A two-phase sintering technique based on time and temperature permits reversible control of the coercive threshold of sintered ferrite cores. Threshold coercivity may be controlled over a substantial range of values by selective control of the cooling rate

Vinal, A. W.

English

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May 1964	 Brief 63-10606 
NASA TECH BRIEF	 Ilk 7 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
New Sintering Process Adjusts Magnetic Value of Ferrite Cores 
Sintering Furnace 
FREE-FALL QUENCHING 
The problem: Manufacturing control of the mag-
netic characteristics of ferrite cores used in memory 
systems of computers and data processing equipment. 
For these purposes it is essential not only to obtain 
the propef threshold coercivity of the magnetic core, 
but also to secure optimum ratio of "one" to "zero" 
electrical response. Standard quality-control proce-
dures dictate that each core be tested before assembly 
and cores not meeting specifications be discarded. 
The solution: A sintering technique based on time 
and temperature that permits reversible control of the 
coercive threshold of sintered cores. The technique, 
called the Quench Rate Annealing Cycle (QRAC), is a 
two-phase sintering process. The first phase is "zero" 
firing and the second phase is the Quench Rate An-
nealing Cycle. Reversible control of the threshold 
coercivity is achieved through control of the quench 
rate of the core when it is removed from the sintering 
temperature.
How it's done: First step in the two-phase cycle is 
to place the cores in a sintering furnace for about 60 
minutes. The "zero" firing is stopped within the time 
range corresponding to the temperature-time product 
that will produce the optimum zero response char-
acteristic. For a given material the cycle may be held 
down by setting the furnace temperature to cause the 
desired temperature-time product to occur within 75 
minutes. Following this treatment, cores can be stock-
piled or reprocessed by the QRAC to establish the 
desired coercive force. 
For the second step, or Quench Rate Annealing 
Cycle, the temperature of the cores is raised to a figure 
not exceeding the temperature of the first cycle firing. 
One of the methods of quenching which produces 
good results, the dual exponential technique, has a 
within-specification yield rate of about 90 percent. 
Dual exponential quenching is actually begun in the 
sintering furnace at the end of the "zero" firing. 
(continued overleal) 
This document was prepared under the sponsorship of the National 
Aeronautics and S pace Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, com pleteness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infrin g e privately-owned 
ri g hts; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000124 2020-03-11T16:48:59+00:00Z
In this process, hot sintered cores are contained in a sible through repetition of the QRAC, utilizing time 
platinum boat, which rests on a substantial thermal- and temperature values selected to yield the desired 
mass brick. The platinum boat is extracted from the product characteristics. For example, cores exhibiting 
hot zone of the sintering furnace by sliding the brick a coercive threshold of 1.3 oersteds may be lowered 
along the hearth plate and onto a similar hearth plate. below 0.9 oersted and then raised above 2.0 oersteds 
The platinum boat ig then placed on a metal slab to by recycling the cores through the annealing cycle. 
cool. Cooling time is determined by a formula which Notes: 
includes the temperature of the boat, ambient temper- I. Salvage of cores rejected for improper values of 
ature, time constant of the platinum boat in contact coercivity may be accomplished at less cost than 
with the metal slab, and thermal conductivity between manufacture of new cores. 
the boat and the metal slab. 2. Since this process has a higher and more predict- Quenching of sintered cores may also be accom-
able rate of yield, automation of the entire process 
plished by the free-fall method. Cores on platinum
may now be considered feasible. boats are removed from the hot zone of the sintering 
furnace in the same manner as in the double expo- 3. For further information about this 	 innovation 
nential technique. Instead of allowing the cooling inquiries may be directed to: 
to take place in thermal contact with a metal plate, Technology Utilization Officer 
cores are allowed to fall freely down a metal cylindri- Goddard Space Flight Center 
cal chamber. The height of the chamber is sufficient Greenbelt, Maryland 20771 
to allow cores to
	
cool	 sufficiently	 before	 striking Reference: B63-10606 
a funnel-shaped collector at the bottom. Patent status:	 NASA encourages the immediate 
As an extension of the free-fall technique, the , tem- commercial use of this invention. It is owned 	 by 
perature gradient along the axis of the cylinder may be NASA and inquiries about obtaining 	 royalty-free 
adjusted through the use of a surrounding radiant rights for its commercial use may be made to NASA 
energy source to yield a specified thermal contour. Headquarters, Washington, D.C. 20546. 
Threshold coercivity may be controlled over a sub- 'I 
stantial range of values by selective control of the Source:	 International Business Machines 
cooling rate. Reversible control of coercivity is pos- under contract to 
Goddard Space Flight Center 
(GSFC-l29)
Brief 63-10606 


New sintering process adjusts magnetic value of ferrite cores

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