JPH08260127A - Screw parts - Google Patents

Abstract

PURPOSE: To reduce the coefficient of friction and wear by subjecting the surface of screw parts made of titanium metal to sliding treatment with durability without deteriorating the corrosion resistance characteristic of titanium metal of its own. CONSTITUTION: Screw parts made of titanium metal composed of pure titanium metal or an alloy of titanium and the other metallic components are subjected to plasma carburizing treatment in an atmosphere contg. gaseous hydrocarbons such as methane homologues shown by Cn H2n+2 under the vacuum heating conditions of 0.5 to 15Torr and 700 to 1100 deg.C, or, the screw face in the obtd. screw parts is moreover coated with a lubricating coating material contg. polytetrafluoroethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw part made of titanium metal.

[0002]

2. Description of the Related Art Generally, threaded parts are required to have sufficient corrosion resistance under the conditions of use, and therefore such conditions (for example, the condition of being exposed to fresh water or seawater under the ground, in the water or under the sea). ), But a molding material that withstands relatively well is adopted.

Steel, especially stainless steel, is known as a molding material for screw parts having excellent corrosion resistance, and titanium metal is known as an industrial material having excellent corrosion resistance.

The titanium metal has high heat resistance, strength almost equal to that of carbon steel, and since it forms an oxide film on the surface, it has excellent corrosion resistance. Also, pure titanium is
It is possible to form alloys with all metals, especially copper, tin, iron, aluminum, vanadium, chromium, cobalt, molybdenum, tungsten, etc., and to improve their workability and mechanical strength in various ways.

[0005]

However, when a threaded part is manufactured from titanium metal as described above, it has excellent properties such as corrosion resistance and mechanical strength. There is a problem in that such a required characteristic is not sufficiently satisfied in order to secure a tightening force (axial force) required for mechanical design in order to make the thread surface have a low friction coefficient.

Therefore, the object of the present invention is to solve the above-mentioned problems and subject a threaded component made of titanium metal to a durable sliding treatment on its surface without deteriorating the original corrosion resistance of titanium metal. To reduce the friction / wear coefficient.

[0007]

In order to solve the above problems, in the present invention, a hydrocarbon gas containing 0.
This is a threaded component made of titanium metal plasma-carburized in an atmosphere of 5 to 15 torr and 700 to 1100 ° C.

Alternatively, 0.5 to 0.5 containing a hydrocarbon gas
In a threaded component made of titanium metal plasma-carburized in an atmosphere of 15 torr and 700 to 1100 ° C.,
The lubrication paint containing polytetrafluoroethylene was applied to the thread surface of this threaded component.

As the polytetrafluoroethylene of the above-mentioned lubricating coating, it is preferable to employ low molecular weight polytetrafluoroethylene having a molecular weight (Mn) of 8000 or less.

The details will be described below. The threaded component referred to in the present invention is not particularly limited in its shape or purpose of use, and may include machine screws, bolts and nuts (for example, polygonal bolts such as hexagon bolts, holed bolts such as hexagon socket head bolts, and implants). Bolts, foundation bolts, square root bolts, etc. and their corresponding nuts), washers, and other well-known screw parts.

The titanium metal used in the present invention may be either pure titanium or an alloy of titanium and another metal component, and the composition of the alloy is not particularly limited. The purity of titanium, which is a commercially available titanium metal, is 9
Although it is about 9.9 to 99.5%, such pure titanium can also be used.

Other metal components of the titanium alloy are not particularly limited because titanium metal forms an alloy with all metals as described above, but for example, copper,
Examples thereof include tin, iron, aluminum, vanadium, chromium, cobalt, molybdenum, and tungsten.

After forming such a titanium metal into a threaded part and before plasma carburizing, it is desirable to immerse the surface in an organic solvent and perform ultrasonic cleaning.

To carry out the plasma carburizing treatment, a treatment chamber surrounded by a heat insulating material such as graphite fiber is formed in the heating furnace, the treatment chamber is heated by a heating element made of rod graphite, and the upper portion of the treatment chamber is heated. Connect the positive electrode of the DC glow discharge to the and the cathode of the processing table, and install the gas manifold at the important points in the processing chamber to install process gas such as hydrocarbon, nitrogen, argon, hydrogen or cleaning. It is possible to use a known carburizing treatment device in which the working gas is introduced while being appropriately dispersed.

