Preparation method of novel hard-surface coating on roller surface

Abstract

The invention discloses a preparation method of a novel hard-surface coating on the surface of a roller. The preparation method comprises the following steps: I, machining; iII, preparing powder: drying the Ni-based alloy powder, the TiC powder and the powder obtained by mixing the Ni-based alloy powder and the TiC powder; iV, preparing a base coat and a transition layer: preparing the base coat and the Ni-based TiC transition layer on the surface of the roller by adopting high velocity oxy fuel (HVOF); v, preparing a working layer: preparing the working layer by adopting a hypersonic flame spraying (HVOF) mode or a chemical vapor deposition mode; vI, grinding; and VII, post-flaw detection. The high-quality TiC gradient composite hard coating is formed by optimizing the components, the structure and the spraying process parameters of the coating, the hardness of the coating is high, the binding force between the coating and a base body is high, the coating has excellent wear resistance, high temperature resistance and extrusion resistance, and the single service life of a roller is prolonged.

Description

Technical Field

[0001] The present invention belongs to the field of material surface technology, and specifically relates to a method for preparing a high-load and high-wear-resistant composite coating on the surface of a roller in the field of non-ferrous metal processing. Background Art

[0002] Rollers used in copper processing must meet high load requirements while maintaining a stable roughness. This means the roller surface must possess both high load-bearing capacity and high wear resistance. During production, reduced roller roughness can lead to slippage before rolling. This has the following drawbacks: 1. It impacts the quality of the copper strip surface, causing scratches and bright lines. These defects cannot be eliminated during subsequent processing of thick strip, directly impacting final product delivery; 2. It also impacts production efficiency. Slippage severely impacts equipment efficiency and significantly increases production costs due to increased regrinding.

[0003] Currently, traditional methods for treating the surface of rolls include surface quenching, carburizing, and chrome plating. However, after use, the roll surface is prone to defects such as cracking, flaking, and crushing. Poor surface wear resistance also leads to a rapid reduction in roughness. At higher temperatures, reactions between the roll surface and the rolled material easily form intermetallic compounds, leading to adhesion. Non-ferrous metal processing strips, such as copper strip, require even higher surface quality. Therefore, improving the roll surface's extrusion and wear resistance, preventing adhesion, and extending roll service life are key factors in ensuring and improving production efficiency.

[0004] Chinese patent CN118441260A (publication date 2024.8.6) discloses "A method for preparing a high-load and high-wear-resistant DLC composite coating on the surface of a rolling mill roll". Since it uses DLC coating as the working layer, it can only use a carbon element gradient, namely Co+WC, as a transition layer. However, there are differences in composition between DLC and Co+WC, resulting in large differences in performance. Therefore, its anti-extrusion ability and matrix bonding strength are not very high, and it cannot be used for rolling mills in the field of non-ferrous metal processing. Summary of the Invention

[0005] The problem to be solved by the present invention is to provide a method for preparing a new type of hard surface coating on the surface of a rolling mill. It forms a high-quality TiC gradient composite hard coating by optimizing the coating composition, structure and spraying process parameters. The coating has high hardness and strong bonding with the substrate, so that the coating has excellent wear resistance, high temperature resistance and extrusion resistance. Therefore, it effectively solves the problems of easy cracking, easy peeling, easy wear and "adhesion" during the existing use of the rolling mill, and extends the single service life of the rolling mill.

[0006] The present invention provides a method for preparing a new quality hard surface coating on the surface of a rolling mill, comprising the following steps: I. machining: removing the fatigue layer and defects on the surface of the rolling mill by turning, and grinding to make the roughness of the rolling mill surface Ra ≤ 0.8 μm; II. front flaw detection: performing surface color flaw detection and ultrasonic flaw detection on the rolling mill; III. powder preparation: drying Ni-based alloy powder, TiC powder, and a mixture of Ni-based alloy powder and TiC powder; IV. preparation of a primer layer and a transition layer: preparing a primer layer, Ni-based alloy powder, and a transition layer on the surface of the rolling mill by using supersonic velocity oxygen fuel (HVOF) spraying. TiC transition layer; V. Working layer preparation: The working layer is prepared by supersonic oxygen fuel spraying (HVOF) or chemical vapor deposition; VI. Grinding: The roller surface is ground to the roughness range required by the drawing. If the working layer is prepared by thermal spraying, grinding is performed after spraying; if the working layer is prepared by chemical vapor deposition, grinding is performed before preparing the working layer; VII. Post-flaw detection: The surface of the roller after grinding is subjected to surface color flaw detection and ultrasonic flaw detection to ensure that the coating is free of cracks after grinding and meets the coating deposition requirements.

