Method for Evaluating Welding Ability of Narrow Lap Resistance Welder

Abstract

The present invention relates to a method for evaluating the welding ability of a narrow lap resistance welder, which successively includes the following steps: collecting the equipment parameters of the resistance welder; collecting the strip steel and welding process parameters; calculating the nugget height and the total heat required for welding; calculating the total resistance at the weld; calculating the effective heat generated at the weld and calculating the objective function value; determining whether the objective function value meets the conditions. If not, the evaluation result is that the welding requirements are not met. If so, calculating the inner stress and outer stress of the frame crossbeam and columns of the resistance welder, and then determining whether the inner stress and outer stress meet the conditions. If so, the evaluation result is that the welding requirements are met. If not, the welding parameters exceed the capacity of the resistance welder. The present invention can evaluate the ultimate strength, width and thickness that the resistance welder can weld, so as to obtain the ultimate specification products and bottlenecks, ensure the weld quality, and improve the actual production efficiency.

Description

Technical field

[0001] The present invention relates to continuous annealing welding technology, and particularly to a method for evaluating the welding ability of a narrow lap resistance welder. Background technology

[0002] Continuous annealing is relative to batch annealing. It is a production method in which strip steel continuously passes through an annealing furnace. The annealing furnace has no seal, and the strip steel is directly coiled without staying. Narrow lap resistance welders are usually used in continuous annealing units. The resistance welder welds the front and rear strip steels to keep the unit running continuously without interruption. The quality of the welding determines the quality and output of the strip steel products, and the key factor determining the welding quality lies in the setting of the welding parameters. At present, for products with existing steel grades and thicknesses, reasonable welding parameters can be obtained through a large number of tests and are within the capacity range of the resistance welder; for new steel grades, without welding tests, the setting of the welding parameters is unreasonable. If it exceeds the capacity range of the resistance welder, it is easy to cause poor weld quality and even lead to the risk of strip breakage in severe cases. Therefore, there is an urgent need for a method for evaluating the welding ability of a narrow lap resistance welder for a continuous annealing unit to evaluate the capacity of the resistance welder for welding ultimate strength, width and thickness products, which is particularly important for improving on-site production efficiency and product quality.

[0003] At present, the research on continuous annealing welding technology mainly includes the following aspects: First, optimizing welding process parameters, such as welding current, welding voltage, weld wheel pressure, welding speed, overlap amount, compensation amount, etc.; Second, welding safety detection and resistance welder maintenance; However, these research aspects are not aimed at evaluating the welding ability of the resistance welder for a continuous annealing unit. Chinese Patent No. 201620475700.0 discloses a support device for rapid maintenance of the electrodes of a resistance welder, belonging to the field of equipment maintenance. The support device is used to stably support the welder electrodes to be repaired and improve the repair efficiency. Chinese Patent No. 201520897172.3 discloses a safety detection device for a resistance welder, which includes an upper limit grating, a lower limit grating and a grating baffle to prevent the generation of iron filings and powder, and improves the stability and service life of the device. Chinese Patent No. 200620045383.5 discloses a disassembly tool for the tool rest of a resistance welder, which can achieve rapid and convenient disassembly of the sizing tool rest without a fixed support point, mainly solving the technical problems of high labor intensity and low work efficiency in manual disassembly. Thus, the above patents do not involve devices and methods that can be used to evaluate the welding ability of a narrow lap resistance welder for a continuous annealing unit. Summary of the invention

[0004] The purpose of the present invention is to provide a method for evaluating the welding ability of a narrow lap resistance welder. The evaluation method comprehensively considers the equipment parameters of the resistance welder, as well as the strip steel and welding process parameters, establishes a mathematical model that can be used to evaluate the welding ability of the narrow lap resistance welder, evaluates the ultimate strength, width, and thickness that the resistance welder can weld, thereby obtaining the ultimate specification products and bottlenecks, ensuring the weld quality, and improving the actual production efficiency.

[0005] The present invention is implemented as follows:

[0006] A method for evaluating the welding ability of a narrow lap resistance welder, the resistance welder including an upper welding wheel, a lower welding wheel, and a frame; the evaluation method includes the following steps:

[0007] Step 1: Collect the equipment parameters of the resistance welder. The equipment parameters include the thickness, elastic modulus, Poisson's ratio, and radius of the upper welding wheel, the elastic modulus and Poisson's ratio of the forward strip steel, the thickness, elastic modulus, Poisson's ratio, and radius of the lower welding wheel, the elastic modulus and Poisson's ratio of the rear strip steel, the vertical force applied to the frame, the neutral line length, moment of inertia, cross-sectional length, inner height, and outer height of the frame crossbeam, the neutral line length, moment of inertia, cross-sectional length, inner height, and outer height of the frame column, and the allowable stress of the frame;

[0008] Step 2: Collect the strip steel and welding process parameters. The strip steel and welding process parameters include the indentation height, welding carbon equivalent, and thickness of the forward strip steel, the indentation height, welding carbon equivalent, and thickness of the rear strip steel, the specific heat capacity of the strip steel, the density of the strip steel, the temperature difference between the normal temperature and the nugget state of the strip steel, the welding speed, the overlap amount, the compensation amount, the welding wheel pressure, the surface temperature of the strip steel, the welding current, and the deviation coefficient;

