Forming mold for polishing and machining curved solar magnesium reflector with reinforcing rib

Reader, A. F.

Russell, W. E.

Werner, E. A.

English

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A. F. READER 
APPARATUS FOR MAKING CURVED REFLECTORS 
iglnai Fi led  Aug. 23, 1367 3 Sheets-Shcci L 
INVENTORS 
AUSTIN F. READER 
- 
WALTER E. RUSSELL 
BY EDWARD A. WERNER 
T T O R N E Y  
Nov. 24, 1970 A. F. READER fl AL 3,541,825 
APPARATUS FOR MAKING CURVED REFLECTORS 
Original  F i l e d  Aug. 23 , 1967 3 Sheets-Sheet 2 
INVENTORS 
AUSTIN F. R E A D E R  
WALTER E. RUSSELL 
EDWARD A WERNER 
ATTORNEYS, 
Nov. 24, 1970 A.  F. READER AL 3,541,825 
APPARATUS FOR MAKING CURVED REFLECTORS 
Originai  F i l ed  Aug. 23 , 1367 3 Sheets-Sheet J 
INVENTORS 
AUSTIN F: READER 
WALTER E. RUSSELL 
EDWARD A. WERNER 
- - 
ATTORNEYS 
3,541,825 United States Patent Ofice Patented 24, 1910 
P 2 
These and other objects of the invention will be ap- 
3,541,825 
APPARATUS FOR MAKlrNG CURVED parent from the specification which follows and from the 
REFLECTOIRS drawings wherein like numerals are used &soughor-rt to 
Anstin F. Reader, Brunswick, Walter E. Russell, Lorain, identify like parts. 
and Edward A. Werner, Parma, Ohio, assignors to the In the drawings, 
United States of America as represented by the Ad- FIG. 1 is a perspective view of a rigid solar mirror 
ministator of the National Aeronantics and Space Ad- constructed in accordance with the *resent invention; 
minis&ation 
Original application Aug. 23,1967, Ser. No. 662,829, now 
Patent No. 3.490.4635. dated Jan. 20, 1970. Divided 
and this appliiiati~n d a y  26, 1969, Se;. No. 852,131 
Int. 61. B21d 11/10,11/20 
U.S. CI. 72-60 4 Claims 
- - 
ABSTRACT OF THE DPSCEOSmE 
Fabricating and forming each curved segment of a light 
weight mirror by polishing one surface of a flat mag- 
nesium plate and then machining stiffening ribs in the 
other side. Each plate is accurately formed on a single 
mold with the application of heat and pressure after the 
machining. 
The invention described herein was made by employees 
of the United States Government and may be manufac- 
tured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
STATEMENT OF COPENDENCY 
FIG. 2 is a plan view of one sectio; of the solar mirror 
shown in FIG. 1 illustrating the reidorcement on the 
back side; 
FIG. 3 is a perspective view of a forming mold utilized 
in the method of the invention; 
FIG. 4 is an elevation view showing the start of the 
forming and shaping of a mirror section; 
FIG. 5 is an elevation view showing a later stage in the 
forming and shaping operation; 
FIG. 6 is an enlarged section vievv taken along the line 
6-6 in FIG. 5; and 
FIG. 7 is an elevation view showing the find heating 
operation. 
Referring now to the drawings, there is shown in FIG. 
1 a rigid solar mirror 10 in the form of a shallow bowl 
that is constructed in accordance with the oresent in- 
vention. The mirror 10 is circular in shape and has a 
reflecting inner surface 12. A centrally disposed opening 
14 receives a solar generator. The reflecting surface 362 
extends between an outer peripheral edge 16 of the 
mirror 10 and an inner edge 18 about the circular opening 
14. The surface 12 is in the form of a paraboloid for 
properly focusing the sun's rays at the beat recciver for 
This is a division of application Ser. NO. 662,829, filed the generator in the Opening 14. 
Aug. 23, 1967, now Pat. No. 3,490,405. Solar mirrors are quite large. By way of example, a 
This invention is concerned with making a curved re- Brayton cycle system will utilize a solar mirror having 
fiector having a thin cross section. More particularly, the a diameter of 20 feet to generate 3 to 4 kilowatts of elec- 
invention relates to a method of fabricating and forming 35 trical power. A similar mirror 30 feet in diameter will 
segments of a solar mirror having compound curves in provide 8 to 10 kilowatts of electrical Power in such. a 
which the reflecting surface is polished prior to any System. 
maching of the opposite surface. Because of their large sizes, solar mirrors are made 
