Flat scrapers

J.4.1 Use of Mechanical Devices Such As Rubber Wipers. In order to reduce the amount of paint left clinging to the walls of a mix tank, rubber wipers are used to scrape the side of the tank. This operation requires manual labor and hence the percentage of waste reduction is a function of the operator. Since the benefits will be offset by increased labor, mechanization/automation should be considered. Many new mixers are available that are designed with automatic wall scrapers (Weismantel 1985). These mixers can be used with either flat or conical bottom cylindrical mix tanks. 

Fig 22. Add some methilated spirits to burner flame sterilize the flat ended scraper. 

Various flat and round files, depending upon what is available to you. A machinist s scraper or a sharp knife is also helpful for removing burrs from inside the tubing. 

Hearth furnaces consist of one or more flat or concave pans, either moving or stationary, usually equipped with scraper-stirrers. Although such equipment is used mostly for ore treating and metallurgical purposes, a few inorganic chemical processes utilize them, for example, Leblanc soda ash, sodium sulfide from salt cake... 

Close-clearance scrapers for viscous liquids are included in the review by Uhl [253]. An application of scraped-surface heat transfer to air flows is reported by Hagge and Junkhan [256] a tenfold improvement in heat transfer coefficient was reported for laminar flow over a flat plate. Scrapers were also suggested for creating thin evaporating films. Lustenader et al. [257] outline the technique, and Tleimat [258] presents performance data. The heat transfer coefficients are much higher than those observed for pool evaporation (without nucleate boiling). 

Fig. 8.62 Photograph of a Kahl flat die with the hopper housing removed showing a roller arrangement with four grooved rollers, the die plate, the scrapers, and the hydraulic nut (courtesy Amandus Kahl, Hamburg, Germany).

In case (1) of Figure 9.20, the separation occurs outside. In cases (2)-(4) the product is accumulated at the bottom of the chamber and discharged by means of a valve. Vibrators and rotating scrapers help convey the powder when the cone angle is too large or the chamber bottom is flat. When necessary, the air sweeper can be nsed to discharge the dry product along the chamber wall, as in case (4). 

Because high resolution depends on small widths of adsorbent zones being scraped, LSC can be very labor intensive and time consuming. Scraping must be done manually with a commercial device such as a sharp, flat spatula because there are no commercial automatic scrapers available. Great care is needed to minimize loss of sorbent during scraping and transfer to vials. 

This type of "belt" conveyor is equipped with a cold-rolled hardened steel band in lieu of a "rubber" belt and is used for special purposes. The thickness of the band is usually in the range of 1.0 to 1.5 mm. Because of the flat and smooth surface of the band, the material can very suitably be discharged by means of ploughs (or scrapers). Such conveyors are not very suitable for the handling of hot materials unless the band acquires a uniform temperature across its whole width otherwise buckling is liable to occur in consequence of differential thermal expansion, causing serious trouble in the operation of the conveyor. 

Disc feeder Horizontal, flat, grooved discs installed at the bottom of a hopper feeding a plasticator to control the feed rate by varying the discs speed of rotation and/or varying the clearance between discs. A scraper is used to remove plastic material from the discs. 

The submerged arc process offers several advantages for hard surfacing. The greater uniformity of the surface makes for better wearing qualities. The speed of SAW creates major economies in hard-surfacing areas that require the deposition of large amounts of metal. These areas may be either flat or curved surfaces. Mixer bottom plates, scraper blades, fan blades, chutes. 

Disk Feeder n A horizontal, flat or grooved, rotating disk at the bottom of a hopper feeding a continuous extruder that controls the feed rate by varying the speed of rotation of the disk, or by varying the clearance between the disk and the scraper that directs the feed from the disk into the feed throat of the extruder. 

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