Thermal stresses glass

Many authors have shown that residual stresses in glass articles can be formally considered as the thermal stresses due to a certain fictitious temperature field. In the general case... 

By virtue of its chemical and thermal resistances, borosilicate glass has superior resistance to thermal stresses and shocks, and is used in the manufacture of a variety of items for process plants. Examples are pipe up to 60 cm in diameter and 300 cm long with wall tliicknesses of 2-10 mm, pipe fittings, valves, distillation column sections, spherical and cylindrical vessels up 400-liter capacity, centrifugal pumps with capacities up to 20,000 liters/hr, tubular heat exchangers with heat transfer areas up to 8 m, maximum working pressure up to 275 kN/m, and heat transfer coefficients of 270 kcal/hz/m C [48,49]. 

An incident attributed to overheating a flask while distilling this is reported. It is implied that it was not really an explosion, but thermal stress shattering glass - however part of that glass was evidently projected a moderate distance with enough force to wound. Explosion indeed seems the right word (Ed.). 

Stainless steel sieves, which can be fitted into a range of stainless steel sorbent tubes, are usually easier to handle than glass/quartz wool. It is, however, their disadvantage that some very labile compounds may degrade in contact with the metal under thermal desorption conditions. In addition, the sieves will often not completely retain the fines fraction of the used sorbents this is particularly problematic for the carbon-based sorbents, which are more brittle than the polymers and can therefore be crushed to fine particles by the thermal stress during use of a tube. The presence of a dark residue on the filters inside the thermal desorption unit is an indication of carbon-based sorbent migration from the tubes. 

We see very thick glass used for kitchenware such as measuring cups and bakeware. Kitchenware receives minimal heat stress (baking is a slow heating process and therefore is not a thermally stressing activity) and is more likely to receive... 

We also see thick and thin glass in the laboratory. Because their concave bottoms could not otherwise withstand the force of a vacuum, filter flasks are made of thick glass. However, do not place a filter flask on a heating plate—it cannot tolerate the (heat) stress. The standard Erlenmeyer, by comparison, is thin-walled, designed to withstand thermal stress. However, a standard Erlenmeyer flask cannot tolerate the physical stresses of a vacuum The flask s concave bottom will flex (stress) and is likely to implode in regions of flaws. 

The shape of glassware can be a clue as to how and/or where it can be used. The more rounded its comers, the better it can diffuse thermal stress. This idea is similar in concept to the sharpness of flaws and can be compared to Eq. (1.1), the stress concentration factor. Although that equation is intended to be used for surface flaws on glass, the principle is the same. 

We propose to rationalize the observation by a phenomenon known as residual thermal stresses. Residual thermal stresses arise from the fact that carbon-fiber and epoxy have different thermal expansion coefficients and a quenching of the composite would conceivably produce residual stresses. Apparently, the quenching process may produce enough residual stresses to lower the toughness of the composite. In the absence of such residual stresses the free volume concept alone would predict a quenched glass to have larger amount of free volume and hence constitute a less brittle substance. 

Another explanation for an abnormal increase in Tgl in polymer blends has been proposed by Manabe, Murakami, and Takayanagi 125). They used a three-layered shell model, which accounts for interaction between the dispsersed and continuous phases of the blend. Abnormal increases in the glass transition of polystyrene in blends with various rubbers were explained by thermal stresses which arise from the difference in thermal expansion coefficients of the component polymers. However shifts in the glass transition temperatures of the SIN s do not appear to arise from differences in the expansion coefficients of the components because samples with the same overall composition and almost identical microstructures have significantly different glass transition temperatures. 

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