US 3662522 A
A cartridge for a getter pump having a pleated strip comprising a substrate having a non-evaporable getter metal thereon. Adjacent surfaces of the pleated strip are held at a predetermined angle by a spacer between the adjacent surfaces. Getter pumps employing such cartridges exhibit maximum pumping rates. Strips suitable to be pleated are also described.
Claims available in
Description (OCR text may contain errors)
United States Patent Della Porta et al. 1 May 16, 1972  GETTEIR PUMP CARTRIDGE 2,831,549 4/1958 Aldert ..55/467 x 2,968,361 l/1961 Buckman..  Inventors: Paolo Della Porta; Bruno Ferrarlo, both of 2,984,314 5/1961 Demon Mlle", Italy 3,144,200 8/1964 Taylor et al 73 Assignee: S.A.E.S. Getter-s S.p.A., Milan, Italy 3,309,844 3/1967 ilemlreet a1 3,490,211 1/1970 Cartler ..55/52l X  Filed: July 15, 1970 Primary Examiner-John Adee [21 1 Appl' 55029 Attorney-David R. Murphy and Murphy and Dobyns  Foreign Application Priority Data  ABSTRACT July 24, 1969 Italy ..869075 A cartridge for a getter pump having a pleated strip comprising a substrate having a non-evaporable getter metal thereon.  US. Cl.. ...55/387, 55/521, 417/51 Adjacent surfaces of the pleated strip are held at a predeter- [5 l Int. Cl .BOld 53/04, F04b 37/02 mined angle by a spacer between the adjacent surfaces. Getter  Field of Search ..55/208, 387, 389,521 p mp mploying such cartridges exhibit maximum pumping rates. Strips suitable to be pleated are also described.  References Cited 5 Claims 11 ng Figures UNITED STATES PATENTS 2,154,131 4/1939 Lederer ..55/387 X PATENTEDMAY 16 :972
SHEET 1 BF 2 Jill:
INVENTORS Paulo rlnllu Pur'lu B rum; Furl-:1 r'in PUMPING RATE PATENTEU m1 6 I972 SHIET 2 [IF 2 58 Hm 52 54 sow- 2 IN DEGREES "Illilll.
INVENTORS Paolo della Porta Bruno Ferramo ATTORNEYS GETTER PUMP CARTRIDGE CROSS-REFERENCE TO RELATED APPLICATIONS a. U.S. application, Ser. No. 761,161, filed Sept. 20, 1968, entitled "Getter Pumps".
b. U.S. application, Ser. No. 866,336, filed Oct. 14, 1969, entitled Getter Pump. (SAES 102) c. U.S. application, Ser. No. 866,335, filed Oct. 14, 1969, entitled Radiant Heat Reflection in Devices Such as Getter Pumps." (SAES 103) d. U.S. application, Ser. No. 878,812 now Pat. No. 3609064, filed Nov. 21, 1969, entitled Getter Pump". (SAES 104) The disclosures of references (a) through (d) are incorporated herein by reference.
Getter pumps are well known in vacuum technology and are useful for removing residual gases from closed vessels such as electron tubes in order to produce and maintain within these vessels a high degree of vacuum. Such getter pumps are described in references (a) through (d). These getter pumps employ a finely divided non-evaporable getter metal on a substrate. In operation the surfaces of the getter metal particles sorb residual gases in the vessel thus reducing the quantity of gases present and producing a high degree of vacuum. The surface of the getter metal will continue to sorb gases until the surface becomes saturated with sorbed gases and reaction products of sorbed gases with the getter metal. At this point it is conventional to heat the getter metal particles in order to drive these sorbed gases and reaction products to the center of each getter metal particle thus exposing a fresh surface of getter metal for continued gas sorption. This process can be repeated until the getter metal particles are completely saturated with sorbed gas and reaction products at which time the getter metal particles must be replaced. To facilitate such replacement it has become conventional to employ a replaceable cartridge having a pleated strip comprising a substrate having the non-evaporable getter metal thereon. This strip is pleated as described in reference (a) in order to minimize the space required for a given quantity of getter metal. By virtue of this pleating adjacent surfaces of the strip are caused to form an angle, alpha.
