Creaking noise during injection

Hi All. We have a Mits 500MSJ. One mold we run is very near the tonnage limit of the machine. We find we are hearing a loud creaking/snapping noise during the pack stage of injection. There is a slight noise again are the screw begins to reload. It seems loudest in the area of the nuts for the tie bars. Wondering this is a sign of a problem that should be addressed, or if it's just an inconvient side effect of running near the limit of the machine. Anyone have a similar experience, know what is happening, or have suggestions how to correct? Thanks.

Might be the sprue bushing (assuming a cold sprue) One often blames the tie bar/nuts

KOM

brent

I've heard this 3-4 times in my career with different brands of machines. The last an Engel 1,000t Duo that did it with EVERY mold it ran regardless of resin, gating, valve gates, and water temperature. Another was a Toschiba 500t hydraulic clamp. It never seemed to make a difference and I know the Engel is still running. Not sure what to tell you or how to stop it.
Rick.

This also happened to me (Kraussmaffei 420t). It sounds like not creaking but breaking sound. But very loudy one, I can hear that from my 75m away office.
It happens in different stages
- This sound I hear from my office is at the end of clamping force build up. Even I do not make injection I hear this sound, lower clamping force brings lower sound. Experts of KM checked but couldnt find any solid reason. Most comments are mechanical cores in mold. I could not find the reason because I did not have any else machine to mount and operate this mold..
- Another sound is at packing stage, and this probably because of venting. If you improve venting channels, sound may be less.

Could be manifold in base making the sounds when fully packed with material and in the holdingstage of injection.

Could be from a very slight flex of the tie bars that occurs during clamp/unclamp since you are running near max due to machine leveling on injection and clamp units. Maybe check that.

I believe what you are describing is high tension, then relief, on the tie nuts. This noise is fairly common. I have heard this before, especially on large machines, at high tonnages and it has never caused us a problem ......other than the noise.

Joel S