JP2019196828A - Gland packing and method for manufacturing yarn for gland packing - Google Patents

Abstract

To provide a gland packing that is excellent in heat radiation property and wear resistance, in a gland packing that is braided with a yarn.SOLUTION: A gland packing is braided with a yarn. The yarn comprises a mixture of PTFE and graphite. The graphite has a circularity within a range of 0.5-0.7. The mixture includes 5-60 pts. mass of the graphite based on 100 pts. mass of the PTFE.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gland packing formed by braiding yarn (knitting yarn), and a method for producing a yarn used for the gland packing.

  As a packing for sealing a shaft of a fluid device, there is a gland packing having a structure in which a seal member is filled in a space formed between a casing and a shaft of the device and the seal member is tightened.

  Among these, as a packing having excellent chemical resistance, a packing having a braided yarn made of PTFE (polytetrafluoroethylene) fiber is known (for example, Patent Document 1).

JP-A-8-93921

  However, since PTFE is a thermoplastic resin, when a gland packing braided with yarn made of PTFE fibers is used for a fluid device whose rotating shaft rotates at high speed, the gland packing becomes deformed due to high temperature due to frictional heat. As a result, there is a problem that the sealing performance is lowered. In addition, PTFE has a problem of low wear resistance because of its low mechanical strength.

  The present invention has been made in view of the above-described problems, and a main object thereof is to provide a gland packing formed by braiding yarn and having excellent heat dissipation and wear resistance.

  The gland packing according to the present invention is a gland packing formed by braiding yarn, and the yarn is made of a mixture of PTFE and graphite, and the circularity of the graphite is in the range of 0.5 to 0.7. The mixture contains 5 to 60 parts by mass of graphite with respect to 100 parts by mass of PTFE.

  A method for producing a yarn for gland packing according to the present invention is a method for producing a yarn for use in gland packing formed by braiding a yarn, a step of producing a mixture containing PTFE and graphite, and extruding the mixture to obtain a filament. And forming a yarn by drawing a bundle of filaments, the circularity of the graphite is in the range of 0.5 to 0.7, and the mixture is 5 to 100 parts by weight of PTFE. ˜60 parts by mass of graphite is contained.

  ADVANTAGE OF THE INVENTION According to this invention, in the gland packing formed by braiding yarn, it is possible to provide a gland packing excellent in heat dissipation and wear resistance.

It is sectional drawing which showed typically the state which mounted | wore the shaft seal part of the fluid apparatus with the gland packing in one Embodiment of this invention. In the sample C of Table 1, it is the figure which showed the result of having observed the surface of the ground packing after evaluating each test item, (a) is a SEM (scanning electron microscope) photograph, (b) is EDX (energy dispersion type). X-ray analyzer). In the sample F of Table 1, it is the figure which showed the result of having observed the surface of the ground packing after evaluating each test item, (a) is a SEM (scanning electron microscope) photograph, (b) is EDX (energy dispersion type). X-ray analyzer).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to the following embodiment. Moreover, it can change suitably in the range which does not deviate from the range which has the effect of this invention.

  FIG. 1 is a cross-sectional view schematically showing a state in which a gland packing according to an embodiment of the present invention is mounted on a shaft seal portion of a fluid device.

  As shown in FIG. 1, a gland packing 3 is mounted in a space formed between a packing box 2 disposed so as to surround the outer periphery of a rotating shaft 1 of a fluid device (not shown) and the rotating shaft 1. Yes. Here, an example in which five gland packings 3 are mounted is shown.

  The mounted gland packing 3 is tightened in the axial direction with the packing presser 4 using bolts 5 to generate a force for pressing the shaft surface, and the internal fluid is sealed by the contact pressure.

  In the present embodiment, the gland packing 3 is composed of a braided body formed by braiding yarn (knitting yarn) made of a mixture of PETE (polytetrafluoroethylene) and graphite.

  A yarn made of a mixture of PTFE and graphite is formed by preparing a mixture containing powdered PTFE and graphite, extruding the prepared mixture to form a filament, and then stretching the bundle of filaments. The

  In this embodiment, in a yarn made of a mixture of PTFE and graphite, PTFE and graphite are bonded to each other by an anchor effect without PTFE and graphite being chemically bonded.

