Acrylic Casting Pressure?

[Didley]

Can anyone tell me if there is a top end of injecting pressure for Diamond D acrylic. I'm using their flasks in a hydraulic press. General pneumatic methods seem to all be around 3-7 bar, but I'm told the Swiss Jet flasks recommend 25 bar. Is more better?
Also my press reads in Kilograms X1000, can anyone give me a conversion to Bar, from what I can deduce 1 bar is around 40kg, That's not Kg /cm2, by the way its Kg weight.

Many thanks popcorn

 

[TomZ]

What system are you using to inject? My Diamond D injection machine uses 90psi which comes in around 6.20-7 bar.

 

[Didley]

Hi Tom, I'm using the Diamond D flasks in a Hydraulic press, so my casting pressure is not limited to pneumatic pressure, I could go up to 250 bar if it was an use!

 

[TomZ]

didley-

I dont see a reason to go much above what standard systems provide.
At higher ratings other concerns such as stone compression properties enter the equation with litle added benefit to the acrylic.
I understand Diamond D is quite popular in New Zealand and Australia due in large part to the efforts of Ultimate Dental Supply..

 

[araucaria]

I'm told the Swiss Jet flasks recommend 25 bar. Is more better?

At that pressure I'd want to be 2 blocks away from where you're working.
We're making dentures - not NASA parts. There's a safety risk if you start going up the scale to the limits you've suggested. - I reckon the figures quoted to you are the maximum test pressures for the flask parts.
6bar is plenty and more than sufficient.

 

[Didley]

Thanks Tom.

araucaria, do you realize in a standard hydraulic dental press, the mid range area where they recommend pressing a conventional press flask to, is around 100-180 bar. The 5-6 bar that pneumatic injection systems work on, you could almost push in with your fingers. It gives me doubts as to the advantage of injecting???

Any thoughts anyone!

 

[droberts]

I inject using the Ivocap. To prove the density of the acrylic being injected, I took 3 eggs ( Hard boiled ) and invested them. Injected them in a clear acrylic, some with transparent colors added to the clear. They are as clear as you will ever get. To understand injection, the acrylic is curing from bottom
( anterior teeth ) up to the posterior palatal seal. This allows the acrylic to be constantly injected while curing under a time format at 6 bar. To put it this way, the acrylic does not have to work harder by pressure, its working smarter by the way the sysyem was designed.

 

[Didley]

droberts, Thanks, the Ivoclar system works a little differently to all other systems with its controlled areas of curing, hence it's more complex and expensive. I'd love to see some independent tests on the different systems, I'd suspect the Ivoclar one would be the stand out. In all other systems I know of your relying on internal pressure to take care of shrinkage not continuous injection I think. Is that right?

 

[droberts]

If you did not have continuous force from the injection, you would not have the pressure in the flask. The pressure and forced acrylic is through out the un-cured acrylic until it is cured. Time is the factor of this system depending on the amount of cases be cured at one time. Maximum up to four in the unit. What I really admire of this system, its very consistant. You do your job, it does its...

 

[TomZ]

To understand injection, the acrylic is curing from bottom
( anterior teeth ) up to the posterior palatal seal.
Say what..

Heat is the activator/initiator for curing. Unless your submerging the flask gradually anterior to posterior into hot water at the rate it cures, I find it impossible to believe its possible to control curing from front to back when the entire flask is filled and encompassed by the heat.

Heat is coming in at the same time from all sides the flask, and the acrylic must be initially filling the mold at 6 or 9 or whatever bar, isnt it? So how is curing acheived selectively from anterior to posterior when the initiation is surrounding the flask.

 

[Didley]

SR-Ivocap | Armstrong Laboratory, Inc.

