MFI what range of deviation is acceptable

[arthurchiang]

thread709-252160

Hi all

Recently, we got a serious hinge and base broken issues and we sent defect samples to SGS lab. for MFI analysis, data shows MFI change from 22(raw material) to 28 g/10min under ASTM D-1238 260degree/2.16kg, We doublt that large ratio of re-cycle material has been added during the process.

Any idea ? or suggestion.

Tks

 

[patprimmer]

22 to 28 is not all that surprising.

Moulded in stress or to much shear in moulding can seriously degrade the impact properties of PC/ABS

MFI is increased by inadequate drying, overheating, being hot to long or to much shear.

Regards
Pat
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[Demon3]

Likely cause of failure is environmental stress cracking whereby someone oiled your hinge and destroyed the plastic. Variations in MFI are not a likely cause.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[Pud]

Or:

Incorrect drying
Too low tool temperature (causing frozen-in stress)

The above are the most comment cause of PC problems (IMO)

Cheers

http://www.tynevalleyplastics.co.uk

 

[arthurchiang]

Hi all

Thanks for the inputs.

Is there any relationship or evidence could show
the MFI deviation between these factors ?

Tks

 

[Demon3]

No, there isn't. MFI is a poor test only good as quality control to make sure there is not something terribly wrong with the polymer that was delivered.

You should check whether someone lubricated your hinge with oil as that could destroy it and cause your failure and check whether the material was dried properly and molded correctly.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[arthurchiang]

Hi all and Dr. Demon

Thanks again !

Our dry process is 80 degree C 4hrs and no any oil will polute the hinge during the process, but we do have a female
screw hot bury within the hinge after injection. is this the root cause ?

Since MFI is the index for the material(PC/ABS) quality
what is it stand for ? purity or something else ?

Tks

 

[patprimmer]

For how easy it will fill the mould.

Regards
Pat
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[arthurchiang]

Hi pat and all

Thanks for the input

Our appalictions are mobile entertainment system, and for fire proof purpose we used PC/ABS with MFI around 22, is it sufficient for tensile strength and impact resistance ?
or what range of MFI should we use ?

any idea or suggestion ?

Tks

 

[Demon3]

Forget about MFI, it has nothing to do with the properties you are focused on.

MFI is Melt Flow Index. All it tells you is the approximate viscosity of the polymer and it's not even very good at that.

Chris DeArmitt PhD FRSC CChem

http://www.phantomplastics.com

Consultant to the plastics industry

 

[patprimmer]

Chris is correct. MFI is a poor test even for flow in the mould as it is very low shear whereas a typical moulding has very high shear by comparison.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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for site rules

 

[arthurchiang]

Dear All

Thanks for input again !

In the other word, what will be the main issues caused by large percent of re-cycled material, and which index can show it as a evidence ?

Tks