Patent Application
20120108474
This application claims priority from Japanese Patent Application Number JP 2010-241371 filed on Oct. 27, 2010, the content of which is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a stick-shaped lubricant member that is excellent in heat resistance and that contains lubricant oil, and relates to a method of manufacturing the lubricant member.
2. Description of the Related Art
The structure described below is a known example of a conventional lubricant composition. The lubricant composition is formed by: polymerizing the monomer or pre-polymer of a thermosetting resin with lubricant oil, or grease containing the lubricant oil as its base oil, and a polymer with a high oil-supply capability; and then thermally hardening the resultant polymerized product. Blending ratios with respect to the total amount of lubricant oil or grease in the lubricant composition are disclosed in a way that: the amount of thermosetting resin is 10 wt % to 90 wt %, preferably 20 wt % to 50 wt %; and the amount of polymer with high oil-supply capability is approximately 5 wt % to 30 wt %, which is practically sufficient although a larger amount of blended polymer with the high oil-supply capability increases the amount of lubricant oil or grease content (This technology is described, for instance, in Japanese Patent Application Publication No. 7-118684, pages 3 to 5).
As described earlier, in the oilless bearing 21 shown in
However, even the oilless bearing 21 and the die-set 31 have the following problems. Specifically, both of the solid lubricants 24, 36 do not contain any lubricant oil; and are so hard as to have low capability of supplying lubricant that becomes the coating film, in comparison to a case where lubricant oil or grease is supplied to the sliding surfaces. In addition, the low capability of supplying the lubricant leaves some portions of the sliding surfaces without the coating film, and these portions are likely to become seized regions, where galling takes place in some cases. Moreover, small pieces chipped off from the solid lubricants 24, 36 existing on the sliding surfaces sometimes damage the sliding surfaces.
In some case, a lubricant composition is made of a thermosetting resin to deal with the above-described problems caused by the hard solid lubricants 24, 36. The use of the thermosetting resin reduces the galling in the sliding surfaces, and increases the amount of the lubricant-oil content, in comparison to the cases of the solid lubricant 24, 36. The lubricant composition made of the thermosetting resin, however, is softer than the solid lubricants 24, 36, and pieces may possibly be chipped off from the lubricant composition while the lubricant composition is used while being exposed on the sliding surfaces, as shown in
Last but not the least, there are industrial demands for a resin-made, heat-resistant, durable and long stick-shaped lubricant composition which contains lubricant oil, and which can be buried in holes in a sliding surface after being cut into pieces depending on the depth of the holes. Despite the demands, such a stick-shaped lubricant composition has not been produced as a product usable in a high-temperature environment. In the case of using, for example, a thermosetting resin, the molded product of lubricant composition is so hard as to have poor workability. In addition, when the lubricant composition is processed into a long stick-like shape, it is difficult to mix the lubricant oil evenly in the entire stick-shaped lubricant composition, which poses another problem that the lubricating properties differ from one cut surface to another. Moreover, forming a long stick-shaped lubricant composition itself is also difficult in some cases of particular blending ratios of raw materials and/or under certain manufacturing conditions.
The present invention has been made with the foregoing situations taken into consideration. A lubricant member of a preferred embodiment of the invention is molded, into a stick-shaped body defined by an axial direction and a radial direction, comprising: a lubricant oil; an ultrahigh molecular weight polyethylene; and a thermoplastic resin having a melting point higher than the ultrahigh molecular weight polyethylene; wherein the thermoplastic resin forms a dense and crystallized portion in a periphery of the stick-shaped body with respect to the radial direction and forms fibrous crystals in an inner portion of the stick-shaped body with respect to the radial direction so that a plurality of pores between the fibrous crystals contain the lubricant oil or crystallized bodies of the ultrahigh molecular weight polyethylene holding the lubricant oil.
A method of manufacturing a lubricant member of another preferred embodiment of the invention is characterized by including the step of: preparing a mixture comprising a granular material of an ultrahigh molecular weight polyethylene, a granular material of a thermoplastic resin having a melting point higher than the ultrahigh molecular weight polyethylene and a liquid lubricant oil; providing a die having an axial cavity defined by an axial direction and a radial direction; filling the cavity of the die with the mixture; heating the die while a pressure is applied to the mixture in the cavity in the axial direction so that the mixture reaches a temperature higher than or equal to the melting point of the thermoplastic resin; and cooling the die so as to form the mixture into a stick-shaped body.
