Usable life

Economics and price of the final article often dictate a specific type of mbber that can be used. The expected usable life for the product is controlled by many factors including end customer awareness, competitive situation in the marketplace, safety, reUabiUty, and other factors. Rubber is almost always used as a functional part of another system. For example tires, hoses, belts, O-rings, and numerous mbber components are used in manufacturing automobiles and tmcks. The overall life of the vehicle as well as its performance level often control or direcdy relate to the service life or quaUty level of the mbber parts. 

Most matrix reference materials are regarded stable for their application within a certain time frame see also Section 2.2. They are usually produced in large batches designed to ensure that the same material is available for a number of years as well as to spread the high cost of production over as many units as is possible. The stability is closely monitored from initial production by the producer lot numbers or even individual unit numbers are allocated and the producers closely monitor, by regular analysis, the condition and quality of their reference materials over time. Because of such careful control, and to minimize waste, the tendency has been for producers to give a usable life from receipt to the customer, commonly 12-24 months. However, the producers can give this shelf life expectancy only for unopened units. 

The relative humidity can also affect the usable life of the liner for many liner-propellant systems. However, studies to determine the usable life of a CTPB liner-propellant system (Table XV) would indicate that the bond is not affected significantly even upon exposure to 70% relative humidity for up to at least 8 days at 77°F. 

Approximately 11.8 million pounds of hexabromobiphenyl were used in commercial and consumer products in the United States, mostly in the production of plastic products. Since the cessation of production of hexabromobiphenyl, all of these products, such as TV cabinet and business machine housings, with a usable life of 5 10 years must have been disposed of by landfilling or incineration (Neufeld et al. 1977). Disposal of these plastic materials in waste disposal sites is an important source of PBBs in soil. The migration of plastic-incorporated PBBs to soil would be very low since PBBs would be tightly bound into the plastic (Neufeld et al. 1977). 

Under MACRS depreciation, different recovery periods are assigned to different kinds of assets, based on a usable life ( class life ) designated by the U.S. Internal Revenue Service (IRS). For chemical plants and most other processing equipment, the class life is 10 to 16 years and the recovery period is 7 years. It should be noted, however, that for roads, docks, and other civil infrastructure, a 15-year recovery period is used, so some offsite investments are depreciated on a different schedule from that used for the ISBL investment. 

There is a direct relationship between water contamination and component usable life. Table 16.2 shows the loss of bearing usable life as a function of water concentration [14]. Water usually enters an oil system as a consequence of condensation from environmental exposure, coolant leak due to a component failure or free water ingress during equipment cleaning. 

Useful in making accurate design decisions early in the usability life cycle without the need for a prototype or costly user testing. 

Although epoxy resin and hardener may be used in unmodified form in adhesive systems, most systems will consist of components that have been modified by incorporation of various additives to achieve specific effects. Formulators will add catalysts or blend hardeners to obtain a specific usable life of the mix and to control the curing temperature. Reactive diluents may be added to modify viscosity or flexibility. Fillers impart improved compression strength and reduce shrinkage and cost. Solvents may be used to reduce viscosity or improve adhesion. Various additives may be added, usually at a low percentage, to reduce aeration, improve adhesion to difficult surfaces, or minimize settlement of fillers. Depending on the application, particular properties such as flame retardency. 

Depending on addition levels, fillers will generally increase the usable life and extend the cure time of the mix. Tensile and compressive strength usually increase maximally then decrease on further additions. Most fillers have relatively little effect on HDT. Chemical resistance will vary from filler to filler. Shrinkage is usually reduced. 

Although any spontaneous redox reaction can serve as the basis for a voltaic cell, making a commercial battery that has specific performance characteristics can require considerable ingenuity. The substances oxidized at the anode and reduced by the cathode determine the voltage, and the usable life of the battery depends on the quantities of these substances packaged in the battery. Usually a barrier analogous to the porous barrier of Figure 20.6 separates the anode and cathode half-cells. 

A) to remanufacture a vehicle for use on such system so as to extend its usable life for 5 years or more, which remanufacture begins (or for which the solicitation is made) after the 30th day following the effective date of this subsection or... 

REMANUFACTURING—It shall be considered discrimination for purposes of section 202 of this Act and section 504 of the Rehabilitation Act of 1973 (29 U.S.C. 794) for a person to remanufacture a rail passenger car for use in intercity or commuter rail transportation so as to extend its usable life for 10 years or more, unless the rail car, to the maximum extent feasible, is made readily accessible to and usable by individuals with disabilities, including individuals who use wheelchairs, as prescribed by the Secretary of Transportation in regulations issued under section 244. 

In the two-part mixed versions the amount of hardener added to the monomer can vary between 5% and 50% depending on the formulation. These are suitable as general purpose adhesives capable of filling gaps up to 5 mm in thickness with a usable life of between 10 and 60 minutes. In the unmixed versions the hardener is applied as a thin film to one of the surfaces to be bonded. The monomer is then applied to the opposite surface, the parts immediately fitted together and held under contact pressure. The polymerisation starts instantaneously after the adhesive touches the hardener and requires about 15-20 minutes before the bonded joint can be handled. Although the overall performance is generally better than with the mixed versions, the gap which can be filled is limited to about 0.5 mm. 

The working characteristics of the adhesive relevant to the application conditions must be determined. For instance viscosity is often temperature, shear-rate and time-dependent, and this will influence the choice of dispensing equipment, the method of application, the usable life and the open time. The viscosity should therefore be regulated bearing in mind the adherend rugosity and surface pretreatment, the method and location of application, and the cure temperature and duration of application. A thixotropic material may be required for application to vertical or soffit surfaces. Generally, relatively thick bondlines are encountered so that the adhesive should be able to cure in thick and/or uneven layers. It should also be remembered that for about every 8 C change in... 

Usable life. The usable life of the mixed adhesive before application to the substrate should be not less than 40 minutes at 20 "C that is, the viscosity should not rise above 150 Pa within this time. 

Prepregs offer high mechanical properties with control of high fibre volume fraction, but require pressure facilities (autoclaves, vacuum tables) to consolidate and elevated temperatures to finalise cure and achieve their high properties. They also have a limited shelf life and need to be stored in freezers to extend their usable life. 

Also called usable life, spreadable life. See working time. 

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