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Madhav
India, Joined Mar 2018, 4

Madhav

India,
Joined Mar 2018
4
07:17 Mar-29-2018
Cracks during casting

we have been casting bushes through manual pouring method with 5% Antimony lead alloy. Cracks are observing in the finished product. is there any way to avoid these cracks.

Pot temperature - 430-460 deg
Mold temperature - 90-100 deg
pouring time - 5 sec

mold material - NS30

Please proide your valuable suggestions in this..

 
 Reply 
 
Rick Lopez
R & D,
John Deere - Moline Technology Innovation Center, USA, Joined Jul 2011, 191

Rick Lopez

R & D,
John Deere - Moline Technology Innovation Center,
USA,
Joined Jul 2011
191
18:13 Mar-29-2018
Re: Cracks during casting
In Reply to Madhav at 07:17 Mar-29-2018 (Opening).

Madhav,
Your problem seems unlikely to be solved through an internet forum, as there are very many details that would need to be considered. I would suggest that you find a casting process simulation (e.g. MAGMA, ProCAST, etc.) resource, and perform destructive analysis to identify when during the process the cracks are forming (e.g. during solidification, after solidification and during removal/ejection from the mold). Virtual simulation and destructive detective work are often necessary to solve problems.
Regards

 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
21:14 Mar-29-2018
Re: Cracks during casting
In Reply to Madhav at 07:17 Mar-29-2018 (Opening).

Dear Madhav
The 5% Antimony Lead alloy is an Eutectic alloy. The melting temperature of this alloy decreases as you increase the percentage of antimony until you reach the eutectic alloy (~17.5% antimony), and then it increases until you reach pure antimony.
The melting point of pure Lead is about 327.5 C and that of pure Antimony is about 630.7 C
The melting point of 17.5% Antimony Lead Eutectic is about 251.2 C
The melting point of 5% Antimony Lead alloy is about 315 C or less
So your pouring temperature should be about 315C + 50 C if you are heating the mold.
You may take the melt to 430 C for dissolving any other eutectics but the pouring should be around 365C
I feel that you are pouring the metal at a clear 60 to 90 C higher temperature which brings many solidification, segregation, degasification problems. (If you have some specific recommendation to pour at the higher temperature please let us know)
I feel the mold temperature is also on the higher side.
What are the measures being taken for degasification just before pouring.
The above opinion is given without knowing the shape/size of the bush and mold.
If you can give these details may be a better opinion can be given.
Also if you give the location and nature (including a picture) of the cracks, more focused interpretation of the defect can be given.
Best wishes,
P V SASTRY

 
 Reply 
 
Madhav
India, Joined Mar 2018, 4

Madhav

India,
Joined Mar 2018
4
07:12 Mar-30-2018
Re: Cracks during casting
In Reply to P V SASTRY at 21:14 Mar-29-2018 .

Download Virus Scan recommended!

Dear Sir,

Thanks for your reply.
we are using air cooling for the bush casting.
The cracks are generating inner side of the bush and sometimes outer side.
Attached the images and manufacturing process for your reference,please have a look.

Regards
Madhav
 
 Reply 
 
Madhav
India, Joined Mar 2018, 4

Madhav

India,
Joined Mar 2018
4
07:28 Mar-30-2018
Re: Cracks during casting
In Reply to Rick Lopez at 18:13 Mar-29-2018 .

Dear Rick,

Thanks for the reply..

we have used the same mold for 3.1% antimony which results 0% cracks but where as 5% antimony cracks are forming. There is slight density difference between 3.1 and 5 % antimony, may this cause any solidifaction issues??? The main purpose of incresing antimony is to attain 15 hv hardness.

Please suggest me if any tool that can explain this..

 
 Reply 
 
Rick Lopez
R & D,
John Deere - Moline Technology Innovation Center, USA, Joined Jul 2011, 191

Rick Lopez

R & D,
John Deere - Moline Technology Innovation Center,
USA,
Joined Jul 2011
191
16:52 Mar-30-2018
Re: Cracks during casting
In Reply to Madhav at 07:28 Mar-30-2018 .

P V Sastry's line of thought looks like a good one. Also, is it possible that normally trace, and therefore typically ignored, elements might be higher than expected? I've never explored lead alloys, but a quick web search suggests that arsenic content can be detrimental and something worth checking.

As an example, I came across a paper describing analysis of battery grid castings that suffered from distortion and cracking due to excessive casting temperature, slow cooling rate, and elevated arsenic. In that study, the high melt temperature led to a coarse structure, and in between the coarse dendrites there was severe segregation of low-strength alloy. The low-strength inter-dendritic alloy was then overwhelmed by stresses during cooling, especially at regions where thick areas met thin areas, which led to cracking (it would appear that your cracks seem to prefer a region near a thick/thin transition). A potential path for detective work.

 
 Reply 
 
Madhav
India, Joined Mar 2018, 4

Madhav

India,
Joined Mar 2018
4
07:36 Mar-31-2018
Re: Cracks during casting
In Reply to Rick Lopez at 16:52 Mar-30-2018 .

Dear Rick,

Thanks for the reply..

I have verified the arsenic content in both 3.1 & 5% antimony lead alloy , there is a decay in arsenic content in 5% Sb when compared to 3.1% Sb. As you said dendritic structure observed during micro structural analysis of bushes..

 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
13:36 Mar-31-2018
Re: Cracks during casting
In Reply to Madhav at 07:12 Mar-30-2018 .

Dear Madhav,

From the information and photos it is clear that you have internal cracking from the solidification shrinkage and hot tears on the outside.

The first one is related to section thickness at that location and solidification dynamics.(that includes the pouring temperature, mold temperature etc.)

The second one is related to the solidification dynamics as well as change of section thickness at that location.

By controlling the pouring temperature and reducing the mold heating temperature, the first one can perhaps be eliminated. If not you have to look for extra chilling or feeding at the location of the internal crack.

Hopefully the hot tearing also will be eliminated by the above factors. If not you have to go for slight contouring of fillet section to eliminate the sudden thickness change and this can be machined off later.

Please take all the usual precautions meticulously for degassing and dross removal, before pouring the metal. Please check the calibration of the temperature indicator/thermocouple or the emissivity setting of infrared thermo meter ( whatever you are using)

With Best wishes,

P V SASTRY

 
 Reply 
 

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