Fabrication of curved reflector segments for solar mirro

Reader, A. F.

Russell, W. E.

Werner, E. A.

English

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
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us I /~c i en t i f i c  & Technical Inf omation Division 
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Patent Matters 
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In accordance with the procedures agreed upon by Code G P  
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U. S. Patent No. 
Government or 
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NASA Patent Case No, 
NOTE - If  t h i s  patent covers an invention made by a corporate 
employee of a NASA Contractor, the following is applicable: 
yes 0 NO Q 
Pursuant t o  Section 305(a) of the National Aeronautics and 
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the f i r s t  page of the patent; however, the name of the actual 
inventor (author) appears a t  the heading of Column No. 1 of 
the Specification, following the words *, , , with respect to 
ion of 
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* ~ l i z a b e t h  - -. A. - - carter -- St ,,&ESSI~N N ~ M ~ ~ ~ '  -Enclosure a 
Copy of Patent oited above 3 
https://ntrs.nasa.gov/search.jsp?R=19710006122 2020-03-17T02:40:23+00:00Z
-- 
Jan. 20, 1979 cC/1 A: F. READER ETAL <3,/190,405 
/ ' 
* '  METHOD AND APPARATUS FOR U K I N G  CURVED REFLECTOfi 
' Filed Aug. 23, 1967 3 Shee s-Sheet 1 
&+ 
INVENTORS 
AUSTIN E READER 
WALTER E. RUSSELL 
EDWARD A. WERNER 
9pC 
Jan. 20, 1970 A. F. READER ETAL 3,490,405 
METHOD AND APPARATUS FOR MAKING CURVED REFIJECTORS 
Filed Aug. 23, 1967 3 Sheets-Sheet 2 
Jan. 20, 1970 A. F. READER ETAL 3,490,405 
METHOD AND APPARATUS FOR M A K I N G  CURVED REFLECTORS 
Fi led  Aug. 23, 1967 3 Sheets-Sheet 3 
BNVENXORS 
AUSTIN F WEhclDER 
WALTER E ?USSELL 
BY 
EDWARD A Vi.'Enb;hEs9 
yL-5~"- 
3,490,4015 United States Patent Ofice ,,,, ,,,. , ,,,, 
C 
1 2 
3,490,405 FIG. 2 is a plan view of one section of the solar nlirror 
METHOD AND APPARATUS FOR MAKING shown in FIG. 1 illustrating the reinforcement on the back 
CURVED RBFLEGTBRS side; 
Austin F. Reader, Brunswick, Walter E. IR~lsselk, Lorain, FIG. 3 is a perspective view of a forming mold utilized 
and Edward A. Werner, Parma, Ohio, assignors to the in the method of invention; United States of America as represented by the Ad- 5 FIG. is an elevation view showing start of the ministrator of the National Aeronautics and Space forming and of a mirror Adminlislsation 
Filed Ang. 223, 1967, Ser, No, 662,829 FIG. 5 is an elevation view showing a later stage in the 
Int. C1. B21d 51/04,51/10,31/06,35/00 forming and shaping operation; 
U.S. el. 113-116 8 claims FIG. 6 is an enlarged section view taken along the 
lice 6-6 in FIG. 5; and 
- FIG. 7 is an elevation view showing the final heating 
ABSTRACT OF THE DISCLOSURE operation. 
Fabricating and forming each curved segment of a Referring now to the drawings, there is shown in FIG. light weight mirror by polishing one surface of a flat 15 1 a rigid solar mirror PO in the form of a shallow bowl 
magnesium plate and then machining ribs in that is constructed in accordance with the present in- 
the other side. E~~~ plate is accurately formed on a single vention. The mirror PO is circular in shape and has a 
mold with the application of heat and pressure after the reflecting inner surface 12. A centrally disposed opening 
machining. 14 receives a solar generator. The reflecting surface 12 
20 extends between an outcr peripheral edge 16 of the mirror 
10 and an inner edge 18 about the circular opening 14. 
The invention described herein was made by employees The surface 12 is in the form of a paraboloid for properly 
of the United States Government and may be manufac- focusing the sun's rays at the heat receiver for the gen- 
tured and used by or for the Government for governmen- erator in the opening 14. 
tal purposes without the payment of any royalties thereon 25 Solar mirrors are quite large. By way of example, a 
or therefor. Brayton cycle system will utilize a solar mirror having a 
This invention is concerned with making a curved re- diameter of 20 feet to generate 3 to 4 kilowatts of elec- 
faector a thin cross section. More particularly, the in- trical power. A similar mirror 30 feet in diameter will 
vention relates to a method of fabricating and forming provide 8 to 10 kilowaits of electrical powcr in such a 
segments of a solar mirror having compound curves in system. 
which the reflecting surface is polished prior to any ma- Because of their large sizes, solar miirors are made in  
chining of the opposite surface. separate sections 28 such as shown in FIG. 2. These 
A problem encountered in space flight is that of pro- sections 20 are subsequ~ntly assemNed into a mirror 10 
