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. Research And Development Techniques For' Fabrication Of Lightq,.veight_%larConcentrators

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Addendum to EOS Report 2100-Final Contract NAS 7-8623 December 1962

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i} Addendum ReportI

RESEARCH AND DEVELOPIENT TECHNIQUES FORFABRICATION OF LIGHTWEIGHT SOLAR CONCZNTRATORS

Prepared for

National Aeronautics and Space Administration

801 19th Street, N.W., Room 526

Washington 25, D.C.

Attn: Mr. Waltcr Scott, Code DA

Contract NAS 7-86

EOS Report 2100-Addendum 21 December 1962 '

{r

Prepared by the staff of

Engineering Deve_ opment DepartmentM A. Pichel

Froject Supervisor

I Approved by Approved byI

l Lee M. Springer J. Neustein ;}

M_nager Manager '_"

Engineering Beve!opment Department Advanced Pc_er Systems Division

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ELECTRO-OPTICAL SYSTEMS, INC. - PASADENA_ CALIFORNIA _i

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1965010096-002

CONTENTS

I. INTRODUCTION 1

2. FABRICATION COATING ANO TESTING OF 5-FOOT DIAMETER

CONCENTRATORS 3

2.1 Fabrication cf the Copper Concentrator 3

2.1.1 Copper Anode Array 3

2.1.2 Fabrication Procedure 3

2.2 Coating the Second Nickel Concentrator 7

2.3 Coating the Copper Concentrator 7

2.4 Calorimetric Testing 8

2.4.1 Calorimetric Test Results 8

3. SUMMARY II

FIGURES

I Concentrator assembly 2

2 Anode array - copper 4

3 Master and anode assembly

4 Electroforming in progress - skin, copperconcentrator 6

5 Mandrel preparation for plating torus to skin 6

6 Test results, 60-POM3:RI2 (second nickel

concentrator) 9

7 Test results, 60-POM3:RI3 (copper concentrator) I0

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2100-Addendum i

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1965010096-003

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i. I_RODUCTION i

i This report gives the results of final experimental work conducted

during a six-week extension of the technical work on Contract NAS 7-86.

i During this period, fabrication of the 5-foot di_rleter copper concen-trator was completed. This unit and the second J)-foot diameter nickel

i concentrator were coated and te3ted. The dimensions and configuration: of these concentrators are shown ir Fig. i.

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2. FABRICATION COATING AND TESTING OF 5-FOOT DIAMETER CONCENTRATORS

2.1 Fabrication of the Copper Concentrator

The electroforming of a complete copper solar concentrator _as

accomplished usin_ essentially the same ma_ter preparation procedure

developed during the preceding work on n_ckel mirrors. The master used

in the completion of the second nickel mirror (master No. 60-POH3) was

employed. The procedures used to prepare the master for skin plating

and silver sensitLzing were identical to the steps outlined on pages

124-127 of EOS Report 2100-Final.

2.1.1 Copper Anode Array

The anode array used in making the copper concentrator

conformed to the geometry of the master and was basically similar to

that used in earlier copper plating work conducted under Contract NAS

7-10. Modifications for current use included an auxil_ary anode assembly

holding a copper bar anode _hac was 16 x 1½ x 1/16 inches in size, and i

certain special support arrangements. A lower view of the array is shown

in Fig. 2_ The purpose of the auxiliary unit was to augme_,t the electro-

deposition of sufficient material into the groove area on the rim of the

skin. The auxiliary anode shape and the arrangement of the attendant

gusher were similar to the auxiliary anode array used in the previous

nic!:ei work.

The entire anode array was suspended from the master

holding fixture shown in Fig. 3.