That is, the plasma carburization of the present invention can be processed by the following operations.

First, after titanium metal is charged into the processing chamber and exhausted, it is heated to a carburizing temperature of 700 to 1100 ° C. by a heater, and a diluting or cleaning gas such as hydrogen, argon or nitrogen is introduced, and 200 A high DC voltage of ˜1500 V is applied and held for 10 to 30 minutes.

At this time, the introduced gas is turned into plasma, but the potential in the plasma is almost uniform from the anode to the cathode, and the potential drops sharply near the cathode. Therefore, the hydrogen ions H ⁺ and the argon ions Ar ⁺ in the plasma are accelerated by the cathode fall and collide with the titanium metal surface to splash oxides and other deposits on the surface to clean the titanium metal surface.

Next, when a hydrocarbon gas such as methane gas is introduced in the range of 0.5 to 15 torr, ionized activated carbon C ⁺ is generated in the plasma gas, which is further adhered to the titanium metal surface and is further adsorbed. Diffuse inside,
The carburization reaction proceeds by the action of sputtering or implantation.

The hydrocarbon gas used in the present invention is a methane congener represented by C _n H _{2n + 2} and is a gas at the above carburizing temperature, and it is possible to use the hydrocarbon gas without particularly limiting its kind. it can. In particular, methane, ethane, propane, and butane, which are gases at room temperature, are preferable because they do not require vaporization equipment when used.

Here, the pressure of the hydrocarbon gas under the above-mentioned plasma carburizing conditions is 0.5 to 15 torr. Such a pressure of the hydrocarbon gas is necessary for forming a treatment layer mainly made of TiC on the titanium metal surface, and at a low pressure of less than 0.5 torr, the treatment layer has a small amount of carbon and has a sliding property. Improvement is not enough. Also, 15t
This is because when the pressure is higher than orr, the carbon content of the carburized layer becomes a saturated value, and the carburizing effect is not improved any more, which is not practical.

The atmospheric temperature of the plasma carburizing treatment in the present invention is 700 to 1100 ° C. Because 70
At low temperatures below 0 ° C, sooting (soot) is likely to occur on the titanium metal surface, so that the partial pressure of the diluting gas (hydrogen, argon, nitrogen, etc.) becomes too high, and the treatment efficiency is extremely reduced. . Further, at a temperature higher than 1100 ° C, titanium transforms from a hexagonal system (α type) to an equiaxed system (β type) at 950 ° C to change the physical properties, and at a temperature higher than 1100 ° C, strength characteristics are secured. Therefore, a treatment temperature higher than this is not practical.

Since the treatment time is set in consideration of the ambient temperature, the kind of gas, the concentration and the treatment pressure, for example, the ambient temperature is 950.degree. (100%) pressure is 1
In the case of Torr, one hour is a guideline and may be appropriately increased / decreased so that the required mechanical strength can be obtained according to the intended use of the titanium metal or titanium alloy screw part to be treated. From this, the most preferable experimentally obtained plasma carburizing condition is 950 ° C. for 90 minutes.

[0023]

The titanium metal screw component of the present invention is plasma-carburized at a predetermined pressure and temperature, so that activated carbon ions are attached to the surface of the threaded component or jump out of the titanium metal surface. The Ti atom is bonded to the activated carbon ion to be deposited on the titanium metal surface and diffused inward, or the accelerated carbon ion in the vicinity of the cathode is directly driven into the titanium metal. A treatment layer mainly made of titanium carbide is formed.

It is considered that the treated layer on the surface of the screw part thus formed is carbonized so that the carbide exhibits lubricity, so that the coefficient of friction and wear is reduced, and when the screw part is tightened. With the required slidability,
Moreover, it has the original excellent corrosion resistance as a titanium metal screw part.

Since the treatment layer can be formed as a relatively thick layer of, for example, about 70 μm, a durable surface treatment layer can be formed.

