Definition of "underfiring"
underfiring1
noun
uncountable
Intentional operation of a boiler, furnace, oven, etc., at a low level.
Quotations
The designer believes that by this combination of a combustion-chamber with the underfiring grate the combustion of the fuel is improved.
1890, Daniel Kinnear Clark, “Systematic Trials of Furnaces and Boilers (continued)”, in The Steam Engine: A Treatise on Steam Engines and Boilers. […], half-volume I, London, Glasgow: Blackie & Son, […], section I (The Principles and Performance of Steam Boilers), page 250
The lowered demand for coke during the depression, the necessity of maintaining the gas output and the ready availability of liquefied petroleum gas for underfiring led to the conversion of the North Shore coke plant of Becker ovens at Waukegan, Illinois, to this fuel. […] The thermal efficiency of the underfiring was about five per cent lower and somewhat more attention was required to keep the ovens in balance.
1934, Wilbert J. Huff, “Gaseous Fuels during 1932 and 1933”, in A Survey of American Chemistry, volume VIII, New York, N.Y.: Chemical Catalog Company for National Research Council, page 339
One of the major factors contributing to high particulate emissions from domestic burners is on-off cycling. […] Modulation and underfiring have been suggested as methods of reducing the significance of the startup transient. […] Underfiring consists of using a smaller (undersized) unit which has to stay on longer and, therefore, cycles less.
1976 April, G. R. Offen, J. P. Kesselring, K. Lee, G. Poe, K. J. Wolfe, “Section 1: Introduction and Summary”, in Control of Particulate Matter from Oil Burners and Boilers (EPA-450/3-76-005), Research Triangle Park, N.C.: Office of Air and Waste Management, Office of Air Quality Planning and Standards, Environmental Protection Agency, page 1-19
A steam temperature transient correction is a signal that is applied to the normal steam temperature control strategy to counter the impact of a transient process change. An example of a transient process change, and the most typical, would be overfiring or underfiring. Overfiring and underfiring are considered transients because they are not required to maintain a steady-state condition.
2010, G. F. (Jerry) Gilman, “Steam Temperature Control”, in Boiler Control Systems Engineering, 2nd edition, Research Triangle Park, N.C.: International Society of Automation, page 125
The state of not burning fuel at the desired level, and thus not providing heat efficiently.
Quotations
In natural gas-fired boilers, gas pressure is critical to proper burner operation and efficient combustion. Variations in gas pressure may cause over- or underfiring of the boiler. […] Underfiring may cause flame instability and poor combustion efficiency due to high levels of excess air.
1999, James E. Piper, “Boiler Systems”, in Operations and Maintenance for Energy Management, Abingdon, Oxfordshire, New York, N.Y.: Routledge, published 2015
Gas-burner maintenance should include these measures: […] Adjust gas input if combustion testing indicates overfiring or underfiring.
2008, John Krigger, Chris Dorsi, “Heating Systems”, in The Homeowner’s Handbook to Energy Efficiency: A Guide to Big and Small Improvements, Helena, Mont.: Saturn Resource Management, page 133, column 1
Damaged or clogged oil piping between the tank and the furnace will result in reduced fuel flow to the burner. This can cause burner underfiring, which is identified by: / Reduced heating capacity / High oxygen readings during combustion test / Low stack or flue temperature / Low temperature rise (temperature differential) across the heat exchanger […]
2012, Eugene Silberstein, “Oil Heat”, in Residential Construction Academy: HVAC, 2nd edition, Clifton Park, N.Y.: Delmar, page 680
(also attributively) Heating from below.
Quotations
[W]hile there were fully as many under-firing as tube-firing boilers, at work, the majority of explosions took place in boilers of the latter class, and they almost invariably commenced with the collapse of the fire flue.
1856 May, William Kemble Hall, “On the Causes of Explosions of Steam Boilers”, in John F[ries] Frazer, editor, Journal of the Franklin Institute of the State of Pennsylvania, for the Promotion of the Mechanic Arts. […], volume XXXI, number 5 (Third Series; volume LXI, number 365 overall), Philadelphia, Pa.: Franklin Institute, page 299
In an underjet coke oven, a distribution system for delivering a combustion-medium into the underfiring system of said coke oven, comprising: a header-pipe having a plurality of outlets therealong; pipe-connections at a region so remote from the active combustion zone of the underfiring system of the oven as to be unaffected by the heat of active combustion in the combustion zone, for delivering said combustion-medium from said header-pipe outlets to different points in conduit means of said coke-oven underfiring system; […]
1944 June 26, W[alter] C[larence] Rueckel, Ceramic Nozzle for Regenerative Underjet Coke Ovens, US Patent 2470112 (PDF version), column 8
The piers should be a minimum of 8″ high (0.2 m) so that underfiring can be used to heat the pieces from below (and traditional overfiring to heat from above).
2004, W[illibald] Trinks, M. H. Mawhinney, R. A. Shannon, R. J. Reed, J. R. Garvey, “Heating Capacity of Batch Furnaces”, in Industrial Furnaces, 6th edition, Hoboken, N.J.: John Wiley & Sons, section 3.8.7, page 103
(ceramics) The state of being insufficiently fired or underfired.
Quotations
Hence it is, I must suppose, that while more effects could be produced with rose if one could only be sure of the fire, yet carmine is the more serviceable, as one is at so much less risk of loss from overfiring, which is more common than underfiring.
1884 January, Aurelio de Vega, “Overglaze Painting on Porcelain. VII.—The Colours—Blacks, Blues, Browns, Carmines.”, in Amateur Work, Illustrated: Help and Guidance for Self-helpers, volume III, London, New York, N.Y.: Ward, Lock, & Co. […], paragraph 133, page 116, column 2
The brick color which you describe as the result of your carmine after firing is generally due to underfiring and a second fire, stronger, will remedy this, but if this is caused by the painting either laid on too thick or spoiled by other colors, there is no remedy.
1892 December, A. R. C., “Answers to Correspondents”, in The China Decorator: A Monthly Journal Devoted Exclusively to this Art, volume XII, number 1, New York, N.Y.: The China Decorator Publishing Co. […], paragraph no. 488, page 19, column 1
After either underfiring (4 minutes at 1,450° F), normal firing (4 minutes at 1,575° F), or overfiring (6 minutes at 1,750° F), the specimens were deenameled with molten sodium hydroxide.
1952 May, “Radioisotopic Study of Porcelain-enamel Adherence”, in National Bureau of Standards Technical News Bulletin, volume 36, number 5, Washington, D.C.: U.S. Government Printing Office, page 74, column 2
Underfiring results when the kiln doesn't reach the cone temperature at which your glaze matures. Underfiring can be caused by improper calibration of kiln sitters or computer controllers, firing a kiln too quickly so that not enough time is allowed for the glazes to develop properly, or by kiln elements that are worn and need to be replaced.
2001, Mark Burleson, “Glaze Faults”, in Katherine Duncan Aimone, editor, The Ceramic Glaze Handbook: Materials, Techniques, Formulas, revised edition, New York, N.Y.: Lark Books, Sterling Publishing, page 85, column 2
Other problems are caused by underfiring or overfiring the glaze. Underfiring, when the kiln doesn't reach the correct temperature for the glaze, can cause pinholes, while overfiring when the kiln is too hot, can cause the glaze to run, resulting in blisters in the glaze.
2019 August, “Glazing Techniques”, in Alice Horne, editor, Complete Pottery Techniques: Design, Form, Throw, Decorate and More, with Workshops from Professional Makers, London: Dorling Kindersley, page 213