JPH0338056B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for tightening fastening parts made of brass-based shape memory alloy. Shape memory alloys are alloys whose shape changes through phase transformation, and when a deformed low-temperature phase (martensitic phase) is heated to become a high-temperature phase (mother phase),
It has the property of returning to its original shape after the deformation caused by the low-temperature phase disappears. Furthermore, if appropriate treatment such as restraint heating is performed to prevent deformation in the low temperature phase from returning to its original state, the shape reversibly changes between the low temperature phase and the high temperature phase. Taking advantage of these properties, Ni-Ti shape memory alloys are used to tighten pipe joints, clamps, etc. However, Ni-Ti-based shape memory alloys have the drawbacks of being difficult to manufacture and expensive. For this reason, fastening parts made of brass-based shape memory alloys, which are cheap and easy to manufacture, have been developed, but the conventional fastening method for these parts is to process martensite phase material at room temperature and set it in the fastening part. This method was followed by heating to the matrix temperature. However, in this conventional method, when the temperature reaches room temperature after heating, the material returns to a low temperature phase (martensitic phase), which caused a problem in terms of strength. On the other hand, the present inventors have discovered that when a brass-based shape memory alloy changes from a low-temperature phase (martensitic phase) to a high-temperature phase (base phase), the deformation caused by the martensitic phase disappears and it returns to its pre-deformed shape. Due to the shape memory effect, at temperatures above 200°C where α phase begins to re-precipitate in the matrix β structure due to further heating, the shape changes one more step in the opposite direction and returns to the deformed shape in the martensitic state. It was discovered for the first time that it has a so-called high-temperature shape memory effect. That is, the present inventors have discovered for the first time that a brass-based shape memory alloy has two types of shape memory properties: a normal shape memory effect and a high temperature shape memory effect. The method of the present invention cleverly utilizes the high-temperature shape memory effect of the brass-based shape memory alloy first discovered by the present inventors, and eliminates the drawbacks of the conventional method. The object of the present invention is to provide a fastening method using a brass-based shape memory alloy that does not require a refrigerant such as nitrogen, is easy to manufacture, has high strength, and is inexpensive. That is, the method of the present invention utilizes the high-temperature shape memory effect, in which the shape further changes when heated to a high temperature of 200°C or higher. After applying deformation processing such as drawing or pushing expansion using a jig, etc., then returning to the matrix state to eliminate this deformation, and setting the clamping part in the matrix state in which the deformation has disappeared in a predetermined clamping part.
This is a method of tightening by simply raising the temperature to 200℃ or higher. The major feature of this method is that it does not require a refrigerant such as liquid nitrogen when final tightening, that is, there is no need for deep cooling at the tightening site, and it will not come off even if the temperature is too high with a burner. This means that there is no such thing. Furthermore, once exposed to high temperatures, a redecipitated α phase is generated in the structure, thereby increasing the strength and elongation. Furthermore, microstructure observation revealed that the change in diameter due to high-temperature heating of 200°C or higher corresponds to the precipitation of the secondary α phase.
It is presumed that phase precipitation is caused by precipitation corresponding to stress-induced martensite that occurs during drawing. In addition, in the present invention, the heating temperature at which the α phase re-precipitates in the matrix and the high-temperature shape memory effect appears is as follows:
Although the temperature is 200°C or higher, temperatures exceeding 800°C are not preferable because the fastening parts themselves will begin to melt. Therefore, heating up to 800°C is possible. However, it can be said that the heating temperature is desirably within 400°C while maintaining sufficient material strength of the fastening parts. FIGS. 1 and 2 diagrammatically illustrate embodiments of the method of the invention. First, referring to Fig. 1, a sleeve made of a brass-based shape memory alloy that has been manufactured as a matrix at room temperature is deep-cooled to -196°C with liquid nitrogen to form a martensitic phase, and after drawing, a reversible treatment is performed. give Note that the reversible processing referred to here refers to two-way (reversible) processing.
(2-way) means processing to give a shape memory effect, and the strong processing method and restrained heating method are known as the processing method. Furthermore, the deep cooling treatment in this case is carried out at the production factory where the sleeve is manufactured, and is not carried out at the above-mentioned tightening site. The sleeve 1b, which has been previously processed in the production factory as described above, is returned to the sleeve 1 at room temperature (matrix state) and set in the tightening part (i). After setting, the sleeve 1 is heated to 200°C to 400°C to form an α precipitate phase (j), and the sleeve 1 transforms into a drawn sleeve 1b, which firmly grips the other tubes 2 and 3 to ensure airtightness. Tighten (k). Even if it is returned to room temperature (l), it will not recover to its original shape, so the clamping force is large and the pipe can be joined with reliable contact (m). Next, referring to Fig. 2, a sleeve manufactured in the martensitic phase at room temperature is drawn at room temperature using a jig, etc., and then restrained.
Perform reversible treatment (constrained heating method) by heating to ~180°C. The sleeve 1 processed in advance in this manner is heated to 50 to 100°C (n) to form the sleeve 1c in a matrix state, and is set in the tightening part (o). After setting, the sleeve 1c is heated to 200°C to 400°C (p) to form the α precipitation phase, and the sleeve 1c changes to the martensitic phase (q), grips the other tubes 2 and 3 tightly, and reduces the tightening force. Forms large pipe joints.
Even when the sleeve 1 is returned to room temperature (r), the sleeve 1 has a large tightening force and is reliably joined (s). In the embodiment shown in FIG. 2, there is no need to carry out deep cooling treatment using a refrigerant not only at the tightening site but also at the sleeve production factory, and it is possible to provide a tightening method with a large tightening force. Note that when imparting the usual shape memory effect in the method of the present invention, it is possible to omit the deep cooling treatment and reversible treatment, but if the deep cooling treatment and reversible treatment are performed, the diameter at the time of α phase precipitation This is preferable because the amount of change in is large. Furthermore, the methods of each of the above embodiments will be explained based on specific examples as follows. Weight ratio: Zn: 30-32%, Al: 2.1%, Fe:
Brass consisting of 2.5% and the balance Cu is melted and cast,
Processed into a sleeve of φ28×φ22×30mm, then heated at 850℃
By heating to and rapidly cooling, it becomes a parent phase or martensitic phase at room temperature. The parent phase or martensitic phase at room temperature can be determined by changing the amount of Zn. If the above-mentioned sleeve is in the matrix phase at room temperature, it is deep-cooled to make it into the martensitic phase, and if it is in the martensitic phase at room temperature, it is expanded or drawn using a jig while being restrained. It was heated to form a reversible shape memory alloy. Note that the pressing and drawing processes were each performed to a diameter of 0.5 mm. The shape memory alloy sleeve treated in this way is
As shown in FIGS. 3 and 4, two stages of shape change were shown. Figure 3 shows push-spreading process (+0.5mm)
In the case of , Figure 4 shows the martensite phase (A), parent phase (B), and high temperature 200 mm in the case of drawing (-0.5 mm).
It is a figure explaining the change of the diameter between degreeC - 400 degreeC (C). In (C), the change in diameter was measured after being held at 40°C for 15 minutes and then air-cooled. By utilizing the changes in diameter shown in FIGS. 3 and 4, the pipes can be easily tightened, joined, etc. by the methods of each of the embodiments described above. The following table shows the room temperature tensile test results for each phase of the example shape memory alloy according to the present invention.

