the matrix and two LCPs as the dispersed phase (20 wt %). The most spontaneous fiber formation was achieved when the viscosity ratio was between 0.5 and 1. In addition to shear forces, elongational forces are important in achieving a highly fibrillar structure and significant mechanical reinforcement. The lubricating effect induced by the low viscosity of LCP was most pronounced for the blends exhibiting a fibrillar morphology. The morphologies of blends produced by different mixing equipment differed only slightly. The greatest variation in the mixing efficiency was found for blends whose components had totally dissimilar melt viscosities. The slight differences in morphology due to melt blending in dissimilar equipment were decreased after injection molding, whereas the differences in morphology due to dissimilar viscosity ratios were still evident in the injection molded blends. Thus, the viscosity ratio at processing in the actual processing conditions is of great importance. © 1994 John Wiley & Sons, Inc.

Sensors in Laser Machining

The goal of laser machining is to maximize the material removal rate, subject to quality constraints. Current industrial practice relies on trial-and-error to find acceptable process parameters. This is time-consuming, does not necessarily result in optimal operating conditions, and does not allow the adaptation of the process parameters to the actual process conditions. An alternative approach is a closed-loop control scheme based on in-process sensing. This paper describes and discusses several techniques for in-process sensing of laser machining.

An introduction to process visualization capabilities and considerations in the environmental scanning electron microscope (ESEM).

Process visualization can be a very powerful tool for understanding dynamic processes. Process visualization requires a non-destructive technique that can be monitored in real time. In this paper various methods of non-destructive inspection will be described and compared. The applicability of these non-destructive inspection methods to process visualization will be compared and contrasted. Particular attention will be paid to a recent development in this area, the environmental scanning electron microscope (ESEM) which is inherently a non-destructive inspection technique with the advantages of electron microscopy for superior magnification and depth of field capability. The ESEM offers a unique platform for process visualization studies. The majority of process visualization is currently done using optical microscopes with hot stages for observing morphological effects top down (optical microscopes) or from the side (contact angle). Major limitations of these optical methods include lack of magnification, poor depth of field, and clouding of optics. Process visualization is best carried out utilizing a non-destructive technique, such as the ESEM, since invasive sample preparation techniques such as conductive coatings alter the sample and make interpretation more difficult. Common process variables such as thermal profiling and the effect of ambient conditions have been examined using the ESEM. Other process variables that could be of interest in the future will be discussed. There are limitations in the ability of the ESEM to reproduce actual process conditions, such as pressure and mass flow rate trade-offs. The ESEM can also be combined directly and indirectly with other analytical techniques to determine the composition of the sample and/or byproducts of a reaction that is being monitored.(ABSTRACT TRUNCATED AT 250 WORDS)

On the values of material property data used in hot isostatic pressing models

Hot Isostatic Pressing (HIP) is used extensively for consolidation of powers and particulates and near net shape fabrication of powder metallurgy products. The last few years have seen significant refinement of the HIP model proposed by Ashby and co-workers. It has been acknowledged by the developers of the maps that the accuracy of the predictions is limited by the precision with which material property data, used in the HIP Maps program are known. Even for materials processed similarly, there are, typically, variations in the values of material properties due to the inherent inaccuracies in the methods used to determine these properties. Such variations significantly affect the accuracy of the HIP model predictions. The objective of the present investigation is to determine the effect of variations in the values of material properties on the HIP model predictions by performing a sensitivity analysis with respect to material property data. The values for material property data used in the HIP Maps program are typically determined in one of the following ways: (a) experimental measurements at consolidation conditions; (b) estimates based on data on other materials; (c) through back calculations using the experimentally determined HIP data; and (d) by extrapolations to get appropriate materialmore » property values for the consolidation conditions. Methods other than (a) could result in the determination of a material property value which is highly unrealistic. The present study discusses this with respect to a recent experimental study [10] on TiAl and resolves the discrepancy by using PLC material parameters determined experimentally for conditions close to the actual HIP process conditions.« less

Interfacial monitoring during the processing of carbon-fiber/PMR-15 polyimide composites