According to recently conducted experiments it has been determined that alpha should generally be between 1 and 15 and should preferably be between 2 and 10. While prior getter pumps such as those described in reference (a) can be manufactured having the desired initial value of alpha this value can be changed for individual adjacent surfaces by mechanical deformation with the undesirable result of a reduction in the pumping speed of the pump.
It is therefore an object of the present invention to provide an improved getter pump cartridge and an improved strip useful in producing such cartridges which is substantially free of one or more of the above disadvantages.
Another object is to provide an improved getter pump cartridge which is not easily deformed.
A further object is to provide an improved getter pump cartridge wherein alpha is constant.
A still further object is to provide an improved getter pump cartridge which exhibits a maximum pumping rate for a given quantity of getter metal.
Additional objects and advantages of the present invention will be apparent to those skilled in the art by reference to the following detailed description and drawings wherein:
FIG. 1 comprising FIGS. la and 1b constitute an exploded view of a getter pump of the present invention employing in FIG. la an improved getter pump cartridge;
FIG. 2 is a top view of the getter pump cartridge of FIG. 1a;
FIG. 3 is a graph of pumping rate versus alpha for three commonly pumped gases;
FIG. 4 is a top view of a strip useful in the present invention;
FIG. 5 is a sectional view taken along line 5-5 of FIG. 4;
FIG. 6 is an enlarged sectional view taken along line 6-6 of FIG. 4;
F IG. 7 is an enlarged sectional view taken along line 77 of FIG. 4;
FIG. 8 is an enlarged sectional view similar to that of FIG. 7 but showing a modified form of a portion of a strip useful in the present invention;
FIG. 9 is an enlarged sectional view similar to that of FIG. 7 but showing another modified form of a portion of a strip useful in the present invention; and
FIG. 10 is a view illustrating the manner in which the strip of FIG. 4 is pleated in order to produce a cartridge element useful in the getter pumps of the present invention.
According to the present invention, there is provided an improved cartridge for a getter pump wherein adjacent surfaces of the strip are held at a predetermined angle by spacer means between the adjacent surfaces. In the broadest aspects of the present invention, the spacer means can be attached to any part of the getter pump. However, it is preferably carried by a segment of the strip and is preferably arranged such that the angle alpha between adjacent outwardly opening segments is maintained at a constant value.
Referring now to the drawings and in particular to FIG. 1a, there is shown a getter pump cartridge 10 of the present invention. The cartridge 10 comprises an upper ring 11 and a lower ring 12 with a circular screen 13 therebetween. Within the screen 13 are a number of cartridge elements of which only elements 14 and 15 can be seen through the cutaway section. The substrate of the elements has a non-evaporable getter metal 16 thereon. The remaining structure of the elements is described more completely below.
The getter pump cartridge 10 shown in FIG. la and the remainder of the getter pump shown in FIG. lb together comprise a complete getter pump. In FIG. 1b there is shown a flange 20 having a supporting ring 21 adapted to receive the lower ring 12 of the cartridge 10. Also carried by the flange 20 is a heater 22 comprising an insulator 23 carried by the flange 20 and having thereon a wire 24 of high ohmic resistance. In order to place the getter pump in operation, the cartridge 10 is moved downwardly until the ring 12 fits within the ring 21. These parts are then held together by means not shown. The entire getter pump is then inserted into a vessel to be evacuated and connected thereto in a gas-tight manner by means of the flange 20. A current is passed through the wire 24 causing it to radiate heat to the getter metal 16, heating and activating it and thereby causing it to become gas sorptive.
