JPS58134717A - Formation of bellows - Google Patents

Abstract

PURPOSE:To form a bellows which is excellent in buckling capacity, wear resistance, bending resistance and durability by blow molding a parison of a specific shape having thickly formed portions corresponding to ridged portions of a bellows and those thinly formed portions corresponding to the trough portions of the bellows. CONSTITUTION:A parison is to be formed so that the thickest portions 6a, 6b, 6c of the thick plate portion of the bellows forming portion 3 of the parison, and the thinnest portions 7a, 7b, 7c of the thin plate portion of the bellows forming portion 3 become equal in thickness respectively. In molding a parison 2 by blowing, the bellows forming portion 3 is to be formed so that its thick plate portion is caused to inflate in the direction of ridged portions of a final bellows forming portion 8 and its thin plate portion is caused to inflate in the direction of its valley portions. Portions between the thick plate portion and the thin plate portion are formed in a straight line or in a smooth curve. When a standard blow ratio of parison for its ridged portion is assumed to be about 1.6, the ratio of plate thickness between the maximum thick plate portion and the minimum thin plate portion if regulated within the range of 2.5-3.0.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bellows molding method for thermoplastic elastomer, and more specifically, it is used as a rotating cover to protect from dust on parts such as joints for independent suspension drive shafts in automobiles. This is a method suitable for easily obtaining as uniform a wall thickness as possible.

Conventionally, it is well known that injection blow molding is effective as a method for molding bellows structures having peaks and valleys. These are molded by expanding a parison, a thick-walled tube with one end closed by injection molding, inside a mold immediately before blow molding, but the expanded final molding Since the film length of the bellows part is significantly longer than that of the parison, during blow molding, the parison needs to extend in the circumferential direction as well as in the @1 direction.Moreover, the troughs of the bellows part in the final molding quickly reach the mold. Although the elongation rate is small because the material contacts and is cooled and hardened, the elongation is the largest at the peaks that ultimately come into contact with the mold, causing severe non-uniformity in elongation in the axial direction.

For example, in a bellows structure with a truncated conical shape having a large diameter part and a small diameter part, as shown in FIG. However, as mentioned above, the thickness of the parison becomes non-uniform in the blowing stage, and in the final molded bellows, the thickness of the valley part 14 is thicker than the thickness of the peak part. It is something that is molded. Therefore, if the large-diameter portion on one side of the molded bellows structure is fixed and subjected to stiffness deformation, only the crests will be deformed, and dents called buckling will easily occur in the crests. It had an unfavorable problem in terms of durability. In addition, when the wall thickness of the crest becomes thinner, it also has the disadvantage that damage due to abrasion and bending is more likely to occur, and especially when used as a rotating cover to protect the joint from dust, there is a problem in that the joint is free from foreign matter. It invades and causes abnormalities in the joint forest condition. □l Therefore, the purpose of this invention is to solve all of the above-mentioned problems with the stem, and form a final molded bellows part that has excellent buckling characteristics, wear resistance, and bending resistance, and is extremely durable. The purpose of this invention is to provide a bellows molding method.

The feature is that in blow molding, the blow ratio of the parison to the peaks and troughs of the final formed bellows part constituting the bellows structure is constant. The parison has a thin wall portion corresponding to the inner surface of the parison, and is formed so that the maximum thick wall portion of the parison and the top of the peak, and the minimum thin wall portion of the parison and the bottom point of each portion are located on the same perpendicular line to the inner surface of each parison. , when the blow ratio of the parison to the peak is approximately 1.6 as the electrical constant,
The parison is injection molded into a straight line or a smooth curved shape with a wall thickness ratio of maximum thickness part/minimum thickness part of 25 to 3.0, and is then blow molded to produce the final molded bellows. Therefore, it was possible to obtain a bellows structure with a uniform thickness of 11 degrees.

Regarding the above wall thickness ratio, the blow ratio of the parison to the peaks and troughs of the final formed bellows is constant, and the above-mentioned speed < tl? The elongation rate of the valley part of the final molded bellows part, which is cooled and hardened by contacting the final molded bellows part, is small, and the volume change of the parison corresponding to the final molded bellows part is small, and the thick and thin parts can be moved in a straight line or It is calculated as a smooth curved shape.

