Reinforced sheets

EPDM is by far the most widely used material in the ballasted roofing system constmction. Because of EPDM s flexibiHty, very large sheets of up to 10,000 square feet (929 m ) can be deHvered to the job site in compact roUs that offer reduced labor on the roof in the seaming process. The typical EPDM sheet size used in ballasted systems is 12 by 30 m and 1.1 mm thick. EPDM is also widely used in both the fully adhered and mechanically fastened roofing systems. In these constmctions, both 1.1- and 1.5-mm thick material is used with widths from 2.1 to 15 m. A majority of the installations use nonreinforced sheet, although reinforced membrane can also be used in all of the system types. The majority of the reinforced sheets go into mechanically fastened systems. 

TS plastics in reinforced sheets and compounds are usually used. Also used are reinforced thermoplastic sheets and compounds. With TSs compression molding (CM) can use preheated material (dielectric heater, etc.) that is placed in a heated mold cavity. The mold is closed under pressure causing the material to flow and completely fill the cavity. Chemical crosslinking occurs solidifying the TS molding material. 

Bi + El) Film stacking Glass mat-reinforced sheet GMT, SMC, TMC Thermoforming Hot pressing Yes... 

Stamp moulding Blank reinforced sheets are preheated in oven and placed between matched metal mould halves press then closed, heatfpressure applied See above... 

Fig. 7-6. Automated-integrated reinforced plastics lay-up process that uses TS preimpregnated reinforced sheet.

Reinforcements of different types and layouts are used. Typically, to make a stampable sheet two layers of reinforcing sheet material are laminated to extruded sheets of thermoplastic (Chapter 3). The resultant sheet is homogeneous and has uniform mechanical properties. 

Marker, L. and Ford, B., Rheology and Molding Characteristics of Glass Fiber Reinforced Sheet Molding Compounds, SPI Composites Inst., Tech. Conf., 1977. 

Van Voom B, Smit HHG, Sinke RJ et al (2001) Natural fibre reinforced sheet moulding compound. Compos A 32 1271-1279... 

The liquid resins are poured onto the reinforcement material and the combined resin-reinforcement sheet is then placed in a horizontal treater, as shown in Fig. 2.12, where the resin is dissolved in a solvent to achieve optimum wetting or saturation of the resin into the reinforcement. The sheets come out of the treater and are sheared to size and stacked and stored in temperature- and humidity-controlled rooms. The preimpregnated, stacked sheets are further stacked into packs with each pack containing 10 laminates. The stacked units are then placed in between two polished steel plates and the press is closed. This process involves molding temperatures ranging from 250 to 400°F (122 to 204°C), with molding pressures in the 200- to SOOO-lb/in range. 

Laminates are plastic materials formed by bonding together reinforcing sheets or webs with a polymer or plastic. Heat and pressure are usually required. The reinforcing sheets may be fabric, mats, or paper, and the binder polymer may be either a thermoset or thermoplastic polymer. Table L.l shows the properties of laminates that are reinforced with different types of fibers. 

Filon, Fiberglass reinforced sheet for RV industry, KemUte... 

The application of lignocellulosic fibres in reinforcing plastics has been known for a long time. As early as 1908 the first composite materials were applied for the production of large quantities of sheets, tubes and pipes for electronic purposes (paper or cotton to reinforce sheets, made of phenol or melamine formaldehyde resins). In 1896, aeroplane seats and fuel tanks were made of natural fibres with a small amount of polymeric binder [1],... 

This glass fiber mat is impregnated by thermoplastic resin which is compounded with additives, under heat and pressure (Fig. 3.13). A double belt press is usually used to apply heat and pressure for the resin impregnation process. After the consolidation process, glass fiber reinforced sheets which have been conveyed through the double belt press, are cut into a desired size and stocked. 

Both mechanical and hydraulic presses can be used to forge, stamp, and compression-mold glass-reinforced sheets. However, to successfully stamp composites between cold, matched metal dies the presses must have a pneumatically or hydraulically operated clutch and brake, tie-rod construction if over 60 tons, and must run between 6 and 30 strokes per minute (spm). Hydraulically operated presses must have an adjustable stored energy system to form at a prescribed force level . 

The directional properties of fiber-reinforced sheet are influenced by the sheet thickness and the viscosity of the melt as it passes through the extruder die. As the sheet thickness is increased, the directional properties converge since the oriented surface layers become a smaller portion of the total thickness. When the glass fiber content is increased, the viscosity of the melt increases and, consequently, the thickness of the oriented skins will increase. Table 4-6 shows the change in directional properties as the glass content is increased. 

TABLE 4-5. EFFECT OF FIBER ORIENTATION IN THE SURFACE SKINS OF 20% GLASS-REINFORCED SHEET ... 

The increased modulus of reinforced sheet will permit reduced sheet thickness over the unreinforced material. For example, under similar loading conditions, a 220-mil HDPE sheet was found to deflect the same amount as a 187-mil sheet reinforced with 10% glass fiber. Also, the total load carrying capacity of the thinner reinforced sheet was about 35% higher. This permits a 24% reduction in the resin requirement. ... 

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