It is accepted widely that the interface between the fiber and the matrix formed during the processing of composite plays a critical role in transmitting the individual properties of the component, to influence the whole behaviour of the composite, such as the off-axis strength and fracture toughness, etc. The processing of composites during their manufacture has a dominant effect on the interfacial character and finally determines the properties of composites. An interfacial monitoring system (IMS) used to direct the processing of fiber-reinforced composites is established in this paper, and the role of IMS in composite processing is illustrated by presenting processing studies of carbon-fiber reinforced PMR-15 polyimide composites. In IMS, a small specimen can be cut from the actual composites produced with different processing parameters, and a diamond probe used to push axially against the end of a single fiber. The load at debond between this fiber and its surrounding matrix is input to a finite-element program, which calculates the interfacial shear strength. The IMS for real composites has the obvious advantages of reflecting the actual processing conditions, the interfacial character being monitored by the user in the composites-processing industry, without the need for specialized model construction, and it can examine carbon-, glass-, SiC- and boron-fiber reinforced polymer- (thermoplastic, thermosetting), metal- and glass-ceramic-base matrix composites materials that may be either uni-directional or multi-directional laminates or chopped-strand materials such as sheet molding compound (SMC). Instead of involving a macrospic destructive test, the specimen for IMS cut from the manufactured composites is very small (2 mm × 2 mm × 2 mm) and the results can provide an indication of the performance of the whole article. Therefore, this IMS will be of great value to the industrial manufacturer of composites materials. In addition, IMS can be used to evaluate the service and storage performance of the parts at any time.

Deformation behaviour and microstructure-mechanical-property correlations for RR58 aluminium alloy

Processing of costly and special materials developed for specific applications needs very careful processing for producing net-shape or near-net-shape components without defects and with controlled microstructures on a repeatable basis. Hence, deformation processing requires science-based methodologies to understand and control the workability and microstructural changes under actual processing conditions. In the present paper, atomistic and systems approaches have been used to analyse the deformation processing of RR58 aluminium alloy in the complete range of strain rates and temperatures involved in industrial metal-forming processes. Both of these approaches have yielded comparable results and can be applied quite easily to the processing of different materials.

Deformation behaviour and microstructure-mechanical-property correlations for RR58 aluminium alloy

Processing of costly and special materials developed for specific applications needs very careful processing for producing net-shape or near-net-shape components without defects and with controlled microstructures on a repeatable basis. Hence, deformation processing requires science-based methodologies to understand and control the workability and microstructural changes under actual processing conditions. In the present paper, atomistic and systems approaches have been used to analyse the deformation processing of RR58 aluminium alloy in the complete range of strain rates and temperatures involved in industrial metal-forming processes. Both of these approaches have yielded comparable results and can be applied quite easily to the processing of different materials.

The effect of shear rate and strain on the pasting behavior of food starches

It is a phenomenon well known by food technologists that the pasting viscosity of most food starches is highly shear rate sensitive. The standard method (i.e. amylograph) adopted by the industry uses poorly defined shear rates. Consequently, processing engineers often find difficulties in attempting to relate quantitatively the amylograph data to the processing characteristics of starch under actual processing conditions. Using commercially available rheometers and well defined shear conditions, such effects due to shear rate and strain variation were studied. The advantages of the new method used, particularly for research and process development, are discussed.

D.c. magnetron sputtering of oxidation-resistant chromium and CrN films monitored by optical emission spectrometry

For applications at temperatures above 500 °C, Ti-6wt.%Al-4wt.%V was protected by sputtering chromium and chromium nitride layers from the embrittlement caused by oxidation. The coating processes were analysed in situ by means of optical emission spectrometry, whereby the deposition rate and the stability of the actual process conditions were monitored. Further, the nitridation of the chromium target (the source of the coating material) and the concentration ratio of the condensing binary compounds (Cr x N y ) can be assessed during the process. Compared with the uncoated material, the mass gain of Ti-6wt.%Al-4wt.%V due to oxidation could be decreased to about 3% by means of chromium and chromium nitride layers 3 μm thick. Also the brittle α case formation at the near-surface region of the titanium alloy is greatly reduced in the course of high temperature oxidation. As far as diffusion and reaction are concerned, an interpretation of the oxidation process on the titanium alloy is given by means of Auger depth profiles. The morphology of the layers is characterized by scanning electron microscopy pictures.

