JPH0443975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in shape memory springs using shape memory alloys.

Various temperature-sensitive parts are being developed using shape memory alloys such as Ti-Ni alloys. The pace of practical application is remarkable, and automatic window opening/closing devices and heat engines have already been created, as well as medical jigs used to straighten teeth and bones.

Currently, the main applications are springs that utilize unidirectional or bidirectional shape memory effects. However, existing means for this purpose are bimetals, and in order for shape memory springs to be used instead, apart from the problem that Ti-Ni alloys are expensive, it is necessary to further improve the spring properties. This is desirable.

The present inventors have found that regardless of whether the shape of the spring is a coil or a leaf spring, its characteristics are basically not affected by whether the material is solid or hollow, but mainly depend on the outer dimensions. The present invention was developed by paying attention to the fact that

The shape memory spring of the present invention is formed by forming a thin, hollow, tubular or plate-like shape memory alloy material into a spring shape, and subjecting it to memory treatment.

Here, "thin" means a thickness within a range that satisfies the mechanical strength and force required for the spring. Of the cross-sectional area of the solid wire or plate that conventionally formed the spring, for example, 50% from the outer shell.
%, the mechanical strength of the hollow body decreases only slightly. If the same mechanical strength as the conventional one is to be obtained, if conditions permit, a hollow tube or plate with a thin wall and large outer dimensions may be used as the material. Therefore, how much wall thickness should be provided should be determined depending on the dimensions of the spring and the required spring force.

Shape memory alloy can be selected arbitrarily, but 45%Ti−
A common material is a 55% Ni-based alloy (Af transformation point is 62°C).

The formation of springs from thin-walled, hollow tubular or plate-like shape memory alloy materials may be performed according to known techniques. The molded spring is also subjected to shape memory treatment according to a conventional method. When using the Ti-Ni type shape memory alloy mentioned above, for example, 400 to 500℃ x 30
The heating time is from 1 minute to 1 hour.

The shape memory spring of the present invention can utilize techniques conventionally known in this field. For example, as shown in the embodiment described later, a shape given by shape memory processing is deformed by a bias spring. It is also possible to apply electric current to the spring itself and utilize the generated Joule heat to reach a temperature exceeding the transformation temperature.

According to the present invention, if the shape memory spring is formed of a thin-walled, hollow tubular or plate-like shape memory alloy material,
Many benefits can be obtained, including:

○ Costs are lower because fewer materials are used.

○ Because the heat capacity is small, the spring operation can quickly follow changes in environmental temperature, and has excellent temperature sensitivity. This effect appears conspicuously due to the combination of a decrease in the absolute amount of material due to thinning and an increase in surface area due to hollowing.

○ Lighter than solid springs. This is significant for applications in the medical field, such as implantation, and generally contributes to faster spring actuation.

○ If the spring is directly energized to raise the temperature with Joule heat, the resistance value will be higher, so the required current can be reduced, or the temperature can be raised faster with the same current.

Example 1 Made of 55%Ti-45%Ni alloy, outer diameter 2.0
A thin tube with an inner diameter of 1.4 mm (thus, a wall thickness of 0.3 mm) and a solid thin wire with the same outer diameter were manufactured. Af of this material
The transformation point is 62°C. Both thin tube and thin wire, winding diameter
It was formed into a 25 mm coil spring and subjected to memory treatment at 400°C for 2 hours.

In these shape memory springs, each turn of the coil is in close contact with each other at room temperature, and by incorporating a bias spring inside the coil, the pitch was expanded to 3 mm.

Temperature sensitivity was measured by alternately putting the spring in and out of hot water kept at a temperature of 80°C and the atmosphere (approximately 22°C). In other words, we put the spring in hot water, confirmed that it had completely returned to its memorized shape, and then pulled it up. We repeated the heat cycle 10 times, and divided the required time by a number of 10 to obtain the response speed.

The results are as follows, proving the high temperature sensitivity of the hollow spring.

Sensitive speed (sec/times) Hollow spring 0.5 Solid spring 1.6 This effect is due to the fact that hollow springs have a smaller heat capacity.
This is thought to be due to the fact that the temperature of the entire spring rises quickly, as well as being relatively lightweight.

Example 2 Terminals were attached to both ends of the shape memory spring manufactured in Example 1, which had been subjected to memory treatment and was equipped with a bias spring, and was energized in an environment of 20°C. The coil spring itself uses the Joule heat generated to return it to its memorized shape (close contact), and the current value required to achieve this within a certain amount of time was measured.

After complete adhesion, the current was turned off to allow natural cooling, and the average time required for the pitch to return to 3 mm due to the repulsive force of the bias spring was measured.

Current value (A) Recovery time (seconds) Hollow spring 1.5 7 Solid spring 3.0 10 The above results show that the amount of current (hollow: solid = 1:2) required to perform the same spring action is the spring's electricity. This shows that it is determined according to the resistance ratio (hollow: solid = 100:51) and that the difference in heat dissipation effect is reflected in the difference in recovery time. The time it takes for a hollow spring to return to its memorized shape can be shortened by increasing the current value, even if it is not more than that for a solid spring, so when combined with the difference in recovery time, the speed of the spring action of a hollow spring is remarkable. Become something.

Claims (1)

[Scope of Claims] 1. A shape memory spring formed by forming a thin, hollow, tubular or plate-like shape memory alloy material into a spring shape and subjecting it to memory treatment. 2. The shape memory spring according to claim 1, wherein the shape memory alloy is a 45% Ti-55% Ni based alloy, and the material has a transformation temperature of 110°C or lower. 3. The shape memory spring according to claim 1 or 2, which is provided with an energizing means for directly energizing the spring and using Joule heat as an operating source. 4 Claim 1 adding a bias spring
Shape memory spring according to any one of items 1 to 3.