Experience of using and testing electronic compression strength tester

1 Use, maintenance and adjustment of electronic compressive strength tester

1) Understanding of testing instruments

The ZSD-3 electronic compressive strength tester is the main testing instrument for testing the physical properties of paper, cardboard and cartons. Understanding and understanding the performance, structure and knowledge of the instrument correctly is an effective guarantee for improving the quality of testing. The instrument is composed of a base, a transmission mechanism, a high-precision pressure sensor, an electric control box and a touch panel. The electric control system is based on a high-end 16-bit single-chip 888196 as the core to form an intelligent detection system. During the test, the sample is placed in the center of the upper and lower pressure plates. After pressing the test key, the upper pressure plate is uniformly lowered at a certain constant speed under the action of the transmission mechanism. When a certain pressure value is reached, the sample is crushed. The test value is immediately displayed on the LCD screen. At the same time, under the action of the electronic control system, the motor automatically rotates back and the upper pressure plate returns to the starting position. Two limit switches are set in the worm gear box of the instrument, which are used to control the limit position of the upper pressure plate when working, to ensure the safety of the instrument. The measuring range of this instrument is 0N ~ 3000N. If the pressure is obviously greater than 3000N, it is easy to damage the sensor. Therefore, it is required to adjust the limit position of the limit switch accurately. If it fails due to damage, it should be replaced in time to ensure the safe use of the testing instrument.

2) Use and maintenance

The applicable working environment of the instrument is: temperature 10 ℃ ~ 35 ℃, relative humidity is less than 80%, so the best environment should be installed air conditioning equipment. The instrument should be placed in parallel on a solid, firm, vibration-free concrete or marble platform to ensure accurate detection values. During the test, pay attention to carefully observe the test situation. If the paper is too soft, the pressure is not enough to produce an induction effect, and the automatic stop cannot be achieved. The upper pressure plate will continue to press down. At this time, you should immediately press the stop button to force the stop. Prevent the upper pressure plate from running out of pressure on the tray or guide block, which may easily damage the instrument. There should be no looseness on the upper and lower pressure plates of the instrument, otherwise, the test value will obviously have errors. A certain amount of grease (butter) should be kept in the screw and worm gear box to prevent the wear and looseness of key components and affect the accuracy of the test data. The flange on the instrument not only supports but also tightens the upper pressure plate. If the screws are loosened due to tremor during use, the flange will become loose and the upper pressure plate will not completely crush the sample. , And the LCD screen shows the test results with significantly lower values, so usually pay attention to check whether the screws tightening the flange are loose, so as to take corresponding measures to tighten. The degree of parallelism between the upper and lower pressure plates is also directly related to the accuracy of the test. If the tightening screws on the base and the housing are loose, it will inevitably affect the parallelism of the upper and lower pressure plates. During the test, there will be biased contact, resulting in inaccurate test data. If the screws are still non-parallel after tightening evenly, the method of adding shims should be used to properly heighten the lower shell, so that the relative parallelism error of the front and back and left and right of the upper and lower pressure plates is less than 0.05mm to ensure detection Accurate.

3) Adjust the instrument

Calibration is an important and meticulous job. After one item is tested, before testing another item, the instrument should be zeroed. Because the weights of the trays, guide blocks and peeling racks for testing the ring pressure strength, edge pressure strength and peeling strength are different, their own weight will inevitably have a size difference to the pressure generated by the lower pressure plate, so they must be zeroed and eliminated. The pressure value of the attachment to the pressure plate to ensure the accuracy of the detection. When zeroing, the detection accessories (such as peeling rack, tray, etc.) should be placed on the lower pressure plate, and the dial switch on the back of the instrument should be turned to the side with red dots, then adjust the zero adjustment knob on the right side It is appropriate to adjust the 1F value on the LCD screen to between 0 and 0.2. After adjustment, turn the dial switch to the side without red dot, and then press the reset button to perform formal detection. In addition, when the instrument is repaired after failure, if it is suspected that the indicated value is not correct, a standard weight can be used for verification. The method is as follows: remove the testing accessories on the lower pressure plate and let the upper pressure plate rise to the distance when the weight can be put into the lower pressure plate. After the zero adjustment is completed, you can press the test button to press the upper pressure plate for a short period, and then put the weight into the lower pressure plate. The error between the value displayed on the LCD screen and the weight should be ≤ ± 1 %; The relative error of the repeatability of the indicated value should be ≤1%, which meets the technical parameters of the instrument.

