JP5530770B2 - High durability bellows and manufacturing method thereof - Google Patents

Description

The present invention relates to a bellows excellent in durability comprising a polytetrafluoroethylene resin (unmodified or modified polytetrafluoroethylene). The present invention also relates to a method for manufacturing such a bellows having excellent durability.

(Manufacture of bellows by machining)
-1-
Bellows made of fluororesin (a bellows body that expands and contracts in the axial direction) can be manufactured by a melt press molding method or a blow molding method. Generally, however, a cylindrical member made of polytetrafluoroethylene resin is mechanically cut. Manufactured by processing.

-2-
According to claim 1 of Japanese Utility Model Publication No. 8-5417 (Japanese Utility Model Laid-Open No. 1-131069) (Patent Document 1), at least one end portion of the bellows body is integrally provided with a cylindrical projecting portion that projects in the axial direction. A synthetic resin bellows is formed by forming a concave groove on the inner peripheral surface of the cylindrical protruding portion, inserting a sleeve portion provided with a metal flange into the concave groove, and fixing by caulking. Has been. In claim 2, it is shown that the bellows body is obtained by cutting a polytetrafluoroethylene resin molded body.

-3-
Japanese Patent Application Laid-Open No. 2001-193836 (Patent Document 2) claims that a synthetic resin (especially polytetrafluoroethylene) that can be expanded and contracted in the axial direction in which peaks and valleys are alternately formed.
In the manufactured bellows, the minimum thickness B of each of the crests (outer diameter part of the bellows forming part) and the troughs (inner diameter part of the bellows forming part) and the side parts located between the crests and troughs Thickness A
The bellows with the ratio (B / A) to 1.2 to 2.5 is shown. And, in paragraph 0013 of this document, “(the bellows in the embodiment of the present invention) is formed by cutting a cylindrical member made of polytetrafluoroethylene with a lathe using a stick tool, a knife, etc.” There is a description.

In this Patent Document 2, the ratio (B / A) is defined between the minimum thickness B of each peak and valley and the thickness A of the side surface located between these peaks and valleys. As in the paragraph 0004, the technical idea of “When A = B, every time the bellows extends in the axial direction, one point is concentrated on the top of the peak and the deepest part of the valley. This is because an excessive load is applied due to stress concentration, and an attempt is made to solve the problem that the strength is lowered early due to repeated loads, and cracks are likely to occur.

-4-
According to the claims of Japanese Patent Application Laid-Open No. 2001-193837 (Patent Document 3), the bellows are fully compressed in the axial direction on at least one of the opposing surfaces of the adjacent crests and troughs. The bellows which formed the "slack part" which prevents that said peak parts and trough parts adsorb | suck is shown. And paragraphs 0003 and 0015 of this document
Describes the conventional art (and the invention of this document) that “a cylindrical member made of polytetrafluoroethylene is formed by cutting with a lathe using a stick tool, knife cutter, or the like”. .

No. 8-5417 JP 2001-193836 A JP 2001-193837 A

(Problems of conventional technology)
-1-
The synthetic resin bellows disclosed in Patent Document 1 is known as “the conventional product shown in FIGS. 6 and 7 in which the flange and the bellows are integrally formed, but when the diameter of the flange is desired to be larger than the diameter of the bellows. In order to solve the problem that the part to be cut off of the bellows becomes large, the material is wasted and the cutting time is lengthened (see page 2, lines 5 to 17). A projecting cylindrical projecting portion is provided, and the sleeve portion provided with the projecting portion on the metal flange is caulked and fixed.

-2-
According to the contrivances of Patent Document 2 and Patent Document 3 relating to the shape of the bellows forming portion (pleat (）) forming portion) when machining a cylindrical member made of polytetrafluoroethylene, the simpleness before that It is possible to improve the durability of the bellows as compared with the conventional method, but there is a limit to the effect of improving the durability. Further, the cutting process for obtaining such a pleat shape has a disadvantage that the operation is considerably complicated as compared with the conventional simple cutting process.

