KR20030071413A - properties elevation on the high-sound part of piano frame by thermal sprayed ceramics coating - Google Patents

Abstract

PURPOSE: A ceramics spray coating method is provided to improve abrasion characteristics, mechanical properties and sound characteristics of high sound part of existing piano frame and particularly improve characteristics of expensive grand piano, and a piano frame manufactured by the ceramics spray coating method is provided. CONSTITUTION: The ceramics spray coating method comprises the process of coating Cr3C2 or WC +12%Co on a matrix of F25C cast ion by plasma spray coating or HVOF (high velocity oxygen fuel) method under the conditions that a bond coating agent is NiCr/A195/5, arc gas pressure is 50 psi, subsidiary gas pressure is 100 psi and powder gas pressure is 40 psi, wherein interfacial structure and characteristics are improved in HVOF method compared to plasma spray coating method when spray coating carbide based material (WC based or CrC based material) by spray coating a WC based or CrC based material on the surface of high sound part of piano frame, and a coating layer having adhesion strength of 50 kg/mm¬2 or more, hardness of 1,000 Hv or more, porosity of 10% or less and thickness of 100 μm or more is formed when spray coating carbide based material on the surface of high sound part of piano frame by HVOF method.

Description

Properties sprayed on the high-sound part of piano frame by thermal sprayed ceramics coating

The present invention relates to a ceramic thermal spray coating method for improving the characteristics of the piano frame treble by thermal spraying or high velocity oxygen fuel (HVOF), and to a piano frame manufactured therefrom. In particular, wear of the treble of an existing piano frame The present invention relates to a ceramic thermal spray coating method and a piano frame manufactured therefrom, which can be expected to improve characteristics, mechanical properties, acoustic properties, and in particular, properties of expensive grand pianos.

The main material of the piano frame is FC25 material, which is manufactured by conventional casting methods. The manufacturing method of the material applied to the present invention was excellent in the compactness of the tissue and improved mechanical properties compared to the conventional gravity casting method by applying a special method called V-process. However, it is difficult to cope with the shortening of the life of the piano frame due to the wear phenomenon caused by the piano wire and the increase of the acoustic characteristics of consumers.

In general, the ceramic thermal spraying technique melts ceramic materials such as WC, Al ₂ O ₃ , Zirconia, etc., which have excellent mechanical and physical properties but have high melting point and poor machinability, by instantaneous melting with a hot flame or plasma, Surface treatment technology that accelerates particles at a very high speed to form a thick film layer of 0.1 to 1.0 mm thickness on a base metal such as metal. Forms a thick film of a ceramic material having various properties on a cheap base material to form corrosion resistance, abrasion resistance, and abrasion resistance. It is a technology that can greatly improve the surface properties such as oxidative property, insulation, and heat insulation, and has the advantage that it can be easily applied regardless of the shape and size of the base material. Such hard facing processes include flame thermal spray, high velocity oxygen fuel (HVOF), detonetion gun, wire arc plasma, plasma spray, and growth. There are welding methods, and proper process selection and process establishment are very important in consideration of the quality, structure, workability and productivity of the double coating layer.

Based on these characteristics and variables of manufacturing conditions, the present invention has been developed in consideration of the following points: that is, the flame temperature, the spray rate of the molten particles, the spraying rate of the molten particles, the power, the gas mixture rate, and the sample rotation. By carefully examining the thermal conditions such as velocity, we will establish the optimum process conditions and improve the characteristics of the treble, that is, the wear resistance and acoustic characteristics of the treble.

The present invention is to improve the characteristics of the existing piano frame treble part by a new process technology to overcome the problems of the prior art in order to improve the characteristics of the treble part of the piano frame and also to apply the ceramic coating method to the piano frame It is an object of the present invention to provide a ceramic spray coating method and a piano frame manufactured therefrom which can improve wear resistance and mechanical and acoustic properties.

1 is a cross-sectional electron micrograph of a piano frame high-pitched part during tungsten carbide coating by HVOF method.

FIG. 2 is an enlarged photograph of FIG. 1.

Figure 3 is a microscopic histogram of the treble section of the piano frame when chromium carbide coating by plasma spray method.

4 is an enlarged view of FIG. 3.

5 is a photograph of a grand piano frame used in the present invention.

6 is a graph showing the results of adhesion strength test with the base material of the plasma coated specimen.