[0009] Step 3: Calculate the nugget height and the total heat required for welding. The calculation formulas are as follows:

[0010] h = A·[(h1 + h2)-(c s + c x )]

[0011] Q 需 = λch(b djl + b bcl )ρΔT

[0012] In the formula, h is the nugget height, A is the penetration rate, h1 and h2 are the thicknesses of the forward strip steel and the rear strip steel respectively, c s and c x are the indentation heights of the forward strip steel and the rear strip steel respectively, Q 需 is the total heat required for welding, λ is the nugget melting coefficient, c is the specific heat capacity of the strip steel, b djl is the overlap amount, b bclis the compensation amount, ρ is the density of the strip steel, and ΔT is the temperature difference between the normal temperature and the nugget state of the strip steel;

[0013] Step 4: Calculate the total resistance at the weld. First, calculate the contact width between the upper welding wheel and the advancing strip steel and the contact width between the lower welding wheel and the trailing strip steel according to the Hertz formula; then, considering the influence of the edge effect and the flow-around phenomenon on the resistance and based on Matthiessen's law, calculate the resistance of the advancing strip steel and the resistance of the trailing strip steel; finally, obtain the total resistance at the weld from the sum of the resistance of the advancing strip steel, the resistance of the trailing strip steel, and the contact resistance.

[0014] Step 5: Calculate the effective heat generated at the weld according to Joule's law and calculate the objective function value. The calculation formulas are as follows:

[0015]

[0016] In the formula, G(x) is the objective function value, and Q1 is the effective heat generated at the weld;

[0017] Step 6: If the objective function value is less than or equal to the deviation coefficient, go to Step 7; if the objective function value is greater than the deviation coefficient, the welding ability evaluation result is that it does not meet the welding requirements.

[0018] Step 7: First, check the resistance welding machine and calculate the upper moment, the inner bending moment of inertia, the outer bending moment of inertia, the inner stress, and the outer stress of the frame crossbeam, and the influence moment, the inner bending moment of inertia, the outer bending moment of inertia, the inner stress, and the outer stress of the frame column; then, judge the calculation results. If the inner stress and the outer stress of the frame crossbeam and the inner stress and the outer stress of the frame column are all less than or equal to the allowable stress of the frame, the welding ability evaluation result is that it meets the welding requirements; if the above conditions are not met, it means that the welding parameters exceed the capacity of the resistance welding machine.

[0019] In Step 3, 60% ≤ A ≤ 80%, 0.9 ≤ λ ≤ 1.2.

[0020] In Step 4, the calculation formulas for the contact width between the upper welding wheel and the advancing strip steel and the contact width between the lower welding wheel and the trailing strip steel are as follows:

[0021]

[0022] In the formula, b dws is the contact width between the upper welding wheel and the advancing strip steel, b dwx is the contact width between the lower welding wheel and the trailing strip steel, P is the welding wheel pressure, b hls and R hls are the thickness and radius of the upper welding wheel respectively, b hlx and R hlxare the thickness and radius of the lower welding wheel respectively, E1 and v1 are the elastic modulus and Poisson's ratio of the upper welding wheel respectively, E2 and v2 are the elastic modulus and Poisson's ratio of the forward strip respectively, E3 and v3 are the elastic modulus and Poisson's ratio of the lower welding wheel respectively, and E4 and v4 are the elastic modulus and Poisson's ratio of the backward strip respectively.

[0023] In the fourth step, the calculation formulas for the resistance of the forward strip and the resistance of the backward strip are as follows:

[0024]

[0025] In the formula, R w1 is the resistance of the forward strip, R w2 is the resistance of the backward strip, K1 is the coefficient of current field diffusion caused by the edge effect, K2 is the coefficient of current field diffusion caused by the flow-around phenomenon, K3 is the influence index of carbon equivalent on resistance, K4 is the coefficient of the molten width of the nugget, C e1 and C e2 are the welding carbon equivalents of the forward strip and the backward strip respectively, b dws is the contact width between the upper welding wheel and the forward strip, b dwx is the contact width between the lower welding wheel and the backward strip, ρ0 is the resistivity of the strip at 0 °C, α is the temperature coefficient of resistance of the strip resistivity varying with temperature, and T is the surface temperature of the strip.

[0026] The ρ0 = 9.78×10 -8 Ωm, α = 6.51×10 -3 , 0.80 ≤ K1 ≤ 0.85, 0.8 ≤ K2 ≤ 0.9, 0.02 ≤ K3 ≤ 0.08, 1.0 ≤ K4 ≤ 2.0.

[0027] In the fourth step, the calculation formula for the contact resistance is as follows:

[0028]

[0029] In the formula, R c is the contact resistance, K c is the first coefficient related to the contact material, surface condition, and contact form, P is the pressure of the welding wheel, and m is the second coefficient related to the contact form.

[0030] The m = 1, 0.1 ≤ K c ≤ 0.4.

