hey Francis,
Can you answer these questions so that I can analyse the cause??
What Investment powder do you use & the mixing procedure adopted ??
What is the Burnout cycle used for the above design??
What was the Flask temperature after burnout & during casting??
What was the metal temperature of cast metal??.
How many times have you used this metal ?? ( Is this a fresh metal or recycled metal)??
If you can reply me to the above questions in detail I will be able to help you solve the problem.
From the picture you have sent it feels like you have the below mentioned problems:
Investment Powder related mixing issue.
Improper Burnout issue.
Flask Temperature maybe too low.
Metal temperature maybe too high.
Issue of gas porosity due to high temperature.
Awaiting for your reply
Prakash V Pai
INDIA