A problem encountered in space flight is that of pro- in separate sections 20 such as shown in FIG. 2. These 
viding the craft with sufficient electrical power. One ap- 40 sections 20 are subsequently assembled h t o  a mirror 10 
preach to solving this problem is the utilization of a Bray- shown in FIG. 1. A twenty-foot-diameter mirror 10 has 
ton cycle system in which the sun's heat is supplied to been constructed in accordance with the inventioil by 
a boiler or heat receiver from a large diameter solar utilizing twelve identical sections 20 that are bolted to- 
mirror. The mirror should have an accurate reflecting gether- 
surface so that as much solar heat as possible can be 45 The under side of the mirror 10 opposite the reflecting 
collected and channeled into the system. Such a mirror surface 12 is ribbed for strength and rigidity as shown 
is quite large and is made up of sections. The weight of in FIG. 2. Ribs 22 in the form of deep rectangular grids 
such a mirror must be kept to a minimum. are used to achieve maximum weight reduction. The re- 
The fabrication of the large compound curved surfaces flecting surface has a thickness of about 0.050 inch, and 
for these mirrors presents difficult problems. Conventional 50 the rib height tapers from 0.62 inch adjacent the edge 
manufacturing techniques have not been satisfactory for 18 of the opening 14 to 1.00 inch at the outer edge 16. 
producing rigid, lightweight sectors to  the dimensional Referring to FIG. 3 there is shown a paraboloidal 
and surface accuracy required. Such accuracy with sta- shaped 24 wed to form the sections 20 of 
bility requires a smooth continuous reflecting surface sup- mirror 10. The mold 24 is of aluminum and has a highly 
ported by an integral stiffening structure. ~h~ weight 55 polished forming surface 26 for engaging the mirror sec- 
limitation placed on such mirrors necessitate structures tions and forming the reflecting surfaces 12. B;rmves 98 
having thin cross sections. in the surface 26 aid in this forming process in a manner 
The fabrication problems have been solved by producing which will be described later in greater detail. Clamps 
reflector segments in accordance with the present inven- 60 30 positioned about the mold 24 are used to draw the 
tion. Polishing of the reflective surface is prior peripheral edge portions of the reflecting surface 12 into 
to  any machining. Each mirror segment is then machined contact with the forming surface 26 when a rnirrw section 
and formed to the proper configuration on a mold by is heated. Electric heaters within the convex mold 24 are 
utilizing heat and pressure. connected to a suitable power source by leads 32. 
It  is, therefore, an object of the present invention to According to the invention, each mirror section is 
provide an efficient method and apparatus for producing 65 machined from a flat magnesium plate having a highly 
lightweight reflectors having high quality reflecting Polished surface. The machined plate is &en formed 
surf aces. into the required paraboloidal shape on the mold 24. 
Another object of the invention is to provide a method The flat plate is first contoured to the outline of the 
and apparatus for producing large reflectors having high section shown in FIG. 2. Then one surface of the flat 
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. PIG. 2 are formed on the reverse side by milling out 
3 4 
metal in predetermined areas after the opposite surface While a preferrcd embodiment of the invention has been 
has been polished. Each central rib has a uniform thick- shown and described, it will be appreciated that various 
ncss 01 abors"L.075 inch while the outer circumferential modifications may be made to the disclosed method and 
sib is abo~lt 0.75 inch thick and has a thirty-degree tilt apparatus without departing from the spirit of the invcn- 
to form a bolting base for the rim of the mirror 310. tion or the scope of the subjoined claims. 
After the rlbs have been machined on the back surface What is claimed is: 