[0031] In the fifth step, the calculation formula for the effective heat is as follows:

[0032]

[0033] Wherein, γ is the effective heat calculation coefficient, h1 and h2 are the thicknesses of the forward strip and the rear strip respectively, φ is the influence index of strip thickness on the effective heat, C e1 and C e2 are the welding carbon equivalents of the forward strip and the rear strip respectively, β is the influence index of strip welding carbon equivalent on the effective heat, I is the welding current, R is the total resistance at the weld, and V is the welding speed.

[0034] It is stated that γ = 0.2, 0.25 ≤ φ ≤ 0.35, and 0.1 ≤ β ≤ 0.2.

[0035] In the seventh step, the calculation formula for the upper moment of the frame crossbeam is as follows:

[0036]

[0037] Wherein, M1 is the upper moment of the frame crossbeam, R is the total resistance at the weld, l1 and I1 are the neutral line lengths and moments of inertia of the frame crossbeam respectively, and l2 and I2 are the neutral line lengths and moments of inertia of the frame columns respectively;

[0038] The calculation formula for the influence moment of the frame column is as follows:

[0039] M2 = Fl1 - M1

[0040] Wherein, M2 is the influence moment of the frame column, and F is the vertical force applied to the frame;

[0041] The calculation formulas for the inner flexural section modulus and outer flexural section modulus of the frame crossbeam, and the inner flexural section modulus and outer flexural section modulus of the frame column are as follows:

[0042]

[0043] Wherein, W n1 and W a1 are the inner flexural section modulus and outer flexural section modulus of the frame crossbeam respectively, W n2 and W a2 are the inner flexural section modulus and outer flexural section modulus of the frame column respectively, b1 is the cross-sectional length of the frame crossbeam, g1 is the inner height and outer height of the frame crossbeam, b2 is the cross-sectional length of the frame column, and g2 is the inner height and outer height of the frame column;

[0044] The calculation formulas for the inner stress and outer stress of the frame crossbeam, and the inner stress and outer stress of the frame column are as follows:

[0045]

[0046] Wherein, σ n1 and σ a1are the inner stress and outer stress of the frame crossbeam, respectively, and σ n2 and σ a2 are the inner stress and outer stress of the frame column, respectively.

[0047] The method for evaluating the welding ability of the narrow lap resistance welder of the present invention calculates the nugget height, the total heat required for welding, the total resistance at the weld, and the effective heat generated at the weld by comprehensively considering the equipment parameters of the resistance welder, the strip steel, and the welding process parameters, thereby obtaining the objective function value based on the total heat required for welding and the effective heat generated at the weld. Then, by judging the objective function value with a preset deviation coefficient and combining the inner and outer side stresses of the resistance welder frame with the preset allowable stress of the frame, the evaluation result of the welding ability of the resistance welder is finally obtained. Thus, by establishing such a mathematical model, the present invention can effectively evaluate the welding ultimate strength, width, and thickness of the resistance welder, and obtain the ultimate specification products and bottlenecks, which can not only ensure good weld quality but also improve the actual production efficiency, contributing to improving the economic benefits of the continuous annealing unit.

[0048] Compared with the prior art, the present invention has the following beneficial effects: A mathematical model for evaluating the welding ability of the narrow lap resistance welder is established based on the equipment parameters of the resistance welder, the strip steel, and the welding process parameters. The method steps are concise and practical and can flexibly adapt to the change of steel grades, ensuring the quality of the continuous annealing welds, and effectively improving the on-site actual production efficiency and product quality. Brief Description of the Drawings

[0049] Figure 1 is a flow chart of the method for evaluating the welding ability of the narrow lap resistance welder of the present invention. Detailed Embodiments

[0050] The present invention will be further described below in conjunction with specific embodiments.

[0051] Refer to Figure 1 , a method for evaluating the welding ability of a narrow lap resistance welder, the resistance welder includes an upper welding wheel, a lower welding wheel, and a frame, and the evaluation method specifically includes the following steps:

[0052] Step 1, collect the equipment parameters of the resistance welder. The equipment parameters include the thickness, elastic modulus, Poisson's ratio, and radius of the upper welding wheel, the elastic modulus and Poisson's ratio of the forward strip steel, the thickness, elastic modulus, Poisson's ratio, and radius of the lower welding wheel, the elastic modulus and Poisson's ratio of the backward strip steel, the vertical force on the frame, the neutral line length, moment of inertia, cross-sectional length, inner height, and outer height of the frame crossbeam, the neutral line length, moment of inertia, cross-sectional length, inner height, and outer height of the frame column, and the allowable stress of the frame.

[0053] Step 2: Collect strip steel and welding process parameters. The strip steel and welding process parameters include the indentation height of the forward strip steel, welding carbon equivalent, thickness, the indentation height of the rear strip steel, welding carbon equivalent, thickness, specific heat capacity of the strip steel, density of the strip steel, temperature difference between the normal temperature and the nugget state of the strip steel, welding speed, lapping amount, compensation amount, wheel pressure, surface temperature of the strip steel, welding current, and deviation coefficient.

