A method and device for detecting the internal stress of a polycarbonate plastic product

Abstract

This invention discloses a method for detecting the internal stress of polycarbonate plastic products, comprising the following steps: S1. Preparing IS reagent; S2. Preparing N standard polycarbonate samples A; S3. Sorting all standard polycarbonate samples A and setting a test deflection γ for each; S4. Measuring the internal stress σ of each standard polycarbonate sample A at the test deflection γ. 内 And the cracking time T, and the internal stress-cracking time standard curve I was obtained by fitting; S5. The cracking time T of the polycarbonate part B to be tested was measured. B S6. Determine the cracking time T of the polycarbonate part B to be tested on the internal stress-cracking time standard curve I. B The corresponding internal stress value is denoted as σ. 内B Then the internal stress of the polycarbonate part B to be tested is σ. 内B The method for detecting internal stress in polycarbonate plastic products based on the external standard method provided by this invention is a standard working curve method, which provides a new method for quantitative detection of internal stress.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of internal stress detection, and particularly relates to a polycarbonate plastic product internal stress detection method and device based on an external standard method. BACKGROUND

[0002] Polycarbonate is a kind of polymer containing carbonate groups in the molecular chain, and can be divided into aliphatic, aromatic, aliphatic-aromatic and other types according to the structure of the ester group. Among them, the mechanical properties of aliphatic and aliphatic-aromatic polycarbonates are relatively low, which limits their application in the field of engineering plastics. Aromatic polycarbonate is a very important engineering plastic with excellent comprehensive performance, and is widely used in various aspects of life. In the automotive industry, it almost monopolizes the application of automobile headlamps due to its high heat resistance and high opticality. Among them, bisphenol A polycarbonate is a commonly used aromatic polycarbonate and is the most widely used one, which can be synthesized by direct phosgene method and ester exchange method.

[0003] Internal stress is generated during the manufacturing and use of a workpiece. Any change in the molecular microstructure will generate internal stress in the material. Almost all plastic products have internal stress. As long as the internal stress does not cause failure and damage to the workpiece and does not affect people's daily production, the goal of controlling internal stress is achieved. Internal stress can be divided into thermal stress, phase change stress and mechanical resistance stress according to different mechanisms. The molding process of a plastic product is actually a phase change process, which is a typical solid-liquid-solid transformation. With the occurrence of phase change, phase change stress is generated in the product. The generation of phase change is closely related to the molecular structure of the material, the structure of the mold and the molding process parameters. For bisphenol A polycarbonate, due to the presence of benzene rings in the molecular chain, the flexibility of the molecular chain segment is poor. If the molecular chain segment cannot be adjusted in time and is frozen during the phase change process, a large "molecular potential energy" will be generated in the material. This "molecular potential energy" is the phase change stress. Phase change stress will be released continuously during the service of the plastic product with the change of the environment. Sometimes, the "violent" release will lead to the destruction or failure of the plastic product, resulting in irreparable loss. Therefore, it is particularly important to monitor and detect the internal stress of polycarbonate plastic products.

[0004] The common internal stress detection methods for polycarbonate plastic products include solvent method, weathering environment method and polarized light observation method, etc. The weathering environment method can quickly determine the risk of internal stress failure of the plastic product from a macro perspective and provide a basis for problem solving, but the setting of the accelerated simulation environment is difficult, often one-sided, and the test takes a long time and costs high. The polarized light method is to place the plastic part to be tested on a polarized light equipment for observation to determine the internal stress level of the part. This method is efficient and the result is intuitive, but it can only be used for qualitative judgment and has limitations on the size of the part. Large parts cannot be tested on the polarized light equipment, and the internal stress level of the part cannot be correlated with failure. The traditional solvent method is simple to operate, short in time and low in cost, but it is powerless for parts that do not fail after being subjected to the solvent. It can only prove that the risk of internal stress failure is small and is strongly dependent on the experience of the operator and the complex evaluation system.

[0005] Therefore, it is necessary to develop a repeatable and quantifiable polycarbonate plastic product internal stress detection method to guide the production and use of parts. SUMMARY

[0006] The purpose of the present application is to solve the problems in the background art and provide a repeatable and quantifiable polycarbonate plastic product internal stress detection method to guide the production and use of parts.

