Film thickness detection method for spray coating on high roughness surface

Abstract

The present invention relates to a method for detecting the film thickness of a spray coating on a high-roughness surface. A test sheet with a relatively small surface roughness is set on a workpiece to be sprayed, and the test sheet is sprayed together with the workpiece to be sprayed. Since the surface roughness of the test sheet is relatively low, the thickness of the first dry film layer thereon can be accurately detected by conventional film thickness detection means, and then the thickness of the second dry film layer on the high-roughness workpiece is calculated in combination with a conversion coefficient. The conversion coefficient represents the ratio of the film layer thickness formed by the coating on two materials with different surface roughnesses, and can be obtained through offline experiments. The above-mentioned film thickness detection method is equivalent to converting the measurement of the film thickness on a high-roughness surface into the measurement of the film thickness on a low-roughness surface, thereby improving the accuracy of film thickness detection.

Description

Technical Field

[0001] The invention relates to the technical field of coating detection, in particular to a method for detecting the film thickness of a spray coating on a high-roughness surface. Background Art

[0002] At present, the commercial vehicle axle assembly painting lines of most automobile companies can only meet the task of spraying one coat of paint. The paint film is relatively thin (thickness less than 40μm), resulting in poor corrosion resistance of the axle surface coating, and the salt spray test can only reach 96 to 120 hours.

[0003] Commercial vehicle axle parts are almost all cast iron parts, and the materials include gray iron, ductile iron, etc. Compared with steel parts, the surface roughness of cast iron parts is very large, and there are visible bumps and undulations on the surface, and the height difference between the convex and concave parts can reach 40 to 50 μm. This makes the paint film thickness uneven after the paint is sprayed on the surface of the cast iron part. The surface film thickness of the concave part may reach 40 μm, while the surface film thickness of the convex part is greatly reduced, and it may not even cover the base material, resulting in easy rust at the corners and edges. In order to avoid the above situation, the total thickness of the paint film on the surface of the cast iron part should be at least 10 to 20 μm greater than the surface roughness of the cast iron part, and generally greater than 30 to 40 μm greater than the surface roughness of the cast iron part.

[0004] Controlling the quality of the surface coating of cast iron parts is the key to ensuring the anti-corrosion performance of the surface coating of cast iron parts. The axle assembly coating line needs to conduct random inspections on the coating thickness of the workpiece to ensure the normal spraying process. However, due to the large surface roughness of the cast iron parts, the value measured by the thickness gauge is very inaccurate. Summary of the invention

[0005] Based on this, it is necessary to provide a film thickness detection method for spray coatings on high roughness surfaces to improve the accuracy of film thickness testing of spray coatings on high roughness surfaces.

[0006] A method for detecting the film thickness of a spray coating on a high-roughness surface comprises the following steps:

[0007] Placing a test sheet on a workpiece to be sprayed, wherein the surface roughness of the test sheet is smaller than the surface roughness of the workpiece to be sprayed;

[0008] Spraying the coating on the workpiece to be sprayed and the test sheet, and drying the coating to form a first dry film layer on the test sheet and a second dry film layer on the workpiece to be sprayed;

[0009] detecting the thickness of the first dry film layer;

[0010] The thickness of the second dry film layer is calculated by formula (1);

[0011] D2=k×D1 Formula (1)

[0012] Wherein, D1 is the thickness of the first dry film layer, D2 is the thickness of the second dry film layer, and k is the conversion coefficient;

[0013] k is obtained by:

[0014] Take a first test piece and a second test piece, wherein the surface roughness of the first test piece is the same as the surface roughness of the test sheet, and the surface roughness of the second test piece is the same as the surface roughness of the workpiece to be sprayed;

[0015] Spraying the coating on the first test piece and the second test piece, and drying the coating to form a third dry film layer on the first test piece and a fourth dry film layer on the second test piece;

[0016] detecting the thickness of the third dry film layer;

[0017] Obtaining the area and weight of the fourth dry film layer, obtaining the dry film specific gravity of the coating, and calculating the thickness of the fourth dry film layer by formula (2);

[0018] D4=M / (Q×S) Formula (2)

[0019] Wherein, D4 is the thickness of the fourth dry film layer, M is the weight of the fourth dry film layer, S is the area of ​​the fourth dry film layer, and Q is the dry film specific gravity of the coating;

[0020] Calculate k by formula (3);

[0021] K=D4 / D3 Formula (3)

[0022] Wherein, D3 is the thickness of the third dry film layer.

