Injection Pressure unstable...

[hendrich]

Hi all,

in my company i work for, there are have plastic molding injection use rubber material. There is issue about injection pressure, if i decrease the injection pressure than the bubble issue coming, this i try to fix the flow line issue. And then i get the good condition, but after 2-3 hours running the machine, the flow mark issue coming again....
please help me what i should to do... newbie..
thanks for any advise....

[brentb]

How are you "decreasing the injection pressure? What "rubber" are you using? Is this being injection molded?


KOM

brent

[hendrich]

How are you "decreasing the injection pressure? What "rubber" are you using? Is this being injection molded?


KOM

brent

Hi brent,

i adjust the injection pressure from control panel of machine. And for the material i use AlphaGary Evoprene™ G 968 SEBS Thermoplastic Elastomer. I already study for cavity to cavity balance and i get the result as my wish ( good) but after running few hours the cavity not balance again and must adjust to get back the balance condition. I wondering what happen with the machine.....

[Suhas]

Is the mold temperature staying constant? Check the temp when you start and then when you start seeing the issues.
How about the vents? Are they staying clean?
Suhas

[brentb]

Also what do you mean by "injection Pressure"? Is this 2nd stage or holding pressure?

KOM

brent

[hendrich]

Is the mold temperature staying constant? Check the temp when you start and then when you start seeing the issues.
How about the vents? Are they staying clean?
Suhas


hi suhas,

the mold temp is stable, also the vents are clean. how to make injection stable, what study i should to do ??

in that case, we use Haitian brand, i already study cavity to cavity balance and i get the result as my wish, but after running few hours the cavity not balance again....

i don't know what happen....

Your suggestion is highly appreciated....

best regards,
hendrich

[hendrich]

Also what do you mean by "injection Pressure"? Is this 2nd stage or holding pressure?

KOM

brent



hi brent,

i adding the value of injection pressure because the part get bubble and i reduce the injection pressure for flow line issue...
for the both issue (bubble and flow line) what the best way to solve it ...??
thanks for any advise..

best regards,
hendrich

[nemanja]

hi,

im useing similar rubber like materials, and i had similar problems, but first i would like to know do you run on hot or cold runner, is material cussion stable, did you measure actual temperatue in cavitys or just read from machine, is it posible that you have somewhere "material leak" after some parts of machine/tool get hot?

regards,
Nemanja.

[RobertPHale]

Hendrich,

It sounds to me what you are experiencing is your process may be becoming unstable due to your machine becoming pressure limited. When dealing with your pressure setting, you need to have an abundance of pressure available so your machine can adjust on it's own when changes in the material occur. What you might do is pay attention to your fill time while the press is making acceptable parts. When it begins making unacceptable parts check your fill time to see if it changed. If it is slower than before my bet is that while the machine is running, the material is changing slightly either through it's viscosity, or maybe something is restricting the materials flow such as a blockage in the nozzle or in the check ring. If you suspect it to be check ring related, then you could always perform a dynamic check ring repeatability test to check for leakage. The result should be less than 3% leakage. If it is more than three, then your process control will be hindered. If you need direction on how to perform that test then let me know and I'll post the process on here. Those would be the two main things at this time I would check if the pressure is varying greatly. The major thing to remember is to not try to control your process by adjusting the available injection pressure. There should always be an abundance and you should process around the core studies such as your in-mold rheology study, your gate seal study, and those studies alike as well as following all material processing recommendations from the manufacturer of the material and starting at the low end of the temperature range as well and pay attention to the temperature of the mold and the recommended mold temperature for the material.

--Robert

[hendrich]

hi,

im useing similar rubber like materials, and i had similar problems, but first i would like to know do you run on hot or cold runner, is material cussion stable, did you measure actual temperatue in cavitys or just read from machine, is it posible that you have somewhere "material leak" after some parts of machine/tool get hot?

regards,
Nemanja.

hi nemanja,

For the cooling system was i used hot water 30 deg celcius for cavity and core both mold ( 2K mold) first shot and second shot mode. and for the cussion material is'nt stable, and also i already measured the actual mold temperature, they are around 34.2 until 34,9 deg celcius. for preventing the material leak and sink mark, i adjust the mold cooling time. The best result i get around 15 second.

Actually now the pressure already stable, because when i solve the sink mark issue and now the injection pressure is good enough.....

best regards,
hendrich

[hendrich]

Hendrich,

It sounds to me what you are experiencing is your process may be becoming unstable due to your machine becoming pressure limited. When dealing with your pressure setting, you need to have an abundance of pressure available so your machine can adjust on it's own when changes in the material occur. What you might do is pay attention to your fill time while the press is making acceptable parts. When it begins making unacceptable parts check your fill time to see if it changed. If it is slower than before my bet is that while the machine is running, the material is changing slightly either through it's viscosity, or maybe something is restricting the materials flow such as a blockage in the nozzle or in the check ring. If you suspect it to be check ring related, then you could always perform a dynamic check ring repeatability test to check for leakage. The result should be less than 3% leakage. If it is more than three, then your process control will be hindered. If you need direction on how to perform that test then let me know and I'll post the process on here. Those would be the two main things at this time I would check if the pressure is varying greatly. The major thing to remember is to not try to control your process by adjusting the available injection pressure. There should always be an abundance and you should process around the core studies such as your in-mold rheology study, your gate seal study, and those studies alike as well as following all material processing recommendations from the manufacturer of the material and starting at the low end of the temperature range as well and pay attention to the temperature of the mold and the recommended mold temperature for the material.

--Robert

Hi robert,

Thanks for your advise, i am very appreciated.

best regards,
hendrich

[nemanja]

Hi,

is good if you menage to get stable injection preassure, but still there is some problem if material cussion is not stable. Process wont be stable if you dont have all the time same volume of material inside cavitys. Maybie you can try to incrise a bit volume and end "move" end of all stages of injection for that value.
But if is overmold there can be also that you dont have stable volume of overmolded parts (it was one of problems in my case).

BR,
Nemanja.