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Increasing Mechanical Properties of Aluminum Castings (4/23/19)
We would like to increase mechanical properties of aluminum castings at A357/E357 alloy considering: chemistry, heat treatment and dendrite arm spacing. Any recommendations?
Improve Mechanical Properties of A357/A356/C355 Aluminum Castings (3/27/19)
We would like to improve mechanical properties of A357/A356/C355 aluminum castings with refiners and/or modifiers. What kind of refiners/modifiers can be used? Quantities? How to use them? etc.
Typical Values for Shell Physical Properties (8/17/18)
I've been researching properties of shell molds for a recent project. I'm having trouble finding typical values for different physical properties and what the industry considers to be GOOD quality...
Properties like: green state MOR, Fired MO, Hot MOR...Density, Permeability etc...
Do typical values exist? Or is there a general understanding of minimum values?
Looking for some guidance if you can point me in a suitable direction.
Standard Values for Wax Physical Properties and Chemistry (8/15/18)
Currently I´m doing master thesis regarding the study of waxes.
I´m reaching you to ask if there are standard values for ash content, thermal contraction/expansion, viscosity, mechanical properties and melting point, for the reapplication of wax. In other words, is there are a limit/average value for the properties referred above. Better explained, I´m trying to understand what’s the limit number of refusion/reapplication of wax, without any treatment of purification.
Detection of Shrinkage in Airfoils (2/27/18)
There exists a critically urgent need to find a technique/supplier/source who possesses the ability to reliably detect internal (not connected to the surface) microshrink porosity located within solid, non-air-cooled, turbine engine blades. These blades are relatively small 1.5" long x .020"-.040" in the airfoil and .250 thick in the fir tree/platform.
The subject blade is vacuum cast in CMSX-6 nickel base single crystal material. This material is notorious for developing unusual amounts of microshrink/microporosity within the blade platform - airfoil base transition area during casting solidification. The porosity cannot be detected by standard radiography. The subject blades have been experiencing fatigue failure during engine operation which; most unfortunately, has resulted in several recent aircraft accidents which in turn, have resulted in passenger fatalities.
These blades are not cast, manufactured, or sold by our company, but the current situation has negatively affected several of our customers. Given the critical nature of the situation, we would like to identify a source who may possess a NDT - CT method capable of detecting the presence of microsink porosity in the CMSX-6 castings. We believe Computed Tomography (CT Radiography) may be an effective solution to detecting any potential presence of the subject porosity after the casting process.
I anyone has any relevant information please contact us. I deeply appreciate our help, if we can sove this issue this will, in my opinion, eliminate further loss of life.
We are pouring S7 and are having gas hole problems. We have trialed low nitrogen material using an Argon blanket to no avail. Any other tricks with this material?
Vacuum Heat Treatment (12/2/17)
Homogenizing the alloys to eliminate dendritic segregation appears to be right on the dot, especially the ductility. We have observed this in a few melts that we got vacuum heat treated. However, how vacuum HT smooths out the as-cast dendritic structure still beats me. Can the expert committee throw some light on this aspect?
Secondly, what in your opinion is the major difference in the variables between a sand foundry & an investment casting foundry? An article by a platinum jewel manufacturer spoke of “a process that really knows how to keep & guard its secrets”. If a sand casting foundry variables number say 1000 or so, will an investment casting foundry number its variables at 10,000 or more? We have noticed same castings manufactured 2 years ago never exhibited defects that are noticed today; so something has changed.
Vacuum Heat Treatment (7/13/17)
With regard to vacuum heat treatment, does it improve mechanical properties, especially ductility and toughness? I know that it totally eliminates surface oxidation of castings and associated defects. I have not been able to get any information on this.
Leaching With Potash (6/6/17)
Currently, I am working on a new leaching autoclave using potash but I have had difficulty finding the right leaching cycle (core material remains in the parts). I’m looking for information regarding leaching with potash, even if it’s not for the same application. Could you help me by providing some information about the use of potash (parameters, used process…)?
Follow Up To Cracking of 430SS Castings (5/9/17)
As a follow up to the Ask the Experts response regarding cracking of 430SS and the precautions required to reduce cracking:
1. Is hot straightening acceptable and what are the recommended hot straightening temperatures?
2. If I wanted to purchase hot straightening jigs, where might I turn to?
3. What is the recommended preheat temperature for welding?
4. Are there any special culprits such as C , N , O or others which should be controlled?
Pin Holes (5/8/17)
On a well-established, robust process, we suddenly began witnessing perfect little pin holes in the resulting parts. We have never had this problem before, and they look exactly like the gas (air entrapment)as described in your Atlas of Casting Defects book page 9. We cannot figure out why all of a sudden this is starting to happen we have not changed anything in our process. We pour right at the cup and the venting is the same we have used for years. The only thing different is that we have a new employee helping with the pouring. Could this possible cause the problem?
Also is there anything we can add to 440-C to help de-gas it to help fix this if that is what is going on and if so why would we all of a sudden have to use an additive to de-gas when we never have before? We have not changed anything in the shelling process, it is all the same as before we started to get these holes. They are causing us to have a lot of scrap in our parts. Just trying to cover all our bases and get this figured out. Any information you can give us on this would be greatly appreciated.
Cracking of 430SS Castings (April 29, 2017)
Our company shies away from 430SS as past experience has shown that the alloy is prone to cracking. Is this especially true of this alloy? And how would one work around this problem?
Colloidal Silica Publications and Support (1/25/2017)
ICI publication list makes no mention of Colloidal Silica, its specifications nor the effect the various properties have on the quality of investment castings produced. For example, effect of Colloidal Silica surface area, particle size, pH, etc. have on the stability, bonding strength, etc. of prime coat slurry, back-up slurry. Can the ICI recommend a good publication for this binder? Alternatively, can the Experts Committee recommend their advice / suggestions on this issue?
Part Cracking (12/19/2016)
We are experiencing cracking on the edge of an A357 casting. The defect only occurs on one of the four parts in the mold cluster. Any ideas?
Shelling of Core Passages (12/5/2016)
We have a valve part that we are trying to shell a core passage of approximately 9 mm diameter and over 25 mm long on both sides of the body. We are getting shell cracking in the 9 mm hole. We are using pre-coats of zircon (first dip slurry) till the hole is filled completely, as back up coats are not possible in such a small area. We have standard 325 zircon slurry with 30 % Colloidal and 70% as water. Is there any other way to coat this small diameter or change/add/remove slurry mixture materials for proper dying in first few coats for more strength? We cannot use a ceramic core as per customer requirements.
Use of Plasticizers (10/13/2016)
I want to understand more on the use of plasticizers in the formation of investment casting patterns. I am currently writing a Ph.D. proposal on the production of investment casting patterns from thermoplastics. Is there anyone with which I can contact to discuss plasticizers in wax patterns? Are there any reference materials available?
Shell Removal for Art Quality Silicone Bronze Parts (10/3/2016)
Our company is having art quality silicone bronze parts shell cast. The company doing this has normally sand blasted the shells to remove them. However, because of the gold-like mirror polish that we desire for these castings, sand blasting of any to-be-exposed outer surfaces is out of the question. We need expert recommendations how to get the most hard shell material out of important nooks and crannies on our castings. Physical vibration would likely damage the S. bronze. A product with a decade-long development is hinging on finding how to get the shell to come off of the castings. We sincerely hope you can help.