Device built for use in heat control, heat measurement, and mechanical actuation by heat include thermometers, thermostats, safety switches, circuit breakers, and mechanical actuators. Silicon rubber has highest coefficient of expansion of any known material and seems suitable for most of these devices

Madey, J. M.

English

NASA Technical Reports Server

Standard 
Pressure 
Gauge With 
Bourdon Tube 
Fluid 
Fill and 
Calibrating Fluid	 ir Screw (e.g., Oil)
Silicone	
--,. Aluminum or 
Rubber	 Copper Tubing 
Cap 
August 1973	 B73-10208 
• 
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce now 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. 
Thermally Responsive Mechanical Actuator 
The problem: 
Most materials expand in heat and contract in cold. 
This property is very useful in heat control, heat 
measurement, and mechanical actuation by heat. Devices 
built for such applications include thermometers, ther-
mostats, safety switches, circuit breakers, and mechanical 
actuators, to name a few. However, in each device, a 
different material is actuated by the heat. It would be a 
major technical improvement to have one material that 
could be used in most if not all of these devices. 
The solution: 
Silicone rubber has the highest coefficient of ex-
pansion of any known material and seems suitable for 
most of these devices. 
How it's done: 
Silicone rubber has the following advantages: 
1. It has the highest coefficient of expansion of any 
known material. The coefficient of expansion ranges 
from 5.9 x 10 to 6.9 x 104/°C. 
2. It is flexible enough to be fitted into all kinds of 
enclosures. 
3. Because it is a solid, it does not require seals as in the 
gas- and liquid-actuated devices. 
4. It provides higher work output per given unit of heat 
than any other material. 
5. It is very inexpensive. 
6. It can be molded into any shape. 
7. It can sustain temperatures up to 6000 F. 
The illustrations below show some practical applica-
tions of silicone rubber. Figure 1 shows the standard 
glass thermometer using silicone rubber and colored 
fluid to indicate temperature. A temperature gauge that 
is activated by expanding or contracting silicone rubber 
is shown in Figure 2. Finally, two mechanical actuator 
models using silicone rubber are shown in Figures 3 and 
4.
	
Colored	 Silicone 
	
Fluid	 Rubber 
Figure 1. Glass Thermometer
Figure 2. Temperature Gauge 
(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.
https://ntrs.nasa.gov/search.jsp?R=19730000208 2020-03-17T07:13:30+00:00Z
Silicone	 Return Stop for Setting 
Plunger	 Rubber	 Temperature at Which 
\	 Plunger Begins to Move (Optional) 
Note: 
No further documentation is available. Specific ques-
tions, however, may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: B73-10208
Fluid	 Silicone 
(e.g., Oil)	 Rubber	 Heater 
-	
Element 
 
, 
4	
Return 
 • • . S S • • S
 Plunger 
Fill	 "0" Ring Seal 
Screw 
Figure 4. Sealed Mechanical Actuator 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Jesse M. Madey 
Goddard Space Flight Center 
(GSC-1 1697) 
Input 
Voltage 
for 
- - -	 Heat 
Force of Mechanism or 
Spring to Return Plunger 
Calibration
Screw 
(Optional)
Figure 3. Unsealed Mechanical Actuator
. 
. 
B73-10208	 Category 07, 04


Thermally responsive mechanical actuator

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