When the lubrication paint containing polytetrafluoroethylene is applied to the thread surface of the threaded part, the sliding characteristics of the thread surface are further improved, so that the axial force at the time of tightening can be reduced and high tightening can be achieved. It becomes a threaded part that exhibits wearability.

[0027]

EXAMPLES First, an experiment on sliding characteristics and corrosion resistance when titanium metal is plasma carburized will be described below.

[Experimental Example 1] A plate-shaped pure titanium having a length of 25 mm, a width of 35 mm and a thickness of 3 mm (made by Kobe Steel Ltd.) was used as 24
After 0 emery polishing, ultrasonic cleaning was performed in acetone, and plasma carburization was performed using the following apparatus and conditions.

That is, there is a treatment chamber surrounded by a heat insulating material such as graphite fiber in the heating furnace. The treatment chamber is heated by a heating element made of rod graphite, and a positive electrode for direct current glow discharge is provided above the treatment chamber. Connect
In addition, a known carburizing treatment device in which a cathode is connected to a treatment table and a gas manifold is installed at a required place in the treatment chamber to appropriately introduce process gas such as hydrocarbon, nitrogen, argon and hydrogen. (Manufactured by JEOL Ltd.) was used.

As the carburizing treatment conditions, the gas composition was 100% propane gas, the gas pressure was 1 Torr, the treatment time was 1 hour, and the treatment temperature was 950 ° C. After the treatment, nitrogen gas was injected into the treatment chamber and cooled to room temperature. .

With respect to the experimental example subjected to the above processing, X
The crystal structure and thickness of the treated layer were observed and measured using a line diffraction and an optical microscope, and a friction / wear test was conducted.

The friction / wear test of (1) was conducted under the following apparatus and conditions, and the results are shown in FIGS. 2 (a) and 3 (a).

That is, by the counter weight,
A pin-type sliding mating material (bearing steel: SUS) is attached to the lower surface of one end of the arm supported so that a load of 1.96 N is applied to one end.
J2 or one made of the same material as the test piece)
While this sliding mating member was pressed against the surface of the flat plate-shaped sample piece under the load, the sample piece was forcibly reciprocated at a speed of 20 mm / sec and a stroke of 5 mm in the direction perpendicular to the longitudinal direction of the arm. . At this time, the frictional force acting between the sliding mating material and the sample piece was detected by the strain gauge as the strain generated in the arm, and the strain amount was input to the computer via the A / D converter to calculate the friction coefficient. ..

In this experiment, the friction time was set to 2 hours,
It was carried out under the conditions of a relative humidity of 50 to 60%, room temperature, and the atmosphere. Regarding the measured value of the friction coefficient in the above experiment, the time change of the friction coefficient for 60 minutes from the beginning of the experiment was calculated,
The results are shown in the graph of FIG.

As to the wear characteristics, the wear weight amount or wear volume was obtained from the cross-sectional shape of the wear mark of the sample piece measured by a surface roughness meter or the weight change of the sample piece before and after the experiment, and the ratio after the friction experiment was calculated. The amount of wear (mm ³ / Nm) was determined.

[Experimental Example 2] Experimental Example 1 except that a titanium alloy (Ti-6Al-4V) (manufactured by Kobe Steel, Ltd., same size) was used in place of the titanium alloy used in Experimental Example 1. Plasma carburization was performed under exactly the same conditions to manufacture a test piece, and the same experiment was performed. The result is shown in FIG.
It is shown in FIG.

In Experimental Example 2, the corrosion resistance of potentiostat was compared, and the current density (μA / c) was measured under the conditions of 3 wt% sodium chloride solution, 21 ° C. and no ventilation.
m ² ) and the potential (mV VS.SCE),
This is shown in FIG.

Comparative Example 1 A test piece was manufactured in exactly the same manner as in Experimental Example 1 except that plasma nitriding treatment was performed under the following conditions instead of performing plasma carburizing treatment in Experimental Example 1. The same experiment was performed, and the results are shown in Fig. 2.
(A), FIG. 3 (a), and FIG.

Further, in Comparative Example 1, the corrosion resistance by potentiostat was compared, and the result is shown in FIG.

