What is basis weight?
Basis weight of paper is the weight per unit area and is also expressed as grammage. When you buy paper at the shops this measurement is expressed as GSM (grams per square meter). In the print industry for high quality brochures and promotional literature a high GSM usually indicates high quality, thick paper or card. As an example 50 GSM means the weight of one square meter is 50 grams whereas 80GSM means the weight per square metre is 80 grams.
Why is basis weight so essential for paper production?
Basis weight is critical in paper production from quality and production point of view. If the basis weight is not kept constant with an accurate level of control then the consistent quality of the paper will not be good and in turn the paper will be of bad quality.
Why is a basis weight valve so important?
All paper machines have outputs that depend on a specific basis weight which is automatically controlled or manually controlled. The easiest way of controlling basis weight is with a reliable and accurate basis weight valve.
So how exactly does a basis weight valve work?
Basis weight control is a critical part in a paper machine operation. As shown below, the basis weight valve, installed in the stock preparation department in front of the paper machine, controls the consistency of the pulp into the Head Box, dictating the paper weight and quality at the end of the process.
The valve is controlled by a control signal showing the difference between the measured basis
weight of the sheet on the reel at the end of the paper machine and the set-point. Too high
measured basis weight makes the valve close to lower the consistency in the system while
too low basis weight causes the valve to open to higher the consistency before the head box.
Improper control adversely affect downstream process sections such as drying and calendar sections resulting in even more deviation from the requirements. Hence, a quick and highly accurate control solution is essential to meet customers’ specifications.
What is the most suitable valve solution for using as a basis weight valve?
Omega Valves offer the Ramén Ball Sector Valve which offers a reliable and highly accurate control solution which is a customized KS Type valve in material execution 1A with a special ball-shaft connection to avoid backlash, suitable for the basis weight application. The high resolution controllability is enhanced by an Oden backlash-free electric actuator with stepper motor controlled by a microprocessor.
Valve features and benefits:
- Compact, low weight and robust design
- High control rangeability (300:1)
- Enhanced control accuracy with minimum backlash
- Equal percentage characteristic
- Low torque operation
- Self-drained with no hidden cavities and no clogging
- Low maintenance and long lifetime
- Backlash free with control precision of 5.000 steps in 90° valve travel
- Adjustable running time and acceleration
- Compact design with hand wheel or key for manual operation
- Built-in feedback positioning on the main shaft with high accuracy
- Duty cycle 100%
- No need for additional control box or cabinet
- Programmable with Oden Valve Program (OVP)
Where else can you use a ball sector valve in the paper industry?
- Bleached Pulp (see KS-1A)
Bleached fibres suspensions
- Recycled Pulp (see KS-1B)
Recycled fibres dissolved in water
- ClO2 – Chlorine dioxide (see KS Titanium)
- Liquor (see KS-1E)
Black, green and white liquor flow
- Steam (see KS-High Temperature)