JPS5837400B2 - Surface treatment method for metal surfaces - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface treatment method for metal surfaces, in which a substance with a low coefficient of friction is infused into the metal surface crank to coat the metal surface with lubricity. .

A typical example is porous chrome plating, which forms an extremely excellent contact surface with excellent load and lubrication properties, but this porous chrome plating is prone to cracks, dents, and microcracks. It is used for piston rings and cylinder walls that require wear resistance and high operating characteristics.

When chromium is deposited during this plating, microscopic cracks are formed in a generally irregular manner due to the stress generated within the deposited layer.

As this stress increases to the ultimate strength of the chromium deposit, the resulting fracture surface will absorb this stress, thus leaving a microcrank in the plating.

The size and type of pores or microcracks can be adjusted by various methods.

For example, it is a known technique to enlarge the formed crank by etching after the plating process.

Generally, during the etching process, the crank initially expands and continues to expand until a balance is reached between the dissolution rate of the crack portion and the dissolution rate of the surface, and the crack depth hardly increases.

After this, unless surface erosion prevention treatment is performed by etching, the plated portion will continue to be dissolved, but the crank depth will not increase significantly.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a means for producing fine cracks that can be adjusted by etching, and in particular for selectively enlarging fine cracks, without altering or affecting the plated surface.

In the present invention, it has been revealed that the first cracks are formed during the initial chrome plating process, and this chrome plating is followed by a heat treatment as a pretreatment for the reverse polarity etching process to enlarge the cracks.

For this reason, chrome plating takes sufficient time to achieve a relatively thick plating thickness {for example, 50.8μ to 101.6μ (0.0
02 to 0.004 inch)}.

The lubrication properties, or low friction properties, of hard chrome plated surfaces are
This can be dramatically increased by introducing perfluorinated carbon such as polytetrafluoroethylene (trademark: Teflon) into the cracks formed on the plated surface.

However, in the above process, it is necessary to physically hold the resin powder in a predetermined position within the crank, and it is also necessary to limit the heating temperature of the plating surface to prevent melting of the polytetrafluoroethylene powder. .

That is, the maximum heating temperature is 343.3°C (650'F), but preferably below 260°C (500'F), 1 2
1. 1℃ (below 250) to 204.4℃ (400'
F) range is desirable.

However, in reality, the expansion caused by heating up to the limiting temperature is negligible, making it difficult to completely infiltrate the crack with unmelted powder.

Furthermore, the shrinkage of the cracks does not uniformly hold the powder in place even upon cooling, especially if the surfaces are subject to expansion and repeated wear over long periods of time.

Therefore, another object of the present invention is to provide a new and improved method of applying a perfluorinated carbon mixture to a porous metal surface in order to dramatically improve the lubrication and low wear properties of the porous metal surface. In particular, it is an object of the present invention to provide a processing method for forming microcracks in a predetermined pattern having a desired width and depth.

Another object of the present invention is to provide a product in which a durable low-friction material is infused into a porous metal surface having fine cracks in order to dramatically improve its lubrication and low-wear properties. It's about doing.

In the present invention, the metal surface is plated in a chromic acid bath to form a pattern of microscopic cracks.

After this plating, the plating surface is heated and oxidized to remove cracks that occurred during plating. This surface is kept unaffected during subsequent etching operations for enlargement purposes.

After this, the above surface is heated to a temperature above the melting point of the low-friction perfluorinated carbon mixture, and the low-friction perfluorinated carbon mixture is then added directly to the above-mentioned surface and melted into the microcracks.

For surface treatment of machine core rods, etc., hard chrome plating is applied at 50%.
．． 8μ~10 1.6μ (0.002~0.00
4 inches) on the surface, and after this plating, 12
1.1°C (2506F) to 315.6'C (600
Baking is carried out at a temperature range of 1 to 5 hours.

These plating surface oxidation methods are optimal as a pretreatment for the reverse polarity etching and fine crack enlarging steps.

This reverse polarity etch is performed by applying reverse polarity to the chromic acid bath tank.

In addition, the temperature is high enough to melt the polytetrafluoroethylene into the surface cracks, i.e., 315.6°C (600'F).
) to 482.2°C (900'F).

In accordance with the invention, a matrix of fine-grained steel, such as AISI 8620 alloy steel, preferably with a grain size of 6:8 or AISI 4000 series alloy steel, with a grain size of 6:7, is coated, for example with a puff finish or cloth. Mechanically finished by polishing.

Next, the surface of the base material is anodically etched for 15 to 30 seconds to expose the grain structure of the base material.

For example, the etching process is carried out by BASF Wy, Michigan, USA.
andotte Corporation of Wy
This is done in a caustic solution using an alkaline derusting metal cleaner such as the cleaner sold under the trademark "FERLON" by andtte.