(Object of invention)
The technical ideas of the above-mentioned Patent Documents 2 and 3 relating to the improvement of the bellows by the conventional machine cutting process are the problems of the prior art prior to that, “the relation between the thickness of the peak / valley part of the bellows forming part and the side part. From the viewpoints of "Contrivance of" and "Formation of slack parts of peaks and valleys of bellows forming part", that is, from the viewpoint of "shape or structure of bellows forming part".

On the other hand, the present invention is produced by cutting the compression molded body by modifying the “material” itself of the cylindrical compression molded body used for the cutting process for forming the bellows (pleats). Providing a highly durable bellows with significantly improved durability of the product bellows, and providing an industrial method for manufacturing such highly durable bellows,
It is intended.

The highly durable bellows of the present invention
It is a bellows (B) formed by machining a cylindrical compression molded body (M) made of polytetrafluoroethylene resin ,
Its cylindrical compression molding (M)
The sintered body (S) at the sintering temperature after sintering of the preform (P) is taken out of the furnace and immediately submerged in a refrigerant below the temperature of ice water to rapidly cool it. That
The volume of the cylindrical compression molded body (M) is 100 cm ³ or more ,
Crystallinity of the inner diameter part (1a) and outer diameter part (1b) of the bellows forming part (1) of the bellows (B) obtained by machining the cylindrical compression molded body (M) by the density method And a and b, respectively, a is 55% or less and b is 56% or less, and
The bellows (B) has a flexion resistance test (using a flexural resistance tester, the stroke length in the tester is 261 mm, and a gauge pressure of 0.09 MPa is applied for each stroke). More than once,
It is characterized by.

The method for producing the highly durable bellows of the present invention is as follows:
(A) preparing a cylindrical preform (P) produced by filling and compressing polytetrafluoroethylene-based resin particles in a mold;
(B) sintering the preform (P) by heating it in a furnace using a free baking method;
(C) The sintered body (S) at the sintering temperature after the sintering is taken out of the furnace and immediately submerged in a refrigerant having a temperature equal to or lower than the temperature of ice water to rapidly cool it at a volume of 100 cm ³ or more. To obtain a cylindrical compression molded body (M), and
(D) The cylindrical compression molding (M)
By performing machine cutting on
When the crystallinity of the inner diameter portion (1a) and the outer diameter portion (1b) of the bellows forming portion (1) is a and b, respectively, a is 55% or less and b is 56% or less. Bellows (B) and
・ The number of expansions / contractions until breakage is 600,000 times or more in the bending resistance test (using a bending resistance testing machine, the stroke length in the testing machine is 261 mm, and a pressure of 0.09 MPa is applied for each stroke). Bellows (B)
Making
It is characterized by.

The bellows of the present invention reliably improves the durability in the bending test compared to the conventional product even when the cylindrical compression molded body (M) is subjected to the same simple cutting as the conventional product. Moreover, the degree of improvement is remarkable (see Examples and Comparative Examples described later).

-1-
In the method for producing the bellows of the present invention, the sintered body (S) at the sintering temperature when the preform (P) is sintered in the furnace by free baking is removed from the furnace. A cylindrical compression-molded body (M) is obtained by immediately taking a measure of rapid cooling by immersing it in a refrigerant having a temperature equal to or lower than the temperature of ice water.

-2-
The rapid cooling of the sintered body when obtaining a compression molded product of polytetrafluoroethylene-based resin itself is a means that can be employed when obtaining a small compression molded product or a thin layer product. However, even when a relatively small compression molded product having a volume of about 80 cm ³ (about 0.17 kg by weight) or less is obtained, the sintered body is cooled at a cooling rate of 30%.
Usually, slow cooling such as ˜50 ° C./hr is used. Furthermore, for example, when obtaining a large compression molded body (M) as in Example 1 of the present invention (volume of about 780 cm ³ , weight of about 1.7 kg), the temperature from the sintering temperature to below the temperature of ice water is all at once. Quenching is considered to be a method outside common sense, and when bellows are manufactured by mechanical cutting using a compression molded body (M) obtained by such quenching means, the bellows quality with excellent durability is achieved. It can be said that the thing which it has is obtained also has the effect which cannot be predicted.

