Furukawa Techno Material

NewNew Products
ProductsNew Products Using Ni Alloys

1.

INTRODUCTION

Furukawa Techno Materials Co., Ltd. was established in1958 under its former name, Furukawa Special MetalIndustries Co., Ltd. Since that time, based on an integrated manufacturing system for nickel-based special alloys
from melting to finished products, we have continued withthe development and marketing of products using thesealloys. In 1992, with the transfer from Furukawa Electric ofits disaster prevention operation, we assumed our present
name of Furukawa Techno Materials. The Special Metals
Division manufactures Ni-based alloys. By means of ourhigh-accuracy melting and casting technology and control of production processes up to wire drawing, we are
manufacturing and marketing the application products
described below.
From among our products using Ni alloys, we would
like to focus here on two products that are used in theelectronics field.

2.

PRODUCTS USING Ni-Ti SHAPEMEMORY ALLOYS

2.1 Ni-Ti Alloys
Ni-Ti alloys are known for their properties of shape-memory and super-elasticity, and many products have beendeveloped using them. By varying the Ni-Ti component
ratio slightly from 50:50, it is possible to change the transformation temperature as desired, from 0°C up to about
100°C.
Taking advantage of this temperature characteristic,these alloys can be used in a variety of products, including wire frames for brassieres, mobile phone antennas,
eyeglass frames and, more recently, medical devices.
Here we will describe an Ni-Ti alloy spring as an example
using the property of shape memory in industry.
2.2 Ni-Ti Alloy Spring
Almost all the products that make use of the shape-memory effect are in the form of a coil spring. Springs made of
Ni-Ti alloy are used as a combined temperature sensor
and actuator. That is to say we utilize the fact that the sensor function operates above the transformation temperature, at the same time producing force to drive the actuator. Since the sensor and actuator are combined, there isno need for such elements as a sequencer, wiring, motor,
thermocouples and the like, power supply, etc., thereby
effecting savings of space, weight and cost.

Ni-Ti alloy springs, like the general run of coil springs,
use a coil molding machine to produce the desired shape.
Because of the shape-memory effect, however, springback is greater than with ordinary metals, so that it must
be deformed to be larger than actual size. Also it is necessary to use a die such that, after molding, shape memory
and temperature characteristics are regulated by heat
treatment, and shape is also retained during heating.
Depending on the product, grinding both ends of thespring, laser marking, hook forming, etc. may be used.
The shape-memory effect is a characteristic whereby
deformation imparted in the martensitic phase will returnby heating to the original shape in the high-temperature
austenitic base material.
2.2.1

Automatic oil volume adjusting unit for
Shinkansen driving gear
As operating speeds for Shinkansen trains are increased,
there has been a change to aluminum casting to form thegear box for the gear device. In such a case the differing
coefficients of thermal expansion for aluminum and steel
have an impact on bearing windage, creating the need tosuppress temperature rise as much as possible. For thisreason an automatic oil volume adjusting unit using Ni-Ti
alloy (Figure 1) was developed. With this gear device,rotation of the pinion gear causes a large volume of lubricating oil to be splashed up, providing an adequate supply of oil to the bearings and thereby assuring lubrication
at lower temperatures when there is a greater possibilityof seizure.

［Low Temperature］
Room B
Room A［High Temperature］
PinionGear

Room B
Room A
Bypass HoleOil Pocket

Figure 1

Driving Gear Unit

Automatic oil volume adjusting unit for Shinkansen
driving gear. (courtesy of Toyo Denki Seizo)

Furukawa Review, No. 32200797

New Products Using Ni Alloys

2.2.2 Water mixing valve
A thermostat water mixing valve senses water temperature and automatically controls the temperature of outflow
water. The biggest problem with the wax-type water mixing valve was its slow response speed. As for its wax element, paraffin-type wax was enclosed in a copper vessel,
one end of which was sealed with a rubber diaphragm. Its
actuator operated on volumetric expansion of solid-liquidtransformation due to temperature change. Since theresponse speed was slow, the overshoot temperature wasapproximately 8°C.
Figure 2 shows a water mixing valve that uses an Ni-Ti
coil spring. Turning the temperature control knob changes
the total length of the Ni-Ti coil spring and the bias spring
thereby controlling the temperature of outflow water. By
this means overshoot is kept to less than 2°C, which is
not clearly perceptible to a person.

temperature that takes advantage of the fact that, when
two types of conductor are electrically connected at one
end and a difference in temperature is applied between
the point of connection and the other end, an electromotive force is generated between the two junctions, in what
is known as the Seebeck effect. Table 1 shows sometypes of thermocouple together with their respective char-

KP: Chromel (Ni-Cr alloy); + axis
Thermocouples

KN: Alumel (Ni-Al alloy); - axis Compensating
lead wires

Figure 33.