2.1.2 Fabrication Procedure

As stated above, all steps in preparing _l_e master for

plating were the same as in previous work on nickel concentrators°

However, in the actual plating, attention was given to several plating

I requirements peculiar to the electroforming of copper. Experiments on

"_ ,.L 2100-Addendum 3

1965010096-006

FIG. 2 ANODE ARRAY - COPPER

FIG. 3 MASTER AND ANODE ASSEMBLY

2100-Addendum 4

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1965010096-007

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the effect of plating parameters on physical properties of electro-

depositcd copper (Ref. 2100-Final, pages 79-81) had indicated that the

current density i.ust be relatively high. Therefore, in the plating of

the copper concentrator, a current density of 65 amps/ft 2 at 96°F was

i selected. Extra rectifier capacity ,and connecting bus bars and cableswere provided. During the plating of the concentrator face skin, a

careful watch of the various electrical connections was maintained;

I especially those onto the Tim and center plate of the master. A moder-

ate heat rise occurred in tfe two connections to the center plate.

1 However, no burnout on the _dge of the pi=ti g appeared. A copper sul-

phate plating solutio, was used, simila_ to that employed in the physi-

cal properties t=st program, with Dayton-Bright hardening additive (Ref.

2100-Final, page 81, S'_mple F-71). The plating arrangement is shown in

' Fig. 4.

The master used ±n plating the copper concentrator

was 60-POM3, the same master as was used in the latter portio_ of the

work in nickel. Sol=r= using, _be c'racks in the glass u._erwent further

repair. Bridge blocks_ "_,ich had worked loose, wzre refastened using

epoxy resin. The epoxy was a1_o used in repaic_ng h_!es along the cracks

in the surface _.f th_ glass.

fhe first copper plated skin was sche4_led to be a test

skin. H_ever, when it was completed, the quality _i _.F_,earance sug-

gested that it should be considered for incorporatio4 _'o a completeji,

concentrator. The techaique of estimating material d_stribution of a

skin resulting from a given anode-cathode relatiop _L_ had be=n checked

favorably in the work _',,nickel concentrators. _ c_,:.sion was then made

to proce_ directly to the comFletion of a c,,o_.,_"c ncentrator. The

torus flange mandrel preparatio_ was similar _ tte procedures used with

nickel concentrators, with the _ame _lange d_s¢_a as on the second nickel

concentrator (60-POM3: RI2). The prepared mandrel flange is shown in

Fig. 5. During th_ plating of the torus flange, 8 bar anodes were used.

The bath temperature (96°F) and current density (65 amp/ft 2) used on the

2100--Addendum 5

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1965010096-008

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FIG. 4 ELECTRO_ORMING IN PROGRESS - SKIN, iCOPPER CONCENTRATOR

FIG. 5 MANDREL PREPARATION FOR PLATING TORUS

TO SKIN

2100..Addendum 6

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1965010096-009

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Iskin plating were held, and the rotation was periodically reversed to

avoid excessive buildup on the sides of the numerous small holes in the

: torus useJ for lock-plating the flange. Partin_ o_ the cc.,pleted e!ec-

troform w_s uneventful, and the concentrator was put into the process of

; cleaning the mandrel wax out of the torus area preparatory to coating.

2.2 Coating the Second Nickei Concentrator

The second nickel concentrator (60-POM3: RI2) was coated in

the same manner as the first concentrator, at a rented 6-foot diameter

vacuum coating facility. Coatings of chromium, silicon monoxide, and

aluminum were applied, as with the first concentrator. The coating ap-

paratus, inclu_ing EOS-supplied electrodes, glow discharge ring, and

vapor sources performed as expected, and the coating process was suc-

cessful. Pressure-sensitive tape tests indicated that the coatings were

firmly adherent.

