Bottom Pour Valve Design?

[jandbn]

I’m in the process of making a PID controlled bottom pour pot. Capacity of the pot will be about 30 pounds. Manufactured bottom pour pots adjust flow rate with valve rod height adjustment. Is it possible to use a valve rod and valve seat design that would reduce the need for adjusting the valve rod or better yet, eliminating the need to adjust the valve rod height as the level in the pot decreases? It would be ideal to have the same flow rate regardless of pot level. Hazarding a guess based on hydraulics, this probably isn’t possible due to the physics involved?

[ku4hx]

All you really need is some sort of pressure regulator for the liquid alloy. I'm certain that can be designed and built but at what cost? Pressure regulation on liquids is well understood and flow rates of some pretty nasty liquids get regulated in modern industrial processes. High costs aside, I'd imagine any such device for lead alloy would require a rather complicated procedure to both clean, unclog, repair and etc.

For over forty years I've though there could be a different way to deliver the alloy to the spout and not have to deal with clogging and periodic flow adjustment while casting. But then I'd think about how simple current designs are and would I really want such a complicated pressure regulated system.

Over the years I've used various devices, Waterpik comes to mind, to clean my teeth. They all had their advantages and worked pretty much as designed, but after a short while with any device I soon moved back to a simple toothbrush and string floss. I have always subscribed to the KISS approach and the occasional spout clog clearing and flow rate adjustments are just too simple to feel a real-world need to mess with.

[handyman25]

My first thought is to use a dog water bowl design. You fill the gallon jug and turn it upside down setting in the dogs water bowl, as the dog drinks it automaticly fills the bowl. A lot of work too make and to me not worth the trouble. I would use a second pot to feed your main pot. When the lead level drops say 1/2 inch add some lead that is already up to temperture or very close from your second pot.

[DrB]

Pressure regulation is an OLD old problem. Have you thought of doing an online patent search? I believe uspto offers the service for free, as do most libraries.

I would bet you can find at least a half dozen different approaches of varying complexity without much trouble. They will even provide you with some simple concept drawings. It'll have to work over a wide temperature range and without being very susceptible to fouling and freezing, so I would keep that in mind when you look at the options. You also want to be sure to consider the very old patents. Newer is often just more complicated (ladles dont have a pressure regulation problem :) ).

The simplest approach I can think of off the top of my head is any kind of separate stand tube... As long as the metal column stays the same height, the pot level doesn't matter. You could have a floating siphon, or you could have a charge reservoir that accepts a preset volume slug of molten alloy (toggle up to charge, down to dispense), or you could add a baffle/filter, to drop the pressure and reduce the apparent effect of pot height.

Or, simplest of all, you could just make a very short but wide pot (like a pan) and figure out a good way to insulate and shield from oxidation the melt (a thick layer of kitty litter, perhaps).

Best regards,
DrB

[DrB]

My first thought is to use a dog water bowl design. You fill the gallon jug and turn it upside down setting in the dogs water bowl, as the dog drinks it automaticly fills the bowl. A lot of work too make and to me not worth the trouble. I would use a second pot to feed your main pot. When the lead level drops say 1/2 inch add some lead that is already up to temperture or very close from your second pot.


gotta be careful with the dog water bowl approach. A vessel with hot molten metal, a sealed void space, and a wide temperature change range.... YIKES! You'd have to fool proof it so it wouldn't be prone to explode, spray molten metal, implode, etc... We all have bad days re operator error.

+1 on any way of isolating the height of your pour vessel from your stock vessel. Like a ladle. :)

[theperfessor]

I've thought about this problem and how to deal with it. One way is to keep the fluid height constant to keep the head pressure constant so that the flow rate remains constant. There have already been several good suggestions made for doing that.

