A technique is described for more reproducible fabrication of electromagnetic levitation coils. A split mandrel was developed upon which the coil is wound. After fabrication the mandrel can be disassembled to remove it from the coil. Previously, a full day was required to fabricate a levitation coil and the success rate for a functional coil was only 50 percent. About eight coils may be completed in one day using the technique developed and 95 percent of them are good levitation coils

Abbaschian, G. J.

Curreri, P. A.

Ethridge, E. C.

Theiss, J.

English

NASA Technical Reports Server

NASA 
Technical 
Memorandum 
NASA TM-82565 
ELECTROMAGNETIC LEVITATION COl L FABRICATION 
TECHNIQUE FOR MSFC CONTAINERLESS 
PROCESSING FACl LlTlES 
E. C. Ethridge, J. Theiss, P. A. Curreri, and G. J. Abbaschian 
Space Science Laboratory 
November 1983 
Nat io~al  Aeronaut~cs and 
Snace Adml~lstration 
George 6. Marshall Space Flight Center 
M S F C  - Form 3190 (Rev.  May 1983) 
https://ntrs.nasa.gov/search.jsp?R=19840010467 2020-03-20T23:24:49+00:00Z
Electromagnetic Levitation Coil Fabrication Technique 
I for MSFC Containerless Processing Facilities I 
George C. Marshall Space Flight Center 
Marshall Space Flight Center, Alabama 358 12 
National Aeronautics and Space Administration 
Washington, D. C. 20546 
Technical Memorandum 
1.1, SPONSORlNG AGENCY CODE 
I 
15. SUPPLEMENTARY NOTES 
Prepared by Space Processing Division, Space Science Laboratory, Science and Engineering. I I 
The technique described in this report has facilitated the more reproducible fabrication of 
electromagnetic levitation coils. A split mandrel has been developed upon which the coil is wound. 
After fabrication the mandrel can be disassembled to remove it from the coil. Previously, it required 
a full day to fabricate a levitation coil. The success rate for a functional coil was still only 50 percent. 
With the new technique described in this note about eight coils may be completed in one day and 1 
Electromagnetic levitation 
Electromagnetic coil 
Containerless processing 
Unclassified - Unlimited 
- pp - -- 
hlSFC - Form 32927*y 1969) 
For sale by National Technical Information Service. Springfield, Virginia 
221 61 

