Green Paper Bonding Technology (3)
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Corrugated board performance test items include edge pressure strength, burst strength, puncture strength, bond strength. The performance test also requires that the pretreatment be performed first. The pretreatment method is to pretreat for 24 hours at a temperature of 23° C.±2° C. and a relative humidity of 50%±5%, and the test is required under this condition.
(I) Side pressure strength
For a specimen of a certain width, the pressure that can withstand the unit length is called the side pressure strength and the unit is N/M. The side pressure strength referred to by the national standard refers to the vertical side pressure strength, that is, the ability of the corrugated cardboard to withstand the pressure in the direction parallel to the corrugation. In the process of transportation, storage and transportation, the carton requires a certain resistance to pressure. The compressive strength of the carton is closely related to the edge pressure of the corrugated cardboard. The size of the side pressure strength of the sample is 25(±0.5)×100(±0.5)mm, and the direction of the corrugation is Short side.
The principle of side pressure strength test is to put the sample in the middle of the upper and lower two pressure plates of the test instrument (generally using the electronic compressor) so that the direction of the corrugation is perpendicular to the pressure plate. The pressure plate is controlled by the mechanical transmission system and moves down at a constant speed and approaches the sample. The sample is subjected to a load that increases at a uniform rate. When the load reaches a certain value, the sample is crushed. The value at this time is the edge pressure of the sample.
The reasons that affect the strength of corrugated board side pressure are summed up in the following points:
The base paper's ring pressure strength, paperboard moisture content, bonding quality, corrugating forming conditions, corrugation height, specimen shape error and dimensional accuracy, and notch conditions.
(B) Adhesive strength
The adhesive strength of paperboard is also called peel strength. The test value refers to the fastness of the adhesiveness of the corrugated paperboard surface and the paper in the certain length. The test principle is to use two rows of metal needles to insert between the crepe paper and the paper. The needle attachment with the sample is then subjected to pressure and allowed to move relatively until it is separated. The test instrument is also an electronic compressor.
The factors that affect the bond strength are: adhesive problems, paperboard moisture content, sizing, and some paper-related indicators. (such as sizing degree, smoothness, surface water absorption and water absorption speed, stretching rate, tightness, etc.) Adhesive strength of corrugated cardboard is important, but strong bonding may not necessarily be good because excessive adhesive strength is often used in adhesives. Excessive, large sizing, high corrugated moisture content, affect the shape of corrugated paper, will also reduce the compressive strength of the carton.
(c) Bursting degree
Corrugated board under certain experimental conditions, in a certain area of ​​corrugated board pressure, so that the corrugated board is stretched to a certain extent to rupture, the pressure at this time is the corrugated board burst strength, which expresses the resistance of corrugated board External pressure capability.
The burst strength is determined by the burst strength of the base paper used, and is generally the sum of the burst strength of the surface, the inside, and the core.
The instrument for testing the burst strength of the corrugated board is the same as that of the test board.
The burst strength measurement results are affected by the pressure rate. In addition, the pressure of the clamped sample, whether there are air bubbles in the hydraulic system, the sharpness of the edge of the small hole, and the nature of the film have a great influence on the measurement result.
(d) Puncture strength
Corrugated cardboard puncture strength refers to the work required to penetrate a paperboard with a specific shape of a pyramid under certain experimental conditions (ie, the energy required for puncturing, stretching, tearing, and bending to form a hole). Because corrugated boxes are used in everyday use, they are often damaged by sudden impact by a sharp object. In order to simulate the damage of the specimen, many kinds of test instruments have been designed. At present, the Ninety-type puncture strength tester is commonly used. In the test, an equilateral triangle is used, with an edge length of 60 mm and a height of 25±0.7 mm. The triangle cone, driven by the pendulum to move the triangle cone, breaks the energy lost when corrugated cardboard is punched, which is equivalent to the resistance of the three edges of the triangular cone to tear the corrugated cardboard. The pendulum initially raises the angle and breaks the cardboard. The difference in the angle after the swing is equivalent to the amount lost by the pendulum.
The difference between the puncture strength and the burst strength is that the burst strength is to apply the pressure evenly to break the sample, and the physical strength is the static strength, and the puncture strength is to suddenly apply an impact force to the corrugated cardboard to puncture it. Dynamic strength.
The puncture strength significantly decreases with the degree of squashing.
(e) Thickness
Thickness refers to the vertical distance between two surfaces of corrugated cardboard under the pressure of a certain unit area. Thickness is one of the most basic characteristics of corrugated board. The thickness directly affects the various properties of the corrugated board such as edge pressure, puncture, and compression.
The thickness test is generally conducted by contact measurement because the basic material of the corrugated box is made of paperboard. The paper is a kind of compressible material with a loose structure, and its surface is uneven, with uneven thickness everywhere, and it needs to be applied when measuring. A certain pressure, and measure its thickness under a certain area. The thickness of the measurement area is 10±0.2cm2, and the measurement pressure is 20±0.5kPa. This is different from a paper thickness gauge.
(6) Water content
Corrugated board moisture content directly affects its various performance indicators. As the water content increased, side pressure strength and burst strength decreased significantly. Moisture content assays include rapid moisture determination and oven determination. The former is to use a rapid moisture meter to measure 4 points in different parts of each sample box, and finally find the average of 5 sample boxes. When using a quick moisture analyzer, the instrument should be calibrated in advance. The oven test method is to weigh about 50g samples (accurate to _0.001g) from different parts of each sample box and tear them into small flakes in a weighing bottle (or aluminum box) of known mass, at 100~. In an oven at 105°C, dry to constant weight. Each weighing should be accurate to 0.001g.
The inspection regulations stipulate that the moisture content of corrugated boxes for export goods ranges from 8% to 16%.