[0007] The technical solution of the present application is a polycarbonate plastic product internal stress detection method, characterized by comprising the following steps:

[0008] S1. Mix gasoline and xylene to obtain IS reagent;

[0009] S2. Prepare N standard polycarbonate sample plates A prepared according to preset materials and preset molding process parameters, N is a positive integer greater than or equal to 5, and all standard polycarbonate sample plates A are straight strip-shaped plates produced according to the same size requirements;

[0010] S3. Sort all standard polycarbonate sample plates A and set a test deflection γ for each, respectively. The test deflection γ starts from a preset lower limit value a and increases by the same step value b in ascending order for each block, ensuring that all test deflections γ do not exceed the limit deflection value γ max ;

[0011] S4. Measure the internal stress σ 内 of each standard polycarbonate sample plate A at the test deflection γ, and then measure the cracking time T of each standard polycarbonate sample plate A at the test deflection γ using the IS reagent, and fit the internal stress- cracking time standard curve I according to the internal stress σ 内 data and the corresponding cracking time T data of all standard polycarbonate sample plates A;

[0012] S5. Prepare the to-be-tested polycarbonate part B according to the same preset material and the same preset molding process parameters as in step S2, and determine the cracking time T of the to-be-tested polycarbonate part B by using the IS reagent B ;

[0013] S6. Determine the cracking time T of the to-be-tested polycarbonate part B on the internal stress-cracking time standard curve I obtained in step S4 B The corresponding internal stress value is denoted as σ 内B Therefore, the internal stress of the to-be-tested polycarbonate part B is σ 内B .

[0014] Preferably, in step S4, the test method of the internal stress σ 内 includes the following steps:

[0015] Place each standard polycarbonate sample A horizontally on the corresponding arc-shaped chuck, and place the center of the standard polycarbonate sample A vertically corresponding to the center of the arc-shaped chuck and the two ends of the arc-shaped chuck corresponding to the two ends of the standard polycarbonate sample A. Pre-set tooling points symmetrically at the two ends of the standard polycarbonate sample A, measure the distance between the two tooling points as L, and press the center of the standard polycarbonate sample A with a pressure head until the test deflection γ is reached, measure the pressure F applied by the pressure head at this time, and calculate the external mechanical stress σ 外 obtained by the standard polycarbonate sample A, and convert it into the internal stress σ 内 Therefore, the internal stress σ 内 is calculated according to the following formula:

[0016] σ 内 = σ 外 = 3FL / 2bh 2

[0017] Wherein, σ 外 = the obtained external mechanical stress, unit: MPa;

[0018] F = the pressure applied by the pressure head, unit: N;

[0019] L = the distance between the two tooling points on the standard polycarbonate sample A, unit: mm;

[0020] b = the width of the standard polycarbonate sample A, unit: mm

[0021] h = the thickness of the standard polycarbonate sample A, unit: mm.

[0022] Further, the shape of the arc-shaped chuck corresponding to each standard polycarbonate sample A satisfies: when the pressure head presses the center of the standard polycarbonate sample A to just reach the test deflection γ, the bottom of the standard polycarbonate sample A just contacts the arc-shaped chuck at this time. The arc-shaped chuck is made of rigid material.

[0023] Further, in step S4, the test of the cracking time T includes:

[0024] The fixture is installed on the inner stress σ 内 During the measurement process, the two ends of each standard polycarbonate sample A are locked on the arc chuck at the preset tool site to maintain the test deflection γ, the pressure head is removed, the IS reagent is uniformly dropped on the surface of the standard polycarbonate sample A, the dropping of the IS reagent is started simultaneously, and the time until the surface cracks is obtained, which is the cracking time T of the standard polycarbonate sample A.

[0025] Further, in step S5, the test of the cracking time T B includes:

[0026] The IS reagent is uniformly dropped on the surface of the polycarbonate part B to be detected, the dropping speed is set to be consistent with the IS reagent dropping speed in the cracking time T test in step S4, the dropping of the IS reagent is started simultaneously, and the time until the surface cracks is obtained, which is the cracking time T of the polycarbonate part B to be detected. B

[0027] Preferably, in step S1, the volume percentage of xylene in the IS reagent is 20% to 50%.

[0028] Preferably, in step S3, the preset lower limit value a satisfies 5mm≥a≥1mm, and the step value b satisfies 5mm≥b≥1mm.

[0029] Preferably, steps S4 to S5 are carried out in a standard environment with a temperature of 21 to 25°C and a humidity of 45% to 55%.

[0030] Preferably, it further includes step S7, which specifically includes: comparing the inner stress σ 内B of the polycarbonate part B to be detected obtained in step S6 with a preset inner stress limit value σ 内max ,

[0031] When σ 内B ≤ σ 内max , it is judged that the polycarbonate part B to be detected has no cracking risk.

[0032] When σ 内B > σ 内max , it is judged that the polycarbonate part B to be detected has a cracking risk.