[0054] Step 3: Calculate the nugget height and the total heat required for welding. The calculation formulas are as follows:

[0055] h = A·[(h1 + h2) - (c s + c x )]

[0056] Q 需 = λch(b djl + b bcl )ρΔT

[0057] In the formula, h is the nugget height, A is the penetration rate, h1 and h2 are the thicknesses of the forward strip steel and the rear strip steel respectively, c s and c x are the indentation heights of the forward strip steel and the rear strip steel respectively, Q 需 is the total heat required for welding, λ is the nugget melting coefficient, c is the specific heat capacity of the strip steel, b djl is the lapping amount, b bcl is the compensation amount, ρ is the density of the strip steel, and ΔT is the temperature difference between the normal temperature and the nugget state of the strip steel. Preferably, to ensure the welding quality, 60% ≤ A ≤ 80%, 0.9 ≤ λ ≤ 1.2.

[0058] Step 4: Calculate the total resistance at the weld. First, calculate the contact width between the upper welding wheel and the forward strip steel and the contact width between the lower welding wheel and the rear strip steel according to the Hertz formula; then, considering the influence of the edge effect and the flow-around phenomenon on the resistance and according to Matthiessen's law, calculate the resistance of the forward strip steel and the resistance of the rear strip steel; finally, obtain the total resistance at the weld from the sum of the resistance of the forward strip steel, the resistance of the rear strip steel, and the contact resistance.

[0059] Specifically, the calculation formulas for the contact width between the upper welding wheel and the forward strip steel and the contact width between the lower welding wheel and the rear strip steel are as follows:

[0060]

[0061] In the formula, b dws is the contact width between the upper welding wheel and the forward strip steel, b dwx is the contact width between the lower welding wheel and the rear strip steel, P is the wheel pressure, b hls and R hls are the thickness and radius of the upper welding wheel respectively, b hlx and Rhlx are the thickness and radius of the lower welding wheel respectively, E1 and v1 are the elastic modulus and Poisson's ratio of the upper welding wheel respectively, E2 and v2 are the elastic modulus and Poisson's ratio of the forward strip respectively, E3 and v3 are the elastic modulus and Poisson's ratio of the lower welding wheel respectively, and E4 and v4 are the elastic modulus and Poisson's ratio of the backward strip respectively.

[0062] Therefore, the calculation formulas for the resistance of the forward strip and the backward strip are as follows:

[0063]

[0064] In the formula, R w1 is the resistance of the forward strip, R w2 is the resistance of the backward strip, K1 is the coefficient of current field diffusion caused by edge effect, K2 is the coefficient of current field diffusion caused by flow-around phenomenon, K3 is the influence index of carbon equivalent on resistance, K4 is the coefficient of fusion core melting width, C e1 and C e2 are the welding carbon equivalents of the forward strip and the backward strip respectively, b dws is the contact width between the upper welding wheel and the forward strip, b dwx is the contact width between the lower welding wheel and the backward strip, ρ0 is the resistivity of the strip at 0 °C, α is the temperature coefficient of resistance of the strip resistivity varying with temperature, and T is the surface temperature of the strip. Preferably, ρ0 = 9.78×10 -8 Ω·m, α = 6.51×10 -3 , 0.80 ≤ K1 ≤ 0.85, 0.8 ≤ K2 ≤ 0.9, 0.02 ≤ K3 ≤ 0.08, 1.0 ≤ K4 ≤ 2.0.

[0065] Specifically, the calculation formula for the contact resistance is set according to experience as follows:

[0066]

[0067] In the formula, R c is the contact resistance, K c is the first coefficient related to the contact material, surface condition, and contact form. Preferably, 0.1 ≤ K c ≤ 0.4. P is the welding wheel pressure. m is the second coefficient related to the contact form. The contact forms include point, line, and surface contacts, and the corresponding m values can be 0.5, 0.7, and 1 respectively. Since the contact form of the resistance welder is usually surface contact, m = 1.

[0068] In addition, the total resistance at the weld seam also includes the contact resistance between the advancing strip and the electrode and the contact resistance between the trailing strip and the electrode. Since the electrode is made of copper with high conductivity and reliable contact, only a very small part of the heat generated by the contact between the strip and the electrode is transferred to the strip, and a part of this heat is used to heat and form the fusion nucleus, which can generally be ignored.

[0069] Step Five: First, calculate the effective heat generated at the weld seam according to Joule's law. The calculation formula is as follows:

[0070]

[0071] In the formula, γ is the effective heat calculation coefficient, h1 and h2 are the thicknesses of the advancing strip and the trailing strip respectively, φ is the influence index of strip thickness on effective heat, C e1 and C e2 are the welding carbon equivalents of the advancing strip and the trailing strip respectively, β is the influence index of strip welding carbon equivalent on effective heat, I is the welding current, R is the total resistance at the weld seam, and V is the welding speed. Preferably, γ = 0.2, 0.25 ≤ φ ≤ 0.35, 0.1 ≤ β ≤ 0.2.

[0072] Then calculate the objective function value. The calculation formula is as follows:

[0073]

[0074] In the formula, G(x) is the objective function value, and Q1 is the effective heat generated at the weld seam.

[0075] Step Six: If the objective function value is less than or equal to the deviation coefficient, go to Step Seven; if the objective function value is greater than the deviation coefficient, the welding ability evaluation result is that it does not meet the welding requirements.