FIG. 2 illustrates the means by which the angle alpha is measured. FIG. 3 illustrates the variation in pumping rate for three gases as a function of alpha. Curve 31 is for nitrogen and illustrates that pumping rate is a maximum when alpha is equal to approvimately 3. Curve 32 is for hydrogen and illustrates that pumping rate is a maximum when alpha is equal to approximately 4". Curve 33 is for carbon monoxide and illustrates that pumping rate is a maximum when alpha is approximately 6. As can be seen by reference to curves 31, 32, and 33 generally optimum pumping rates occur at values for alpha of 1 to 15 and preferably 2 to 10. At values above or below these, the pumping rate is considerably reduced.
Referring now to FIG. 4, there is shown a flat strip 40 of indefinite running length suitable to be pleated and circularly bent into a cartridge element 14 of the present invention. The strip 40 comprises rectangular segments 41, 42, 43, and 44. Each segment 41, 42, 43, and 44 has a substrate 45 which is common to all segments. The central portion of each segment 41, 42, 43, and 44 is coated with particles 46, 47, 48, and 49 of a non-evaporable getter metal. Each segment 41, 42, 43, and 44 has a first getter free margin 50 common to all and a second getter free margin 51 common to all. The getter free margins 50, 51 are parallel to the running length of the strip 40. These segments 41, 42, 43, and 44 are each connected to the respective i next adjacent two segments by foldable bridging attachments. Thus segment 42 is attached to segment 41 by attachments 52 and 53, and is attached to segment 43 by attachments 54 and 55. The bridging attachments 52, 53, 54, and 55 are defined by slots 56 and 57 which extend across the strip 40 transverse to the running length thereof and extend into the getter metal free margins 50 and 51. By virtue of this structure, each of the bridging attachments 52, 53, 54, and 55 has a line of weakness about which the adjacent segments 41 and 43 can be most easily folded. Each of the odd numbered segments are provided with two elevations. Thus segment 41 is provided with elevations 58 and 59, and segment 43 is provided with elevations 60 and 61. All elevations 58, 59, 60, and 61 project the same direction, in this case upwardly, from the substrate 45. As shown in FIG. 5, they all have the same height, h; i.e. h h, 12,. Furthermore, the elevations 58, 59, 60, and 61 are all the same distance from the next adjacent line of weakness, i.e. I =1, 1,. Although the even numbered segments can also be provided with elevations in the preferred embodiment depicted, the even numbered segments 42 and 44 are free of elevations in order to obviate the necessity for carefully controlled alignment of the elevations.
FIGS. 6 and 7 illustrate the preferred structure by which the elevations are attached to the substrate. As shown, the elevation 59 constitutes an integral deformation of the metallic substrate 45 inthe getter metal free margin 51 of the segment 41. The structure shown in FIG. 6 is most easily produced by simply pressing the substrate 45 into a mold, not shown, having a depth equal to h,. The elevation 59 is preferably located in the getter metal free margin in order to preclude the possibility of releasing particles of getter metal concurrently with the pressing operation. As shown in FIG. 7, the elevation 59 comprises an upwardly extending segment 62, a horizontally extending segment 63, having a planar upper surface 64, and a downwardly extending segment 65. The planar upper surface 64 is parallel to the plane of the substrate 45 and provides a larger area of contact between the surface 64 and the back of the surface of the next adjacent segment 42 when the substrate 45 is pleated.
Referring now to FIGS. 8 and 9, there are shown modified forms of elevations also useful in the present invention. These figures represent enlarged sectional views taken through the elevations in a manner analogous to that of FIG. 7. The elevation 67 shown in FIG. 8 has a rounded upper surface 68. The elevation 69 shown in FIG. 9 is designed to contact the back of the surface of the next adjacent segment with its edge 70. The most preferred form of elevation is the elevation 59, the next preferred is the elevation 67, the least preferred being the elevation 69.
