Why cant i get the corners right! (see picture)


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8900120d
8900120d
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Hi guys, 
ive done a few infusions now, but im struggling to get the corners right! 
- Perfectly sealed bag
- everything is room temp
- i tuck the bag in all of the edges
- use an edge peice to push all of the corners in
- all of the resin is degassed 

i always end up with corners bad corners! 
im using the FM100 mesh and i feel like it doesnt 'tuck' into the corners properly even after the bag has been pressurised
should i be using mesh on the corners?

is there a way of fixing the corners after the infusion?

thank you Smile




Edited 5 Years Ago by 8900120d
MarkMK
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Not always easy to tell from pictures, but the overall finish of your part doesn't look great, despite the evidence of the resin surface being broken away after de-mould. Did the infusion go okay with not air ingress prior to final cure?

I say this as, even if your part showed signs of bridging in the corners, this would usually show itself as a thicker section of resin in these areas with the accompanying un-evenness in the weave. The picture appears to show a quite broken surface generally, which might indicate an issue beyond some partially bridged angles? That said, bridged areas can also be air traps, so bubbles are not uncommon, but more likely to occur where the infusion process hasn't gone too well

Getting the fabric down initially into tight corners and angles is usually best achieved via cutting and jointing the fabric, so that you're apply flat sections with the join hidden as best as possible in the apex of the angle. A good spray tack helps with this process. This is less likely to lead to bridging as a single piece of fabric can be pulled tight in opposing areas as vacuum is applied

If your backing fabric is not too heavy and is quite drapable, you can usually get away with applying in one piece, but neat cutting and jointing of the surface fabric should give some initial certainty of it being in close contact with the mould (although a bridged bag will likely cause it to 'float' away from the mould once the resin flows)
  The standard infusion mesh can also be cut into sections if this would help it to conform better to changes in angle and even if there are small areas without mesh, it shouldn't be a huge problem as the resin should still be able to flow well in good temperatures on moulds that aren't overly large

You'll always struggle to get perfect consolidation on complex shapes via infusion, when compared with laying-up pre-pregs, but it should be possible to get the corner sections in quite tightly on the pictured piece without visible bridging or broken surfaces. If not doing so already, adjust the bag as best as possible whilst pulling vacuum, then back-off again, just enough to allow some bag movement and press-in the corners for a final time. Try to use a tool that's thin enough to press everything into the corners without too much risk of causing punctures. I use the rounded end of the handle from a scraper tool and it's quite thin, so helps with tight corners. Careful handling is still required, though, as causing tiny holes is always a risk if you're a bit heavy-handed. 

Also, if your part is quite small, take steps to slow things down a bit, so that the resin has plenty of time to fill the part. This is usually best achieved via a resin break, which can be made quite wide if your part usually infuses very quickly. Leaving the inlet open for a while after clamping the exit port can also help ensure that lack of resin is an issue.

 

 


8900120dd
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MarkMK - 7/8/2019 9:04:09 AM
Not always easy to tell from pictures, but the overall finish of your part doesn't look great, despite the evidence of the resin surface being broken away after de-mould. Did the infusion go okay with not air ingress prior to final cure?

I say this as, even if your part showed signs of bridging in the corners, this would usually show itself as a thicker section of resin in these areas with the accompanying un-evenness in the weave. The picture appears to show a quite broken surface generally, which might indicate an issue beyond some partially bridged angles? That said, bridged areas can also be air traps, so bubbles are not uncommon, but more likely to occur where the infusion process hasn't gone too well

Getting the fabric down initially into tight corners and angles is usually best achieved via cutting and jointing the fabric, so that you're apply flat sections with the join hidden as best as possible in the apex of the angle. A good spray tack helps with this process. This is less likely to lead to bridging as a single piece of fabric can be pulled tight in opposing areas as vacuum is applied

If your backing fabric is not too heavy and is quite drapable, you can usually get away with applying in one piece, but neat cutting and jointing of the surface fabric should give some initial certainty of it being in close contact with the mould (although a bridged bag will likely cause it to 'float' away from the mould once the resin flows)
  The standard infusion mesh can also be cut into sections if this would help it to conform better to changes in angle and even if there are small areas without mesh, it shouldn't be a huge problem as the resin should still be able to flow well in good temperatures on moulds that aren't overly large

You'll always struggle to get perfect consolidation on complex shapes via infusion, when compared with laying-up pre-pregs, but it should be possible to get the corner sections in quite tightly on the pictured piece without visible bridging or broken surfaces. If not doing so already, adjust the bag as best as possible whilst pulling vacuum, then back-off again, just enough to allow some bag movement and press-in the corners for a final time. Try to use a tool that's thin enough to press everything into the corners without too much risk of causing punctures. I use the rounded end of the handle from a scraper tool and it's quite thin, so helps with tight corners. Careful handling is still required, though, as causing tiny holes is always a risk if you're a bit heavy-handed. 

Also, if your part is quite small, take steps to slow things down a bit, so that the resin has plenty of time to fill the part. This is usually best achieved via a resin break, which can be made quite wide if your part usually infuses very quickly. Leaving the inlet open for a while after clamping the exit port can also help ensure that lack of resin is an issue.

 

 


Thank you for your detailed response! 
The infusion went well as far as im aware. 
i like the idea of cutting the fabric in the corners and jointing, however im afraid spray tack might ruin the appearance of the part? if i use spray tack, is there any time limit in which i need to infuse? im pretty new so i takes me a while to get a perfectly sealed bag, i guess my question is, would the spray tack loose its 'tackyness' and go hard after a couple of hours? 


MarkMK
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Well.laid sections will often look much better than a single piece with weave distortion, even if the join is visible so this might be a better approach. 

I can only comment on using Cytec's Aerofix 3 with EC's resins, but I've found that it leaves next to no trace if used sparingly

I've also left moulds overnight with just the fabric apllied, including on vertical sides and nothing has come away so this shouldn't be an issue either. It will lose some of the initial tack but not enough for it to just fall away.






8900120d
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MarkMK - 7/9/2019 12:21:45 PM
Well.laid sections will often look much better than a single piece with weave distortion, even if the join is visible so this might be a better approach. 

I can only comment on using Cytec's Aerofix 3 with EC's resins, but I've found that it leaves next to no trace if used sparingly

I've also left moulds overnight with just the fabric apllied, including on vertical sides and nothing has come away so this shouldn't be an issue either. It will lose some of the initial tack but not enough for it to just fall away.






thank you for your response. 

would you guys recommend using Knitted mesh for moulds with very tight corners?
GO

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