Another way to give a constant flow rate, especially for system where the valve is essentially a binary device in operation (fully on, fully off) is to adjust the amount the valve can be opened by tying that into the fluid height. You need an adjustable stop that would let the valve be opened all the way when the fluid level and head pressure are low but limit the travel of the valve stem when the fluid level is high. This type of system can yield a near-constant output by dealing with two non-constant conditions.

Think in terms of floats (to measure fluid height) and methods to translate that position to a wedge or cam to limit valve travel. All of it could be kept above the fluid level (no freezing, easy cleaning).

Not really sure which design would be easiest, simplest, and/or cheapest to build. Just offering some thoughts here...

[longbow]

The best way I have found to avoid all the problems with valves and flow is to use a ladle.

It may not be the way for everyone but it is simple, dependable and works well for every mould I have ~ especially those that need fast pours of high volume.

+1 one on what ku4hx says... KISS. The more parts there are, the more there is to go wrong.

Longbow

[mpmarty]

I modify my bp pots by changing the leverage on the valve mechanism. My "handle end" moves about three inches from closed to fully open giving me finite control over volume discharged.

[theperfessor]

Mpmarty, that's a really simple approach. I might try that on my Mag20. I have my valve travel adjustment set wide open and simply manually compensate for flow rate, but after I get tired it gets harder to do.

I was thinking over a better valve design when I inherited a piece of stainless steel tubing that I could make up into a 35-40 lb pot. It isn't hard to drain a 20-pounder when using large caliber 5-6 cavity molds.

[ku4hx]

Lots of good responses, but an approximate 10 degree counterclockwise turn of the adjustment screw every 15-20 minutes or so is just too simple to try and improve on from a practical standpoint.

I do it as the alloy cools in the mold. EZPZ! The "Kentucky Windage" of boolit casting.

[jandbn]

Sorry for not providing more of a description as to what I was asking! I did not mention this before, but don't have any experience with bottom pours and have only used a ladle. What was also not mentioned is that I was specifically referring to modifying the valve rod and valve seat to a shape/form which would reduce the flow into the top of the valve body so that outflow at the spout end is under less pressure. In other words the flow area/space when the valve rod is lifted is less than the spout's hole area (small into larger).

As an example the spout hole on my RCBS ladle is 5/32 inch. The area of the spout's hole that helps to control the flow rate is .0192 square inch. If a 1/4 inch rod was inserted into a .290 diameter hole in the valve seat body, the area that the alloy could flow through is .0170 square inch. Thus the inflow rate is being restricted into the body of the spout; a smaller "hole" in than out. I was even thinking three machined “steps” (middle step used as the on/off seat) to allow the bottom end of the valve rod to be designed to self clean the bottom end of the spout. This would depend on length of the spout diameter needed at the bottom of the spout so as not to affect the stream into a mold. I am guessing that the spout hole cylinder length would need to be long enough to prevent the alloy stream from spraying out instead of pouring out in a steam the same size as the exit hole of the spout. Such a design could easily be machined into a spout the same length as factory bottom pour spouts to avoid heat loss at the spout tip.

What type of tolerances would need to be maintained to avoid any junk in the alloy from binding up the valve rod in the spout? Would alloy even flow through the tolerances in the example above? I want to keep it simple, but at the same time and if possible, “build a better mouse trap”. One other enhancement I am also even envisioning is a mechanism on the top of the valve rod to rotate the rod a little bit (star wheel) each time it is lifted to keep the junk in the alloy “moving” through the spout.

I watched and helped my Dad, Grandpa, and Uncle who were all mechanics. When I was young, it amazed me with the things they would tinker with to make better or fix and I fell into the same foot steps for a short time. Although I am no longer a mechanic, I still like tinkering and “because I can”, I am building my own bottom pour. With that being said, two heater bands will be used on the vertical pot and insertion heaters will be placed horizontally in the base of the pot close to the spout (Got the heaters cheap on evilBay). I welcome all input about the above mentioned valve/spout design and will use it as “food for thought”.

