US 3078839 A
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Feb. 26, 1963 E. R. MITCHELL ETAL 3,078,839
- DUMP GRATE Filed Feb. 17, 1961 INVENTOR %wcd ca 1 PATENT AGENT United States Patent 3,078,339 DUMP GRATE Earland R. Mitcheil and Frank D. Friedrich, Ottawa, On-
tario, Canada, assignors to Her Mafiesty the Queen in right of Canada, as represented by the Minister of Mines and Technical Surveys Filed. Feb. 17, 19,61, Ser. No. 90,029 1 Ciairn. (Cl. 126-479) This invention relates to dump grates and more particularly to a grate bar therefor.
Conventional grate bars in the usual type of spreaderfired and like stokers'have avery limited life, particularly when burningcoals possessing strong caking characteristics, because such coals produce a very hot fire-bed. It will be apparent that, due to the conditions of operation, every time a grate is dumped and is exposed to the radiant heat of the furnace, and then to the very hot fresh fire, without the insulating protection of ash, its surface temperature rises sharply up to, say, about 1350 Then, as the ash builds up, the grate cools back down to room temperature. This temperature cycling from 80 to 1350 F. and back to 80 F. every two or three hours, as occurs with strongly caking, low ash fusion coals, causes thermal cracks in the bars, and this in conjunction with accelerated oxidation growth, which occurs to standard grey iron above 800 F., can destroy a grate in a relatively short time. Although the bars are normally cast in grey iron, it has been found that iron containing 1% chromium and 1% nickel resists oxidation growth up to about 1200 Moreover, certain types of standard dump grate bars are of substantial width (approximately six inches) and are provided with a multiplicity of pinholes serving as air openings. These air openings quickly become filled with slag under normal operation with low ash fusion coals, and it is necessary frequently to shut down the heating plant and remove the slag from the air openings, a laborious and time-consuming step. Otherwise, objectionable smoking occurs, grate bars break from thermal stresses, and it is diflicult to maintain steaming capacity in boiler operation.
It is an object of this invention to provide a grate bar with better heat transfer to cool the bar, thereby increas' ing its life.
It is a further object to provide a grate bar which affords improved combustion for longer periods of time without failure of the grate bar and without substantial adverse effect on operating conditions.
It is a further object to provide a grate bar of a shape providing superior physical strength.
The invention will be described with reference to the accompanying drawing, in which FIGURE 1 is a partial side elevation of a grate in accordance with the invention,
FIGURE 2 is a plan view of the grate,
FIGURE 3 is an enlarged bottom plan view of a grate bar in accordance with the invention, and
FIGURE 4 is a section of the grate taken on line 4-4 of FIGURE 1.
Referring to the drawing, the dump grate illustrated comprises a plurality of dump grate bars I mounted by means of keyways 2 on conventional supporting and actu ating means (not shown).
Preferably, each grate bar is of relatively narrow width, say, 2 inches, and comprises a supporting web 3 with flanges 4 projecting therefrom and forming a fuel receiving surface 5. The web 3 has substantial thickness relative to the flanges 4 and preferably such thickness is at least one eighth of the width of the grate bar. For example, with a 2 inch bar, the thickness of the web should be at least inch whereby each flange projects only about 3,078,839 Patented Feb. 26, 1963 %inch from the web. substantial thickness, and, in a 2 inch bar, have a thickness of about inch.
The web 3 has a length such that its shortest overall (including'keyway) longitudinal extent (along the bottomedge thereof), is preferably at least two thirds of the overalllength of the bar. Each section of the web (on each.
side of the keyway) may be provided with a plurality of, heat dissipating fins 6 extending perpendicularly of the flanges 4 and throughout or part of the depth of the web. The Web sections are not perforated.
