Sine bar design in unscrewing mold

Hi RTG,

First, it's unclear (at least to me) what you mean by an "unscrewing mold". Is it an assembly or part used for unscrewing using a rack-and-gear mechanism?

Second - "sine bar". Although it may be a term pertinent to injection mold design (I don't know it), a little more elaboration on what it is and where/how it is incorporated may pique the interest of some of our more trigonometrically-minded people here and get you some results.

Looking forward to your answer to my reply.

P.S. It's all about learning

Mike

Hi Mike,

First, thank you very much for your reply.

I'm designing a mold which is for the closure of shampoo container. There is thread with this closure. In order to de-mold the thread, I chose to use unscrew core. There is gear on the unscrew core. In order to create the unscrew motion, the rack is used to drive the gear's unscrewing. In addition, there is stripper plate which is used to eject the part in this mold. The motion of the mold is: As soon as the mold opens, I need to unscrew first.Once it is done the stripper plate needs to be activated to eject the part. While the mold closes, the unscrewing core is not rotating. I want to use sine bar to synchronize the rack and stripper plate.

Is it clear? Sorry for my bad English. If there are still some questions, just feel free to ask me.

Thanks a lot!

Best regards,

Lianna

Hi Lianna,

I really do not know injection molding. My purpose in replying was to get you to give a clearer picture of your particular situation (which you have done), hopefully to allow some others that DO know injection molding to be able to see it and give advice. I will be Googling & such in the next few days and reply as I am able. However, in the same time frame, you will probably get some replies from some who have actual experience.

Mike

Hi Mike,

I really appreciate your help. Thank you very very much!

You gave me very good advice. I'll take a picture of my mold and put it here tomorrow. (it's in another computer)

Thanks again

Best regards,

Lianna

Lianna,

You're quite welcome - it really is fun doing this!

Mike

P.S. I'll be seeing the replies and I'll learn a lot myself!

I don't know how you would use a sin bar for this. D-M-E uses a two stage ejector so that the unscrewing happens during the first stage then the ejection during the second. You can google D-M-E and contact them on your design issue. There is also a good article on unscrewing molds at www.moldmakingtechnology.com .I hope this helps.

Hi,

Thank you very much for your reply. I will spend some time reading the article . It would be a great help.

Thanks a lot!

Best regards,

Lianna

I have seen Injection Molding machines with such molds. I am not able to recollect full details as it was many years back. The unscrewing in the model I have seen is a DC motor that got signal from the machine PLC. Some use Hydro motors also. Using the extra I/Os of the machine PLC/ microcontroller they are syncronized; I think. Contact www.cipetindia.com for more help.

Hi,

Thank you very much for your reply.

Since I chose the sine bar, I want to finish it. But what you said is different way. I'm interested in it. Once I finish this one , I will try the website you provided. Thanks a lot for your help.

Best regards,

Lianna

Hi Lianna,

Is this :- http://en.wikipedia.org/wiki/Sine_bar what you mean by a "sine bar".

Hi,

Thank you very much for your reply. It is the sine bar I want to see. It updated my imagination on sine bar.Thanks a lot for your help.

Best regards,

Lianna

Hello. We have molds with this design and they work very well. The pitch on your threaded core is going to be the angle on your sine bar. The action will be, mold will open. A cylinder will activate a rack drive that turns the threaded cores at the same time the sine bar mounted on your rack starts to advance your stripper plate. The cores are unthreaded at the same rate that your plate strips forward. You will need to design in something on the rim of your part to keep it from turning like a small rib or bump. I think this will help you out.

Hi,

Thank you very much for your reply. The design you described is what I need.

I have six ribs on my part preventing the part from rotating while the core is unscrewing. Is this what you meant?

Thanks a lot for your help.

Best regards,

Lianna

The ribs need to be on the bottom of the rim of your part. I think you are talking about the side of the part. Your design needs to have the parting line at the rim. So if you are looking at the ejector side of the mold the only thing you will see is the threaded core sticking out with small ribs or bumps on your stripper plate that keep the part from turning. The out side of the part will be formed in the front half.If you have ribs on the side of the part this will not hold the part from unscrewing when the mold is all ready open.

Could be please share us the consolidated learning of this topic

Phani

"Could I get a 3D model of the sine bar?"

Shown here <http://en.wikipedia.org/wiki/Sine_bar&gt; is a device for measuring relatively small angles.

It is not something you would incorporated into an injection mold but use as a measuring device to ensure that the angle of the thread was correct.

Hi,

Thanks a lot for your reply.

I was always wondering what the sine bar looked like.

Now I got the idea of the sine bar through this website. Thank you very much.

Best regards,

Lianna

I thank this forum as I have first time learned about sine bar.

I am finishing manufacture of a 2 cavity unscrewing mold for 7/16-20un thread with rack and gear actuation right now. I will take a couple of pictures and put them on my site: injectionmoldtips.com later this week, or first week of june (latest). i am using dp8 rack and dp8 18tooth actuation connected to dp10 60teeth turning dp10 25teeth gears on the part shafts. One important thing to take into consideration in your design is how you will adjust the timing of your unthreading core to control the height of the core easily without changing any other portions of the mold. On your design you seem to be stuck how to progress the stripper plate forward in conjunction with the unscrewing action. I would instead unscrew the thread back into the plate and push the plate forward after the part is released from the internal threaded core.