[0076] Step Seven: Check the resistance welding machine and calculate the upper moment, inner bending moment of inertia, outer bending moment of inertia, inner stress, and outer stress of the frame crossbeam, and the influence moment, inner bending moment of inertia, outer bending moment of inertia, inner stress, and outer stress of the frame column. Make a judgment based on the calculation results. If the inner stress and outer stress of the frame crossbeam are both less than or equal to the allowable stress of the frame, and the inner stress and outer stress of the frame column are both less than or equal to the allowable stress of the frame, the welding ability evaluation result is that it meets the welding requirements; if the above conditions are not met, the welding parameters exceed the capacity of the resistance welding machine.

[0077] Specifically, the calculation formula for the upper moment of the frame crossbeam is as follows:

[0078]

[0079] Wherein, M1 is the upper moment of the frame crossbeam, R is the total resistance at the weld, l1 and I1 are respectively the neutral line length and moment of inertia of the frame crossbeam, and l2 and I2 are respectively the neutral line length and moment of inertia of the frame column.

[0080] The calculation formula for the influence moment of the frame column is as follows:

[0081] M2 = Fl1 - M1

[0082] Wherein, M2 is the influence moment of the frame column, and F is the vertical acting force on the frame.

[0083] The calculation formulas for the inner bending resistance section modulus and outer bending resistance section modulus of the frame crossbeam, and the inner bending resistance section modulus and outer bending resistance section modulus of the frame column are as follows:

[0084]

[0085] Wherein, W n1 and W a1 are respectively the inner bending resistance section modulus and outer bending resistance section modulus of the frame crossbeam, W n2 and W a2 are respectively the inner bending resistance section modulus and outer bending resistance section modulus of the frame column, b1 is the cross-section length of the frame crossbeam, g1 is the inner height and outer height of the frame crossbeam, b2 is the cross-section length of the frame column, and g2 is the inner height and outer height of the frame column.

[0086] The calculation formulas for the inner stress and outer stress of the frame crossbeam, and the inner stress and outer stress of the frame column are as follows:

[0087]

[0088] Wherein, σ n1 and σ a1 are respectively the inner stress and outer stress of the frame crossbeam, σ n2 and σ a2 are respectively the inner stress and outer stress of the frame column.

[0089] Example 1

[0090] For ultimate welding, there are two extreme cases. One is the relatively soft and thin strip steel, which is prone to over-welding; the other is the relatively hard and thick strip steel, which is prone to incomplete penetration. Therefore, two extreme specification strip steels are selected: (1) 270JD steel grade strip steel with an ultimate thickness of 0.3 mm and an ultimate width of 1430 mm; (2) 590CQ steel grade strip steel with an ultimate thickness of 1.6 mm and an ultimate width of 1430 mm. Table 1 lists the strip steels of the two extreme specification strip steel grades and the welding process parameters.

[0091] Table 1

[0092]

[0093] For the strip of steel grade 270JD, using the described welding ability evaluation method, the specific method steps and calculation results are as follows:

[0094] Step 1: Collect the equipment parameters of the resistance welding machine, specifically: the thickness b of the upper welding wheel hls = 25 mm, elastic modulus E1 = 2.1×10 5 MPa, Poisson's ratio ν1 = 0.28, radius R hls = 150 mm; the elastic modulus E2 of the forward strip = 2.2×10 5 MPa, Poisson's ratio ν2 = 0.3; the thickness b of the lower welding wheel hlx = 25 mm, elastic modulus E3 = 2.1×10 5 MPa, Poisson's ratio ν3 = 0.28, radius R hlx = 150 mm; the elastic modulus E4 of the backward strip = 2.2×10 5 MPa, Poisson's ratio ν4 = 0.3; the vertical force F on the frame = 50 KN; the neutral line length l1 of the frame crossbeam = 3.2 m, moment of inertia I1 = 8.6×10 -3 m 4 、 cross-sectional length b1 = 5.3 m, the inner height and outer height of the frame crossbeam are equal, i.e., g1 = 0.2 m; the neutral line length l2 of the frame column = 0.8 m, moment of inertia I2 = 3.6×10 -3 m 4 、 cross-sectional length b2 = 5.3 m, the inner height and outer height of the frame column are equal, i.e., g2 = 0.25 m; the allowable stress σ of the frame 许 = 40 - 50 MPa.

[0095] Step 2: Collect the strip and welding process parameters, specifically: the indentation height c of the forward strip s = 0.03 mm, welding carbon equivalent Ce1 = 0.096, thickness h1 = 0.3 mm; the indentation height c of the backward strip x = 0.03 mm, welding carbon equivalent Ce2 = 0.096, thickness h2 = 0.3 mm; the specific heat capacity c of the strip = 0.46×10 3 J / (kg·℃), strip density ρ = 7.85 g / cm 3 , temperature difference ΔT between normal temperature and nugget state of the strip = 1515℃, welding speed V = 14 m / min, overlap amount b djl = 1.2 mm, compensation amount b bcl= 1 mm, the welding wheel pressure P = 6.5 KN, the strip surface temperature T = 25 °C, the welding current I = 10.5 KA, and the deviation coefficient δ = 10%.

