Cavity blocking 1

[mjh368]

Hey all,
Just a little survey, what do you use to block cavities??

 

[patprimmer]

An insert in the runner that can be turned 90 deg so as to block flow in that runner.

A different sprue bush.

By rotating the sprue bush to align to with different runners.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mjh368]

Thanks pat. Anyone using anything else for a temporary block on existing tooling . brass, glue etc???

 

[dgowans]

I'd be hesitant to use anything on a temporary basis unless I were absolutely certain it wouldn't end up in a place where it could potentially damage the cavity you want to block.

Scrapping parts is easy compared to having to fix a parting line that got hosed up because something got smashed in it.

 

[Pud]

Temporary blocking:

Cyanoacrylate to glue a runner section in - works best with styrenics.

For small tools, part design permitting, do one shot, take out moving half before ejection stage (leaving part in cavity) and remove ejector pins from that cavity.

Cyano part into fixed half ( a bugger to get CA off but can be done with hardwood pointy stick without damage to even aluminium tools).

dgowans:
set the mould protection correctly and no damage will be caused....

Cheers

Harry (with stuck together fingers)

 

[dgowans]

Harry,

Thanks for blowing the dust off my brain. It's been a while since I worked for a molder, and even then I wasn't involved in processing. I'd forgotten all about mold protection....

 

[Pud]

dgowans,

Ah! that explains it! Modern kit has very, very accurate mould protection - 1-2KN closing force - 0.1mm before clamp9ng comes on. Should be able to put a small piece of cigarette carton between the clamping faces and it will not clamp up... All achieved at over 100mm/s speed. Clever stuff.


Cheers


Harry

 

[dgowans]

Now that you mention it, I remember seeing stuff like this. Like I said, it's been a while. Now all I do is design things that give molders fits.

"What do you mean you can't hold +/- .005" on the overall length of an 8" long polypropylene part?!?!?!?!!?"

 

[patprimmer]

A part left on the mould certainly works if ejection disabled.

Simply run semi auto so you can confirm it is safely in place between shots.

A rough house way to quickly disable ejection is to cut a hole in the part where the ejection pushes against it.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[smokehouse]

99% of all molds we build have tunnel gates so having said that, most molders that want to block a cavity will already have the rotating sprue or if it's an 8 cavity for example, this will have A & B plate rotating inserts. (1" dia)..

When they get in a hurry and DON'T have this capability...Then they fashion a brass tapered little "pin" that they tap into the tunnel gate..

PS: They're *always* in a hurry..

 

[Pud]

Pat: Forgot the old cut away ejector pin bits - actually got one tool we have to do that on! Don't run semi auto though..........full auto.

Smokehouse:

Other trick: small piece of electrical solder in tunnel gate (called submarine or sub gates here in UK), suitable size rounded end ejector pin utilised as a punch to tap into gate opening. Easy to get out with (another suitably sized) self-tapping screw!

Cheers


Harry