TABLE OF CONTENTS 
Page 
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1 
COIL DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  1 
COIL FABRICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2 
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  3 
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15 
BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15 
iii 
Figure Title 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  10kW Lepelgenerator 
Laboratory vacuum system used for containerless processing experiment 
development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Top view into the vacuum chamber 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Top and bottom view of a set of levitation coils 
. . . . . . . . . . . . . . . .  Schematic of a levitation coil with hypothetical magnetic field lines 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Electromagnetic levitation coil winding jig 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Steps 1 and 2 in winding a levitation coil 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Steps 3 and 4 in winding a levitation coil 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Steps 5 and 6 in winding a levitation coil 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Step 7 attaching fittings to  the levitation coil leads 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  Photograph of the lead connector jig 
Page 
4 
TECHNICAL MEMORANDUM 
ELECTROMAGNETIC LEVITATION COIL FABRICATION TECHNIQUE FOR 
MSFC CONTAINERLESS PROCESSING FACILITIES 
INTRODUCTION 
Containerless processing is expected to  be of great importance to the materials processing in 
space program. One traditional way to  achieve containerless levitation of molten alloys is with elec- 
tromagnetic induction techniques. Typically a multi-kW induction generator operating in the 400 kHz 
frequency range is used to  provide the power delivered to a coil. The coil is inductively coupled to  
the metallic sample in it. Sample heating results from eddy current loss while levitation arises from 
Lorentz magnetic forces due to  the interaction between eddy currents in the sample and applied 
currents in the coil. 
The electromagnetic levitation facilities at Marshall Space Flight Center (MSFC) consist of a 
10 kW, 400 kHz Lepel generator installed at the 100 m drop tube and another 15 kW Lepel generator 
in the containerless processing facilities of the Space Science Laboratory. Figure 1 illustrates the 10 kW 
Lepel generator that is now installed at the drop tube. Figure 2 illustrates the laboratory vacuum system 
used for containerless processing experiments and for testing drop tube coils while Figure 3 shows a 
levitation coil in position in the chamber. 
The levitation coil designed during this work has successfully levitated and melted a variety of 
alloys including Cu, Ag, Ag-Ni, Cu-Fe, Fe-C, and Nb-Ge. The highest sample melt temperature achieved 
was 2400°C for the Nb-Ge samples. W was levitation heated to  2700 '~ .  
Efficient inductive coupling between the levitation coil and the sample is critical t o  both heating 
and levitation. The total length of tubing in the coil, the diameter of the turns, the tightness of the 
turns, and the spacing of the turns affect this coupling. The fabrication of levitation coils has tradi- 
tionally been an art. It has been our experience that if one tries to  manually wind several "identical" 
coils, the coils do not respond in the apparatus in the same way. A few of the coils will efficiently levi- 
tate and melt test samples such as Cu while other coils may levitate Cu but will not melt it. The 
purpose of this paper is to  describe a technique for making coils that is much more reproducible than 
manual freehand winding onto a mandrel. 
COIL DESIGN 
Efficient design of an electromagnetic levitation coil ultimately is the limiting factor in successful 
levitation melting of a given sample. Theoretical work on coil design coupled with trial and error coil 
fabrication techniques have proven successful in levitation of a large number of materials as listed in 
Table I [1,2,3]. The fabrication of coils that produce successf~il evitation with a given eleclromagiletic 
levitation facility largely rernains an a r t  Also the coil designs in the literature are in general suitable to 
a specific range of materials due to the electrical and magnetic properties as well as the sample diameter, 
density, and melting temperature. 
A conductor placed in an electromagnetic field will move from a stronger to a weaker part of the 
field. For levitation to occur, a lifting force must be generated by a field strength decreasing in the 
upward vertical direction. Two coaxial coils generating opposiiig magnetic fields provide this requirement. 
To obtain lateral stability, the field strength must decrease radially toward the field axis providing a 
rcstoskg force toward the center of the coil. In general, a levitation coil is composed of two parts. The 
lower part provides levitation forces and heating to  the sample while the upper oppositely wound bucking 
coil keeps the sample forced down into the heating coil. 
Empirical studies [4] have shown that a design with the lower coil of conical shape with an angle 
of about 30 deg (each side 15 deg off vertical) gives maximum stability. If a larger angle is used, the 
lateral stability tends to  decrease. Figure 4 shows a bottom and top view of a coil with seven turns 
below the sample and two turns above it used in our laboratory to  levitation melt, undercool, and 
solidify metals. Figure 5 is a schematic which illustrates the magnetic field distribution in a typical coil. 
The equilibrium position for a sample is indicated by the letter S. The precise position of the sample 
ultimately is determined by the magnetic forces lifting the sample and the gravitational forces pulling 
down on the sample. 
Some degree of temperature control can be obtained by adjusting the output power level. 
Control runs contrary to  first impression. For most materials, to increase the heating effects thereby 
increasing the sample temperature, the power must be lowered so that the sample rests lower in the bottom 
coil where the ratio of coil diameter to  sample diameter is smaller. The spacing between the upper and 
lower coils also provides some control over heating. Larger spacings result in less heating than small 
spacings. 
With a constant electrical current in the coil, the levitation force increases with the number of 
turns. Thus, the smallest diameter tubing possible is generally used in order t o  obtain more turns per 
