Simple Dip Test Equipment

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.

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.

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.

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*.

Malcolm,

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

Scott

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

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

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 ]

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

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