[0096] Step three, calculate the nugget height and the total heat required for welding, specifically:

[0097] h = A·[(h1 + h2)-(c s + c x )] = 0.43 mm

[0098] Q 需 = λch(b djl + b bcl )ρΔT = 6.2 J

[0099] Among them, A = 75%, λ = 1.15.

[0100] Step four, calculate the total resistance at the weld, specifically:

[0101] The contact width b dws of the upper welding wheel and the forward strip, and the contact width b dwx of the lower welding wheel and the rear strip are calculated as follows:

[0102]

[0103] The resistance R w1 of the forward strip and the resistance R w2 of the rear strip are calculated as follows:

[0104]

[0105] Among them, ρ0 = 9.78×10 -8 Ωm, α = 6.51×10 -3 , K1 = 0.83, K2 = 0.83, K3 = 0.05, K4 = 1.5.

[0106] The contact resistance R c is calculated as follows:

[0107]

[0108] Among them, m = 1, K c = 0.25.

[0109] Thus, the total resistance R at the weld is calculated as follows:

[0110] R = R w1 + R c + R w2 = 8.25×10 -5 Ω

[0111] Among them, the contact resistance between the forward strip and the electrode and the contact resistance between the backward strip and the electrode are ignored.

[0112] Step 5: Calculate the effective heat generated at the weld and the objective function value, specifically:

[0113] The calculation result of the effective heat Q1 generated at the weld is as follows:

[0114]

[0115] Among them, γ = 0.2, φ = 0.32, β = 0.16.

[0116] The calculation result of the objective function value G(x) is as follows:

[0117]

[0118] Step 6: Compare the objective function value with the deviation coefficient. That is, if the objective function value G(x) = 8% is less than the deviation coefficient δ = 10%, then proceed to Step 7.

[0119] Step 7: Check the resistance welding machine and perform the following calculations, specifically:

[0120] The calculation result of the upper moment M1 of the frame crossbeam is as follows:

[0121]

[0122] The calculation result of the influence moment M2 of the frame column is as follows:

[0123] M2 = Fl1 - M1 = 51.525 KN·m

[0124] The inner bending moment of inertia coefficient W n1 and the outer bending moment of inertia coefficient W a1 of the frame crossbeam, and the inner bending moment of inertia coefficient W n2 and the outer bending moment of inertia coefficient W a2 of the frame column are calculated as follows:

[0125]

[0126] The inner stress σ n1 and the outer stress σ a1 of the frame crossbeam, and the inner stress σ n2 and the outer stress σ a2 of the frame column are calculated according to the following formulas:

[0127]

[0128] n1 ​, the outer stress σ of the frame crossbeam a1 , the inner stress σ of the frame column n2 and the outer stress σ of the frame column a2 are all less than the allowable stress σ of the frame 许 = 40 - 50 MPa, then the welding ability evaluation result is in line with the welding requirements.

[0129] For the strip of 590CQ steel grade, using the said welding ability evaluation method, the specific method steps and calculation results are as follows:

[0130] Step 1, collect the equipment parameters of the resistance welder. The specific equipment parameters, their values are the same as those in Step 1 for the strip of 270JD steel grade.

[0131] Step 2, collect the strip and welding process parameters, specifically: the indentation height c of the forward strip s = 0.16 mm, the welding carbon equivalent Ce1 = 0.387, the thickness h1 = 1.6 mm; the indentation height c of the rear strip x = 0.16 mm, the welding carbon equivalent Ce2 = 0.387, the thickness h2 = 1.6 mm; the specific heat capacity c of the strip = 0.46×10 3 J / (kg·℃), the density ρ of the strip = 7.85 g / cm 3 , the temperature difference ΔT between the normal temperature and the nugget state of the strip = 1515℃, the welding speed V = 8 m / min, the overlap amount b djl = 1 mm, the compensation amount b bcl = 0.8 mm, the wheel pressure P = 17 KN, the surface temperature T of the strip = 25℃, the welding current I = 20.5 KA, the deviation coefficient δ = 10%.

[0132] Step 3, calculate the nugget height and the total heat required for welding, specifically:

[0133] h = A·[(h1 + h2) - (c s + c x )] = 2.2 mm

[0134] Q 需 = λch(b djl + b bcl )ρΔT = 24.6 J

[0135] Among them, A = 70%, λ = 1.1.

[0136] Step 4, calculate the total resistance at the weld, specifically:

[0137] The contact width b dws between the upper welding wheel and the forward strip, and the contact width b dwx between the lower welding wheel and the rear strip are calculated as follows:

[0138]

[0139] The resistance R of the forward strip steel w1 and the resistance R of the rear strip steel w2 are calculated as follows:

[0140]

[0141] Among them, ρ0 = 9.78×10 -8 Ωm, α = 6.51×10 -3 , K1 = 0.82, K2 = 0.85, K3 = 0.05, K4 = 1.5.

[0142] The contact resistance R c is calculated as follows:

[0143]

[0144] Among them, m = 1, K c = 0.25.

