Screening method for heavy metal elements in automotive brake lining

Abstract

The invention relates to a method for screening heavy metal elements in automobile brake linings, which comprises the following steps: S1, selecting a base material matched with a to-be-detected sample matrix, and preparing a standard powder tabletting group by adding heavy metal compounds in a gradient manner; s2, detecting the standard tablet by using an X-ray fluorescence spectrum, synchronously verifying by adopting ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry), and establishing an XRF standard curve for matrix effect correction; s3, preparing a to-be-detected lining into a powder tablet matched with a base material, and realizing quantitative screening of heavy metals through XRF detection and standard curve comparison; wherein the base material is selected from a ceramic type or semi-metal type brake pad base material, and the deviation between the component content of the base material and the to-be-detected sample is less than or equal to 5wt%. The invention provides a heavy metal screening method with rapidness, accuracy and economical efficiency, provides a reliable online quality control means for the automobile brake lining, and reduces the risk of heavy metal pollution.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal detection, and in particular to a method for screening heavy metal elements in automobile brake linings. Background Art

[0002] The automobile braking system is a key component to ensure the safe driving of the vehicle, and the performance of the brake lining, as an important part of the braking system, directly affects the braking effect and driving safety of the car. With the development of the automobile industry, the performance requirements for brake linings are increasing, especially in the production materials of brake linings, there may be some harmful substances, such as asbestos, lead, hexavalent chromium, cadmium, mercury, arsenic, copper, antimony and flame retardants, etc. These substances will not only pollute the environment, but also may cause potential harm to human health during the use, wear and even disposal of brake linings. The problem of harmful substances in brake linings cannot be ignored, and it is necessary to strictly screen the heavy metal elements in brake linings.

[0003] In the prior art, inductively coupled plasma emission spectrometry (ICP-AES) is often used to detect heavy metal elements in brake linings. Among them, the linear range of the ICP-AES method is wide, and it can adapt to the detection of heavy metal elements at different levels, so that this method has a wider range of applications when detecting harmful elements in automobile brake linings. The ICP-AES method can simultaneously determine multiple elements, which improves the detection efficiency. However, the ICP-AES method requires a complex pre-treatment process for the sample, including digestion, dilution and other steps, which not only increases the detection time and cost, but also may introduce errors. In addition, during the digestion process, if the operation is improper, it may cause the loss or contamination of some elements. The price of ICP-AES instruments is relatively high, and the maintenance cost is also high.

[0004] Conventional X-ray fluorescence spectroscopy (XRF) technology is fast and non-destructive, but it is significantly affected by matrix effects, especially in complex matrices with multiple components and high heterogeneity such as brake pads, where direct detection errors are large. In existing technologies, the base materials of standard samples and samples to be tested are not well matched, resulting in poor applicability of calibration curves, which are difficult to meet actual screening needs.

[0005] Therefore, it is necessary to develop a heavy metal screening method that takes into account rapidity, accuracy and economy, especially to solve the problem of matrix effect interference and achieve high-throughput detection. Summary of the invention

[0006] In the prior art, the substrate matching between the standard sample and the sample to be measured in the conventional X-ray fluorescence spectroscopy technology is insufficient, resulting in poor applicability of the calibration curve and difficulty in meeting the actual screening requirements. Therefore, the present invention provides a screening method for heavy metal elements in automotive brake linings to solve the above problems.

[0007] In a first aspect, the present invention provides a screening method for heavy metal elements in automotive brake linings, which includes the following steps: S1. Select a substrate that matches the matrix of the sample to be measured, and prepare a standard powder tablet group by adding heavy metal compounds in gradients. S2. Use X-ray fluorescence spectroscopy to detect the standard tablets, and simultaneously use ICP-AES for verification to establish an XRF standard curve corrected for matrix effects. S3. Make the sample brake lining to be measured into a powder tablet that matches the substrate, and achieve quantitative screening of heavy metals through XRF detection and comparison with the standard curve. Among them, the substrate is selected from ceramic-type or semi-metallic brake pad substrates, and the component content deviation from the sample to be measured is ≤5 wt%.

[0008] In one implementation, in S11, the specific steps include: S11. Select a ceramic-type brake pad substrate or a semi-metallic brake pad substrate, and grind it into fine powder to obtain substrate powder. S12. Conduct element screening on the substrate, and add compounds corresponding to heavy metal elements with known concentrations to the substrate powder to prepare a primary masterbatch. S13. Dilute the primary masterbatch to prepare a secondary masterbatch. S14. Accurately weigh the substrate powder and the secondary masterbatch according to the formula ratio and mix them evenly. S15. Put the mixed powder into a mold and press it into a sheet sample under high pressure. S16. Dry the pressed sample to obtain powder tablets with different heavy metal concentration gradients.