[0023] In one embodiment, the surface roughness of the test sheet is no greater than 2 μm.

[0024] In one embodiment, the surface roughness of the test sheet is 0.1 μm to 2 μm.

[0025] In one of the embodiments, the surface roughness of the workpiece to be sprayed is 8 μm to 50 μm.

[0026] In one embodiment, the workpiece to be sprayed is a cast iron part.

[0027] In one embodiment, the test sheet is a steel piece.

[0028] In one embodiment, the test sheet is a magnetic sheet, and the test sheet is adsorbed on the workpiece to be sprayed by magnetic force.

[0029] In one embodiment, different test sheets are attached to multiple areas of the workpiece to be sprayed, and an average value of the thickness of the first dry film layer is taken.

[0030] In one embodiment, the first test piece and / or the second test piece is a sheet-like structure.

[0031] In one embodiment, the method for obtaining the weight of the fourth dry film layer is:

[0032] The weight of the second test piece before and after the fourth dry film layer is formed is respectively weighed, and the weight change is the weight of the fourth dry film layer.

[0033] Compared with the traditional solution, the above-mentioned film thickness detection method of the spray coating on the high roughness surface has the following beneficial effects:

[0034] The above-mentioned film thickness detection method of the spray coating on the high-roughness surface can be applied to the quality sampling inspection of the spray coating on the coating line of cast iron workpieces. By setting a test sheet with a smaller surface roughness on the workpiece to be sprayed, the test sheet is sprayed together with the workpiece to be sprayed. Since the surface roughness of the test sheet is relatively low, the thickness of the first dry film layer on it can be accurately detected by conventional film thickness detection means, and then the thickness of the second dry film layer on the high-roughness workpiece is calculated in combination with the conversion coefficient. The conversion coefficient can be obtained offline through experiments. Specifically, a first test piece with the same surface roughness as the test sheet and a second test piece with the same surface roughness as the workpiece to be sprayed are taken, and the same coating as on the coating line is used for spraying. The third dry film layer on the first test piece can be accurately detected by conventional film thickness detection means, and the fourth dry film layer on the second test piece can be calculated by the area, weight and dry film specific gravity of the dry film of the coating, and then the thickness ratio of the fourth dry film layer to the third dry film layer, i.e., the conversion coefficient, is further calculated. The conversion coefficient represents the ratio of the film thickness formed by the coating on two materials with different surface roughness. Therefore, the above-mentioned film thickness detection method is equivalent to converting the measurement of the film thickness on a high-roughness surface into the measurement of the film thickness on a low-roughness surface, thereby improving the accuracy of film thickness detection. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0036] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0037] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0039] A method for detecting the film thickness of a spray coating on a high-roughness surface according to an embodiment of the present invention comprises the following steps:

[0040] Step S1, placing a test sheet on a workpiece to be sprayed, wherein the surface roughness of the test sheet is smaller than the surface roughness of the workpiece to be sprayed.

[0041] In one example, the workpiece to be sprayed is a cast iron part, such as an axle component. It can be understood that in other examples, the workpiece to be sprayed is not limited to a cast iron part, and other materials with rough surfaces may also be applicable.

[0042] In one example, the surface roughness (Ra) of the workpiece to be sprayed is 8 μm to 50 μm, and specifically can be 8 μm, 12.5 μm, 15 μm, 25 μm, 35 μm, 50 μm, etc.

[0043] In one example, the test sheet is a steel piece, which has a smooth surface and a surface roughness much less than that of a cast iron piece. It can be understood that in other examples, the test sheet is not limited to being a steel piece, and other materials with smooth surfaces may also be applicable.

[0044] In one example, the surface roughness of the test sheet is no greater than 2 μm. When the surface roughness is no greater than 2 μm, the coating thickness thereon can be accurately detected by conventional film thickness detection means. It can be understood that, in general, the smaller the surface roughness, the higher the accuracy of the coating thickness thereon when directly measuring it.

