Sheet inflation

To generate equibiaxial extension, sheet inflation, lubricated squeeze flow, and the rotary clamp technique have all been used [9, p. 261]. The most rehable of these is the one based on the rotary clamp technique, and the latest version of this instrument has been described by Hachman and Meissner [160]. This impressive instrument is presently the only rheometer capable of generating homogeneous biaxial extension, but it is somewhat complex and difficult to use. Lubricated squeeze flow is much simpler, but there are important limitations on its capabilities due the difficulty of maintaining lubrication [220].Isakief a/. [161] used lubricated squeeze flow to carry out stress relaxation experiments for determination of the damping... 

The market for PPVC film and sheet is only slightly less than for wire and cable insulation. Uses are as diverse as seepage barriers, factory doors, inflatables, baby pants, car trim, covering materials for book bindings and document cases and shower curtains. UPVC film has also been widely used for packaging of food, particularly for shrink-wrap purposes, but this market has been subject to some substitution by polypropylene. 

Although plastic sheet and film may be produced using a slit die, by far the most common method nowadays is the film blowing process illustrated in Fig. 4.20. The molten plastic from the extruder passes through an annular die and emerges as a thin tube. A supply of air to the inside of the tube prevents it from collapsing and indeed may be used to inflate it to a larger diameter. 

As previously discussed in earlier topics, extensional flow occurs when the material is not in contact with solid boundaries, as is the case during drawing of filaments, film, sheets, or inflating... 

Fig. 97.—Comparison between theoretical and experimental stress-strain curves for vulcanized rubber for elongations =0.40 to 2.0. Points are experimental data those for a <1 were obtained by inflating a rubber sheet. (Treloar. )...

Retaining dikes and berms. Retaining dikes and berms include earthen embankments, earth-filled cellular and double-sheet pile walls, water inflated dams, and so on, which aim to minimize the transport of contaminated sediments. 

Vacuum forming has limitations due to the non-uniform wall thicknesses of its products. As the sheet is drawn into the mold, its thickness decreases, especially in the corners. For this reason, just as in blow molding, we design vacuum formed products to have rounded corners. If the depth of the cavity is excessive, walls can become locally so thin that they are unacceptably weak. One strategy that we use to alleviate this problem is to pump air into the cavity after the sheet has been clamped. This inflates the sheet, pushing it upwards and expanding its area approximately uniformly. When we subsequently apply a vacuum the expanded sheet is drawn back down into the mold. The finished product has a more uniform wall thickness than if we had applied the vacuum directly. 

Equi-biaxial extension results have been obtained by inflating sheets of unimodal and bimodal networks of PDMS [114,115]. Upturns in the modulus were found to occur at high biaxial extensions, as expected. Also of interest, however, are pronounced maxima preceding the upturns. Such dependences represent a challenging feature to be explained by molecular theories addressed to bimodal elastomeric networks in general. 

Some inflatable furniture uses sheets or films of PVC or polyethylene. 

Rubber sheets are the most important materials for the construction and fabrication of much chemical plant equipment such as storage tanks, reactor vessels, pipelines, seals, hoses and rubber lined mild steel equipment of different sizes and shapes, inflatables, etc., and almost all equipment subjected to different corrosive environments. The rubber sheets can be either plain or fabrics coated with rubber. The fabrics used for coating are nylon, rayon, cotton or various other synthetics. Rubberized fabric cords are also used as reinforcing members in various products. 

The calendering process and its conditions are developed or modified according to the requirements of subsequent operations and the purpose for which the sheet is used. Thus for sheets which are to be open cured, such as in chemical plant lining and custom built items such as inflatables and ebonite pipes, roll coverings for paper and steel mills, the calendering needs to be more exact than the sheets which are used for blank preparation for molding of... 

Apart from the above three types there are custom built rubber products such as expansion joints, flexible cell covers and large size rubber foils for the caustic soda industry, and many inflatables, fabric reinforced products and thick moulded sheets for specialty applications in certain process plants. These are all hand formed in aluminium or cast iron moulds or forms by laying up process and then cured in autoclave. Here the flow of the un-vulcanized rubber during cure is not very important as the shape is already formed rather the green strength and the stiffness of rubber stock with a low scorch time are the important requisites. A rubber expansion joint made by a hand layup method and cured in autoclave is shown in the following figure 14.1. 

There are currently no ISO standard methods for biaxial extension and such measurements are rarely made in industrial laboratories. However, biaxial stressing is of value in the consideration of the theory of elasticity and is preferred by many for producing data for input to finite element programmes, as well as being involved in certain practical applications of rubber. The British standard for finite element analysis on rubber19 outlines the two approaches, equibiaxial stretching of a flat sheet and inflation of a flat sheet. The principles of these are illustrated in Figure 8.14. 

The second major metabolite from T. inflation is structurally closely related to cyclosporin A, as can be deduced by elemental analysis, mass spectrum (m/z 1217), IR and NMR spectra. Furthermore, the presence of the double bond and OH group of the unusual MeBmt was established. Sulphonic acids in methanol or dioxane effected the typical rearrangement reaction by N, O-acyl migration to the iso-compound (13). Hydrolysis furnished the same amino acids as cyclosporin A with the exception of L-a-aminobutyric acid, which is replaced in cyclosporin C (12) by L-threonine. The amino-acid sequence could be deduced by conversion of cyclosporin C into cyclosporin A via the corresponding tosylate (14) and iodo derivatives (15) [7]. Position 2 for L-threonine as well as the assumed twisted -pleated sheet conformation of the molecule were confirmed by 13C-NMR spectra. 

Huterer D, Starkman GD, Trodden M (2002) Is the universe inflating Dark energy and the future of the universe. Phys Rev D 66 043511 Hyde WT, Crowley TJ, Baum SK, Peltier WR (2000) Neoproterozoic snowball Earth simulations with a coupled climate/ice-sheet model. Nature... 

FEM is the only practical tool to handle the problem. Not surprisingly, this method was first applied to membranes or thin shells in the field of structural analysis, a field where, in fact, FEM was pioneered, with a much later penetration to fluid mechanics and polymer processing. Indeed, Oden and Sato (81) were the first to apply FEM to examine the three-dimensional membrane inflation problem. Two other engineering fields that apply a similar FEM approach are metal sheet forming and glass bottle blowing (82). 

Fabrication of the Infusion Device. The external rigid casing of the compression device was made from 2.5 mm thick plastic sheets, preferably optically clear. The leak-proof inflatable sacs were made by heat sealing of heavy-duty polyethylene sheets which also had good optical clarity and at the same time were resistant to swelling when in contact with an aerosol propellant. 

In the burst test a flat sheet of paper is clamped by a cireumferential ring and a small rubber diaphragm underneath is gradually inflated with fluid, foreing the sheet to bulge until it ruptures. The hydrostatic pressure at the moment of failure is measured. The virtues of the burst test are its simplicity and the speed with which it can be undertaken. The reeorded hydraulic pressure offers a quantitative measure of bonding between fibres. It is linearly related to tensile strength. 

In pressure-bag molding the reinforcement and the resin mixed with catalyst are placed in a mold, and a flexible bag is placed over the wet lay-up after a separating sheet (such as cellophane) is laid down. The bag is then inflated with an air pressure of 20-50 psi (1.4—3.5 kg/cm ). The resin and reinforcement follow the contours of the mold (Figure 2.47). After the part is hardened, the bag is deflated and the part is removed. The technique has been used to make radomes, small cases, and helmets. 

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