[0009] In one implementation, in S11, the ceramic-type brake pad substrate includes the following materials in parts by weight: 24 parts of K-160, 8 parts of phenolic resin, 3 parts of flake graphite, 3 parts of friction powder, 8 parts of artificial graphite, 5 parts of petroleum coke, 6 parts of spinel, 10 parts of high-titanium powder, 5 parts of rubber powder, 8 parts of calcium sulfate whiskers, and 10 parts of ceramic fiber + barium sulfate (1:1).

[0010] In one implementation, in S11, the semi-metallic brake pad substrate comprises the following materials in parts by weight: 30 parts of steel fiber, 10 parts of PF211 resin, 2 parts of rek-160 fiber, 6 parts of calcium sulfate whisker, 6 parts of cryolite, 10 parts of ceramic fiber + barium sulfate (1:1), 4 parts of flake graphite, 6 parts of rubber powder, 3 parts of friction powder, 8 parts of high-titanium powder, and 5 parts of petroleum coke.

[0011] In one implementation, in S12, the heavy metal elements include lead, chromium, mercury, and cadmium. The preparation of the primary masterbatch includes: mixing a compound containing the target heavy metal element with barium sulfate in proportion to form a high-concentration heavy metal element mixture; wherein, the compound includes: lead sulfate, mercury sulfide, chromite, and cadmium sulfide.

[0012] In one implementation, in S13, the secondary masterbatch is the primary masterbatch diluted 10 times.

[0013] In one implementation, in S14, it specifically includes: preparing mixed powders according to gradients 1-5 respectively, wherein the addition amount of the secondary masterbatch is 0.05-1.00 g / 10 g of substrate powder, and the heavy metal concentration ranges corresponding to the gradients are 50-1000 mg / kg for lead, 50-1000 mg / kg for chromium, 50-1000 mg / kg for mercury, and 10-100 mg / kg for cadmium.

[0014] In one implementation, in S15, boric acid powder is used as an auxiliary material for tableting. The tableting equipment and accessories include a 40-ton tablet press, a boric acid-edged sample pressing die, and a tungsten carbide gasket; the specific steps of tableting include: using a 40-ton tablet press to press the mixed powder into a sheet sample, the pressure during the pressing process is 30 tons, and the pressure holding time is 30 seconds.

[0015] In one implementation, in S16, it specifically includes: drying the pressed sample at a temperature between 50°C and 150°C, and the drying time is 1 hour to 5 hours.

[0016] In one implementation, in S12, after obtaining the XRF characteristic signal intensities of the heavy metal elements, it is also necessary to combine the quantitative values of the heavy metal elements determined by inductively coupled plasma emission spectrometry to establish an XRF detection standard curve.

[0017] Beneficial effects: In the present invention, by selecting a substrate that highly matches the matrix of the sample to be measured, combining with the gradient addition of heavy metal compounds and verifying the preparation of the XRF standard curve by ICP-AES, the matrix interference in XRF detection is significantly reduced, and the accuracy of the standard curve is improved; and through XRF detection and the standard curve, non-destructive and rapid screening is achieved, providing a heavy metal screening method that takes into account rapidity, accuracy and economy, providing a reliable means for on-line quality control of automotive brake linings, and reducing the risk of heavy metal pollution. Description of the Drawings

[0018] Figure 1 is the flowchart of the steps of the screening method for heavy metal elements in the automotive brake lining provided by the present invention; Figure 2 is Figure 1 the specific flowchart of S1 in Figure 3 is Figure 2 the back view of the powder compact of the automotive brake lining prepared in Figure 4 is Figure 3 the finished product view of the powder compact of the automotive brake lining shown in

[0019] The realization, functional features and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the drawings. Detailed Embodiments

[0020] In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0021] Referring to Figure 1 and Figure 2 , Figure 1 is the flowchart of the steps of the screening method for heavy metal elements in the automotive brake lining provided by the present invention, Figure 2 is Figure 1 the specific flowchart of S1 in

[0022] The present invention provides a screening method for heavy metal elements in automotive brake linings, which includes the following steps: S1. Select a substrate that matches the matrix of the sample to be tested, and prepare a set of standard powder compacts by adding heavy metal compounds in gradients. S2. Use X-ray fluorescence spectroscopy to detect the standard compacts, and simultaneously verify them by ICP-AES to establish an XRF standard curve for matrix effect correction. S3. Make the substrate to be tested into a powder compact that matches the substrate, and achieve quantitative screening of heavy metals through XRF detection and comparison with the standard curve. Wherein, the substrate is selected from ceramic-type or semi-metal-type brake pad substrates, and the component content deviation from the sample to be tested is ≤ 5 wt%.

