Determination of Stiffness of Single-coated Whiteboard with Self-made Simple Stiffness Meter (I)

As the overall quality of domestic OCC waste paper is getting lower and lower (the ratio of KP pulp in boxboard is reduced, and even dyed with waste newspaper pulp, some of the corrugated paperboards are coated with medium and low-grade single coats containing very little KP pulp. White paperboard veneers, etc. Of course, under the premise of satisfying the functional specifications of the products, this change should be called technical progress, otherwise, it should be referred to as shoddy), and the single-coated whiteboard manufacturers are themselves To survive or seek higher profits, you have to make efforts to reduce production costs. The consequence is that the stiffness index of a large proportion of middle and low-end single-coated whiteboards is low, and the wrinkling of low-quantity prints is more or less brought about. This is currently a product on the market. Universal quality issues. All manufacturers are also actively exploring solutions, and it is said that some manufacturers have achieved certain results. The effect is good or bad need to determine the instrument, unfortunately, many manufacturers do not configure the stiffness tester, in determining the stiffness of the cardboard, only rely on seeing, hearing, hand touch (many companies call it feel) Depending on the experience, the stiffness of the board can be determined. This is extremely detrimental to guiding production, storage, sales, and the identification of new process improvements. This is because if the cardboard stiffness function is excessive, the production cost will be increased, and if the stiffness function is insufficient, the user's needs cannot be satisfied. Users are their own food and clothing parents, the paper mill owners will not be unaware of this. When I was engaged in a technical service in the near future, I suffered from a lack of stiffness meter in the paper mill. The boss naturally was not willing to pay for it. However, I was eager to learn the stiffness of the cardboard sample before and after the production test of the additive. Whether or not the indicator has changed or changed in the end, it is necessary to come up with such a simple measurement method. This test method still applies to stiffness test of other paperboard such as cardboard. This tester does not have a transmission part. The test process is intuitive and credible. The self-made price is only a few hundredths of the product stiffness meter.

The stiffness of the cardboard, according to the current national standards, is: under the specified conditions, the moment when bending a specimen of a specified size clamped at one end to an angle of 15 degrees is expressed in mN.m. This is a physical quantity that measures the ability of cardboard to resist deformation. According to the specified conditions, it is necessary to use the Taber stiffness tester specified in the national standard to obtain correct conclusions.

According to the principles of classical mechanics of materials, the components under study are assumed to be continuous, the properties of the components are identical, and all directions have the same performance. Obviously, if the cardboard sample is used as such a component, it does not fully comply with these assumptions. However, we can still use the material mechanics research method to determine the stiffness of the board (bending stiffness for material mechanics).

Material Mechanics Flexural Stiffness = EI 12
Homogeneously bleached cardboard stiffness = KE T×T×T 3 Because I do not know how the website's page represents the nth power of X, so here is expressed as the stiffness of the paperboard theoretically = E(W×T×T× T / 12) / (L × L) 4
In the formula: E - Elastic modulus, is the basic attribute of the material, and has nothing to do with the size of the material;
I--inertia moment, only the geometric amount related to the cardboard sample size, the stiffness of the paperboard sample I = W × T × T × T / 12; 5
Stiffness coefficient of K-homogeneous bleached board;
T─the thickness of the cardboard sample;
W - the width of the paperboard specimen (this method is shown as a longitudinal dimension for single-coated white paperboard);
L - the length of the paperboard sample (this method is shown as a lateral size for single-coated white paperboard).

Although the elastic modulus E is a basic property of the material, it is the most active variable for paperboard, and there are many factors that affect it, such as: raw materials, pulp, pulping, beating, fiber length , Fiber width; ratio of pulp raw materials for each layer; quantitative ratio of different layers of slurry; water quality; sizing; filling; adding; wet copy; pressing; drying; calendering; characteristics of various chemical raw materials; , coating; gloss calendering; temperature of each section of paper machine; paper moisture; atmospheric humidity and so on. Any problems and changes in any link can lead to changes in the elastic modulus and changes in stiffness. Some process changes may bring about the momentum of “diseases come down”. Before symptomatic treatment without increasing the cost of products, it is not easy to criticize illnesses. wire".

