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Wax injector...help


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Hi guys,

I 've a problem and I hope someone can help me. I know that here there is some goldsmith or jewelmaker ...

I bought an used wax injector (very very old) but I have big problems: Some work are good, others have always bubbles trapped in the wax. I read books, but no one explains the problem of air bubbles! After several attempts I realized that I need a small sprue but with some shape work well with other not ... I hope someone can help me, I enclose some photos of good models and bad models (the failure is always the same).

 

Hope this is the right room for this topic.

 

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CIAO FROM ITALY

 

Marco Di Francesco

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It appears from the photo that the mold may be too thin in the problem area. The waxes are a lighter color in that area, indicating thinness. Also the fact that the problem is always in the same area would suggest a uniform thinness there. To me the holes don't look like air bubbles they look like the wax could not reach that area. You might try a higher temperature, but I think the problem is as above. The other waxes above are all the same uniform color.

 

Jim

Edited by Jim Kelso
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slightly higher temp may fix it. are you using talc (fine powder) on the inside of your moulds? also, you could try cutting a vent opposite the sprue to allow some air bleed.

Jake Cleland - Skye Knives

www.knifemaker.co.uk

"We can't solve problems by using the same kind of thinking we used when we created them."

"Everything should be made as simple as possible, but not simpler."

"Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."

 

Albert Einstein

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Marco,

 

The problem that you are having is because the section in that area is thin. As the wax flows into the mold it is cooling faster in the very thin sections and therefore hardens before it can fill this area all the way. Molten metal will behave in the same way as the wax here. You can solve this in two ways. 1) Make the section thicker. 2) Add an auxiliary sprue, or sprues, to feed wax (and metal, when you get there) to the thinnest sections of the casting. Lapidary Journal has a good article titled "When in Doubt, Add a Sprue" There are illustrations showing the correct and incorrect way to sprue a little way down in the article.

 

~Bruce~

 

Edited to add: Check out the bit about adding an air vent as well. That could be all it takes to solve this but, as they said, "when in doubt, add a sprue!"

Edited by B. Norris

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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Thank you so much guys, I really appreciate your advice and I hope to solve the problem and sorry for my poor english language, hope you understand!

 

But I can assure you that the thin section is not the problem. I enclose some pictures showing some previous perfect models (cast in bronze).

Initially I made the silicon mould but get only very few good phalerae, the others were always bad and always in different parts (I attach an image of the firsts defects) then when I made the second model (rectangular) I noticed that with a small air vent worked perfectly so I also made ​​a vent in this to solve the problem but now the fault is always the same, so it's definitely a problem of air bubbles

 

Jim, I tried with higher temperatures have the same result, the section of the rectangular model is thinner then this section so this is not the problem.

 

Jake, yes, use talcum powder and is indispensable but in this case I have the same defect, and yes I made an opposite air vent...

 

Bruce, as I said to Jim the section is not the problem because I did even more subtle models, however now I read this article carefully.

 

I have read many books about jewelry, everyone talks but not examines in detail air bubbles problem ... I made ​​several attempts with different temperatures and pressures, but I can not understand ...

 

Now I attach some pictures of previous defects before I do the small air vent, you can see that defects were very large, different and numerous, but some (about 5%) good model was ...

 

1-6.jpg

2-6.jpg

3-5.jpg

4-5.jpg

5-5.jpg

CIAO FROM ITALY

 

Marco Di Francesco

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Marco,

 

How are the air bubbles getting into the wax in the first place? Is it happening during the injection or are they present in the wax before it is melted? Adding the air vent helped but, you are still getting small voids in approximately the same place every time? I would try adding another air vent right where the voids are happening.

 

~Bruce~

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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Variables I'd consider are:

 

Wax temperature- Either higher as Jim suggested, or even lower. Injection waxes I have bought have all had fairly specific temperature ranges, and too hot can be a problem as well as too cold.

 

Wax composition- Is the wax designed for injection? Really old wax can lose beneficial chemical additives.

 

Air pressure- Not enough? Too much air pressure can also shoot wax too quickly, causing it to cool too soon, or include air bubbles.

 

Air venting- Sometimes I have had to make thin cuts in rubber molds to help prevent bubbles or incomplete injections.

 

Mold pressure- How tightly are you squeezing the mold? Compressing too tight can prevent air from venting out as wax goes in.