[0045] In one example, the surface roughness of the test sheet is 0.1 μm to 2 μm, and specifically may be 0.1 μm, 0.3 μm, 0.6 μm, 1 μm, 1.3 μm, 1.6 μm, etc.

[0046] In one example, the test sheet is a magnetic sheet, and the test sheet is adsorbed on the workpiece to be sprayed by magnetic force.

[0047] Step S2, spraying the coating on the workpiece to be sprayed and the test sheet, drying, forming a first dry film layer on the test sheet, and forming a second dry film layer on the workpiece to be sprayed.

[0048] Step S3, detecting the thickness of the first dry film layer.

[0049] The thickness of the first dry film layer can be measured using a thickness gauge.

[0050] In one of the examples, the thickness of the first dry film layer was tested according to standard GB-T 13452.2-2008 (Determination of film thickness of paints and varnishes).

[0051] Since the surface roughness of the test sheet is relatively small, the thickness of the first dry film layer thereon can be accurately detected by conventional film thickness detection means.

[0052] In one example, different test sheets are attached to multiple areas of the workpiece to be sprayed, and the thickness of the first dry film layer is averaged. The number of test sheets can be, for example, 2, 3, 4 or more.

[0053] Step S4, calculating the thickness of the second dry film layer by formula (1).

[0054] D2=k×D1 Formula (1)

[0055] Wherein, D1 is the thickness of the first dry film layer, D2 is the thickness of the second dry film layer, and k is the conversion coefficient.

[0056] The conversion factor k can be obtained offline through experiments. k is obtained by the following method:

[0057] Step S41, taking a first test piece and a second test piece, the surface roughness of the first test piece is the same as the surface roughness of the test sheet, and the surface roughness of the second test piece is the same as the surface roughness of the workpiece to be sprayed.

[0058] In one example, the first test piece is a sheet-like structure, which may be, but is not limited to, a circular sheet-like structure, a square sheet-like structure, etc.

[0059] In one example, the second test piece is a sheet-like structure, which may be, but is not limited to, a circular sheet-like structure, a square sheet-like structure, etc.

[0060] In one example, the first test piece is made of the same material as the test sheet. In one example, the second test piece is made of the same material as the workpiece to be sprayed.

[0061] Step S42, spraying the above-mentioned coating on the first test piece and the second test piece, drying, forming a third dry film layer on the first test piece, and forming a fourth dry film layer on the second test piece.

[0062] Step S43, detecting the thickness of the third dry film layer.

[0063] The thickness of the third dry film layer can be tested using a thickness gauge.

[0064] In one of the examples, the thickness of the third dry film layer was tested according to standard GB-T 13452.2-2008 (Determination of film thickness of paints and varnishes).

[0065] Since the surface roughness of the first test piece is relatively small, the thickness of the third dry film layer thereon can be accurately detected by conventional film thickness detection means.

[0066] Step S44, obtaining the area and weight of the fourth dry film layer, obtaining the dry film specific gravity of the coating, and calculating the thickness of the fourth dry film layer by formula (2);

[0067] D4=M / (Q×S) Formula (2)

[0068] Wherein, D4 is the thickness of the fourth dry film layer. M is the weight of the fourth dry film layer. S is the area of ​​the fourth dry film layer. Q is the dry film specific gravity of the coating, which is equivalent to the density of the coating after drying.

[0069] Step S45, calculate k by formula (III).

[0070] K=D4 / D3 Formula (3)

[0071] Wherein, D3 is the thickness of the third dry film layer.

[0072] In one example, the weight of the fourth dry film layer is obtained by:

[0073] The weight of the second test piece before and after the fourth dry film layer is formed is respectively weighed, and the weight change is the weight of the fourth dry film layer.

[0074] The above-mentioned film thickness detection method is equivalent to converting the measurement of film thickness on a high-roughness surface into the measurement of film thickness on a low-roughness surface, thereby improving the accuracy of film thickness detection.

[0075] The following specific examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0076] Example 1

[0077] This embodiment is to conduct a random inspection on the quality of the spray coating on the cast iron workpiece coating line to detect whether the coating thickness on the cast iron workpiece is qualified.

[0078] The dry film density of the coating used in this example is 1.13 g / cm 3 .

