Warm-box

This process is very similar to the hot-box process and uses the same production techniques. Only the type of resin differs, allowing curing at a lower temperature. However, this kind of resin is significantly more expensive than those in use in the hot-box process. Therefore the warm-box process, in spite of some real advantages, is not generally find widespread use. 

The binder is furfliryl alcohol-based, with a typical composition containing around 70 % furfliryl alcohol or a low polymer of furfuryl alcohol. The catalysts are copper salts derived from aromatic sulphonic acids, in water or an alcohol solution. The distinctive feature of these catalysts is their excellent stability at ambient temperature and their relatively low dissociation temperature, which is 150 - 170 °C. Accordingly, the tool temperature can be held at around 180 °C, which leads to major energy savings of about 15 to 25 % compared to the hot-box. 

This process is the only one among all moulding and core-making processes that can use precoated sand, directly available from suppliers and ready for use, although pre-coating of the sand may also be performed at the foundry. 

The sand is cured by heating it in a metallic pattern, producing a hardened surface layer. The unheated or uncured sand may be discarded by turning the pattern upside down and then reused. The cured sand forms a shell , which has given its name to the process. 

The resin used for pre-coating is a phenolic novolac , with a formaldehyde/phenol ratio lower than 1. Hexamethylenetetramine is added to the resin as a hardener. Hexa decomposes at 160 C into its 2 basic components formaldehyde and ammonia. When pre-coated sand contacts the heated pattern, the hexamethylenetetramine decomposes and the formaldehyde cross-links the resin binder to form the characteristic strong bond. 

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We have already met carbon dioxide, C02, many times throughout this book. It is formed when organic matter burns in a plentiful supply of air and during animal respiration. It is normally present in the atmosphere but there is widespread and well-founded concern that an increase in atmospheric carbon dioxide due to the combustion of fossil fuels is contributing to global warming (Box 14.2). 

Warm-box process. The binder, 1.3 to 1.5% of sand weight, is a reactive, high FA binder. The catalyst, 20% of sand weight, is usually a copper salt of sulfonic acid. Sand, binder, and catalyst are mixed and blown into a heated core box. The heat activates the catalyst, which causes the binder to cure. Curing time is 10 to 30 s depending on thickness. The final tensile strength can be 3000 to 4000 kPa (400 to 600 psi). 

Another fast hardening process that can be used is CO2 gassing in a warm box (about 60-80°C) or gassing with heated CO2. 

Warm-box furfuiyl alcohol-based 1.0-1.5 Cu salts of sulphonic acids 10-30 aa aa... 

Warm-box emissions Compared to the hot-box process, the emissions are significantly lower. The emissions do not contain phenol or ammonia, and also formaldehyde emissions are diminished by a factor of 4. As Ae pattern temperature is also lower compared to the one used for the hot-box process, the woiking conditions are also improved. The environmental impact is considered to be relatively low... 

Five basic fabrication processes are used by the foundry industry. These are the no-bake, cold-box, hot-box or warm-box, oven bake, and shell processes. 

Furan no-bake resins are two-component, r.t.-cur-ing, acid-catalyzed systems of furfiiryl alcohol prepolymer with additional monomer. Hot and warm box resins are mainly based on urea-modified fur-ftiryl alcohol-formaldehyde condensates that are cured at 100-170 °C. Also phenol-formaldehyde resins, modified with furfiiryl alcohol, are used. In cold box binder systems, the sand is mixed with a low-viscosity fiiran resin and a peroxide. The core is formed, and SO2 is blown into or generated in situ in the sand to cure the resin rapidly. 

There yawns a large gap between commercial (micro)calorimeters with maximum vessel volumes of 25, 30 or 100 mL and instruments of many litres for smaller domestic animals. The only exception known to the authors is the Seta-ram GF 108 1-L instrument used in the Leyden group [72]. A low-price solution for an intermediate size calorimeter was found in cooling/warming boxes sold as picnic equipment for less than US 200 [73], They are equipped with a Peltier battery as a heat pump between the inner volume of the box and the environment. In the same way the heat pump can work as a Seebeck heat flow sensor to determine heat production rates inside the box. The inner walls of the box may be additionally covered by copper foil of high thermal conductivity to facilitate heat flow to the sensor. 

Sodium sulfite [7757-83-7] M 126.0, d 2.63. Crystd from warm water (0.5mL/g) by cooling to 0°. Purified by repeated crystns from deoxygenated water inside a glove-box, finally drying under vacuum. [Rhee and Dasgupta J Phys Chem 89 1799 1985.]... 

Provide local air movement. Creating local air movement, even with warm air, provides a reduction in effective temperature and is inexpensive. A punkah type fan may be used, although this can have the effect of drawing down warmer air from a high level, or a portable fan in a box . It is advisable to have a multispeed fan to allow the effect to be adjusted by the operator for maximum comfort. 

Other than longer-term supply issues the main driver for moving away from fossil resources is pollution. Since pre-industrial times the level of atmospheric CO2 has risen from 280 ppm to 360 ppm, and whilst some observers believe this may be a natural cycle in the Earth s history, most believe it is a direct consequence of burning fossil fuels. This additional CO2 is now thought to be the main cause of global warming via the greenhouse effect (see Box 6.1). 

The formation of dew and fog are consequences of this variation in relative humidity. Warm air at high relative humidity may cool below the temperature at which its partial pressure of H2O equals the vapor pressure. When air temperature falls below this temperature, called the dew point, some H2 O must condense from the atmosphere. Example shows how to work with vapor pressure variations with temperature, and our Chemistry and the Environment Box explores how variations in other trace gases affect climate. 

Worked Example 4.7 What is the increase in entropy when warming 1 mol of chloroform (III) from 240 K to 330 K Take the value of Cp for chloroform from the Aside box on p. 142. 

Heat 30 mL hybridization solution to 60°C in a separate container. A hybridization box is filled to approx. 80% full with water and warmed to 55-60°C. 

Solid nitrosyl chloride stored in a dry-ice box is quickly melted by warming, and as rapidly as possible the liquid nitrosyl chloride is weighed into a flask contained in a hood. Nitrosyl chloride is simply allowed to volatilize into the reaction from this flask under ambient conditions rapid addition of nitrosyl chloride causes a decrease of the yield of a-chlorooxime. It may sometimes be necessary to control the rate of addition by cooling the nitrosyl chloride container with ice water. 

Box 3.3 Hibernation, migration or insulation in warm-blooded animals. Manipulations to overcome the effects of low temperatures... 

One example is the mosquito. Conversion of forests into farmland in many developing countries produces places that accumulate water which are ideal breeding grounds for mosquitoes. Global warming may increase the size of areas that are warm enough for mosquitoes to breed (Box 17.8). 

After many days and nights of this, I awoke feverish in the middle of the night, the air redolent with curried food, excrement, and machine oil. I made my way to the exposed deck on the stem. The night was warm, the smell of curry not altogether lost even there. I sat down with my back against a heavily painted metal box... 

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