posted January 15, 2007 02:07 AM            

I am facing one problem in 3-layer blown film plant. when I am running the machine my bubble shape is a pragnant shape in 50% periphery of the bubble. My film application is shrink film. when I am measuring the shrinkage in that film, I can not get shrinkage in TD ( tranverse direction ) in 70% periphery of film.

I am running the 100% LDPE, I have increased and decreased temeperatures also. but no effect. always pragnant shape is coming from the same side.

please advice me what could be the reason behind this problem.

Awaiting for your reply,

Thanking you with best regards,

posted January 18, 2007 01:07 PM            

If you center all of the pieces and there is still a problem, you might try "rotating" pieces and figuring out which one makes the bubble flare move. In other words, try removing your die pin and rotating it 90 degrees to see if that makes it move. Then try the sizing ring, the air ring lips, and so on, until you figure out which part is causing the problem.

posted March 12, 2007 04:56 AM            

thanx for your kind reply,

I have set die gap very perfectly 3 times, I have rotated inner lip and outer lip by 180 degree. but still the pragnant shape is one the same side, I am getting big thickness variation in film and shrinkage variation in Tranverse direction also big.

also I have rotated air ring, but still problme is on the same side.

Awaiting for you reply,

thanking you with best regards,

posted March 12, 2007 10:50 AM            

Are you sure the heat is even all the way around the die?

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Best Regards,

Tom Cunningham

posted March 12, 2007 11:49 AM            

Is it rotating or stationary?

If stationary, does the material enter through the side of the die or through the bottom?

There are many, many potential answers / solutions to this problem. There are many issues having to do with the die itself (such as parts being centered), but also your air ring, IBC, melt pipe, and so on could also be contributing to the problem. If the die was not running the polymer it was originally designed for, that is another potential issue (although that usually leads to port line). A potential answer could even be a static mixer, if your melt is not homogeneous (a variable-depth melt temperature probe could tell you).

posted March 12, 2007 02:23 PM            

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Steve Hodgson

posted March 13, 2007 02:36 AM            

Die is conventional type 3-layer spiral mandrel die. die is stationary. I am not sure that all heating in die are proper or not? I checked amp and registor of heater, it was ok.

best regards,

posted March 13, 2007 02:38 AM            

suppose, my one die zone is getting over heating then how the material flow behave in die? Please explain me.

posted March 13, 2007 10:33 AM            

Another cause could be poor flow characteristics inside the die. Spiral die design is complex, and today computer simulation programs are used to predict the flow patterns inside the die. By adjusting the design more even flow patterns can be developed. Typically a poorly designed spiral die will have a periodic uneveness of flow rate around the die caused by the spiral pattern. This is not your problem

Since polymer viscosity is lowered with temperature, areas of the die which are hotter will have less flow resistance than colder areas. The polymer will preferentially flow in the hotter area giving a distorted product. This is most likly your trouble and can be readily sourced using an IR gun or surface thermocouple probe.

Another possibiliy is the design and arrangement of channels feeding the die. Usually this is symmetric and if wrong leads the the periodic flow problem mentioned.

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Best Regards,

Tom Cunningham

posted March 14, 2007 02:42 AM            

Thank you very much for your reply,

I have used IR gun go measure temperature on die heaters. I found that in some part of heaters are getting more heating then opposite side. the heaters are ceramic type heaters.

Thanx with regards,