[Table] * Temperature at which the parent phase begins to change to the martensitic phase As is clear from this table, the tensile properties of the parent phase at room temperature or once heated to high temperature are much superior to those of the martensitic phase at room temperature. I know that there is. As explained above, the method of the present invention eliminates the drawbacks of the conventional methods, and provides a fastening method for fastening parts that does not require a refrigerant such as liquid nitrogen, is easy to manufacture, has high strength, and is inexpensive, at least at the fastening site. can be provided.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are diagrams explaining each embodiment of the method of the present invention. FIG. 3 and FIG. 4 are explanatory diagrams showing the shape memory effect of the method according to the embodiment of the present invention.

Claims (1)

[Claims] 1. In a fastening part made of a brass-based shape memory alloy, the shape memory effect in which the shape changes between the martensitic phase and the matrix phase, and furthermore, the α phase regenerates in the matrix at a high temperature of 200°C or higher. Utilizing the high-temperature shape memory effect in which the shape changes again during precipitation, the above-mentioned fastening parts manufactured in the parent phase or martensitic phase at room temperature are drawn or expanded using a jig etc. in the martensitic phase. It is characterized by applying deformation processing such as machining, then returning it to the matrix state to eliminate this deformation, and heating the tightening part in the matrix state where the deformation has disappeared to a predetermined tightening part and raising the temperature to 200 ° C or more. A method for tightening fastening parts made of brass-based shape memory alloy. 2 A tightening part manufactured in the martensitic phase at room temperature is deformed in the martensitic phase, then subjected to reversible treatment, then returned to the matrix state to eliminate this deformation, and tightened in the matrix state in which this deformation has disappeared. 200℃ after setting the parts in the specified tightening area
The tightening method according to claim 1, characterized in that the tightening method is heated to a temperature higher than that.