Scorch temperature

When the U.S. was preparing to invade Iraq, there was great concern that our soldiers would be exposed to nerve agents. They were required not only to mask, but also to wear full body protective suits despite scorching temperatures. To me, this is overkill. The suits are extremely uncomfortable, and studies have shown that they hinder military performance by 40-50%. 

Preforming. Extmsion preforming is easily accompHshed if relatively cool barrel temperatures are used with either a screw or piston type extmder (BarweU). It is important that the gums be used in the appropriate viscosity ranges, and that scorching be avoided. 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

Mooney viscometer is also used to measure the time it takes, from initial exposure of the compound to a particular temperature, to the time of onset of cure at that temperature [2]. This is known as the scorch time. Scorch time is an important parameter to the rubber processor, as a short time may lead to problems of premature vulcanization. As the test is taken past the onset of cure, the rotor tears the cured rubber, and therefore this device cannot be used to investigate rheological properties after the scorch time. 

The temperature window for mixing of silica compounds is rather narrow, limited by the decreasing silanization rate and increasing risk of scorch. High temperatures improve the sUaniza-tion rate due to the temperature dependence of the reaction and the enhanced rate of alcohol... 

High operation temperature (limited by scorch phenomena) in order to raise the speed of the silane reaction with silica and the diffusion coefficient of ethanol... 

In the presence of ZnO, the dump temperature is a parameter of paramount importance in mixing of a silica compound containing a couphng agent with a polysulfidic moiety The sulfur eliminated from the coupling agent causes premature scorch in the presence of ZnO. This problem is partially solved when ZnO is added in the productive mixing step on the two-roU mill. 

When a parison or preform is inflated, it displaces the air around it within the mold. If no provision is made to vent the mold, compression of the air around the parison or preform can raise its temperature to such an extent that it can scorch the surface of the product. To avoid this problem, we equip blow molds with vents. These can consist of slit vents at the parting line between mold halves, porous plugs of sintered metal, or small holes drilled into the cavity walls. 

An accelerator which permits processing of rubber compounds to be carried out with less risk of scorching but which does not slow down the rate of cure at normal vulcanisation temperatures. Demoulding... 

In the processing of mbber compounds (mixing, rewarmings, calendering, extrusion) heat history is a term used to indicate the total heat which has been received by the compound, particularly the temperatures reached by the mbber and the time it has been held at these temperatures. See Scorching. 

Synthetic aluminosilicate materials having a structure with regularly spaced channels of molecular dimensions. Accelerators may be adsorbed on this structure and remain inactive at processing temperatures but are released at curing temperatures, thus preventing any possibility of scorching. 

A development of plasticity determination by means of the Mooney viscometer. The same instrument is used but the temperature of operation is higher and the test is continued until the sample vulcanises. A curve of Mooney reading against time is drawn, from which the scorch and cure characteristics are estimated (BS 903-A58). 

If added at too high a temperature, scorching of compound will result. 

Even higher shear rates in the extruder cannot prevent laminar flow in the screw flights and therefore resultant unmixed particles being carried over the shearing sections. Lengthening of the residence time in the barrel also has to be restricted to limit unacceptable temperature build-up, which would result in scorched compound. It is thus necessary to have an effective means of... 

Control of the temperature of rubber compound whilst being processed in extruders and injection moulding machines is vital if the product from these processes is to be uniform in quality. Failure to control temperatures in processing equipment can lead to scorching of the compound as it emerges from the extruder die or injection machine nozzle. Most modem items of processing equipment are fitted to a temperature control unit using either oil or water as the circulatory medium. 

Solarization effects on weed population was hypothesized to be due to different mechanisms, such as changes in cell metabolism and ultrastructure (Singla et al. 1997), microbial parasitism on seeds weakened by sublethal temperatures, seed dormancy interruption by raising temperatures, and foliar scorching of weeds under the plastic mulch (Egley 1990 Katan and DeVay 1991). Moreover, imbalance of 02 and C02 or release of acetaldehyde, ethylene, and other volatile toxic compounds were also reported as accounting for weed death (Rubin and Benjamin 1984 Gamliel et al. 2000). 

The care of microfiber products is similar to that of the normal fiber materials made from the same polymer. One caution is heat sensitivity. Because the fibers are so fine, heat penetrates easily causing them to scorch or glaze more quickly than normal fibers if too much heat is applied or heat is applied over too long a period. Typically, microfibers are wrinkle-resistant, but if ironing is done, it should be accomplished using lower temperatures and only as directed. 

Place fresh mushrooms on a screen rack and either air dry, or dry in an oven at the lowest temperature. Make sure you don t scorch them. 

---