  Therefore, the present inventors considered that the anchor effect indicating the binding force between PTFE and graphite depends on the circularity of graphite, and prepared graphite by mixing graphite having different circularity with PTFE, and produced the yarn. The gland packing braided and used was evaluated for its heat dissipation and wear resistance.

(Production of gland packing)
With respect to 100 parts by mass of PTFE, 60 parts by mass of graphite whose circularity was changed in the range of 0.4 to 0.8 was mixed, and a yarn was formed from this mixture by a predetermined method. Also, a gland packing was produced by lattice knitting this yarn.

  Here, the circularity is a spherical index when the particles are projected two-dimensionally, and is calculated by the following formula (1), where S is the projected image area and L is the length of the contour line. . For example, in the case of a circle, the circularity is 1.

Circularity = 4πS / L2 (1)
Said measurement can be performed, for example using powder image analyzer "PITA-3" (made by Seishin Enterprise Co., Ltd.).

  The following test items were evaluated for each of the prepared samples using a rotation tester (manufactured in-house) simulating an actual machine.

(1) Leakage amount Five prepared samples were mounted in the packing box of the rotation tester, and the packing presser was tightened with a predetermined surface pressure. Then, rotation of the shaft was started at a peripheral speed of 8.5 m / sec while applying a water pressure of 0.5 MPa at room temperature. Thereafter, while measuring the amount of leakage from the shaft seal, the tightening pressure was gradually increased to measure the amount of leakage when the amount of leakage was stable.

(2) Temperature change (heat dissipation)
In the above test, the temperature of the sample when the amount of leakage was stabilized was measured from the temperature of the sample at the start of startup, and the temperature change was measured. The temperature of the sample was measured with a thermocouple attached through the packing presser in contact with the packing.

(3) Mass reduction rate (wear resistance)
In the above test, the mass M ₁ of the sample before the test and the mass M _{2 of} the sample taken out from the rotation tester when the leakage amount is stabilized are measured, and the mass reduction rate of the sample (M ₂ / M ₁ × 100 )

  Table 1 is a table showing the evaluation results of the above test items.

  Here, Samples B to F are samples in which a gland packing was produced using a yarn obtained by mixing 60 parts by mass of graphite whose circularity was changed in a range of 0.4 to 0.8 with respect to 100 parts by mass of PTFE. . Sample A is a sample in which a gland packing was produced by braiding yarn not containing graphite. Further, the circularity of graphite is the average circularity obtained by calculating the circularity of 1000 or more graphites and averaging them.

  As shown in Table 1, in Samples B to F containing PTFE containing graphite, it can be seen that the temperature change is reduced as compared with Sample A containing no graphite. This is presumably because the heat dissipation of the ground packing was improved by incorporating PTFE with excellent thermal conductivity into PTFE.

  However, in Samples C to F containing graphite having a circularity of 0.5 to 0.8, the temperature change is reduced to 1/10 or less compared to Sample A not containing graphite. In the sample B containing graphite having a degree of 0.4, the temperature change is only about ½. This is because the graphite of Sample B has a distorted shape, and the graphite exposed on the surface of the yarn locally contacts the stem (rotating part) of the rotary tester in a non-uniform state. This is considered to be because the heat dissipation property of was not fully demonstrated.

  On the other hand, as shown in Table 1, it can be seen that in Samples B to F in which graphite is contained in PTFE, the mass reduction rate is reduced as compared with Sample A in which graphite is not contained. This is presumably because the wear resistance of the ground packing was improved by including PTFE with graphite having excellent mechanical strength.

  However, in Samples C to E containing graphite having a circularity of 0.5 to 0.7, the mass reduction rate is reduced to 1/5 or less compared to Sample A not containing graphite. In the sample B containing graphite with a circularity of 0.4, the mass reduction rate is about 2/3 as compared with the sample A not containing graphite. This is probably because the graphite of Sample B has a distorted shape, and the graphite exposed on the surface of the yarn has fallen off due to abrasion with the stem (rotating portion) of the rotating tester.

