Invar, Established a New Standard in the Way Precise Surveying Measurements Were Made, Both in Reliability and Accuracy

I N VA R The Breakthrough for a Low Expansion Alloy

he discovery of the low expansion alloy, Invar, established a new standard in the way precise surveying measurements were made, both in reliability and accuracy. It became the first successful attempt to produce a metal alloy exhibiting a nearly zero coefficient of thermal expansion. In 1889, James Riley of Glasgow, Scotland, brought before the Iron and Steel Institute his investigations into the making of an alloy through a series of tests which combined up to 49 percent nickel with iron. Seven years later, in 1896, Charles Edouard Guillaume, a Swiss-born metallurgist and employee with the International Bureau of Weights and Measures near Paris, began looking specifically for an alloy to be used for surveyors’ wires that would not noticeably change when exposed to temperature variations. While experimenting with nickel contents between 30 and 60 percent, Guillaume discovered the coefficient of expansion at room temperature was lowest when mixing a nickel content of 36 percent with 64 percent iron. Since his new alloy exhibited the least amount of thermal expansion, and because Guillaume considered it invariable, it quickly became known as “Invar”. In 1920, Guillaume was awarded the Nobel Prize in Physics for his discovery of Invar

>> By Jerry Penry, PS

Displayed with permission • The American Surveyor • Vol. 9 No. 10 • Copyright 2012 Cheves Media • www.Amerisurv.com The Sokkia BIS30 3-meter Invar bar code leveling staff in use during a high precision survey. Image courtesy of Sokkia Corporation.

Displayed with permission • The American Surveyor • Vol. 9 No. 10 • Copyright 2012 Cheves Media • www.Amerisurv.com I N VA R the metal inside the case, designating a sign of quality. The Hamilton Watch Company used the name Elinvar which was stamped on the inside of their watches which utilized the Invar alloy. The United States Coast & Geodetic Survey (C&GS) used steel tapes as an additional method to measure precise base lines in triangulation networks as early as 1891. The variance of the temperature was a problem when using steel tapes since expansion and contraction continually had to be factored in during the measurements. It had always been a goal of C&GS to develop an instrument that would not be affected by temperature change. The Ice Bar, invented in 1891, is arguably the most precise instrument ever invented which remained a constant length, but it could only measure a distance of 5 meters at one time which was time consuming. (See The American Surveyor, April 2007). Geodetic agencies in other countries began hearing the favorable applications in which Invar could be used for precise measuring. Serbia obtained a set of Invar wires and measured a base line with the Jãderin apparatus in 1904. Sweden tested a length of Invar wire without making any corrections for temperature on one of their previously measured base lines and determined a difference of only 19mm in 10 kilometers. The countries of Argentina, Australia, Germany, France, Japan, Mexico, Romania, Russia, and Switzerland also purchased lengths of Invar wire for their own geodetic surveying. It soon became appar- ent that the United States would lose its international edge in precise measuring if it didn’t at least begin its own experi- ments with the new alloy. Image courtesy of David Ingram. courtesy of Image On April 1, 1904, a French Five different Lo-Var base line tapes were available through the Keuffel & Esser company trademarked the Company in their 1954 product catalog. word Invar. Successors to that company have kept the trademark going, so it which by then was common in many Hirsch, founded the Invar Watch is active today with the fifth precision instruments such as clocks, Company. For many years preceding renewal in 2007. seismic gauges, and surveyors’ steel the discovery of Invar, watchmakers Invar became the answer tapes. Guillaume is the only scientist to struggled with even the best compensat- C&GS had been seeking for be honored with the Nobel Prize for a ed watches and chronometers because of measuring base lines, but the alloy metallurgical achievement. the non-linear variation of the elasticity tapes needed to be fully tested. In Swiss watchmakers began using the of the steel in the hair spring. Invar was December of 1905, C&GS purchased new alloy for clock pendulums and in the answer to this problem. Watches six Invar tapes from J. H. Agar Baugh the balances in pocket timepieces at produced by the Invar Watch Company in London, England, for the purpose the beginning of the twentieth century. began appearing with the word “Invar” of subjecting them to the rigors of field In 1901, a Swiss watchmaker, Achille printed on the dial and stamped on work while comparing them to existing

