Title: Disable alpha character in Edit
You may use OnKeyPress event of your Edit. You should check, if key parameter is not in set '0'..'9' then you must write Key:=#0;
var
NumSet: set of Char = ['0'..'9'];
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
begin
if not (Key in NumSet) then
Key:=#0;
end;