If necessary, etching is performed in the acid bath tank at a temperature of 54.4°C (130'F) and a voltage of 4 to 6 volts using a reverse polarity etching method with the base material immersed in the tank. It can be carried out.

The base material is etched for about 10 seconds, then the anode and cathode are reversed and etched for 5 seconds, and finally the base material is washed in clean water.

Here, the base material is immersed in hot water to warm it up for the next plating process.

As the next step, the base material is plated with hard chrome in a chromic acid bath.
．． 002 to 0.004 inch) is desirable.

Although other plating mixtures and plating methods may be employed in accordance with the present invention to obtain a surface with microcracks that will accept polytetrafluoroethylene, the use of polytetrafluoroethylene to provide the desired wear and lubrication properties to the surface of the base material may be difficult. Hard chrome plating has been shown to be optimal in combination with fluorinated ethylene.

To perform hard chrome plating with microcracks, the general procedure follows conventional plating methods, except for the prescribed order of baking and etching steps described below.

But essentially, chromium with microcracks, also called double chromium, is electrodeposited onto a conventional copper-nickel substrate or a nickel substrate, and this chromium has a number of microcracks exposing the underlying nickel. It looks like this.

The desired crank pattern depends on the acid bath temperature, chromic acid concentration,
Can be adjusted by fluoride content and plating thickness.

A continuous chromium bath method is a typical method for multilayer chromium plating, but in the present invention, an initial crack pattern is formed during a single chromium plating process using a chromic acid bath containing a catalytic acid group such as S04. It is desirable to do so.

The ratio of C r 0 3 and SO4 shall be strictly controlled. For example, at 60°C (140'F)
A ratio of rO3 to SO of 100:1 would produce a medium density crank pattern, while a higher ratio of 125:1 at the same temperature would produce a denser crack pattern.

The crack area generally exhibits a clear network of fine cracks.

Although the bath concentration has little effect on the size of the crack pattern within limits, temperature changes have been shown to have a significant effect on the fineness or roughness of the microcracks.

Therefore, the temperature ranges from 48.9℃ (below 120℃) to 60℃
(below 140), the microcrank becomes quite rough.

Although current density is very important for controlling plating rate, it has relatively little effect on crack pattern size, with a typical range of 6.
．． 4 5 i (1 inch2) from 1.0 to 4
．． It is 0 ampere.

A preferred chrome plating solution is from New Jersey, USA.
Unichrome SRHS chrome plating solution CR-10, manufactured by M&T Chemicals, Rahway, State, specifically contains 3.8% chromic acid.
680.4 to 1 134 g (24 to 1 gallon) per t (1 gallon)
It is intended for use in a concentration of 40 oz.).

This solution is characterized by high current efficiency and fast plating speed, and low sensitivity to momentary electrical interruptions, as well as excellent adhesion, high hardness and low fatigue resistance loss.

The tin-lead alloy anode is preferably used in conjunction with the bath liquid, and the cross-section of the anode must be such that it can carry the required current without overheating.

Auxiliary anodes should be lead or lead-coated if placed opposite bare steel.

For the hard chrome plating operations described above, a 6 to 9 volt power supply is used to fully utilize the maximum allowable power density.

The chromic acid bath is first filled with fresh water to about % of the tank and then heated to about 12.2° C. above the required working temperature.

The chromic acid mixture is then added with stirring, and at the same time the remaining water is added so that the solution reaches the working level, and the bath liquid is adjusted to the working temperature.

The anode is placed in a tank, and a dummy cathode is used to electrolyze at 6 volts and at a given working temperature for several hours with occasional stirring of the solution.

In addition, in the hard plating process, the concentration range is 48.9℃
(24 to 40 ounces) per gallon of chromic acid over a working temperature range of 120'F (120'F) to 150'F (65.6°C).

At this time, if the temperature is lowered, the electric power can be well covered, and if the temperature is raised, a higher current density can be obtained, the plating speed is faster, and the usable current density range is wider.

When using a Cr-110 plating solution, the desired solution concentration is 32 to 36 ounces per gallon for chromic acid.
And for sulfates, 3.8 tons (1 gallon)
．． 4 g (0.12 oz).

Temperatures should preferably be maintained at a minimum of 51.1°C (124'F) for fine crank patterns and 58.3°C (137'F) for coarse crack patterns.

Regarding the current density, 6. 4.1 ampere per 5 cffl (1 inch2) and 6.5 amps for coarse crack patterns. 4 5
Use 2 amps per aA (1 inch2).