[0079] First, a test experiment of the conversion coefficient k is carried out. The experimental steps are as follows:

[0080] Take a cast iron sheet, the surface area of ​​one side of which is 31cm 2 , the surface roughness is 8μm.

[0081] Take a magnetic iron sheet, the surface roughness of which is 0.8 μm.

[0082] The cast iron sheet and the magnetic iron sheet are sprayed with the coating material at the same time, and then dried.

[0083] The dry film area on the cast iron sheet is the surface area of ​​the cast iron sheet, which is 31cm 2 The weight of the dry film on the cast iron sheet, i.e., the weight increase of the cast iron sheet, is 0.1436 g.

[0084] The dry film thickness on the cast iron sheet was calculated to be 41 μm according to the above formula (II).

[0085] The dry film thickness on the test sheet was measured according to standard GB-T 13452.2-2008 and the result was 45 μm.

[0086] According to the above formula (III), the film thickness conversion coefficient k of the cast iron sheet and the magnetic iron sheet is calculated to be 0.91.

[0087] The film thickness detection of the spray coating on the coating line is as follows:

[0088] A number of cast iron workpieces to be sprayed are selected on the coating line, and three magnetic iron sheets are set on representative areas of the cast iron workpieces.

[0089] The paint on the coating line is sprayed on the workpiece to be sprayed and the test sheet, and dried to form a first dry film layer on the magnetic iron sheet and a second dry film layer on the cast iron workpiece.

[0090] The magnetic iron sheet on which the first dry film layer is formed is removed, and the thickness of the first dry film layer on the magnetic iron sheet is measured according to the standard GB-T 13452.2-2008.

[0091] The thickness of the second dry film layer on the cast iron workpiece is calculated according to the above formula (I).

[0092] Example 2

[0093] This embodiment is to conduct a random inspection on the quality of the spray coating on the cast iron workpiece coating line to detect whether the coating thickness on the cast iron workpiece is qualified.

[0094] The dry film density of the coating used in this example is 1.13 g / cm 3 .

[0095] First, a test experiment of the conversion coefficient k is carried out. The experimental steps are as follows:

[0096] Take a cast iron sheet, the surface area of ​​one side of which is 23cm 2 , the surface roughness is 12.5 μm, which is the same as the surface roughness of the cast iron workpiece to be coated.

[0097] Take a magnetic iron sheet, the surface roughness of which is 0.8 μm.

[0098] The cast iron sheet and the magnetic iron sheet are sprayed with the coating material at the same time, and then dried.

[0099] The dry film area on the cast iron sheet is the surface area of ​​the cast iron sheet, which is 23cm 2 The weight of the dry film on the cast iron sheet, i.e., the weight increase of the cast iron sheet, is 0.1014 g.

[0100] The dry film thickness on the cast iron sheet was calculated to be 39 μm according to the above formula (II).

[0101] The dry film thickness on the test sheet was measured according to standard GB-T 13452.2-2008, and the result was 43 μm.

[0102] According to the above formula (III), the film thickness conversion coefficient k of the cast iron sheet and the magnetic iron sheet is calculated to be 0.91.

[0103] The film thickness detection of the spray coating on the coating line is as follows:

[0104] A number of cast iron workpieces to be sprayed are selected on the coating line, and three magnetic iron sheets are set on representative areas of the cast iron workpieces.

[0105] The paint on the coating line is sprayed on the workpiece to be sprayed and the test sheet, and dried to form a first dry film layer on the magnetic iron sheet and a second dry film layer on the cast iron workpiece.

[0106] The magnetic iron sheet on which the first dry film layer is formed is removed, and the thickness of the first dry film layer on the magnetic iron sheet is measured according to the standard GB-T 13452.2-2008.

[0107] The thickness of the second dry film layer on the cast iron workpiece is calculated according to the above formula (I).

[0108] Example 3

[0109] This embodiment is to conduct a random inspection on the quality of the spray coating on the cast iron workpiece coating line to detect whether the coating thickness on the cast iron workpiece is qualified.

[0110] The dry film density of the coating used in this example is 1.13 g / cm 3 .

[0111] First, a test experiment of the conversion coefficient k is carried out. The experimental steps are as follows:

[0112] Take a cast iron sheet, the surface area of ​​one side of which is 21cm 2 , the surface roughness is 15 μm, which is the same as the surface roughness of the cast iron workpiece to be coated.

