Back Pressure ( still )

So back pressure still seems to be a problem.


so much so i blew out the hot end had to torch the brass to clean it and retighten it down.


trying to fix this i have

1. Calibrated the excruder motor ( per reprap guide )

2. slowed down the printing speed.

3. Limited the layer height of 0.2mm ( nozzle is .4)

4. tested the excruder ( told it to spit out 20mm of filiment and it did measured with a digi mic) with the hotend not attached.

5. told slic3r that the filiment was 3.5mm when its 3 hoping that would work - fail

6. Black PLA i have tried printing from 185 to 210 doesnt seem to matter. except when it got to hot it caused a leak and had to be cleaned.


So what am i missing here. All parts seem to be functioning as intended ?

When you say back pressure, do you mean that the nozzle just isn't extruding filament while printing and the extruder is failing to push the filament down?

Have you got a fan cooling down the cold end of the nozzle?

Is this with your DIY Tech Shop hot end? Where did you buy your PLA from? Have you tried any other PLA? Cheap black PLA filament may have significant quality issues, including contaminants.

It tries to step and failed intermittently. Ya I should try new filiment. Even failing still plastic comes out. Thinking maybe it's not .4 after all hmm need to check that

Yea the diy one.

Ill put a fan on it as well.

Try a different colour first. I know black ABS is full of all sorts of crap (regrinds is the proper word).
PLA is probably the same.

Ok so recommendations for where i should get a good role of filiment ?

Doug, I have the same hot end. I have printed 1/2 a roll of my black from www.pushplastic.com and not had a single clog. My first hot end leaked as well like yours, but after DIY replaced the hot end, it has not leaked. pushplastic claims 100% virgin, no regrind. The filament is working great for me.

Here is a pic, I just printed both of these in black on the same platter, 3.5 hour print, no leaking and no clogs.
[www.mediafire.com][1].jpg

I do not own stock nor am I anyway connected to pushplastic, I just bought their filament and seems to be working good.

Quote
Doug1
Ok so recommendations for where i should get a good role of filiment ?

For nozzle testing, I always use natural ABS or natural PLA; less liklihood of contaminents.

You could try getting samples (a few feet might be enough) from the manufacturers for evaluation purposes, but any natural filament should be good enough to get you going. Black filament has always given me the most problems, except for the Tuxedo Black from Printrbot.

Filament quality still seems to be all over the place. If I have clogging issues, I just go to a bigger nozzle; that usually works.

Contaminates is what clog's a nozzle.
The reason black plastic has a higher probability of clogging a nozzle is because it's easier to
hide contaminates such as (dirty resin, toxic waste by products) in the black resin.

Regrind Contamination
It has been my experience that the biggest problem with regrind is not excessive heat history but contamination, both foreign plastic and foreign materials. How many of us have seen production stop due to a plugged hot tip. This has forced many to use nozzle filters to prevent downtime and the significant cost of cleaning out the hot runner system. A nozzle filter creates a pressure drop and further reduces process robustness. This is the reason why you can save money by running only virgin in hot runner tools and use the regrind for cold runner tools. Not many have this luxury but when possible it is a winning strategy.

Further if there is contamination how do you purge the resin system? The only sure way is to sell all of your regrind and start over. There is no way to purge the resin stream of contamination with 20% regrind.
[articles.ides.com]

Compounding
Compounding consists of preparing plastic formulations by mixing or/and blending polymers and additives in a molten state.
[en.wikipedia.org]

Fillers
Lower the consumption of more expensive binder material or to better some properties of the mixtured material.
Modified and reinforced plastics provide increased mechanical performance and allow plastics to be
used to solve the unique and challenging material requirements.

carbon black
glass fibers
carbon fibers
mica
talc
gypsum
calcium carbonate (limestone)
kaolin (clay)
alumina trihydrate
[en.wikipedia.org])
[www.plasticmaterials.net]

Regrind
Regrind materials include ground or chopped flash, runners, sprues and non-contaminated rejected parts that are produced in-house by the molder in initial molding processes. These materials are crushed to smaller size and recycled with virgin materials. Regrind excludes materials that are chemically reconstituted or repolymerized, or regrind bought in bulk and used by another company. It only applies to post-industrial (pre-consumer) waste from the same manufacturer.
[www.ul.com]


Degraded Polymer in the Regrind
Most consider that using up to 25% regrind does not significantly compromise virgin resin properties. Unfortunately this statement can get you in trouble. For example: Resins such as nylon, polycarbonate, poly(butadieneterephthalate) (PBT), poly(ethyleneterephthalate) (PET), etc, if not dried properly before initial processing will undergo a chemical reaction, called hydrolysis, in the barrel of the molding machine which causes significant lowering of the polymer chain length. This is not visible to the naked eye; parts look good but have lower physical or chemical properties. Often the problem is not found until the parts are in service, which can be a costly issue. Blending regrind of this quality into virgin at 25% levels may significantly alter subsequent part performance and function. Further each processing history may influence the virgins additive levels and if fiber filled the length of the fibers. Processing grinds up the fibers to shorter lengths. Then there is the problem with processing the virgin at higher than recommended temperatures, a sure way to accelerate polymer degradation. These are only a sample of the potential problems of using regrind and all of them can narrow the processing window.

Temperature or heat history is commonly believed to be the biggest issue in polymer degradation. However a study done by Sue Janicki et al. Antec 1992 pgs 1201-1204; "The Material Cascade: An Alternative Form of Regrind Utilization" (pdf) provides data showing excellent retention of physical properties through five passes through an injection molding machine. The study included High Impact Polystyrene (HIPS), Ignition Resistant HIPS and Polycarbonate (PC). This indicates that if treated properly in processing that many resins can hold their physical properties for a short number of regrind passes.
[articles.ides.com]

A2: you have provided a lot of interesting information there.

I think if the plastic is being used for injection molding, making low tec items like plastic buckets, etc., the contamination is less critical. For us home printers that use filament the spec is critical. I have never seen manufacturers state 100% virgin in the spec.

@dave3d:

I've designed plastic products that were injection molded, extruded, thermoformed, cast, dipped, and foamed, maybe more, and in every case I've used 100% virgin plastic, and I specified zero regrind or blended with fillers, etc.

It was frustrating that I couldn't use compounded resins to improve the material properties, or save a little money by using regrind.
Using 100% virgin plastics can also make it a challenge to design some products.

I've been in high volume mold shops that injection mold pails, and they are very high tech, and competitive, they use cutting edge technology, and the resins they use are tightly controlled, and tested. They typically are using hot runners, so there isn't any sprue or gate to reuse. The product might be low tech, but not the equipment that manufactures them.

The amount of contaminate allowed typically has a specification, like a black spec particle count.
Most contamination stems from a one time mistake, like leaving the cover off of the hopper, and burnt resin.
Unless you're sourcing your parts from Asia, they will if not told explicitly, will sweep up spilled pellets off the floor, blow it off with air and toss it into the hopper. I've seen hair, bug parts, dirt, etc molded into the product sourced from Asia, they don't waste any thing.
I've been in injection mold shops in Asia with chickens running around, and cow poo on the floor.

Black plastic from Asia, omg, anything could be in it, and probably is.