[0023] Specifically, in S11, the specific steps include: S11. Select a ceramic-type brake pad substrate or a semi-metal-type brake pad substrate, and grind it into fine powder to obtain substrate powder. S12. Conduct elemental screening on the substrate, and add compounds corresponding to heavy metal elements with known concentrations to the substrate powder to prepare a primary masterbatch. S13. Dilute the primary masterbatch to prepare a secondary masterbatch. S14. Accurately weigh the substrate powder and the secondary masterbatch according to the formula ratio and mix them evenly. S15. Put the mixed powder into a mold and press it into a sheet sample under high pressure. S16. Dry the pressed sample to obtain powder compacts with different heavy metal concentration gradients.

[0024] Specifically, in S11, the ceramic-type brake pad substrate includes the following materials in parts by weight: 24 parts of K-160, 8 parts of phenolic resin, 3 parts of flake graphite, 3 parts of friction powder, 8 parts of artificial graphite, 5 parts of petroleum coke, 6 parts of spinel, 10 parts of high-titanium powder, 5 parts of rubber powder, 8 parts of calcium sulfate whiskers, and 10 parts of ceramic fiber + barium sulfate (1:1). In S11, the semi-metal-type brake pad substrate includes the following materials in parts by weight: 30 parts of steel fiber, 10 parts of PF211 resin, 2 parts of rek-160 fiber, 6 parts of calcium sulfate whiskers, 6 parts of cryolite, 10 parts of ceramic fiber + barium sulfate (1:1), 4 parts of flake graphite, 6 parts of rubber powder, 3 parts of friction powder, 8 parts of high-titanium powder, and 5 parts of petroleum coke.

[0025] The present invention covers the two main types of brake pad substrates in the market by selecting ceramic and semi-metallic substrates. The ceramic substrate is composed of materials such as K-160, phenolic resin, and flake graphite, and the semi-metallic substrate is composed of materials such as steel fibers, PF211 resin, and rek-160 fibers, ensuring excellent performance of the brake lining. In particular, the substrate is pre-screened and selected by XRF full-spectrum analysis to select a substrate formula with a matching degree of more than 95% with the elemental composition of the sample to be tested. Specifically, the elements in the substrate need to be screened one by one with XRF, the components with a proportion of more than 1% in the substrate are listed and recorded, and the detection of target heavy metal elements (including lead, chromium, cadmium, mercury, copper, and antimony, etc.) is concerned. At the same time, the substrate is digested one by one, and the content of target elements such as chromium, cadmium, and mercury in it is detected by ICP-OES and recorded and analyzed. By screening the elements of the substrate, adding heavy metal elements with known concentrations, preparing primary masterbatch, and diluting to prepare secondary masterbatch, the content of heavy metal elements can be accurately controlled to ensure the safety and environmental protection of the product.

[0026] Specifically, in S12, the heavy metal elements include lead, chromium, mercury, and cadmium, and the preparation of the primary masterbatch includes: mixing a compound containing the target heavy metal element with barium sulfate in proportion to form a high-concentration heavy metal element mixture; wherein, the compound includes: lead sulfate, mercury sulfide, chromite, and cadmium sulfide. These compounds have low solubility in water and are relatively stable, and can form solid precipitates, thereby reducing the dissolution and release of ions, reducing toxicity and environmental risks, and relatively ensuring the health and safety of operators.

[0027] Specifically, in S13, the secondary masterbatch is the primary masterbatch diluted 10 times.

[0028] Specifically, in S14, the mixing and homogenization treatment includes: weighing the substrate powder and the secondary masterbatch according to the formula ratio, and performing manual mixing and mechanical ball milling treatment to ensure the uniformity of the mixture. Using manual mixing and mechanical ball milling treatment can ensure the uniform distribution of the powder, improve the uniformity and stability of the brake lining, and avoid the problem of inconsistent performance. Further, the mixed powder is prepared according to gradients 1-5 respectively, wherein the addition amount of the secondary masterbatch is 0.05-1.00 g / 10 g of substrate powder, and the corresponding heavy metal concentration ranges for the gradients are 50-1000 mg / kg for lead, 50-1000 mg / kg for chromium, 50-1000 mg / kg for mercury, and 10-100 mg / kg for cadmium.