[0033] The principle of the polycarbonate plastic product inner stress detection method is: the IS reagent is used to calibrate the cracking time T of the standard polycarbonate sample A with different inner stress levels (i.e. at different test deflections γ), and then a standard inner stress-cracking time curve I of the standard polycarbonate sample A is drawn. For the polycarbonate part B to be detected, the same IS reagent is used for cracking time test, and then the cracking time T​B Substitute into the internal stress-cracking time standard curve I, the internal stress σ of the polycarbonate part B to be detected can be obtained 内B .

[0034] The principle of calibrating the cracking time of IS reagent is that IS solvent molecules can penetrate between polycarbonate macromolecules, reduce the interaction between macromolecules, and macroscopically reduce the strength of the material. If the internal stress σ of a certain position on the polycarbonate plastic product is very large, which exceeds the strength σ of the material after soaking, that is, σ 内 > σ M，IS , cracking occurs at that position; if the internal stress σ of a certain position on the polycarbonate plastic product is relatively large, which has not exceeded the strength σ of the material after soaking macroscopically, that is, σ 内 ≤ σ M，IS , cracking does not occur at that position. 内 M，IS 内 M，IS

[0035] IS reagent is a mixture, which has strong permeability and similar solubility parameter with polycarbonate molecules, can reduce the interaction between molecules in a short time, and is a mixture of xylene and gasoline, the volume percentage of xylene is 20% to 50%, and the rest is gasoline, and the gasoline is preferably 92# gasoline.

[0036] Preferably, the mathematical function relationship of the internal stress-cracking time standard curve I is

[0037] y = mx n ,

[0038] Wherein: y represents the internal stress value, unit MPa; x represents the cracking time, unit min; m, n are constants obtained by fitting.

[0039] The application also provides a cracking time detection device used in any one of the above polycarbonate plastic product internal stress detection methods, comprising a base and a vertical rod arranged on the base, a horizontal cantilever is vertically movably connected to the vertical rod, a liquid storage tank is arranged on one end of the horizontal cantilever away from the vertical rod for placing IS reagent, and a liquid outlet is arranged at the lower end of the liquid storage tank and a flow rate adjustable ball valve is arranged at the liquid outlet.

[0040] Preferably, a drainage line is arranged at the liquid outlet and the drainage line is hung on the object to be detected, a closed ring or C-shaped support is arranged at one end of the horizontal cantilever away from the vertical rod, and the liquid storage tank is inverted conical and placed on the support.

[0041] In the above cracking time detection device, the drainage line can directly guide the IS reagent to the object to be detected, avoiding splashing caused by droplet impact on the surface. ​​​​

[0042] The beneficial effects of the present application are:

[0043] 1. By preloading a certain external mechanical stress on a standard polycarbonate sample A, the external mechanical stress is converted into corresponding internal stress, the internal stress which is inconvenient to measure is quantified, and the cracking time T of the standard polycarbonate sample A at different internal stress levels is calibrated, so that the internal stress-cracking time standard curve I of the performance of the reaction material can be quickly and accurately obtained.

[0044] 2. The chemical environmental stress release is carried out on the polycarbonate parts B to be detected of the same material, the cracking time is recorded, and the internal stress-cracking time standard curve I is substituted, so that the internal stress σ of the polycarbonate parts B to be detected can be quickly obtained. 内B The internal stress σ 内B Compared with the preset internal stress limit value σ 内max , it can be judged whether there is a cracking risk; it is also convenient to directly compare the internal stresses of different polycarbonate parts B to be detected to determine which one is more prone to cracking.

[0045] 3. The method for detecting the internal stress of polycarbonate plastic products provided by the present application is a standard working curve method, which provides a new internal stress quantitative detection method, forms a method system from the test principle, test device, test process and test result evaluation, and through the implementation examples and effect evaluation, the internal stress of the polycarbonate plastic products obtained by the method can well guide the design and development of the early stage and the quality improvement of the later stage, greatly improve the work efficiency and effect, reduce the cost waste in the design stage and the quality risk in the batch production stage, and provide strong technical support for the engineering personnel to control the internal stress. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 The step flow chart of the present application

[0047] Figure 2 The pressure schematic diagram of the standard polycarbonate sample A

[0048] Figure 3 The schematic diagram of the standard polycarbonate sample A being locked by the clamp

[0049] Figure 4 The schematic diagram of the cracking time detection device

[0050] Figure 5 The shape schematic diagram of the polycarbonate parts B to be detected

