SQL Server transaction log growing without control We have a database growing uncontrolled and filling the hard drive every 2 days. Database maximum log size is set to 6 gb but id doesn't seem to be working because it continues growing beyond 6 gb.

The only way to "solve" it somehow is backing up and truncating after that. 

First, wow's that possible database continues growing if maximum log size is set to a specific size?

Second, if transactions are opened and closed properly, we know it's working well, why my log file grows uncontrolled?
The only way to "solve" it somehow is backing up 


Because that is the only way to truncate the log. See How to Shrink the SQL Server log for an explanation on what happens. Normally log backups are scheduled very frequently (think 10 minutes) and they truncate the log. You want a frequent log backup not only because it eliminates the growth problem, but primarily because you want to minimize the amount of transactions lost in case of disaster (crash).

If you want a different behavior, change the recovery model to SIMPLE. In case of failure you will loose all the transactions since your last full backup, but there is no free lunch, is there?