viding the craft with sufficient electrical power. One ap- shown in FIG. 1. A twenty-foot-diameter mirror 10 has 
proach to solvillg this problem is the utilization of a 3j  been constructed in accordance with the invention by 
Brayton cycle system ir, which the sun's heat is supplied utilizicg twehe identical sections 20 that are bolted to- 
to  a boiler or heat receiver from a large diameter solar gether. 
mirror. The mirror should have an accurate reflecting The under side of the. mirror 10 opposite ihe reflecting 
surface so that as much solar heat as possible can be surface 12 is ribbed for strength aad rigidity as shown 
collected and channeled into the system. Such a mirror in FIG. 2. Ribs 22 in the form of deep rectangular grids 
is quite large and 1s made up of sections. The weight of are used to achieve maximum weight reduction. The re- 
such a mirror must be kept to a minimum. flecting surface has a thickness of about 0.050 inch, and 
The fabrication of the large compound curved surfaces the rib height tapers from 0.62 inch adjacent the edge 18 
for these mirrors presents difficult problems. Conventional of the opening 14 to 1.00 inch at the outer edge 16, 
manufacturing techniques have not been satisfactory for q5 Referring to FIG. 3 there is sl~own a paraboloidal 
producing rigid, lightweight sectors to the dimensional shaped mold 24 used to form the seclio~~s 20 of the mirror 
and surface accuracy required. Such accuracy with stability 10. l-he mold 24 is of aluininum and has a highly polished 
requires a sn~ooth continuous reflecting surface supported forming surface 26 for engaging the mirror sections and 
by an integral stiffening structure. The weight limitation forming the surfaces 12. Grooves 28 in the 
placed on such mirrors necessitate structures having thin 50 sllrface 26 aid in this forming process in a manner which 
cross sections. will be described later in greater detail. Clamps 30 posi- 
The fabrication problems have been solved by produc- tioned about the mold 2.2 are used to draw the peripheral 
ing reflector segments in accordance with the present in- edge portions of the reflecting surface 12 into contact with 
vention. Polishing of the reflective surface is performed the forming surface 26 when a mirror section is heated. 
prior to any machining. Each mirror segment is then 55 Electric heaters within the convex mold 24 are connected 
machined and formed to the proper configuration on a to a ,,itable power source by leads 32. 
mold by utilizing heat and pressure. According to the invention, each mirror section is It  is, therefore, an object of the present invention to 
machined from a flat magnesium plate havhn highly 
~rov ide  an efficient method and apparatus for producing surface. 7he machilled is Ihen formed lightweight reflectors having high quality reflecting sur- 60 illto the required paraboloidal shape on the mold 2.2. 
faces. 
Another object of the invention is to provide a method The flat plate is first contoured to the o~itline of the 
and apparatus for producing large reflectors having high Section shown in 2. Then One surface Of 
reflectivity in which all polishing of the reflective surface plate is polished to a high finish. The ribs 22 shown in 
is performed prior to any machining and forming. FIG. 2 are formed on the reverse side by milling out 
~h~~~ and other objects of the invention will be ap- 65 metal in predetermined areas after the opposite surface 
parent from the specification follows and from has been polished. Each central rib has a uniform thick- 
the drawings wherein like numerals are used throughout ness of about 0.075 ivch while the outer circumferential 
to identify like parts. rib is abont 0.75 inch thick and has a thirty-degree lilt 
In the drawings: to form a bolting base for the rim of the mirror 10. 
FIG. 1 is a perspective view of a rigid solar mirror 70 After the ribs have been machined on the back sur- 
constructed in accordance with the present invention; face of the magnesium plate, the flat segment is placed 
3,490,405 
3 4 
on the mold 24 as shown in FIG. 4. Clamps 30 engage heating said plate to the softening temperature, 
peripheral edge portions-of the machined plate for proper bending said heated, plate into peripheral contact with 
positioning. a mold having a forming surface facing said one 
Current is passed through heaters within the mold 24 surface on said plate, said forming surface having 
from the leads 32 thereby heating both the mold and the compound curvature to which the reflecting 
plate to an elevated temperature a t  which magnesium surface is to be curved, 
starts to soften. The mold 24 typically contains about evacuating the @ace between said forming surface and 