Displayed with permission • The American Surveyor • Vol. 9 No. 10 • Copyright 2012 Cheves Media • www.Amerisurv.com I N VA R steel tapes under the same conditions. Willamette Base, Oregon; Tacoma Base, to measure the comparator line at least Unlike the alloy wire used by other Washington; Brown Valley Base, South four times each. All of the tapes were also countries, the United States obtained Dakota; Stephen Base, Minnesota; and standardized at the Bureau of Standards lengths of flat Invar ribbon similar to Royalton Base, Minnesota. Three existing before beginning the field work to test the steel tapes they had already been 50-meter steel tapes 403, 405, and 406, strength and elasticity. During part of the using in the field. The new Invar tapes and three of the new 50-meter Invar standardization process, Invar tape 438 were numbered 437 through 442. The tapes, 438, 439, and 440 were used for was subjected to one hundred reelings and Invar tapes were the color of nickel and the experiment. A fourth tape of each unreelings, on several occasions, without they did not oxidize like steel tapes. type was utilized as a check while the showing any change in length. Another The downside was that they were soft others were held in reserve in the event Invar tape, 437, was kept outdoors when and easily bent which required larger of damage. To calibrate the tapes, a not in use and subjected to a temperature aluminum reels, 16 inches in diameter, to comparator line was established in the range of 14° to 86° F. It also did not show prevent permanent bending of the Invar tunnel joining two buildings at the Bureau any change in length. tapes when not in use. of Standards. The line was repeatedly At the conclusion of the field tests, The field test came in 1906 under measured with the Ice Bar to ensure the it was found the Invar tapes could be the direction of Owen B. French when probable error of the derived 50-meter handled and manipulated in identically C&GS decided to re-measure six existing length did not exceed +/- 0.03 mm. The the same manner as the steel tapes except baselines: Point Isabel Base, Texas; steel and Invar tapes were then used for placing them on larger reels. The Invar

I N VA R Wat c h e s

From various sources on the Internet: “I used to work for a company which made a high-tech soldering iron which used an “Invar, if memory serves, is a metal alloy alloy similar to Invar to control when the tip with an unusually low coefficient of thermal was heated by current and when it wasn’t. expansion (that is, it doesn’t grow or shrink By adjusting the alloys used, they were much when it gets hot or cold). Its use in key able to control the temperature at which components of a watchworks means the the crystal structure, and thus the magnetic watch will not change speed significantly properties, changed.” with changes in temperature. Apparently it can also make the watch less susceptible to “The Invar watch company was founded in “As far as the watch itself goes, it’s a good interference from strong magnetic fields.” 1901 by Achille Hirsch in Le Chaux de Fonds, (but not great) example of a swiss bridge but they didnt’ register the name until 1925. design, with somewhat fanciful bridge “Invar is a wonderfully odd alloy. If I Your watch has medallions from the 1906 modifications. The crescent shaped regulator remember right, one of its first commercial Worlds Fair, so it would have been made after is quite nice, if rather impractical. Well worth uses was in surveyor’s chains.” that. The timing of the company’s founding is getting serviced and passing down through interesting, because Invar (the material) was the generations! Protect that case; that style only invented in 1896. Mr. Hirsch was a rather is rare, and good quality examples have a prolific watch distributor around the turn of hard time surviving the years.” the century, who registered literally hunderds of trademarks, so to some degree this watch represents an attempt to profit from the new material. Around that time, there was a fairly large industry in what’s known as “Swiss Fakes”...low-grade swiss watches that were meant to look like better quality watches. One of the ways these “Swiss Fakes” kept costs down was to not use the split bi-metallic balance wheels that better quality watches used to help offset temperature differences. The new Invar material made the split bi-metallic balance obsolete, but looked similar to the cheap balances used by the swiss fakes. So branding the watch “Invar” meant that the consumer didn’t have to worry about that.”

Displayed with permission • The American Surveyor • Vol. 9 No. 10 • Copyright 2012 Cheves Media • www.Amerisurv.com I N VA R Image from USC&GS from Image Report 1916. Annual The ‘Fischer Rod’ was the latest precise leveling rod put into service in 1916 by the U. S. Coast & Geodetic Survey.

