getting air out

[GMan]

I made a two peice mold and am using it to cast hard plastic jerk baits, My first two had some air in the top which left a puddle mark on the top of the lure. I have a hole in the top half mold which I pour into, and the air/puddle mark forms just about an inch down the back of the lure from it. Any ideas for getting the air out?

[aka anglinarcher]

GMan, I assume you made the mold from HS2 or HS3. I know of three ways to remove air from the initial mold making process, some of which are easy, and some not so much.

I am assuming that you already started by pouring from one corner and pouring slowly so that the silicone pushes the air out as it slowly encapsulates the master.

The easiest way is to paint the lure with the HS2 or HS3 first, then pour the rest of the mold. The painted portion is so thin the air escapes easy and leaves a clean "skin" against the lure. Of course, to make a two part mold you need to paint only the part that will get molded at that time.

The second method requires equipment, but is easy. You can degas the silicone by putting the freshly mixed silicone under a vacuum to remove the air bubbles before pouring. Alumilite sells the pumps and the chambers from their alumilite.com site. I have had excellent results by using my home food saver vacuum motor and the canisters they make for it. Of course, my food saver canisters are not that large so this works for smaller molds.

The third way is also easy, but ......

You don't remove the air, you collapse it. Your pour your mold and while it is still fresh you place it into a pressure vessel at 60 to 80 PSI for the entire time it takes for the silicone to cure. I don't have any pressure vessel that my wife will let me continue to use, but ..... but .... a pressure cooker with a pressure hose attached to the steam exit valve..... never mind. The pressure was probably not safe when I tested it.

The following link will take you to other molding methods with Alumilite that Mike has posted. They talk about all three methods if you go through all of the examples.

http://www.alumilite.com/howtos.cfm

[GMan]

archer...thanks for responding, but its not the making of my mold that is the issue. I made it, two parts, from HS2 and its flawless. Its the new peices I am trying to cast in the mold that are coming out with the air bubble mark or dimple. This happens when I pour the plastic mix into the mold. Any other suggestions? Larry? Mike? After reading the FAQs I realize I did not use any mold release spray, but I did use alumidust on the mold...could this be the answer?

[Mike - Alumilite]

To me it sounds as if air is floating to the top of your cast and is piling up there and has no where to go. What happens is the resin is flowing in the pour hole but the air in the mold needs somewhere to escape. Where ever the air is pooling at the top, I'd recommend cutting a vent that will allow the air to push out right there. You can do this by making two small "V" cuts with your Excel or Exacto knife in the middle of the pooled area - 1 on each half of the mold. This will make a diamond shaped vent that allows the air to escape rather than getting caught at the top with no where to go. When you pour your resin, make sure you don't pour resin over that vent hole or the air will get trapped again.

This would definitely be the case if the pocket or air is in the same basic place every time as I think you described.

If you look on this how to: http://www.makelure.com/HowTos/Swim%20W ... 0Piece.pdf ... the wide tongue depressor acts as the pour hole while the split in half stir sticks act as vents. This allows the air somewhere to escape. If you look at the last 3 or 4 pictures you can see where the resin started to fill up those vent holes after the air pushed out. Those are not all pour holes ... just the big one in the middle is.

Mike

[aka anglinarcher]

Sorry GMan, I missed the point. Thanks again Mike for catching this one.

One thing I have done if you can't cut an excape hole, but you need one, is to heat a piece of metal, like a straigntened out paper clip, until it is cherry red and then push or burn a hole from the outside to the spot where the air pocket is. This creates a little air vent that will need to be cut off when you remove your piece.

Note, this is NOT easy (Silicone takes a LOT of heat), and I won't do it inside, but, if necessary......................... Mike's way is soooo much better if it is at all possible.

[GMan]

Thank you Mike and Archer...I will try cutting a vent hole in my mold where the air seems to be holding.