[0007] In step III: the element content of the Ni-based alloy powder is: Cr content ≤15wt.%, C content ≤1.0wt.%, Si content 3.0-4.5wt.%, and the rest is Ni, and the powder particle size is 15-53μm; the purity of the TiC powder is ≥99.5%, and the powder particle size is 15-53μm.

[0008] In step III: the Ni-based alloy powder and the TiC powder are weighed and mechanically mixed according to a given mixing ratio, and the mixing time is not less than 2 hours.

[0009] In step III: after the powder mixing is completed, the powder is placed in an oven at a temperature of 80-100°C for 2-3 hours.

[0010] In step IV: the surface is roughened before spraying to ensure the bonding strength of the coating. The surface roughness of the roller after roughening is Ra5 to 8 μm.

[0011] In step IV: the HVOF spraying process parameters are: oxygen flow rate 850-1000 L / min, kerosene flow rate 20-25 L / h, powder feeding rate 60-80 g / min, and spraying distance 300-400 mm.

[0012] There are 4 transition layers in step IV. The thicknesses (μm) of the primer layer, 4 transition layers and working layer are: 20-30, 10-20, 10-20, 10-20, 10-20, respectively; thermal spraying: 50-100 or vapor deposition: 20-30.

[0013] There are a total of 4 transition layers in step IV. The compositions of the base layer, 4 transition layers, and working layer are: 100% Ni-based, 80% Ni+20% TiC, 60% Ni+40% TiC, 40% Ni+60% TiC, 20% Ni+80% TiC, and 100% TiC.

[0014] The surface hardness of the coating obtained by the preparation method is greater than 2200 HV, and the bonding strength between the coating and the substrate is greater than 70 MPa.

[0015] Among them, the purpose of the flaw detection before step II is to ensure that the substrate has no defects such as cracks and pores, and meet the preparation requirements of the thermal spray coating; the purpose of drying the powder in step III is to remove water vapor in the powder; the purpose of the flaw detection after step VII is to ensure that the coating has no cracks after grinding and meet the coating deposition requirements.

[0016] The present invention adopts HVOF spraying to prepare the base layer and multi-layer transition layer of the roller surface, and adopts HVOF spraying or vapor phase layer deposition to prepare the working layer according to different processes, thereby preparing a high-hardness gradient composite coating combining "base layer + multi-layer transition layer + working layer" on the roller surface, which has the following advantages: 1. The multi-layer gradient structure alleviates the performance difference between the working layer and the roller base material, and the coating will not peel off from the base when local deformation occurs, thereby improving the extrusion resistance; at the same time, the thermal expansion coefficient from the base to the working layer changes in a gradient, and the difference in thermal expansion coefficient between the layers is small, so that under high temperature conditions, it has a higher ability to resist thermal deformation and cracking, that is, high high-temperature bonding strength; 2. The material of the gradient composite coating is further improved. A reasonable formulation was carried out: a transition of Ni-based powder content from 100% to 0, and a transition of TiC powder content from 0 to 100%. As the TiC content increased, the hardness continued to increase. After spraying four transition layers, the surface hardness of the coating reached more than 2200HV, and the wear resistance was also improved accordingly; at the same time, the bonding strength was increased. After spraying four transition layers, the bonding strength of the coating reached more than 70MPa, making it not easy to peel off; 3. TiC is a ceramic material and it is difficult to form a compound with the rolled material, thus reducing the probability of "adhesion"; 4. For rolls with extremely high loads and low vibration during service, the working layer is prepared by chemical vapor deposition; for other working conditions, the working layer is prepared by HVOF spraying. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the composite coating prepared in Example 4 and Example 5 of the present invention.

[0018] Figure 2 1 is a comparison chart of the surface hardness of the coatings in the comparative example and Examples 1 to 4 of the present invention.

[0019] Figure 3It is a comparison chart of the bonding strength of the coatings in the comparative example and Examples 1 to 4 of the present invention. DETAILED DESCRIPTION

[0020] In order to better understand the present invention, the present invention is further described in detail below with reference to comparative examples and embodiments.

[0021] Comparative Example

[0022] In this comparative example, the working layer is directly prepared on the base layer.

[0023] Step 1: Preparation of base layer: Before spraying, the roller surface is roughened to make the roughness reach Ra5-7μm, and then the base layer is prepared by supersonic flame spraying (HVOF). The spraying process parameters are 850-900L / min, kerosene flow rate 20-23L / h, powder feeding rate 65-75g / min, spraying distance 300-330mm, and thickness 20-30μm.

[0024] Step 2: Preparation of working layer: The working layer is prepared on the basis of the base layer by supersonic flame spraying (HVOF). The spraying process parameters are 970-1000 L / min, kerosene flow rate 23-25 L / h, powder feeding rate 60-65 g / min, spraying distance 350-380 mm, and thickness 50-100 μm.

