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Bob La Londe[_7_] Bob La Londe[_7_] is offline
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Default Springs in a Mold

"Ed Huntress" wrote in message
...

On Wed, 1 May 2019 13:27:47 -0700, Bob La Londe
wrote:

Typo corrected below ***

On 5/1/2019 1:23 PM, Bob La Londe wrote: Yesterday I had a customer
request I add springs to a mold at the last
minute. (Literally at the last minute. I had just sent him a screen

shot
of the cut simulation and was getting ready to take it to the machine.)

Other than the irritation and disruption of last minute changes on fully
approved designs I'm not against doing it, but I don't think I've seen
that before. Now, I am not talking about ejector pins. I am familiar
with them, although the types of molds I make don't make use of them. He
was talking about springs to help open the mold. I can't


** help but

think about
how I would do it, but I'm not sure its really of any use. Most hand
injected or hand poured molds are just easily pried apart. For most of
what I do the media doesn't not have any significant bond to the mold
material and a release agent is not even used. Sure for some resins a
release agent is used, but again the mold opens fairly easily.

I don't think I'd use springs in any automated operation either. The
molds halves are just attached to the platens (?) of the hydraulic press
portion of the injection machine. Hydraulic pressure pushes them
together and hydraulic pressure pulls them apart. What purpose would
springs serve?

I explained that adding a new feature at the last minute would delay his
order and increase the cost. I also asked him if he had seen that
before and how it was used. He decided to go with the original design,
never answered if he had seen that before, but he did specify he wanted
that on future molds. Ok... more money for me I guess.

Have any of you seen a mold with springs built in to assist with opening
the mold? I visualize them in the types of molds I make and I just see
them being an encumbrance.


Bob, return springs for injectors and springs to open molds were
common not many years ago, when I was covering the field. The
mold-opening springs were being replaced by hydraulics at the time so
maybe they're gone now.

But I'm not sure what kind of molding you're doing. Injection molding?
If so, there's plenty of design data around for mold springs. I just
did a quick check on Google to make sure I haven't lost my mind - yet.
d8-)


My work is 99.99% cold low pressure (100 psi peak maybe if somebody is ham
handed and puts their body weight on the injector) injection or low temp
(under 1000F) casting molds. Split about 50:50. I have done a handful of
"high pressure" molds for ABS and other thermo plastics, but its not my
primary market. This particular one was for a low pressure cold silicone
media. They also have a very heavy steel core which is removed after
injection media has fully cured. The core will probably eject the molding
from its weight alone. This customer also wants some ABS molds down the
road, so maybe that's what he was thinking of.

I sometimes make master molds from which I make silicone molds for various
things. Candy molds, resin casting molds, etc. Molds to make molds, but
this is my first mold to make a final product from silicone.

Ok. I guess I could see using springs in a mold that is used in a vise
under a table top injection machine. Still unless its a speed vise I
suspect it would be better to attach the mold to the vise jaws just like you
do on a hydraulic clamping system on a bigger injection machine. Opening
the vise opens the mold. I figured out how I would do it anyway, and I will
make the springs easily removable. Then if he decides they are more trouble
than they are worth he can just popped them out and pitch them.