Powder Weight Proportion Measurement Gage R&R

[sinned]

Help!
We have a measurement on powder particle size proportion using a set of sieves and an electronic scale. During measurement, the powder is sieve to obtain particles of certain sizes and use a scale to weight how much powder is left in the different sieves.

Question: to perform a GRR study of the measurement system, should i include the sieving into the system? Or just the electronic scale measuring the weight of powder ?
If it's the former case, I need to get the 10 samples through sieving and weighing. Should i?

 

[Bev D]

We have a similar process in my organization. The sieves are a critical element of measuring the particle size distribution so you must have replicate measures of the whole system not just the scale. This is a functional measurement system - so how you set up the test is critical. Technically it is a nested study as the powder cannot be measured twice (lots of powder in the sieves during the first measurement will seriously effect the study results. And different particle sizes will be effected differently due to their mass and the effect of static and vanderwall's forces...

The approach that I found to work best is to take a large sample of powder that will most likely be homogenously mixed and break it into enough sub samples for each replicate you will be testing (If doing the common 10 X 3 X3 study you will need 6 sub samples of 10 different lots).

Make sure you clean the sieves fully in between each rep...

 

[sinned]

If this is true, what about the measurement on ash content of powder ?
This involves measuring the weight of material before and after burning in oven with a scale. Do i also need to include the burning process into the system?

 

[Bev D]

yes - it is part of the measurement system.

 

[sinned]

Thanks for your advice.
I will try to arrange for that and see how well we can get about the GRR. I am not optimistic on the result as it will be difficult to get samples of full tol. range. To your experience, how well will the GRR be ?

 

[Bev D]

Why do you think you need batches with the full range of the tolerance?

The outcome of the GRR will depend on many things, primarily your specifications I'm guessing. In our case the specifications were fairly narrow - and unfortunately they needed to be. so our GRR wasn't great at all. We compensated by always taking 3 PSD readings. WE also discovered that PSD is not homogenous within a lot and so we took PSD measurements for each sub-batch of material that we were going to make product with. while our GRR wasn't great we could see the differences between batches and this allowed us to greatly reduce our scrap due to poor PSD.