Furthermore, the thickness ratio of the maximum thickness part/minimum thickness part of the parison is mainly determined by the blow ratio, the shape and size of the parison,
Alternatively, since it changes under the control of the outer mold shape of blow molding, this blow ratio is used as the standard, and if there is an increase or decrease in the blow ratio, the wall thickness ratio is corrected according to that ratio, Therefore, bellows are molded to accommodate these changes.

The thermoplastic elastomer used in this bellows structure is preferably, for example, a normal thermoplastic urethane elastomer, a thermoplastic polyester elastomer, a polyamide elastomer, a polyolefin elastomer, a styrene/diene block elastomer, a vinyl chloride elastomer, or the like.

Next, embodiments of the present invention will be specifically described based on drawings showing an example of implementation.

Fig. 1 shows a longitudinal section of a conventional parison, and Fig. 2 shows a sectional view of an example of a parison according to an embodiment of the present invention. It is a hollow parison with an almost truncated conical shape.
It is composed of a bellows forming part (3) that gives a bellows shape when blow molding, a large diameter part (4), and a small diameter part (5).

The material is thermoplastic polyester elastomer P7.
0B (manufactured by Toyobo Co., Ltd.).

The bellows forming part (3) is sandwiched in the direction of the small diameter part (5) at a constant angle with respect to the axis connecting the centers of the large diameter part (4) and the small diameter part (5) on its inner peripheral surface, and The surface has an undulating shape consisting of a thick part and a thin part, and as shown in FIG. 3, the thickest part (6a) (6b) (6c) of the thick part
and the smallest thin part of the thin part (7a) (7h) (7r
) is formed each time.

(8) is the final molded bellows part which is made by blow molding this parison (2) and has peaks and valleys, and the thick part and peak part of the bellows forming part (3) of the parison, The thin peaks and valleys correspond to each other. In other words, the maximum thickness part (6
a) (6b) (6c) and the top of the mountain (9a) (9b) (9
c) and the minimum thin wall portion (7a) (7b) ('c) and the valley bottom point (10a) (10/J) (10c) are located on the same perpendicular line to the inner surface of each parison. The bellows forming part (3) is formed, and the parison (2)
When the material is blow-molded, the thicker portions expand toward the peaks and the thinner portions expand toward the valleys.

Further, the space between the thick and thin portions of the parison (2) is formed into a straight line or a smooth curved shape, and in this embodiment, it is formed into a smooth curved shape. In addition, in this parison (2), the parts to be expanded by blow molding are the bellows forming part (3) and the small diameter part (5),
The large diameter portion (4) is designed to have the final shape at the injection molding stage.

By the way, the thickness of the maximum thick part and the minimum thickness of the bellows forming part (31) are specified by a certain relationship based on certain conditions, as mentioned above. When the ratio (R) is about 1.6, the wall thickness ratio (P) of the maximum thickness part/minimum thickness part is 2.
5~:<, Favorable results can be obtained if O is kept within the allowable range. It is shown in Table 1.

Table 1.

Table 1 shows the final result when blow molding is performed using a conventional parison (Fig. 1) in which the inner and outer circumferential surfaces of the bellows forming part of the parison are straight-shaped, and the parison of the above embodiment (Fig. 2) in which the bellows forming part is in an undulating shape. This figure comparatively shows the wall thickness of the molded bellows part and the bellows forming part before blow molding. As shown in FIG.
The ratio of the distance (m) passing through a) to the axis perpendicular to the inner surface of the parison and the distance (, +) from the point on the inner surface of the parison of the maximum thickness part (6a) to the axis on the same perpendicular line (
”/), and is approximately the same at other peaks or thick sections.Also, the wall thickness ratio (P) of the wall thickness of the minimum thin wall section to the wall thickness of the maximum wall wall section is calculated by dividing the former by the latter. However, the wall thickness ratio (
B) is the value obtained by dividing the valley wall thickness by the peak wall thickness.