As the plasma nitriding treatment conditions, the gas composition was 100% nitrogen gas, the gas pressure was 2 Torr, the treatment time was 3 hours, the treatment temperature was 790 ° C., and the furnace was cooled to room temperature after the treatment.

Comparative Example 2 A test piece was prepared in exactly the same manner as in Experimental Example 2 except that plasma nitriding treatment (same conditions as in Comparative Example 1) was performed instead of performing plasma carburizing treatment in Experimental Example 2. It was manufactured and the same experiment was performed, and the results are shown in FIGS. 2 (b) and 3 (b).

[Comparative Example 3] Pure titanium (manufactured by Kobe Steel Ltd.)
A test piece was manufactured in the same manner, and the same experiment as in Experimental Example 1 was performed on the test piece (in the state where the surface treatment was not performed), and the results are shown in FIG.

In Comparative Example 3, the corrosion resistance of potentiostat was compared, and the results are shown in FIG.

[Comparative Example 4] Titanium alloy (Ti-6Al-
4V) (manufactured by Kobe Steel Ltd.), and the same experiment as in Experimental Example 1 was performed on this (without surface treatment), and the results are shown in FIG. It is shown in b).

Experiments of Experimental Examples and Comparative Examples described above
The results of are described below.

First, regarding the crystal structure and thickness of the treated layer using X-ray diffraction and an optical microscope, the Ti alloy:
Ti ₂ N> TiN, pure Ti: TiN> Ti ₂ N,
The carburized layer formed on the surface of pure titanium or titanium alloy had a thickness of 70 μm. In this case, the treated layer of pure titanium was clear, whereas the treated layer of titanium alloy had a diffused layer and was somewhat unclear. These treated layers were predominantly TiC.

Next, regarding the comparative test of corrosion resistance by potentiostat, as is clear from the result of FIG. 1, the experimental example 2 consisting of the titanium alloy subjected to the plasma carburizing treatment is the titanium alloy subjected to the plasma nitriding treatment. Compared to Example 1 or Comparative Example 3 which is untreated pure titanium, the potential increased, the current decreased, and the corrosion resistance was improved.

Regarding the friction and wear test, as is clear from the results of FIGS. 2 and 3, the friction and wear characteristics of Comparative Example 1 or Comparative Example 2 in which pure titanium or a titanium alloy was plasma-nitrided were not found to be pure titanium. There was no improvement over the treated Comparative Example 3 or the untreated Comparative Example 4 with the titanium alloy, respectively.

The reason for this is considered to be that the nitride layer is very thin as described above, so that the nitride layer peels off or wears at the initial stage of friction, and thereafter shifts to friction with the base material.

On the other hand, in Experimental Example 1 in which pure titanium is plasma carburized or Experimental example 2 in which titanium alloy is plasma carburized, when the treated sample pieces rub (FIG. 2), the sample piece and the bearing are In both cases where the steel was rubbed (FIG. 3), both the friction coefficient and the specific wear amount were considerably reduced, and the friction / wear characteristics were improved.

Further, as is clear from the result of FIG.
The titanium metal subjected to the plasma carburizing treatment had not only a small coefficient of friction but also a very small variation in these values over time.

From the above results, it is understood that the material obtained by subjecting pure titanium to the plasma carburizing treatment under the predetermined condition has the required corrosion resistance and the required sliding property as the screw part.

Next, Examples 1 to 3 or Comparative Example 5 in the case where a lubricating paint is appropriately used in combination with the above threaded component made of titanium metal will be described.

[Examples 1 to 3] Hexagon bolts and nuts (M
(10 × P1.5 × 60: mm) was molded from pure titanium metal, and plasma carburization was performed in exactly the same manner as in Experimental Example 1 described above except that the treatment temperature and the treatment time shown in Table 1 were used.・ The following lubricating paint was applied to both nuts.

Lubricating paint: Lubrication consisting of a polytetrafluoroethylene content of 7 ± 0.5% by weight having a molecular weight (Mn) of 8000 or less and 93% by weight of a solvent (alternative CFC: HCFC-225, including 0.3% by weight of an adhesive resin). It is paint.