[DrB]

regarding your general idea, a drawing would be helpful... But I think I get the gist. I have no idea as to the necessary tolerances. It seems to me that debris of any size that gets in between sealing surfaces will tend to prevent a good seal. If you have a slip fit/wiper seal to start with that should preclude the problem as the sealing surfaces are always in proximity?

What do you think of a charge bar or tube approach? Sort of like a powder meter. If you have a "lock" type system, the pressure is isolated, and the volume per pour could be metered if you desired. Regardless, the pressure at the spout will only depend on the lock/spout drop height, and not the pot column.

I like the idea of a rotary lock better than a slide bar or tube, as stick/slip tugging on a vessel full of molten metal seems inherently more hazardous than a twisting motion?

Seems certain that such an approach has been tried before...

[jandbn]

DrB,

Now I need a drawing to understand what you are describing! What I'm imagining doesn't sound like keeping it simple, but I understand the concept. I just don't know how to keep a contraption such as I'm visualizing from leaking.

The pic below is an example of the design I was trying to describe. The upper portion of the valve rod has tolerances close enough to center the valve rod in the valve spout. The valve rod also has recesses (3 or 4?) milled into the outer surface to allow the alloy to flow from the pot down into the seat. As for crud in the valve, the seat and valve rod mating surfaces would be minimal, even if lapped in for a proper seal. The middle "step" of the valve rod below the seat is large enough to reduce the area of the seat area that allows lead to flow so that the seat area is less than the area bottom of the cylinder of the spout. This effectively restricts the inflow of allow to be less than the out flow. (Man this is hard to describe decently!)

http://castboolits.gunloads.com/imagehosting/102444eb87c228fa29.bmp

Lastly, the bottom step of the valve rod. The size if the rod is small enough to fit in the bottom of the spout without binding, but when the bottom of the rod is lifted above the bottom portion of the spout which it fits into, when the rod is dropped down, the bottom of the valve rod will "clean out" the spout on the way down.

One of the unknowns is what I would need for tolerances at the top and bottom of the spout so the rod does not bind when using "clean" alloy.

Seeing as how I have zero experience with a bottom pour, can anybody tell me how far the valve rod typically moves in and out of the spout?

Maybe this is all a pipe dream regardless of an 'improved' valve rod/spout design in a pot which is gravity fed? I still foresee head pressure in the pot varying the flow rate as the alloy level drops regardless if a design can restrict the inflow to the spout.

[DrB]

OK, so four sets of thoughts related to your problem...

1) LOCK ISOLATION:
I think I can do better than a picture if you have a powder measure... the principle of using a lock I'm suggesting is the same, and you can pull yours out and look at it. Powder measures work by having a "lock" or plenum that is opened first to the powder reservoir (here your lead pot) and then your pour spout, but isn't opened to both at once... hence the fluid level from the primary vessel doesn't necessarily affect the pour.

If you want to be able to do flood casting/pour a solid sprue across a multi-cavity mould, I don't think having settable volume for each cavity/sprue is necessarily a good thing. You may just want to have your plenum larger than you would ever need. Also, you presumably want to have your pressure fairly constant during a pour, and so you presumably want head pressure in the lock to vary negligibly during it's emptying. You could help do this with a large flat volume of the lock, or by having a tall spout relative to the lock, or both.

One approach to a lock design would be a ball joint, with openings at right angles like 'L' pivoted about the vertex of the 'L'. So the leg of the L first connects to the reservoir, then you turn it 90 degrees and the initially horizontal leg becomes vertical and connects to the spout. Another approach would be a hollow hockey puck shape reservoir with non-coaxial holes in the top and bottom... you rotate it to one stop and the top hole connects to the pot reservoir charging the puck, then you rotate it the opposite way for your pour and the top hole connects to ambient air and the bottom drain hole connects to the spout. Another would be a sliding rectangular charge bar with a cavity that first connects to the reservoir to charge the cavity, and then when slid over dumps it's charge of metal down the spout. All are variants on a lock design... I can think of several others. I don't know how well they would work, but again, seems to me they would have been tried before and some old grey beard around here might know?