[0029] Specifically, in S15, the tableting uses boric acid powder as an auxiliary material, and the tableting equipment and accessories include a 40-ton tablet press, a boric acid rimmed sample pressing mold, and a tungsten carbide gasket; the specific steps of the tableting include: using a 40-ton tablet press to press the mixed powder into a sheet sample, the pressure of the pressing process is 30 tons, and the pressure is maintained for 30 seconds. Using boric acid powder as an auxiliary material in the tableting process reduces the emission of harmful substances, meets the requirements of environmental protection regulations, and protects the health of operators.

[0030] Specifically, in S6, the drying and stabilization step includes: drying the pressed sample at a temperature between 50°C and 150°C for 1 hour to 5 hours.

[0031] Example 1 S11. Selection of substrate and powder preparation: A ceramic brake pad substrate or a semi-metal brake pad substrate having the formula in Table 1 or Table 2 is selected and ground into fine powder to obtain substrate powder.

[0032] Table 1. Ceramic brake pad base material formula Table 2. Semi-metallic brake pad base material formula S12. Screening of heavy metal elements and preparation of primary masterbatch: Screen the elements of the substrate and add heavy metal elements of known concentration to prepare the primary masterbatch. The masterbatch raw materials include lead sulfate (PbSO4, Pb 68.3%), mercury sulfide (HgS, Hg86.2%), chromite (Cr 23%), cadmium sulfide (CdS, Cd 77.8%), wherein the masterbatch concentrations are: lead masterbatch (0.1% Pb), mercury masterbatch (0.1% Hg), chromium masterbatch (0.1% Cr), cadmium masterbatch (0.01% Cd). Among them: Lead masterbatch (10% Pb): weigh 1.465g lead sulfate and 8.535g barium sulfate, mix and grind until uniform; Mercury masterbatch (10% Hg): weigh 1.16g mercuric sulfide and 8.84g barium sulfate, mix and grind in a closed fume hood; Chromium masterbatch (10% Cr): weigh 4.348g chromite and 5.652g barium sulfate, grind to a particle size of ≤50 μm; Cadmium masterbatch (1% Cd): weigh 0.129g cadmium sulfide and 9.871g barium sulfate, store separately and mark as "highly toxic".

[0033] It should be noted that the handling of mercury and cadmium masterbatches must be carried out in a negative pressure fume hood.

[0034] S13. Preparation of secondary masterbatch: Dilute the above-mentioned four masterbatches of lead, mercury, chromium, and cadmium that have been mixed evenly by 10 times to prepare a secondary masterbatch for the preparation of later gradient positive specimens, improving the uniformity after mixing. Take 1 g each of the 10% masterbatches of lead, chromium, and mercury, and mix them evenly with 7 g of barium sulfate powder to prepare a secondary mixed masterbatch with a concentration of 1%. Take 1 g of the cadmium masterbatch with a content of 1% and mix it evenly with 9 g of barium sulfate powder to prepare a secondary cadmium masterbatch with a concentration of 0.1%.

[0035] S14. Mixing and homogenization treatment: Accurately weigh the substrate powder and the secondary masterbatch according to the formula ratio and mix them evenly. The number of parts in the substrate formula corresponds to the specifically set number of grams. Generally, at least one part corresponds to 1 g. If the sample weighing amount is too small, it is easy to increase the error and the sample uniformity becomes worse. Weigh the substrate according to the number of parts and pour it into a plastic jar with a lid. After all weighing is completed, tighten the bottle cap and shake it manually repeatedly for primary mixing.

[0036] Select 5 gradients for each positive sample tablet pressing and weigh according to the ratio in Table 3.

[0037] Table 3. Positive tablet pressing formula table (10 g per gradient) Table 4. Heavy metal concentration calculation results Put the mixed sample into a ball mill for secondary mixing. The ball mill grinds at 750 r / min for 3 min to avoid the volatilization of mercury additives caused by overheating.

