Injection Machine Temperature Vs. Pressure

[J lure]

Hey guys I recently bought a Jacob's injection press and can’t seem to get the set up how I want. I been playing around with the temperature and pressure, trying to fine dial it in. At first I was getting dents in the cavity and next I was getting flash around the cavity. Is there any correlation between temperature and pressure with dents and flash? Well of course there is but it seems like I'm not make the connection 100%. I had the heat at 3.5 and the pressure at 22 psi, which gave me the best results but not perfect results.... Any help?

What causes flash, temperature or pressure, and what causes dents pressure or temperature?

[DaBehr]

Controlling pressure and temperature is the issue of ALL plastic molding machines ...not just the bait making kind!

Flash is due to high pressure (speed) (assuming there is no defect in the mold)

Dents are the result of one section of the part cooling faster than the surrounding plastic, so if you are using a mold that others have had good results with (not a mold design problem)...then your plastic is too hot.

As with any plastic molding machine (even the big multi-million dollar ones!)...inject at the lowest pressure and temperature possible. (over simplification...but true).

Without going through a series of mold trials...it would seem that your temperature is too hot.

[carolinamike]

DaBehr is right. Time, temperature and pressure are your main variables when producing any plastic by machine. But, soft plastic is a little different. Soft plastic needs twice as much venting as hard plastic because it flows so much faster. And he's also correct about keeping your temperature as low as possible. If you're getting dents, then there's three things you can do to stop the shrinkage. A harder material will help, with your temperature as cool as possible and holding continual pressure on the mold is also something else you'll need to do. After your cavity fills you might have to hold pressure on the mold for 10-20 seconds, it's according to the size of the bait and how many cavities. You need to know what the temperature of your material is. As far as flashing goes, that's a temperature pressure thing. At 22psi if your plastic is say 360 degrees, and it flashes, then you can adjust your temperature down to probably 335. And you may not get flashing at the same pressure. If you feel like your temperature is where it needs to be and you're getting flashing, then just adjust your pressure down a little. I actually try to flash my first shot or two and then adjust my pressures down. That way I'm shooting at maximum pressure. Also you can take a small half round file or round file and open up the gates to the cavity of the mold. This will help material get into the mold faster and help you hold longer pressure on the bait before freeze off occurs. Feel free to PM me if you have any more questions. I'll help if I can.

[Frank]

I pretty much keep mine at 310 and 12 psi. The temp is so low as long as it gets into all parts of the mold I am good. I am guessing you are talking about the number on your heat controller ,mines at the w on the word low. Frank

[XFactorTackle]

When I used that machine I set it at 10psi most of the time and had the temp at 350. Not all molds are the same though, you'll find that some molds need to be shot hotter then others. I would say to use as low of a temp as you can be effective with. My guess is your pressure is way to high, like others have said.

Jeff

[J lure]

Thanks to all. I'm going to fine dial it in this weekend, well hopefully.

[CNC Molds N Stuff]

I've not got the same experience as most of these guys, but for the most part I found I got the best baits and even the best laminates (if both plastics feel about the same viscosity) by shooting with a warm mold and plastic as low temp as possible. I don't have an injection machine so perhaps my experience is not as relevant as some of the others.

Edited September 7, 2012 by Bob La Londe