According to JIS, the obtained bolts and nuts are
In accordance with 1084-1990 "Tightening test method for threaded parts", the torque coefficient, axial force, total friction coefficient, and screw part friction coefficient were measured with a tightening torque of 150 kgf · cm (proof strength value minimum 215 N / mm), and the results were obtained. It is also shown in Table 1.

[0057]

[Table 1]

[Comparative Example 5] Hexagon bolt / nut (M10
XP1.5x60: mm) was formed from pure titanium metal, and plasma carburization was not performed.
The bolts and nuts were manufactured in exactly the same manner as the above, and the above-mentioned "tightening test of screw parts" was performed under the lubricating conditions also shown in Table 1, and the obtained results are also shown in Table 1.

As is clear from the results shown in Table 1, Comparative Example 5 in which only the lubrication treatment was performed without performing the predetermined plasma carburizing treatment had a higher torque coefficient than those of Examples 1 to 3 in which the plasma carburizing treatment was performed. It was a numerical value, the coefficient of friction was high, the axial force was low, and it was a screw part that could not obtain a sufficient tightening force with an appropriate torque.

The torque coefficient value indicating the lubricated state of the threaded part is usually 0.4 or more in the case of the threaded part made of titanium metal and not subjected to lubrication treatment, and the torque coefficient value of the threaded part made of ordinary steel is shown. Is 0.14 to 0.26.

In contrast to the comparative example described above, Examples 1 to 3 satisfying all the conditions had low torque coefficient values, low friction coefficients, high axial forces, and excellent tightening characteristics. . And, pure titanium and titanium alloys from the above-mentioned experimental examples are equivalent to ordinary steel or alloy steel in terms of mechanical strength such as wear coefficient, so without changing the design of the machine using conventional screw parts, Titanium metal screw parts with excellent corrosion resistance (durability) can be used.

That is, the threaded parts of the examples have the inherent corrosion resistance of titanium metal, and the friction and wear coefficients are reduced by the durable slidable layer which is work hardened by plasma carburization on the surface thereof. there were.

[0063]

As described above, the present invention is a threaded component made of titanium metal which is plasma carburized in an atmosphere containing a hydrocarbon gas at a predetermined degree of vacuum and a predetermined temperature. In addition to having the corrosion resistance of 1., there is an advantage that the friction and wear coefficient is reduced by the durable and slidable layer on the surface.

Further, in a screw part in which a lubricating coating containing polytetrafluoroethylene is applied to the screw surface, there is an advantage that the sliding property becomes more remarkable.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between the current density and the potential by a potentiostat.

FIG. 2 (a) is a diagram showing the friction coefficient and the specific wear amount of the same type materials of Experimental Example 1, Comparative Example 1, and Comparative Example 3 (b) The same type materials of Experimental Example 2, Comparative Example 2, and Comparative Example 4 Chart showing friction coefficient and specific wear amount of

FIG. 3A is a diagram showing the friction coefficient and the specific wear amount of the bearing materials of Experimental Example 1, Comparative Example 1 and Comparative Example 3; and FIG. 3B is the friction of the bearing materials of Experimental Example 2, Comparative Example 2 and Comparative Example 4. Chart showing coefficient and specific wear amount

FIG. 4 is a chart showing the relationship between friction coefficient and friction time for bearing steels of Experimental Example 1, Comparative Example 1 and Comparative Example 3.

Claims (3)

[Claims] 1. 0.5 to 15 t containing a hydrocarbon gas
A screw part made of titanium metal subjected to plasma carburization in an atmosphere of orr at 700 to 1100 ° C. 2. 0.5 to 15 t containing a hydrocarbon gas
Orr, threaded parts made of titanium metal plasma-carburized in an atmosphere of 700 to 1100 ° C., wherein threaded surfaces of the threaded parts are coated with a lubricating coating containing polytetrafluoroethylene. . 3. The screw part according to claim 2, wherein the polytetrafluoroethylene of the lubricating coating is a low molecular weight polytetrafluoroethylene having a molecular weight (Mn) of 8000 or less.