Automating 24hr Corrosion Dip Test: Motorized Lift for 1-3lb Stainless Parts, 5 Travel

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#1 21673146 13 Jan 2015 15:47

Scott Brown Scott Brown

Anonymous

Post #1
21673146 13 Jan 2015 15:47

I've been tasked at my job to find or build a test fixture that can be used for a 24hour corrosion test. This test consist of submerging stainless steel part in water for 1 hour then raise the part out of the water for 1 hour. I'm not experienced with electronics and could really use some help.

I can handle the design of the test equipment itself, just not sure how to actuate the parts in and out every hour. The parts being tested will way no more than 1-3 lbs and the maximum lift would be no more than 4-5 inches.

Thank you in advance for your help.
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#2 21673147 13 Jan 2015 20:28

Malcolm Whinfield Malcolm Whinfield

Anonymous

Post #2
21673147 13 Jan 2015 20:28

Hi it is an interesting test to solve, although i have not done this test I believe the only way you will be able to do this is to detect the amount of insulation formed over the period of time.

For such a short time the test will possibly need some very precise test equipment (milliohmeter would be the best) to see how much oxidation has formed on the metal in question.

Simply all rust is oxidisation which is an insulator, but as it won't oxidise completely there will be some metal contact but some reduced.

You will not be able to use alligator clips to measure as this will pierce the oxide layer so a calibrated contact is required that only touches the metal without piercing the oxide layer.

There would be more to it, maybe a bit of an experimentation or maybe there is something already available.
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#3 21673148 13 Jan 2015 21:11

Steve Lawson Steve Lawson

Anonymous

Post #3
21673148 13 Jan 2015 21:11

How about a couple of pulleys, one passive and one connected to a geared down motor. Over the two pulleys is a rope. One end of the rope is connected to the DUT [Device Under Test] and the other end tied to a weight that is equal to the weight of the DUT [the "counter weight". Thus, the only energy the motor needs to add to the system is what is necessary to overcome friction and the inertia of starting and stopping the rope.

Place a switch under the counter weight to stop the motor when lifting the DUT out of the bath. Then, either use a timer to stop the motor when the DUT is fully in the bath [determine the timing by experimentation] or find a way to rig a switch to the top of the counter weight's travel path.

The switch(s) could be pushbutton, pressure switch, magnetic reed switch [with magnet on the counter weight] or light beam and photo sensor. In fact, one end could simply a photo sensor that is covered by the counter weight when it bottoms out. Then a light beam at the top that is interrupted when the counter weight reaches it's upper limit.

Why two pulleys? To convey the rope beyond the extent of the water bath container.

And, of course, the "pulleys" can be gears and the "rope" a chain, etc.
#4 21673149 13 Jan 2015 21:19

Steve Lawson Steve Lawson

Anonymous

Post #4
21673149 13 Jan 2015 21:19

The shaft of the powered "pulley" could be the shaft of the motor or, if using gears, the motor shaft could have a gear mounted on it, that drives the gear with the chain on it.

In the later case, the motor might not have to be geared down. Just run it with a smaller gear than the chain gear. For the former, there are many sources of geared down motors. For instance *All Electronics*. Also consider Auto Window Lift motors, available at your local Auto Parts Store.

If using a magnetic reed switch, you will probably need to use it to drive a relay, and use the relay contacts to drive the motor. Pay attention to the maximum current and voltage ratings on whatever switch you use. Make sure the switch/relay contact ratings exceed the motors *Stall Current rating*.
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#5 21673150 14 Jan 2015 07:59

Scott Brown Scott Brown

Anonymous

Post #5
21673150 14 Jan 2015 07:59

Malcolm,

Thank you for your response. Sorry for not being clear, I'm looking to build a text fixture for conducting the test.

Scott
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#6 21673151 14 Jan 2015 08:05

Scott Brown Scott Brown

Anonymous

Post #6
21673151 14 Jan 2015 08:05

Thanks Steve. I'm looking for a simple desktop version. I've been looking at actuator motors that can be programed to extend 4"-5" for 60 minutes, then retract back to 0 for 60 minutes. It will need to be capable of doing this for 24 hours.

Thanks, Scott
#7 21673152 14 Jan 2015 12:08

Steve Lawson Steve Lawson

Anonymous

Post #7
21673152 14 Jan 2015 12:08

How about considering the world of toys? Programmable robot arm, toy crane, erector set, LEGO, or this:

http://www.lynxmotion.com/p-882-servo-erector-set-ses-v11.aspx
#8 21673153 14 Jan 2015 12:09

Steve Lawson Steve Lawson

Anonymous

Post #8
21673153 14 Jan 2015 12:09

Or how about a fully programmable toy robotics building set:

http://www.lego.com/en-us/mindstorms/?domainredir=mindstorms.lego.com

couple this with other LEGO building sets and you might find the material to solve your problem [just keep the door locked until you got a working model -- least you get fired for horsing around on the job ]
#9 21673154 14 Jan 2015 13:25

Richard Gabric Richard Gabric

Anonymous

Post #9
21673154 14 Jan 2015 13:25

Another option is pneumatics. Companies like Festo have linear actuators, controlled with electric valves. You need a source of compressed air, but in this application it would be low volume,
cheers,
Richard
#10 21673155 14 Jan 2015 14:41

Scott Brown Scott Brown

Anonymous

Post #10
21673155 14 Jan 2015 14:41

The sites you suggested are AWESOME!! I think I can figure something out now and maybe build something for myself too.

Thank you for your suggestions

Scott
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Topic summary

The discussion addresses the design of an automated test fixture for a 24-hour corrosion dip test involving stainless steel parts weighing 1-3 lbs, requiring a 4-5 inch vertical travel. The test cycle involves submerging parts in water for one hour, then raising them out for one hour, repeated over 24 hours. Solutions focus on mechanical actuation methods suitable for precise, repetitive motion with low load. Proposed mechanisms include a motorized pulley system with a counterweight to balance the load, using geared-down motors or automotive window lift motors for controlled vertical movement. Position detection can be implemented with switches such as pushbuttons, pressure switches, magnetic reed switches paired with relays, or optical sensors to automate start/stop of the motor at travel limits. Alternative suggestions include programmable linear actuators, pneumatic actuators from companies like Festo requiring compressed air, and programmable toy robotics kits such as LEGO Mindstorms or Lynxmotion servo erector sets for prototyping. The importance of motor stall current ratings and switch/relay contact ratings is emphasized to ensure reliable operation. The original poster seeks a simple desktop solution with programmable extension and retraction cycles for continuous 24-hour operation.
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Automating 24hr Corrosion Dip Test: Motorized Lift for 1-3lb Stainless Parts, 5 Travel

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Topic summary