Air Cushion Headbox
Index Quality of Head Box
The head box is designed to meet stringent quality standards, ensuring consistent paper formation and superior paper quality. The key quality indices are as follows:
- Cross Base Weight Difference: ≤ ±1.5% (for an appraisal base weight of 200 g/m²)
- Opening Width Difference: Between the upper slice and bottom lip is ≤ 0.1mm
- Surface Roughness Inside the Head Box: ≤ 0.4μm (achieving a mirror surface result)
- Liquid Level Accuracy: ≤ 0.5mm
- Pressure Accuracy Inside the Head Box: ≤ 0.5%
- MD CD Ratio: Variable from 1.25:1 to 1.8:1
Design Parameters
Box Body:
- Airtight attenuation pond with overflow holes on both sides.
- Can be installed with overflow on one or both sides.
- Uses an oblique stock-inlet to reduce stock retention.
- Features PMMA view holes for quick cleaning.
Inlet Taper Manifold:
- Consists of tapered and rectangular manifolds with a pressure balance observing pipe.
- Square taper manifold can be adjusted up and down for easy cleaning.
Distribution Elements:
- Three-step diffuser made of organic glass integral casting.
Holy Roll:
- Double holy roll head box with throat roll and slice roll.
- Roll body holes are in a spiral helix with an opening ratio of 35-39% for the throat roll and 49-52% for the weir plate roll.
- Driven by a worm reduction with a TEFC motor, the gear box can adjust the holy roll speed according to the paper machine’s operating speed.
Upper-lip Regulator:
- Includes whole width regulating device, part micrometric setting, and frame against deformation.
- Up/down regulation range: 0-100mm
- Front/back range: 5-30mm, with scale index.
- Micro-adjuster allows precision adjustments to maintain cross base-weight differences within allowable ranges.
Lower Lip: Fixed.
Injection Spray Pipe: Fixed, made of stainless steel with special stainless steel shower nozzles.
Material of Construction (MOC)
- Inlet Pipe: Stainless steel (304), including companion flange.
- Stepped Hole Diffuser: PMMA.
- Side Wall: Stainless steel plate (304).
- Upper Part: Stainless steel (304).
- Bottom Beam: Stainless steel (316L) with mild steel reinforcing ribs.
- Upper-lip Frame: Stainless steel (304).
- Vertical Small Lip Plate: Stainless steel (316L).
- Holy Roll: Stainless seamless steel tube (304).
- Bottom Lip: Stainless steel (304).
- Micro-adjuster: Cast aluminum.
Head Box Controlling System
A. Controlling Parameters:
- General pressure, liquid level, stock speed/wire speed ratio.
- Uses pressure transmitter to test general pressure head and differential-pressure transmitter to test stock level.
- Computer control signals (4-20mA DC) regulate the pulp-distributing fan pump frequency converter and roots blower to maintain stable stock jet speed.
B. PIC – General Pressure Head Control:
- EJA flange differential pressure transmitter.
- PLC regulating loop with AI & AO interface circuit.
- Pulp distributing fan pump VFD (supplied by customer).
C. LIC – Level Control:
- EJA flange-type level transmitters.
- PLC regulating loop with AI-AO interface circuit.
- Roots blower.
D. Control Accuracy:
- Level control within ±1mm.
- General pressure fluctuation control within ±0.5%.
Advantages
- High dewatering efficiency.
- Space-saving design.
- Improved paper symmetry.
- Enhanced web strength and reduced/eliminated porosity.
- Better fiber formation in paper sheets.
- Improved dewatering capacity monitoring.
This design ensures high-quality paper production, meeting stringent industry standards and offering flexibility for various paper grades and production requirements.