Injector keeps getting stuck when pressing forward into the molds

[MCYNitroZ-7]

I am new to mold pouring soft plastics.  I cannot seem to get my soft injector to go but just a very short distance into the mold before it gets impossible to inject into the mold.  I tried to just pour out of my pyrex mixing cup but the plastic does not get all the way down into every crevice of the mold.  Can someone help me with this problem?

[basskat]

I'm not really understanding your question. Is the plastic getting hard before your through injecting or is the injector binding up?

If the plastic is getting hard inject the mold faster. Make sure your plastic is warm enough to inject. Also warm the injector and mold before starting.

Edited March 15, 2021 by basskat
Can't spell

[MCYNitroZ-7]

7 minutes ago, basskat said:

I'm not really understanding your question. Is the plastic getting hard before your through injecting or is the injector binding up?

If the plastic is getting hard inject the mold faster. Make sure your plastic is warm enough to inject. Also warm the injector and mold before starting.

Thanks for the quick response.  Yes the injector itself is binding up quickly. 

I am extracting the liquid into the injector then going straight to my molds and it is super hard almost immediately to push it in to pour into the molds. 

I have tried to spray pam into the rod slid of the injector but it is not working.  

[Dink Master]

What Injector are you using?

What temperature is your fully cooked plastic?

What is the temperature of your work area?

You might need to preheat your mold and Injector?

[MCYNitroZ-7]

 I am using the 120 ml Aluminum Injector for Soft Plastic Plastisol Fishing Lure Mold Tackle DIY Making.

The temp is close to 350 degrees.

The temp in my work area in ambient temp for outside.  75 - 80 right now. 

 

[SlowFISH]

Is the plastic cooling/setting up in your injector stopping it from moving???  That seems to be what you're describing but if your plastics is really close to 350 and your ambient temps 70-80 you shouldn't be having too much trouble with this.

I'd recommend 1 thing.... try to get your injector hot before shooting the mold.... if all you have is a microwave - heat up your plastic.... pull it up into the injector - wait 2-3 seconds and immediately push it back into the pyrex.... reheat the plastic and clean the injector out.... do this as quick as possible to keep heat in the injector.  This should help if its the plastic freezing up the injector.  When I'm testing a mold (in the winter) and use a micro/pyrex I have my injector setup on some blocks a few inches up over a small alcohol lamp to put and keep heat in the tip/barrel... otherwise i have same issue.

A very warm or even hot injector is your friend.... when an injector is cold - and even 80 degrees is cold - it will cool the plastic really fast and lock it up.

J.

[MCYNitroZ-7]

Thank you SlowFISH.  Great tips and pointers.  I will give this a try.  

[Dink Master]

SlowFISH gave you some good tips.

Suck up the hot plastic and purge it back into your cup a few times, this will warm up your Injector and will let you know it's working

What mold are you using?

If your Injector only holds 4 ounces it might be to small for your mold.

[mark poulson]

Oil your O rings and injector with PAM.

[Les Young]

That injector is 100 % the problem. Oil the inside. . Musky Gary done a mod to his that made it work good. I had one of  those  that you have, but  in a dual injector & i replaced the orings & cut a notch to be able to use a screw driver to twist & remove the tips from the tubes & it worked alright. Since i had one like you're talking about my advice would be to replace  with either a basstackle, a do-it or one from quality injector. Basstackle is the best on the market however & is what i'd get if i were you.  Never skimp on an injector.

Edited March 16, 2021 by Les Young

[Dink Master]

15 minutes ago, Les Young said:

That injector is 100 % the problem. Oil the inside. . Musky Gary done a mod to his that made it work good. I had one of  those  that you have, but  in a dual injector & i replaced the orings & cut a notch to be able to use a screw driver to twist & remove the tips from the tubes & it worked alright. Since i had one like you're talking about my advice would be to replace  with either a basstackle, a do-it or one from quality injector. Basstackle is the best on the market however & is what i'd get if i were you.  Never skimp on an injector.

The first 4 Reviews on Amazon says it all. Thank for the input Les.

I was trying to help not knowing the Injector was junk.

[Frank]

Wow I did not even realize those existed. I take it for granted that when injecting 350 deg plastic people would not make something that would not work well. Live and learn. I have had at one time had all the injectors that were made and settled on the one I thought was made like a tank. To this day i still have the original ones I bought and they are just as good now as when I bought them. Don’t skimp on the injector it will pay for it self fast. It may cost more now and may be hard to get but when you have it you will see and feel the quality. 

[Les Young]

On 3/16/2021 at 11:52 AM, Frank said:

Wow I did not even realize those existed. I take it for granted that when injecting 350 deg plastic people would not make something that would not work well. Live and learn. I have had at one time had all the injectors that were made and settled on the one I thought was made like a tank. To this day i still have the original ones I bought and they are just as good now as when I bought them. Don’t skimp on the injector it will pay for it self fast. It may cost more now and may be hard to get but when you have it you will see and feel the quality. 

Agree 100%

[SlowFISH]

3 hours ago, CNC Molds N Stuff said:

Its almost certainly binding up.  It could be air locking, but that seems unlikely since you are able to draw plastic in. Air locking happens when the rod guide is to close of a tolerance to the piston rod.  