[0145] Thus, the calculation result of the total resistance R at the weld is as follows:

[0146] R = R w1 + R c + R w2 = 6.74×10 -5 Ω

[0147] Among them, the contact resistance between the forward strip steel and the electrode and the contact resistance between the rear strip steel and the electrode are ignored.

[0148] Step Five, calculate the effective heat generated at the weld and the objective function value, specifically:

[0149] The calculation result of the effective heat Q1 generated at the weld is as follows:

[0150]

[0151] Among them, γ = 0.2, φ = 0.31, β = 0.15.

[0152] The calculation result of the objective function value G(x) is as follows:

[0153]

[0154] Step Six, compare the objective function value with the deviation coefficient, that is, if the objective function value G(x) = 1% is less than the deviation coefficient δ = 10%, then proceed to Step Seven.

[0155] Step 7: Check and calculate the resistance welding machine. The specific calculation steps and results are the same as those in Step 7 for the strip steel of 270JD steel grade. Thus, the inner stress of the frame crossbeam, the outer stress of the frame crossbeam, the inner stress of the frame column, and the outer stress of the frame column are all less than the allowable stress of the frame, and the welding ability evaluation result is obtained as meeting the welding requirements.

[0156] The welding ability evaluation method of the narrow lap resistance welding machine of the present invention can effectively evaluate the ultimate strength, width, and thickness of the resistance welding machine. According to the on-site application situation, the provided welding ability evaluation result is practical and feasible, and can be further promoted to other similar continuous annealing units in China, with a relatively broad promotion and application prospect.

[0157] The above are only the preferred embodiments of the present invention and are not used to limit the protection scope of the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for evaluating the welding ability of a narrow lap resistance welder, the resistance welder comprising an upper welding wheel, a lower welding wheel and a frame; characterized in that: The evaluation method includes the following steps: Step 1: Collect the equipment parameters of the resistance welder. The equipment parameters include the thickness, elastic modulus, Poisson's ratio, and radius of the upper welding wheel, the elastic modulus and Poisson's ratio of the forward strip steel, the thickness, elastic modulus, Poisson's ratio, and radius of the lower welding wheel, the elastic modulus and Poisson's ratio of the backward strip steel, the vertical force applied to the frame, the neutral line length, moment of inertia, cross-sectional length, inner height, and outer height of the frame crossbeam, the neutral line length, moment of inertia, cross-sectional length, inner height, and outer height of the frame column, and the allowable stress of the frame. Step 2: Collect the strip steel and welding process parameters. The strip steel and welding process parameters include the indentation height, welding carbon equivalent, and thickness of the forward strip steel, the indentation height, welding carbon equivalent, and thickness of the backward strip steel, the specific heat capacity of the strip steel, the density of the strip steel, the temperature difference between the normal temperature and the nugget state of the strip steel, the welding speed, the overlap amount, the compensation amount, the welding wheel pressure, the surface temperature of the strip steel, the welding current, and the deviation coefficient. Step 3: Calculate the nugget height and the total heat required for welding. The calculation formula is as follows: h = A·[(h1 + h2)-(c s + c x )] Q 需 = λch(b djl + b bcl )ρΔT Wherein, h is the nugget height, A is the penetration rate, h1 and h2 are the thicknesses of the forward strip and the backward strip respectively, c s and c x are the indentation heights of the forward strip and the backward strip respectively, Q 需 is the total heat required for welding, λ is the nugget melting coefficient, c is the specific heat capacity of the strip, b djl is the overlap amount, b bcl is the compensation amount, ρ is the density of the strip, and ΔT is the temperature difference between the normal temperature of the strip and the temperature of the nugget state; Step 4: Calculate the total resistance at the weld. First, calculate the contact width between the upper welding wheel and the forward strip steel and the contact width between the lower welding wheel and the backward strip steel according to Hertz's formula. Then, combine the influence of the edge effect and the flow-around phenomenon on the resistance and calculate the resistance of the forward strip steel and the backward strip steel according to Matthiessen's law. Then, obtain the total resistance at the weld from the sum of the resistance of the forward strip steel, the resistance of the backward strip steel, and the contact resistance. Step 5: Calculate the effective heat generated at the weld according to Joule's law and calculate the objective function value. The calculation formula is as follows: In the formula, G(x) is the objective function value, and Q1 is the effective heat generated at the weld. Step 6: If the objective function value is less than or equal to the deviation coefficient, go to Step 7; If the objective function value is greater than the deviation coefficient, the welding ability evaluation result is that it does not meet the welding requirements; Step 7: First, check the resistance welder and calculate the upper moment, inner bending section modulus, outer bending section modulus, inner stress, and outer stress of the frame crossbeam, and the influence moment, inner bending section modulus, outer bending section modulus, inner stress, and outer stress of the frame column. Then, judge the calculation results. If the inner stress and outer stress of the frame crossbeam and the inner stress and outer stress of the frame column are all less than or equal to the allowable stress of the frame, the welding ability evaluation result is that it meets the welding requirements. If the above conditions are not met, the welding parameters exceed the capacity of the resistance welder.

2. The method for evaluating the welding ability of a narrow lap resistance welder according to claim 1, wherein: In Step 3, 60% ≤ A ≤ 80%, 0.9 ≤ λ ≤ 1.