EMF MATERIALS (THERMOCOUPLE
FILAMENTS)

Schematic of thermocouple.

80

3.1 Thermocouples
The thermocouple (Figure 3) is a device for measuring

−40

200

CodeComponent materials

el800

inum

1200

1600

Temperature (℃)

Water mixing valve. (courtesy of TOTO Ltd.)

Table 1omumalel--pla t3 %)ium (1dohr
um-400Mixed water

Figure 2

anPla tin−30
Temperature
control knobr
Ch

op−50

Spoolnttanscorpe

Bias spring

CSMA spring

40

mel-c

Cool Hotwater water

ChroEMF (mV)onstant

an60

Figure 4

Effect of temperature on EMF.

Selected thermocouples and their characteristics.

Measuring range

Note+Axis-Axis

B

Pt-30%Rh

Pt-6%Rh

0°C ~ 1500°C

JIS-designated thermocouple with the highest working temperatureR

Pt-13%Rh

Pt

0°C ~ 1400°C

Used as a standard thermocouple, suitable for measuring high temperatures.
EMF is small, so not suitable for measurement at low temperature.

S

Pt-10%Rh

Pt

0°C ~ 1400°C

Suitable for measuring high temperatures. EMF is small, so not suitable for measurement at low temperature.

K

Chromel (Ni-Cr)

Alumel (Ni-Al)-200°C ~ 1000°C

Linear relationship of temperature vs. thermal EMF. Most widely used in industrial
applications.

E

Chromel (Ni-Cr)

Constantan (Cu-Ni)-200°C ~ 700°C

JIS-designated thermocouple with the highest thermal EMF characteristic.
Excellent resistance to oxidation, but not suitable for use in reducing atmospheres.

JIron wire (Fe)Constantan (Cu-Ni)

0°C ~ 600°C

Highest thermal EMF characteristic after Type E, used industrially at mid-range
temperatures. Since iron is used it is not suitable for use in oxidizing atmospheres.

T

Copper wire (Cu)Constantan (Cu-Ni)-200°C ~ 300°C

Widely used for accurate measurement at low temperatures. Since copper isused it is not suitable for use in oxidizing atmospheres at high temperatures.

NNickel-chrome-silicon Nickel-silicon alloy
alloy (Ni-Cr-Si)(Ni-Si)-200°C ~ 1200°C

Improved version of Type K, excellent for use at high temperatures.
(not available from Furukawa)

Furukawa Review, No. 32

200798

New Products Using Ni Alloys

acteristics. Figure 4 shows the effect of temperature onEMF. Type K is the most widely used thermocouple, andsince both terminals are made of nickel-rich alloys, they
form one of our main product lines and we have madesuccessive improvements.
The factors with particular influence on the characteristics of thermocouple filaments are variations in the components of the alloys, and control of oxygen and otherimpurities. Alloy components not only influences the initialcharacteristics of the thermocouple, but thermal EMF values change over time due to oxidation at high temperatures and concentration of alloy components. This causes
service life to be reduced and reliability to be lost.
3.2 Compensating lead wires
The compensating lead wires used to connect the thermocouple and the meter are also of the greatest importance to the reliability of measurement accuracy.
Compensating lead wires are made of alloys having substantially the same EMF characteristics as the thermocouple. For this reason the lead wire used must be specifically matched to the type of thermocouple. Note that when
we say “having substantially the same EMF as the thermocouple”, this applies solely to the range of temperatures at which the compensating lead wire is used (leadwire junction temperature).

4.

CONCLUSION

wet environments, remain relatively little known in general. One factor mitigating against their more general use isthat even though the transformation temperature limit ishigh, it is in the neighborhood of 100°C. In the future weintend to publicize the characteristics and applications ofthese alloys, and to extend their use in automotive andsimilar applications. With respect to thermocouple materials, there is an increasing need for higher temperaturesand more accurate temperature control with respect tofuel cells and other industrial equipment. Thus thermocouples, which play a crucial role in these temperature
control mechanisms are similarly subject to requirementsof higher accuracy, higher reliability and longer life.
For many years we have had an integrated productioncapability, ranging from the casting of various thermocouples and the drawing of filaments right through to manufacturing finished products such as thermocouples withprotective tubes, sheathed and PVC coated thermocouples. In recent years we have developed the Type K thermocouples described above, which offer outstanding
high-temperature characteristics and high durability, andhave been highly evaluated worldwide. We intend to continue our efforts at sales promotion.
For more information, please contact:
Special Metals Sales Dept., Metals Co., Furukawa
Electric		 TEL: +81-463-21-7316 FAX: +81-463-21-7385

Examples of applications of Ni-Ti alloys as combined
temperature sensors/actuators, although widely seen in

Furukawa Review, No. 32

200799