I think if you use a lock you should keep in mind that it will need to vent to ambient for good flow when you turn it to the pour position. Good heating will also be important to keep it from freezing... and it should probably allow for disassembly and cleaning, if possible without first heating it to high temps to unsolder it. Also have to keep in mind that fasteners may tend to work themselves loose with heat/cool cycling... so you need to prevent that from being a disaster (a screw comes out holding a lock in for example, causing your pot to dump 20 pounds of melt). Lastly components generally need to have similar thermal coefficients of expansion/good thermal conduction paths internally so you don't have thermal expansion problems.

2) VALVE REGULATION:
Regarding your spout, does the first conical surface from the top come all the way out to allow the pour to start, or does liquid flow through the space between the two cylindrical surfaces (blue/red) towards the top of the drawing?

Keep in mind that the lead is an incompressible fluid, so Bernoulli's Law applies... also, conservation of mass means the product of area and velocity at each station in the flow will be constant. In order to keep flow rate constant at the spout, the flow area will have to be variable to compensate for different heads of pressure. If you open the valve the same amount regardless of the head of pressure, you will not have constant pressure out the bottom. You should be able to use these two relations (BL's and conservation of mass) to size your spout dimensions based on what range of head in the pot you wish to compensate for.

3) PASSIVE APPROACHES:
Back to a point I made earlier -- the head variation is directly a function of the height of the pot. A pot that is flat (like a hockey puck as contrasted to a grain silo) compared to the height of the spout shouldn't show much variation in pressure at the spout as compared to a very tall lead pot. A large, flat reservoir with small height compared to the spout drop height will show comparatively little rate of change in fluid head at the spout over a casting session as compared to a taller (or smaller capacity) pot. Also, adding weight to the fluid column by floating a heavy object on top of the lead will tend to pressurize it and reduce variation in pressure over a session as long as the object is floated (an insulated steel cylinder?).

4) BACK TO THE FUTURE:
Or, you could use a ladle. :) But that wouldn't be as much fun, mechanically.

Anyway, that's my 2c. I'd refine a few concepts that seem attractive to you and compare their merits, then go from there to either try to prototype a couple or select one if I thought I could. Pot design using 3) combined with properly sized 2) with a good handle/throw distance (for control) as folks mentioned would probably be my first bet, if not 4).

[jandbn]

To all those that have posted to the thread other than DrB, I apologize for not acknowledging your contributions. I wasn’t ignoring you. And to DrB, I also apologize for not answering some of your direct questions. While reading the replies, the old gray matter meanders into the “tinkering zone” looking for a solution or goes off on a related tangent. At that point, I don’t seem to pay attention to everything I’m reading. Sorry!

I admit that the ideas already mentioned are just too complex without the proper tools. I do not have direct access to the machines needed but I can call in some small favors from machinists at work where their department has about every type of CNC there is (and then some). So when I do ask for a return favor, I don’t want to be wishy-washy when explaining exactly what is needed. It has to be in “black and white”. I don’t really have any room for experimentation, so thus the questions about tolerances.

KISS is best by far, but tinkering is something I enjoy. As you said, the benefit when adding the complexity factor and expense better be worth while or it really has no added value; That adjustment screw is about as simple as it gets. With the dog bowl concept, I couldn’t envision how it would work until DrB helped fill in details of what to watch out for. The suggestion still has the wheels turning though trying to figure out solutions to any possible gotchas. There is also considerable merit to the automatically adjusted valve height which is dependent on fluid level. Changing the leverage is a very good and simple idea. If the bottom pour manufacturers are reading, maybe they could redesign their pots to have adjustable leverage!