Processing preshear and orientation effects on the rheology of an LCP melt

Independent LCP melt rheological measurements were performed using both capillary and slit rheometer die equipment. The latter was attached to the end of a laboratory extruder so that the attending rheological measurements were obtained under actual processing conditions. The viscosity–shear rate behavior determined by these two methods for the subject LCP melts was significantly different. For a specified melt temperature and shear rate, the viscosity measured by the slit rheometer was as much as 10× lower than that measured by capillary rheometry. The above measured viscosity differences appear real since corresponding viscosity measurements on conventional polymers such as LLDPE and HDPE by these two methods produced equivalent results. Thus, the rheology of these LCP melts is strongly dependent upon preshear history, die geometry, and residence time. This dependence is attributed to the highly anisotropic nature of the LCP melt, the tendency of the polymer ‘‘domains’’ or chains to orient when processed and a long relaxation time for the oriented structure. Knowledge of LCP rheological behavior under actual processing conditions is of paramount importance to properly design extruder or injection molding screws, as well as corresponding dies and molds.

In situ plasma contamination measurements by HeNe laser light scattering: A case study

Using a simple, inexpensive HeNe laser and a video camera to measure light scattering intensity and location, particulate contamination in an SiO2 sputtering process used in semiconductor manufacturing has been studied under actual process conditions in a class 10 cleanroom. Particulates were observed during all aspects of the sputtering process. It was seen that portions of the process which resulted in mechanical stress on the tool walls produced the greatest flux of particles inside the tool. However, the sputtering step was the major contributor to contamination in this chemically simple process, because of its long duration and the stress‐inducing nature of the plasma. The contamination level in this plasma is estimated to exceed the cleanroom ambient by three orders of magnitude. As in other process plasmas, the particles were suspended at the sheath/plasma boundary. It is argued that a relatively weak electrostatic field is required for gravitational counterbalance of these highly charged particles...

Apparatus for direct measurement of ash fusion and sintering behavior at elevated temperatures and pressures

Ash fusion, sintering, and deposition may impose serious operational difficulties in conventional and advanced coal-combustion systems. Conventional ash fusion techniques (e.g., ASTM methods) determine the qualitative behavior of ash samples at atmospheric pressure. Presently, there is no known available technique that can measure the behavior of coal ash at elevated temperatures and pressures. In the literature, methods based on electrical resistance or shrinkage of coal ash have been reported at atmospheric pressure (elevated temperatures) conditions. A high-pressure microdilatometer (HPMD) has been developed to investigate ash fusion and sintering behavior at elevated pressures and temperatures by the simultaneous measurement of the temperature of initial contraction and electrical resistivity of samples. This novel technique facilitates the measurement of ash properties over a wide range of temperature, pressure, and gas atmosphere (oxidizing, reducing, or inert). The operating principle of the HPMD includes measuring the temperature at which there is a significant ‘‘shift’’ in the electrical resistivity (and/or sample volume) that represents ash sintering and fusion. Sintering occurs through the formation of solid-state, particle-to-particle ‘‘necks’’ or the appearance of a molten phase, which allows a path for electrical conductance. The ability to perform both resistivity and shrinkage measurements simultaneously or independently at elevated pressures makes the HPMD truly unique. The HPMD can also be used to investigate the swelling and softening behavior of pyrolyzing coal at elevated pressures and relatively rapid heating rates. The HPMD can provide insights into the sintering/fusion of coal ash or coal swelling at a range of conditions: (a) the influences of various gas atmospheres can be investigated, (b) the effects of pressure can be studied, (c) different temperature/heating rate schemes can be used (constant rates, isothermal holds below or above the sintering temperature, etc.), and (d) studies can be performed to investigate the influence of increased heating rate at elevated pressures (which were not performed previously) on coal swelling and plasticity. It can also be applied to other fossil fuels such as oil shale or carbonaceous materials (e.g., graphite) to measure their electrical conductivity or expansion and contraction behavior at ambient or elevated pressures and temperatures. The HPMD allows researchers to gather novel data and thereby facilitate a fundamental understanding of the behavior of coal or coal ash at actual processing conditions.

