A bell hammer grease was used instead of the grease used in the air cylinder, and a durability test was conducted, but swelling was confirmed in the urethane rubber of the component parts.

The Bell Hammer series is manufactured as a classification that is compatible with No. 1 rubbers as fats and oils.
Although there is no problem with urethane rubber, there are three causes below.
1. The oil and fat of bell hammer grease soaks into urethane and swells
2. The urethane rubber you are using
"Polyester (AU) has good oil resistance, but poor hydrolysis resistance, and polyether (EU) has excellent cold resistance, but poor oil resistance."
Is applicable to
3. If you wash with a parts cleaner etc. just before using the bell hammer, the parts cleaner will swell due to rubber
As a precaution, we will attach our oil list as a pdf.
http://www.suzuki-kikoh.com/data/tech/oilprooftable.pdf?20180730052325