JPH0259357B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a rubber hose for transmitting hydraulic pressure to each hydraulic device in a hydraulic circuit of a machine tool, etc., and particularly to a rubber hose for a hydraulic circuit using water-based hydraulic fluid as the hydraulic fluid. (Prior Art) Conventionally, rubber hoses used in hydraulic circuits of machine tools, etc. often use mineral oil such as process oil as the hydraulic fluid, and as shown in Fig. 1, the inner tube 1 is made of nitrile rubber (NBR). ), etc., with a metal wire reinforcing layer 2 on its outer surface for pressure resistance, and an outer tube 3 made of a rubber material with excellent weather resistance. is known, and an inner tube fitting 4 and an outer tube fitting 5 are attached to the end of the hose, and the outer tube fitting 5 is crimped at a tightening rate of about 50% of the hose wall thickness to connect and seal. gender is now being secured. However, on the other hand, instead of the above-mentioned mineral oil, phosphate ester-based synthetic oil or water-based hydraulic oil whose main component is water may be used as the hydraulic oil, and in conventional hoses with inner tubes made of NBR, Phosphate ester-based When used with synthetic oil, NBR has a tendency to swell significantly, and when used with water-based hydraulic oil, NBR has the property of allowing water to permeate through it, causing problems with corrosion of the wire reinforcement layer and reducing durability. There's a problem. Therefore, in view of this situation, we decided to use a rubber material that is difficult for water to pass through the inner tube, such as ethylene-propylene.
It is conceivable to form it with diene rubber (EPDM). However, compared to NBR, regular EPDM has
The flow characteristics are poor when the outer cylindrical metal fitting is crimped and in a high-temperature atmosphere, and as a result, there are problems such as a decrease in sealing performance and the occurrence of bulges at the metal fitting connection part. Here, flow refers to a phenomenon in which the inner tube material escapes from the metal fitting connection part due to stress due to crimping during connection or stress increase due to thermal expansion of the inner tube material at high temperatures. (Problems to be Solved by the Invention) The present invention was invented based on the above circumstances, and solves the problems of the flow of the inner pipe material as described above, and prevents corrosion of the wire reinforcing layer and sealing performance. An object of the present invention is to provide a rubber hose for a water-based hydraulic circuit that has excellent durability and does not cause deterioration or bulges. (Solution Means) The rubber hose for water-based hydraulic circuits of the present invention (hereinafter simply referred to as hose) is characterized by a water-resistant inner tube,
In a hose that has a weather-resistant outer tube installed on the outside, the inner tube is made of a special EPDM compound that satisfies the following conditions A, B, and C and uses ENB or DCPD as the diene component. be. (A) Molecular weight distribution Weight average molecular weight (Mw) / Number average molecular weight (Mn)
= 4 or less (B) Propylene content: 30 to 55 wt% (C) Iodine value: 10 to 13 (when the diene component is ENB) 15 to 20 (when the diene component is DCPD) Molecular weight distribution of EPDM used in the present invention The reason for setting the above value is that if it exceeds 4, the entanglement of molecular chains will increase, and the flow of the inner tube material under the above conditions will increase, which is undesirable. In addition, when the propylene content is less than 30wt%, the ethylene crystal part increases and the flow becomes large.
If it exceeds 55 wt%, the glass transition point (Tg) will increase, which is not preferable. Furthermore, the iodine value is closely related to the vulcanization rate and crosslink density; when the lower limit of the above range is outside the range, the crosslink density is small and the flow becomes large, and when it is outside the upper limit, the polymer molecule This decision was made in view of the problem that branching of chains increases, entanglement of molecular chains increases, and the flow increases. (Example) Next, the advantages of the present invention will be explained in detail based on Examples and Comparative Examples. The composition used as the inner tube material is shown in Table 1 (NBR) and Table 2 (EPDM). Table 3 also shows the polymer composition of EPDM. An inner tube (inner diameter 12 mm, wall thickness 2.1 mm) is formed using the NBR compound and EPDM compound, a metal wire braid reinforcing layer is applied to the outer surface of the inner tube, and an outer tube made of a chloroprene rubber compound ( (wall thickness 1.4 mm) and vulcanization molding (150℃ x 60
) and obtained the specified hose. These hoses were then examined for the flow characteristics of the inner tube material, the performance of the metal joints (sealability, presence of bulges), and the presence or absence of wire corrosion. The results are shown in Table-3. In addition, the evaluation method of the above-mentioned various performances was based on the following method. (Flow characteristics) Regarding the various compounds used for the inner pipe material, JIS K
-Compliant with 6301, compression creep test (100℃ x 70
The creep amount was expressed as an index with the NBR compound (Comparative Example 1) set as 100. (Sealability) Attach the inner and outer fittings to the end of the hose,
The hose was swaged at a swage rate of 50% using the outer cylindrical metal fitting, and then subjected to a pressure test after oil aging at 120°C for 168 hours. The oil used was water/glycol = 50/
A water-based hydraulic oil containing 50% by weight was used. As for the results of the pressure test, those that withstood 500 kg/cm ² were marked with an ○, and those that leaked oil at a pressure lower than that were marked with an x. (Presence or absence of bulge generation) The presence or absence of bulge generation was examined for the hose before the above pressure resistance test. 〇 indicates no bulge occurrence, × indicates bulge occurrence. (Presence of wire corrosion) Water-based hydraulic oil (water/glycol = 50/50 weight ratio) is filled in the hose assembly, and after heat aging at 120°C for 360 hours, the hose is taken out and the outer tube etc. is stripped off.
The presence or absence of corrosion of the wire was observed.

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[Table] (Effects of the invention) As is clear from the results of the examples shown above, according to the rubber hose for hydraulic circuits of the present invention, the inner tube is made of a compound using EPDM with a special composition. Therefore, unlike compounds using normal EPDM, there are no problems with the flow of the inner tube when tightening the outer tube metal fittings or in high-temperature atmospheres, and good sealing performance is obtained without the occurrence of bulges. . In addition, since the inner tube is made of an EPDM compound with excellent water resistance, even when used for hydraulic circuits using water-based hydraulic oil, there is no problem of wire corrosion, and durability is improved. It also has the effect of being usable for phosphate ester hydraulic fluids.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the structure of a fastening part showing a state in which a rubber hose for a hydraulic circuit is fastened to a metal fitting. DESCRIPTION OF SYMBOLS 1... Inner tube, 2... Reinforcement layer, 3... Outer tube, 4... Inner tube metal fitting, 5... Outer tube metal fitting.

Claims (1)

[Scope of Claims] 1. A rubber hose for a hydraulic circuit having a water-resistant inner tube and a weather-resistant outer tube provided outside the inner tube, wherein the inner tube satisfies the following conditions A, B, and C.
A rubber hose for a hydraulic circuit characterized by being constructed from an ethylene-propylene-diene rubber compound using ethylidene norbornene (ENB) or dicyclopentadiene (DCPD) as a diene component. (A) Molecular weight distribution: Weight average molecular weight (Mw) / Number average molecular weight (Mn) = 4 or less (B) Propylene content: 30 to 55 wt% (C) Iodine value: 10 to 13 (when the diene component is ENB) 15 ~20 (when the diene component is DCPD)