Description is given below of a lubricant member of a preferred embodiment of the invention.
As
The lubricant member 1 is formed by: mixing, for example, at least a thermoplastic resin, an ultrahigh molecular weight polyethylene, and lubricant oil together; filling the resultant mixture in a die; heating the mixture in the die under a certain pressure; and then cooling the resultant mixture. As shown in the drawing, the lubricant member 1 is designed to be 4.2 mm to 12.2 mm in a dimension in the diametrical direction (D), and in a range of 30.0 mm to 200.0 mm in a dimension in a lengthwise direction (L). Note that the dimensions both in the diametrical direction (D) and in the lengthwise direction (L) may be changed appropriately to meet the needs of the use of the lubricant member 1.
A polyamide resin is used as the thermoplastic resin. For example, Nylon 6 (produced by Toray Industries, Inc.) or Nylon 66 (produced by Ube Industries, Ltd.) is used as the thermoplastic resin. Fine particles of Nylon 6 have an average particle size of 13 μm (TR-7) or 20 μm (TR-2). Nylon 6 has a sharp particle-size distribution and a characteristically porous structure. Nylon 6 has an excellent capability of supplying oil and is dispersed well in water. In addition, Nylon 6 is highly resistant against heat. The polyamide resin forms the skeletal structure of the lubricant member 1, and has a melting point which is as high as 230° C. to 260° C., as well as enhances the heat resistance and durability of the lubricant member 1. The lubricant member 1 thus formed is usable under a high-temperature conditions where the sliding surfaces are at 200° C. approximately. In comparison to thermosetting resins, the polyamide resin has better capability of supplying oil and thereby serves also as a lubricant without sacrificing the mechanical strength. Hence, even if pieces of polyamide resin chipped off from the lubricant member 1 exist on the sliding surfaces, the pieces do not adhere to the sliding surface, or impair the sliding property. In addition, pieces of polyamide carbonize due to the frictional heat generated by the sliding motions, so that no layer of carbonized pieces that would physically damage the sliding surfaces is formed at all. Note that other polyamide resins such as Nylon 12 and PET may also be used in place of Nylon 6 or Nylon 66.
Examples of the usable ultrahigh molecular weight polyethylene are HIZEX MILLION® (produced by Mitsui Chemicals, Inc.) and MIPERON® (produced by Mitsui Chemicals, Inc.). HIZEX MILLION® is an ultrahigh molecular weight polyethylene with an average particle size ranging of 150 μm to 200 μm, and an average molecular weight ranging from 0.5 million to 6 million. HIZEX MILLION® has excellent mechanical properties. MIPERON® is an ultrahigh molecular weight polyethylene with an average particle size ranging of 25 μm to 30 μm, and an average molecular weight ranging of 1.5 million to 3 million. MIPERON® has an excellent lubricating ability, and is well resistant to abrasion. The melting point of each ultrahigh molecular weight polyethylene is 130° C., approximately.
A mixture of poly-α-olefin and ester is used as the lubricant oil. Other possible materials used as the lubricant oil are: hydrocarbon-based ones such as a-olefin oligomer; ester-based ones such as polyphenyl ester; ester-based ones such as ethylhexyl sebacate; silicone-based ones such as polysiloxane; fluorine-based ones such as fluorocarbon. Alternatively, the lubricant member 1 may be formed by using either plant-derived lubricant oil such as olive oil or animal-derived lubricant oil such as lard. In such cases, the lubricant member 1 can be used in the sliding surfaces of various food-processing machines.
The lubricant member 1 contains various other materials including: solid lubricant such as graphite granular; graphite; and molybdenum disulfide. When these materials are mixed in the lubricant oil and coat the sliding surfaces, the sliding performance between sliding parts is improved further.
As
As
To be more specific, in the layer of the film 2, multiple plate-shaped crystal layers 4, in each of which the polyamide resin is densely crystallized, are presumably crystallized adjacent to one another in the lengthwise direction of the lubricant member 1. For descriptive convenience,
Fibrous crystals extending from the inner layer 6 and/or from the adjacent crystal layers 4 are presumably formed in these gaps 5. As described earlier, in the layer of the film 2, mainly the crystal layers of the densely-crystallized polyamide resin are formed due to the difference in the melting point. Hence, the layer of the film 2 has a smooth and flexible surface, and offers a function of: minimizing the leakage of the lubricant oil in the diametrical direction (D); and increasing the supply of the lubricant oil in the lengthwise direction.
