hydraulic valve - opens on set pressure, closes no pressure



That's a "vibrophore", isn't it, if you apply that conept ot fatigue testing machines?
Electro-mechanical device.
You would always use one of these if you could, for the project I'm planning (?) Test rates to 150Hz and higher. Energy consumption so low many will plug into a "domestic" wall socket.
Never met one in real life. Would desperately like to. Idea of running a sample to 20 Million cycles no problem is like a dream come true.
But the problem is when you go beyond "research test samples" to testing representations of full-sized welds.
The biggest machines are 100Tonnes-force (1000kN; 1MN).
I've indicated the discussions would get very favourable if a 250kN (25Tonne-force) "vibrophore" were available.
The rig I've sketched is for if say you needed to test a weld to hundreds of tonnes cyclic stress range.
Rich S
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On Wed, 19 May 2021 17:42:41 -0400, "Jim Wilkins"

[snip]

In the patent reference above, the oscillation cycle is controlled by an external "variable speed motor" of unspecified kind, designated is item 25 in the figures and accompanying text.
If the motor runs slow, so does the oscillation cycle, in direct proportion.
Joe Gwinn
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"Joe Gwinn" wrote in message ... If the motor runs slow, so does the oscillation cycle, in direct proportion.
Joe Gwinn ---------------------- If the expected fatigue life is 2 million cycles, the test time at 1 cycle per second is three weeks. I think a good solution would be a closed loop based on a pressure sensor that shows when the high and low limit pressures have been reached, so the controller can switch between the fill and dump solenoid valves as rapidly as fluid flow permits.
If I had to build a prototype of the tester the controller would be an old laptop (or desktop) with a printer port, the data bits driving a successive-approximation A/D converter to measure the pressure sensor and two control bits operating the fill and dump solenoid valves.
QBasic running in DOS gives full unhindered access to all of the printer port bits for input and output, unlike Windows. An Arduino could also work but the laptop has the advantages of a huge hard drive to store data, the keyboard for control, and the LCD on which QBasic can display the cycle count and a graph of the pressure. http://www.nicolasbize.com/blog/30-years-later-qbasic-is-still-the-best/
This simple resistor network outputs a voltage proportional to the binary code from the port bits: https://www.tek.com/blog/tutorial-digital-analog-conversion-r-2r-dac
The other electronics are an analog comparator (LM311) driving a printer port status bit that tells if the sensor output voltage is more or less than the DAC output, and the two high current solenoid valve drivers.
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Stunning detail. I see that with * test method and hardware * control and data acquisition 2million cycles would be a start. With well-performing welds, you'd want to get out to 20million cycles or more (200Million is something around what a ship or bridge gets in its entire period of service, but can be a bit of an ask in test). I've programmed in Basic. Access to devices / ports - hadn't thought about it being that convenient and tailor-made.
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"Richard Smith" wrote in message ... I've programmed in Basic. Access to devices / ports - hadn't thought about it being that convenient and tailor-made.
----------------------
I can't claim credit for the idea, it was the engineer's suggestion when we (Unitrode / Texas Instruments) wanted to design and operate evaluation boards for new user-configurable ICs from customers' unmodified laboratory computers, which at the time were typically former office desktops and laptops running Win98. We started with Visual Basic but quickly found that it lacks the hardware control instructions of QBasic, and Windows polls the printer port to detect newly attached devices. DOS + QB give full read/write access to the I/O address space, interrupted only to update the clock.
The only change to the computer was setting the BIOS to boot from a DOS floppy if present, else to Windows. The same can be done with a USB flash drive using HPUSBFW. FAT32 USB flash drives are big enough to store programs and large data files without access to the NTFS internal drive though older FAT32 hard drives could handle either DOS or Windows, up through XP. https://www.handheldgroup.com/knowledge-base/create-a-bootable-usb-drive/
The computer boots normally with the flash drive removed and you can read any data log files the QB program created, such as cycle intervals which might increase when the sample began to stretch, and indicate the point of failure if you can't otherwise sense it.
I had previously assembled one-time computer to hardware interfaces with added plug-in boards, a purchased digital I/O card and a 16 bit A/D converter for the Macintosh that I designed. The printer port and DOS/QB method turned out to be easier for relatively simple tasks. I'm also very familiar with relay ladder logic controls if you choose to go that way.
Do you have the equipment or machinist friends to consider custom machining as part of solutions? I couldn't do nearly as much without my lathe and milling machine.
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Machining, making parts and equipment... My cider-maker / cider supplier could feature in that... Can see a need to trade favours...
Digression into computing. I often put "emacs" on a CD-ROM, take it by IT-support and invite them to check it (fully up-to-date virus check software, etc, etc.) If it's a write-once CD-ROM, it can't be altered ever again. So if they trust that is all I will ever put in the drive of "my" networked computer, that's sound in terms of IT security.
The reason for this is; I have a range of suites of functions for various engineering tasks which run in the test-processor I am using now - the famous / well-known "emacs". They will inject the answer straight into the document you are writing. You can quote the function and the values you fed to it, and the answer it gave. Complete record. "sketching" your way to often high-value decisions. Plus I do most other text-based thing in emacs. For examples I didn't just type " Thermo-Mechanically Controlled-Processed High-Strength Low-Alloy " I typed tmcpqc hslaqc When you are typing documents with huge strings of standard quotes of Standards, Company Specifications, etc, that can save a huge amount of time and effort, and leave your mind clear to think of the big picture. Boot off a CD-ROM? Could do?
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"Richard Smith" wrote in message writes: ...

