Polypropylene thickness

The double-bubble process may be used to produce biaxiaHy oriented film, primarily polypropylene. In this process the first bubble formation is similar to the conventional blown film, except that the bubble is not coUapsed. Rather it is reheated to the orientation temperature and blown and drawn further in a second stage. It is then coUapsed, sUt, and wound. This process is generally limited to a final film thickness of less than 24 p.m. 

Most manufacturing methods now available are similar to this but with the following modifications in the first step, the polymers for fibers are mainly made of polyester, nylon, or thein blends. AcryUcs and polypropylene are also sometimes employed. A regular fiber as thick as 0.01—0.4 tex (0.1—4 den) may sometimes be used instead of the special fiber to imitate the hard leather. 

Film manufacture also requires special considerations in the case of polypropylene in order to ensure small crystal structures and hence high clarity. Chill-roll casting processes may be used and these give films of high clarity and minimal thickness variations at high rates of production. Blown film processes can, however, give superior mechanical properties and in addition equipment costs are lower, and in consequence the process is more economic for lower tonnage production. 

Electrochemical cells are assembled in the glove-box. The cell is a 2320-type coin cell (23 mm OD and 2.0 mm thickness) as schematically shown in Fig. 5. The cell includes the electrolyte, the cell cap and can which are stainless steel, a polypropylene gasket used to seal the cell, the two electrodes, the separator between the electrodes, as well as a stainless spacer and a mild steel disc spring which are used to increase the pressure on the electrodes. Once the cell is assembled in the right order, the cell is sealed by a pressure crimper inside the glove-box. 

This is used most often in process plants. It is a tough, low-cost material with probably the widest range of chemical resistance of any of the low-cost plastics. On a volume basis, PVC is more favorable than polypropylene because the modulus of PVC is considerably higher than that of polypropylene, so it will form more rigid structures when used at the same thickness. On a weight basis it is not as favorable as PVC because it has a specific gravity of 1.4 compared with 0.92 for polypropylene. 

Example 2.1 A ball-point pen made from polypropylene has the clip design shown in Fig. 2.11. When the pen is inserted into a pocket, the clip is subjected to a deflection of 2 mm at point A. If the limiting strain in the material is to be 0.5% calculate (i) a suitable thickness, d, for the clip (ii) the initial stress in the clip when it is first inserted into the pocket and (iii) the stress in the clip when it has been in the pocket for 1 week. The creep curves in Fig. 2.5 may be used and the short-term modulus of polypropylene is 1.6 GN/m. ... 

Example 23 A cylindrical polypropylene tank with a mean diameter of 1 m is to be subjected to an internal pressure of 0.2 MN/m. If the maximum strain in the tank is not to exceed 2% in a period of 1 year, estimate a suitable value for its wall thickness. AVhat is the ratio of the hoop strain to the axial strain in the tank. The creep curves in Fig. 2.5 may be used. 

Example 2.5 In a small polypropylene pump the flange on the cover plate is 2 mm thick. When the rigid clamping screws are tightened, the flange is reduced in thickness by 0.03 mm. Estimate the initial stress in the plastic and the stress after 1 week... 

Example 2.8 A polypropylene sandwich moulding is 12 mm thick and consists of a foamed core sandwiched between solid skin layers 2 mm thick. A beam 12 mm wide is cut from the moulding and is subjected to a point load, IV, at mid-span when it is simply supported over a length of 200 mm. Estimate the depth of a solid beam of the same width which would have the same stiffness when loaded in the same way. Calculate also the weight saving by using the foam moulding. The density of the solid polypropylene is 909 kg/m and the density of the foamed core is 6(X) kg/m. ... 

A polypropylene pipe with an outside diameter of 80 mm is required to withstand a constant pressure of 0.5 MN/m for at least 3 years. If the density of the material is 909 kg/m and the maximum allowable strain is 1.5% estimate a suitable value for the wall thickness of the pipe. If a lower density grade of polypropylene (p = 905 kg/m ) was used under the same design conditions, would there be any weight saving per unit length of pipe ... 

If a polypropylene tank of radius, R = 0.625 m, and height 3 m is to be fllled with water for a period of one year, calculate the thickness of the tank material so that the change in its diameter will not exceed 12.5 mm. The density of the polypropylene is 904 kg/m. ... 

An underground polypropylene storage tank is a sphere of diameter 1.4 m. If it is to be designed to resist an external pressure of 20 kN/m for at least 3 years, estimate a suitable value for the wall thickness. Tensile creep data may be used and the density of the polypropylene is 904 kg/m. ... 

A circular polypropylene plate, 150 nun in diameter is simply supported around its edge and is subjected to a uniform pressure of 40 kN/m. If the stress in the material is not to exceed 6 MN/m, estimate a suitable thickness for the plate and the deflection, 6, after one year. The stress in the plate is given by... 

A cylindrical polypropylene bottle is used to store a liquid under pressure. It is designed with a 4 mm skirt around the base so that it will continue to stand upright when the base bulges under pressure. If the diameter of the bottle is 64 mm and it has a uniform wall thickness of 2.5 mm, estimate the maximum internal pressure which can be used if the container must not rock on its base after one year. Calculate also the diameter change which would occur in the bottle after one year under pressure. 

In a particular application a I m length of 80 mm diameter polypropylene pipe is subjected to two dimetrically opposite point loads. If the wall thickness of the pipe is 3 mm, what is the maximum value of the load which can be applied if the change in diameter between the loads is not to exceed 3 nun in one year. 

A cylindrical polypropylene pressure vessel of 150 mm outside diameter is to be pressurised to 0.5 MN/m for 6 hours each day for a projected service life of 1 year. If the material can be described by an equation of the form s(t) = At" where A and n are constants and the maximum strain in the material is not to exceed 1.5% estimate a suitable wall thickness for the vessel on the assumption that it is loaded for 6 hours and unloaded for 18 hours each day. Estimate the material saved compared with a design in which it is assumed that the pressure is constant at 0.5 MN/m throughout the service life. The creep curves in Fig. 2.5 may be used. 

In practice the clamping pressure will also depend on the geometry of the cavity. In particular the flow ratio (flow length/channel lateral dimension) is important. Fig. 4.42 illustrates typical variations in the Mean Effective Pressure in the cavity for different thicknesses and flow ratios. The data used here is typical for easy flow materials such as polyethylene, polypropylene and polystyrene. To calculate the clamp force, simply multiply the appropriate Mean Effective Pressure by the projected area of the moulding. In practice it is... 

During the blow moulding of polypropylene bottles, the parison is extruded at a temperature of 230°C and the mould temperature is 50°C. If the wall thickness of the bottle is I mm and the bottles can be ejected at a temperature of I20°C estimate the cooling time in the mould. 

Figure 4 Light permeability of polypropylene as a function of the sample thickness 1-3-quenched polypropylene 4-6-normal polypropylene 1 and 4-100 /ac thick 2 and 5-150 jLtc thick 3 and 6-500 /jlc thick.

Since the glass mat supplies sufficient stiffness, high backweb thickness was no longer needed These fleeces are made of organic fibers (polyester and polypropylene, as well as so-called synthetic pulp , i.e., fibrillated polypropylene) on paper machines. 

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