Referring now to FIG. 10, there is illustrated the manner in which the strip 40 is pleated and circularly formed into a cartridge element 14 of the present invention. As can be seen, each of the bridging attachments illustratively shown by attachments 53 and 55 are bent in alternate directions in order to pleat the strip 40 and cause the elevations 59 and 61 to contact that portion of the getter free margin 51 present on the next adjacent even numbered segments 42 and 44. Since the height h of the elevation and its distance I from the fold line determines alpha, it can be seen that It must be substantially equal the tangent of alpha. In that preferred embodiment of the present invention wherein the attachment 53 is sharply bent h/l is exactly equal to the tangent of alpha. In other cases wherein the attachment 53 has a finite radius of curvature 11/! will depart somewhat from the tangent of alpha. Those skilled in the art can readily adjust values of h and l to compensate for the radius of curvature such that alpha is within the abovedescribed limits. After the strip 40 is pleated, it is circularly formed along circles 73 and 74 until a complete circle is obtained resulting in a cartridge element 14 useful in the getter cartridges of the present invention as shown in FIG. 2. The inwardly opening angle, beta, shown in FIG. 9, is not critical and can have any value from zero upwards.
Any non-evaporable getter metal can be employed in the present invention. By non-evaporable getter metal is meant metals which are sorptive to gases and which have a vapor pressure less than torr at 1,000" C. Examples of suitable getter metals include among others niobium, tantalum, vanadium, zirconium, titanium, mixtures thereof and alloys thereof with one another and with other metals such as aluminum which do not materially reduce the gas sorptive capacity of these metals. The preferred getter metal is an alloy of l to 40 and preferably 13 to 18 weight percent aluminum balance zirconium. The preferred specific alloy is that of 16 percent aluminum and 84 percent zirconium available from SAES Getters S.p.A. under the tradename St 101. The finely divided getter metal can have widely varying particle sizes such that it passes through a U.S. standard screen of IO mesh/inch and preferably passes through a screen of mesh/inch and is retained on a screen of 600 mesh/inch.
The substrate 45 can be of any metal but is preferably of a metal which is softer than the getter metal. Suitable substrate metals include among others iron and stainless steel.
The getter cartridges of the present invention can be employed in getter pumps with or without heat shields as described in reference (c). In an alternate embodiment of the present invention, the heater 22 can be eliminated by employing a substrate 45 of high ohmic resistance in the manner described in reference (d).
Although the invention has been described in considerable detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.
What is claimed is:
l. A cartridge for a getter pump having at least one cartridge element comprising a circularly formed pleated strip of segments comprising a substrate carrying a non-evaporable getter metal, each segment being joined to the next adjacent segments wherein the angle between adjacent outwardly opening segments is maintained at 1 to 15 by at least one elevation attached to one of the segments such that the elevation lies between the adjacent outwardly opening segments.
2. The cartridge of claim 1 wherein the elevations are placed in a getter metal free margin along the edges of the strip.
3. The cartridge of claim 1 wherein the elevations are integrally formed from the metal of the substrate.
4. A cartridge for a getter pump having at least one cartridge element comprising a circularly formed pleated strip of segments comprising a metallic substrate the central portion of which is coated with a non-evaporable getter metal leaving a getter metal free margin, each segment being joined to the next adjacent segments by folded bridging attachments wherein the angle between adjacent outwardly opening segments is maintained at 2 to 10 by two elevations, one each in the getter metal free margins of alternate segments.
5. A planar strip of indefinite running length suitable to be pleated and circularly bent into a cartridge element for a getter pump, said strip comprising:
A. rectangular segments each comprising:
1. a metallic substrate the central portion of which is coated with particles of a non-evaporable getter metal,
2. a getter metal free margin adjacent to the side of the segment which is parallel to the running length thereof;
B. foldable bridging attachments attached to the getter metal free margin of each segment and foldably connecting it to the two next adjacent segments, each attachment having a line of weakness about which folding most easily occurs;
C. two elevations on each of the odd numbered segments,
each of the elevations:
l. constituting a deformation of the metallic substrate in the getter metal free margin of the segment,
2. projecting the same direction from the substrate,
3. having equal heights above the substrate,
4. being the same distance from the next adjacent line of weakness, with the proviso that the height of an elevation above the substrate divided by the distance from the elevation to the next .adjacent line of weakness is equal to the tangent of an angle between 2 to 10;
D. the even numbered segments being free of elevations.