Reading the "tightness" of corrugated paper

Base paper is the basic raw material for making corrugated boxes. How the quality of raw materials directly affects the quality of corrugated boxes. In the past, people often paid attention to the quality of the base paper only, such as quantitative, ring pressure index, folding resistance, moisture content, etc., and seldom paid attention to its “tightness”. As everyone knows, "tightness" is an important indicator of the quality of base paper.

The “tightness” of the base paper, as the name implies, is the degree to which its fiber structure becomes firm by the processing force during the manufacturing process. The “tightness” is large, the stiffness of the paper is good, and the carton puncture strength, breakage resistance, folding resistance, and compressive strength made by the carton are high; the “tightness” is small, the stiffness of the paper is poor, and the cardboard box is made to be punctured. The strength, bursting resistance, folding resistance, and compressive strength are low. Therefore, "tightness" has a dominant effect on various strength indicators. Therefore, it is an important quality indicator of the base paper.

The "tightness" of the base paper is directly related to the production equipment and technology level. Modern large paper mills are generally equipped with long wire paper machines. The "tightness" of paper produced by it is unmatched by small paper mills. Corrugated cartons used plain paper and should be made of paper with “toughness”. This is self-evident.

The "tightness" test of the base paper is calculated based on the same amount and thickness of the sample. According to the national standard GBl51-79, the formula is:

D2 W/d X 1000 formula:

D a raw paper tightness (g/cm3)
W raw paper quantitative (g/m2)
d a base paper thickness (mm)

For example, a 200g/m2 C-class linerboard produced by a long wire machine has a thickness of 0.26mm and its "tightness" is calculated:

D=200/0.26 X 1000
= 0.77 (g/cm3)

Its "tightness" value is higher than the "stiffness" value of the A-class linerboard specified by the national standard GBl3024-91. Carton made with it, the quality indicators have reached excellent standards.

The interpretation and use of "tightness". Here, based on the definition and unit of “tightness”, a formula is deducted to calculate the remaining weight of the web. Whenever the tile production is completed, the remaining weight of the web must be registered and returned to the warehouse. For the remaining weight of the paper, first, the workers estimate according to experience, and the second is to pound one by one. The former method has a larger error, and the latter method is more troublesome. If a formula is deduced based on the definition and unit of “tightness” and used to calculate the weight of the remaining paper, it is relatively simple and accurate. The calculation step is divided into two steps:

First, calculate the "stiffness value" of a web (g/cm3):

D=C÷(R2丌一80)S. . . . (1)

D. The tightness value of a web C The weight of a web S The width of a web R2,rr The end (circle) area of ​​a web 80 A constant (web core area)

Second, calculate the remaining weight of the web:

C + = DX (R2 a 80) S. . . . (2)

C remaining weight of a roll of paper

D. "The tightness value" of a web

(R2丌80) End (circle) area of ​​the remaining portion of a web

S-web width.

Example: A web width of 1655mm, factory calibration weight. 1106 kg, measuring the diameter of one end of the web is 1070mm, find the web g/cm3 (grams per cubic centimeter). Calculate D using formula (1)

D=1106000÷(53.52丌165.5)
=0.75(g/cm3)

The end of the production of the web, measuring the diameter of the remaining part of the round end of 530mm, seeking the remaining weight (kg):

C I = 0.75 (26.5 2丌-80) 165.5
=264kg

Due to the paper produced by each paper mill, its "tightness value" is basically stable. Therefore, in the calculation, the "tightness value" of the same paper mill does not have to be counted each time. It is only necessary to substitute it for formula (2).


(Ren Yingyong)

China Packaging News