unit length of coil. Practically, 118 in. diameter tubing (0.020 in. wall thickness) is about the smallest 
that can be adequately cooled. 
COl L FABRICATION 
The technique developed for fabricating coils on a reproducible basis is based upon a split mandrel 
jig. With the split mandrel it is a relatively simple process to  wind coils such that the coil parameters 
are held constant. Figure 6 is a photograph of the jig with a partially wound coil in position. Figures 
7, 8, and 9 illustrate the winding process. 
The first step in fabricating a levitation coil is to cut a piece of precision bore copper capillary 
tubing. For our two induction heaters we used two different sizes. Number 3 Precision-Bore Restrictor 
Capillary air conditioning tubing (BULLET Restrict0 Cap) 0.095 in. OD and 0.053 in. ID was found to  
be most satisfactory for the 10 kW generator installed on the 100 m drop tube while Number 4 (0.120 
in. OD and 0.063 in. ID) with the larger inside diameter was required for use with the 15 kW generator 
in our containerless processing laboratory. A section of tubing about 36 in. long is cut. It is then 
positioned as shown in Step 1 of Figure 7. In the first step the inside four turns of the lower coil are 
wo i l~d  tightly against the mandrel. In Step 2, the other lead is wound three turns in the opposite direc- 
tion and spaced between the willdings of the first layer. This completes the bottom coil with two layers 
of windings having a total of  seven turns. Step 3 (Fig. 8) illustrates how a loop is fabricated that 
connects the lower coil with the upper bucking coil. First three forms are positioned in the jig in order 
to  accurately position the bends. Then a 90 deg bend is made at form A. Form A is then removed and 
a 180 deg bend is made at form B. At this point the coil is as illustrated in Figure 8 Step 4 and is 
ready for making the bucking coil. The lead is bent around the upper cylindrical mandrel 2-112 turns 
as indicated in Step 5. 
At this point the coils are wound but the leads need to be bent and positioned to fit into the 
connections on the electromagnetic induction furnace. A form block is installed and the leads pressed 
against grooves in the block (Step 6, Fig. 9). The final step is to attach the leads to Swagelock connec- 
tors. The position of the connections on the coil are very important since the center of the coil must 
be precisely positioned over the center of the drop tube. This is achieved using another jig (Fig. 10, 
Step 7). Each lead is fitted with a Swagelock connector and an adaptor sleeve turned out of brass. The 
coil is then mounted on the horizontal rod and the connectors attached to  the jig (Fig. 1 I). While posi- 
tioned in the jig, the coil lead is silver soldered to the adapter sleeve. The coil is then removed and the 
leads cut flush with the end of the connector, deburred, and slightly flared. Processing time is about 
1 hr from starting with the cut piece of tubing until ending with a completed coil with connectors 
attached. 
Forming the coil with a fiberglass sleeve has been found to be convenient. The sleeve serves to  
electrically insulate the coils as well as to precisely set the spacing between turns. The sleeving also tends 
to protect the coil from samples that jump out of levitation. One source of tubing used is Refrasil 
Sleving (HITCO, Gardenia, California). 
CONCLUSIONS 
A technique has been developed for fabricating electromagnetic induction coils in a reproducible 
manner. The process utilizes a split mandrel upon which the coil is wound. After winding, the mandrel 
is disassembled to remove the mandrel from the coil. The technique has increased coil production rates 
by a factor of 8 over the freehand winding method. The success rate for producing a functional levita- 
tion coil has been increased from 50 to 95 percent. The coils can reliably melt a number of alloys with 
melting points as high as 2400°C. It is possible in some cases to acheive sample temperatures as high as 
2700°C. 
Figure 1. 10 kW Lepel. generator. 
Figure 2. Laboratory vacuum system used for containerless processing experhent development. 
Figure 3. Top view into the vacuum chamber. 
Figure 4. Top and bottom view of a set of levitation coils. 
Figure 5. Schematic of a levitation coil with hypothetical magnetic field lines. 
Figure 6. Electromagnetic levitation coil winding jig. 
\ 2" BOLT FOR HOLDING MANDREL TOGETHER 
KING COIL MANDREL 
) ~ L E V ~ T A T ~ ~ N ~ H E A T I N G  COIL MANDREL 
STEP 2 
Figure 7. Steps 1 and 2 in winding a levitation coil. 
Figure 8. Steps 3 and 4 in winding a levitation coil. 
1 1  
Figure 9. Step 5 and 6 in winding a levitation coil 
12 
Figure 10. Step 6, attaching fittings to the levitation coil leads. 
Figure 11. Photograph of the lead connector jig. 
REFERENCES 
I .  Polonis, D. H., Butters, R. G., and Parr, J. B.: Levitation Melting Titanium and Titanium Alloys. 
Research, Vol. 7, 1954, p. 5 10. 
2. Peifer, W. A.: Levitation Melting - A Survey of the State of the Art. J. Metals, Vol. 17, 
1965, pp. 487-493. 
3. Downey, J. W.: Levitation Melting of Metals and Alloys. ANL-7398 Argonne National Labs., 
Metals, Ceramics and Materials (TID-4500) AEC Res. and Dev. Report, December 1967. 
4. Slater, W. J., Barton, J. W., and Taggard, R.: Science and Industry, Vol. 7, 1960, pp. 89-96. 
BIBLIOGRAPHY 
Abbaschian, G. J. and Ethridge, E. C.: Containerless Electromagnetic Levitation Melting of Cu-Fe and 
Ag-Ni Alloys. NASA TM-825 5 3, September 1983. 
Comenetz, G. and Salatka, J. W.: Ten-Gran Levitation Melted Ingots. Electrochem. Soc. J., Vol. 105, 
1958, pp. 673-676. 
Ethridge, E. C. and Curreri, P. A. : Containerless Electromagnetic Levitation Processing in Microgravity 
Conditions. Electromagnetic Moldless Casting, North Holland Publihsing Company, 1983. 
Okress, E. C., Wroughton, D. M., Comentz, G., Brace, P. H., and Kelly, J. C. R.: Electromagnetic 
Levitation of Solid and Molten Metals. J. Appl. Phys., Vol. 23, 1952, pp. 545-552. 
ELECTROMAGNETIC LEVITATION COIL FABRlGATlON TECHNIQUE FOR 
MSFC CONTAINERLESS PROCESSING FACIblTlES 
By E. C. Ethridge, J. Theiss, P. A. Curreri, and G. J. Abbaschian 
The information in this report has been reviewed for technical content. Review of any informa- 
tion concerning Department of Defense or nuclear energy activities or programs has been made by the 
MSFC Security Classification Officer. This report, in its entirety, has been determined to be unclassified. 
I I 
A. J. DESSgER 
Director, Space Science Laboratory 
f? U.S. GOVERNMENT PRINTING OFFICE 1984-746-070/124 


Electromagnetic levitation coil fabrication technique for MSFC containerless processing facilities

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