Forming Flashcards
(31 cards)
What materials are commonly used in forming fabrics?
Mainly polyester but sometimes polyamides too.
Compare the water absorptiveness of polyester and polyamide
Polyamides have 10x the water absorptiveness of polyesters.
What are the main requirements for forming fabrics?
- good dewatering properties
- predictable and long fabric life
- former cleanliness
- low calliper & void volume
- low sheet dry content
- controlled paper profiles
- low power consumption
What are the important requirements for forming fabrics manufacturing packaging grades?
- z-directional distribution
- sheet formation
- sheet strength properties
- sheet profiles
What is SSB and how many MD and CD yarns are typical for this type?
Sheet Support Binder
2 MD yarns
4-5 CD yarns
What are the benefits of SSB compared to Double Layer or Triple Layer?
- finer fabric surface -> more fibre support points
- less fabric marking
- better printability
- higher CD bending stiffness
- even paper profiles
- longer running times (higher wear potential)
- higher retention -> higher smoothness
What are the functions of binding yarns in SSB’s?
- to bind the paper and wear side layers together
- to make part of the paper side layer, which gives support to the paper sheet
What is the most common type of forming fabric currently?
SSB
Name some technical specification terms for forming fabrics
- yarn count = number of MD or CD yarns in 1cm
- T count = number of MD + CD yarns in 1 cm)
- SP count = number of yarn knuckles in 1 square cm
- Fibre Support Index (FSI)
- Drainage Index (DI)
- Air permeability
- Surface open area %
- Caliper and wear margin
- Polishing (where they lightly grind the paper side to improve smoothness of fabric)
- Void volume
What is Weft Ratio?
The ratio of CD (weft) yarns on the paper side vs the wear side.
What are the pros and cons of a 2:1 weft ratio?
Pros:
- more CD yarns on paper side = better fibre support, higher retention
Cons:
- less CD yarns on wear side = lower wear potential
What are typical challenges of forming fabrics in hybrid formers?
- drainage = if web is too dry going into top unit, then formation is risked. If web is too wet, then crushing can occur.
- paper side of top ply fabric should not be too fine to avoid web stealing
- ply bond = you need the right consistencies going into ply join
- low internal sheet bonds = too high initial dewatering can weaken internal sheet bond strength
What are typical challenges for forming fabrics for gap formers?
- too fast drainage = poor formation, low internal bond, sheet sealing (& low dry content)
- limited drainage = crushing, low dry content
- higher machine speeds = misting (counteract with thin fabric), dirtiness and run ability issues (avoid by improving retention)
What are the four former categories?
- OptiFormer Gap for container board
- OptiFormer Gap with shoe blade
- OptiFormer Hybrid with shoe blade
- OptiFormer Multi
Name the production steps for forming fabric manufacturing
- Warping
- Weaving
- Inspection
- Heat Setting
- Relaxation
- Cutting
- Seaming
- 2nd heat setting & Finishing
- Packing and shipping
What happens to the yarns during heat setting of former fabrics?
The MD yarns stretch and the CD yarns narrow under controlled conditions
What is the air permeance and caliper like at the seam in forming fabrics?
Typically the seam is denser (I.e. lower permeance) and with a lower caliper.
What is the difference between normal and polarised forming SSB fabrics?
Normal = straight through drainage
Polarised = offset wear side yarns
What are the benefits of polarised forming fabrics?
- initial drainage is controlled
- higher dry content
- improved former cleanliness
- improved retention
- improved formation
- longer fabric life
Why do forming fabrics need to be cleaned?
- less dirt accumulation and sheet breaks
- less fabric damage
- to keep the fabric open for optimum drainage
What materials can be used for HP shower nozzles?
Conventional steel nozzles - not recommended due to easy wearing
Ceramic - poor squirt quality
State of the art ruby nozzles - high wear resistance
What effect does diameter have on the water consumption and kinetic energy of HP nozzles?
Lower diameter = less water consumption but also less jet kinetic energy
At what distance is optimum for forming HP cleaning nozzles?
Medium distance, when droplets just start to come off from the jet
What can occur to the forming fabric if the HP shower jet is poor quality or the pressure is too high?
- damaged fabric
- yarns become fibrillated by the HP showers