  Further, even in Sample F containing graphite with a circularity of 0.8, the mass reduction rate remains at about 2/3 as compared with Sample A containing no graphite. This is thought to be because the circularity of the graphite of sample F is large, and the anchor effect indicating the binding force between PTFE and graphite is smaller than those of samples C to E having a small circularity.

  The inventors of the present application confirmed the anchor effect indicating the bonding force between PTFE and graphite by the following method.

  2 and 3 are diagrams showing the results of observing the surface of the ground packing after evaluating the above test items in the sample C having a small mass reduction rate and the sample F having a large mass reduction rate. (A) is an SEM (scanning electron microscope) photograph, and (b) in each figure is an EDX (energy dispersive X-ray analyzer) photograph. The EDX photograph is graphite (carbon) in the SEM photograph. Is a mapping of the distribution of. In the SEM photograph and EDX photograph, the one indicated by the arrow A is graphite.

  As shown in FIG. 2B, it can be seen that in Sample C, there is no gap between PTFE and graphite, and PTFE and graphite are strongly bonded. In Sample C, the circularity of graphite contained in PTFE is small (0.5), so the anchor effect is large (the coupling force is large), and it is also caused by wear on the stem (rotating part) of the rotary tester. This is probably because graphite did not fall off.

  On the other hand, as shown in FIG. 3B, in Sample F, a gap is observed between PTFE and graphite. This is because in Sample F, the circularity of graphite contained in PTFE is large (0.8), so the anchor effect is small (binding force is small), and due to wear with the stem (rotating part) of the rotary tester, It is considered that a gap was generated between PTFE and graphite due to the rotation of graphite.

  From the above observations, a gland packing produced by braiding a yarn made of this mixture in which a mixture of PTFE mixed with graphite having a low circularity (0.5 to 0.7) is firmly bonded by the anchor effect. This is considered to have improved the wear resistance.

  Returning to Table 1 again, in Samples C to E containing graphite having a circularity of 0.5 to 0.7, the amount of liquid leakage is about 1/20 as compared to Sample A not containing graphite. It can be seen that it has decreased. As described above, since the circularity of graphite contained in PTFE is small, the anchor effect is large, and as a result, PTFE and graphite are strongly bonded to improve wear resistance (mass reduction rate). This is probably because of

  On the other hand, in sample B containing graphite with a circularity of 0.4, it can be seen that the amount of liquid leakage is larger than samples C to E. This is because, as described above, the graphite of Sample B has a distorted shape, so that heat dissipation and wear resistance were lower (mass reduction rate was larger) than Samples C to E. It is done.

  In addition, it can be seen that in Sample F containing graphite with a circularity of 0.8, the amount of liquid leakage is larger than Samples C to E. As described above, since the circularity of graphite contained in PTFE is large, the anchor effect is small. As a result, the bonding force between PTFE and graphite is weak, and the wear resistance is low (the mass reduction rate is low). This is probably because it was large.

  From the above results, by configuring the gland packing with a braided body formed by braiding a yarn formed by mixing PTFE and graphite having a circularity of 0.5 to 0.7, heat dissipation and wear resistance are improved. An excellent gland packing can be obtained. Thereby, for example, when the gland packing in this embodiment is applied to the shaft seal portion of the rotating shaft of the fluid device, the rotating shaft is used under a high PV value where the rotating shaft rotates at a high speed (for example, the peripheral speed is 20 m / sec or more). Even so, it can have sufficient heat dissipation and wear resistance. As a result, high sealing performance and durability can be maintained even when used for a long time under high PV.

  By the way, since graphite has higher thermal conductivity and mechanical strength than PTFE and graphite, a certain amount of graphite having a circularity of 0.5 to 0.7 is mixed with PTFE to produce a yarn. The gland packing produced by braiding this yarn can be expected to improve heat dissipation and wear resistance. Therefore, in the ground packing produced in this way, the following sample was prepared for the optimum range for obtaining excellent heat dissipation and wear resistance with respect to the graphite content mixed in PTFE. investigated.

(Production of gland packing)
As a mixture of PTFE and graphite, samples G to M in which the content of graphite having a circularity of 0.6 was changed in a range of 0 to 70 parts by mass with respect to 100 parts by mass of PTFE were prepared. The resulting yarn was braided to produce a ground packing. And with respect to each produced sample, each test item of leakage amount, temperature change, and mass reduction rate was evaluated by the same test method as described above.

