Var
  I : Integer;
begin
  For I:=0 to Form1.ComponentCount-1 do
    begin
      if Form1.Components[I].ClassType = TButton then
        TButton(Form1.Components[I]).Visible := False;
    end;
end;

var
  i: Integer;
  t: TComponent;
begin
  for i:=1 to 10 do
  begin
    t := FindComponent('Button' IntToStr(i));
    if (t<>nil) and (t is TButton) then
      (t as TButton).Visible := false;
  end;
end;