entropy
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Post by entropy on Jul 6, 2020 20:23:58 GMT -5
knave I'm not worried about the thermal expansion of the HDPE. I am worried about the thermal expansion of dissimilar metals on the hotplate. If I attach an aluminum ring to a steel using flat-head capscrews from the underside (a cross-sectional sketch shown below). And if the screw holes are on a 7 inch spacing at room temperature, once warmed up to 450 degrees F, the screw holes in the steel will be 7.019" spacing, and the aluminum holes will be on a 7.036" spacing (due to the different rates of thermal expansion between aluminum and steel). This probably isn't going to shear the screws, or deform the holes in the aluminum into an oval shape (unless I use extremely tight tolerances for the holes). However what it does show is that the aluminum is going to be sliding across the steel. And just the slightest air gap (a few thousandths) between the aluminum and steel could introduce cold spots on the aluminum ring during welding. If I could find a thermal grease that's good to 500 degrees F, that would solve a lot of problems. By fabricating the whole plate from solid steel, this concern is eliminated (but introduces another of needing a non-stick surface) EricD , the heat-application is supposed to create a 3/16" melt-bead (based on the diameter of pipe I'm welding). This is why I desire a raised-face (of ideally 1/4") - so that only the weld-area is preheated & beads-out on weld plate - when heating the end-caps.
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EricD
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Post by EricD on Jul 6, 2020 20:43:43 GMT -5
Yes, but what harm would heating the entire disc surface do to a tumbler application?
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EricD
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Post by EricD on Jul 6, 2020 20:57:15 GMT -5
I mean, why not heat the entire HDPE end disc, instead of just part of it? The heated parts are still as resilient as the unheated parts. No need to complicate things and build heat rings or anything like that. Heat the tube, heat the disc, and apply them to themselves. Done
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Post by knave on Jul 6, 2020 20:59:13 GMT -5
With a 1” plate to work with, and small scale production, it would work to lathe remove HDPE from the areas you don’t want to weld.
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entropy
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Post by entropy on Jul 6, 2020 21:25:35 GMT -5
knave , and EricD I thought about machining a cup into the end-plate - essentially making the plate into an end-cap. The problem is I would need to do this on two sides for the 8" x 6" reducer end. If I cut a 1/4" cup into the 8" end, and remove another 1/4" from around the 6" end, I'm left with a cap that's 1/2" thick. The next size up HDPE sheet is 2" thick. This would be doable (actually machining a pipe reducer). The problem is that's a crap-load of machining. The private sector would never attempt this - they'd simply extrude the part. I'm reluctant to heat the entire cross-section. Would it hurt anything to heat the entire end-cap surface? I honestly don't know. My gut tells me I shouldn't do it. (As a general rule of thumb, I've found it's best to minimize unnecessary heat-input whenever possible). Also - I contacted a mold-maker (specializing in injection-molding HDPE parts). I inquired about making finished tumbler barrels in a 2-piece mold (just like how milk jugs are made). So is it possible? The answer is probably not. He said the maximum possible thickness would be around 0.100" thick. I told him I wanted 1" thick. He laughed and said never in a million years could you inject HDPE that thick. (I think he's blowing smoke - it will likely be possible in 750,000 years. . . . 800,000 years max) FWIW - the thick HDPE pipe parts (caps, reducers, and the pipes themselves) are all extruded - and specifically not injection molded. The pipe I have was made in Canada. Not sure where the sheet is made. I'll let you know when I pick it up (hopefully soon)
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jamesp
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Post by jamesp on Jul 7, 2020 4:54:17 GMT -5
If doing this in a production situation I would buy a dozen $10 single burner hot plates and do 6 joints at a time. Using $10 frying pans. And rings cut from $10 frying pans mounted in frying pans. There must have been 40-50 fine frying pans/plates made of highly conductive aluminum and well coated with teflon at Home Goods. Selection and quality were pretty much incredible. Some were almost 1/4" thick with dead flat heating faces.
It would make a great Mom Pop business.