 

Mold temperature- Here's one that really helps me get good models, and it's counter-intuitive: cold molds will actually inject better than warm ones. I frequently stick tricky molds in the freezer for 5-10 minutes or so. I'll get 3-4 good injections before they're heated up inside and need to be refrigerated again.

 

Good luck!

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Marco, a fun experiment would be to: insert a little piece of wax(could try plastic too), the correct thickness, into the problem area before injecting. After injecting, if the mold fills well this could indicate that perhaps, as J. suggested, the mold is being held too tight.

 

Jim

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Wax composition- Is the wax designed for injection? Really old wax can lose beneficial chemical additives.

 

 

Hi Marco,

 

I am chemist for car care chemicals. So I have experiance in wax and additives for wax. If you are interestet in a surfactant to add to wax to reduce the surface tension of the wax, please give me your adress and you get a christmas present.

 

Servus

 

Manfred

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Thanks guys!

 

to reply to all:

 

Bruce, the air is not trapped in the wax, but it is in the model, so when I inject the wax that creates problems, to avoid this I did another 2 air vents, but the result is always the same, a hole in the usual position.

 

Jim, I've tried all the pressure ranges up to about 0.9,more than 0.9 is impossible because too much pressure over the wax pops out, however, low-pressure, or high-pressure have the same small defect.

However, your idea to use a small piece of wax is very good, I had not thought of and will be the next test that I will

 

J. , the wax is new and specific for wax injector so I exclude this problem.

As I told Jim I've used pressure range at regular intervals from 0.4 to 0.9 and the problem is always the same so I guess that this is not a problem.

Air venting in my opinion this could be the problem, now I have 3 air vents, but maybe I have to add more or mine are incorrect, Wednesday I post a photo of the mould with air vents.

But I do not understand how these are made​​, you make small channels or simple cuts are sufficient?How deep? I never saw how are made ​​these air vent and maybe mine are wrong, you have an image to display a silicone mould with air vents?

I also noticed while I cooled my molds in the freezer to cool the wax who work a lot better

 

Manfred, I thank you so much, I also used a special spray product suitable for jewelmaker but I noticed that with simple talc works much better!

 

I hope to do further tests on Wednesday and post some pictures of the result with different parameters and measures...

 

If anyone has pictures of air vents on silicon mold I would be curious to see.

CIAO FROM ITALY

 

Marco Di Francesco

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Looking at the good wax model at the top of your post I'm noticing that there is a constriction where the sprue meets the model. Perhaps enlarging this connection by cutting a small amount of mold off will help, or making a bigger sprue / connection on your original model.

 

I'm still thinking that how tight you squeeze the mold when injecting can be an issue. I have plexiglass pieces that I use to hold my mold when injecting. I use a C clamp to gently hold the mold together. I find that too much pressure creates air bubbles and compressed waxes, and that too little pressure lets wax squeeze out of the sides of the mold.

 

The mold you are trying is a tricky shape! I find that long or broad thin shapes are the hardest to inject well. Somewhere, in all these variables, is your answer!

 

The air vent cuts are simple cuts. You don't need to remove any material- you are just making a cut with a razor so that a tiny amount of air can go there and help prevent air bubbles from being trapped in the model itself. Sometimes you get small flanges where the cut is, but they are usually very easy to clean up.

 

Here's a picture of one that used to get little bubbles right toward the end. I am here holding the cut open. Normally you might not even notice it. It lets the air that gets pushed to the very end of the mold escape, and stopped the little bubbles from forming.

 

ventcut.jpg

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Thanks J.

Today I did more testing and finally thanks to your advice I got good models!

The first test I did what suggested Kelso, and finally I realized that one of the problems that are too compressed ... as you said, too J. I have very little compressed with a clamp, I also did a lot of air vents like those I saw in your model (simple cut) and I used a very low pressure ... perfect result.

However there are many variables, I need to learn because I do other more complex...these are some models for roman cavalry harness.

 

Thanks again for your advice guys!!!!

 

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CIAO FROM ITALY

 

Marco Di Francesco

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Hi guys,

I really appreciate your tips and finally got good results so I will share with you this picture, some first pieces are finally ready for casting in bronze, I hope you like them.

 

Wax1800x600.jpg

CIAO FROM ITALY

 

Marco Di Francesco

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  • 3 weeks later...

well, finally I can show you some results, of course, these are unfinished raw pieces , still need other biggest piece and a lot manual finishing ...

 

IMG_0038800x600-3.jpg

 

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CIAO FROM ITALY

 

Marco Di Francesco

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