Each bar, instead of having pinhole air openings, is provided with a notch 7 extending along each edge of the flanges 4, such notches coinciding with those in adjoining bars, as shown in FIGURE 2, to provide elongated air opening slots 8. Each slot 8 extends throughout the major portion of the length of the grate bar, i.e., each air opening slot extends throughout at least of the length of the grate bar. Thus, the extent of air openings in a grate burning surface is at least 5% of such surface.
The section of greatest stress in the bar is through the keyway, and to provide adequate strength, a flange 1'0 is provided around the keyway of each bar. At the top of the keyway, the flange is preferably the full width of the bar, thus providing a wide-flange I-section through the section of greatest stress. On each side of the keyway, the flange tapers inward in width (FIGURE 4) so that it is about one-half the width of the bar at the bottom of the keyway.
The grate described provides improved air distribution with the increased air opening area. The extra thickness of the web results in increased heat transfer and the enlargement of the area of the surface of the web provides extra cooling surface. The heat dissipating fins on the web provide substantially increased dissipation of heat.
In actual tests, it has been found that the grate bars described result in a substantially lowered maximum temperature of the burning surface of the grate composed of such bars. Thus, such temperature has been reduced from approximately 1350 F. to approximately 1008" R, this being the average of 46 readings. The previously described material of construction, namely, grey iron with 1% chromium and 1% nickel, will easily withstand this reduced maixmurn temperature.
The following are the results of tests of breaking strengths, all bars being supported at their ends and loaded over the semi-circular notch 9 in the keyway 2: Bars 5 through 10 had stepped flanges along the sides of the keyway, whereas bars 11 through 13 had tapered flanges as described above. The results clearly show the increased breaking strength obtained by tapering the flanges.
Breaking load, lbs.
(-1) Conventional 6 inch bar, grey iron 7100 (2) Conventional 2 inch bar, grey iron 3680 (3) Conventional 2 inch bar, grey iron 3850 (4) Conventional 2 inch bar, grey iron 3630 (5) Bar as described, 2 inch, grey iron but having stepped flanges along the keyway 7150 (6) Bar as described in (5) above 9300 (7) Bar as described in (5) above 7250 (8) Bar, as described, 2 inch, Fe alloy (1% Cr,
1% Ni) but having stepped flanges along the keyway 7880 (9) Bar as described in (8) above 7950 (10) Bar as described in (8) above 7750 (11) Bar, as described, 2 inch, Fe alloy (1% Cr,
1% Ni) having tapered flanges along the keyway 11,600 (12) Bar as described in (11) above 11,800 (13) Bar as described in (11) above 11,400
We claim: A dump grate bar comprising an imperforate support- Preferably, also, the flanges have ing web having side surfaces, an irnperforate flange extending laterally from each said side surface of said web adjoining one longitudinal edge thereof, each said flange extending from end to end of said web and having an outer free edge, a plurality of heat dissipating fins on each said side surface of said web, each said fin being in substantially perpendicular relation to one of said flanges and extending from one of said flanges to the other longitudinal edge of said web, each said fin having an outer edge substantially contiguous with an outer free edge of one of said flanges, said web having a keyway extending in wardly from said last-mentioned longitudinal edge, said kcyway having a mouth and a flange extending laterally outwardly from each edge of said keyway, each said keyway flange having side portions extending perpendicularly from said mouth and each being of increasing width to a point lying opposite said mouth and a connecting portion extending from one of said points to the other of said 4 points, each said connecting portion being substantially parallel to one of said imperforate flanges and having an outer free edge, the distance between said outer free edges of said connecting portions being at least as great as the distance between said outer free edges of said imperforate flanges.
References Cited in the file of this patent UNITED STATES PATENTS 838,906 Roller Dec. 18, 1906 1,822,034 Jessen Sept. 8, 1931 1,902,595 Thompson Mar. 21, 1933 1,911,007 Watson May 23, 1933 2,000,473 OConnor May 7, 1935 2,377,209 Carroll May 29, 1945 FOREIGN PATENTS 490,306 Great Britain Aug. 12, 1938