[0025] Coating performance test: mainly divided into coating surface hardness, coating cross-section hardness, and bonding strength between coating and roller substrate. The test results are shown in the following table:

[0026]

[0027] Example 1

[0028] The difference between this embodiment and the comparative example is that a transition layer 1 is added between the working layer and the primer layer, and the primer layer, the transition layer 1 and the working layer are prepared in sequence.

[0029] Step 1: Preparation of base layer: The thermal spraying parameters and coating thickness of the base layer are the same as those in Example 1.

[0030] Step 2: Preparation of transition layer 1: The transition layer 1 is prepared by supersonic flame spraying (HVOF), with spraying process parameters of 900-950 L / min, kerosene flow rate of 22-24 L / h, powder feeding rate of 65-70 g / min, spraying distance of 380-400 mm, and thickness of 10-20 μm.

[0031] Step 3: Preparation of working layer: The thermal spraying parameters and coating thickness of the working layer are the same as those of the comparative example.

[0032] Coating performance testing: mainly divided into coating surface hardness, coating cross-section hardness and coating bonding strength. The test results are shown in the following table:

[0033]

[0034] Example 2

[0035] The difference between this embodiment and the comparative example is that a transition layer 1 and a transition layer 2 are added between the working layer and the primer layer, and the primer layer, the transition layer 1, the transition layer 2 and the working layer are prepared in sequence.

[0036] Step 1: Preparation of base layer: The thermal spraying parameters and coating thickness of the base layer are the same as those of the comparative example.

[0037] Step 2: Preparation of transition layer 1: The thermal spraying parameters and coating thickness of transition layer 1 are the same as those in Example 1.

[0038] Step 3: Preparation of transition layer 2: The transition layer 2 is prepared by supersonic flame spraying (HVOF), with spraying process parameters of 950-1000 L / min, kerosene flow rate of 23-25 L / h, powder feeding rate of 65-70 g / min, spraying distance of 380-400 mm, and thickness of 10-20 μm.

[0039] Step 4: Working layer preparation: The thermal spraying parameters and coating thickness of the working layer are the same as those of the comparative example.

[0040] Coating performance test: mainly divided into coating surface hardness, coating cross-section hardness and coating bonding strength. The test results are shown in the following table:

[0041]

[0042] Example 3

[0043] The difference between this embodiment and the comparative example is that transition layer 1, transition layer 2 and transition layer 3 are added between the working layer and the primer layer, and the primer layer, transition layer 1, transition layer 2, transition layer 3 and working layer are prepared in sequence.

[0044] Step 1: Preparation of base layer: The thermal spraying parameters and coating thickness of the base layer are the same as those of the comparative example.

[0045] Step 2: Preparation of transition layer 1: The thermal spraying parameters and coating thickness of transition layer 1 are the same as those in Example 1.

[0046] Step 3: Preparation of transition layer 2: The thermal spraying parameters and coating thickness of transition layer 2 are the same as those in Example 2.

[0047] Step 4: Preparation of transition layer 3: The transition layer 3 is prepared by supersonic flame spraying (HVOF), with spraying process parameters of 970-1000 L / min, kerosene flow rate of 23-25 L / h, powder feeding rate of 65-70 g / min, spraying distance of 380-400 mm, and working layer thickness of 10-20 μm.

[0048] Step 5: Preparation of working layer: The thermal spraying parameters and coating thickness of the working layer are the same as those of the comparative example.

[0049] Coating performance test: mainly divided into coating surface hardness, coating cross-section hardness and coating bonding strength. The test results are shown in the following table:

[0050]

[0051] Example 4

[0052] The difference between this embodiment and the comparative example is that transition layer 1, transition layer 2, transition layer 3 and transition layer 4 are added between the working layer and the base layer, and the base layer, transition layer 1, transition layer 2, transition layer 3, transition layer 4 and working layer are prepared in sequence.

[0053] Step 1: Preparation of base layer: The thermal spraying parameters and coating thickness of the base layer are the same as those of the comparative example.

[0054] Step 2: Preparation of transition layer 1: The thermal spraying parameters and coating thickness of transition layer 1 are the same as those in Example 1.

[0055] Step 3: Preparation of transition layer 2: The thermal spraying parameters and coating thickness of transition layer 2 are the same as those in Example 2.

[0056] Step 4: Preparation of transition layer 3: The thermal spraying parameters and coating thickness of transition layer 3 are the same as those in Example 3.

[0057] Step 5: Prepare the transition layer 4 by supersonic oxygen fuel spraying (HVOF). The spraying process parameters are 970-1000 L / min, kerosene flow rate 23-25 L / h, powder feeding rate 65-70 g / min, spraying distance 350-380 mm, and working layer thickness 10-20 μm.

[0058] Step 6: Working layer preparation: The thermal spraying parameters and coating thickness of the working layer are the same as those of the comparative example.