80 kilowatts of resistance heaters. The mold 24 is heated said polished reflecting surface whereby said plate 
to about 400" F, and the clamps 30. are tightened as the is forced into contact with said mold, and 
-edges of the machined plate bends into contact with the heating said mold and said formed plate to an elevated 
surface of the mold as shown in FIG. 5. Pins 34 extend- temperature to stress relieve the plate while the same 
-ing outward from the forming surface 26 pass through is forced into contact with said mold. 
openings in the section 20 and guide the surface 12 into 2. A methqd of making a curved reflector as claimed 
proper *engagement with the forming surface. in claim 1 including the steps of 
The section edge to mold joint is then sealed with high 15 polishing a flat magnesium plate, 
temperature silicon adhesive tape 36 about the entire heathg the mold to an elevated temperature of about 
periphery. A vacuum is established in the space between 400" F. while guiding the marginal peripheral edges 
the surface 12 of the mirror section 20 and the forming of the magnesium plate into contact with the mold. 
surface 26 of the mold 24 to bring these surfaces into .3. A method of making a curved reflector as claimed 
Mimate contact. The creation of this vacuum is facili- 20 in claim 2 including the step of heating the mold and 
tated by the grooves 28 which are in communication with magnesiuq reflector to a temperature of about 550" P. 
$assages 38 that extend through the mold 24 to a suitable for about one hour subsequent to forming the reflecting 
vacuum pump. surface to the configuration of the forming surface. 
'-After the section 20 has been drawn into contact with 4. A method of making a curved reflector as claimed in 
the mold 24, both are heated to approximately 550" F. 25 claim 3 including the step of enclosing the mold and 
'his heating is facilitated by surrounding the mold and magnesium reflector while heating the same. 
reflector section with heat shields 40 to form an oven 5. A method of making a curved reflector as claimed 
as shown in FIG. 7. This temperature is maintained for in claim 4 includiqg the step of cooling the mold and 
about one hour as atmospheric pressure forces the mirror magnesium reflector to about 200" F. prior to releasing 
section to conform to the surface of the mold 24. 30 the vacuum. 
'This assembly is slowly cooled to approximately 200' 6. + method of making a curved reflector as claimed 
F., and the vacuum is then released. The mirror section in clalm 1 jncluding the step of sealing the marginal pe- 
is removed from the mold 24 for subsequent machining. ripheral edge of the plate and the adjacent surface of the 
Edge machinisg and bolt hole drilling is done on a forming mold after the heated plate is bent into peripheral 
vacuum machining fixture which is identical with the 35 contact with said mold and prior to evacuating the space 
mold 24 except no heaters are required. Accurate hole therebetween. 
diilling is accomplished by positioning two adjacent sec- 7. A method of making a reflector as claimed in claim 
tions on the machining fixture and drilling body fit bolt 1 including the steps of 
holes. The mirror sections are rigidly held on the machin- forming p plurality of plates on the same mold, and 
in'g fixture by vacuum in the same manner as the sections 40 assembling said formed plates into a reflector. 
are .held on shaping mold 24. The sections are then in- 8. A method of making a reflector as claimed in claim 
dividually cleaned, epoxy coated, and aluminized for 7 including the steps of 
high reflectivity prior to final assembly. machining the edges of each of said formed plates 
,While a preferred embodiment of the invention has while positioned and held by vacuum on a fixture 
Liken shown and described, it will be ap$reciated that 45 having a surface idenhkal ,with the forming surface 
various modifications may be made to the disclosed meth- of said mold. 1 
od and apparatus without'departing from the spirit of References Cited 
 the^ invention or the scope of the subjoined claim; UNLTED STATES PATENTS 
What is claimed is: 
, A method of making a reflector having a reflecting 50 2,858,603 11/1958 Hmmann ---------- 113-116 
surface with a compound curvature comprising the steps 3,067,507 12/1962 Titus ---,-----,,-,,, 2 9 4 7 5  
of 3,342,049 9/1967 Devine -------------- 72-364 
polishing one surface of a flat plate to a final surface R ~ ~ H m  J. HERBST, .Primary Exa-er finish, 
machining smening riLs on the opposite surfabe of 55 . ,  . U.S. C1. X.R, ' 
. said flat plate? 2 9 6 2 8 ;  72-364 ' 
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Method and apparatus for making curved reflectors Patent

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