Infusing on convex surface

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Infusing on convex surface - fibre kinking

Infusing on convex surface - fibre kinking

Author	Message
Grrrrrene	G Grrrrrene posted 7 Years Ago Topic Details
G Group: Forum Members Posts: 3, Visits: 9	I was wondering if anybody here has experience with using infusion on a convex mould (dome shaped). Anything I've produced so far is more or less flat or concave, which means that if you place the fibreglass material in the mould and apply the vacuum, the fibres will be stretched or remain in place. In the past I've seen issues with fibres kinking due to compression in moulds for pre-bent blades. The problem with a convex shape is that the distance from one side of the mould to the other side becomes smaller closer to the mould, which means that once you apply the vacuum, the glass fibres need to shorten and they simply won't do that, obviously. Instead of that, you get kinks in the fibres, weird creases in the fabric. This is very bad for the strength of the laminate and ruins the looks. Are there any tips to avoid this kinking behavior? I have not tried this in practise yet, because I don't want to waste money, time and material on a "let's see what happens" project ;-) I do however have an idea, but I'm not sure if that will work. My plan is to apply the vacuum on the very top of the dome and have the resin runner around the base of the dome. That way the resin will spread nice and evenly around the base of the dome and start impregnation of the fabric all around the product, hopefully achieving a nice and level flow front. But as an added benefit I expect the glass to be pushed down first directly under the vacuum hose and continue to be compressed further down the dome until it reaches the runner. There the material is free to shift a bit without creating kinks.
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MarkMK	MarkMK posted 7 Years Ago HOT Post Details
Group: Forum Members Posts: 338, Visits: 2K	You haven't specified just how high the dome shape is, but I think it's key to make sure that your bag has enough slack in it to not pull and distort the fabric too much when pulling down. Clearly this looks like it might call for some fairly big and numerous pleats. I'd suggest quite a slow pull-down also, taking time to adjust the bag in several stages before fInally pulling down to full vacuum A complete dome shape sounds difficult to do whilst maintaining good cosmetics using a single piece of surface fabric, so using cut sections might give you a better chance of not having the weave crimped and pulled. The downside is having several sections with a weave pattern going in different directions, but with neat cuts and good placement I'm sure that it would still look impressive. I've had issues with crimping fabric when laying into a mould that had a mix of concave and convex angles, but the suggestions above have helped to eliminate these issues Added to this, I'd recommend using a good spray tack to hold the fabric in place prior to making your bag.
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Warren (Staff)	Warren (Staff) posted 7 Years Ago HOT Post Details
Group: Administrators Posts: 2.5K, Visits: 7.9K	For relatively shallow domes, you will be surprised how much you can tease the fabric, especially with looser woven cloths. Obviously there is a limit, and putting it under vacuum will compress the layers down, making it more likely for excess fibre to bunch up and cause a crease. Running your spiral around the base is a good idea as when infusing, the area around the resin feed and the spiral will have less vacuum and the bag can feel loose. This might allow the fabrics to move around a little bit more thus reducing the likely hood of it creasing up. Warren Penalver Easy Composites / Carbon Mods - Technical Support Assistant
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Grrrrrene	G Grrrrrene posted 7 Years Ago HOT Post Details
G Group: Forum Members Posts: 3, Visits: 9	+x MarkMK - 12/20/2017 11:17:34 AM You haven't specified just how high the dome shape is, but I think it's key to make sure that your bag has enough slack in it to not pull and distort the fabric too much when pulling down. Clearly this looks like it might call for some fairly big and numerous pleats. I'd suggest quite a slow pull-down also, taking time to adjust the bag in several stages before finally pulling down to full vacuum A complete dome shape sounds difficult to do whilst maintaining good cosmetics using a single piece of surface fabric, so using cut sections might give you a better chance of not having the weave crimped and pulled. The downside is having several sections with a weave pattern going in different directions, but with neat cuts and good placement I'm sure that it would still look impressive. I've had issues with crimping fabric when laying into a mould that had a mix of concave and convex angles, but the suggestions above have helped to eliminate these issues Added to this, I'd recommend using a good spray tack to hold the fabric in place prior to making your bag. We have several moulds with dimensions ranging from 300mm in diameter and a height of just under 100mm to a diameter of 5500mm and a height of 1350mm. I don't see much of a problem with the larger products because their radii are so large, but especially with smaller products the radius is very small, which (I think) increases the risk of kinks in my fibres. Don't forget the wall thickness is between 5mm for the smaller products and (locally) up to 60mm for the larger products. That means that there is quite a significant amount of compacting going on once you apply the vacuum. I don't worry too much about the aesthetics since the surface will be usually coated in a colour and whats more: I'm working with glass fibre, not carbon fibre, so the weave is much more difficult to see anyway I also already expected to have to cut and overlap the weave in several places. Good tip about the spray tack. Never worked with it before in combination with polyester (only with epoxy), but I'm sure there is something available that works. I can't have a whole bunch of fabric sliding off during dry placement
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Hanaldo	Hanaldo posted 7 Years Ago Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	Spray tacks are even easier with polyester compared to epoxy, as there are loads available that polymerise into the matrix and leave no trace on the surface. I've yet to find one that does it to the same extent with epoxy.
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MarkMK	MarkMK posted 7 Years Ago HOT Post Details
Group: Forum Members Posts: 338, Visits: 2K	I use Cytec's Aerofix 3 with both 'bare' epoxy and in moulds with a polyester-based coating and it works great with both with little or no visible traces left behind If that's available where you are I'd recommend trying that and a light mist is usually all that's necessary to hold things well, even on vertical surfaces
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Hanaldo	Hanaldo posted 7 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	+x MarkMK - 12/21/2017 11:47:03 AM I use Cytec's Aerofix 3 with both 'bare' epoxy and in moulds with a polyester-based coating and it works great with both with little or no visible traces left behind If that's available where you are I'd recommend trying that and a light mist is usually all that's necessary to hold things well, even on vertical surfaces Yeh I've used Aerofix 3 in the past, but I've found it depends on the specific epoxy you are using. It worked well with the resin I used to use which was actually just a low viscosity hand laminating resin and not an infusion resin. But now I'm using Gurit Prime 20LV infusion epoxy and it doesn't work any better than 3M Super 77. Given I need to import the Aerofix 3 at a cost of about $70 per can, I just buy the 3M stuff and try to avoid using it or use it very sparingly.
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