[0051] Figure 6 The internal stress-cracking time standard curve I in Example 1

[0052] Figure 7Figure 1 shows a schematic diagram of the internal stress-cracking time standard curve I in Example 2

[0053] Wherein: 1-base 2-vertical rod 3-horizontal cantilever 4-liquid storage tank 5-liquid outlet 6-ball valve 7-drainage line 8-support 10-standard polycarbonate sample A 11-pressure head 12-arc-shaped pressing plate 13-clamp. DETAILED DESCRIPTION

[0054] The technical solutions of the present application will be further described in detail below by means of the accompanying drawings and by listing some embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0055] Example 1

[0056] As Figure 1 shown, the present application provides a polycarbonate plastic product internal stress detection method based on external standard method, comprising the following steps:

[0057] S1. According to the volume ratio of 92# gasoline: xylene = 50:50, IS reagent is prepared and mixed, and after the preparation of IS reagent is completed, it is put into a polypropylene inert container for standby;

[0058] S2. Prepare N standard polycarbonate sample A prepared according to the preset material and preset molding process parameters, in this embodiment, N = 10, the preset material is SABIC Lexan LS1 (i.e. LEXAN LS1 type polycarbonate produced by SABIC company), and the preset molding process parameters are: vacuum drying machine 120℃ drying for 4 hours; double screw extruder, screw diameter 35mm, length-diameter ratio L / D = 40, screw speed 40r / min; barrel segmented control temperature, from the feeding port to the die exit in turn 260℃, 270℃, 270℃, 290℃, 290℃, 290℃, injection pressure 80MPa, mold temperature 90℃, back pressure 0.8MPa, injection time 16s, cooling time 24s, holding pressure 65Mpa, holding time 10s.

[0059] All standard polycarbonate sample A is a straight strip according to the same size requirement, in this embodiment, the size requirement of standard polycarbonate sample A is: length = 200±1mm, width = 10±0.2mm, thickness = 3±0.2mm.

[0060] S3. Sort all standard polycarbonate specimens A from 1 to N and set a test deflection γ for each. The test deflection γ starts from the preset lower limit value a (5mm ≥ a ≥ 1mm) and increases by the same step value b (5mm ≥ b ≥ 1mm) for each specimen in ascending order, ensuring that all test deflections γ do not exceed the limit deflection value γ of the standard polycarbonate specimen A. max γ max These are empirical values ​​or experimental values ​​using the same material. In this embodiment, the preset lower limit value a = 1 mm, the step value b = 2 mm, and γ... max =30mm, then the test deflection γ of standard polycarbonate sample A from the 1st to the 10th sample is as follows: 1mm, 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 17mm and 19mm.

[0061] S4. First, determine the internal stress σ of each standard polycarbonate sample A under the corresponding test deflection γ. 内 The specific steps are as follows:

[0062] like Figure 2 As shown, each standard polycarbonate sample A10 is placed horizontally on the arc-shaped chuck 12 with a radius of curvature corresponding to its value. Figure 2 The standard polycarbonate sample A10 is placed vertically along its length (left and right) and thickness (up and down). The center of the standard polycarbonate sample A10 is vertically aligned with the center of the arc-shaped chuck 12, with both ends of the arc-shaped chuck 12 extending beyond the ends of the standard polycarbonate sample A10. Pre-set tooling points symmetrically at both ends of the standard polycarbonate sample A10, and measure the distance L between the two tooling points. Press down the center of the standard polycarbonate sample A10 using the pressure head 11 until the test deflection γ is reached. At this point, the bottom of the standard polycarbonate sample A10 is in contact with the arc-shaped chuck 12. Measure the pressure F applied by the pressure head at this point, and calculate the external mechanical stress σ obtained by the standard polycarbonate sample A10. 外 And transformed into internal stress σ 内 Then the internal stress σ 内 Calculate according to the following formula,

[0063] σ 内 =σ 外 =3FL / 2bh 2

[0064] Where, σ 外 = The external mechanical stress obtained, in MPa;

[0065] F = Pressure applied by the pressure head, in N;

[0066] L = the distance between two tooling points on standard polycarbonate template A, in mm;

[0067] b = standard polycarbonate sample A width, unit: mm;

[0068] h = standard polycarbonate sample A thickness, unit: mm;

[0069] The clamp 13 is installed on the inner stress σ 内 The preset fixture site during the measurement process is shown in Figure 3 The two ends of each standard polycarbonate sample A are locked on the arc chuck 12 to maintain the test deflection γ, the pressure head 11 is removed, and the IS reagent obtained in step S1 and the cracking time detection device are used to measure the cracking time T of each standard polycarbonate sample A under the test deflection γ.

