Applications heat buildup

Viscoelastic damping The same approach can be used in designing power transmitting units such as belts. In most applications it is desirable that the belts be elastic and stiff enough to minimize heat buildup and to minimize power loss in the belts. In the case of a driver which might be called noisy in that there are a lot of erratic pulse driven forces present, such as an impulse operated drive, it is desirable to remove this noise by damping out the impulse and get a smooth power curve. 

The important vulcanizate properties demanded by this application, low heat buildup, and low dynamic set have been determined in the Goodrich Flexometer test. The compound containing the antireversion agent exhibits a marked decrease in heat buildup and dynamic permanent set (Figures 14.21 and 14.22). 

Dynamic heat buildup in applications such as wheels is important. Polyurethanes with a high resilience or a low tan 8 in the operating range are important. Polyurethane elastomers used in wheel applications can be evaluated using a test rig where the urethane can be run under load for a fixed period or until failure. 

HDI Heat buildup An abbreviation for hexamethylene diisocyanate. The temperature rise within an elastomer due to hysteresis. In many end-use applications, an elastomer can be subjected to repeated cycles of deformation-relaxation. As this occurs, friction between the elastomer molecules generates heat. As elastomers have relatively poor thermal conductivity, the heat generated builds up over time, progressively increasing the internal temperature of the elastomer. If the temperature increases above 70°C, the elastomer physical properties can begin to reduce. Design of the elastomer part can play an important role in minimizing the effects of heat buildup. 

Polyurethane wheels may be small components in a piece of machinery or a large part of drive wheels on items such as forklifts or rod mills. Speed is the normal limiting factor in the use of polyurethane wheels. This is a result of heat buildup. Special polyurethanes find an application as spare motor car wheels. 

Polytetrafluoroethylene is a slippery material with a smooth surface due to its low coefficient of friction. Numerous mechanical applications have been developed for PTFE with slight or without lubrication, particularly at low velocities and pressures above 35 kPa. Table 3.26 contains values for coefficient of friction as a function of velocity. D5mamic coefficient of friction of PTFE is larger than its static coefficient of friction and grows with increasing speed until the motion is destabilized. Static coefficient of friction remains unchanged in the temperature range of 27°C-327°C which is important in applications where a polytetrafluoroethylene part may experience heat buildup and temperature increase. 

The prime factor in choosing an abradant is its relevance to service, but it also has to be available in a convenient form and, for anything but ad hoc tests, it is essential that it be reproducible. In consequence of these considerations, abrasive wheels and papers or cloths predominate where cutting by sharp asperities is to be simulated. The abrasive wheel is probably the most convenient, because of its low cost, its mechanical stability, and the ease with which it can be refaced to maintain a consistent surface. Abrasive papers and cloths are cheap and easy to use but are not so readily refaced and will deteriorate in cutting power more quickly. Although basically low in cost, both wheels and papers are a considerable c.xpense when bought as standard reference materials. Materials such as textiles or smooth metal plates are more relevant for some applications, but they abrade relatively slowly, and if conditions are accelerated they give rise to excessive heat buildup. 

The challenge for the R D effort was to develop a methodology to predict propensity for heat buildup for new experimental formulations in addition to the D4803 method. The new method needed to be empirically based and applicable to the data base of performance al-... 

Reducing the monol content also improves the dynamic properties of cast elastomers. Figure 9.3 shows the DMTA response for the two polymers described above. The polymer derived from the ultra-low monol polyol has a flatter rubbery plateau region. The higher modulus in the rubbery plateau is consistent with the polymer s higher tensile modulus. The substantial reduction in tan delta (8) across the entire temperature range should also be noted. Lower tan delta translates into improved performance in dynamic applications due to lower heat buildup and improved rebound as noted above. 

The same approach can be used in designing power transmitting units such as belts. In most applications it is desirable that the belts be elastic and stiff enough to minimize heat buildup and to minimize... 

UV/EB coatings (formulations) are traditionally 100% reactive solids so that the need for solvents is eliminated. This feature as well as speed (cure literally in a second or so) and minimal heat buildup (applicable to a wide variety of substrates) make UV/EB an attractive alternative to bake systems. 

The variable-speed operation can generate high frictional heat buildup and sidewall stresses. The wide, thin section is more easily subject to coUapsing under high loads. In the past few years, manufacturers have developed improved materials and constructions to withstand the heat and high belt sidewall stresses. As a result, variable-speed belts are moving into more demanding applications. 

This method measures the heat buildup of a sample inside an insulated wooden box under a 250 W heat lamp. Thermocouples are placed beneath the samples, which are least 3x Bin size. A carbon black reference is also measured. The equilibrium temperature for each is recorded, and the temperature differences above ambient are used to predict theoretical heat buildup of the sample according to Eq. (24.4). The maximum external heat buildup for the black sample (ATc) is 41 °C for vertical orientation and 50 °C for horizontal orientation. The method is defined for PVC but can be applied to other colored objects. While the test does not measure solar reflectance, it does provide useful information on the expected performance of the object in the end application. The practical nature of this test makes it an effective tool for demonstrating the difference between objects colored with and without high-performance pigments. It is important to note that the method clearly states that while the test provides data on relative heat buildup, it cannot predict actual temperatures the object will experience in its service hfe. The ambient conditions of the test are controlled, and the field conditions have numerous factors (incident sunlight angle, weather, insulation) that will affect... 

Vamac can be calendered and fabricated into roll covers for specialty applications. Compositions for roll covers should be formulated to minimize heat buildup (Table 6.41). 

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