[0113] Take a magnetic iron sheet, the surface roughness of which is 0.8 μm.

[0114] The cast iron sheet and the magnetic iron sheet are sprayed with the coating material at the same time, and then dried.

[0115] The dry film area on the cast iron sheet is the surface area of ​​the cast iron sheet, which is 21cm 2 The weight of the dry film on the cast iron sheet, i.e., the weight increase of the cast iron sheet, is 0.0878 g.

[0116] The dry film thickness on the cast iron sheet was calculated to be 42 μm according to the above formula (II).

[0117] The dry film thickness on the test sheet was measured according to standard GB-T 13452.2-2008, and the result was 48 μm.

[0118] According to the above formula (III), the film thickness conversion coefficient k of the cast iron sheet and the magnetic iron sheet is calculated to be 0.88.

[0119] The film thickness detection of the spray coating on the coating line is as follows:

[0120] A number of cast iron workpieces to be sprayed are selected on the coating line, and three magnetic iron sheets are set on representative areas of the cast iron workpieces.

[0121] The paint on the coating line is sprayed on the workpiece to be sprayed and the test sheet, and dried to form a first dry film layer on the magnetic iron sheet and a second dry film layer on the cast iron workpiece.

[0122] The magnetic iron sheet on which the first dry film layer is formed is removed, and the thickness of the first dry film layer on the magnetic iron sheet is measured according to the standard GB-T 13452.2-2008.

[0123] The thickness of the second dry film layer on the cast iron workpiece is calculated according to the above formula (I).

[0124] Example 4

[0125] This embodiment is to conduct a random inspection on the quality of the spray coating on the cast iron workpiece coating line to detect whether the coating thickness on the cast iron workpiece is qualified.

[0126] The dry film density of the coating used in this example is 1.13 g / cm 3 .

[0127] First, a test experiment of the conversion coefficient k is carried out. The experimental steps are as follows:

[0128] Take a cast iron sheet, the surface area of ​​one side of which is 27cm 2 , the surface roughness is 25 μm, which is the same as the surface roughness of the cast iron workpiece to be coated.

[0129] Take a magnetic iron sheet, the surface roughness of which is 0.8 μm.

[0130] The cast iron sheet and the magnetic iron sheet are sprayed with the coating material at the same time, and then dried.

[0131] The dry film area on the cast iron sheet is the surface area of ​​the cast iron sheet, which is 27 cm 2 The weight of the dry film on the cast iron sheet, i.e., the weight increase of the cast iron sheet, is 0.1098 g.

[0132] The dry film thickness on the cast iron sheet was calculated to be 36 μm according to the above formula (II).

[0133] The dry film thickness on the test sheet was measured according to standard GB-T 13452.2-2008, and the result was 42 μm.

[0134] According to the above formula (III), the film thickness conversion coefficient k of the cast iron sheet and the magnetic iron sheet is calculated to be 0.86.

[0135] The film thickness detection of the spray coating on the coating line is as follows:

[0136] A number of cast iron workpieces to be sprayed are selected on the coating line, and three magnetic iron sheets are set on representative areas of the cast iron workpieces.

[0137] The paint on the coating line is sprayed on the workpiece to be sprayed and the test sheet, and dried to form a first dry film layer on the magnetic iron sheet and a second dry film layer on the cast iron workpiece.

[0138] The magnetic iron sheet on which the first dry film layer is formed is removed, and the thickness of the first dry film layer on the magnetic iron sheet is measured according to the standard GB-T 13452.2-2008.

[0139] The thickness of the second dry film layer on the cast iron workpiece is calculated according to the above formula (I).

[0140] Example 5

[0141] This embodiment is to conduct a random inspection on the quality of the spray coating on the cast iron workpiece coating line to detect whether the coating thickness on the cast iron workpiece is qualified.

[0142] The dry film density of the coating used in this example is 1.13 g / cm 3 .

[0143] First, a test experiment of the conversion coefficient k is carried out. The experimental steps are as follows:

[0144] Take a cast iron sheet, the surface area of ​​one side of which is 35cm 2 , the surface roughness is 29 μm, which is the same as the surface roughness of the cast iron workpiece to be coated.

