Drying Flashcards
(15 cards)
What is the purpose of a dryer fabric?
- to press the sheet against the dryer cylinder
- sheet transfer
- sheet drying
How much water is removed in the dryer section vs how much energy is consumed?
1% water removed
65% energy consumed
What are the design requirements of dryer fabrics?
- correct air permeability - too high = bad runability, too low = poor drying
- suitable raw materials
- stable and flexible structure
- optimal surface contact
- thickness and strength of seam
- thickness of fabric
- sufficient edge wear margin
- sufficient friction and grip
- soiling - suitable structure and material used to avoid contamination
What are the requirements for dryer fabric seams?
- easy to seam
- strong and durable
- non marking structure
What are the main raw materials used for dryer fabrics?
- PET = economic, strong, stable, satisfactory alkaline and hydrolysis resistance
- PPS = expensive, low loop elasticity, sensitive to cleaning heads, excellent alkaline and hydrolysis resistance
What speed, tension, and temperature do you need for maximum heat exchange?
Low speed, high tension, high temperature
What are the benefits of double warp fabrics?
- less fabric consumption
- longer life (50% higher wear potential)
- increased safety
- 25% higher fabric strength
What is the most important parameter for dryer fabrics?
Permeability
What are the two types of dryer fabric design?
Woven and spiral
What are the pros and cons of spiral dryer fabrics?
Pros
- better wrinkling resistance
- easier to seam
- higher seam strength
- better wear resistance
Cons:
- thicker and heavier
- more expensive
- if edge wears, then a more serious problem
What are the pros and cons of woven fabrics?
Pros:
- lower weight and thinner
- strong edges
- better aerodynamics
- more economic
Cons:
- higher wrinkling risk
What are drivelines used for?
They are silicone strips at the edge of the paper side to increase grip to the cylinders to prevent fabric slipping and wearing.
What are the negative effects of dryer fabric contamination?
- paper quality issues = marking, particles in sheet
- runnability issues = sheet breaks, lower vacuums
- poor heat transfer = increased energy costs, worse efficiency
- poor sheet moisture profile
- higher fabric costs = loss in permeability = fabric change
How does hydrolysis affect the dryer fabric?
The edges hydrolyse quicker as they are in constant contact with the cylinder (I.e. heat and humidity) compared to the sheet area which is in contact with the paper limiting the temperature.
What are the benefits of impingement drying?
- most effective
- best for high speeds
- fabrics require PPS edges
