Pressure drop through hot runner

[Daveveal]

What is an acceptable pressure loss through a hot bush? We have trialled a tool recently which is taking 78 bar hydraulic pressure to purge though the hot runner using melt 7 pp with 20% talc with melt temp 260C. Does this seem normal? Machine has 10:1 ratio.

[rickbatey]

What does it take to fill the mold? Then you can run the differance between the two as a percentage and see if it is acceptable. The 7 melt with talc makes the resin harder to flow, but without the mold numbers, you can't make a decision.
Rick.

[Daveveal]

Pressure to fill the mold is 146 bar hydraulic with a fill time of 1.2 seconds. I was just wondering if the pressure to get through the bush is abnormally high because it is the wrong design/size for this application. We did not design the tool and the hot runner supplier reckons this is the correct size for the job.

[rickbatey]

Well that looks like a 53% variance. Could be little on the high side.....but what is the max of the press? Do you have enough left over for viscosity changes?
Rick.

[Suhas]

Hi Daveveal,
Can you give us the (as Rick asked) - the max machine pressure, the part weight, approximate longest flow length, is there are cold runner - if yes longest flow length, number of cavities the approximate length of flow in the manifold from the entry point to the exit point into the mold. Just give us an idea, nothing exact. That will help.
Thanks,
Suhas

[Daveveal]

Max Machine pressure 160 Bar, Part weight 70g, 4 Cavity. Hot bush flow length approx 200mm then cold runner flow length 175mm. Each cavity has 2 gates 1.5mm dia and a maximum flow length of approx 220mm. Thanks guys.

[rickbatey]

So you're at 91% of the machine max pressure...I think there could be some room for improvement, without seeing a part or the mold. Could you change to a higher MFW resin,? That could open the window more. What is the orifice or size of the hot tip? Could be some changes there.