Recirculating oven

Following is a list of the kinds of operations performed drying the materials for at least 4 hours at 160°C in a dehumidyfying, recirculating oven injection molding in an Engel machine (barrel temperatures 274-288°C, mold temperature 52°C, overall cycle time 1 min.) mechanical testing (flexural modulus... 

For medium or low temperature furnaces/ovens/dryers operating below about 1400 F (760 C), a forced recirculation furnace or recirculating oven delivers better temperature uniformity and better fuel economy. The recirculation can be by a fan and duct arrangement, by ceiling plug fans, or by the jet momentum of burners (especially type H high-velocity burners—fig. 6.2). 

Figure 3.17 shows a batch-type direct-fired recirculating oven, and figure 1.13 illustrates the principle of a continuous belt direct-fired recirculating oven. All require thoughtful circulation design and careful positioning relative to the loads. 

Fig. 3.17. Batch recirculating oven passes gases through the loads many times, saving fuel. The circulating gases have burner poc, and thus help uniformity.

During thermal oxidation of polypropylene, the definitive end of material stability is indicated by local embrittlement, the so-called polypropylene pest . Figure 5.160 in Section 5.4.3.I.2. This is a powdery decomposition that spreads out radially from a center and can be precisely timed because of its striking appearance it is therefore well suited for comparative stability investigations. DIN 53383-2 [164] is based on this behavior. Here, specimens are stored in a recirculating oven at 140°C. Following a defined length of time, preferably once a day, the rig is removed from the chamber, and the specimens are visually inspected. Specimens that show local embrittlement are removed. The test time until occurrence of this phenomenon is recorded [86]. 

The source of heat used for pre-heating can vary considerably recirculating ovens are generally found to be most efficient, since an even temperature can be more easily maintained throughout. Radiant heaters are also used, but these can cause trouble where a variety of metal surfaces are encountered, since reflective surfaces may be impossible to heat sufficiently, or may take up costly time and fuel in attaining the required temperature. 

Catalysis is utilized in the majority of new paper filter cure ovens as part of the oven recirculation/bumer system which is designed to keep the oven interior free of condensed resins and provide an exhaust without opacity or odor. The apphcation of catalytic fume control to the exhaust of paper-impregnation dryers permits a net fuel saving by oxidation of easy-to-bum methyl or isopropyl alcohol, or both, at adequate concentrations to achieve a 110—220°C exotherm. 

The study shows, however, that the air curtain in the original design is bent off the wall due to the presence of the open oven with induced airflow inside the oven. This unexpected flow feature finally leads to a recirculation zone below the oven, and dust particles on the floor can be carried into the oven (class B quality). This effect was then also confirmed by smoke experiments in the real room and the existing ventilation system. 

In a cosmetic laboratory, a recirculating system would have been adequate except for one very special condition. The noses had to perform their fragrance evaluations in a clean atmosphere. This called for once-through ventilation and included placing drying ovens under a simple hood extending part way down from the ceiling. The result was excellent. 

The destruction of fuzes and supplemental charges has changed. Instead of using a standard detonation chamber, they are simply placed in the MPT and allowed to decompose or detonate. At the same time, the MPT design has changed—it now uses a steam-heated industrial oven with internal steam recirculation, which has not been demonstrated for destruction of fuzes and supplemental charges. 

Tray or shelf dryers are commonly used for granular materials and for individual articles. The material is placed on a series of trays which may be heated from below by steam coils and drying is carried out by the circulation of air over the material. In some cases, the air is heated and then passed once through the oven, although, in the majority of dryers, some recirculation of air takes place, and the air is reheated before it is passed over each shelf. As air is passed over the wet material, both its temperature and its humidity change. This process of air humidification is discussed in Volume 1, Chapter 13. 

A very feasible and promising approach was to arrange the hot process parts of the machine in total in an oven enclosure provided with means for controlled hot air recirculation. The process parts, including tanks, chemical lines, metering cylinders or pumps, valves, mixing head and mold, can be arranged in different compartments of the oven enclosure for the individual temperature control of the chemicals. 

Referring to Figure 410, in the simplest process approximately 30-35% of the coal mixture is briquetted. Coal preparation for briquetting includes grinding, addition of binder, and heating with steam in a suitable mixer. The hot mixture is then briquetted, possibly screened to remove fines (which are recirculated), and cooled. The briquettes are mixed with the remaining (65-70%) coal mixture and conventionally charged into the coke ovens. 

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