Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01K—ELECTRIC INCANDESCENT LAMPS
  • H01K3/00—Apparatus or processes adapted to the manufacture, installing, removal, or maintenance of incandescent lamps or parts thereof
  • H01K3/02—Manufacture of incandescent bodies

Definitions

• li y invention relates to the manufacture of metallic filaments for incandescent electric lamps, and it has for its object to provide a method of treating filaments of tungsten and other equivalent refractory metals 15 for the purpose of imparting to such filaments an internal structure which resists alteration duringburning and which, therefore, adds materially to the operating life of the filaments.
• the life of a metal incandescent-electric lamp filament is limited by the alterations which take place in the filament during burning, such alterations comprising mainly the bodily discharge or evaporation of particles of metal from the filament and rearrangements and crystalline growth within the filament.
• Such internal changes render the filament brittle and cause it to become deformed or break after a limited period of service, particularly if the filament is of the small diameter required in the smaller types of lamps.
• One such internal change manifests itself in a displacement in sections of a filament with respect to its longitudinal axis and it is usually designated .by the term offsetting.
• the object ,of the invention may beachieved which, more specifically stated, is to impart, to a finished filament, adapted to function as the incandescent ele- Application filed @ctoher 15, 1917. Serial No. 196,686.
• the grain structure of which has been deformed by mechanical working there is a certain temperature known as the critical or equiaxing temperature at which the metal assumes anunstressed or natural cell-like structure, known as the equiax-ed condition.
• the critical or equiaxing temperature at which the metal assumes anunstressed or natural cell-like structure, known as the equiax-ed condition.
• the zone of rapid grain growth be passed through rapidly, i. e., the heattreatment is not prolonged for any appreciable period of time in the rapid grain growth range, thus avoiding detrimental crystal growth.
• the equiaxing temperature is approximately 1800 C. It is to be understood that there are several factors which influence the critical and germinative temperatures of a filament such as the kind and purity of the material comprising the same, size thereof, operating efiiciency, etc., but generally speaking, these temperatures cover a range from 1800 C. to 2100 C. for tungsten filaments containing a small percentage of an offsetresisting material such as thoria. As herefibrous condition.
• the germinative range is not a fixed temperature range for all metals, but nevertheless may be regarded as substantially fixed for given conditions as to kind, quality, and mass of the substance composing the filament.
• the germinative range of temperatures shall be considered as that range including the critical temperature and the range of rapid grain growth and excluding the range in which slow grain growth takes place.
• initial grain structure is meant that structure the filament has when it begins its commercial useful life.
• My invention is directed to influencing the grain structure when thefibrous structure is changed to crystalline. This latter conversion has always occurred in the manufacture of tungsten lamp filaments when the latter have been heated for the first time by a flashing process, which consisted in increasing the applied voltage at a uniform and comparatively slow rate from a fractional part of the normal voltage to a value somewhat in excess of the normal; the structure resulting from such heating, however, has resulted in theforma- 'tion of a filament having. an initial grain structure non-uniform in size.
• My invention therefore, is directed to a properly controlled method of converting the fibrous structure of the drawn wire to the optimum crystalline condition and the process is therefore begun when the filament is in the Furthermore, by practicing my method, a filament is produced having an initial grain structure that is uniform.
• the metal may be raised to just below the critical tem perature thereof and then by a subsequent heat-treatment the germinative range or zone may be passed through very rapidly to a relatively high temperature, i. e., a ternperature which is higher than the extreme limit of the germinative range, which tam-- perature should be less than the fusion point of the metal.
• the high temperature may be maintained for predetermined maniac period, care being exercised not to reach the fusion point.
• This treatment contem-. plates two stages. However, the treatment may be practiced in one stage by raising the temperature in one step to the ,high temperature.
• the intermediate germinative range In passing rapidly through the critical point to a relatively high temperature, the intermediate germinative range is necessarily also passed rapidly. ln maintaining the filamentary body at the relatively high temperature above the 'germinative range, the duration of time in which it is so maintained is dependent on the grain size which it .is desired to produce.
• a heat-treating schedule may be determined which will produce a given grain structure for any size filament.
• a proper heattreating schedule may be devised for afilament of given size by applying the proper voltage for the proper period of time.
• This ternperature control permits the regulating or governing of the initial grain structure of a lamp filament, and upon the initial grain structure depends the life of the filament.
• a given grain formation depends upon the use of a certain heat-treating schedule, and the life of the lamp is dependent upon a given grain formation.
• a heat-treating schedule which will produce a grain size or formation of between say, 12000 to 18000 grains per sq. mm. results in a tungsten filament destined for a considerably longer-life than one in which no attempt has been made to control the grain growth.
• W hen lamps treated according to the schedule mentioned were life-tested, they did not burn out for substantially 1400 hours. Since the average life of a lamp not subjected to my heat seasoning schedule is approximately 1100 to 1200 hours, it IS evident that a lamp treated as contemplated by this invention has an increased life efficiency of at least 10%.
• heat-treatment causes the grain growth to start, and that the proper control of the heat-treatment determines whether the grain structure shall be regular or irregular. i. e., uniform or non-uniform, and also determines the fineness of the grain at the beginning of the life of the lamp. Also, it would appear that the life of the lamp is dependent on the rate of grain growth, and any means which will have a tendencv to retard grain growth during the-service of the lamp will increase its efiiciency by prolonged life.
• a filament of tungsten or equivalent refractory metal consisting of grains sub stantially uniform in size.
• An offset-resisting filament consisting essentially of crystallized tungsten only, said tungsten having crystals substantially uniform in size.
• a metallic filament of tungstenor equivalent refractory material having a crystalline structure in which the grains are of uniform size and within a range of 12,000 to 18,000 grains per square millimeter.
• a crystallized filament formed from tungsten having initially a fibrous structure, said filamentfi consisting of grains which number 12,000 to 18,000 per square millimeter.
• the step which comprises rapidly raising the temperature of the filament to a degree above the germinative range but below the fusion point of the metal.
• the method of imparting a definite crystalline structure to a tungsten filament which comprises rapidly raising the temperature of the filament to a degree above the germinative range but below the fusion point of the metal and maintaining said temperature for a predetermined interval.
• the method of imparting a definite crystalline structure t a tungsten or equivalent metal filament mounted in an incandescent lamp which comprises rapidly raising the temperature of the filament to a degree above the germinative range but below the fusion point of the metal and maintaining such temperature for a predetermined interval.
• a filament consisting essentially of crystallized tungsten only and possessing, after having its temperature rapidly raised above the germinative range, crystals substantially uniform in size.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Resistance Heating (AREA)
• Lighting Device Outwards From Vehicle And Optical Signal (AREA)

Priority Applications (3)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22726417

Family Applications (1)

Country Status (3)

Cited By (5)

• 1917
  • 1917-10-15 US US196686A patent/US1461140A/en not_active Expired - Lifetime
• 1918
  • 1918-09-24 GB GB15523/18A patent/GB120040A/en not_active Expired - Lifetime
  • 1918-10-08 FR FR492203A patent/FR492203A/fr not_active Expired

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