I think it would more likely be that the piston is to close to the size of the cylinder bore, and maybe not be machined straight to the piston rod.  When drawing against minimal force it can sort of rattle down the tube ok, but when pressing against stronger more uniform force it binds up in the cylinder.  If the piston rod guide is bored off center it could also cause or contribute to binding.  

I do not sell injectors, but I have made a number of them over the years.  I've made and learned from all the mistakes you can make I think.  If you would like I will take a look at yours no charge, but you pay shipping both ways.  I might not be able to make it "right", but I bet I can make it work.  

lol.... I had some leftover aluminum from various things and decided to replicate my Bass Tackle Injector - seemed super simple... crank up the lathe and I'd be done in a couple hours... lol...  it drove me nuts.

These injectors seem super simple - and they are - but all the little details that have to be just right to get it to seal correctly and I had to monkey around to get a smooth pull/push... so I know the pain.  I also think you are dead on with a little sloppy machining locking it up when the piston is retracted.... on mine I had every thing perfect - but rushed threading the piston/piston rod and that caused the piston to be slightly off center... first pull back on the assembled injector and it locked solid in the tube and I had to hit it hard to release the tension in order to disassemble.  So you probably right with a little slop on piston, end cap hole alignment, etc. that could totally lock that thing up tight.

[mark poulson]

4 hours ago, CNC Molds N Stuff said:

... and there are some things you can just make sloppier and get it to work.  For instance the piston only has to connect solidly to the piston rod, and support the o-ring.  The rest can all be relieved away.  Also the rod guide can be much sloppier than they are often drilled or bored.  It just has to keep the piston from cocking over so far as to lose the seal.  It doesn't have to be at all close tolerance.  It actually works better even if its well built if it isn't. 

Its been a long time since I made my first injectors.  First time I made one for a customer (he bought a mold to big to fill with his injector) I actually made three of them (parts pictures are in the gallery here somewhere) and picked the best parts for the one I sent to the customer.  (Sort of a Shelby Engine Approach.  Buy three engines, to build one with all the best parts, and send the other two back.)  I don't think anybody made one that big back then.  I never really wanted to make and sell injectors, although I have made a few...  Bass Tackle does a really nice job, and in the grand scheme of things their price is very reasonable even if my Bass Tackle 6oz injectors don't quite hold six ounces. (I remember the flack I received when I brought that up some years back.  LOL)  Its my understanding their six ounce injectors actually hold six ounces now.  I always send people to them for injectors.  The only complaint I have ever heard is they don't make enough injectors to keep up with demand.  

interestingly the only injectors I have left at the moment are my old Bass Tackle twinjectors.  Had a customer buy my old Jacobs injector because he didn't want to wait for one to ship (he still had to order plastic), and another bullied me into selling him the two rejects I had left from that "Shelby Engine" injector.  All my others have gone over the years too.  I've got some tubes machined up in the back shop right now because I have some molds on the bench to big to shoot with the injectors I have.  What's old is new.  LOL. 

I still have the one you sent me.

 

[Les Young]

That injector will also expand & contract very badly if you really try to shoot it a bunch & it will get so hot that  you’ll think it’s going to burn you. 

Edited March 18, 2021 by Les Young

[SlowFISH]

2 hours ago, CNC Molds N Stuff said:

Using voice to text here. Please ignore syntax and spelling errors due to vagaries thereof.

SlowFISH

One trick to getting Pistons wind up right is the drill and tap them, Mount them on the piston rod, and then finish machining them with the piston rod clamped in the chuck Jaws.  I did all of my first injectors on a Harbor Freight 7x10 POS hobby lathe.  The setup seem to work out okay. The o-ring groove was concentric and perpendicular that way. Well within the tolerances of a POS machine anyway.

 

Mark

You have mentioned my giving you an injector a couple of times, and I just didn't recall doing that until recently. I remember I gave you a mold with a Senko like body and twin tails like a twin tail grub, but I didn't remember giving you an injector.  Then I remembered I had made one more of those early injectors. One with a really lousy cone shaped nozzle if I remember correctly. That must be the one I gave you. I do recall sending you that mold and you saying thanks but you didn't have an injector.  

 

 

Bob - I did exactly that - by the time I attached and turned down the original piston (trying to fix it) I felt I took too much material off - so machined a second piston - left it slightly oversized to start - threaded and attached it the to piston rod and then remounted it in the lathe and removed the last couple thou to get those two parts dead on together... should have done it that way to start! 

I have one of the Grizzly g9972z lathes - not the best machine - but perfectly suitable for a hobbist who isn't worried about perfect tolerances and having to remake a part or two every now and then... addition of cheap Igauging DRO's on it helps IMMENSELY on these machines... as it all but eliminates the backlash issues and makes things simple for someone with basic skills.

J.

[mark poulson]

Bob, the injector still works.  I made some molds with a smaller sprue that it fills just fine.

[Cami]

On 3/15/2021 at 3:19 PM, SlowFISH said:

A very warm or even hot injector is your friend.... when an injector is cold - and even 80 degrees is cold - it will cool the plastic really fast and lock it up

Dear J., this sentence should be written in the stone: yesterday, for the first time, I shoot in my pre heated molds, no more only oiled, with the injector pre heated by a thermo gun and ... its movement changed at all, smooth, sliding, a real pleasure to use it. Thank you.

Cami