7A and 7B are graphs of XRD test results of chromium and tungsten carbide coated specimens by HVOF method.

The present invention for achieving the above object

Cr ₃ C ₂ or WC + 12% Co is coated on the base material of F25C cast iron by plasma spray spraying or HVOF method. As the bond coating material, NiCr / A195 / 5 is used. Arc gas pressure is 50psi, auxiliary gas pressure is 100psi, Powder gas pressure is characterized in that the spray coating to 40psi.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In order to improve the abrasion resistance and acoustic properties of the piano frame high-pitched part, which is a main object of the present invention, manufacturing processes by the following thermal spraying processes are required. In general, F25C, a cast iron material, is used as the base material for the piano frame, and the coating material is WC + CO, bond coating + Al ₂ O ₃ , Cr ₃ C _2, etc. for the purpose of improving wear resistance. However, considering the compatibility with the base material (carbide series) is known to be excellent. The base material used in the present invention is F25C cast iron material. As the spraying method, HVOF and plasma coating methods were used. However, HVOF method requires attention because of the possibility of phase change due to oxidation atmosphere during combustion. NiCr / A195 / 5 (metco443) was used as the bond coating material for oxide coating. Markings of specimens melted on the material metal were defined as HWCO for WC + 12% Co coating using HVOF method and PCRC for Cr ₃ C ₂ coating using plasma method. Process parameters of the thermal spray coating and HVOF method applied to the present invention are shown in [Table 1] and [Table 2], respectively.

Table 1: Process Variables for Plasma Spray Spraying

spraying materials Cr ₃ C ₂ nozzle 730 rod 120 gas ring 112 Arc gas pressure (Ar) 50 psi aux gas pressure (He) 100 psi powder gas pressure (Ar) 40 psi ampere (A) 800 voltage (V) 40 hopper rpm 3.00 spray distance (mm) 60 spray angle (degree) 90 ± 5 ° sliding velocity (mm / sec) 100 robot sliding distance (mm) 3

<Table 2> Process Variables for Thermal Spray by HVOF Method

spraying materials WC-12% Co barrel length 8 oxygen pressure (psi) 160 oxygen flow (scfh) 1800 fuel pressure (psi) 110 fuel flow (gph) 6.0 spray distance (mm) 380 spray angle (degree) 90 sliding velocity (mm / sec) 200 robot sliding distance (mm) 8 powderfeeder Auger Size (inch) 1/4 Pitch 4 Speed (RPM) 200

In addition, hardness test and adhesion strength test are essential for measuring the hardness and strength of the sprayed layer. The microhardness of the spray-sprayed and vacuum heat treated specimens was tested using the Vickers hardness tester, and the bond strength test between the sprayed layer and the base material was tested using a tensile tester (Instron model 4485) according to ASTM-02714 It was.

In addition, the formation of the structure and phase at the interface between the thermal sprayed layer and the matrix has a great influence on the properties of the material. For this purpose, the tissue test and the X-ray diffraction test were performed. The microstructure observation and phase analysis of the coating layer produced by the thermal spraying were carried out using a scanning electron microscope equipped with an optical microscope and an energy dispersive X-ray spectroscopy (EDS). Phase analysis was performed continuously and stepwise at a rate of 0.05 ° per second using an X-ray diffraction tester.

The coating layer, hardness test and adhesive strength test results for the evaluation of mechanical properties improvement are as follows. The hardness test results for the spray-coated specimens are shown in Table 3. Generally, carbide series is known to be superior to oxide series, and the WC-Co-based HVOF method has a higher hardness value (Hv) of about 660 than the CrC-based plasma spray method.

<Table 3> Vickers hardness test results of WC + 12% Co coating by plasma spray method and Cr ₃ C ₂ coating by HVOF method

as-sprayed specimen hardness (Hv) PCRC 842 HWCO 1502

1 and 3 are cross-sectional fine after performing a ceramic coating on the high-sound part of the existing piano frame according to the thermal spraying method (plasma thermat spray), high velocity oxygen fuel (HVOF), etc. A cross-sectional microstructure picture. In other words, as observed in the microstructure photograph, an optimal microstructure without the densification and pores of the interface between the thermal spray coating layer and the base metal and the thermal spray particle structure is observed. It is possible to produce a material capable of always the characteristics of the thermal spray coating layer and the high-pitched portion of the piano frame through such a microstructure.