[0070] As shown in Figure 4 The cracking time detection device has the following specific structure: a square base 1 and a vertical rod 2 arranged on the base 1, a horizontal cantilever 3 movably connected vertically on the vertical rod 2, a liquid storage tank 4 arranged on the end of the horizontal cantilever 3 away from the vertical rod 2 for placing the IS reagent, a liquid outlet 5 arranged at the lower end of the liquid storage tank 4 and a flow rate adjustable ball valve 6 arranged at the liquid outlet 5, a drainage line 7 (ordinary cotton thread can be used) arranged at the liquid outlet 5 and hanging down to the measured object, a closed ring or C-shaped support 8 arranged at the end of the horizontal cantilever 3 away from the vertical rod 2, and the liquid storage tank 4 is inverted conical and placed on the support 8.

[0071] The specific steps for detecting the cracking time T are as follows: the IS reagent prepared in step S1 is placed in the liquid storage tank 4, the lower end of the drainage line 7 is in contact with the measured object (herein, the standard polycarbonate sample A), the ball valve 6 is opened to make the IS reagent drip uniformly on the center of the upper surface of the standard polycarbonate sample A along the drainage line 7, and the dripping of the IS reagent is started simultaneously with the timing until the surface cracks, and the obtained time is the cracking time T of the standard polycarbonate sample A, which is accurate to seconds.

[0072] The inner stress σ 内 of the standard polycarbonate sample A in this embodiment is as follows.

[0073] The data of the inner stress σ 内 and the cracking time T of the standard polycarbonate sample A in this embodiment are shown in Table 1 below.

[0074]

[0075] According to the inner stress σ 内 data of all standard polycarbonate samples A and the corresponding cracking time T data, the inner stress-cracking time standard curve I is fitted, as shown in Figure 6 The mathematical function relationship of the inner stress-cracking time standard curve I is as follows:

[0076] y = 11.74 * x -0.27

[0077] y represents the internal stress value, in MPa.

[0078] x represents the cracking time, in minutes.

[0079] S5. Prepare the polycarbonate part B to be tested, made with the same preset material and the same preset molding process parameters as in step S2. In this embodiment, the polycarbonate part B to be tested is a daytime running light cover, shaped as follows: Figure 5 As shown, the cracking time detection device for standard polycarbonate sample A in step S4 is used to detect the cracking time of the polycarbonate part B to be tested. The detection steps are the same as in step S4: the IS reagent prepared in step S1 is placed in the storage tank 4, the lower end of the drain line 7 is brought into contact with the surface of the polycarbonate part B to be tested, and the ball valve 6 is opened to allow the IS reagent to drip evenly along the drain line 7 onto the polycarbonate part B to be tested. Figure 5 On the surface (within the dashed box), set the drip rate to be consistent with the IS reagent drip rate during the cracking time T test in step S4 (i.e., keep the ball valve 6 opening constant). Start timing synchronously as the IS reagent drips, and record the cracking time T of the polycarbonate part B to be tested. B Cracking time T B Accurate to the second, in this embodiment T B =3min. In this embodiment, steps S4 to S5 are all carried out in a standard environment with a temperature of 21 to 25°C and a humidity of 45% to 55%.

[0080] S6. Determine the cracking time T of the polycarbonate part B to be tested on the internal stress-cracking time standard curve I. B The corresponding internal stress value is denoted as σ. 内B The internal stress of the polycarbonate part B to be tested is σ. 内B In this embodiment, σ 内B =11.74*3 -0.27 =8.73MPa.

[0081] S7. The internal stress σ of the polycarbonate part B to be tested obtained in step S6 is... 内B Compared with the preset internal stress limit value σ 内max Comparison,

[0082] When σ 内B ≤σ 内max At that time, it was determined that the polycarbonate part B to be tested had no risk of cracking;

[0083] When σ 内B >σ 内max At that time, it was determined that the polycarbonate part B to be tested was at risk of cracking.

[0084] Specifically: In this embodiment, σ内max =5MPa, then the σ of the polycarbonate part B to be tested is... 内B =8.73MPa>σ 内max If so, it is determined that the polycarbonate part B to be tested is at risk of cracking.

[0085] In this embodiment, there can be one or more polycarbonate parts B to be tested. When there are multiple parts, the internal stress values ​​of each polycarbonate part B to be tested are obtained according to steps S5-S6. The internal stress values ​​of multiple polycarbonate parts B to be tested can be compared with each other, and the larger value indicates a greater risk of cracking.

