Need help with melted lipstick injector machine. 911

[Effcap]

Hello, I am a new user and not an engineer in any sense of the word and I need help solving a problem in a machine I'm helping to complete.

I usually work in the electonics automation control field but got pushed into a undermanned project that involves injecting melted lipgloss (180 degree) into very thin applicators. We tried traditional waxmelter heaters and pumps but none were accurate enough to inject a 4 gram volumn of melted product into the applicator. A Nordson type glue gun approach was suggested but the heat requirements of lipstick are very intolerable of high surface area heating and can seperate the product destroying it in the process. In the prototype stage traditional hospital 10cc syringes were used to inject melted lipstick drawn from a heated pot into the narrow containers. That got us looking at ServTec's food cylinder pump systems but even they said the small 4 gram shots were too small for their smallest system to handle. But when looking at photos of how their systems work, we go the idea to build our own, very scaled down version of a cylinder pump.

We built it from stainless steel 1/2" pipe fittings. It has a small heated hopper on top. The melted lipstick exits the bottom and is controlled by a solenoid valve that is connected to a T pipe junction. The center of the T goes to a small modidfied pneumatic air cylinder that is controlled by a linear actuator. It is essentially pulling the melted product into its chamber which is limited to fill to exactly 4.5 grams of volume. Then the hopper valve shuts off and the solenoid valve on the lower part the T opens which is connected to the injector nozzle and fills the applicator. We've got heat trace cable and insulation on all fluid control pipes and all the electronics are working as designed. Friday we tested the system with water and it worked perfectly as designed - injecting out 4.5 grams of 180 degree water.

Then we did the test yesterday with the melted lipstick. I knew the viscosity was much higher (more like very thick oil) than water but naively thought that if the system was air tight - whatever we pull into the cylinder will be able to pushed out the injector nozzle with enough force. What we got from the test was a total wash.

Only a few drops of melted lipstick came out the nozzle. My first thought was the injector solenoid couldn't handle the 180 degree heat wrap around it and was not opening anymore. But the hopper solenoid is the same type and was working fine. It seems the system is not air tight or at least became un-airtight with the higher viscosity fluid.

I tested it by pushing the control rod of the air cylinder in and out. Even with both valves closed, the arm could be pushed in and out pretty easily. I could see the fluid in the hopper rise up and down with each push and pull and each guggling coming of the nozzle at the other end. This means the valves themselves were leaking air and my cylinder had no chance at pulling in product and pushing it out. I can only assume at this point that these $40 solenoid valves could not handle the higher viscosity fluid and were therefore not closing all the way under spring power (normally closed).

So what kind of valves are used in these type of high viscosity systems? And are solenoid valves strong enough to stay closed and air tight passing these kinds of products? Are air valves better suited for this type of machine so they can use more force to close and seal the valves? And finally, how do you bleed a system like this of air so it will operate right? Where do I add bleed valves in the piping? Or if I have true air tight valves, would they do the work for me?

I know... long winded but I'm really in a bind to get this machine operating quickly. I'm looking over valves now and have seen mentioned "through conduit valves" and "gate valves" and pinch valves but some of these are massively huge for a system this contained.

Any help you can give me on how to get this working as it did with water would be greatly appreciated.

Overview of system:

Small hopper on top heated to 180 F.
18" total of 1/2" (i.d.) stainless and brass piping also heated to 180F.
Modified air cylinder (1/2" diameter) used as piston cylinder.
Two off the shelf $40 solenoid valves designed for water, air and light oil.

Thank you,

Frank

 

[MikeHalloran]

The quickest surest path to success involves renting an actual mechanical engineer to show up in person at your place, stay there for (quite) a while, and start over.

The person you want will instantly point out that 4.5 grams is a measure of mass, not volume, so a cylinder calibrated to pump 4.5 grams of water will pump a different mass of hot wax.
(S)He will then point out that 4.5 grams of water has a volume near 4.5 cm^3, which is not a lot to be sending through 1/2" pipe or even 1/2" tube, which is not the same thing and not even close to the same diameter.
(S)He will also point out that air cylinder seals are not like hydraulic cylinder seals, and are unlikely to behave as you would like with wax.
(S)He will also laugh, and leave, when you piss and moan about spending a measly 40 bucks for a solenoid valve, so you might want to table that discussion.





Mike Halloran
Pembroke Pines, FL, USA

 

[Effcap]

Why the condecending attitude from someone who 1) stated they were not an engineer and 2) was not pissing and moaning about a 40 buck solenoid?

So let me ask a simple question: What's happening when I draw 4.5 grams of melted lipstick into a 10cc syringe and then inject that 4.5 grams of product into the applicator? Whether you call it volumn or mass - isn't this the same thing I'm trying to do with this system? Displace 4.5 grams of melted product? If I'm way off base, then help me out - at least point me in the right direction so I can actually learn what I need and I am a very fast learner.

 

[MikeHalloran]

The question remains: Did you draw 4.5 cm^3 of wax into a 10 cm^3 syringe, or did you draw 4.5 gm, e.g. by using a weight measuring balance of some sort, or by using a correction for the specific mass of the wax?

See, 4.5 cm^3 of water weighs the same as 4.5 gms (of anything), at a single temperature.
It's possible that 4.5 cm^3 of wax weighs the same as 4.5 gms, depending on what fillers are present, but neat wax is not that dense.

It's possible to dispense liquids by weight, and it's possible to dispense them by volume, but the necessary mechanisms are different, and volume and weight and mass are not the same things.

Your unsuccessful prototype sounds like a volumetric dispenser, but you confuse the issue by using mass units. ... and your description of its composition and geometry is not sufficiently detailed for us to make a reasonable guess about why it fails to meet your expectations.

Given the symptoms you report, I will make some completely unsupported WAGs:
- The internal volume of a 1/2" pipe ell exceeds the volume that I think you want to dispense, so there's a fair chance you're not bleeding all the air out of the system, and may never be able to.
- Rumbling in the hopper when you move the dispense cylinder manually suggests that the valves are not able to close against the wax. ... which may mean their construction, so far unrevealed, is unsuitable for the job, or their pressure rating is insufficient, or they are too large and the wax is hardening in the orifice because the temperature at the center of the valve is not high enough to allow the poppet to close, or you haven't allowed enough time for that to happen.
- The air cylinder seals might be pumping air into the dispensing volume, or leaking wax out, or both.
- Did you know that you have to use a sealant on pipe threads, and specifically an anti-galling sealant on stainless steel pipe threads?

Would you be giving away the store by providing photographs of the prototype, with and without the heat tape and insulation? We'd be specifically interested in exactly what sort of valves and what exact fittings and cylinders you used, and how they all fit together.

I'll reiterate that it will be faster and ultimately cheaper to get skilled help locally.









Mike Halloran
Pembroke Pines, FL, USA