Mechanical fastening systems

There are also mechanically fastened systems where large sheets are laid over the substrate and seamed together. The mechanical fastening system to hold the membrane to the deck is placed at the appropriate density either over the membrane to fasten the system to the deck or under the membrane to which it is affixed. 

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. 

Despite unfavorable mechanical properties of polyethylene compared to polypropylene, PVC, ABS, and Nylon, HDPE is the most popular plastic in WPCs. Polypropylene is too tough and makes difficult to use nails and screws as fasteners at a deck installation. Polypropylene-based composites require special fastening systems. PVC is typically considered as not environmentally friendly. Other polymers are not weather stable, brittle, or expensive. 

A mechanical fastening system is a separate device or integral component feature that will position and hold two or more components in a desired relationship to each other. The joining of parts by mechanical fastening systems can be generally classified as ... 

Quick release mechanisms for rapid securing and release of parts, e.g. doors, access panels, tooling jigs and fixtures. Various types available, such as clips, locks, latches, cams, clamps and quarter turn fastening systems. 

All mechanical fastening systems can be manually or semi-automatically performed during assembly or installation, however, not all fastening systems readily lend themselves to full automation. 

Provision for anti-vibration mechanisms in the fastening system where necessary, e.g. Nyloc, lock nuts in combination with split pins, spring washers. 

Single-ply membranes offer the widest range of systems in the roofing industry. The three basic systems are ballasted, fuUy adhered, and mechanically fastened. From a cost standpoint, the fuUy adhered system is the most expensive to install, the ballasted system the least. The protected-membrane roofing system can be used with any of the basic systems. The specifications for these systems are pubHshed by the various manufacturers. The following gives a brief description of the roof assembhes. 

Fully Adhered. The substrate, ie, insulation, cover board, etc, that the single-ply membrane is to be attached to is either fuUy adhered or mechanically fastened to the deck. However, there are also appHcations where the membrane is adhered directly to the deck. The membrane is then adhered to the substrate. The typical method for adhering the membrane to the substrate is by applying a contact adhesive to the membrane and substrate, rolling the membrane into place, and brooming once the adhesive is ready. There are one-sided appHcations where the membrane is roUed directly into the adhesive that has been appHed to the substrate only. The membrane used in this appHcation method may be fleece-backed. FuUy adhered systems can be installed on any slope. The fuUy adhered appHcation offers a smooth surface that is easy to maintain and inspect, as weU as exceUent wind resistance on account of positive attachment. 

CPA. Copolymer alloy membranes (CPAs) are made by alloying high molecular weight polymeries, plasticizers, special stabilizers, biocides, and antioxidants with poly(vinyl chloride) (PVC). The membrane is typically reinforced with polyester and comes in finished thicknesses of 0.75—1.5 mm and widths of 1.5—1.8 m. The primary installation method is mechanically fastened, but some fully adhered systems are also possible. The CPA membranes can exhibit long-term flexibiHty by alleviating migration of the polymeric plasticizers, and are chemically resistant and compatible with many oils and greases, animal fats, asphalt, and coal-tar pitch. The physical characteristics of a CPA membrane have been described (15). 

BP. These nitrile alloy membranes are compounded from PVC, flexibilized by the addition of butadiene—acrylonitrile copolymers, PVC, and other proprietary ingredients. Typically reinforced with polyester scrim, NBP membranes are 1 mm thick and have a width of 1.5 m. They ate ptedominandy used in mechanically fastened roofing systems. NBP membranes exhibit excellent teat and puncture resistance as well as good weatherabihty, and remain flexible at low temperatures. They ate resistant to most chemicals but ate sensitive to aromatic hydrocarbons. The sheet is usually offered in light colors. The physical characteristics of NBP membranes have been described (15). 

The greater portion of PVC is installed in the mechanically fastened roofing system a lesser portion is installed in fully adhered appHcations. Although PVC was once heavily used in ballasted roofing systems, there are only a small number installed in the 1990s. Fleece-back membrane is popular in the PVC constmction for both fully adhered appHcations as well as in appHcations where a separator sheet is needed. PVCs ate resistant to vafious weather conditions, bactefial growth, and industfial chemicals. These membranes ate chemically incompatible with bituminous materials. PVCs ate offered in a variety of colors. The physical characteristics of a PVC membrane have been described (15). 

Tramp metal Provide suitable protection (e.g., magnetic separa-reaching mill tors, screens, etc.) resulting in fric-, Secure all potential sources of tramp metal (e.g., tional heat- fasteners etc.) in upstream equipment ing/mechanical spark which pro- enclosed feed systems, not operator fed vides an ignition system source. CCPS G-23 CCPS G-29 CCPS G-34... 

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