of th, magnesium plate, the flat segment is placed on the 31. Apparatus for making a curved reflector from a 
n1o1d 24 as shown iil FIG. 4. Clamps 30 engage peripheral flat plate having a highly polished reflecting surface com- 
edge pol:rons of the machined plate for proper position- prising 
~ng. a mold having a forming surface for contacting said 
Current is passed through heaters within the mold 24 polished reflecting surface on said plate, 
from the lcads 32 thereby heating both the mold and means for heating said plate to the softening tempera- 
nlate to an clevated temperature at which magnesium lure, 
;tarts to soften. The mold 24 typically contains about 80 a plurality of clamps positioned about the periphery of 
kilowatts 01 resista-ice heaters. The mold 21 is heated to 15 said mold for engaging marginal surface portions of 
about 400" F., and the clanlps 30 are tightened as the said hzated plate and bending the same into con- 
edgec of the machined plate bends into contact with the formity with said forming surface, 
iurface of the rndd as shown in FIG. 5. Pins 34 extend- means for evacuating the space between said forming 
3ng outward from the forming surface 26 pass through surface and said polished reflecting surface for forc- 
openings m the section 20 and guide the surface 12 into 20 ing said plate into contact with said forming surface, 
proper engagement with the forming surface. and 
The section edge to mold joint is then sealed with high means for heating said mold and said formed plate to 
temperature silicon adhesive tape 36 about the entire an elevated temperature to  stress relieve said plate 
periphery, A vacuum is established in the space between while the same is forced into contact with said mold 
the surface 12 of the mirror section 20 and the forming 25 by saidvacuum. 
surface 26 of the mold 24 to bring these surfaces into in- 2. Apparatus for making a curved reflector as claimed 
tinlate contact. The creation of this vacuum is faciliated in claim 1 including 
by the grooves 28 which are in communication with pas- a plurality of heaters in said mold for heating said 
sages 38 that extend through the mold 24 lo a suitable plate. 
vacuum pump. 20 3. Apparatus for making a curved reflector as claimed 
Aiiez. rhc section 2,O has been drawn into contact with in claim 2 including 
the mold 24, both ale heated to approximately 550" F. a plurality of heat shielda about said niold and aaid 
This hcdtlng is facilitated by surrounding the mold and fo~med plate for forming an oven. 
reflector section with heat shields 40 to form an oven as 4. Apparatus for making a curved reflector as claimed 
shown In FIG. 7. Ihis  temperature is maintained for 35 in claim 1 wherein said forming surface has a plurality 
about one hour as atmospheric pressure forces the mirror of grooves therein and said mold has a plurality of pas- 
section to conform to the surface of the mold 24. sages in communication with said grooves and a vacuum 
This assembly is slowly cooled to approximately 200" source. 
F., and the vacuum is then released. The mirror section is References Cited 
rcmoved from the mold 24 for subsequent machining. 40 UNITED STATES PATENTS 
kdge machining and bolt hole drilling is done on a 
vacnium n-iachining fixture which is identical with the 2,752,982 7/1956 Lalli ---------------- 72-342 
mold 24 except no heaters are required. Accurate hole 27944~500 7/1960 Raynes -------------- 72-342 
drilling is accomplished by positioning two adjacent set- 3,3 15,s 13 4/ 1967 Ellenburg ----------- 72-342 
tlons on hhe machining fixture and drilling body fit bolt 45 39342~049 9'1967 Devine --------------- 72-60 
holes. The mirror sectibns are rigidly held on the machin- A. LARSON, Primary Examiner inr fixture bv vacuum in the same manner as the sec- 
ticks are $el2 on shaping mold 24. The sections are then U.S. Cl. X.R. individually cleaned, epoxy coated, and aluminized for 50 72-342 
high reflectivity prior to final assembly. 


Apparatus for making curved reflectors Patent

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