cleaning injection mold screws & barrels 1

[injectionmold]

i was curious if any of you might share how you are going about cleaning your screws and barrels. we are trying to re evaluate the way we do it at my company to try and reduce contamination. and help would be greatly appreciated. thanks

 

[injectionmold]

currently we are just going over the screw with a wire brush.. any ideas to inprove cleaning and reduce contamination by left over plastics still attatched to screw?? thanks

 

[Like2Strike]

Something that has been used for a long time is to mix your purging material (PE or PP) with powdered Tide (yes the laundry detergent) half-and-half. No special technique, purge as normal. Frank M.
Tradewind Resources

http://www.tr-usa.com

 

[injectionmold]

we currently are purging the machine with glass filled polypro, but we were looking for a better way to get the screw clean when we take it out.
we also just use a brass wire brush attatched to a large drill to clean out the barrel.

about the tide idea....we use radel at 740degrees F. would the tide gas off at that temp or cause any internal damage??

 

[JeffdlS]

I've heard all types of methods for cleaning screws & barrels. One of the most interesting is to run kitty litter (unused, of course) through the machine. The granuals seem

If you have brass scrapers, you can get the poly off as the screw is pushed out. Using some WD-40 will usually help get some of the poly off the screw.

As for the barrel, the brass wire brush is a good idea. Possibly some copper gauze wrapped around the brush would help as well.

Hopefully, that'll help you out some.

JeffdlS

 

[chaving]

Any foreign material you put into your barel runs a risk of contaminating further.

The best I have come across so far is to mix 1 or 2 % of water with some natural PP and purge it through. The melt will fizz, pop and bang a fair bit but you will find the the vapourised water has a great cleaning effect. It also foams the PP, this also apears to have an effect.

If after this you still have contamination it is likely that your nozzle seat or screw tip need cleaning.

In cases where the material is degrded to carbon and fussed to you screw you have little option but to strip it and clean it properly, check the damage to your seats and re-machine if required.

If you find that you spend too much time stripping and cleaning screws and barrels you may consider a furnace. It is like a fluidised bed, the sand inside is airated with super hot air, the parts are lowered in and burnt clean - the advantage is that it is non-abraisive.

Good luck

 

[gambro]

We use an extrusion-grade Polystyrene. It is comparatively cheap and it works quite well, even in hot-runner systems. You can improve the cleaning performance a bit by adding some water.

 

[shashak]

Everyone has their own methodology and ideas when it comes to purging. It is a choice between degree of purging required, permissable downtime and availability of operators.
A) PS resins of low MFI are popular generic purging agents.
B) If PS is difficult to clean out, many others try PVC, allowing it to come out gelled and then add water till they see water coming out. By far, HDPE or PP are easier to clean out as they stick lesser, and do not degrade inside the barrel.
C) Proponents of chemical cleaning use Dynapurge or other suitable commercial compounds. These compounds have an initial light abrasive action. When you dead-stop the machine (5-10 minutes) and allow the chemical additive (solvent) in it to diffuse out, you either swell or dissolve the resin inside the barrel and flush it out.
E) Open cleaning with solvent and brass brushes (operator intensive)
F) Procedyne or suitable hot-sand bath (fluidized bed) can burn and clean out all material sticking to the walls and elements. However, it takes about 4 hrs to get the parts cleaned and ready for re-loading into the machine.

Note: It is imperative that the operator keep the purge agent's viscosity high enough (you should see high torque, high current draw on the extruder) to get good purging action due to enhanced shear effects. This is achieved by lowering the temperature on various zones, and running at low RPM. (20-25 on single screw and about 100 on twin)

 

[jimboa]

Jimboa
We are looking for someone who can lead us to a manufacturer of Hot Sand bath units to clean nozzles and tips

 

[unclesyd]

jimboa, check the previous post by shashak

 

[ozchevy]

I always used to use virgin natural styrene to purge the barrel, set the barrel temps at around 300 degrees C and blast the styrene through on a long stroke and rapid screw revolutions. Never had to remove a screw from the barrel for cleaning, they come up clean with the styrene purge.

 

[automatic2]

When we pull screws to measure, we'll clean with a mix of light oil and ajax.

 

[injectionmolder]

For this purpose, all methods work, some better then others however. Which one is the most inexpensive, I will say is the question. Pulling the screw it is the most efficient while the most expensive. As one member pointed, wet PP works fantastic and cost almost nothing. Cast acrylic it also does wonders for the purpose about which we are talking.
Now when you say:
we are trying to re evaluate the way we do it at my company to try and reduce contamination.

It seems to me there is contamination even after the barrel/screw have been pulled and cleaned, if so we might be dealing another issues for example:
*Running PVC if the melt temperature is too high, molded parts will show not only burning but also “black specs.”
*Polysulfone mixed with liquid dye colors that are not a resin grade comparable will show as contamination.
*A worn out screw and barrel with all kinds of deep drag marks, collecting a small amount of molted plastic, and then at some point and time now carbonized breaking lose from the barrel during the run.
Could there be any resemblance?

Best regards.

 

[polina]

At my company we use hot sand bath or hot fluid bad were we submearch the screw an other parts for regular clean up.