There are at least the following ways to determine the stiffness of a cardboard sample:

1. Twist the end of a certain size of the paperboard sample clamped to the end of a certain angle, mN.m;

2. Deflection or angle, in mm or degrees, of a cardboard specimen of a specified size clamped at one end to a certain torque;

3. Horizontally placed cardboard samples clamped at one end, using the paperboard's own quality, the bending angle, degree of the sample produced by gravity;

4. Horizontally placed cardboard samples clamped at one end, using cardboard's own mass, are deflected by the free end of the cardboard due to gravity. mm.

For a stiffness tester that does not have the standard and wants to be able to easily calculate the stiffness value, it is clear that the fourth method is the most convenient and practical. This is like testing the viscosity of liquid chemical materials and coatings. The current standard method uses the rotational viscometer method. The test result is expressed in units of mPa.s; and many companies still use the coated-4 cup method. The unit of indication of the test result is s. Although the apparatus for testing and the unit for expressing the result are different, the application of the -4 cup method has direct guidance for production, use, and sales.

The fourth method is still of direct significance to the mathematical expression of stiffness. It can intuitively explain the influence of the thickness, size, and quantitative (load) of the sample on the stiffness. This is a very recommendable method (can be set as a corporate standard. If the company has already prepared or is preparing to carry out ISO 9000 certification, then the technical indicators of the product standard should be modified: the stiffness indicator is still retained and only its annual or quarterly The technical supervision department takes the form of a sample test; the deflection index of the new product is a must-test item for each batch of products. For the enterprise product standard converted from a national or industrial product standard, the technical indicator lacks one item. Absolutely not, but one more indicator is beyond reproach.
It should be noted here that the fourth test method is not a test method recommended by the national standard. Just as grammage (quantitatively known as “common name”) is not a term that is recommended by the national standard standard, users are using it and producers are also using it. This is true of the few single-coated whiteboard manufacturers that they have experienced. In use, I would like to correct it but I cannot correct it.

The production and assembly of the instrument (due to the author's inconvenience in uploading the drawings, this production method uses text descriptions, such as a geometric problem without graphics, which can be solved and proved by the text description. In the following, dimensions do not indicate the unit All in mm. The production method is not limited to this one, rustic can also be more rustic than this instrument, some of the Western style, you can use the sample holder with upper and lower cleats, optical or photoelectric reading instrument, etc.):

1. Specimen lower plate: a piece of undeformed steel strip prepared with a planed surface, size 260×35×15; if no steel strip, undistorted wooden strip of the same size can be used. The author is made of fiber slats.
2. Pole: height 225, made of φ32 pipe; wood can also be, cross-section size 40 × 40, 45 × 45 will do.
3. Floor plate: Steel plate size 50×50×6. Such as using wood poles, this piece can be free.
4. Base: Wooden board 350×300×25.
5. Side panel: 350×275×10 resin laminated board, wood board, fiber board, plastic board, etc.
6. A 200mm steel ruler with a calibrated size.
7. A circular level (flat sealed small glass bulb filled with water) one.
8. Moving scale plate: 100×10×250 resin laminate or flat grey plastic plate.
9. Large iron clips for office documents should be straight. The clamp length of the iron clip used by the author is 145, the maximum opening distance is 45, and the jaw depth is 30. Can also be used on the plywood instead, slightly different size and the lower plate, the effect is better, but also need to install fastening bolts.
10. Assembly:
The floor plate is welded under the support bar, and the center of the floor plate coincides with the center of the support bar;

One end of the lower plate is welded to the support rod, and the short side of the clamp plate is cut out in the outer diameter of the support rod. The center of the support bar is on the center line of the lower clamp plate in the longitudinal direction;