Process FMEA - Help in deciding "detection ranking" of a failure mode

A

alokb

#1
While doing a PFMEA for a six sigma project "To improve silver purity of a Pyro refining operation " I do need some help in deciding "detection ranking" of a failure mode .

The Potential Cause(s)/ Mechanism(s) of Failure : Due to small capacity of Bottom blowing oxygen cupel of smaller size it is difficult to control temperature because of small thermal capacity.

Since We know that our furnace is having a limitation with regard to size .

Result :- Occurrence rating =10

What about Detection rating ????

We are almost certain about this fact.
At present no design control exist.

A case study would also help in this regard.

Alok
 
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#2
alokb said:
While doing a PFMEA for a six sigma project "To improve silver purity of a Pyro refining operation " I do need some help in deciding "detection ranking" of a failure mode .

The Potential Cause(s)/ Mechanism(s) of Failure : Due to small capacity of Bottom blowing oxygen cupel of smaller size it is difficult to control temperature because of small thermal capacity.

Since We know that our furnace is having a limitation with regard to size .

Result :- Occurrence rating =10

What about Detection rating ????

We are almost certain about this fact.
At present no design control exist.

A case study would also help in this regard.

Alok
How do you go about detecting "failure?" What is "failure?" Does the non-silver part of the mix not absorbed into the cupel? What happens if the temperature is too hot? too cold?

OK. You have to help me out here. I do not know about the commercial side of refining silver. I remember from college chemistry more than 40 years ago (using very small quantities) that a porous dish called a cupel ("kew pull") holds the mixture. Everything is heated to about 1500 degrees in the presence of air. The non-silver stuff oxidizes somehow and is absorbed into the cupel, leaving the silver (and gold, if any is present.) We could dissolve the silver out with acid, leaving the gold. We further refined the silver by electrolytic action.

What is the exact failure? Is non-silver, non-gold residue left with the silver when the temperature isn't right? Is some of the silver destroyed? How do you detect the failure mode? The method used to detect whether the silver is sufficiently pure is what you are looking at, not the detection rate of the temperature variance. (i.e. how do you detect non-silver residue?)

What's the base ore you start with (lead? zinc?)
 
Last edited:
C

cncmarine

#3
Occurence = 10 with no design controls = normally the DFMEA Detection Rating would be 10.


But the question is can you detect when the NC condition occurs ?
 
B

BSpitler

#4
How do you detect the failure? What is the evaluation method? Measurement error? Sampling plan? Error/mistake proofing?

Though I do not know the details of the process, I would not be concerned at all with detection at this point since you already know the failure almost certain to occur. Improvement efforts should be focused on reducing occurrence.
 
A

alokb

#5
:thanx: Dear all,

Thanks for reply.

I am sorry that question led every one in technicality of the process.
Let me frame a general question about detectability.

Suppose we are studying the process of safe traffic management from a particular Traffic Circle .

One of the potential cause of failure mode is " The traffic signal system not available/not in place'

Here since we know it very well that the system does not exist .what about the detetection ranking ?


(As far as this process is concern I am going to post the complete PFMAE for perusal and suggestion shortly)

Alok
 
C

cncmarine

#6
The question is the same:
What type of controls do you have in place to detect the " The traffic signal system not available/not in place'

Is there some type of inspection that occurs to detect the nonconfoming condition ?????


Once that is established then you can assign a ranking.
 
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