VESTAMID® compounds can be processed on conventional three-zone screws with a minimum length of 24 D to produce profiles, tubing (including multilayer tubing), secondary fiber optic jacketing, cable sheathing, films, and sheets. Other screw designs, such as barrier screws, can also give good processing results.
- Conventional three zone screw with a length of ≥ 24 D
- Flight depth ratio ranging from 2.5 to 3.5 : 1
- Suitable ratios between feeding / compression / metering zone: 2:1:3, 2:2:2, 1:1:1
- Radial clearance between screw and barrel: 0.1 - 0.2 mm
- Mixing and shear elements may be useful to increase the melt homogeneity (e.g. processing films from resins colored with pigment concentrates.
Not necessary for the processing of virgin material, recommended only as support for screen packs, e.g. when processing regrind
- Recommended when processing regrind or if tolerances have to be kept in an absolute narrow range (e.g. for barrier layers in multilayer tubing)
- In general not required with properly designed screw
- Cooling of the feeding section is mostly required.
- General temperature setting strongly depends on resin to be processed and type of extrudate (tube, film, coating), thus a general recommendation can not be given. Temperatures in first heating zone should be set app. 20 K above melting point of resin. Increasing temperature profile from first heating zone to tip of extruder. It might be of advantage to reduce the temperature setting in the adapter and die slightly to increase stiffness of melt leaving the die (e.g. when manufacturing tubing).
- Optimizing temperature setting by monitoring the temperatures of the heating zones, the melt temperature and the consistency of the melt leaving the die: high pressure build-up and a dull surface of the melt leaving the die: increase temperature profile; melt with a low stability: decrease temperature profile
In case of large discrepancies between temperature setting and measured temperature the screw design might not be suitable for processing VESTAMID®. Temperature setting of heating zones should always be >10 K above melting point of resins.
- Raise temperature of all heater bands for about 20 °C and purge by using polypropylene (PP with MFI 230/5 = 12 g/10 min) (MFI 230/5 ≈ 12 g/10 min)
- Dissemble the die
- Continue to purge extruder with PP and reduce temperature to about 170 °C
- At this temperature replace PP by a commercially available cleaning mixture. If you would like a recommendation, please contact us.
- Release the screw out from extruder barrel and remove plastic residues
- Remove plastic residues from the die for polishing
Pulsation of melt caused by the extruder
- Insufficient cooling of feeding section
- Insufficient lubrication of pellets
- Shape of pellets inhomogeneous (e.g. when processing regrind)
- Pressure build-up at die too low
- Improper design of feeding section (grooved/smooth)
- Improper screw design
- Problems with motor/gear box
Note: Pulsation of melt can be caused by the downstream equipment as well, e.g. see trouble shooting when processing tubing.
Inconsistencies in temperature measurement
- Dirt in bore of thermocouple
- Tip of thermocouple not in contact with metal surface
- Problems with thermocouple and/or recording device
Typical tubing outer diameters are in the range of 6 and 16 mm. For information concerning larger diameters please contact us.
- For monowall tubing conventional extrusion dies (mandrel carried by a breaker plate or by spiders) are sufficient.
- Land length between 20 and 50mm
- Draw down ratio (DDR = mean diameter of die gap divided by mean diameter of tubing): 2:1 to 1.7:1
- Wall thickness ratio (WTR = die gap width divided by tubing wall thickness: (almost) equal to DDR.
- Extrusion line should be equipped with an air hood located close to the die to take off vapors evaporating from melt leaving the die.
- Calibration by disk or perforated tube sizing
- Inlet of sizing should be rounded, r = 5 to 6 mm
- Inlet of sizing must be covered by a well balanced water film to pre-quench the melt entering the sizing. This will avoid the sticking of melt on metal surface of sizing. Sandblasting of front plate and inlet of sizing helps to evenly distribute water film around the tubing.
- Tolerances in water flow must be kept to a minimum, e.g. variation in pressure level of water supply can be eliminated by using a water reservoir generating constant static pressure.