tapes, when properly manufactured, were found to vary less than one part in 500,000 after six months of use in the field. Measurements could be made with the Invar tapes during the heat of the day and repeated standardization was not necessary. This was a savings of time in both the field and laboratory. Measuring with an Invar tape was therefore deemed superior to using a standard steel tape. During the 1915 field season, C&GS began using a meter-long Invar bar to determine if any changes were occur- ring with their leveling rods. This bar David Ingram. courtesy of Image provided calibration information to deter- Lo-Var precise leveling rods, manufactured by the Keuffel & Esser Company, could mine how the leveling rods were affected be ordered with a built in thermometer as shown in their 1954 product catalog. by changes in temperature. With the obtained information, C&GS made the name. C&GS ordered several alloy strips were brought into the agency for use decision to use strips of graduated Invar which were graduated in metric and inset during the 1920-1922 seasons. on their geodetic level rods beginning into the face of nine wooden rods and The United States Geological Survey with the 1916 field season. A manufac- anchored to the hardened steel feet. The also began using Invar tapes to precisely turer in the United States, Midvale Steel alloy strips were 26mm wide, 0.9mm measure their base lines. While the exact and Ordnance Company of Philadelphia, thick, and 122 inches long and fastened year that Invar tapes came into use for began producing Invar. Previously, Invar to the rod with six pairs of thin brass that agency is not clear, the Manual was only produced in Europe. The plates. The entire leveling rod, named of Topographic Instructions published equivalent American alloy was named the Fischer Rod in honor of the chief of in 1913 by USGS included a 300-foot “Gamma steel” so as to not infringe upon the instrument division, Ernst G. Fischer, Invar tape among the standard items for the trademarked Invar manufacturing weighed 14 lbs. An additional 14 rods a surveying crew.

Displayed with permission • The American Surveyor • Vol. 9 No. 10 • Copyright 2012 Cheves Media • www.Amerisurv.com Each iron-nickel alloy tape had its own individual serial number. Minvar was the name associated with the Lufkin Rule Company. Image courtesy of David Hoffart collection.

By the 1930’s, alloy tapes were pur- 36 percent nickel and slightly less than the balance being iron. Most manufactur- chased by various government agencies, 63 percent iron. The remaining elements ers of the nickel/iron alloy sell it by the and private and municipal engineering are typically small traces of aluminum, pound. One source recently contacted companies in lengths of 100 feet, 300 carbon, chromium, cobalt, magnesium, had a scrap piece of 1-inch diameter Invar feet, 50 meters and 100 meters. To meet phosphorus, silicon, sulfur, and titanium rod 18 inches in length available for $150. the needs of surveyors for a lower priced added for machinability and because a Today uses for Invar continue to alloy tape, at least two manufacturers pure mixture is difficult to obtain. advance even outside of the surveying began producing tapes similar to Invar The word “Nilvar” was trademarked industry. Invar is used in microscopes, that were of a slightly different composi- by the Driver-Harris Company in telescopes, thermostats, computers, wave tion and coefficient of expansion. The 1932. “Kovar” was trademarked by guide tubes, orbiting satellites, lasers, Keuffel & Esser Company began using Westinghouse Electric & Manufacturing gyroscopes, and many other high-tech the name “Lo-Var” on May 24, 1934, Company in 1936. Today, the Kovar applications. and trademarked the name the following name is held by CRS Holdings, Inc., and year. The name “Minvar” was introduced contains 29 percent nickel, 17 percent Jerry Penry is a licensed land surveyor by the Lufkin Rule Company in the mid cobalt, and the balance iron. Super Invar, in Nebraska with nearly thirty years of 1960’s, but was never trademarked. These more difficult to obtain, contains 32 experience. He is also a public speaker names were acronyms of the words Low percent nickel and 5 percent cobalt, with and a published author. Variation and Minimum Variation. The precision tapes manufactured by these companies were individually numbered and had to be calibrated by the National Bureau of Standards. The name “Invar” has become synonymous with the alloy despite the various other names. A 1962 Keuffel & Esser catalog stated their Lo-Var tapes had a coefficient of thermal expansion approximately 0.00000022 per degree of Fahrenheit which was 1/30 that of carbon steel. Lengths available at that time were 50, 100, and 150 feet, and 30 and 50 meters. Prices for these alloy tapes in 1962 ranged from $86.00 to $170.00. Today, that price would exceed $1,300. Today, few if any surveyors still use alloy tapes due to the advance in EDM and GNSS technology. The leveling staff rods and bipods, however, are still in use for first order leveling. One manu- facturer states the most severe irregular graduation errors on their precision Invar leveling staffs are less than +/- 0.005 mm. This is achieved by directly engraving the graduation into the lacquering with an interferometrically controlled laser beam. The cost for a 3-meter Invar staff can be as much as $3800 today. Lengths of Invar rod have also been used as supports for GPS base antennas. Invar is also known as FeNi36, Invar The National Bureau of Standards certified iron-nickel 36, NILO 36, Pernifer 36, and Invar alloy tapes to provide the owner with the exact length Steel. Most Invar produced today con- of their tape to five decimal places of a meter. tinues to have a chemical composition of Image from USC&GS Special Publication No. 247, 1950.