2.3 Coating the Coppe r Concentrator

The copper concentrator (60-POM3: RI3) w_s to be given the

same type vacuum deposited coatings as were applied to the two nickel

i concentrators. The same 6-foot diameter facility was rented and themirror was placed in the chamber, which was then pumped down to a vacuu,r

of auproximately 1.5 x I0-5 nm, of Hg. The chromium _nd silicon monoxide

were deposited in the same manner used with the nickel units. However,

: during deposition of the aluminum reflective layer an electrical failure

] occurred in the rectifier used to supply power for evaporation. There

was no interruption in the vacuum during a temporary repair period of

35 minutes, after which time the aluminum was promptly deposited. Upon

removal from the chamber, however, the pressure-sensitive tape test ;

revealed low adherence of the coating, even tl,ough it presented a good

appearance. Two days later the coating had started to flake off, and

appearance steadily deteriorated, Apparently the time lapse between the

I silicon monoxide and aluminum coatings allowed contamination of the sur-

face. The mirror was allowed to proceed to testing because the

'_ _ 2100-Addendum 7 .

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1965010096-010

possibility existed that _'tripping the partially adherent coating might

degrade the quality of the mirror, and the area affected by the flaking

was only an estimated one-tenth to one-fifth of the surface.

2.4 Calorimetric Testing

The concentrators produced during this final technical phase

were tested for efficiency, employing the calorimetric technique detailed

in EOS Report 2100-Finai (pages 128-129).

2.4.1 Calorimetric Test Results

Concentrator 60-POM3: RI2, the second nickel concen-

trator, represents a moderate improvement in efficiency over the first

all-nickel concentrator, 60-POMb: R7. An average efficiency of 64.2

percent with the I/2-inch orifice is still somewhat below the level

desired on this program. Peak performance at the 2-inch diameter orifice

was approximately 84 percent. An overall edge roll, effecting a 5_nd

I to I_ inches in width at the periphery, reduced performance somewhat

and prevented "peaking" of perforL_ance at smaller orifice sizes. Much

of the loss, however, may be attributed to several deformities in the

skin, resulting from the degraded master and related parting difficL:Ities.

Test results for this unit are given in Fig. 6.

The copper concentrator, 60-FOM3: RI3, yielded a hi_er

efficiency than either of the two nickel units, with an average of 68

percent efficiency at the i/2-inch orifice. As in the case of the nickel

units, it had some distortions due to poor master quality and parting,

and the test results indicate the effect of the poor adherence of the

aluminum coating. Test results are presented in Fig. 7. The overall

geometry was better than either of the two nickel concentrators, as

evidenced by the flatter performance curve in the larger orifice region.

Extrapolation of the measured performance to the higher Teflectivity

value, which would be experienced with a better reflectJve coating,

indicates a performance capability of _5 to 80 percent with the i/2-inch

orifice diameter.

2100-Addendum 8

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1965010096-011

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FIG. 6 TEST RESULTS, 60-POH3: RI2 (SECOND NICKEL CONCENTRATOR)

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FIG. 7 TEST RESULTS, 60-POM3: RI3 (COPPER CONCENTRATOR)

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1965010096-013

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3. SUI_4ARY

The completion of several representative concentrators during thet

course of this program further confirms the feasibility of producing

high-efficiency solar concentrators entirely by the electroforming

process.

_,e basic design approach was directed coward development of an

improved concentrator configuration having a maximulm diametex of 60

inches and employing a rear-mounted corus to provide necessary rigidi-

zation and points of attachment without sacrificing the high performance

and lightweight characteristics of previous aIl-electroformed units.

These concentrators illustrate the practicality of the design that re-

quires a secondary plating operation for effective locking together of

the torus and reflective akin into an efficient, thin-shelled structure.

Although the final edge configuration (Fig. 1) does not give a fulI

60-inch diameter reflective area due to the edge radius required and

associated edge effect, the design does represent a considerable improve-

ment over the front-mounted torus used earlier.

Tests of the three representative concentrators resulted in per-

formance levels which were somewhat lower than desired. However, the

progressive, step-by-step increase in performance, which was evident

with each successive concentrator produced, indicates that a continued

production effort involving further development of the techniques asso-

ciated with this modified design concept, especially those related to {

the control of the edge effect and parting procedures, plus the use of

better masters, will substantially improve concentrator efficiency.

[1•_ 2100-Addendum II

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