[0086] Example 2

[0087] like Figure 1 As shown, the present invention provides a method for detecting internal stress in polycarbonate plastic products based on the external standard method, comprising the following steps:

[0088] S1. Prepare IS reagent by mixing 92# gasoline and xylene at a volume ratio of 60:40. After the IS reagent is prepared, place it in a polypropylene inert container for later use.

[0089] S2. Prepare N standard polycarbonate samples A prepared according to preset materials and preset molding process parameters. In this embodiment, N=10. The preset material is COVESTRO Makrolon AL2647 (i.e., Makrolon AL2647 polycarbonate produced by COVESTRO). The preset molding process parameters are: drying in a vacuum dryer at 120°C for 4 hours; twin-screw extruder with a screw diameter of 35mm, a length-to-diameter ratio L / D=40, and a screw speed of 40r / min; segmented temperature control of the barrel, from the feed port to the die outlet, is 260°C, 270°C, 270°C, 290°C, 290°C, 290°C, 290°C; injection pressure is 80MPa; mold temperature is 90°C; back pressure is 0.8MPa; injection time is 16s; cooling time is 24s; holding pressure is 65MPa; and holding time is 10s.

[0090] All standard polycarbonate samples A are straight strips produced according to the same size requirements. In this embodiment, the size requirements for standard polycarbonate sample A are: length = 200±1mm, width = 10±0.2mm, and thickness = 3±0.2mm.

[0091] S3. Sort all standard polycarbonate specimens A and set a test deflection γ for each. The test deflection γ starts from the preset lower limit value a (5mm ≥ a ≥ 1mm) and increases by the same step value b (5mm ≥ b ≥ 1mm) for each specimen in ascending order, ensuring that all test deflections γ do not exceed the limit deflection value γ of the standard polycarbonate specimen A. max γ maxThese are empirical values ​​or experimental values ​​using the same material. In this embodiment, the preset lower limit value a = 1 mm, the step value b = 2 mm, and γ... max =30mm, then the test deflection γ of standard polycarbonate sample A from the 1st to the 10th sample is as follows: 1mm, 3mm, 5mm, 7mm, 9mm, 11mm, 13mm, 15mm, 17mm and 19mm.

[0092] S4. First, determine the internal stress σ of each standard polycarbonate sample A under the corresponding test deflection γ. 内 The specific steps are as follows:

[0093] like Figure 2 As shown, each standard polycarbonate sample A10 is placed horizontally on the arc-shaped chuck 12 with a radius of curvature corresponding to its value. Figure 2 The standard polycarbonate sample A10 is placed vertically with the center of the arc-shaped chuck 12, with both ends of the arc-shaped chuck 12 extending beyond the ends of the standard polycarbonate sample A10. Pre-set tooling points symmetrically at both ends of the standard polycarbonate sample A10, and measure the distance L between the two tooling points. Press down the center of the standard polycarbonate sample A10 with the pressure head 11 until the test deflection γ is reached. At this point, the bottom of the standard polycarbonate sample A10 is in contact with the arc-shaped chuck 12. Measure the pressure F applied by the pressure head at this point, and calculate the external mechanical stress σ obtained by the standard polycarbonate sample A10. 外 And transformed into internal stress σ 内 Then the internal stress σ 内 Calculate according to the following formula,

[0094] σ 内 =σ 外 =3FL / 2bh 2

[0095] Where, σ 外 = The external mechanical stress obtained, in MPa;

[0096] F = Pressure applied by the pressure head, in N;

[0097] L = the distance between two tooling points on standard polycarbonate template A, in mm;

[0098] b = Width of standard polycarbonate sample A, in mm;

[0099] h = Thickness of standard polycarbonate sample A, in mm;

[0100] Then install clamp 13 on the internal stress σ 内 At the preset tooling points during the measurement process, such as Figure 3As shown, the two ends of each standard polycarbonate sample A are locked on the arc-shaped chuck 11 to keep the test deflection γ, and then the pressure head 12 is removed. The cracking time T of each standard polycarbonate sample A under the test deflection γ is measured by using the IS reagent obtained in step S1 and the cracking time detection device.

