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 Post subject: How long pump has to work?
PostPosted: Sat Jun 07, 2008 7:07 am 
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Joined: Tue Jun 03, 2008 5:11 pm
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Does the vacuum pump has to work through the whole dry process?

Can I use a manual pump to release the air for 10 min and after that close the valve?

give me your opinion on these issues
tks :wink:


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 Post subject: Re: How long pump has to work?
PostPosted: Sun Jun 08, 2008 12:03 am 
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Joined: Thu Aug 17, 2006 9:44 pm
Posts: 698
Location: Taranaki New Zealand
Vac pump has to run till the resign has gone off, about 6>8 hrs with epoxy.

The ideal is to use peel ply over the wet out laminate, then bleed cloth over the peel ply, then shade cloth or similar over the bleed cloth.

Leaving the pump running during the cure time ensures that all excess resign is drawn out of the laminate into the bleed cloth ( felt or similar ) and ensures that the layers of cloth in the laminate are bagged down without pockets of air or resign between them. This is vital for strength and weight.

The shade cloth helps the vac bag to come down with even pressure over the whole area cos it allows the air to be drawn out of the bag and not trapped in different areas . The shade cloth only needs to be a strip running the length of the bag, with the vac hose sitting on top off it.

If you try what you were asking ie bag down then lock off and remove pump the bag will lose pressure and you will end up with voids in the laminate that will delaminate quickly in use.

The best type of home vac pump is an old fridge compressor. They are cheap and can be converted to suck easily and can be left running for extended times with out any problems.

Hope this all helps :thumb:


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 Post subject: Re: How long pump has to work?
PostPosted: Thu Jun 12, 2008 9:42 pm 
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Joined: Tue Jun 03, 2008 5:11 pm
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Thanks kevin, it is so helpful your advice!

I am going to find a old fridge to proceed with the surgery!!! :cool2:

Could you give me technical samples of bleed cloth and shade cloth?

i.e. shade cloth =poliuretane 20 mil.

the bleed cloth is the breather?

poliuretane
breather
poliuretane
glass
foam (divinicel)
glass
poliuretane
breather (am not so sure about set this in the bottom)
poliuretane

Tks


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 Post subject: Re: How long pump has to work?
PostPosted: Thu Jun 12, 2008 11:03 pm 
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Joined: Thu Aug 17, 2006 9:44 pm
Posts: 698
Location: Taranaki New Zealand
Bleed cloth can be felt carpet underlay or poly fibre ,like for duvet inner, or polar fleece, cotton material, any thing that will absorb the excess resin that is drawn out of the laminate, through the peel ply.

The peel ply provides a barrier between the bleed cloth and the laminate, so when the job has gone off, you remove the vac bag, remove the bleed cloth, then peel of the peel ply. Peel ply is just a polyester cloth ( nylon taffida ) that can be bought at fabric shops if it costs less than branded peel ply.

Shade cloth is like wind cloth, it is a plastic small square pattern, which allows the air to be drawn out of the bag. Garden shops sell it in rolls and will cut off and sell by the mtr. It is the stuff you see around stakes to protect new trees from the wind and sun.

When setting up the bag run the vac hose in from one end to the middle of the job and have the vac hose sitting ontop of the shade cloth , Make sure the vac hose doesn't pull the bag over the end of the hose and block it. That is why the shade cloth is needed . Also make sure the vac hose is strong enough that it doesnt collapse before the bag is pulled down properly.

If you are bagging on pvc to a blank ,the bag can go straight onto the pvc, it is only when you are bagging the outside laminate that you need peelply and bleed cloth, cos if you didn't use it ,the bag would pull down onto the resin and trap air in pockets creating uneven pressure in the bag which would lead to delamination problems.

What are you intending to bag ?

The whole idea of using peelply and bagging is to end up with a smooth surface that doesn't require any further sanding and is ready for top coat application. This is achieved when the peelply is wet out over the whole surface, cos when you remove the peelply it peels off the top layer of excess resin leaving a matt even surface on the epoxy.

Some jobs are easier to hand lay up using a wet on wet, with out the need for vac bagging etc, especially the outer laminate in epoxy for a home built board. Epoxy has a long pot life and can be mixed up in small amounts and applied to the job evenly with out building up excess resin.

So it depends what you are doing.

The main reason you would use a vac bag is to laminate on pvc sheets or inserts into or on to a blank.


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 Post subject: Re: How long pump has to work?
PostPosted: Sat Jun 14, 2008 9:12 am 
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Joined: Thu Nov 02, 2006 5:12 pm
Posts: 76
emokiter wrote:
Does the vacuum pump has to work through the whole dry process?

Can I use a manual pump to release the air for 10 min and after that close the valve?

give me your opinion on these issues
tks :wink:


Hi

No your fridge pump does not have to run all the time, 6-8 hours will be a huge fire risk and will most likely kill the pump.

I suggest If you seal the bag correctly and build a vac switch the pump should not be on for more than 2 mins at first and maybe only a few times over the cure cycle depending on how good your bag is sealed.


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 Post subject: Re: How long pump has to work?
PostPosted: Mon Jun 16, 2008 5:18 pm 
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Joined: Tue Jun 03, 2008 5:11 pm
Posts: 8
SXwind

So, do you suggest that we can use a manual pump?...in case got a consistent sealed!


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 Post subject: Re: How long pump has to work?
PostPosted: Mon Jun 16, 2008 6:32 pm 
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Joined: Thu Nov 02, 2006 5:12 pm
Posts: 76
go and build or make a vac switch to automatically turn the pump on and off as required.

this is a pic of mine.

http://www.zen101724.zen.co.uk/images/D ... -small.jpg


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 Post subject: Re: How long pump has to work?
PostPosted: Tue Jun 17, 2008 12:39 am 
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Joined: Thu Aug 17, 2006 9:44 pm
Posts: 698
Location: Taranaki New Zealand
Some people use a vac switch to regulate the running of the pump and others even use a vac pressure reg to control the amount of pressure in the bag.

Alot of back yard builders have used pumps of various kinds unregulated and left them running the whole time with good results.

Fridge compressors reversed to suck can handle running for long periods with out any drama.

So it all depends what you are bagging and how often you are going to use the bag and how much time and money you want to put into it.

I assumed your were looking for a non commercial set up for home projects.

To set up properly and build a surfboard say for kiting can be a lot more money than you think , so I would suggest that you price out the job first to see if it is economical .


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 Post subject: Re: How long pump has to work?
PostPosted: Tue Jun 17, 2008 7:48 am 
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Joined: Thu Nov 02, 2006 5:12 pm
Posts: 76
Kevin Salter wrote:
Some people use a vac switch to regulate the running of the pump and others even use a vac pressure reg to control the amount of pressure in the bag.

Alot of back yard builders have used pumps of various kinds unregulated and left them running the whole time with good results.

Fridge compressors reversed to suck can handle running for long periods with out any drama.

So it all depends what you are bagging and how often you are going to use the bag and how much time and money you want to put into it.

I assumed your were looking for a non commercial set up for home projects.

To set up properly and build a surfboard say for kiting can be a lot more money than you think , so I would suggest that you price out the job first to see if it is economical .


My switch regulates both, same pump for 8 years and still going.


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