Flexible Web Research Articles

Modification of Active Carbon by Hydrophobic Plasma Polymers: II Fabric Substrates

Active carbon, used in various types of chemical protection devices, can absorb an extremely wide range of hazardous compounds. Unfortunately, this “universal” absorption includes ubiquitous water molecules, which can result in saturation and premature loss of efficacy. The purpose of this work has been to treat active carbon-impregnated fabric with appropriate low-pressure plasmas, so as to render the carbon surface “hydrophobic”, while minimally affecting its ability to absorb toxic gases or vapors (simultated here by CCl4). The best results have been achieved using plasma polymerization of organosilicon (PP-HMDSO) thin films onto the fabric surface: This has been done in a pilot-scale microwave plasma reactor system, designed for treating continuously-moving flexible web materials up to 30 cm in width. Under “optimal” treatment conditions, a plasma exposure duration of 10 s (PP-HMDSO film thickness, d ∼ 40 nm) is found to be sufficient to reduce water absorption by 85%, while the corresponding reduction in CCl4absorption is small (<20%). The treatment demonstrates long-term stability, and it holds promise for commercial implementation on existing roll coaters.

BT WebWorld

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Elastic tripping analysis of asymmetrical stiffeners

An energy method is developed for analyzing the flexural-torsional and lateral-torsional buckling (“tripping”) behavior of flanged stiffeners subjected to axial force, end moment, lateral pressure and any combination of these. A strain distribution is assumed and the total potential energy functional is then derived. The strain assumptions coincide with van der Neut's assumption. However, unlike the somewhat obscure differential equation approach given by van der Neut, this study provides a simple, clear, energy approach. Both the rigid web case and the flexible web case are studied. The study explores the effect of plate rotational restraint, and a previously unresolved question regarding plate mode shape is answered. The method requires only four degrees of freedom and therefore the solution process is rapid. A number of sample stiffened panels are analyzed using the ABAQUS finite-element program; the results are in quite good agreement. The method has also been extended to inelastic tripping, and this generalized form shows excellent agreement with experimental tests on typical steel panels. This work will be presented in a second paper, to avoid an overly long publication.

Finite-element analysis of the mechanism of instability of an I-beam with a flexible web

A finite-element analysis is made of the stability and supercritical behavior of a steel I-beam with a thin flexible web. The evolution of the stress-strain state of the beam is analyzed with allowance for the joint work of the web and ribs. A method is proposed for obtaining solutions after branching occurs. The qualitative change in the stress state in the web during instability is studied in detail, it being found that one-way supercritical bifurcation occurs, i.e. the branched solutions are stable. Numerical analysis showed that the beam moves to the branch of the equilibrium path when the load exceeds the critical value. However, the beam can still sustain some increase in load after this point.

Stability of cold-formed members

A finite element method capable of predicting the buckling capacity of arbitrarily shaped thin-walled structural members under any general load and boundary conditions is presented. A rectangular thin plate element with 30 degrees of freedom is used. The linear and geometric stiffness matrices for this element are derived explicitly using symbolic manipulation, thereby eliminating the need for the expensive process of numerical integration. Further, the explicit form of the stiffness matrices makes it easier to interpret the physical significance of the various stiffness terms. For sections composed of rigid flanges and flexible web, a lower-order plate element is used in combination with a general beam-column element to form a super element for predicting distortional buckling modes. Formex formulation is used for the automatic generation of the data necessary for the analysis. Numerical examples of thin-walled structural members involving local, distortional and flexural-torsional buckling modes are presented to demonstrate the accuracy, efficiency and versatility of the method.

Stability of thin-walled members having arbitrary flange shape and flexible web

A finite element method is presented for analysing thin-walled structural members comprising a flexible web connected to one or two rigid flanges of arbitrary shape. A general thin-walled beam-column element is used to model the flanges while a thin plate element is used to model the web. Based on the derived total potential energy functional, explicit linear and geometric stiffness matrices for the two types of element are obtained. Using static condensation and appropriate transformations, the beam-column element and the plate element are combined to yield a super element with 22 degrees of freedom capable of modelling the flexural, torsional, web distortional and coupled web and flange local buckling modes of a general thin-walled member. The technique may be used to predict the elastic buckling load of members under any loading and boundary conditions. Several numerical examples are presented to demonstrate the accuracy, efficiency and versatility of the method.

Heatsealability of Flexible Web Materials in Hot-Bar Sealing Applications

Heatsealability of flexible web materials is critical to the economics of their use on commercial form-fill-seal machines. Our objective was to determine which factors in the heatsealing process affect seal strength significantly and should be included when testing for heatsealability A recently-available precision laboratory heat sealer was used to study the response of low density polyethylene (LDPE) coextruded film and high density polyethylene/ethylene vinyl acetate-polybutylene (HDPE/EVA-PB) coextruded film to sealing die configuration, plus the usual variables of temperature, time and pressure. Interface temperature and dwell time were confirmed as primary factors in controlling heatseal strength. Pressure normal to the seal surface had little effect above the level required to flatten the web for good contact. Serrated dies moderately improved seal strength of HDPE/EVA-PB at high die force, but had no advantage with LDPE. Variables in measuring seal strength were critical in interpreting results, particularly with serrated dies Results were gen erally compatible with the theory of chain-end diffusion.

