How to decrease interface contamination

[Zhiguo]

hello friends,

I am troubled by sand blasting interface contamination these days.
We are doing HVOF coating on a landing gear axle (material is 300M,hardness is about 57HRC).
we sand blasted with the following parameters:
sand: F70 white alumina
Pressure:3.5-3.8bar
Nozzle diameter:5.8mm (two pressure gun)
angle:60
distance:200-250mm

The requirement is: check under ×200 microscope, in each field of view (not average), the interface contamination should lower than 10%.

I have tried many times, I even brushed the samples with nylon and copper brush, and then put it in the supersonic cleaning.
But in one or two field of view, we still can see some sand embed.

Have you ever sand blasting on this material?
Is it possible to achieve that criteria?

[derek]

Here are some thing you can do to reduce the interface contamination:
1, F70 is very fine grit for blasting, try to use bigger size.
2, 3.5-3.8 bar can be reduce to 2 bar.
3, How often do you change the grit? Maybe the blaster is too dirty.

[Zhiguo]

Here are some thing you can do to reduce the interface contamination:
1, F70 is very fine grit for blasting, try to use bigger size.
2, 3.5-3.8 bar can be reduce to 2 bar.
3, How often do you change the grit? Maybe the blaster is too dirty.

Thank you Derek! I will try as you advised.
Our sand is recycled. After sand blasting, the sand will be seperated by screens. Some good size particles will be collected and recycled.