Welcome!

Regarding the mold cooling, you should first have a detailed diagram of the cooling line/themolator layout. This diagram should document the coolant temperature entering and leaving the mold for each temperature profile. Over time, you should consider adjusting the tooling to accommodate these complications.

-Andy

Is there any standard (ISO or ASTM) that can be reference
for a polypropylene spiral flow test?

My Response

Yes, there is a standard for this within ASTM D-4101. If you are looking to publish the results, then this can be very helpful. Unfortunately, the conditions, flow rates, and pressures used may not directly replicate your processing conditions. In practice, most of the companies I have dealt with create their own procedure based on the conditions of their process.

For example, if they are looking to compare the viscosity of two grades of material. they might replicate the melt temperatures and flow rates of the actual product, and measure the difference in pressure at transfer to represent viscosity.

Another company I have worked with uses many older, pressure-controlled, molding machines. This company uses a constant pressure with position transfer. The change in injection time and flow distance provides excellent information for comparing one material grade to another.

Additional Thoughts

Basically, I recommend you review the standard procedures for the spiral flow test, but adjust the test parameters to meet the specific needs of your production facility. The key factor is to perform a test which provides information which helps the production department.

-Andy

 

This could also be chalked up as a documentation issue. Since we don’t know the melt temperature, 1st stage fill time, part weight, or other machine-independent parameters during the good runs, we cannot quickly identify ‘what changed’ between then and now. 

-Andy

In the old days of pressure-controlled injection molding machines, the first stage pressure was used to completely fill the mold slowly while a lower pressure (approx. 40-60%) was used to compensate for shrinkage while waiting for the gate to freeze.In the newer machines, if the mold is completely filled during first stage, then the old 40-60% rule of thumb is often applicable.

If a scientific or decoupled type of process is being used, where the mold is not completely filled during first stage, then there are many factors which play into the final second stage packing pressure. Essentially, the only rule of thumb is to select a pressure which produces an acceptable part. The first stage injection pressure should have no bearing on the second stage packing pressure. I have seen thick parts using second stage packing pressures as low as 25% of the pressure at transfer, and I have seen thin-walled parts use as much as 125%.

The fundamental underlying basis of good injection molding is to separate mold filling from mold packing. This means you should first establish a good fill, and then establish your part packing.

-Andy