Columns in partially restrained construction: analytical studies

The American Institute of Steel Construction Proposed Load and Resistance Factor Design Specification recognizes the ability of connections that function as less than fully rigid to transmit limited moments and to provide some measure of end restraint to columns in its definition of partially restrained (PR) construction. An analytical procedure for determining the response up to collapse of subassemblages in which semirigid beam-to-column connections are present is derived. This employs a nonlinear finite element column analysis together with analytical representation of experimentally determined connection moment–rotation [Formula: see text] curves. To trace the full response under any load path produced by a combination of beam loads and direct column load, it is necessary to allow for possible reversal in the direction of rotation of any of the connections. The program is used to study the effect of different connection types (ranging from very flexible web cleats to almost rigid extended end plates) and different load paths on column behaviour in nonsway subassemblages. It is found that the degree of rotation required from each connection is an important parameter in determining column response. Key words: buckling, columns, connections, frames, stability, steel, structural design, structures.

High-power selfshielded electron processors and their application to stack gas treatment

The increasing industrial demands for large width (approximately 2 m), high dose rate (1 Mrad at 1500 m/min) electron beam machinery has led to a relatively rapid improvement in this field over the past several years. Selfshielded machinery capable of up to 1000 mA of current at 300 kV is now in commerical use, and the essential features of these designs are presented. A variety of product handling geometries for use with these accelerators has been developed for processes involving flexible web, rigid sheet, and three-dimensional objects in both the polymerization and sterilization applications. One of the major power-intensive processes to which these machines are currently applied is that of the reduction of pollutants (NOx, SO2, etc.) in the flue gas from fuel combustion — particularly those fossil fuels used in power production. The preferred technique utilizes the treatment of the ammoniated gas at modest dose levels (0.5–2.0 Mrads) to enhance the formation of ammonium salts which are then removed from the gas stream by conventional filtration. Some results from a 180 kW × 300 kV pilot installation in Karlsruhe, Fed. Rep. Germany + are presented.

Interferometric measurements of the surface profile of moving samples

An acoustooptic cell frequency-shifts 632.8-nm radiation reflected off moving low-reflectivity surfaces. Surface asperities produce phase shifts in an 80-MHz carrier frequency. Surface profile plots and quality parameters are obtained by analyzing digitized phase shifts. Rigid samples may be turntable mounted, and flexible web samples are moved over a smooth stationary guide. A spatial resolution of 1 μm and a vertical resolution of 1 nm are obtained. Reproducibility of rms measurements is also within 1 nm.

Distortional buckling of thin-web beam-columns

An approximate finite element method of analysis is developed for the distortional buckling of beam-columns. The member consists of a flexible web, to which is connected two rigid flange assemblies of arbitrary shape which remain undistorted during buckling. The method permits an economic computer analysis to be made of elastic distortional buckling of members under various conditions of loading, end support and restraint. Following studies of the convergence and accuracy of the buckling solutions, the method is used to demonstrate the effects of web distortion on the elastic buckling of lipped channel beams under moment gradient.

A 1.4 meter electron curing system for the finishing of sheet wood products

The advantages of high performance electron curable clear and pigmented topcoats, suitable for both wood and paper application, have been known for some time. Since 1978, great progress has also been made in the application of this technology to laminating for the flexible web converting industry. The combination of these systems with a single electron curing station offers the opportunity for “single-pass” finishing of laminated board which performs both the lamination and topcoat steps inline. A system is described which is used for the simultaneous laminating and topcoating of printed paper or vinyl to board. Typical panel dimensions are 1.2 × 2.5 meters (4 feet × 8 feet) and the product-handling Selfshield TM system used in-line to convey the panel products continuously through the electron curing station is 12.4 m × 1.56 m × 1.67 m (40 feet × 5 feet × 5.5 feet). The system is designed for use at speeds to 60 meters/minute (200 fpm). The performance specifications of both the Electrocurtain ® curing unit, and of typical topcoats and adhesives used with this system, will be discussed. The provisions required for inerting and venting of the processor zone when using these 100% reactive coatings will also be presented.

The Coloration of Wallcoverings

It has not been my intention to give an in‐depth study of wallcoverings, but more an appreciation of its development from its early beginnings to the present day. It is hoped, however, that the contents of this summary may encourage the reader to delve a little further into the various areas of interest.The term “wallcovering” in this article is used to describe all forms of flexible web supplied in roll form for hanging onto walls or ceilings by means of an adhesive.

Electron curing for high speed paper, film and foil converting

The status of self-shielded, compact electron processors for flexible web converting applications is reviewed. The uses of these units for a variety of laminating applications are described, with emphasis on the application techniques appropriate for low weight, (1–2 gm/m 2) 100% convertible adhesives. Performance data for electron cured adhesives with polyester/polyethylene systems is presented and compared with conventional urethane systems. The unique surface features of electron cured gravure coatings applied and cured at high speed are discussed, with reference to both paper and film substrates. An important advantage of electron curing of buried adhesive layers is the process quality control permitted by this “all-electric” system. The performance characteristics of curing atmosphere control (inerting) for coatings are reviewed. Industrial experience with these processors has shown that effective inerting of coated flexible webs at speeds to 250 m/minute is both practical and economical.