Étude de la cristallisation dans la mise en forme des polymères. Application à l’extrusion de films de polypropylène

Crystallization of a polymer in an industrial process is highly dependent on the mechanical (flow), thermal (cooling rates, thermal gradients) and geometrical (walls of the processing devices) conditions encountered by this polymer in the process. Cast film extrusion of polypropylene is chosen as an example of interrelations between processing conditions and microstructure. In this process, the polymer is extruded through a slit die, slightly stretched in air and then cooled on a chill roll. Our analysis is based on the combination of a thermomechanical model and morphological observations, which makes it possible to discuss the respective influences of stretching in air and cooling on the roll. Stretching in air essentially affects spherulite nucleation and growth during subsequent crystallization on the roll. The existence of a transcrystalline region is attributed to heterogeneous nucleation at the roll surface Finally, the observation of a zone near the roll with a finer microstructure is related to the cooling rates and the thermal gradients calculated by the thermo- mechanical model. A conclusion of this work is that a complete quantitative interpretation requires the development of crystallization models taking into account the actual processing conditions.

The measurement of mixing efficiency of continuous mixers

A radiotracer method for testing the mixing characteristics of industrial continuous mixers in actual process conditions is described. The tracer is fed into the input of the mixer at a constant rate and the radiation in the output is measured by two properly collimated radiation detectors. The measurement yields data in the form of two time series which contain information about the radial and axial homogeneity of the tracer in the measuring point. The formulas connecting the information in the measurement data and the axial and radial concentration variation of tracer are derived by the methods of statistical mathematics. The values for experimental parameters are obtained by computer simulation of the radiation measurement geometry. The method was tested by measuring the increase of the homogeneity as a function of mixing distance in a static tube chlorine mixer in a pulp bleaching plant. Also some results obtained on another type of mixers showing the effect of pulp type on mixing are given.

Application of tower bioreactors with forced circulation in biomass production

Characteristic hydrodynamic parameters of three selected types of bubble-type column reactors with forced liquid circulation were studied experimentally. Application of these units for the fermentation process - production of fodder protein by continuous cultivation of Candida utilis yeast on the synthetic ethanol was tested. Two modifications of the column reactor with the ejector gas distributor and the bubble type tower reactor with the central tube and forced internal circulation of the gas-liquid dispersion were selected. Diameter of all three reactors used was 0.3 m. The volumetric mass transfer coefficient (kLa) and gas holdup (εG) were determined both for the standard water-air system and under actual fermentation process conditions. The effect of the inlet ethanol concentration and of the dilution rate on the cultivation characteristics was determined during the cultivation experiments. The obtained results have proved that the studied reactor types are suitable for fermentation. Equipment with the ejector gas distributor can be recommended even for processes with high requirements on the oxygen consumption, while by the proposed construction arrangement the undesired foam formation in the system was successfully eliminated.

The applicability of tracer techniques for studies on sewage treatment process dynamics

The applications of tracer techniques in studies of sewage treatment process dynamics are reviewed and discussed. Among the different tracer methods for flow-rate measurements, the dilution method is best applicable under sewage treatment plant conditions. In sedimentation basin studies, tracers have been used mainly in order to characterize the hydraulic efficiency of the basin. However, the practical value of these studies has been somewhat limited, because there is no explicit connection between the hydraulic behavior expressed in terms of the tracer test results and the solids removal efficiency. The unsteady character of sewage treatment processes creates difficulties in the application of tracer techniques. In the case of aeration basins having relatively steady flow patterns these difficulties are much slighter than in the case of sedimentation basins. The double-tracer method developed for the aeration capacity measurements under actual process conditions seems to have remarkable potential in aeration process development.

Frictional behavior of solid polymers on a metal surface at processing conditions

AbstractThe frictional coefficients of three glassy polymers (polystyrene, polycarbonate, and polymethylmethacrylate) and three crystalline polymers (high density polyethylene, low density polyethylene and polypropylene) on a highly polished steel surface were measured at high temperatures, high pressures, and high speeds, all comparable to actual processing conditions. The frictional behavior of these polymers was found to depend on temperature, pressure‐and speed in a very complicated manner. There appears to exist inter‐relationships among the temperature, pressure and speed dependences of the frictional coefficients. The frictional coefficients of ductile, crystalline polymers as a function of temperature appear to undergo two distinct transitions: one associated with yielding and the other associated with melting. The frictional coefficients of glassy polymers go through only one transition, associated with the glass transition. The friction‐generated heat at high pressures and high speeds can increase the sliding interface temperature of a polymer to values much greater than the metal surface temperature, and thus the polymer can start to melt (or plasticate) at metal surface temperatures appreciably below its thermodynamic melting (or glass transition) temperature.