Application: Strain Gages on Polypropylene

1)What design strain gage do you recommend for use on polypropylene (PP) ?

For testing plastics, we normally suggest our EA Series strain gages with an Option L or LE.  The EA Series gages will be flexible and offered in a variety of sizes and the Option L or LE will add small ribbon leadwires so no soldering would be needed at the gage site which could damage the gage, the adhesive or the plastic.  I would also suggest a 350 ohm strain gage.  Some possibilities that we currently have in stock are the following: 

EA-06-062AQ-350/LE http://www.vishaypg.com/docs/11080/062aq.pdf

EA-06-062AQ-350/L http://www.vishaypg.com/docs/11080/062aq.pdf

EA-13-062AQ-350/LE http://www.vishaypg.com/docs/11080/062aq.pdf

2)What adhesive and surface treatment do you recommend to bond the strain gage on polypropylene (PP) ?

The M-Bond AE-10 is a two part epoxy adhesive that cures at room temperature. It’s a 100% solids epoxy so you don’t have to be concerned about solvent sensitivity and reacting with the plastic. M-Bond AE-10 can be found on our Web site at the following address:  http://www.vishaypg.com/docs/11011/bondae10.pdf

       3) What about preparing the surface?

Surface preparation for polypropylene is similar to polyethylene:

Step 1: Degrease the plastic with GC-6 Isopropyl Alcohol

Step 2: Abrade the surface with 400-grit SCP-3 Silicon-carbide paper

Step 3: Locate the gage location lines

Step 4: Scrub the surface with M-Prep Conditioner A

Step 5: Scrub the surface with M-Prep Neutralizer 5A

Alternate to Step 2:  Scour the surface with a household cleanser and rinse with water

4)What coating do you recommend over the strain gage to water proof it in 75-degree C water?

This is really a balancing act between the higher temperature and the moisture protection that is needed and minimizing the reinforcement from the coating.  The M-Coat W-1 Microcrystalline wax is an excellent moisture barrier but you are operating just above its maximum temperature. I would start with 3140-RTV and see how well it holds up.  If you are expecting the project to last a few days then I believe it will survive. 

 http://www.vishaypg.com/docs/11034/3140rtv.pdf

 5)      Do you have temperature compensation values for the strain reading at elevated temperature (at 75 degree C)?

We offer strain gages that have higher Self Temperature Compensation (STC) values such as 30, 40 and 50.  Keep in mind that if the temperature is at a constant 75 C, then the STC doesn’t matter as long as you zero it at temperature. The following are some examples. We don’t normally stock these gages so they would be built when you ordered them, and currently we have a 6 to 8 week leadtime:

EA-30-062AQ-350/LE

EA-30-125AC-350/L

EA-30-250BF-350/L

EA-30-125RD-350/L

For additional information regarding the gage installation on plastic or specific questions, please feel free to contact our Applications Engineering Department.