Basis Weight of paper

The basis weight or grammage is basic physical property of paper and paperboard. The Basis weight of paper is calculating by the weight per unit area. It is mainly expressed as GSM (grams per square meter) and pounds per ream (500 sheets) of a specific size. It is also expressed in kg/m2, pounds per 1000 sq. ft etc. Grammage are used in non-metric countries. There are many grade of paper are found in market such as printing 80 GSM, 60 GSM, 70 GSM etc. 80 GSM means, the weight of one square meter is 80 grams.

Basis weight is very important for paper production, productivity and quality of paper. If the basis weight fluctuates then it will be hamper the quality of the paper such as bad formation, uneven drying and calendaring, calendar cutting, bad mother roll development, blackish etc. Moreover cutter machine have to face problem for bad mother roll development. So it is very important for a papermaker to controlling basis weight.

Every paper machine is designed depends on specific range of basis weight. Some paper machine has auto controlling system. On the other hand some paper machine has manual control system. You can control basis weight by speed adjustment, valve control or by slice adjustment. Papermakers always make every effort to obtain all desired properties of paper with minimum probable basis weight.

Generally papermakers check the basis weight after every half an hour during paper production. It may be weight with moisture or without moisture. Without moisture is a standard system. For this purpose the paper sheet is drying into an oven at 105ºC temperature.

Production of a paper machine is depends on speed of the machine, deckle and basis weight. If the basis weight is 80 GSM, deckle 3.00 m and the paper machine speed is 200 m/min then the production would be 80*3.00*200g per minute.

Normally ream weight is calculated for commercial purpose. It is given a specific size and it’s weight in kg or pounds for a ream. For example 23’×36′ = 36 pounds. Here 23’×36′ is a paper size and the ream weight is 36 pounds. Off course it is related to basis weight.

Explanation of the size 23’×36′ = 36 pounds:
Area of a sheet = 23’×36′ = 828 ins2 ≈ 5341.9 cm2
Area of a ream or 500 sheet = (5341.9*500) cm2 = 2670950 cm2 = 267.095 m2
Total ream weight = 36 pounds ≈ 16290 g
Hence, Basis weight of the paper = 16290/267.095 ≈ 61 g/m2