I have a 6 gun Sand blasting machine for sandblasting Denim garments but my dust collection system is not working properly. What is the most suitable and effective dust collection system for Sand dust.
Your question is about as clear as asking "How long is a piece of string?". Dust collection depends on a multitude of issues such as density of the particle to be trapped, particle size and distribution of particles, dust load, entrainment velocity, etc.
When you say "...my dust collection system is not working properly." how is it not working properly? Are you getting dust fines from the exhaust? What equipment do you have?
If you are getting fines carry over, you either have too high a velocity in the equipment (Was it designed for four guns and you've added two more?), you need to change your sand bed to remove the fines or add equipment that will automatically remove the fines continuously such as will a second stage separator.
Again the fix depends on the specific problem. At this point, I don't know what the problem is.