6 shows the results of the adhesion strength test on the thermally coated specimens. Carbide series is known to be very superior to about 200MPa of oxide based on overall adhesive strength of about 500MPa or more. The melt adhesion strength of carbide series by plasma spraying was better than that by plasma method in hardness test results and ground HVOF method. It means that the law is excellent. In some cases, the epoxy layer was separated from some specimens during the bond strength test. It is considered that shear stress is applied to some interfaces, not pure tension, depending on the flatness of the epoxy bonding interface. In addition, when calculating the cross-sectional area for stress calculation, the diameter of the specimen corresponding to the coating area cannot be regarded as the interface showing the adhesive strength, and thus, the actual cross-sectional area of the coated layer was calculated using the actual cross-sectional area.

FIG. 7A is an X-ray diffraction (XRD) test result of a specimen sprayed with Cr ₃ C ₂ . Although not fully stabilized in the X-ray diffraction pattern, some peak sharpening as well as stabilization of the carbide phases can be seen. In addition, it can be seen that, due to the thermal spraying, the Cr carbide phase is partially present as Cr ₃ C ₂ and Cr ₂₃ C ₆ as a stable phase. Presence and tissue densification of Cr ₂₃ C ₆ phase is believed to have contributed to the improvement of adhesion and hardness.

<Table 4> Pin-Disk Wear Test Results

Specimen Coefficient of friction (μ) Remarks Early Stabilization End of stabilization PWCO-B 0.36 0.36 0.37 HWCO-B 0.22 0.22 0.21 HCRC-B 0.25 0.23 0.24

Table 4 shows the coefficients of friction by pin-disk type abrasion testing for spray coated specimens. As a result of testing, the carbide series generally had a lower friction coefficient than the alumina series. The friction coefficient of the carbide sprayed layer by plasma spraying was relatively higher than that by the HVOF method. In addition, the results of spray carbon spraying by HVOF method showed that the HWCO series had better friction characteristics than HCRC series.

Abrasion resistance by weight loss rate according to the wear test was confirmed that the fusion of the carbide wear resistance by HVOF method relative to the plasma method as shown in FIG. In addition, the thermal spray coated alumina thermal spray coating layer showed severe spot digging during abrasion test. Carbide spraying results by HVOF method showed that HWCO series was somewhat better than HCRC series.

In terms of mechanical properties, abrasion resistance test, and tissue test, it can be expected that the WC spray coating by HVOF method will show excellent characteristics for improving the piano frame treble, but considering the economy, carbide by HVOF method is considered. Warrior is desirable.

<Example>

FIG. 1 is a scanning electron micrograph in the case of spray coating of WC + 10O% Co by HVOF method, and shows that the HVOF method is dense in comparison with the plasma spray method in comparison with FIG. A rough porosity measurement showed about 10%.

FIG. 2 is a scanning electron micrograph of the HVOF specimen of FIG. 1 in which the interface between the coating layer and the base metal is enlarged. The base metal shows a typical cast iron structure, and in the case of the WC + 10% Co coating layer, FIG. Compared to the Cr ₃ C ₂ spray coating layer, densification of the tissue and the bonding interface and shrinkage of the pores are observed. Due to the opened microstructure, it is possible to manufacture a material capable of improving the mechanical properties of the piano frame and particularly the treble.

As described above, according to the present invention, the surface of the treble part of the piano frame is WC-based or CrC-based sprayed coating, and when the carbide-based (WC-based or CrC-based) spraying, the HVOF spraying method has an interface structure and characteristics compared to the plasma spraying method. Improved. In addition, a coating layer having an adhesion strength of 50 kg / mm 2 or more, hardness of 1,000 Hv or more, porosity of 10% or less, and thickness of 100 μm or more was formed during carbide spraying by HVOF method. From these results, the thermal spray coating is expected to improve mechanical characteristics as well as voice characteristics of the high-pitched part by having excellent wear resistance when comparing mechanical properties with existing materials.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited thereto and may be improved or modified by those skilled in the art within the scope of the technical idea of the present invention.

Claims (1)

Cr ₃ C ₂ or WC + 12% Co is coated on the base material of F25C cast iron by plasma spray spraying or HVOF method. As the bond coating material, NiCr / A195 / 5 is used. Arc gas pressure is 50psi, auxiliary gas pressure is 100psi, Powder spraying pressure is 40psi ceramic spray coating method characterized in that the spray coating.