Tape

Plastic tapes are used to meet many different requirements that range from being flexible to strong, water to chemical and other environmental resistance, soft to wear resistance, and so on. This review is on the overall performance of tapes. Even though tape is a market in its own, there are other markets such as for belts that have some similar features that they both meet rigid and versatile requirements.

One of many different performing types is a low-profile long conveyor belts with prolonged high-speed operating life and minimal maintenance for use in plants, in underground mines, etc. The conveyors can have different belts for different applications including part accumulation, hot or cold processes, or chemical resistance. Closed-top and open-mesh versions are available. There are accumulation belts that use a blend of acetal and Teflon and meets FDA standards. It can withstand temperatures up to 180°C. For higher temperatures, a flat or cleated line of nylon belts operates at temperatures as high as 375°F. Chemical-resistant applications can use a flat, side walled, or cleated belt that resists bleaches and acids while functioning. For electronic applications, the flat or cleated static-conductive belt made from polypropylene meets FDA standards for Class 11 type charges.

This review on tapes highlights the historically Du Pont's research leading to Dymetrol® elastomeric tape that began in 1974. The General Motors Corp. in the USA had developed a new lightweight window regulator, to replace the heavy metal segment window regulators, but cold not make it work adequately with the metal and plastic tapes used at that time. Using its plastics processing know-how, Du Pont developed what is now known as highly engineered oriented elastomeric tape, or as the Dymetrol mechanical drive tape, and General Motors have been using it since 1979 in manual and electric window car regulators. Today this tape with its applications has evolved into a multi-tape/multi-application proposition that include safety passive restrainers, windshield wiper linkages, sliding car roofs, garage door openers, vending machines, etc.

This high modulus material composition provides tape with steep stress/strain characteristics. In other words higher dimensional stability under applied loads or higher tensile loading capability at the same elongation (vs. the standard material composition tapes). High modulus material composition tapes also have higher stiffness, resulting in a much-improved push vs. pull load transfer efficiency. In practice this means for instance that window regulator mechanisms can be constructed with tape lifting the window as well in the compressive as in the tension mode which provides the automotive design engineer with more possibilities and flexibility to conceive car doors with optimum cost, performance and design characteristics.

Another novelty is the abrasion resistant material composition option diat confers much improve abrasion resistance and somewhat lower coefficient of friction. The mechanical drive tape will also transfer tension and compressive forces when used in non-linear directions. Contributing factors are not only the tape's axial stiffness, providing the push and pull, but also its torsional and edge-bend flexibility.

Fig. 4.33 shows the flexibility of high modulus vs. standard tape

Figure 4.33 Dymetrol mechanical drive tape: (a) flexural modules and (b) beam flexure versus tape thickness (unpunched)

TAPE THICKNESS. miUflimn iO 10 1} 2.0 2 5

TAPE THICKNESS. miUflimn iO 10 1} 2.0 2 5

Figure 4.33 Dymetrol mechanical drive tape: (a) flexural modules and (b) beam flexure versus tape thickness (unpunched)

materials and also the effect of punching and of temperature on tape stiffness. Naturally tape thickness and width also affect a tape's stiffness. The obvious user benefit of this tape flexibility is greater versatility in the design of energy transfer mechanisms, since allowing for push/pull in non-linear modes, thereby advantageously replacing more complex movement transmission devices such as lever arm systems, pulleys, or gear systems. By using this feature, a cigarette vending machine offers a 50% increase in brand choice without increase in machine dimensions. Metal wire cable may rapidly fail in energy transfer mcchanisms due to its frequendy inadequate alternate flex cycle life, and spiral metal cable due to its spiral collapse, these mechanical drive tapes have proved to be extremely tough.

From these data, taken from various points of the tape's stress/strain curve, it can be concluded that the strength of the mechanical drive tapes, and in particular of the high modulus materials composition, is appreciable and adequate indeed for the low to medium load transfer service applications to which it addressed itself, and more than what is needed for window regulators for instance. The user benefit here naturally is long-term performance dependability or tape driven energy transfer mechanisms and proved for instance by the low GM car aftersale replacement rates of tape driven window regulators. Another example is the. use of tape to drive outdoor Venetian blinds in which the previous drive device failed frequendy causing expensive repair.

Contributing significandy to this tape toughness is its property to recover from strain caused by permanent or intermittent operating stress, even after exposure to temperatures as high as 80°C.

There is virtually no creep and very littie permanent deformation. Similar tests have furthermore shown that there is not much more deformation even after 8000 hours exposure to 4000 psi. The added benefit of this low creep and strain recovery characteristic of tape is that it confers operating shock absorbency and smoothness to energy transfer mechanisms, not or less provided by other energy transmission devices since featuring steeper stress/strain characteristics or no stress elasticity at all.

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