[0101] As shown in the figure, the cracking time detection device has the following specific structure: a square base 1 and a vertical rod 2 arranged on the base 1, a horizontal cantilever 3 movably connected vertically on the vertical rod 2, a liquid storage tank 4 arranged on the end of the horizontal cantilever 3 away from the vertical rod 2 for placing the IS reagent, a liquid outlet 5 arranged at the lower end of the liquid storage tank 4 and a ball valve 6 with adjustable flow rate arranged at the liquid outlet 5, a drainage line 7 (ordinary cotton thread can be used) arranged at the liquid outlet 5 and hanging down to the measured object, a closed ring-shaped or C-shaped support 8 arranged at the end of the horizontal cantilever 3 away from the vertical rod 2, and the liquid storage tank 4 is inverted conical and placed on the support 8. Figure 4 The specific steps for detecting the cracking time T are as follows: the IS reagent prepared in step S1 is placed in the liquid storage tank 4, the lower end of the drainage line 7 is in contact with the measured object (here, the standard polycarbonate sample A), the ball valve 6 is opened to make the IS reagent drip uniformly on the center of the upper surface of the standard polycarbonate sample A along the drainage line 7, and the dripping of the IS reagent is started simultaneously with the timing until the surface cracks, and the obtained time is the cracking time T of the standard polycarbonate sample A, which is accurate to seconds.

[0102] In this embodiment, the internal stress σ 内 of the standard polycarbonate sample A is as shown in the following table 2.

[0103] Table 2 Internal stress σ 内 and cracking time T of the standard polycarbonate sample A in Example 2

[0104]

[0105]

[0106] According to the internal stress σ 内 data and the corresponding cracking time T data of all standard polycarbonate samples A, the internal stress-cracking time standard curve I is fitted, as shown in the following figure. Figure 7

[0107] y = 10.88 * x -0.16

[0108] y represents the internal stress value, unit: MPa

[0109] x represents the cracking time, unit: min.

[0110] ​​S5. Prepare the polycarbonate part B to be tested, made with the same preset material and the same preset molding process parameters as in step S2. In this embodiment, the polycarbonate part B to be tested is a daytime running light cover, shaped as follows: Figure 5 As shown, the cracking time detection device for standard polycarbonate sample A in step S4 is used to detect the cracking time of the polycarbonate part B to be tested. The detection steps are the same as in step S4: the IS reagent prepared in step S1 is placed in the storage tank 4, the lower end of the drain line 7 is brought into contact with the surface of the polycarbonate part B to be tested, and the ball valve 6 is opened to allow the IS reagent to drip evenly along the drain line 7 onto the polycarbonate part B to be tested. Figure 5 On the surface (within the dashed box), set the drip rate to be consistent with the IS reagent drip rate during the cracking time T test in step S4 (i.e., keep the ball valve 6 opening constant). Start timing synchronously as the IS reagent drips, and record the cracking time T of the polycarbonate part B to be tested. B Cracking time T B Accurate to the second, in this embodiment T B =2.8min. In this embodiment, steps S4 to S5 are all carried out in a standard environment with a temperature of 21 to 25°C and a humidity of 45% to 55%.

[0111] S6. Determine the cracking time T of the polycarbonate part B to be tested on the internal stress-cracking time standard curve I. B The corresponding internal stress value is denoted as σ. 内B In this embodiment, the internal stress σ of the polycarbonate part B to be tested is... 内B =10.88 * 2.8 -0.16 = 9.23 MPa.

[0112] S7. The internal stress σ of the polycarbonate part B to be tested obtained in step S6 is... 内B Compared with the preset internal stress limit value σ 内max Comparison,

[0113] When σ 内B ≤σ 内max At that time, it was determined that the polycarbonate part B to be tested had no risk of cracking;

[0114] When σ 内B >σ 内max At that time, it was determined that the polycarbonate part B to be tested was at risk of cracking.

[0115] Specifically: In this embodiment, σ 内max =5MPa, then the σ of the polycarbonate part B to be tested is... 内B =9.23MPa>σ 内max If so, it is determined that the polycarbonate part B to be tested is at risk of cracking.

[0116] The polycarbonate parts B to be detected in the embodiment can be one or more. When there are multiple polycarbonate parts B to be detected, the internal stress values of each polycarbonate part B to be detected are obtained according to steps S5-S6. The internal stress values of the multiple polycarbonate parts B to be detected can be compared with each other. The polycarbonate part B with a larger value has a greater risk of cracking.