DrB,

1) In answer to “What do you think of a charge bar or tube approach?”, again, before I even finished reading the whole question, my brain ended up on another tangent again, but it wandering directly to my RCBS Uniflow powder measure for inspiration which is what you mentioned in your last post. With the lock techniques mentioned, I can easily conceive of how to heat the parts with the assortment of heaters available and account for the safety factors. But I do not know the tolerances needed to prevent the drips. It seems with all the complaints of leaky bottom pour pot spouts that basically use a simple needle and seat configuration (as in an old style carburetor bowl with a float where the needle attached to the float plugs the seat), it doesn’t take much to leak. Molds have vent lines and are not under head pressure so I can’t use the vent lines as a guide for tolerances. I plain just don’t know enough. Maybe with enough research, I can find some guide lines. Even then as you suggest, any added complexity with what ever design is used will need to take into account maintenance and or cleaning.


2) In answer to “does the first conical surface from the top come all the way out”, the answer is no. The alloy will not necessarily flow between the red and blue. What you are referencing are the bearing and alignment surfaces for a slip fit intended to align the centerline of the valve rod with the center line of the spout. The red rectangle in the rod is a machined slot that allow can always flow through.

To try give a better explanation, in the picture below is a bottom view of valve rod. In this picture the full diameter of the rod is the green circle. In this green circle are white lines that represent machined flutes/galleys that extend vertically toward the top of the valve rod. These flutes/galleys start just above the seat and extend above the top of the spout so that there is always head pressure at the seat. The remainder of the green valve rod in the spout is the bearing/alignment surface. The yellow circle represents the cylindrical portion of the valve rod just below the seat. This is the portion of the valve and spout that provides the restriction of the concept. And the small red circle is the very bottom cylindrical portion of the valve rod which is also a slip fit. This is the “self-cleaning” idea. But again, without knowing tolerances needed for a slip fit, all this is just concept. The slip-fit would also need to be enough to account for the occasional piece of junk that might end up inside of the valve. If tolerances for the junk force the slip fit tolerances to be to large, this whole idea is as I said, a pipe dream.


http://castboolits.gunloads.com/imagehosting/102444ebb46742714b.bmp

3) You alluded to “A pot that is flat” in your first post and I completely missed it. This concept is so simple and uncomplicated it didn’t even dawn on me when alluded to by others and until you had to mention it again. I like it! It sure wouldn’t take much of a change to the current designs of bottom pour pots. I think I already have a solution for the surface area of the alloy; A while back, I had posted about the possibility of using a metal “cover” to lie directly on top of the alloy and act as the oxygen barrier. As much as I like the “flat” pot, it is going to have to wait. I already have the majority of stuff needed as I designed around 4 1/2 inch ID band heaters. About all I have left to rustle up are the machined parts (pot base, valve rod, and spout).

4) All said and done, if I can come up with another workable design, I can always build another at some point in the future. And yes, as many others (including me) already enjoy, I can just revert back to the ladle!

[blikseme300]

Se here what I did for a valve: http://bliksemseplek.com/boolits.html

I too searched the forums before I started to build my pots and this is what I made up. I have been using this design for 2 years and a few hundred pounds of alloy later I have had no problems at all. There is no adjustment required for flow control.

When I cast the spout is at eye level and I can cast more than 50 lbs in a single session without stopping. The Lee six-bangers can quickly create a mountain of boolits.

There is no secret in preventing crud from getting into the spout - don't use dirty alloy! My other pot is used to render ingots from WW's and other sources. I flux and clean the melt prior to casting ingots for use in my boolit casting pot.

The preparation for casting boolits includes fluxing again and placing a handful of wood shavings into the pot. I leave the remaining ash on top to form an oxygen barrier. This prevents excessive oxidation from occurring on the surface. Sprues pass through this without disturbing it too much. I typically need to reflux after only about every 20lbs of casting.

Bliksem

[jandbn]

Bliksem,

Your's is the valve design for prompting me :idea: to "fix what isn't broke". I just can't seem to leave well enough alone. :)