I researched exotic heat transfer plates with plug heaters mounted in them. Pretty much concluded it was overkill for this application.
Try making some welds out of short sections of pipe or pieces for that matter. It is not a precision process. The bead at the edge of the heated contact point prompts weld timing. Put a mark on the hot plate dial once heat level is dialed in for a given time.
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jamesp
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Post by jamesp on Jul 7, 2020 5:23:59 GMT -5
The biggest problem I anticipate using an electric range burner is that they're pulse-width modulated. Example: on medium, the burner turns on for a few seconds, then turns off for a few seconds (cycle repeats). On low, it turns on for just a second or two, then it's off for several seconds (cycle repeats). On high, there is no off-time. It's simply on. If you've ever powered an electric range off a generator, you can hear the burner cycling off & on by listening to the tone of the generator's exhaust. For welding HDPE, I probably need a medium to medium-high temp setting (assuming an 800 watt electric range burner). The on and off temperature regulating nature of electric ranges will introduce temperature transients in the hot-plate. My idea of using a thick steel plate was to provide some thermal buffer to these variations (dampening). Probably a much better solution would be to use a natural-gas/propane burner. The flame is super precise with a steady-state energy input. In this case, the plate would still need to have enough mass (thermal reserve) for the transient nature of making the weld. I think you are over thinking things here entropy. The frying pan(or heated metal face) will not fluctuate near as quickly as the electric burner. But more importantly thick HDPE is incredibly difficult to heat up, or cool down after weld is complete. I filled a cooler with water and some ice for immersing the entire unit to speed cooling rate after welds. Cold tap water took too long. Ever had a drop of melted polyethylene land on your skin ? Try to speed the heat rate and the contact surface easily gets too hot and the weld quality is ruined. I'd call this rule #1.
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entropy
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Post by entropy on Jul 7, 2020 12:29:57 GMT -5
The commercial mirrors/heating elements are normally temperature feedback controlled (thermocouple). They ramp up towards the temperature set-point quickly. The chances of large overshoot are significantly reduced, and the chances of being under-temp is virtually nonexistent.
The least-precise temperature controls you can find are the non-feedback type (kitchen range). It's like disconnecting the speed-signal from your cruise control in the car - where the only control-feedback on the burner is the operator's input. I'm not worried about this, because I've got a nice inferred thermometer. I'll ensure the the hot-plate is at the proper temperature.
I am more worried about the "weld-force" in making the joint. One HDPE weld instructions says the clamping force must be sufficient & maintained, or the joint will be weak. Too much force, and the melted material will be pushed out from between the joint, resulting in the weld cooling too fast (weak joint). Thus I might need a jig (clamps) for welding on the end-caps - where pushing the parts together by hand & walking away might not be enough. I'm assuming it will take upwards of 10 minutes for the weld to cool. If clamping pressure needs to be maintained for 5 minutes, then I simply need clamps. No big deal (or shouldn't be).
I'm assuming the welding process will be slow - where I make a weld, then work on something else for 15 minutes - then do another weld (repeat).
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entropy
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Post by entropy on Jul 7, 2020 13:35:02 GMT -5
According to plasticpipe.org HDPE should have between 60 to 90 psi weld-clamping force, with 75 psi clamping force being typical.
8" DR-11 has 19.31 square inches of HDPE area. The acceptable clamping force for welding is as follows: 1159 pounds at 60 psi 1448 pounds at 75 psi 1738 pounds at 90 psi
6" DR-11 has 11.39 square inches of HDPE area. The acceptable clamping force for welding is as follows: 683 pounds at 60 psi 854 pounds at 75 psi 1025 pound at 90 psi
4: DR-11 has 5.26 square inches of HDPE area. The acceptable clamping force for welding is as follows: 315 pounds at 60 psi 394 pounds at 75 psi 473 pounds at 90 psi
Needless to say, none of these values are within the range of my bare hands - let alone simple gravity-force. It looks like I will be constructing a small hydraulic press in support of this project - for achieving proper clamping force during welding.