Claims

1. A method for detecting internal stress in polycarbonate plastic products, characterized in that, Includes the following steps: S1. Mix gasoline with xylene to obtain IS reagent; S2. Prepare N standard polycarbonate samples A prepared according to preset materials and preset molding process parameters, where N is a positive integer ≥5, and all standard polycarbonate samples A are straight strips produced according to the same size requirements; S3. Sort all standard polycarbonate specimens A and set a test deflection γ for each. The test deflection γ starts from the preset lower limit value a and increases by the same step value b in ascending order for each specimen, ensuring that the test deflection γ does not exceed the limit deflection value γ of the standard polycarbonate specimen A. max ; S4. Determine the internal stress σ of each standard polycarbonate sample A under the test deflection γ. 内 Then, using IS reagent, the cracking time T of each standard polycarbonate sample A under the test deflection γ was determined. Based on the internal stress σ of all standard polycarbonate samples A... 内 The internal stress-cracking time standard curve I was obtained by fitting the data and the corresponding cracking time T data; Internal stress σ 内 The test method includes: placing each standard polycarbonate sample A horizontally on a corresponding arc-shaped chuck, with the center of the standard polycarbonate sample A vertically aligned with the center of the arc-shaped chuck, and the ends of the arc-shaped chuck extending beyond the ends of the standard polycarbonate sample A. Pre-set tooling points symmetrically at both ends of the standard polycarbonate sample A, and measure the distance L between the two tooling points. Press down on the center of the standard polycarbonate sample A with an indenter until the test deflection γ is reached, measure the pressure F applied by the indenter at this point, and calculate the external mechanical stress σ obtained by the standard polycarbonate sample A. 外 And transformed into internal stress σ 内 Then the internal stress σ 内 Calculate according to the following formula, s 内 =s 外 =3FL / 2bh 2 Where, σ 外 = The external mechanical stress obtained, in MPa; F = Pressure applied by the pressure head, in N; L = the distance between two tooling points on standard polycarbonate template A, in mm; b = Width of standard polycarbonate sample A, in mm; h = Thickness of standard polycarbonate sample A, in mm; The cracking time T test includes: mounting the fixture on the internal stress σ 内 During the measurement process, at the preset tooling position, the two ends of each standard polycarbonate sample A are locked on the arc chuck to maintain the test deflection γ. The pressure head is removed, and the IS reagent is dripped uniformly onto the surface of the standard polycarbonate sample A. The dripping of the IS reagent begins to be timed synchronously until the surface cracks. The time obtained is the cracking time T of the standard polycarbonate sample A. S5. Prepare the polycarbonate part B to be tested, made with the same preset materials and the same preset molding process parameters as in step S2, and determine the cracking time T of the polycarbonate part B using IS reagent. B ; Cracking time T B The test includes: uniformly dripping IS reagent onto the surface of the polycarbonate part B to be tested, setting the dripping rate to be consistent with the IS reagent dripping rate during the cracking time T test in step S4, and timing synchronously from the start of IS reagent dripping until the surface cracks. The time obtained is the cracking time T of the polycarbonate part B to be tested. B ; S6. Determine the cracking time T of the polycarbonate part B to be tested from the internal stress-cracking time standard curve I obtained in step S4. B The corresponding internal stress value is denoted as σ. 内B The internal stress of the polycarbonate part B to be tested is σ. 内B ; S7. The internal stress σ of the polycarbonate part B to be tested obtained in step S6 is... 内B Compared with the preset internal stress limit value σ 内max Comparison, When σ 内B ≤σ 内max At that time, it was determined that the polycarbonate part B to be tested had no risk of cracking; When σ 内B >σ 内max At that time, it was determined that the polycarbonate part B to be tested was at risk of cracking; The cracking time detection device used in the method for detecting internal stress of carbonate plastic products includes a base (1) and a vertical rod (2) set on the base (1). A horizontal cantilever (3) is vertically and movably connected to the vertical rod (2). A liquid storage tank (4) is provided on the end of the horizontal cantilever (3) away from the vertical rod for placing IS reagent. An outlet (5) is provided at the lower end of the liquid storage tank (4), and a ball valve (6) with adjustable flow rate is provided at the outlet (5). A drain line (7) is provided at the outlet (5), and the drain line (7) hangs down to the test object. A closed ring or C-shaped support (8) is provided at the end of the horizontal cantilever (3) away from the vertical rod (2). The liquid storage tank (4) is an inverted cone and is placed on the support (8).

2. The method for detecting internal stress in polycarbonate plastic products as described in claim 1, characterized in that, In step S1, the xylene volume percentage in the IS reagent is 20% to 50%.

3. The method for detecting internal stress in polycarbonate plastic products as described in claim 1, characterized in that, In step S3, the preset lower limit value a satisfies 5mm≥a≥1mm, and the step value b satisfies 5mm≥b≥1mm.

4. The method for detecting internal stress in polycarbonate plastic products as described in claim 1, characterized in that, Steps S4 to S5 were all carried out in a standard environment with a temperature of 21 to 25°C and a humidity of 45% to 55%.

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