-3-
In addition, when the bellows of the present invention is manufactured, the cooling time from the sintered body (S) at the sintering temperature is significantly shorter than that of the conventional slow cooling method (cylindrical compression in Example 1 described later). Molded body (M
) Is an example from the viewpoint of productivity, which is shortened from about 7 hours to less than 1 hour.

Hereinafter, the present invention will be described in detail.
The crystallinity measurement method includes a wide-angle X-ray diffraction method, NMR method, IR method, density method, DSC heat of fusion method, etc. The crystallinity in the present invention is “crystallinity by density method”. The conversion of the crystallinity from the density will be described later in the example section.
Regarding the terminology, the term “sintering” such as “sintering preform (P)”, “sintering temperature”, “sintered body (S)” is used to describe the present invention. This “sintering” is synonymous with “firing”.

[Production method of high durability bellows]
(Polytetrafluoroethylene resin)
As the polytetrafluoroethylene resin in the present invention, unmodified polytetrafluoroethylene is preferably used, and polytetrafluoroethylene modified with perfluoroalkyl vinyl ether or the like is also preferably used.

((A) Preparation of cylindrical preform (P))
Cylindrical preform (preform) (P) is manufactured by filling polytetrafluoroethylene resin particles in a cylindrical mold and compressing them (single-pressing or double-pressing methods). is there). The preforming pressure at this time is about 200 to 400 kg / cm ² , preferably 220 to 380.
Often set to about kg / cm ² . By this preforming, the particles filled in the mold are approximately 1
Compressed to about / 4. After completion of the preforming, the preform is removed from the mold.

((B) Sintering of preformed product (P))
Next, the preform (P) obtained above is sintered by heating in a furnace by a free baking method. In the present invention, in order to obtain a medium-to-large compression molded body (M), a preformed product
It is preferable to gradually raise the temperature to the sintering temperature after putting (P) in a room temperature furnace. The sintering temperature is often 30 to 50 ° C. (for example, 360 ° C. or 370 ° C.) higher than the melting point of the polytetrafluoroethylene-based resin. The sintering time is often from several hours to about one day.

((C) Cooling of sintered body (S) / Acquisition of compression molded body (M))
-1-
In general, when trying to obtain a thick-walled or large-sized compact, the sintered compact (S) is allowed to cool slowly while being left in the furnace, especially in the vicinity of the melting point where shrinkage occurs rapidly. It is usual to take care to cool down slowly over time.

-2-
On the other hand, in the present invention, after the above-described sintering, the sintered body (S) at the sintering temperature is taken out of the furnace and immediately cooled immediately by being immersed in a refrigerant having a temperature equal to or lower than the temperature of ice water. . “Immediately” means as soon as possible (for example, within a few seconds to a few tens of seconds). And this submerged state is maintained for a predetermined time (for example, 30 minutes or 1 hour), and the sintered body
Care should be taken that the inside of (S) is sufficiently cooled.

-3-
Since the temperature difference at the time of the liquid immersion operation in the refrigerant becomes, for example, about 360 ° C. or more, it becomes a drastic (conceived) cooling operation. The “refrigerant” is not limited as long as it has a temperature equal to or lower than the temperature of ice water, but literally ice water is particularly desirable. This is because ice water is advantageous in terms of cost, and since ice coexists, the coolant temperature does not rise rapidly even when the sintered body (S) is submerged.

-4-
A cylindrical compression-molded body (M) is obtained as described above. For the purpose of the present invention, the volume is 100 cm ³ or more (that is, a medium to large-sized cylindrical compression-molded body (M)). Is necessary). Volume is 120cm ³ or more, 150cm ³ or more, 200cm ³ or more, 250cm
^The larger the value is ³ or more and 300 cm ³ or more, the more conspicuous the effect (durability) of the present invention is compared to a bellows obtained by mechanically cutting a compression molded body by a conventional slow cooling method.