[0038] S15. Tablet pressing: Put the mixed powder into a mold and press it into a sheet sample through high pressure. The auxiliary material required for tablet pressing is boric acid powder, and the tablet pressing equipment and accessories are a 40-ton tablet press, a boric acid-lined sample pressing mold, and a tungsten carbide gasket. Weigh 2.0 g of the sample powder and use the boric acid-lined tablet pressing method to make gradient specimens with a pressure of 30 tons and a pressure retention time of 30 s. Pay attention to wiping the gasket and the mold clean with anhydrous ethanol each time the sample is changed. Press 3 tablets for each sample, which can be used for parallelism inspection.

[0039] S16. Drying and stabilization treatment: Conduct drying treatment on the pressed sample to stabilize the physical properties of the sample, obtaining the required powder tablet of automotive brake lining. Specifically, dry the pressed sample at 100 °C for 3 hours.

[0040] Refer to Figure 3 and Figure 4 , Figure 3 is Figure 2 the back view of the powder tablet of automotive brake lining prepared in Figure 4 is Figure 3Finished product drawing of the powder tablet of the automotive brake lining shown. In this embodiment, one set of powder tablets of ceramic type (t series) and semi-metallic type (j series) brake linings are prepared by tableting. Each set contains five concentration gradients, which are represented by t1, t2, t3, t4, t5 and j1, j2, j3, j4, j5 respectively.

[0041] In S2, after obtaining the XRF characteristic signal intensities of each heavy metal element, it is also necessary to combine the quantitative values of the heavy metal elements measured by inductively coupled plasma optical emission spectrometry (ICP-OES) to establish an XRF detection standard curve. Specifically, in the present invention, after obtaining the powder tablets of the automotive brake lining, they are used as standard samples to establish the standard curve of XRF and quantitatively analyze the heavy metal elements in the brake. Among them, the powder tablets of the automotive brake lining are detected by XRF respectively, and the powder tablets of the automotive brake lining are tested by ICP-OES. The uniformity of the content of the target heavy metal elements between parallel samples is compared. The difference between the test results is not higher than 5%, indicating that the uniformity is good. The average value of not less than 5 ICP test results is taken as the fixed value of the sample piece. Using the count value of the XRF test result as the ordinate and the fixed value of the ICP test result as the abscissa, a gradient curve is made and the curve correlation is checked.

[0042] In the present invention, the powder tablets of the automotive brake lining obtained are used to establish the standard curve of XRF. The concentrations include lead, chromium, and mercury gradients of 50-1000 mg / kg, and a cadmium gradient of 10-100 mg / kg; the amount of masterbatch used is 0.05-1.00 g / 10 g of sample, and the operation is simple and the error is controllable. In the present invention, the risk of direct contact with toxic substances is reduced by designing a low-concentration masterbatch. The method of the present invention can prepare standard sample pieces with different concentration gradients for XRF (X-ray fluorescence spectrometry) detection, help establish an accurate detection standard curve, and improve the accuracy and reliability of detection.

[0043] Generally speaking, the screening method for heavy metal elements in automotive brake linings provided by the present invention significantly reduces the matrix interference in XRF detection and improves the accuracy of the standard curve by preparing standard tablets (ceramic type / semi-metal type) that highly match the matrix of the sample to be tested (component deviation ≤ 5 wt%), combined with gradient addition of heavy metal compounds and ICP-AES verification. The heavy metal quantification error can be controlled within 5%. By using XRF technology for non-destructive and rapid screening and combining with an optimized powder tablet preparation process, the pretreatment steps are simplified, which is applicable to batch sample detection, and the cost is reduced by more than 60% compared with the traditional wet chemical method. Through the gradient dilution of the primary masterbatch and the design of the secondary masterbatch mixing, the low concentration (ppm level) to high concentration detection range of heavy metal elements (such as Pb, Cr, Hg, Cd, etc.) is covered, and the detection limit is as low as 10 ppm, meeting the detection requirements. For the typical formulations of ceramic type and semi-metal type brake pads, through accurate reproduction of the base material composition and tablet pressing process, the physical properties of the tablets are ensured to be consistent with those of the real samples, avoiding signal deviation caused by density differences. The present invention realizes non-destructive and rapid screening through XRF detection and standard curves, provides a heavy metal screening method that takes into account rapidity, accuracy and economy, provides a reliable means for on-line quality control of automotive brake linings, and reduces the risk of heavy metal pollution.