2.

3. The welding ability evaluation method of the narrow lap resistance welder according to claim 1, wherein: In Step 4, the calculation formulas for the contact width between the upper welding wheel and the forward strip steel and the contact width between the lower welding wheel and the backward strip steel are as follows: where b dws is the contact width between the upper welding wheel and the forward strip steel, b dwx is the contact width between the lower welding wheel and the rear strip steel, P is the welding wheel pressure, b hls and R hls are the thickness and radius of the upper welding wheel respectively, b hlx and R hlx are the thickness and radius of the lower welding wheel respectively, E1 and v1 are the elastic modulus and Poisson's ratio of the upper welding wheel respectively, E2 and v2 are the elastic modulus and Poisson's ratio of the forward strip steel respectively, E3 and v3 are the elastic modulus and Poisson's ratio of the lower welding wheel respectively, and E4 and v4 are the elastic modulus and Poisson's ratio of the rear strip steel respectively.

4. The welding ability evaluation method of the narrow lap resistance welding machine according to claim 1, characterized in that: In Step 4, the calculation formulas for the resistance of the forward strip steel and the resistance of the backward strip steel are as follows: Wherein, R w1 is the resistance of the forward strip steel, R w2 is the resistance of the rear strip steel, K1 is the coefficient of current field diffusion caused by the edge effect, K2 is the coefficient of current field diffusion caused by the flow-around phenomenon, K3 is the influence index of carbon equivalent on resistance, K4 is the coefficient of the molten width of the nugget, C e1 and C e2 are the welding carbon equivalents of the forward strip steel and the rear strip steel respectively, b dws is the contact width between the upper welding wheel and the forward strip steel, b dwx is the contact width between the lower welding wheel and the rear strip steel, ρ0 is the resistivity of the strip steel at 0 °C, α is the temperature coefficient of resistance of the strip steel resistivity varying with temperature, and T is the surface temperature of the strip steel.

5. The welding ability evaluation method of the narrow lap resistance welder according to claim 4, characterized in that: where ρ0 = 9.78×10 -8 Ωm, α = 6.51×10 -3 , 0.80 ≤ K1 ≤ 0.85, 0.8 ≤ K2 ≤ 0.9, 0.02 ≤ K3 ≤ 0.08, 1.0 ≤ K4 ≤ 2.

0.

6. The method for evaluating the welding ability of a narrow lap resistance welder according to claim 1, characterized in that: In Step 4, the calculation formula for the contact resistance is as follows: where R c is the contact resistance, K c is the first coefficient related to the contact material, surface condition, and contact form, P is the wheel pressure, and m is the second coefficient related to the contact form.

7. The method for evaluating the welding ability of a narrow lap resistance welding machine according to claim 6, characterized in that: where m = 1, 0.1 ≤ K c ≤ 0.

4.

8. The method for evaluating the welding ability of a narrow lap resistance welder according to claim 1, characterized in that: In Step 5, the calculation formula for the effective heat is as follows: In the formula, γ is the effective heat calculation coefficient, h1 and h2 are the thicknesses of the front and rear strip steels respectively, φ is the influence index of strip steel thickness on the effective heat, C e1 and C e2 are the welding carbon equivalents of the front and rear strip steels respectively, β is the influence index of strip steel welding carbon equivalent on the effective heat, I is the welding current, R is the total resistance at the weld, and V is the welding speed.

9. The method for evaluating the welding ability of a narrow lap resistance welder according to claim 8, wherein: γ = 0.2, 0.25 ≤ φ ≤ 0.35, 0.1 ≤ β ≤ 0.

2.

10. The method for evaluating the welding ability of a narrow lap resistance welding machine according to claim 1, characterized in that: In Step 7, the calculation formula for the upper moment of the frame crossbeam is as follows: Wherein, M1 is the upper moment of the frame crossbeam, R is the total resistance at the weld, l1 and I1 are respectively the neutral line length and moment of inertia of the frame crossbeam, and l2 and I2 are respectively the neutral line length and moment of inertia of the frame column; The calculation formula for the influence moment of the frame column is as follows: M2 = Fl1 - M1 Wherein, M2 is the influence moment of the frame column, and F is the vertical force applied to the frame; The calculation formulas for the inner bending resistance section modulus and outer bending resistance section modulus of the frame crossbeam, and the inner bending resistance section modulus and outer bending resistance section modulus of the frame column are as follows: Wherein, W n1 and W a1 are respectively the inner bending resistance section modulus and the outer bending resistance section modulus of the frame cross beam, W n2 and W a2 are respectively the inner bending resistance section modulus and the outer bending resistance section modulus of the frame column, b1 is the cross-sectional length of the frame cross beam, g1 is the inner height and the outer height of the frame cross beam, b2 is the cross-sectional length of the frame column, and g2 is the inner height and the outer height of the frame column; The calculation formulas for the inner stress and outer stress of the frame crossbeam, and the inner stress and outer stress of the frame column are as follows: Where, σ n1 and σ a1 are the inner stress and outer stress of the frame crossbeam respectively, and σ n2 and σ a2 are the inner stress and outer stress of the frame column respectively.

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