Typical Strain Gage Bonding Procedure and Dampproofing
The bonding procedures for strain gages differ depending on the type of the adhesive applied. The description below applies to a case where the lead-wire-equipped KFGS gage is bonded to a mild steel test piece with a typical cyanoacrylate adhesive, CC-33A. The dampproof treatment shows a scenario using a butyl rubber coating agent.
Using sandpaper (#320 grade or similar), polish the bonding site with circular motions across a considerably wider area than the strain gage size.
(If the measuring object is a practical structure, wipe o paint, rust and plating with a grinder or sand blast. Then, polish with sandpaper.)
Using an absorbent cotton, gauze or SILBON paper dipped in a highly volatile solvent that dissolves oils and fats such as acetone, strongly wipe the bonding site in a single direction to remove oils and fats.
Reciprocated wiping does not clean the surface. After cleaning, mark the strain gage bonding position.
Make sure of the front (metal foil part) and the rear of the strain gage. Apply a drop of adhesive to the rear face and immediately put the strain gage on the bonding site.
(Do not spread the adhesive over the rear face, as doing so may cause the adhesive to cure too quickly to adhere to the bonding site.)
Cover the strain gage with the accessory polyethylene sheet and strongly press the strain gage over the sheet with a thumb for approximately 1 minute (Do not remove your thumb partway through).
Perform steps 3 and 4 quickly, or the adhesive will cure prematurely. Once the strain gage is put on the bonding site, do not put lift up to adjust the position.
When the adhesive is cured, remove the polyethylene sheet and check the bonding condition. Ideally, the adhesive should be protruding slightly from around the strain gage.
If the adhesive is protruding excessively from around the gage base, remove the protruding adhesive with a cutter or sandpaper.
Place the gage leads in a slightly slackened condition.
Lift up the lead wire to the point where the adhesive is applied. Place a block of the coating agent below the lead wire with the gage leads slightly loose.
Completely cover the strain gage, protruding adhesive and part of the lead wires with another block of the coating agent. Without tearing the block into small pieces, slightly flatten it with a finger to fully cover the strain gage and part of the lead wires. Completely hide protrusions including gage leads behind the coating agent.