[0044] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A screening method for heavy metal elements in automotive brake linings, characterized in that, It includes the following steps: S1. Select a substrate that matches the matrix of the sample to be tested, and prepare a standard powder tablet group by adding heavy metal compounds in gradients. S2. Use X-ray fluorescence spectroscopy to detect the standard tablets, and simultaneously verify them by ICP-AES to establish an XRF standard curve for matrix effect correction. S3. Make the powder tablets of the substrate to be tested into tablets that match the substrate, and achieve quantitative screening of heavy metals through XRF detection and comparison with the standard curve. Among them, the substrate is selected from ceramic-type or semi-metal-type brake pad substrates, and the component content deviation from the sample to be tested is ≤5wt%.

2. The screening method for heavy metal elements in the automotive brake lining according to claim 1, characterized in that, In S11, the specific steps include: S11. Select a ceramic-type brake pad substrate or a semi-metal-type brake pad substrate, and grind it into fine powder to obtain substrate powder. S12. Conduct an elemental screening of the substrate, and add compounds corresponding to heavy metal elements with known concentrations to the substrate powder to prepare a primary masterbatch. S13. Dilute the primary masterbatch to prepare a secondary masterbatch. S14. Accurately weigh the substrate powder and the secondary masterbatch according to the formula ratio and mix them evenly. S15. Put the mixed powder into a mold and press it into a sheet sample under high pressure. S16. Dry the pressed sample to obtain powder tablets with different heavy metal concentration gradients.

3. The screening method for heavy metal elements in automotive brake linings according to claim 1, wherein, In S11, the ceramic-type brake pad substrate includes the following materials in parts by weight: 24 parts of K-160, 8 parts of phenolic resin, 3 parts of flake graphite, 3 parts of friction powder, 8 parts of artificial graphite, 5 parts of petroleum coke, 6 parts of spinel, 10 parts of high-titanium powder, 5 parts of rubber powder, 8 parts of calcium sulfate whiskers, and 10 parts of ceramic fiber + barium sulfate (1:1).

4. The screening method for heavy metal elements in the automotive brake lining according to claim 1, characterized in that, In S11, the semi-metal-type brake pad substrate includes the following materials in parts by weight: 30 parts of steel fiber, 10 parts of PF211 resin, 2 parts of rek-160 fiber, 6 parts of calcium sulfate whiskers, 6 parts of cryolite, 10 parts of ceramic fiber + barium sulfate (1:1), 4 parts of flake graphite, 6 parts of rubber powder, 3 parts of friction powder, 8 parts of high-titanium powder, and 5 parts of petroleum coke.

5. The screening method for heavy metal elements in automotive brake linings according to claim 1, characterized in that In S12, the heavy metal elements include lead, chromium, mercury, and cadmium. The preparation of the primary masterbatch includes: mixing the compound containing the target heavy metal element with barium sulfate in proportion to form a high-concentration heavy metal element mixture; among them, the compounds include: lead sulfate, mercury sulfide, chromite, and cadmium sulfide.

6. The screening method for heavy metal elements in automotive brake linings according to claim 1, characterized in that, In S13, the secondary masterbatch is a primary masterbatch diluted 10 times.

7. The screening method for heavy metal elements in the automotive brake lining according to claim 1, characterized in that, In S14, it specifically includes: preparing the mixed powder according to gradients 1-5 respectively, wherein the addition amount of the secondary masterbatch is 0.05-1.00 g / 10 g of substrate powder, and the heavy metal concentration ranges corresponding to the gradients are 50-1000 mg / kg for lead, 50-1000 mg / kg for chromium, 50-1000 mg / kg for mercury, and 10-100 mg / kg for cadmium.

8. The screening method for heavy metal elements in automotive brake linings according to claim 1, characterized in that, In S15, the tablet pressing uses boric acid powder as an auxiliary material, and the tablet pressing equipment and accessories include a 40-ton tablet press, a boric acid-rimmed sample pressing mold and a tungsten carbide gasket; the specific steps of the tablet pressing include: using a 40-ton tablet press to press the mixed powder into a sheet sample, the pressure of the pressing process is 30 tons, and the pressure is maintained for 30 seconds.

9. The screening method for heavy metal elements in the automotive brake lining according to claim 1, wherein In S16, specifically including: drying the pressed sample at a temperature between 50°C and 150°C, and the drying time is 1 hour to 5 hours.

10. The screening method for heavy metal elements in automotive brake linings according to claim 1, characterized in that In S12, after the XRF characteristic signal intensity of each heavy metal element is obtained, it is also necessary to combine the quantitative value of the heavy metal element determined by inductively coupled plasma emission spectroscopy to establish an XRF detection standard curve.

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