((D) Machining / Production of bellows (B))
-1-
Next, mechanical cutting is performed on the cylindrical compression molded body (M) obtained above. As the mechanical cutting, for example, a method of cutting with a lathe using a stick tool or a knife cutter is employed. At this time, the outer surface on one end side of the cylinder is usually cut smoothly to an amount corresponding to the width of chucking, and then that portion is usually chucked.

-2-
Then, the bellows forming portion (1) is formed by alternately incising the chucked cylindrical compression molded body (M) from the inner diameter side and the outer diameter side to form pleats (襞).
Is made. When the bellows (B) has a flange, the flange is also formed by machining. The flange can be provided with a groove or a bolt hole for fitting an O-ring as needed at an appropriate stage.

(Crystallinity of bellows forming part (1))
-1-
The degree of crystallinity of each part at the stage of the cylindrical compression molded body (M) is as follows:
-The type of polytetrafluoroethylene resin that is the raw material and the factor of particle size,
・ Molding pressure factor when manufacturing the preform (P),
-Factor of cooling condition of sintered body (S) at sintering temperature,
・ We know that it is almost determined by the volume factor of the compression molded product (M). Therefore, according to the crystallinity of each part of the compression molded body (M), the crystallinity of each part of the bellows (B) obtained by machining it is also practically determined.

-2-
In the present invention, a bellows (B) obtained by machining a cylindrical compression molded body (M)
The degree of crystallinity of the bellows forming part (1) by the density method is
-The degree of crystallinity a of the inner diameter part (1a) of the bellows forming part (1) is 55% or less, and
The crystallinity b of the outer diameter portion (1b) of the bellows forming portion (1) is set to 56% or less.

-3-
The smaller the degree of crystallinity a of the inner diameter portion (1a), such as 54% or less, 52% or less, 51% or less, and even 50% or less, the more preferable (the lower limit may be up to about 45%). Many, but not particularly limited). The crystallinity b of the outer diameter portion (1b) of the bellows forming portion (1) is 5
The smaller it is, such as 5% or less, 54% or less, and further 53% or less (the lower limit is often up to about 45%, but there is no particular limitation).

  The following examples further illustrate the invention.

Example 1
FIG. 1 is a process diagram of a method for producing a highly durable bellows of the present invention.
FIG. 2 is a longitudinal sectional view of a cylindrical compression molded body (M).
FIG. 3 shows a bellows (B) obtained by machining the cylindrical compression molded body (M) of FIG.
) Is a vertical cross-sectional view (schematic diagram depicting a very small number of peaks of the bellows forming portion (1)).

-1- (Preparation of preformed product (P))
Polytetrafluoroethylene-based resin particles are filled into a mold and compressed with a press pressure of about 300 kg / cm ² to form a cylindrical preform (preform) having an outer diameter of 120 mm and an inner diameter of 50 mm (preform) ( The required number of P) was produced.

-2- (Preparation of sintered body (S))
Next, the preform (P) obtained above is put into a furnace at room temperature and heated up to the sintering temperature (365 ° C.) over about 5 hours. It was kept until it became translucent, and became a cylindrical sintered body (S).

-3- (Acquisition of compression molded product (M))
Subsequently, the sintered body (S) at the sintering temperature is taken out of the furnace and immediately cooled (in 1 to 2 seconds) into ice water (refrigerant) to be submerged and rapidly cooled. Removed after a minute.
As a result, a cylindrical compression molded body (M) having a volume of about 800 cm ³ was obtained (see FIG. 2).

-4- (Preparation of bellows (B))
The cylindrical compression molded body (M) of FIG. 2 obtained in this way was machined to produce the bellows (B) shown in FIG. In FIG. 3, (1) is a bellows forming portion and (2) is a flange. The bellows forming portion (1) was formed using a knife cutter, and the number of folded portions (number of peaks) in the bellows forming portion (1) was set to 60. The flanges (2) and (2) can be provided with grooves or bolt holes for fitting O-rings if necessary, but are not shown in FIG.

