Layer gaps

Hello,
I built a mendelmax myself and now I have still a problem with the print.
After months of "trial and error" I was able to eliminate a lot of errors.
But now....
My problem is that I have layer gaps in large objects.
See attached pictures.
Can someone give me a hint?

I print in ABS with 240C and Bedtemp of 120C
0.4 Nozzle
Layer High 0.25
Shell thickness 1 mm
Print Speed 50mm/s

Retraction Speed 40 mm/s

With CURA 13.12


Bild 2

Edited 1 time(s). Last edit at 12/25/2013 07:13AM by Dusi.

I don't know what the root cause is of your delamination,
but I have a list of some material parameters for you to consider to help you debug.

You're at the upper limit of the extrusion, and substrate/bed temperatures.

Higher extrusion, and Substrate/Bed temperatures = more shrinkage = greater force to delaminate marginal fusion welds.

Substrate/Bed temp: 120C is above the glass transition temperature, that will increase the forces to delaminate.

The glass transition temperature (Tg), is the temperature at which the amorphous
phase of the polymer is converted between rubbery and glassy states.

The following physical properties undergo a drastic change at the glass transition temperature of any polymer:
a) hardness
b) volume
c) modulus (Young’s module)
d) percent elongation-to-break
[web.missouri.edu]


ABS, (Acrylonitrile butadiene styrene, Type: extruded):

Drying Temperature:
Range: 70°C to 93.3°C, (158ºF to 200ºF)
Average: 80.9°C, (178ºF ).

Dry time:
Range: 2 to 4 hours.
Average: 3.2 hours.

Glass-transition temp:
Range: 108°C to 109°C.
Average: 108°C, (226.4ºF ).
Wikipedia: 105°C, (221ºF ).

Begin testing around this temp:
Substrate/bed temperature: 105°C, (221ºF ).
Enclosure temperature: 105°C, (221ºF ).

Reprap wiki suggest a extrude temperature range of:
210 C ~ 240 C.
[reprap.org]


A poor-mans enclosure can be fabricated with a Nylon oven bag.

Sizes Oven Bags:
Large size (16"x17 ½").
Turkey size (19"x23 1/2").

Material of Oven Bags:
Never exceed 400 degrees F.
Melt Points up to 493 degrees F.

Hi A2,
i will try it with 105C (Bedtemp) ans 235C (ExtruderTemp)
Thanks a lot