 

[droberts]

The flask is submerged in the boiling water yes. What you may not know, there are insulating plates on both sides of the flask restricting the heat. So that forces it to cure as I stated. What keeps it from curing up in the injection tube is the height of the water bath, and the time for curing. Back to my eggs Tom. One that I injected in clear, I removed the clear and backed it up with a color. It shows that the color forced into the clear proving that the force is still due to the acrylic has not been fully cured yet. Not only one egg did i do this to, I did it to two. Same result.
I happen to be in a lab that was using the Ivocap as I am. I just happen to be there when one of the employees removed it from the cold water bath to de-flask. When he opened it de-flasking the stone, the width from one tuberosity to the other at a depth of 6mm was still soft. The rest toward the labial of the denture was solid acrylic.
What had happend? He forgot when he set the time and guessed at it. If he would have stuck a wire down in it after removing the injector tube and noticed this, he could have put the injector back on and cured it. Lesson learned...

 

[TomZ]

Dan-

Im sorry but I dont believe the balls and plate will allow for selective curing from top to bottom. It controls the heat, but it doesnt direct the heat from top to bottom.

The thing that makes Ivocap unique is the material, not the injection. You can maintain pressure from a success system with constaint pressure on the plunger with a spring.
The key is the fact that there are no initiators to kick off the curing without heat in the Ivocap.

What if I could show you that one could switch from clear to color and get the same effect using a success or similar system?

I could swallow the fact that the curing comes from outside in, but not from front to back.

 

[TomZ]

Before anyone jumps my ****, we are just discussing this topic.
But after much discussion with polymer chemists, I find many of the claims a bit of a stretch..

 

[droberts]

Its curing from the bottom up. The denture is straight up and down, teeth on the bottom. I really cant say much more to prove it. I own it and know. Also not to push this too far. I am in more favor of air pressure using the injectors over springs. Springs eventually get weak. You could switch colors and get the same effect. Its still the process of the Ivocap that makes it happen. Bring a case of beer and some steaks over, and I'll show you. I know better than to play poker with you, but I would bet my life as to what I have said above is correct, I'm doing it every day

 

[hydent]

The flask is submerged in the boiling water yes. What you may not know, there are insulating plates on both sides of the flask restricting the heat. So that forces it to cure as I stated. What keeps it from curing up in the injection tube is the height of the water bath, and the time for curing. Back to my eggs Tom. One that I injected in clear, I removed the clear and backed it up with a color. It shows that the color forced into the clear proving that the force is still due to the acrylic has not been fully cured yet. Not only one egg did i do this to, I did it to two. Same result.
I happen to be in a lab that was using the Ivocap as I am. I just happen to be there when one of the employees removed it from the cold water bath to de-flask. When he opened it de-flasking the stone, the width from one tuberosity to the other at a depth of 6mm was still soft. The rest toward the labial of the denture was solid acrylic.
What had happend? He forgot when he set the time and guessed at it. If he would have stuck a wire down in it after removing the injector tube and noticed this, he could have put the injector back on and cured it. Lesson learned...

Cool that you did your own study and I'm not trying to contradict you but an egg is a large mass whereas a denture is thin all around don't you think that may dilute your study a little bit.

 

[droberts]

No. The large mass is proving the density of it. If you can process acrylic that thick with out porosity, minimal shrinkage, dimensional change and have it look like glass, I believe that says alot right there of the material and process.

 

[TomZ]

Better yet, Ill introduce you to a guy with a phd in polymer chemistry who says what you interpret is not the way it is. With that said, I will grill steaks or have dinner anytime, as long as we can avoid dental talk.

As was said before, injection is a good production tool, and the marketing of the idea has tons of money behind it. Which works for labs looking to piggyback on the marketing.

There are many ways to skin a cat, its all good as long as it gets skinned.

 

[Brian Hyde]

I agree Tom.. I have used both systems and perfer the sucess system just my own personal prefrence.. But the Ivocap system is great too... But I agree and dont beleive a plate and insulating balls resists the heat, curing bottom to top.. Unless its some kind of special metal from planet pluto or someting we dont even know about yet..lol J/K..

 

[TomZ]

Bart does have a point, but I better not go there. Your not saying you cant get a crystal clear egg using pack pressing are you? Porosity is something people who dont understand the materials get.