(Comparative Example 1)
The sintered body (S) at the sintering temperature obtained in the step -2- of Example 1 was gradually cooled in the furnace as it was without being taken out from the furnace. The cooling rate (furnace temperature lowering rate) at this time is about 35 ° C./hr up to the melting point of the polytetrafluoroethylene-based resin according to a conventional method, and the furnace temperature is about 3 ° C.
When the temperature dropped to 15 ° C., the furnace temperature was kept at this temperature for a long time to wait for the inside / outside temperature of the molded body to uniformly pass the melting point, and then the temperature was lowered at a rate of about 35 ° C./hr. Since the compression molded body (M) was obtained by this slow cooling operation, the bellows (B) was produced by cutting according to the process of -4- of Example 1.

(Density measurement / conversion to crystallinity)
-1-
For the measurement of density, relative density (based on “5.1 (Method A (submersion method) in water)” of “Measurement of density and specific gravity of non-foamed plastics” specified in “JIS K7112: 1999” (
In addition to measuring the specific gravity, the density was determined by performing “temperature conversion of water density” based on Table 1 of the same rule.

-2-
Conversion from the density α obtained above to the crystallinity β (%) is as follows:
β = ((23α−46) / 3α) × 100
by. The conversion formula is “PTFE,” published on page 29 of the lexical literature “Plastic Materials Course [6], Fluoroplastics, Nikkan Kogyo Shimbun, published first edition 51 prints on January 30, 1981”. The relationship between the degree of crystallinity and the specific gravity (23 ° C.) ”is coincident (by the way, β is 0 % when α is 2.00, and β is 100 % when α is 2.30).

(Measurement of crystallinity / Example 1)
1. The sliced portion of the cylindrical compression-molded body (M) shown in FIG. 2 cut into a 1 mm thickness in the radial direction is cut into an inner diameter portion (black circle 1 in FIG. 2) and an outer diameter portion (black circle 2 in FIG. 2). ), And an intermediate portion (black circle 3 in FIG. 2) between the inner diameter portion and the outer diameter portion was sampled. This intermediate portion is the boundary between the outer diameter side having a transparent feeling and the inner diameter side having a white feeling.
2. Further, the inner diameter portion (1a) and the outer diameter portion (1b) of the bellows (B) at the product stage in FIG. 3 were sampled. The inner diameter portion (1a) (white circle 1 in FIG. 3) corresponds to the white circle 1 in FIG. 2, and the outer diameter portion (1b) (white circle 2 in FIG. 3) corresponds to the white circle 2 in FIG.
3. These samples were subjected to measurement of crystallinity. The results are shown in Table 1 below.

[Table 1]

(Measurement of crystallinity / Comparative Example 1)
Similarly, the inner diameter part and outer diameter part of the bellows (B) produced in the above Comparative Example 1 (corresponding to the inner diameter part (1a) and outer diameter part (1b) of the bellows (B) in the product stage of FIG. 3) Were sampled and subjected to measurement of crystallinity. The results were as follows.
Crystallinity of inner diameter (corresponding to white circle 1 in Fig. 3): 59.0%
Crystallinity of outer diameter (corresponding to white circle 2 in Fig. 3): 59.2%

(Durability test (flexibility test))
A test was conducted using the same bending resistance tester using a total of six product bellows (B) produced in Example 1 and three product bellows produced in Comparative Example 1 described above. The tester has a stroke length of 261 mm) and 0.09 MPa (approx. 1 atm) is applied as a gauge pressure for each stroke in consideration of the actual usage pattern. Since the outside is almost vacuum and the inside of the bellows is often atmospheric pressure, the conditions are selected so that a difference of about 1 atm is produced between the inside and outside of the bellows). Note that this test condition is much stricter than the actual on-site use condition. The results are shown in Table 2. The number of expansions / contractions is one reciprocation.