[0059] Coating performance test: mainly divided into coating surface hardness, coating cross-section hardness and coating bonding strength. The test results are shown in the following table:

[0060]

[0061] Example 5

[0062] For rolls with extremely high loads and low vibration during service, the working surface is coated with TiC by chemical vapor deposition (CVD) to meet its high wear-resistant requirements. The coating prepared by chemical vapor deposition has high density, high hardness and higher load-bearing capacity, but the coating prepared by this method is also more brittle and is therefore suitable for low-vibration working conditions.

[0063] Steps 1 to 5 are the same as those in Example 4.

[0064] Step 6: Grinding: Grind the thermal spray coating surface to the specified roughness requirement according to the use requirements.

[0065] Step 7: Prepare a TiC working layer by chemical vapor deposition with a thickness of 20 to 30 μm.

[0066] Coating performance test: mainly divided into coating surface hardness, coating cross-section hardness and coating bonding strength. The test results are shown in the following table:

[0067]

[0068] From the above, it can be seen that: 1. Comparison between the examples of the present invention and the comparative examples shows a significant increase in the coating surface hardness and bonding strength; 2. Comparison between the five examples of the present invention shows that the coating surface hardness and bonding strength increase with increasing the number of transition layers and changing the material ratios of the different transition layers. Therefore, by adding gradient transition layers and increasing the number of transition layers, the present invention improves the coating's resistance to wear, spalling, cracking, and "adhesion." The surface hardness is significantly increased compared to the base material, effectively solving the problems of roller surface crushing, cracking, and spalling in the copper processing industry and effectively extending the roller's single-use service life.

Claims

1. A method for preparing a new hard surface coating on a roller surface, comprising the following steps: Ⅰ. Machining: Turning to remove the fatigue layer and defects on the roller surface, and grinding to make the roller surface roughness Ra≤0.8μm; II. Front flaw detection: Perform surface flaw detection and ultrasonic flaw detection on the roller; III. Powder preparation: drying Ni-based alloy powder, TiC powder, and a mixture of Ni-based alloy powder and TiC powder; IV. Preparation of base layer and transition layer: The base layer and Ni-based TiC transition layer are prepared on the surface of the roll by using high velocity oxygen fuel (HVOF) spraying; V. Preparation of working layer: The working layer is prepared by supersonic oxygen fuel spraying (HVOF) or chemical vapor deposition; VI. Grinding: Grind the roller surface to the roughness range required by the drawing. If the working layer is prepared by thermal spraying, grinding is performed after spraying; if the working layer is prepared by chemical vapor deposition, grinding is performed before preparing the working layer; Ⅶ. Post-inspection: The rollers after grinding are subjected to surface color inspection and ultrasonic inspection to ensure that the coating is free of cracks after grinding and meets the coating deposition requirements.

2. The preparation method according to claim 1, characterized in that: in step III: the element content of the Ni-based alloy powder is: Cr content ≤15wt.%, C content ≤1.0wt.%, Si content 3.0-4.5wt.%, and the remainder is Ni, and the powder particle size is 15-53μm; the purity of the TiC powder is ≥99.5%, and the powder particle size is 15-53μm.

3. The preparation method according to claim 1, wherein in step III, the Ni-based alloy powder and the TiC powder are weighed and mechanically mixed according to a given mixing ratio, and the mixing time is not less than 2 hours.

4. The preparation method according to claim 1, characterized in that: in step III: after the powder mixing is completed, the powder is placed in an oven at a temperature of 80-100°C and a holding time of 2-3 hours.

5. The preparation method according to claim 1, characterized in that: in step IV: a surface roughening treatment is performed before spraying to ensure the bonding strength of the coating, and the surface roughness of the roller after roughening is Ra 5 to 8 μm.

6. The preparation method according to claim 1, characterized in that: in step IV: the HVOF spraying process parameters are: oxygen flow rate 850-1000 L / min, kerosene flow rate 20-25 L / h, powder feeding rate 60-80 g / min, and spraying distance 300-400 mm.

7. The preparation method according to claim 1, wherein: There are 4 transition layers in step IV. The thicknesses (μm) of the primer layer, 4 transition layers and working layer are: 20-30, 10-20, 10-20, 10-20, 10-20, respectively; thermal spraying: 50-100 or vapor deposition: 20-30.

8. The preparation method according to claim 1, characterized in that: there are four transition layers in step IV, and the compositions of the primer layer, the four transition layers, and the working layer are: 100% Ni-based, 80% Ni + 20% TiC, 60% Ni + 40% TiC, 40% Ni + 60% TiC, 20% Ni + 80% TiC, and 100% TiC, respectively.

9. The preparation method according to claim 1, wherein: The surface hardness of the prepared coating is greater than 2200 HV, and the bonding strength between the coating and the substrate is greater than 70 MPa.

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