Pack and Hold

[Suhas]

How many of you differentiate between Pack and Hold in your process settings?
Suhas

[brentb]

I mostly call it "pack/hold"

In the "old days" we called it "2nd stage injection"

Keep on Molding
brent

[rickbatey]

I normally just call it hold, but I'm a bit odd as many of you know!
Rick.

[Josue]

I call it same way, but some machines say Dweling...

[brentb]

I call it same way, but some machines say Dweling...

¿Empacar y retener o sostener?
O 2ndo etapa?

Keep on molding!

brent

[EBSMITH]

were you talking about what it is called or did you mean having different pressure settings between the two?

[Suhas]

No, I was asking when you were establishing the process do you use one pressure & time for pack and another to hold? I think in about 20% of the cold runner molds and in almost all hot runner molds I differentiate between the two.
Suhas

Brent, I think you will have a good Spanish audience for your next class :)
Rick, Odd people come up with some of the best solutions, so keep on it my friend!

[EBSMITH]

well on a machine that has the option of multiple settings, we do have different settings for numerous reasons. On all electric machines we would use lower hold settings just to keep the servos from over heating. if you can get away with out losing part weight I recommend the lower hold setting just from energy savings stand point.

[Chris]

i try to keep my pack up kind of high, just so the transfer pressure is not a huge gap, then drop off more with the hold.

chris

[brentb]

How about velocity VS pressure in pack/hold?

keep on Molding!
brent

[EBSMITH]

Velocity in pack/hold needs to be set high enough so you are not velocity limited, same as pressure during fill.

[Josue]

Si Senor!!!!

[jonturka]

In european machines I have never seen two different 2nd stage (pack and hold). There is only 1 and called hold :) (There is 16 stage profile you can add of course but all called hold)
Also in Turkey, nobody pays attention %100 to holding time. Most molds are working with 3-4 secs.

As I learned from Suhas book (tell me if i am wrong) Packing is to compensate shrinkage and to reach final weight and hold is time to gate seal. But to be honest, I think differentiate these steps is too much effort. Also explaining this to technicians is very difficult for them to understand.

@EBSMITH in Europen machines I have seen, there is no velocity for holding phase. I have seen velocity only in Chinese and Taiwan machines. Why it is necessary ? I think pressure and time also creates a speed which means if you increase pressure. You can answer me saying "then same thing also for injection phase, why we there is speed". I would say it is more speed related :) In holding speed is very low mostly. Please dont misunderstand, I just want to learn why there is velocity.

[EBSMITH]

terminology used by machine manufacturers bugs the hell out of me, I wish they would all use the same. the effect of velocity in pack or hold is dependent of the wall thickness of the part you are making, if you have a very thick wall the velocity could have a large effect, while the machine is in pressure control, the microprocessor is only trying to achieve the set pressure, so if the set velocity is too low the machine cannot make the pressure and therefore becomes velocity limited.

velocity in pack is more critical than in hold, since all you are trying to do is freeze the gate.

I am not sure if I have ever seen a machine without some sort of control for velocity, whether it is a set point on the controller or flow control valve that can be manually adjusted.

the three phases I teach our technicians are fill, pack and hold, regardless of the press terminology, if you have only hold with 16 profiles, I would teach the techs that the first hold after fill is pack, lol how much fun is that?