The thickness of chrome plating is greatly affected by time, but for a thickness of 50.8μ (0.002 inch), the plating time will be 45 minutes, and for a thickness of 101.6μ (0.004 inch), it will take 1 hour. It will take 2 hours.

During the plating operation, the area of the part plated at one time in the chromic acid bath should not exceed % of the anode part in order to prevent overloading of the electrode.

Generally, the plating thickness is determined by actual measurements during the plating process until the desired thickness is obtained.

After the first plating step, the plated parts are washed in water and then placed in an oven at a temperature of 1 2 1. 1℃ (250'F
) to 315.6°C (600'F) for 1 to 5 hours.

In this case, the temperature and time are selected to completely oxidize the plated surface and eliminate hydrogen, protecting it from the subsequent reverse polarity etching step.

After baking, the parts are immersed in a chromic acid bath of the concentration described above and the solution is of opposite polarity to further enlarge the cracks formed during the initial plating operation.

This operation is important to ensure that the polytetrafluoroethylene enters the final stage crack reliably and uniformly.

The degree of etching of the plated part has an important influence on the depth and width of the cracks, and therefore on the selection of the degree and type of porosity.

Anodic etching in chromic acid solutions with or without sulfate is generally carried out in the plating bath at the same temperatures mentioned for plating operations, with conventional methods of controlling crack size and propagation, and with current densities. is 6.4 s=(
Use 2 to 4 amps per inch (2).

However, in the etching process, the prescribed formulation of the chromic acid etching solution and the working conditions such as temperature and current density are not very important.

In both the plating and etching processes, appropriate support equipment is used to suspend the parts to be plated and etched.

In this case, the most important thing to consider is to properly cover the edges of the parts to be plated and the edges of the openings with a protective film to prevent excessive adhesion.

What I would like to emphasize again here is that the baking process as a pretreatment for the reverse polarity etching process is a new method for adjusting the shape of cracks, and in particular it does not alter the plating surface.
This method can selectively increase the width and depth of cracks without making them worse.

It is also worth noting that the degree of porosity can be adjusted to a certain extent by the final mechanical finishing described below, i.e., the degree of porosity is determined by the degree of cutting of the etched or porous layer. .

As the next step, each plated part is mounted on the lathe shown in Figure 2, and the surface speed of the part is set at 1.22 to 2.44 m/min (4 to 4 m/min).
8 feet) and rotate.

Furthermore, the plated surface is heated to a temperature higher than the melting point of polyethylene fluoride 1/N.

For example, heat it with a propane torch for a few minutes.

Next, polytetrafluoroethylene is applied to the surface of the part, for example, by pressing a solid rod made of polytetrafluoroethylene against the heated surface, as shown in FIG.

When applying polytetrafluoroethylene to a plated surface, use a 2.54 cIrL (1 inch) rod with the upper half cut at an angle less than a right angle so that the powder can be funneled through the funnel while the part is rotating. to fulfill its role.

315.6°C (600'F) to 482.2°C (900'F)
At the high temperature of 'F), polytetrafluoroethylene immediately softens and melts when it comes into contact with the surface of the part, so it can be quickly spun.

By applying even more slight pressure to the solid bar, the softened and dissolved polytetrafluoroethylene becomes more uniformly incorporated into the crank.

If desired, powdered polytetrafluoroethylene can be applied to the heated surface of the rod and used with the solid rod, the powdered polytetrafluoroethylene melting quickly at the end of the solid rod. , it blends into cracks that are enlarged and formed on the plated surface of the part.

Generally, the supply of polytetrafluoroethylene is complete when the polytetrafluoroethylene no longer softens at the interface with the plated surface of the part, after which the part is cooled to room temperature.

During the final finishing stage, the part was moved at a surface speed of 45 m/min.
．． Polishing is accomplished by pressing a cotton cloth against the plated surface while rotating at a relatively high speed of 150 to 250 feet.

The following work example is a tube bend core rod member.
This is an example of hard chrome plating of ingmandrel assemblies).

Example 1 A steel shank with a diameter of 9.8 8 CIrL (3.8 91 inches) and a length of 25.4 cm (10 inches) is used in the component.

As mentioned above, the temperature was 54.4°C (130°C) in an alkaline solution.
(Bottom), washing was performed for 15 seconds at a voltage of 4 to 6 volts.

Additionally, the shank was cleaned in a chromic acid etch solution under reverse polarity for less than 1 minute.

After washing with water, this shank has a concentration of 3.87 (1 gallon)
907.2g (32oz) per serving, temperature 57.2℃ (
135'F), current density 6.45cr7t (1 in
Plating was carried out using a chromic acid bath under the condition of 1.25 amperes per ch2).

The plating time was 2 hours and 10 minutes, and the plating thickness was 127μ (0.
．． 005 inches).