Furthermore, like the layer of the film 2, the layer 6 at the inner side of the film 2 includes multiple plate-shaped crystal layers 7 which are presumably crystallized adjacent to one another in the lengthwise direction (L) of the lubricant member 1. The crystals in the crystal layers 7 are not so densely formed as those in the crystal layer 4. This is presumably because: the slower decrease in the temperature allows the chains of the ultrahigh molecular weight polyethylene to inhibit the crystallization of the polyamide resin alone; and the crystallization of the crystal layers 7 progresses while the crystals of the polyamide resin and the ultrahigh molecular weight polyethylene intertwine with each other. Consequently, a structure with multiple pores 3 formed among the crystal layers 7 is presumably formed without each of the polyamide resin and the ultrahigh molecular weight polyethylene being densely crystallized into lumps.
Though details are described later, if the heating and the cooling are performed under the conditions where a certain pressure is applied to the cylindrical-shaped cavity of the die in the lengthwise direction (L) of the cavity, the fibrous crystals of the polyamide resin and those of the ultrahigh molecular weight polyethylene extend longer in the lengthwise direction (L) of the lubricant member than in the diametrical direction (D). This structure facilitates development of each of the pores 3 formed among the fibrous crystals into a long cavity which extends longer in the lengthwise direction (L) of the lubricant member 1. Consequently, the lubricant oil held in the pores 3 has a structure allowing easy supply in the lengthwise direction (L) of the lubricant member 1.
Though not illustrated in
Note that, in the crystal layers 4 and 7 Rained on the inner side of the film 2, including regions which are not illustrated, multiple pores 3 may be formed among crystals through a process in which: multiple fibrous crystals develop into corrugated crystal bodies due to their connections; and the resultant crystal bodies extend longer in the lengthwise direction (L) of the lubricant member 1 than in the diametrical direction (D) of the lubricant member 1 . The crystal layers included in each layer has different sizes and thicknesses in the diametrical direction (D) from one layer to another due to the different cooling speeds.
Next, an example of how to use the lubricant member 1 is described below by referring to
As
As described earlier, the film 2 of the lubricant member 1 is formed as a thin film without sacrificing the mechanical strength, and fibrous crystals of the polyamide resin and fibrous crystals of the ultrahigh molecular weight polyethylene extend in the in the lengthwise direction (L) of the lubricant member. Hence, it is easier to cut the lubricant member 1 in the diametrical direction (D). Furthermore, although the diametrical (D) sections of the cut-out lubricant members 1A, 1B are exposed to the sliding surface of the slidable plate 8, pores 3 containing the lubricant oil are arranged in the depth direction of the holes 10 formed in the slidable plate 8. Hence, the lubricant oil is supplied to the sliding surface gradually and slowly, and thereby each of the lubricant members 1A, 1B can have a longer service life.
In addition, since the fibrous crystals of the polyamide resin and the fibrous crystals of the ultrahigh molecular weight polyethylene extend in the lengthwise direction (L) of the lubricant member, the width of each of the fibrous and corrugated crystal bodies is smaller in the exposed surfaces of the lubricant members 1A, 1B. Hence, multiple fibrous and corrugated crystal bodies are exposed to the exposed surfaces of the lubricant members 1A, 1B, so that the contact area of these crystals with the sliding member (i.e., the counterpart of the sliding plate 8 decreases). Consequently, the lubricant members 1A, 1B can respond to the movement of the sliding member in a smooth and flexible manner, and thus the mechanical stress which the lubricant members 1A, 1B receive from the sliding member can be reduced a lot.
In addition, the columnar shape of the lubricant member 1 makes the shape of each hole 10 easier to form in the sliding surface of the slidable plate 8 with drill 9 or something similar. In addition, the workability is enhanced in fitting each cut-piece of the lubricant member 1 into the corresponding hole 10.
In addition, the inhibition of the leakage of the lubricant oil from the side surface of the lubricant member 1 provides a structure which makes the lubricant member 1 less likely to come off the holes 10.
Table 1 shows results of a test examining the workability and the heat resistance of the lubricant members 1 of Examples 1 to 17. The lubricant members 1 of Examples 1 to 17 had the same amount (60 wt %) of the lubricant oil (i.e., the mixture of poly-α-olefin and ester), but differed from one another in the amounts of the polyamide resin (Nylon 6) and the ultrahigh molecular weight polyethylene (MIPERON®) mixed in the corresponding lubricant members 1. For each lubricant member thus formed, the heat resistance was assessed on the base of the result of an actual sliding test done by burying cut pieces of the lubricant member in a sliding surface.