2 Detection and operation technology

Keep a good sampling technique. Sampling is a meticulous and serious work, which can't be tolerated. Otherwise, the accuracy of the test is impossible to talk about. Sampling should be cut from different positions, such as roll paper should be taken from different parts of the paper on both sides and in the middle. Corrugated box should be selected as three test samples, each of which 7 samples were cut from different parts, a total of 21 pieces, 12 of which were used to detect the adhesive strength, 9 pieces were used to detect the edge pressure strength. The basic requirement for sampling is that the paper sample taken must be of good paper flatness, no creases, no wrinkles, no dents, no bends, no deformation and no damage; corrugated cardboard should be free of collapsed tiles, no flats, No damage, no blistering, no degumming and no deformation, this is the basis for determining the accuracy of the inspection. Sampling should be divided into three links, namely hair sample, large sample, small sample (ie standard sample). The wool sample is mainly the first selected paper pattern, and cut out with a knife or scissors, the paper edge does not need to be very neat. The large sample is taken according to the size of the standard sample, and the hair sample is cut into a rectangular shape with an appropriate area as appropriate, and the cut edge is perpendicular or parallel to the wire or corrugated paper, so that the standard sample can be cut accurately. After the large sample is cut, it can be easily and accurately divided into standard small samples. For the standard sample of the ring compression strength, its long side must be parallel to the transverse thread of the paper, so that the transverse ring compression strength of the paper can be detected. For standard samples of edge compressive strength and adhesive strength, their corrugated grooves should be perpendicular to the long side of the cardboard. The deflection of the test pattern, the size deviation of the specifications, and the burrs will all affect the detection effect. Therefore, the rules of the sampler must be accurate, and the knife edge must be kept sharp. In order to improve the accuracy of the test, the paper wool samples should be hung in a constant temperature and humidity laboratory and processed for 24 hours, while the corrugated cardboard samples need to undergo 48 hours of constant temperature and humidity treatment to achieve the characteristics of the sample Relatively stable.

3 Test requirements and conversion methods for test values

1) Test requirements and conversion formula of ring compression strength

The specifications of the standard sample should be: length (longitudinal) 152.0 ± 0.2mm, width 12.7 ± 0.1mm, take 10 pieces for inspection, 5 of them are tested with the front side facing out, and the other 5 are placed in the ring tray for inspection Then the results of these 10 pieces of detection are used to calculate an average value for conversion. In order to improve the accuracy of the detection, attention should be paid to the quantitative indicators carefully, because the value of the quantitative detection value and the result of the conversion of the ring pressure index have a direct impact. Therefore, the quantitative test samples should have a certain representativeness. It is best to take 10 samples from different parts of the paper tube for testing and find the average value, so that the test is relatively accurate. If 10 samples are taken from a longitudinal part of the paper tube, the detection value is often not representative, because the lateral thickness error of the paper tube is relatively larger than the longitudinal error. In addition, the accuracy of the sample thickness detection is also related to the conversion result of the ring compression strength. Because the thickness of the sample is different, the diameter of the tray core used to detect the ring compression strength is also different. Therefore, the thickness test should also be used to test several points in different parts, and find the average value as the final test result. The thickness index is detected accurately, and the gap of the sample into the tray is more appropriate, which can better ensure the accuracy of the ring pressure strength test. This requires that the diameter of the tray must be selected strictly according to the thickness of the sample. Table 1 is a comparison table of ZSB-3F1 ring pressure tray and sample thickness.
The conversion formula of ring pressure strength and ring pressure index is as follows:

â‘  Ring compression strength: R = F / 152. In the formula: R represents the ring compression strength, unit KN / m; F is the pressure value read when the sample is crushed, unit N; 152 is the length of the sample, unit mm.

② Transverse ring pressure index: Rd = 1000R / W. In the formula: Rd means ring pressure index, unit N • m / g; R means ring pressure strength, expressed by KN / m; W is the quantitative value of the sample, unit g / m2. The simple calculation formula of the lateral ring pressure index is: the average value of the detection of paper sample crushing ÷ 0.152 ÷ quantitative of the sample.

2) Test requirements and conversion formulas for edge pressure strength

Edge compression strength refers to the pressure that can be withstood per unit length, that is, the ability to withstand the pressure parallel to the direction of the corrugation. According to the relevant standard rules, the samples of edge compression strength are cut out of three samples from each of the three sample boxes without mechanical indentation, printing marks and damage. The corrugated direction of the sample should be the short side. The specification is 25mm × 100mm, and the error is ± 0.5mm. It is required that the knife edge of the sampler should be kept absolutely sharp, and the blade installation position on the knife holder should be appropriate, and the angle between the blade edge and the knife groove should be adjusted to 45 °. In addition, the tip of the knife should not touch the bottom of the knife slot to prevent the blade from bending and deforming, so as to avoid the edge of the sample from being easily damaged and fluffed, which affects the accuracy of detection. The conversion formula of edge pressure strength is: R = F / L × 103. In the formula: R is the compressive strength of the corrugated cardboard sample edge, expressed in N / m; F is the pressure value read when the sample is crushed; L is the size of the long side of the sample, the unit is mm.

3) Test requirements and conversion formula of bond strength

The conversion formula of adhesive strength is: P = F / L. In the formula: P is the adhesive strength of the corrugated cardboard sample, expressed in N / m. Where F is the pressure value read when the sample is separated and the unit is N; L is the size of the long side of the sample and the unit is m. Only by bonding corrugated cardboard into the whole structure, can the overall compression of the corrugated cardboard box be improved, so it is very important to correctly detect the bonding strength index of corrugated cardboard. The purpose of testing the adhesive strength of corrugated cardboard is to check the fastness of corrugated cardboard mounting. For the detection of A-type corrugated cardboard, the pin of the peeling frame should be about 3mm, while the corrugated holes of the B and C-type corrugated cardboard are thinner, and the pin of the peeling frame should be Φ2mm. Each pin on the stripping rack should be exactly aligned with the center of the corrugated notch, and after the spacing is adjusted equal, tighten each screw. For the detection of the adhesive strength, 12 samples are required, that is, 4 samples from each of the three sample boxes with the corrugated direction as the short side (that is, 25 mm). The material is intact, non-degumming, and no blistering. The size of the sample block is 25mm × 80mm, and the error is ± 1.0mm, which can better ensure the accuracy of the detection.

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