[0145] Take a magnetic iron sheet, the surface roughness of which is 0.8 μm.

[0146] The cast iron sheet and the magnetic iron sheet are sprayed with the coating material at the same time, and then dried.

[0147] The dry film area on the cast iron sheet is the surface area of ​​the cast iron sheet, which is 35 cm 2 The weight of the dry film on the cast iron sheet, i.e., the weight increase of the cast iron sheet, is 0.1383 g.

[0148] The dry film thickness on the cast iron sheet was calculated to be 35 μm according to the above formula (II).

[0149] The dry film thickness on the test sheet was measured according to standard GB-T 13452.2-2008, and the result was 46 μm.

[0150] According to the above formula (III), the film thickness conversion coefficient k of the cast iron sheet and the magnetic iron sheet is calculated to be 0.76.

[0151] The film thickness detection of the spray coating on the coating line is as follows:

[0152] A number of cast iron workpieces to be sprayed are selected on the coating line, and three magnetic iron sheets are set on representative areas of the cast iron workpieces.

[0153] The paint on the coating line is sprayed on the workpiece to be sprayed and the test sheet, and dried to form a first dry film layer on the magnetic iron sheet and a second dry film layer on the cast iron workpiece.

[0154] The magnetic iron sheet on which the first dry film layer is formed is removed, and the thickness of the first dry film layer on the magnetic iron sheet is measured according to the standard GB-T 13452.2-2008.

[0155] The thickness of the second dry film layer on the cast iron workpiece is calculated according to the above formula (I).

[0156] Example 6

[0157] This embodiment is to conduct a random inspection on the quality of the spray coating on the cast iron workpiece coating line to detect whether the coating thickness on the cast iron workpiece is qualified.

[0158] The dry film density of the coating used in this example is 1.13 g / cm 3 .

[0159] First, a test experiment of the conversion coefficient k is carried out. The experimental steps are as follows:

[0160] Take a cast iron sheet, the surface area of ​​one side of which is 39cm 2 , the surface roughness is 50 μm, which is the same as the surface roughness of the cast iron workpiece to be coated.

[0161] Take a magnetic iron sheet, the surface roughness of which is 0.8 μm.

[0162] The cast iron sheet and the magnetic iron sheet are sprayed with the coating material at the same time, and then dried.

[0163] The dry film area on the cast iron sheet is the surface area of ​​the cast iron sheet, which is 39 cm 2 The weight of the dry film on the cast iron sheet, i.e., the weight increase of the cast iron sheet, is 0.1631 g.

[0164] The dry film thickness on the cast iron sheet was calculated to be 37 μm according to the above formula (II).

[0165] The dry film thickness on the test sheet was measured according to standard GB-T 13452.2-2008, and the result was 49 μm.

[0166] According to the above formula (III), the film thickness conversion coefficient k of the cast iron sheet and the magnetic iron sheet is calculated to be 0.76.

[0167] The film thickness detection of the spray coating on the coating line is as follows:

[0168] A number of cast iron workpieces to be sprayed are selected on the coating line, and three magnetic iron sheets are set on representative areas of the cast iron workpieces.

[0169] The paint on the coating line is sprayed on the workpiece to be sprayed and the test sheet, and dried to form a first dry film layer on the magnetic iron sheet and a second dry film layer on the cast iron workpiece.

[0170] The magnetic iron sheet on which the first dry film layer is formed is removed, and the thickness of the first dry film layer on the magnetic iron sheet is measured according to the standard GB-T 13452.2-2008.

[0171] The thickness of the second dry film layer on the cast iron workpiece is calculated according to the above formula (I).

[0172] The above-mentioned film thickness detection method for spray coatings on high-roughness surfaces can be applied to the quality random inspection of spray coatings on cast iron workpiece coating lines. A test sheet with a smaller surface roughness is set on the workpiece to be sprayed, and the test sheet is sprayed together with the workpiece to be sprayed. Since the surface roughness of the test sheet is relatively low, the thickness of the first dry film layer thereon can be accurately detected by conventional film thickness detection means, and then the thickness of the second dry film layer on the high-roughness workpiece is calculated in combination with the conversion coefficient.