In Example 1, as
In Example 2, the inclusion of 1.0 wt % of the ultrahigh molecular weight polyethylene made it possible to shape the lubricant member 1 like a stick. However, the portion of the film 2 made of Nylon 6 (see
In Example 3, although 1.5 wt % of the ultrahigh molecular weight polyethylene was included, the content of Nylon 6 was so much that the lubricant member 1 was able to be cut in the diametrical direction (D) in some portions, but not in other portions, depending on the crystal state of Nylon 6 as shown in
In Examples 4 to 7, the content of the ultrahigh molecular weight polyethylene was in a range of 2.0 wt % to 4.5 wt %, and the lubricant member 1 was able to be cut in the diametrical direction (D) at any position of the lubricant member. In addition, since the content of Nylon 6 was large enough, the lubricant member 1 kept its shape after the sliding test, and its heat resistance was accordingly satisfactory.
In each of Examples 8 to Example 10, the content of the ultrahigh molecular weight polyethylene was increased to a range of 5.5 wt % to 10.0 wt %. As
In each of Examples 11 to 13, the content of the ultrahigh molecular weight polyethylene ranged from 11.0 wt % to 13.0 wt %. The lubricant member 1 thus formed was able to be cut in the diametrical direction (D) at any position, and the cutting-workability was enhanced. Despite the increased amount of the ultrahigh molecular weight polyethylene, the lubricant member kept its shape after the sliding test, and the heat resistance was accordingly satisfactory. Incidentally, an amount of ultrahigh molecular weight polyethylene that flowed out of the lubricant member after the sliding test was larger in Examples 11 to 13 than in Examples 8 to 10, and a depressed area was formed in the central region of the lubricant member 1 in each of Examples 11 to 13. However, this raised no problem.
In Example 14, the content of the ultrahigh molecular weight polyethylene was 13.5 wt %. The lubricant member 1 was able to be cut in the diametrical direction (D) at any position, and the cutting-workability was enhanced. On the other hand, an amount of ultrahigh molecular weight polyethylene that flowed out of the lubricant member after the sliding test was larger. A depressed area was formed in the central region of the piece of the lubricant member 1 which is indicated by Circle A in
In each of Examples 15 to 17, the content of the ultrahigh molecular weight polyethylene ranged from 14.0 wt % to 16.5 wt %. The lubricant member 1 was able to be cut in the diametrical direction (D) at any position, and the cutting-workability was enhanced. On the other hand, an amount of ultrahigh molecular weight polyethylene that flowed out of the lubricant member after the sliding test was much larger in Examples 15 to 17 than in the case of Example 14. The lubricant member 1 assumed a shape that impaired the sliding performance, and the lubricant member 1 was poor at the heat resistance.
The experiment results of Examples 1 to 17 proves that if the content of the ultrahigh molecular weight polyethylene ranges from 2.0 wt % to 13.0 wt %, the lubricant member 1 with adequate workability and heat resistance can be formed. Conversely, it is proved that: if the content of the ultrahigh molecular weight polyethylene is less than 2.0 wt %, the lubricant member is poor at the workability, and it is accordingly difficult to form a lubricant member having the desired characteristics; and if the content of the ultrahigh molecular weight polyethylene is greater than 13.0 wt %, the lubricant member is poor at the heat resistance, and it is accordingly difficult to form a lubricant member having the desired characteristics as well.
Note that although the embodiment have been described taking the case where the film 2 of the lubricant member 1 is single-layered, the embodiment is not limited to this case. For example, the film 2 may have multiple layers, for example, by adjusting the cooling temperature, the cooling method and the like. As described earlier, a thick layer of the film 2 impairs the cutting-workability of the lubricant member 1. Hence, any change can be made to the design with the mechanical strength and the workability of the lubricant member 1 taken into consideration. In addition, various other changes can be made without departing from the essence of the invention.
Next, description is given of another preferred embodiment of the invention, that is, a method of manufacturing a lubricant composition.
