Foam thickness

Figure 6.21. Example of panel rigidity/facing rigidity ratio versus foam thickness...

The parameters C7j and G of the cushion curve can be calculated from the energy density function [/(c7 ,), using Equations (13) and (14). These equations only contain the ratio t/h of the foam dimensions, so the resulting cushion curves can be labelled with the reduced foam thickness = t/h. 

Some foam products are subjected to up to 10 major impacts in their lives, therefore a foam may need to be selected so that the performance is still adequate. Products, subjected to hundreds of thousands of impacts as in running shoe midsoles, were dealt with under fatigue. It appears that the higher density HDPE (419) and PP foams loose a significant amount of their protection after several impacts, but nevertheless it may be possible to use sufficient foam thickness to provide the required protection. If low density EVA foams are used, the impact energy densities are much lower, as the majority of the resistance is from compressing the cell gas. Ankrah and co-workers (33) performed multiple impacts on LDPE/ESI blend foams, and found... 

Temperature variations during the formation of LDPE foam sheet were investigated. A thermal model was coupled with a viscoelastic growth model, and an iterative finite difference technique was used to solve unsteady heat transfer equations and viscoelastic growth equations. The heat transfer characteristic time became comparable to the expansion time when the sheet thickness decreased to the millimetre range, during which foam thickness and density became sensitive to temperature effects. 12 refs. USA... 

The selection of EB equipment depends on the foam thickness and production rate. The foam manufacturers throughout the world are using equipment with electron accelerators with voltages ranging from 0.5 to 4 MV and power ratings from 10 to 50 kW. The penetration depth of a 1 MV unit is approximately 3 mm (0.12 in.). Irradiation on both sides doubles the thickness capability. ... 

At short wavelengths, the curves collapse on lines of constant D—of like polycarbonate thickness. At long wavelengths, the curves collapse on lines of constant k of like foam thickness and modulus. 

Both allergic and irritant mechanisms have been proposed as explanations for eye symptoms. More rapid tear-film break-up time, a measure of tear film instability, is associated with increased levels of symptoms. Fat-foam thickness measurement and photography for documentation of ocular erythema have also been used. Some authors attribute eye symptoms at least in part to increased individual susceptibility based on those factors. In addition, office workers with ocular symptoms have been demonstrated to blink less frequently when working at video display terminals. Conjunctival staining with fluorescent dyes is a common clinical test for conjunctivitis sicca. 

Friction Coefficient vs. Speed, Load = 1713g, Foam Thickness 1cm... 

Thermal interlining can be made by flame bonding thin-sliced, low-density (1-1.5 Ib/ft ) polyester-based fabric. The flame melts about one-third of the foam thickness, and the molten surface adheres to the fabric. 

Rigid polyurethane foam, injected as a liquid, forms a good adhesive bond to most surface layers, and it has a relatively high Young s modulus. Consequently, the sandwich structure performs efficiently in terms of bending stiffness per unit panel mass (Chapter 4). Lightweight sandwich panels are used in roofs and walls. If thermal insulation is of paramount importance, as in cold stores, the foam thickness can be increased to 125 mm. 

To avoid bottoming out, the foam thickness T must exceed 1.25 Xmax-... 

The thickness of the foam layer appears to be the key parameter for both product quality and process performance. An overview by Zbicinski et al. [Ill] indicates that the foam layer thickness determined the drying time through the moisture evaporation rate but also density and porosity of the solidified structure. Typically, the foam thickness is kept within 1-5 mm, but for some materials like banana, the foam layer can be as deep as 10-20 mm. Foams thicker than 20 mm caused undesirable changes in the final product (e.g., caramelization, nonenzymatic darkening, loss of aromatic components) due to high content of sugars and acids. 

Skin material Skin thick- ness mm Foam material Foam thickness mm Amount of gasoline dm Burning period of gasoline Time to ignition (fire-side) Period of flaming Period of post-glowing Time to break of flaming... 

Foam thickness was scaled to simulate stress conditions encountered by insulation on a large diameter tank. Insulation specimens were bonded to a thin, flat aluminum tank, which had separate compartments for six specimens. The tests were conducted by filling the compartments with liquid hydrogen and exposing the outer surface of the insulations to a cyclic thermal environment representative of repeated subsonic aircraft flight. The boil-off rate in each compartment indicated insulation thermal performance. 

Most quantitative studies on foams have been carried out using foam films. As discussed above, microscopic horizontal films were studied by Scheludko and coworkers [2-4]. A schematic representation of the set-up used to study horizontal foam films is given in Figure 8.2. The foam thickness was determined by interferometry. Studies on vertical films were carried out by Mysels and collaborators... 

To be at 40g level and keep the 2.2 pcf foam thickness the same, reduce loading from 1.35 to 0.87 psi can be used. Although this approach... 

Two important parameters, cell size and foam thickness, are taken directly into account for the model. The predicted increase of the thermal conductivity with the cell size is the same as that shown in the experimental results. The model predicts an increase of the thermal radiation term for thicknesses lower than 10 mm, with the thermal radiation being almost constant for foams of higher thicknesses. Experimental results confirm this behavior. Moreover, black foams have a lower conductivity than white foams of the same density and cell size due to the higher extinction coefficient of the black cell walls [69]. Thermal conductivity increases linearly with temperature for PO foams in a temperature range between 24 and 50 °C. 

Density profile of the stmctural foams was measured by a commercial X-ray QMS density profiler model QDP-OIX. A scanning speed of 0.6 mm/sec was used with a scanning resolution of approximately 0.02 mm across the foam thickness. Figure 1 shows typical examples of density profile obtained for neat HDPE and its foam produced under different conditions. 

First, a mathematical model is proposed to represent typical symmetric density profiles as shown in Figure 1. The total foam thickness is 8 and its width is constant and equal to B. For a monotonic decreasing density fi om the outer edge of the skin (a = SI) to the centerline (x = 0), a relative density (R) is defined as ... 

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