Therefore, the desirable wall thickness of the bellows structure is one in which the wall thickness ratio (B), which indicates that a uniform wall thickness has been obtained, is 1 or close to 1. While the wall thickness ratio (B) is 2.78,
The parison according to the present invention has a wall thickness ratio (B) of 1.05, which is a desirable wall thickness. That is, the minimum thin part wall thickness of the bellows forming part is 1.1++o++, the maximum thick mountain part wall thickness is 2.9 rtrm, and the wall thickness ratio (P) is 2.
The wall thickness of the final molded bellows obtained by injection molding a parison of No. 6 and blow-molding this parison at a blow ratio (R) of approximately 1.6 is 1.05 mm at the troughs and 1.05 mm at the peaks. 00
A desirable wall thickness ratio (B) of 1.05 was obtained for the throat.

By the way, next, the wall thickness ratio (B
A buckling test was conducted on buckling characteristics and durability such as abrasion resistance or bending resistance using a bellows structure of a final molded bellows portion having a wall thickness of 1.05.

In other words, the buckling characteristics are as shown in Figure 4.
The large diameter part (4) of the bellows structure is fixed to the constant velocity joint OB.
After fixing it with a tightening band (2) and assembling it, bending deformation is applied in the direction shown using the rod 03 inserted from the small diameter part (5), and a part of the peak part of the final formed bellows part is bent. It is determined by determining the angle at which inward denting occurs, that is, the buckling angle. If this buckling angle is small, buckling will occur repeatedly during actual use, resulting in a significant loss of durability. It is something.

Durability is 36' buckling angle at room temperature.

It is expressed as the time it takes for the peaks of the bellows structure to break due to bending fatigue or abrasion when buckling is repeated at a rotational speed of 40 Orpm.Of course, the longer the time, the more durable the final molded bellows will be. This indicates that it is a bellows structure with a bellows structure.

The results of these tests are shown in Table 2. For comparison,
Bellows structures obtained using the conventional parisons shown in Table 1 were also tested in the same manner and are also listed.

Table 2 The buckling angle of the bellows structure using the conventional parison is 10°, whereas the bellows structure according to the embodiment of the present invention has a buckling angle of 42°, which clearly has excellent buckling characteristics. It is something that Therefore, as mentioned above, it is presumed that even if buckling is repeatedly performed during actual use, the durability will not be significantly impaired. Therefore, in a test in which durability was judged by repeated buckling, as expected, in the conventional example, the peak of the bellows broke in 01 hours due to bending fatigue due to repeated buckling, whereas in this example, the peak part of the bellows broke in 01 hours. The bellows structure was damaged after 60 hours due to contact wear between the ridges, and the durability was improved by about 6.00 times compared to the conventional example.

As described above, 1.1. Bellows molding method □ according to the present invention.

According to the above, not only can the variation in the wall thickness of the final molded bellows part be minimized, but also the adjustment of the wall thickness is extremely easy, resulting in improved buckling characteristics, durability, etc.
It exhibited extremely excellent effects and was able to better match the purpose of use.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a parison used in a conventional bellows forming method, FIG. 2 is a sectional view showing an example of a parison used in a bellows forming method according to the present invention, FIG. 3 is an enlarged sectional view of the main part in FIG. 2, and FIG. 4 is an explanatory diagram of a buckling test of a bellows structure formed using the parison in FIG. 2. (2)...Parison (6a) (6b) (6C)
...Maximum thick part (7/7) (7b) (7c) -Minimum thin part (8)...Final molded bellows part (9 (7) (9b) (9C) -Apex of peak (10a)
) (10/J) (10C) - Tanibe Top Attorney Patent Attorney Hata Hata Oshima Figure 1

Claims (1)

[Claims] (1) In blow molding in which the blow ratio of the parison to the peaks and valleys of the final molded bellows portion is constant, the parison has a thick wall portion corresponding to the peak and a thin wall portion corresponding to the valley,
The thickest part and the top of the peak, and the thinnest part and the bottom of the valley are formed so that they are located on the same perpendicular line to the inner surface of each parison, and the blow ratio of the parison to the peak is approximately 1.6.
The parison is made by injection molding into a straight line or a smooth curved shape between the thick and thin parts, with the wall thickness ratio of the largest thick wall part/the smallest thin wall part being 2.5 to 3.0. of,
A bellows molding method characterized by blow molding to form a final molded bellows part.