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Post by MrP on Jul 7, 2020 15:29:06 GMT -5
I sure am glad that I did not have all this information when I built my tumblers. 8" scrap HDPE, 3/4" used white cutting board from a used restaurant supply store, 6" gray electrical conduit and two old electric fry pans. For what we use these for, even if the weld is not perfect, it is not going to break, mine are proof of that. I am very sure yours are going to look way better than mine but I have been using mine steady for 3 years. It sure is fun watching this thread though.................MrP
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entropy
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Post by entropy on Jul 7, 2020 16:44:48 GMT -5
I sure am glad that I did not have all this information when I built my tumblers. 8" scrap HDPE, 3/4" used white cutting board from a used restaurant supply store, 6" gray electrical conduit and two old electric fry pans. For what we use these for, even if the weld is not perfect, it is not going to break, mine are proof of that. I am very sure yours are going to look way better than mine but I have been using mine steady for 3 years. It sure is fun watching this thread though.................MrP Do you ever watch the TV show Gold Rush? I really enjoy it. It's too bad the environmental-activist politicians are killing the gold mining industry (by vindictively withholding water permits) - but that's a tangent. . . . They use HDPE pipe for gold mining - lots of pressure (well over 100 psi), lots of volume (thousands of GPM), and they drag around 1000 foot sections of pipe across the dirt with a dozer - and the welds virtually never fail (joints as strong as the pipe itself). Question: are pipe-quality welds necessary for tumbler barrels? Probably not (you have the proof). That being said - if something as simple as clamping the joint results in pipe-quality welds, then why not do it?
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EricD
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Post by EricD on Jul 7, 2020 18:19:21 GMT -5
I sure am glad that I did not have all this information when I built my tumblers. 8" scrap HDPE, 3/4" used white cutting board from a used restaurant supply store, 6" gray electrical conduit and two old electric fry pans. For what we use these for, even if the weld is not perfect, it is not going to break, mine are proof of that. I am very sure yours are going to look way better than mine but I have been using mine steady for 3 years. It sure is fun watching this thread though.................MrP I think entropy would be more comfortable in a engineering forum personally. If and when he is done engineering his tumbler to hitler specifications, he could always come back here for tumbling advice. Which also is not perfect and can vary considerably.
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jamesp
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Post by jamesp on Jul 7, 2020 18:35:13 GMT -5
I was sold on the weld quality after pushing two sawed sections of 3/4" thick pipe sawed 3" x 3". Welding the 3/4" x 3" faces together... I pushed them together with my hands for about a minute until about a 1/16" bead squeezed out. Immediately cooled them under tap water. Walked outside and smashed on the welded section with a 12 pound sledge hammer about 5 times and was unsuccessful at breaking the weld. More than strong enough for a tumbler. People get seriously injured by HDPE pipe laying on the ground when a rupture occurs. At 100 psi in an 8 inch I.D. pipe(50 sq in) makes 250,000 pounds of total force. Nothing to play with. Kaolin(the clay I use for slurry) mines in Georgia run pipe up to 35 miles. atef.helals.net/mental_responses/misr_resources/kaolin-wet-processing.htm
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entropy
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Post by entropy on Jul 7, 2020 20:09:05 GMT -5
jamesp , point taken. You've successfully welded 3/4" x 3 faces together, using hand-force - equal to 2.25 square-inches of surface area being welded. The industry would recommend 168 pounds-force for clamping that size joint (again, that's industry recommendation - not mine). If you applied the equal hand-force on an 8" pipe joint as you did making the 3/4" x 3" joint, you'd generate 8.5 times less pressure because the pipe joint has 8.5 times more surface-area. Can you do that by hand? I don't know. It depends on how hard you squeezed the smaller pieces together. Would the weld-joint performance suffer from 8.5 times less compressive force during welding (compared to your test piece)? I don't know? Probably? And is it possible that extra heat-input can decrease the required clamping force? Maybe. Again, I don't know. And how much reduction in strength is there from reducing the clamping force below industry recommendations? I don't know. I do however have the ability to accomplish pull-tests. I could experiment with different welding methods, and directly measure which method works best. Honestly this is something I have very little interest in doing. It is likely that I'd only be verifying industry standards (reinventing the wheel). Thus I'm simply going to follow the plasticpipe.org recommendations for welding, and not think twice about it. EricD , I was very polite when you told me I had no idea how brakes work. This was in lieu of the fact that some of your early comments on this thread were condescending. Now you're suggesting that I stop participating on these forums all together, and you've openly directed a Hitler comparison towards me (not cool). If you are uncomfortable with the content of this thread, then simply don't read it.