Machining, making parts and equipment... My cider-maker / cider supplier could feature in that... Can see a need to trade favours...
----------- So not easily, perhaps shortening a bolt but not to the full custom extent I would otherwise suggest, like the small piston in the cylinder end cap. Experimenting is difficult when you are limited to only what you can afford to buy. My shop is what an inventor would have dreamed of in 1960 though perhaps not today, after 50~60 years of wear.
How about electronic test equipment? Capturing the brief peak value from an analog pressure sensor during rapid cycling will be difficult without a digital storage oscilloscope.
https://www.aliexpress.com/price/200-bar-pressure-sensor_price.html
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Could be more than that... Device with an eccentric crank? Simple and presents a huge bearing area to take high forces.
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"Richard Smith" wrote in message .. Boot off a CD-ROM? Could do?
_____________ Can do easily.
Hit the key during startup that enters the BIOS setup and put the CD-ROM ahead of the hard drive in the Boot Sequence. On my Dells it's F2 before the self-test completes. F12 lets me select any bootable source for this session only.
My Lenovo laptop is a little different. It came in a Fastboot mode that bypassed the chance to enter the BIOS. https://support.lenovo.com/us/en/solutions/ht501793-how-to-turn-on-or-off-fast-startup-in-windows-1081
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There's a mini-computer called a "Raspberry Pi". Designed by group endeavour of hobbyists. Meant for education. Uses a "merchant" embedded-chip for eg. washing machines as its processor. Might look if that offers a way. Lots of devices been matched to it.
However, note you "PC architecture / QBasic" way.
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"Richard Smith" wrote in message

There's a mini-computer called a "Raspberry Pi". Designed by group endeavour of hobbyists. Meant for education. Uses a "merchant" embedded-chip for eg. washing machines as its processor. Might look if that offers a way. Lots of devices been matched to it.
However, note you "PC architecture / QBasic" way.
---------------------------- Sure. The Pi has the advantage that you can buy and plug in an A/D converter to read the pressure sensor, and a keyboard and display to monitor the test, no technician bench skills required. I haven't played with one and don't know the learning curve for it. Are you generally familiar with computer hardware and software architecture?
As for the eccentric, I considered it because you could vary the piston stroke, but you'd need a lathe to make it, the pump drive is more than a friend could whip out in a spare hour. A pump built into the cylinder end might give the fastest cycle rate because there's no flow restriction. You could fine tune the peak pressure during operation with a screw that displaces oil. A cheap used tie-rod cylinder with a scratched bore could be cut down to be your pressure chamber. Cylinder rebuilders can provide the tubing in any length.
On my tractor's homebrew bucket loader attachment hydraulics I turned the head of a bolt round and grooved it for an O ring, so it can screw into or out of the oil space without leaking. It operates the variable pressure relief valve I made to replace the fixed relief the control valve came with. The tractor's front tires turned out to be the weakest link that limited how high I could set the pressure.
The decision comes down to what you can build or buy. I've spent significant time and money becoming able to build what I or the customer wanted, electrical, optical and mechanical. Right now I'm upgrading my sawmill and its overhead gantry hoist to handle a larger log than it was designed for.
The sawmill is a large horizontal bandsaw made from salvaged motorcycle wheels. Thursday was lost to the miserable task of prying off the drive wheel's tubeless tire, scrubbing the corroded bead seating surfaces and getting it to hold air. The slow air leak reduced the blade's initial 500 lb tension and let it wander in the >20 inch long cut. I learned manual tire repair at the Hardway School (an Army motor pool) on split rim truck tires. As the tire store manager told me, a 2" right angle air sander is the perfect tool for cleaning up a leaking rim. My tractor's rusted wheels will be its next victims.
Would fatigue cracking in oil be similar enough to cracking in air, which oxidizes freshly exposed steel?
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On Sat, 22 May 2021 09:01:35 -0400
<snip>

