Hot bar method

Note 3 Hot bar and other methods for determining ignition (or explosion) temperature are described in the following refs Refs 1) A.P. Sy, JFrankllnst 155, 171 (l 903) (Early US Ordnance method, also described in Refs 2 4) 2) Marshall 2 (l917), 434-35 (same method as in Ref 1) 3) Marshall 2 (1917), 435 (Hot bar method) 4) Reilly (1938) 83 (same method as in Ref 1 is listed as Deflagration Test) 5) PATR 2700, Vol 1 (1960) pp XVl XVII (description of two tests and list of 11 refs) 6) AMCP 706-177 (1971), p 3 (current US Ordnance Explosion Temperature Determination) 7) PATR 2700, Vol 6 (1973) p E387-R (Explosion Temperature)... 

Melting Point, Determination. Most methods for the detn of mp are microprocedures, and may be conveniently classified on the basis of the type of app used for the detn (1) the capillary tube method. (2) the heating bar method, and (3) the microscope heating stage (micro hot stage) method. 

Steady-state periodic heating and unsteady-state methods can be applied to measure the thermal conductivity and diffusivity of coal. Methods such as the compound bar method and calorimetry have been replaced by transient hot-wire/line heat source, and transient hot plate methods that allow very rapid and independent measurements of a and X. In fact, such methods offer the additional advantage of measuring these properties not only for monolithic samples but also for coal aggregates and powders under conditions similar to those encountered in coal utilization systems. 

In the U.S. in 1957, McCrone presented a review of fusion methods, techniques, equipment, and applications (12). His definition of fusion methods included the methods and procedures useful in research and analysis, which involved heating a compound or mixture of compounds on a microscope slide (12). His text comprises five parts. Chapter I is an introduction discussing the scope and limitations of fusion microscopy, and Chapter II discusses the commercially available equipment at the time. Chapter III details the general techniques for hot stages, cold stages, and hot bars, characterization and identification of organic compounds, purity estimations,... 

In 1728 Hanbury was joined by John Payne, and the same year they introduced the method of rolling the hot bars of iron into sheets between metal rollers. This was an enormous improvement. Not only could sheets be produced more rapidly but they were more uniform and even. The specification of the patent announced that barrs, being heated... pass between two large mettall rowlers (which have proper notches or furrows on their surfuss) by the force of the inventor s engine or other power into such shapes and forms as required. ... 

The polymer melt temperature (PMT) is the temperature at which a specimen begins to leave a trail when drawn along a hot bar with a temperature gradient. This method also depends primarily on the viscoelastic behavior of the sample but has not been correlated with known transitions. These values are not included in the table. 

Solid solder coatings such as hot air-leveled pads, solder-plated boards, or stenciled solder paste reflowed prior to hot-bar bonding are preferred for this bonding method. 

FIGURE 47.40 Just as in any other soldering method, a thermal profile hoard is needed for hot-bar soldering. Care must be taken that the thermocouple bead does not interfere with seating of the lead to pad or with the hot-bar blade to the lead and pad combination (a, b). Instead, the thermocouple can be attached with a high-temperature solder alloy in front of or behind the component lead (c) so that a common lead, pad, and bar seating plane is maintained. 

Ex. 1. Tuftane film is ideally suited for bonding emblems, numerals, and letters to many fabrics by heat and pressure alone. It also flame-bonds well to both polyester- and polyether-urethane foams at commercial bonding speeds. Since it contains no volatiles it does not require cure times as do solvent- or water-based adhesive systems. All Tuftane films can be adhered thermally by hot bar, thermal impulse, ultrasonic, or dielectric methods over a wide range of temperatures. Adhesive lamination to many substrates is possible by the heated drum, curing oven, or multiple can methods. Fabric bonds made with Tuftane are strong and withstand laundering and dry cleaning. 

There are numerous extensions of these basic techniques, such as hot wire instead of a hot bar, pressure clamps instead of rollers, etc. Methods (a), (b) and (c) are applicable to sheet welding, whilst method (d) is more readily adaptable to mouldings and extrusions. 

Many numerical methods have been proposed for this problem, most of them finite-difference methods. Using a finite-difference technique, Brode (1955) analyzed the expansion of hot and cold air spheres with pressures of 2000 bar and 1210 bar. The detailed results allowed Brode to describe precisely the shock formation process and to explain the occurrence of a second shock. 

Figure 2.9 Electron relaxation dynamics for GaAs (100). (a) Compares the hot electron lifetimes as a function of excess energy (above the valence band) of a pristine surface prepared using MBE methods with device-grade GaAs under the same conditions. The higher surface defect density of the device-grade material increases the relaxation rate by a factor of 4 to 5. (b) The electron distribution as a function of excess energy for various time delays between the two-pulse correlation for MBE GaAs. The dotted lines indicate a statistical distribution corresponding to an elevated electronic temperature. The distribution does not correspond to a Fermi-Dirac distribution until approximately 400 fs. The deviation from a statistical distribution is shown in (c) where the size of the error bars on the effective electron temperature quantifies this deviation.

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