- Inner diameter of sizing 3 to 6% larger than nominal tubing outer diameter.
- Vacuum level in the range of 0.1 to 0.3 bar. Vacuum should be used only for fine adjustment of outer diameter. For example: If a higher vacuum level is needed to achieve the nominal tubing outer diameter, another sizing with a slightly higher diameter should be used.
Smooth belt type puller is preferable over block type (caterpillar) puller.
- Applied to improve adhesion of printing and mechanical properties.
- Positioning of burners must be circumference to the tubing, not only on one side of the tubing.
- Additional quenching bath behind flame treatment is recommended.
Many problems from the processing of PA12 tubing are caused by an improper water flow at the sizing inlet. Thus, the adjustment of a proper water flow is of major importance.
- Dull surface: Melt temperature too low; Improper water flow at sizing inlet; Contamination of resin with incompatible thermoplastics
- Grooves and stripes on outer surface: Hole in guiding discs of vacuum tank too small; Improper water flow at sizing inlet, Die damaged; Sizing damaged; Contamination of resin with incompatible thermoplastics
- Bubbles on tubing surface: Too high moisture content of resin; Vacuum too high; S-water splashing on melt due to too large water flow at sizing inlet; Water drops on tubing surface before flame treatment; Large air bubbles on tubing surface in vacuum tank
- Wave structure on outer or inner surface of tubing: Vibration of components of extrusion line (e.g. cutter, puller); Hole in guiding discs to small; Line speed too small when using a disk type sizing
- Uneven tubing surface: Draw down ratio (wall thickness ratio) too small or too high; Water in vacuum tank sloshing
- Ovale tubing: Vacuum too small; Distance between belts of puller too small; Tube too hot when winded to coil;
- Uneven wall thickness: Improper centring of die; Uneven water flow at sizing inlet;
- Twisting of tubing: Uneven water flow at sizing inlet; Improper alignment of tubing and pulled belt
- Curvature of tubing: Inhomogeneous wall thickness distribution; Uneven water flow at sizing inlet; Flame treatment from one side only; Offset between longitudinal axis of die and sizing; Too hot when winded to coil
Mechanical performance of tubing
- Ultimate elongation too low: Vacuum level to high; Sharp edges in sizing; Radius of sizing inlet too small; Improper water flow at sizing inlet; Melt temperature too low; Flaming from one side only (or no flaming used at all); Offset between longitudinal axis of die and sizing; Contamination of resin with, e.g. other thermoplastics, dirt, dust etc.; Degradation of resin
- Insufficient cold impact resistance: Contamination of resin with, e.g. other thermoplastics, dirt, dust etc.; Melt temperature too low
- Splitting of tubing: Melt temperature too low; Contamination in weld lines
- Maximum line speed up to 2000 m/min
- Sleeve coating die
- Draw down ratio (DDR = cross section of die divided by cross section of coating): 15 to 20:1
- Vacuum level app.: 0.2 bar
- Calibration unit: Apply cold water cooling
- Sleeve coating die
- Draw down ratio (DDR = cross section of die divided by cross section of tube): 9:1 at extrusion speeds > 200 m/min: 12:1 to 15:1
- Draw ratio balance (DBR = ratio of die to mandrel diameter divided by ratio of outer to inner diameter of tubing): 1:1 at extrusion speeds > 200 m/min: 1.2 to 1.3
- Calibration unit: Apply cold water cooling
Roll: Temperature setting in the range of 45 - 110°C
Thermoforming of PA12 tubing
Data listed are meant only for monowall tubing, with multilayer tubing thermoforming conditions might be different.
- Polyethylene Glycol: forming temperature: 150 to 155°C, forming time: < 5 min
- Hot air: forming temperature: 150 to 170°C, forming time: 15 to 30 min
- Steam: forming temperature: 130 to 145°C (3 to 5 bar pressure), forming time: < 1 min
- Other thermoforming procedures (e.g. infrared radiation, high frequency) are possible.