Procedure to Generate Core dump of a process in Linux system

Hello All,
I have one machine where some customized applications written in C++ (process) are getting hanged frequently.
In order analyze the same , I require to generate a core dump when the application starts responding slow or processing slow.

I have done the following to enable core dump of the system.

1) In /etc/security/limit.conf, I have enabled the following lines which are #shed.

•      * soft core 0
•      * hard core 0

and then save the file.

Run the following command at the time of hang but it did not create any core dump.

#kill -s SIFSEGV <PID of the hang process>

But it has not generate any core dump. I think I am doing some fundamental mistake being not aware much about it.

Can you help me to generate the same? I have gdb installed in my system.My RHEL version in 5.9.

I do not know much about it.Can somebody help me out to generate the core dump.