[Table 2]

Sample Number of expansions / contractions Damaged part
Example 1 1 No damage even after 600,000 times (no abnormality)
2 No damage even after 600,000 times (no abnormality)
3 No damage even after 600,000 times (no abnormality)
Comparative Example 1 1 Damaged after 201,000 cycles Back side of the outer diameter of the first mountain from the top
2 Damaged after 184,000 cycles The back side of the outer diameter of the first mountain from the top
3 Damaged after 225,000 cycles Front side of outer diameter at 19th mountain from top

(Evaluation)
1. As shown in Table 2 above, the flex resistance of “Comparative Example 1” is about 200,000 times of expansion / contraction under the above test conditions (because the lower value should be used as a reference, It can be seen as about 180,000 times).
2. On the other hand, the bending resistance of “Example 1” was not damaged even when the number of expansion and contraction reached 600,000 times (the test was terminated at 600,000 times, and the result far exceeded the original target was obtained. Therefore, it can be seen that the bending resistance is remarkably improved as compared with Comparative Example 1.

(Examples 2 to 4)
In Example 1, the sintered body (S) at the sintering temperature is taken out from the furnace, and immediately cooled into the ice water (refrigerant) by submerging in a cylinder having a volume of about 800 cm ³ . In the same manner as in Example 1, the volume was about 150 cm ³ (Example 2). , About 200 cm ³ (Example 3), about 300 cm ³ (Example 4), about 500 cm ³ (Example 5) cylindrical compression molded body
After obtaining (M), when the bending resistance of the product bellows (B) was measured by cutting for bellows processing, the bending resistance was much better than the bellows made from the corresponding annealed product. It has been confirmed that sex can be obtained.

The highly durable bellows of this invention is used for fluid control apparatuses including valves and pumps. For example, it is used as a bellows incorporated in a piping system for circulating or transferring a chemical solution in a semiconductor manufacturing apparatus, a pharmaceutical product or a bio-related product.

It is process drawing of the manufacturing method of the highly durable bellows of this invention. It is a longitudinal cross-sectional view of a cylindrical compression molded body (M). FIG. 3 is a longitudinal sectional view of the bellows (B) obtained by machining the cylindrical compression-molded body (M) of FIG. 2 (a schematic diagram depicting the number of peaks of the bellows forming portion (1)).

(P) ... preformed product,
(S) ... sintered body,
(M) ... compression molding,
(B)… Bellows,
(1) ... Bellows forming part,
(1a) ... inner diameter part, (1b) ... outer diameter part,
(2)… Flange

Claims (2)

It is a bellows (B) formed by machining a cylindrical compression molded body (M) made of polytetrafluoroethylene resin ,
Its cylindrical compression molding (M)
The sintered body (S) at the sintering temperature after sintering of the preform (P) is taken out of the furnace and immediately submerged in a refrigerant below the temperature of ice water to rapidly cool it. That
The volume of the cylindrical compression molded body (M) is 100 cm ³ or more ,
Crystallinity of the inner diameter part (1a) and outer diameter part (1b) of the bellows forming part (1) of the bellows (B) obtained by machining the cylindrical compression molded body (M) by the density method And a and b, respectively, a is 55% or less and b is 56% or less, and
The bellows (B) has a flexion resistance test (using a flexural resistance tester, the stroke length in the tester is 261 mm, and a gauge pressure of 0.09 MPa is applied for each stroke). More than once,
High durability bellows characterized by (A) preparing a cylindrical preform (P) produced by filling and compressing polytetrafluoroethylene-based resin particles in a mold;
(B) sintering the preform (P) by heating it in a furnace using a free baking method;
(C) The sintered body (S) at the sintering temperature after the sintering is taken out of the furnace and immediately submerged in a refrigerant having a temperature equal to or lower than the temperature of ice water to rapidly cool it at a volume of 100 cm ³ or more. To obtain a cylindrical compression molded body (M), and
(D) The cylindrical compression molding (M)
By performing machine cutting on
When the crystallinity of the inner diameter portion (1a) and the outer diameter portion (1b) of the bellows forming portion (1) is a and b, respectively, a is 55% or less and b is 56% or less. Bellows (B) and
・ The number of expansions / contractions until breakage is 600,000 times or more in the bending resistance test (using a bending resistance testing machine, the stroke length in the testing machine is 261 mm, and a pressure of 0.09 MPa is applied for each stroke). Bellows (B)
Making
A manufacturing method for highly durable bellows.