The pressure test is suitable for evaluating the compressive strength of the transport package when it is under pressure, and the ability . This method is also applicable to the pressure test of transport packaging containers, such as the compression test of cartons and the compression strength test of corrugated boxes. The principle of the pressure test is to place the sample between two parallel platens of the pressure testing machine, and then apply pressure evenly until the sample ruptures, or the direct load or the displacement of the platen reaches the specified value. According to the position of the package to be tested, the pressure test is divided into three types: plane pressure test, diagonal pressure test and diagonal pressure test.
1. Pressure testing machine
(1) Structure and working principle
The pressure testing machine is used to determine the compressive performance of transport packages and other non-metallic materials. It consists of ALWEROW CT 30 pressure machine, CMU-2 control machine measurement unit and DLH plane function Recorder. The press part is shown in Figure 6-17, which is composed of a frame, an upper and a lower platen, and the like. The sample is placed between two pressing plates, and the upper pressing plate is stably installed on the bracket connected to the transmission mechanism, and can also be connected with a 10° universal joint to ensure good contact between the pressing plate and the sample. The pressure testing machine is driven by a DC servo motor with stepless speed regulation, and two trapezoidal screws with the same parameters are driven by a worm reducer . The upper platen can be moved, guided by four upright columns and has good transmission stability. The drive unit of the motor is composed of a servo amplifier with silicon controlled rectifier control, a transformer and an interference suppression filter. The pulse transmitter, which registers the position of the beam movement, is driven by a lead screw. The lower platen is supported on four load bearing elements, one of which is vertically adjustable. If the specimen is centered between the two platens, each load bearing element bears 1/4 of the load. However, the load distribution on the pressure plate cannot be uniform, so the load-bearing element is designed according to 50% overload. Concentrated loads should be avoided, and the force on any one load-bearing element should not exceed 35% of the maximum load of the instrument. In order to make the instrument run safely, limit switches are installed at 5~10mm from the upper and lower movement limit positions of the pressure plate.
(2) Main technical parameters
①Rated pressure: 30kN.
②Beam stroke: 1000mm.
③Loading speed: 1~50mm/min.
④ Return speed: 300mm/ min.
⑤Platen size: 1000mmX600mm. (
(3) Calibration procedure
① Turn on the power and preheat for 15 minutes.
②Turn the force value display selector on the control and measurement unit to the "MEM OFF" position, use the "ZE-RO" knob on the left to zero carefully, then turn the selector to the "CHECK" position, the displayed on the display The value should be consistent with the calibration value specified by the instrument, and the deviation should be less than ±1%.
③ If the deviation is greater than ±1%, it can be adjusted with the trimmer potentiometer on the left side of the top surface of the load connector on the rear panel.
In addition, the XYD-15K carton compression testing machine produced by Jinan Languang Electromechanical Technology Co., Ltd. is not only suitable for the pressure resistance, deformation and stacking tests of corrugated boxes, honeycomb boxes and other packages, but also can be used for plastic barrels (edible oil , mineral water), paper barrels, cartons, paper cans, container barrels and other packaging containers compression test. The main technical parameters of this instrument include the following points.
①Rated pressure: 15kN, 45kN.
②Deformation resolution: 0.1mm.
③Loading speed: 5mm/min, 10mm/min, 12.7mm/min.
④ Test space: 1m (length) × 1m (width) × 1.3m (height).
2. Test method
There are two types of pressure test methods, one is the fixed platen pressure test method, and the other is the floating platen pressure test method. The national standard GB4857.4 and most of the standard test methods adopt the fixed platen pressure test method.
(1) Fixed pressure plate pressure test method
Before the test, each part of the sample should be numbered according to GB4857.1, and a condition should be selected according to GB 4857.2 to adjust the temperature and humidity of the sample. Test according to the national standard GB4857.4 "Packaging and transport package pressure test method". The specific test steps are as follows.
① Place the sample in the center of the platen in the state of normal transportation, so that the upper platen is in contact with the sample. Apply an initial load of 220N first, so that the sample is in good contact with the upper and lower pressure plates. Adjust the displacement recording device and use this as the starting point for recording.
② Move the platen evenly at a speed of (10±3) mm/min, and the load should be applied to one of the following two situations.
a. The compressive load reaches the limit value, and the sample ruptures.
b. The size of the sample is deformed, or the compressive load reaches a predetermined value.
When carrying out the diagonal pressure test and the diagonal pressure test of the transport package, it is necessary to use a pressure testing machine whose upper platen cannot be tilted freely. A pair of metal accessories with a 120° conical hole shall be prepared for the diagonal pressure test, and the depth of the accessory hole shall not exceed 30mm. A pair of metal accessories with right-angle grooves should be prepared for the edge pressure test, and the depth and angle of the grooves should not affect the compressive strength of the sample. During the test, the metal accessories are installed on the symmetrical positions of the center of the upper and lower platens to ensure that the sample is subjected to diagonal compression and diagonal compression during the test. Measures should be taken during the test to ensure the safety of personnel and equipment.
(2) Floating platen pressure test method
The floating platen pressure test is carried out on a pressure testing machine in which the upper platen can float up and down freely. The specific test method is to place the sample on the bottom plate of the testing machine, and then move the floating upper platen to pressurize the sample. This pressure test method can make the upper pressure plate close to the upper surface of the sample, measure the pressure-resistant weak parts of the packaging container or package, and find out the defects in the design. However, on the floating pressure testing machine, the edge pressure test and diagonal pressure test cannot be performed on the package.
(3) Compressive strength
The compressive strength required for packaging containers or packages is:
P=k(n-1)W=k(H/h-1)W
In the formula, P——the compressive strength that the packaging container or package needs to have, N;
w —— package weight, N;
k - safety factor;
n —— the maximum number of stacking layers of the package, and n=H/h;
H——The maximum stacking height of packages during storage, mm;
h - the height of the packaging container or package, mm.
The general warehouse stacking height is 3~4m, the stacking height limit for cars is 2.5m, the stacking height limit for trains is 3m, and the stacking height limit for ocean-going cargo ships is 8m. The safety factor is determined according to the specific requirements of product packaging. If there is no specific regulation, h=3 is used for wooden box packaging, and k=2 is used for corrugated box packaging. If the storage period of the corrugated box package is known, then when the storage period is less than 30 days, take k=1.6; when the storage period is within 30 to 100 days, take k=1.65; and when the storage period is greater than 100 days, take k =2.