After washing with water, shank at 3 o'clock 7 stj 17 6.7'C
(350'F).

The shank was further tested at a chromic acid concentration of 79 g (28 oz) per gallon, a temperature of 56.1°C (133"F), and a current density of 6.45
Etching was performed for 3 minutes in a bath solution under the condition of 2 amperes per ffl (1 inch2).

I inspected the shank before applying the polytetrafluoroethylene and found some erosion, but a clear crack pattern.
It was formed uniformly and relatively finely.

After heating the shank to a temperature of 329.4°C (625'F''), tertiary polytetrafluoroethylene was applied to the surface of the shank.
It was added in the form of powder and solid bar as shown in the figure.

Example 2 Three steel balls, each 9.8 6 CrrL (3.8 8 2 inches) in diameter, were cleaned and etched as described in Example 1 and then reduced to a chromic acid concentration of 3.8 CrrL (3.8 8 2 inches) in diameter. sz (1 gallon)
935.5 g (33 oz) per unit, bath temperature 56
．． At 7°C (134.'F), the current density is 6.45 Makoto (
Plating was performed in a chromic acid bath at 1.25 amperes per inch.

Steel balls were plated for 2 hours and 30 minutes, and the average plating thickness was 88.
It was set to 9μ (0.0035 inches).

After washing with water, it was baked at a temperature of 176.7°C (350″F) for 3 hours.

Furthermore, this steel ball has a chromic acid concentration of 3.8 tons (1 gallon).
Etching was performed for 2 minutes at a bath temperature of 125'F (51.7°C) with 28 oz.

Powdered polytetrafluoroethylene was added to this steel ball at a temperature of 315.
．． Lubrication at 6°C (600'F) for 5+ minutes resulted in a very smooth surface, but the amount of polytetrafluoroethylene on the surface was slightly exceeded.

Example 3 A sphere that has been cleaned, plated, baked, and etched according to Example 2 above, and adhesive polytetrafluoroethylene is applied to the surface of the sphere heated to 315.6°C (600″F) or higher for 6 minutes. I tried to lubricate it by giving it some water.

The lubricant spread evenly and melted into the crack pattern formed.

For other spheres treated according to the method described above, the time was varied from 45 seconds to 12 minutes and the temperature was varied from 315.6°C (600”F) to 482.2°C.
(900'F) to apply polytetrafluoroethylene to the sphere surface.

In this case, both powder and rod forms of polytetrafluoroethylene were used, and a smooth and even surface film was formed.

The following is an example of the coefficient of friction obtained by surface treatment of the core rod shank used in the above member.

The shank was coated as described in Examples 2 and 3 above and compared to a shank that was hard chrome plated but not coated with polytetrafluoroethylene.

These pairs of shanks are suspended by 5.0 8 crrL (2 inch) wide steel bands.
Friction tests were conducted with a static weight of 4Kp (25 pounds) applied.

The other end of this steel band is 22.68Ky (50
(lb) is fixed to the scale and is positioned above each type of shank as it rotates at a surface speed of 25.9 m/min (85 ft).

The coefficient of friction was measured by assuming that the rotational resistance of each type of shank was indicated by the shake of the scale.

In a comparative test using a load of 11.34K7 (25 pounds), a shank coated in accordance with the present invention was compared to a steel band with a load of 11.34Ky (25 pounds).
It exhibited significantly improved lubrication and wear properties while being resisted by a suspended load of 5 lbs.

It will be appreciated that the metal surfaces treated as described above have many uses other than the specific uses described above with respect to the core of the component.

Although the embodiments and implementation methods of the present invention have been described above, the present invention can be implemented in ways other than those described above within the scope of the claims.

[Brief explanation of drawings]

Figure 1 is a rough process diagram of a typical surface treatment operation based on the present invention, Figure 2 is a schematic diagram showing a method of applying lubricant to the plated surface of a metal sphere, and Figure 3 is a diagram showing the method of applying lubricant to the plated surface of a metal sphere. FIG. 2 is a schematic diagram showing a method of applying plating to the surface of a metal sphere.

Claims (1)

[Claims] 1 After cleaning the metal surface, a chromium plating layer with a fine crack pattern is formed by electroplating using a chromic acid bath, and this is coated with 121 to 316 plating in an oxidizing atmosphere.
The surface of the chromium plating layer is baked by heat treatment at ℃ for 1 to 5 hours, and the fine crack pattern of the chromium plating layer is enlarged by reverse electric etching treatment, and the carbon perfluoride is added into the enlarged fine crack pattern. A surface treatment method for metal surfaces characterized by applying a lubricating coating to the metal surface by melting and infiltrating the metal surface.