Stock, heating

The driving forces of heat and mass transfer are temperature and concentration gradients, respectively. To a considerable extent, they are limited by the characteristics of the specific processes involved, such as stocks, heat sources, and equipment materials, etc. In most cases only a limited increasing magnitude is permitted. 

Hemicellulose fractions from pulp stock heated at 90 °C and 50% rh for 20 days. 

Note Specimens were 7.9 mm (0.312 in.) fastener stock heat treated as indicated. Source Beta Titanium Alloys in the 1980 s, R.R. Boyer and H. W. Rosenberg, Ed., TMS/AIME, 1984... 

Optional) If using the nM or NM marker stocks, heat shock larvae, WPP, or pupae just before dissection to express the Myc epitope. Place larvae, WPP, or pupae in a petri dish with a moist tissue, wrap the edges of the petri dish twice with electrical tape, and float the dish in the 37"C water bath. In our hands, late third-instar to 6-hour AP tissues need 1.5 hours of heat shock, whereas 24- 0-hour AP tissues require 3 hours. 

Laminated Strand Products. The most recent developments in the family of wood-based composites are a group of laminated strand products, made with strands oriented in the long direction of the product and marketed as stmctural composite lumber. One product is made with long, narrow strips of softwood veneer. The strips or strands are about 2.5 x 13 x 600 mm (0.1 x 0.5 x 24 in.), coated with a PRE adhesive, and pressed under heat and pressure into large blocks. After the resin is cured the blocks are resawn and planed into lumber dimension stock. 

Temperature and pressure are not considered as primary operating variables temperature is set sufficiendy high to achieve rapid mass-transfer rates, and pressure is sufficiendy high to avoid vaporization. In Hquid-phase operation, as contrasted to vapor-phase operation, the required bed temperature bears no relation to the boiling range of the feed, an advantage when heat-sensitive stocks are being treated. 

Gut Rubber. To produce cut mbber thread, smoked mbber sheet or crepe mbber is milled with vulcanizing agents, stabilizers, and pigments. This milled stock is calendered into sheets 0.3—1.3 mm thickness, depending on the final size of the mbber thread desired. Multiple sheets are layered, heat-treated to vulcanize, then sHt into threads for textile uses (Fig. 2). Individual threads have either square or rectangular cross-sections. 

A continuous extmsion process, as weU as mol ding techniques, can be used as the thermoforming method. A more rapid rate of cure is then necessary to ensure the cure of the mbber before the ceUular stmcture coUapses. The stock is ordinarily extmded at a temperature high enough to produce some curing and expansion and then oven-heated to complete the expansion and cure. 

A furnace may be dkect-fired or indkect-fired. The indkect-fired is known as a muffle furnace, and in such furnaces the combustion gases are separated from the stock being heated to prevent contamination. 

The processing methods for siHcone mbber are similar to those used in the natural mbber industry (59,369—371). Polymer gum stock and fillers are compounded in a dough or Banbury-type mixer. Catalysts are added and additional compounding is completed on water-cooled roU mills. For small batches, the entire process can be carried out on a two-roU mill. Heat-cured siHcone mbber is commercially available as gum stock, reinforced gum, partially filled gum, uncatalyzed compounds, dispersions, and catalyzed compounds. The latter is ready for use without additional processing. Before being used, sihcone mbber is often freshened, ie, the compound is freshly worked on a mbber mill until it is a smooth continuous sheet. The freshening process eliminates the stmcturing problems associated with polymer—filler interactions. 

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