[0173] The conversion coefficient can be obtained offline through experiments. Specifically, a first test piece with the same surface roughness as the test sheet and a second test piece with the same surface roughness as the workpiece to be sprayed are taken, and the same paint as on the coating line is used for spraying. The third dry film layer on the first test piece can be accurately detected by conventional film thickness detection means, and the fourth dry film layer on the second test piece can be calculated by the area, weight and dry film specific gravity of the paint, and then the thickness ratio of the fourth dry film layer to the third dry film layer is further calculated, that is, the conversion coefficient. The conversion coefficient represents the ratio of the film thickness formed by the paint on two materials with different surface roughness. Therefore, the above-mentioned film thickness detection method is equivalent to converting the measurement of film thickness on a high-roughness surface into the measurement of film thickness on a low-roughness surface, thereby improving the accuracy of film thickness detection.

[0174] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0175] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for detecting the film thickness of a spray coating on a high-roughness surface, characterized in that: The following steps are involved: Placing a test sheet on a workpiece to be sprayed, wherein the surface roughness of the test sheet is smaller than the surface roughness of the workpiece to be sprayed; Spraying the coating on the workpiece to be sprayed and the test sheet, and drying the coating to form a first dry film layer on the test sheet and a second dry film layer on the workpiece to be sprayed; detecting the thickness of the first dry film layer; The thickness of the second dry film layer is calculated by formula (1); D2=k×D1 Formula (1) Wherein, D1 is the thickness of the first dry film layer, D2 is the thickness of the second dry film layer, and k is the conversion coefficient; k is obtained by: Take a first test piece and a second test piece, wherein the surface roughness of the first test piece is the same as the surface roughness of the test sheet, and the surface roughness of the second test piece is the same as the surface roughness of the workpiece to be sprayed; Spraying the coating on the first test piece and the second test piece, and drying the coating to form a third dry film layer on the first test piece and a fourth dry film layer on the second test piece; detecting the thickness of the third dry film layer; Obtaining the area and weight of the fourth dry film layer, obtaining the dry film specific gravity of the coating, and calculating the thickness of the fourth dry film layer by formula (2); D4=M / (Q×S) Formula (2) Wherein, D4 is the thickness of the fourth dry film layer, M is the weight of the fourth dry film layer, S is the area of ​​the fourth dry film layer, and Q is the dry film specific gravity of the coating; Calculate k by formula (3); K=D4 / D3 Formula (3) Wherein, D3 is the thickness of the third dry film layer.

2. The method for detecting the film thickness of a high-roughness surface spray coating according to claim 1, characterized in that: The surface roughness of the test sheet is no greater than 2 μm.

3. The method for detecting the film thickness of a high-roughness surface spray coating according to claim 2, characterized in that: The surface roughness of the test sheet is 0.1 μm to 2 μm.

4. The method for detecting the film thickness of a high-roughness surface spray coating according to claim 1, characterized in that: The surface roughness of the workpiece to be sprayed is 8 μm to 50 μm.

5. The method for detecting the film thickness of a spray coating on a high-roughness surface as claimed in claim 1, characterized in that: The workpiece to be sprayed is a cast iron part.

6. The method for detecting the film thickness of a spray coating on a high-roughness surface according to claim 1, characterized in that: The test sheet material is a steel piece.

7. The method for detecting the film thickness of a spray coating on a high roughness surface as claimed in claim 1, characterized in that: The test sheet is a magnetic sheet, and the test sheet is adsorbed on the workpiece to be sprayed by magnetic force.

8. The method for detecting the film thickness of a spray coating on a high-roughness surface as claimed in claim 1, characterized in that: Different test sheets are respectively attached to multiple areas of the workpiece to be sprayed, and the thickness of the first dry film layer is averaged.

9. The method for detecting the film thickness of a spray coating on a high-roughness surface as claimed in claim 1, characterized in that: The first test piece and / or the second test piece is a sheet-like structure.

10. The method for detecting the film thickness of a high-roughness surface spray coating according to any one of claims 1 to 9, characterized in that: The method for obtaining the weight of the fourth dry film layer is: The weight of the second test piece before and after the fourth dry film layer is formed is weighed respectively, and the weight change is the weight of the fourth dry film layer.