  Table 2 is a table showing the evaluation results of the above test items.

  Here, the sample G is the same as the sample A in Table 1, and the sample L is the same as the sample D in Table 1.

  As shown in Table 2, in Samples H to M in which 100 parts by mass of PTFE contains 5 to 70 parts by mass of graphite, the temperature change is reduced to ¼ or less compared to Sample A in which graphite is not contained. You can see that This is presumably because the heat dissipation of the ground packing was improved by incorporating PTFE with excellent thermal conductivity into PTFE.

  On the other hand, in Samples H to L containing 5 to 60 parts by mass of graphite in 100 parts by mass of PTFE, the mass reduction rate was reduced to 1/2 to 1/5 compared to Sample A not containing graphite. However, in the sample M containing 70 parts by mass of graphite, the mass reduction rate is about 2/3 as compared with the sample A not containing graphite. This is because, in a mixture of PTFE and graphite, graphite does not have a binding property, and PTFE plays the role of a binder. Therefore, when the graphite content exceeds 70 parts by mass, it is made of a mixture of PTFE and graphite. This is thought to be due to the fragile yarn becoming brittle. Moreover, in the sample M, with the increase in the mass reduction rate, the amount of liquid leakage also increases as compared with the samples H to L.

  From the above results, in the gland packing produced by braiding a yarn made of a mixture of PTFE and graphite having a circularity of 0.5 to 0.7, the mixture of PTFE and graphite is based on 100 parts by mass of PTFE. It is preferable that 5 to 60 parts by mass of graphite is contained. Thereby, the gland packing excellent in heat dissipation and abrasion resistance can be obtained. Furthermore, it is more preferable that the mixture of PTFE and graphite contains 20 to 60 parts by mass of graphite with respect to 100 parts by mass of PTFE. Thereby, the gland packing more excellent in heat dissipation and abrasion resistance can be obtained.

  The yarn in the present embodiment is made of a mixture containing PTFE and graphite, but the mixture may contain carbon fibers, glass fibers, and the like. Thereby, the mechanical strength and wear resistance of the gland packing can be further improved.

  Moreover, although the method of knitting the yarn in the present embodiment is not particularly limited, for example, a knitting method such as eight knitting, lattice knitting, bag knitting, or the like can be used.

  In the present embodiment, the particle size of graphite mixed with PTFE is not particularly limited, but the average particle size of graphite is preferably smaller than the average particle size of PTFE. Thereby, a larger anchor effect can be obtained in the mixture of PTFE and graphite. Moreover, it is preferable that the average particle diameter of graphite is typically in the range of 10 to 100 μm.

  Moreover, in this embodiment, the kind of graphite mixed with PTFE is not limited, but artificial graphite, natural graphite, etc. can be used, for example. In addition, since the circularity of these graphite has a fixed distribution, the graphite used in this embodiment should just select and use the graphite which has an average circularity in the range of 0.5-0.7.

  In addition, the yarn in this embodiment is formed by extruding a mixture containing PTFE and graphite to form a filament, and then stretching the bundle of filaments. You may shape | mold to a shape (for example, rectangle).

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible. For example, in the above-described embodiment, an example in which the gland packing is applied to the shaft seal portion of the rotating shaft of the fluid device has been described, but the present invention is not limited to this. Of course, the gland packing in this embodiment can be applied.

1 Rotating shaft
2 Packing box
3 Gland packing 4 Packing retainer 5 Bolt

Claims (2)

A gland packing made of braided yarn,
The yarn is made of a mixture of PTFE and graphite,
The circularity of the graphite is in the range of 0.5 to 0.7,
The mixture is a gland packing containing 5 to 60 parts by mass of graphite with respect to 100 parts by mass of PTFE. A method for producing a yarn for use in a gland packing formed by braiding a yarn,
Producing a mixture comprising PTFE and graphite;
Extruding the mixture to form a filament;
Stretching the bundle of filaments to form a yarn,
The circularity of the graphite is in the range of 0.5 to 0.7,
The method for producing a yarn for gland packing, wherein the mixture contains 5 to 60 parts by mass of graphite with respect to 100 parts by mass of PTFE.