Granulated granular of Nylon 6 is used as the thermoplastic resin. Granulated granular of MIPERON® is used as the ultrahigh molecular weight polyethylene. A mixture of poly-α-olefin and ester is used as the lubricant oil. All of these components are mixed together at the ordinary temperature to form a gel mixture. The air contained in the mixture is removed by agitating the mixture. Then, the resultant mixture 13 is filled into a cavity 14 of a die 12, and then the cavity 14 is shielded, as
In this respect, a pusher mechanism 16 is connected to an open-close plug 15. The pusher mechanism 16 applies a certain pressure to the inside of the cavity 14 in the lengthwise direction (L) of the cavity 14, as indicated by arrows 17 in
Thereafter, the die 12 is placed in a furnace, and the die 12 is heated up to a temperature at which the mixture 13 in the cavity 14 is melted (i.e., at least to a temperature equal to or higher than the melting point of Nylon 6).
Then, the die 12 is taken out of the furnace, and is left in the workroom to be, for example, air-cooled down to room temperature.
One may consider that, as described above, the fibrous crystals of the polyamide resin and those of the ultrahigh molecular weight polyethylene extend mainly in the lengthwise direction (L) of the lubricant member 1 and the multiple pores 3 are formed, because, as described above, both the heating and the cooling of the die 12 are performed with the pressure applied to the mixture 13 in the die 12 in the lengthwise direction (L) of the cavity 14. In addition, each of the pores 3 tends to have a shape extending in the lengthwise direction (L) of the lubricant member 1, so that the lubricant member 1 can have a longer service life.
In addition, like the cavity 14 which has a cylindrical shape, the die 12 has a columnar shape that facilitates the dissipation of heat. Hence, the cooling of the mixture 13 in the cavity 14 progresses from the outer side, in the diametrical direction (D). Consequently, the densely-crystallized film 2 of Nylon 6, which has the smooth and flexible surface, is formed in the outermost portion of the lubricant member 1. Thus, the film 2 realizes a structure which prevents the leakage of the lubricant oil from the side surface of the lubricant member 1 as effectively as possible, and which makes it easy for the lubricant oil to be supplied to the sliding surface.
In addition, because the open-close plug 15 is moved by the elastic mechanism 18 in accordance with the state of the mixture 13, the lubricant member 1 is securely formed into a columnar shape although the Nylon 6 shrinks while the Nylon 6 is hardened.
Note that, although the embodiment has been described taking the case where the die 12 is air-cooled in the workroom, the cooling method is not limited to this case. The cooling time may be shortened, for example, by air-cooling the die 12 in the workroom for a certain length of time; and thereafter cooling the resultant die 12 with warm water. That is to say, a step-by-step manner of cooling the die 12 can be employed as long as both a desirable extending direction of the crystals of the lubricant member 1 and a desirable structure of the pores 3 can be achieved as described earlier. In short, changes can be made to the design of the cooling method. In addition, various other changes can be made without departing from the essence of the invention.
The invention realizes the lubricant member, which is good at heat-resistance and durability while maintaining the certain lubricating property, because the thermoplastic resin that contains the lubricant oil and has the lubricating property is used.
In addition, the invention realizes the lubricant member whose shape is easy to keep, and which is good at supplying the lubricant oil in the lengthwise direction, because its external circumferential surfaces is coated with the thermoplastic resin which is in the densely-crystallized state.
Furthermore, the invention increases the amount of lubricant oil to be included in the lubricant member, and makes the lubricant member contains the lubricant oil more homogeneously, because: the thermoplastic resin is crystallized in the fibrous state more in the lengthwise direction than in the diametrical direction; and the multiple pores are accordingly faulted.
Moreover, the invention enhances the workability of the lubricant member while maintaining the mechanical strength of the lubricant member, because the lubricant member contains the 2 wt % to 13 wt % of ultrahigh molecular weight polyethylene.
Besides, the invention enhances the workability of the lubricant member when the lubricant member is used in the sliding surface, and makes it easier to place the lubricant member in the sliding surface, because the lubricant member is formed into the columnar shape.
Additionally, the invention forms the lubricant member that is processed in the stick-shaped shape, because the heat treatment is performed on the mixture placed in the cavity of the die under pressure applied in the lengthwise direction of the cavity.
In addition, the invention forms the lubricant member which dissipates heat homogeneously, and which has an excellent process shape, because the cavity of the die is shaped like a cylinder.
In addition, the invention forms the lubricant member which is long in the lengthwise direction, because the movement of the open-close plug of the die is adjusted by use of an elastic mechanism in accordance with the state of the mixture placed in the cavity.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-241371 | Oct 2010 | JP | national |
