Toroidal transformer cores are often banded together by means of strap. Spot welds secure strap. Proper tension is obtained by use of special fixture in conjunction with winding of wire which is placed temporarily on core; winding is excited by dc current to hold core halves together magnetically during alignment

Mclyman, W. T.

English

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September 1973	 B7340391 
•	 NASA TECH BRIEF 
NASA Pasadena Office
	 4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Flat-Band Assembly for Toroidal Transformer Cores 
The cut halves of toroidal transformer cores are 
often banded together by means of a strap and se-
curing buckle; however, the buckle produces a large 
bump and has sharp edges which could cut into the
temporarily on the core; the winding is excited by a 
dc current to hold the core halves together magnet-
ically during alignment. Subsequently, the temporary 
winding is excited by an ac current so that the B-H 
Spot Weld 
winding that is subsequently placed on the assembled 
core. Additionally, since conventional strapping tools 
permit only coarse tightening of the straps, there can 
be wide variations in the force applied during assem-
bly of cores and, therefore, optimum tensioning in 
terms of a proper B-H loop for each core is difficult 
to attain reproducibly. 
The strap shown in the diagram minimizes protu-
berances on the assembled core because the notches 
permit overlapping to form a smooth periphery over 
the core; the strap is secured by spot welds. Proper 
tension is obtained by use of a special fixture. in 
conjunction with a winding of wire which is placed
loop may be observed on an oscilloscope as the ten-
sion of the band is adjusted. 
The special fixture has a nest for supporting the 
core halves; two pivoted arms, also on the fixture, 
each have a friction arrangement for holding one end 
of the strap. A torque wrench is used to apply tension 
to each strap by rotation of the pivoted arms; after 
being established empirically by observation of sev-
eral core B-H loops on the oscilloscope, the torque-
wrench values are used for guides when tightening 
bands during the assembly of other cores. Final ad-
justment of strap tension is made while observing the 
B-H loop on an oscilloscope as more or less torque is 
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
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applied with the wrench. If too much torque is ap-
plied, the ends of the core halves will distort, and 
there will be an increase in magnetizing current; if 
too little torque is applied, the air gap will be large, 
and a larger magnetizing current will be required. 
After the strap has been tightened properly, the 
notched band at the points of overlap and at the strap 
ends are spot welded, as indicated in the diagram. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP 73-10891
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial de-
velopment should be addressed to: 
NASA Patent Counsel 
Mail Code 1 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Source: Colonel W. T. McLyman of 
Caltech/JPL
under contract to 
NASA Pasadena Office 
(NPO-11966)
N 
BM. 1313 
KSC HQS 
— 1—
S 
B73-10891	 Category 08


Flat-band assembly for toroidal transformer cores

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