And what about heat? Flexing metal creates heat. If you accelerate flexing to speed up failure detection you will likely create heat that would not be present in its actual use...
--
Leon Fisk
Grand Rapids MI
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"Leon Fisk" wrote in message wrote:
<snip>

And what about heat? Flexing metal creates heat. If you accelerate flexing to speed up failure detection you will likely create heat that would not be present in its actual use...
--
Leon Fisk
Grand Rapids MI
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Heating is pretty negligible. On a resonant machine you can test at up to around 300Hz and there is no drift in values obtained compared to at much slower rates. You have full elastic energy recovery.
Servo-hydraulic - not recovering elastic energy with the drive heats the oil away from the sample where you dump the pressure - and you dump that heat through "raditiators" (forced convectors transfering oil-to-air).
But the sample is seeing full energy recovery / negligible energy loss.
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I think so - very little difference. Well my instinct says for environment in general that * negligible difference at high stresses * possible significant effects at low stresses / huge numbers of cycles to crack / break I suspect the difference between in-air and in-oil would be negligible.
Another thing I must test though.
Rich S
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"Richard Smith" wrote in message writes:

I think so - very little difference. Well my instinct says for environment in general that * negligible difference at high stresses * possible significant effects at low stresses / huge numbers of cycles to crack / break I suspect the difference between in-air and in-oil would be negligible.
Another thing I must test though.
Rich S
--------------
Racing engine builders might know.
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Variable - you have many eccentrics, each with a slightly different throw?
I thought - one eccentric, but many different "pistons" with their "collar" they go through into the fluid volume.
Yes one thought is that the mechanism could be built onto the lower cylinder end.
With the "bar" driven by the eccentric simply pushing in and out of the cylinder volume. For the "170Tonne-force" test it would need to displace about 270cc - would be 70mm diameter and stroke (or some other combination of diameter and stroke which gives that displacement).
One advantage of this arrangement is, seeing as it's so stiff, plus bits can't fly around with being inside the cylinder, the test rate could be high. Fastest induction motor speed? 3000rpm on 50Hz supply = 50Hz test rate :-) That would be 60Hz on N.Am. supply.

Knowing the metallurgical and fatigue stuff has cost me a lot - money in various ways and time ...
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"Richard Smith" wrote in message writes:

Variable - you have many eccentrics, each with a slightly different throw?
I thought - one eccentric, but many different "pistons" with their "collar" they go through into the fluid volume.
-----------------------
One circular eccentric disk, mounted on an offset pivot pin so it can be centered or swung out as needed. The clamp for the swinging side might have to include a custom stepped bushing to withstand the torque, rather than just a bolt that holds by friction, but its surface finishes aren't critical like the eccentric's. Lathes don't necessarily leave surfaces good enough to be running bearings, that's extra hand work.
It's easy to turn two cylindrical surfaces with different centers when holding the work in a 4-jaw lathe chuck. http://s3.cnccookbook.com/CCLatheEccentricTurning.htm
The eccentric disk could be a slice of hydraulic cylinder rod with a case-hardened, chromed and polished surface. The strap could be lined with replaceable slices of Oilite bushing. You don't need the historical accuracy many British model engineers strive for. http://www.stockbridgelocomotiveworks.com/2019/10/14/eccentrics-and-valve-gear/
You have ideas that need machine tools to create. Good new ones and hired custom shop work are quite expensive, so I saved by finding older industrial machines which had become obsolete and too worn to be economical in a production shop, like a lathe made in 1965. You have an excellent equivalent: http://www.myford-lathes.com/used.htm I have no experience with the current imports.
I can't easily hit the tolerances on a customer's drawing but I can still make two pieces fit each other although they may not be quite to spec, so my antique machines are fine for making single devices for my own use (and for fixing each other). From the reference above: "I turned the final diameter on a good portion of the bar and then machined each eccentric one at a time, individually match-fitting each eccentric strap."
The trick is that two parts of a complementary operation may not be equally difficult, for example the piston is easier to turn and finish than the cylinder, so make the difficult one first and fit the easier one to it. The boring head he used on the eccentric has a micrometer adjusting screw to change size, I have an identical one. Many shortcuts are possible when you control the design.
I made the prototype of an inch-long diode laser and lens mount in a few evenings that later cost $4000 apiece from a job shop that normally made parts for BAE. Mine wasn't quite as well finished but it worked and proved my ideas. First I needed approval to charge it as overtime, but the project engineer knew how expensive the company's main machine shop was. I suspect part of the high cost was due to the electrical engineers' inexperience with mechanical design and machining.
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"Jim Wilkins" wrote in message
... http://s3.cnccookbook.com/CCLatheEccentricTurning.htm
-----------------
I made a split bushing to hold short 3/8" Grade 8 bolts in a 5C collet like in the "I love this tooling." example shown. Grooves near the ends hold O rings that keep it together. Neither the hex head, shank nor threads run true to each other so I have to clamp the bolt by the section I'm modifying. OK, they are technically hex head cap screws when they go in a tapped hole but 'bolt' is their common name.
The bushing's center hole is 0.370" diameter to match the shanks of the bolts at the store, and before splitting I tapped it 3/8-16 to grab the thread crests without damaging them, as rolled threads can be larger than the shank. It lets me modify bolts to within as little as 1/2" from the head, for instance to trim back the slightly-long shank so a nut bears on the parts being clamped, or to cut a root-diameter pilot and pointed end on the threads for simultaneous alignment of multiple 40 Lb parts with 0.370" bolts in 0.375" holes. Those piloted bolts are longer and go at the outer ends to stop the trolley after using them to align the center splice. Most of the bolts joining my gantry track sections had to be modified to put their shanks in the shear planes and clear the moving trolley.
My previous 5C bolt-holding fixtures are bushings with tapped holes, but this version is more versatile and clamps tight on either shank or threads. I split it with a hacksaw after scribing the end with a tool point aligned with the 5C splits.
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I haven't got this for certain. Not grasped the idea for sure, yet.
Forces would be in Tonnes to tens of Tonnes. The size of the eccentric - both what it will withstand as a bend or shear, and preesenting enough bearing surface for the bearing to take the load - can make these things quite big. Maybe 200mm diameter with 190mm shaft for 10mm "throw", for some enormous tests in high yield steels. As I calculate / estimate as best I can.
If it came to making one of these things, there would have been a lot of proof-of-principle with "testing lab. scale" samples, and the stakes would be quite remarkable by that stage, if we got there.
The main point is to have plans in place. In a political world, you have to have everything covered, so every interjection, objection, etc. is smoothly put in its place. As I've experienced. I've certainly had the skill of predicting what the ploys might be tested. Having big efforts to derail the plan slapped down in seconds.
So it's about being able to see a way ahead, far along a perceived path. What would actually be going on, where you would actually be by then, what method you would use given experience had by then but ahead of you now - that might be a different story. But for now - you are "covered"...
With the beam tests, you can tune the testing force by moving the beam end supports in and out - present different spans. So one fixed throw / movement drive would cover all purposes.
For the "hydraulic inner fatigue test", I think different diameter "spuds" sliding in and out of the fluid volume, on a fixed eccentric drive, might be easiest?
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