Патент USA US2405075код для вставки
J. P. VOLLRATH 2,405,075 PROTECTING TUBE Filed Nov. 27, 1945 6 2 3 4 5. INVEN TOR. JOSEPH P. VOLL'RATH Patented July 30, 1946 ‘ 2,405,075 PATENT '- ' OFFICE ‘ Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Application November 27, 1943, Serial No. 512,058 1 Claim. (Cl. 136-4) 1 The present invention relates to temperature measurement, and more particularly to a protect ing tube which is used to protect a temperature measuring thermocouple. 2 When a thermocouple such, for example, as chromel-alumel is used in a metal tube contain ing iron, at temperatures above 1500° F., the wires thereof change their composition for some It is customary in the measurement of tem reason not at present known. It is thought how peratures by means of thermocouples to enclose ever that this change in composition may be due to the fact that the atmosphere within the tube the latter in a protecting tube. This is done for several reasons amongst which is to prevent con is oxygen free. Above 1500° F. the iron in the tamination of the thermocouple and to increase its metal tube will combine with the oxygen of the life. The protecting tube must have the char 10 air in the tube to form an iron oxide. The re acteristic of being unaffected by the medium maining constituents of the air, or the iron oxide, with the heat cause a change in the composition which surrounds it and of rapidly transmitting of the thermocouple wires, with a consequent heat from the process to the temperature re sponsive element. It has been particularly dif change in the thermocouple calibration. In order to avoid this change in thermocouple ?cult to ?nd a protecting tube that will satisfy 15 calibration, a gas impervious ceramic tube 4 is these requirements when used in a molten salt bath of the carburizing type. inserted within the metal tube 2. The thermo It is, accordingly, an object of to provide a protecting tube for which will withstand the action baths, and particularly baths of this invention couple to be used is inserted in this ceramic tube. thermocouples The tube 4 is preferably made of a ?ne grain of carburizing 20 vitri?ed ceramic material which is known as sil limanite and which has the chemical composition cyanide salts, of AlzSiOs. A tube of this type will not permit for a longer period than has heretofore been possible. the passage of gases through it at the tempera tures that are encountered in a carburizing bath It is a further object of the invention to pro so that the atmosphere therein is normal. Such vide a protecting tube for thermocouples which will permit the rapid transfer of heat from its a tube, however, if immersed directly in the bath would be disintegrated by the action of the salts exterior to a thermocouple located in the same, forming the same. Thus the ceramic tube 4 pro and with a minimum thermal lag. tects the thermocouple from the action of the It is a further object of the invention to pro vide the combination of a carburizing bath with 30 atmosphere that is found in the interior of the metal tube 2, and the ceramic tube is protected a protecting tube of the type disclosed herein. from the action of the carburizing salt bath by The various features of novelty which charac metal tube 2. terize this invention are pointed out with particu larity in the claim annexed to and forming a part Since the dead air space between the two tubes of this speci?cation. For a better understand 35 2 and 4 will slow down the heat transfer from the exterior of the protecting tube to the thermo ing of the invention, however, its advantages and couple, the space between the two tubes is ?lled speci?c objects obtained with its use, reference with a refractory material 5 which will rapidly should be had to the accompanying drawing and transfer heat so that temperature changes to descriptive matter in which is illustrated and de which the protecting tube is subjected will be scribed a preferred embodiment of the inven more quickly re?ected by the thermocouple than tion. would otherwise be possible. A suitable refrac In the drawing the single ?gure shows a pro tory material has been found to be silicon car tecting tube made in accordance with the pres bide. This refractory material is powdered and ent invention. The protecting tube is made of a plurality of 45 is poured into the space between the metal and the ceramic tubes as shown in the drawing. parts each of which has its own characteristics and serves a de?nite purpose. As shown in the The upper end of the metal tube 2 is shown as drawing the outer portion of the protecting tube being threaded at 6 so that any convenient type of support may be attached thereto. Such a sup is formed of a closed end metal tube 2 that is port would also serve to hold the thermocouple made of mild steel. This tube is covered with a thin layer of chromium 3 which may be deposited wires so that they could be connected with a thereon in any suitable manner such as electro suitable pyrometer. It is noted that the protect plating. A tube of this type when properly heat ing tube of the present invention can be used in other places than in carburizing salt baths treated will withstand the action of molten cya nide salts which are used for carburizing baths. 55 although it is primarily intended for that pur 2,405,075 ' V , 3' a V V . a 4‘ pose. Any desired type of thermocouple may be used in the protecting tube to measure the tem vantage without a corresponding use of other perature thereof provided this thermocouple is Having now described this invention, what I claimas new anddesire to secure by Letters Pat features. suitable for the ranges of temperatures that are encountered. » . , ' ' Ul ent is: , While in accordance with the provisions of the A thermocouple protecting tube comprising an statutes, I have illustrated and describedithe best form of thisinvention now knowntome, it would: outer closed-end tube made ‘of mild steel and covered with a thin layer" ofochromium', an inner closed-end tube received in telescoping relation be apparent to those skilled in the art that changes may be made in the form of the'appa ratus disclosed without departing from the spirit’ 10. :by said outer tube and made of a ?ne grained, vitri?ed, gas impervious ceramic material, the of this invention as set forth in the appended I space between said tubes being ?lled with a granue this claim,invention and that may in some sometimes cases .certainrfeatures vvbe;iilsreld ‘toiled-‘ft of lar refractory material. " JOSEPH P. VOLLRATH.