Tension, back

Figure 14.14 Schematic of the continuous dieless forming machine showing the vertically moving crosshead cylinder, the fixed forming roller, and the dead weights used for workpiece back tensioning...

Because the equipment components noted in (2) above are subject areas unto themselves, we will limit our consideration to the general condition of the interaction of components at this time. For example, the simplest, least costly slitting line arrangement possible is a pull-through type, wherein the rewinder drive provides the power to pull the strip through the slitter head assembly against the back tension created by a brake on the payoff. 

In order to operate properly, the systems relies on constant material speed as well as consistent shear reaction time. If material speed or shear reaction time vary even slightly, tolerances are affected. The loop located between the reel and straightener is used to reduce back tension on the straightener (Fig. 11). This, in turn, helps to minimize roll spin and material slippage in the straightener. Another influence is the flying shear head. Because the shear head is relatively heavy, the mechanism required to accelerate it quickly is subject to wear. Left unchecked, the wear and tear on the shear can eventually affect shear reaction times as well. 

Even bringing in these cells into a level rack is problematic. The containers are constructively identical with those of the vented batteries. If a cell is first put down on the front crossbar before the cell is pushed to the back, tensions appear in the container and damage occurs in the structure of the plastic. This leads inevitably to rips in the container if the valve is put in too tight, which causes it to open because the inside pressure is too high. 

Figure III-l depicts a hypothetical system consisting of some liquid that fills a box having a sliding cover the material of the cover is such that the interfacial tension between it and the liquid is zero. If the cover is slid back so as to uncover an amount of surface dJl, the work required to do so will he ydSl. This is reversible work at constant pressure and temperature and thus gives the increase in free energy of the system (see Section XVII-12 for a more detailed discussion of the thermodynamics of surfaces).

Work on plasmas has roots extending back to the Greeks who found that amber mbbed with various materials tended to attract certain objects. The concept of plasma as the fourth state of matter can be traced to Sir William Crookes (2) in 1879. "So distinct are these phenomena from anything which occurs in air or gas at the ordinary tension, that we are led to assume that we are here brought face to face with Matter in a Fourth state or condition, a condition so far removed from the State of gas as a gas is from a Hquid." This description has been shown to be accurate over many years of experimentation and appHcation of plasmas. 

Sulfonates for Enhanced Oil Recovery. The use of hydrocarbon sulfonates for reducing the capillary forces in porous media containing cmde oil and water phases was known as far back as 1927—1931 (164,165). Interfacial tensions between 10 and 10 N/m or less were estabUshed as necessary for the mobilization and recovery of cmde oil (166—169). 

Kiss-Roll Colters. In kiss-roU coating, the web passes over a roU wet with the coating fluid, and has no backing roU. There are many types of kiss-roU coaters. The kiss roU can turn in the dkection of the web or in the reverse dkection but usually operates in the web dkection. Kiss-roU coaters are tension sensitive and are often used to apply excess coating prior to a metering device. 

Take-Up and Hold-Back. An elevator chain wears and elongates, and a belt stretches during service life. A chain also elongates when handling hot materials. Therefore, a take-up adjustment is needed to maintain tension between the head and foot shafts. A manually adjusted screw take-up that moves the tail shaft or head shaft or a self-adjusting weighted take-up that maintains a constant gravity force on the tail shaft may be used. 

The overhead eccentric jaw crusher Nordberg, Telsmith Jnc., and Cedarapids) falls into the second type. These are single-toggle machines. The lower end of the jaw is pulled back against the toggle by a tension rod and spring. 

The pay-off roll is unwound by the tension of the sheet, caused by the speed of the recoiler at the finishing line and the bridles positioned at different locations. The pay-off roll motors therefore operate in a regenerative mode and can feed-back the energy thus saved to the source of supply, if desired. This can be done by using a full-wave synchronous inverter, as shown in Figures 6.31 or 6.33. 

Figure 8.3. Wave interactions in planar tensile fracture experiment, (a) Shows the distance-time plot of interacting compression C , rarefaction R , and tension T , waves (b) Shows the corresponding particle-velocity profiles including the initial compressive shock wave (tj, tj), the pull-back signal (tj, tj), and subsequent reflection >h).

Impact of a thin plate on a sample of interest which is, in turn, backed by a lower impedance window material leads to an interaction of waves which will carry an interior planar region into tension. Spall will ensue if tension exceeds the transient strength of the test sample. A velocity or stress history monitored at the interface indicated in Fig. 8.4 may look as indicated in Fig. 8.5. The velocity (stress) pull-back or undershoot carries information concerning the ability of the test material to support transient tensile stress and, with appropriate interpretation, can provide a reasonable measure of the spall strength of the material. 

At any instant, pressure is uniform throughout a bubble, while in the surrounding emulsion pressure increases with depth below the surfaee. Thus, there is a pressure gradient external to the bubble which causes gas to flow from the emulsion into the bottom of the bubble, and from the top of the bubble back into the emulsion. This flow is about three times the minimum fluidization velocity across the maximum horizontal cross section of the bubble. It provides a major mass transport mechanism between bubble and emulsion and henee contributes greatly to any reactions which take place in a fluid bed. The flow out through the top of the bubble is also sufficient to maintain a stable arch and prevent solids from dumping into the bubble from above. It is thus responsible for the fact that bubbles can exist in fluid beds, even though there is no surface tension as there is in gas-liquid systems. 

A hardened-steel or hardwood shoe bearing against the back of the chain is another method of controlling chain tension. The method is satisfactory for small horsepower drives operating on fixed centers at slow or moderate speed with ample lubrication. 

---