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EricD
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Post by EricD on Jul 7, 2020 20:14:52 GMT -5
I'll continue reading. I love a good laugh as much as the next person does.
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Post by knave on Jul 7, 2020 20:21:31 GMT -5
The clamping force is not required for bond strength, entropy. See multiple YouTube videos showing 100% melting/bonding using only gravity. Clamping is helpful during cooldown which begins instantly. If not controlled it can warp as it cools. Useful if making your own flat HDPE sheet out of caps or other recycled plastic. In the case of a tumbler barrel you can draw your own assumptions.
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entropy
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Post by entropy on Jul 7, 2020 21:44:15 GMT -5
The clamping force is not required for bond strength, entropy . See multiple YouTube videos showing 100% melting/bonding using only gravity. Clamping is helpful during cooldown which begins instantly. If not controlled it can warp as it cools. Useful if making your own flat HDPE sheet out of caps or other recycled plastic. In the case of a tumbler barrel you can draw your own assumptions. I've found one engineering article on the subject (presumably someone's doctoral thesis). It says the long hydrocarbon chains of the HDPE molecule unroll (straighten out) when heated, and after physically joining the two halves, the hydrocarbon chains curl back up around each other during cooling (entanglement - on the molecular level) resulting in a very strong joint - a weld as strong as the base material. Additionally, it was specifically stated that the applied-pressure must be maintained on the joint to optimize entanglement throughout the cooling process. There it is. We can accept it, or reject it. . .
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Post by knave on Jul 7, 2020 22:16:32 GMT -5
There’s even an app! apps.apple.com/us/app/mccalc-fusion-calculator/id376891708I appreciate your abhorrence for halfassery. Let’s return to your analogy of using a pillow block bearing rated for many tons and only loading it to maybe 1000 lbs per bearing, a waste of resources. My opinion is that building a tumbler barrel with 1” thick HDPE walls and clamped and welded to ISO 21307:2011-05 specifications would also be at least a slight waste.
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entropy
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Post by entropy on Jul 7, 2020 22:39:29 GMT -5
A waste of resources? I suppose. I was referring more to a waste of money. Large bearings are more expensive. Large bearings typically consume more power (greater internal drag).
Why do you believe it's wasteful to build a tumbler using 1" thick HDPE end-caps that are clamped when welded?
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Post by knave on Jul 7, 2020 23:10:49 GMT -5
Its just my opinion, but since you asked: (Keep in mind, this started as a way to upcycle an inexpensive scrap of large diameter steel pipe...) To engineer and fabricate a 4 clamp system for 2 pipe diameters to achieve specified “bead-up” pressure, “heat soak” pressure, and “weld” pressure, all while staying within the “transfer time” window from mirror release to full weld pressure, then maintain that exact pressure throughout weld cooldown, etc. would take significant resources, time, money, brain cells, etc. When you COULD be tumbling already with a nice large DP tumbler at less expense. (and working on your Miata project) Why reinvent the wheel? 😎 fdotwww.blob.core.windows.net/sitefinity/docs/default-source/structures/cadd/standards/approvedptdrawings/hdpe-pipe-butt-welding-procedure_2-27-2018.pdfGood luck on your adventures. I’m hoping to goad you onward headstrong into the project, past the point of no return, so the world can benefit from near-eternal tumbler barrels. You would have a market with the reloading crowd.
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