It is vital for paper & packaging manufacturer to understand the purpose and standard operating procedure of Cobb sizing tester for quality assessment of paper or corrugated fibreboards.
Purpose of Cobb Sizing Test
Cobb sizing tester determines the amount of water or any liquid absorbed by the paper, corrugated fibreboard, and paperboard in a given period of time under some conditions. Water absorptiveness is a function of various characteristics of paper or board such as porosity, sizing, etc. The high Cobb value of the papers and cardboards indicates the ability of the materials to retain or absorb the moisture. Depending upon the application of the board, the Cobb value needs to be maintained. The test includes examining of the quantity of water absorbed in a particular period of time by non-bibulous paper having a thickness of 0.1 mm.
Standard Operating Procedure for Cobb Sizing Tester
Presto Stantest manufactures the best quality of Cobb Sizing Tester as per the standard methods – TAPPI – T 441 and ISO – 1060 (Part 1) – 1966. The standard operating procedure of Presto’s Cobb Sizing Tester as per the mentioned standards is:
1. A sample of paperboard or corrugated box more than the edges of the fixture is taken. Now weigh it to nearest 0.1 gram.
2. Now place a cork sheet on the metal plate and then place the weighed specimen on it and clamp the specimen firmly to prevent any kind of leakage between the sample and the ring.
3. To ensure the leak-free clamping between the ring and the upper surface of the sample during the test, use soft elastic and non-absorbent gasket of same internal dimension as of the ring.
4. Now pour water into the fixture as per the requirement of the sample (reference 10mm marking & 25mm. marking) for 100ml & 250ml respectively and start your stopwatch immediately.
5. Let the sample inside the cylindrical ring for 120 seconds (in case of Paper) and 300 seconds (in case of corrugated boards)
6. Reject the samples that show any sign of spillage or leakage.
7. If any liquid is passed through the sheet to the rubber mat, the test is not acceptable and will be rejected.
8. The standards time period of 120 seconds on a single sheet using 10 mL of water to wet is 1 cm deep. (Time of the test can also be adjusted as per the nature of the paper).
9. Once the buzzer of the stopwatch buzz, take out the sample from the cylinder.
10. Now with the help of hand roller drain out the excess water from the sample without exerting any pressure and rotating the roller one time forward and one-time backward direction.
11. On corrugated boards, the roller is applied in the direction parallel to flutes of the corrugated board.
12. Now again weigh the sample.
Formula to Calculate COBB value
Cobb Value = Weight of the sample after testing – Weight of the sample before testing
It is very easy to operate Presto’s Cobb Sizing by following above mentioned, operating procedure.