.SB files keep appearing in Finder...

I keep getting files appearing in Finder with names like "myfile.rtf.sb-7c9f15d0-gf4mro"

They always have a .SB extension, then various other alphanumerics after the .SB

What are they, and why do they keep appearing? Are they 'versions' of 'sandbox' files, or something?

And what can I do to get rid of them?

Or should I just do nothing, and learn to live with them. (Although there are quite a lot)

Not urgent, but any help or ideas would be appreciated.

Thanks.

:-)