Patent attributes
A metal cap 12 is fitted over a vessel (vial 2), into which a rubber plug 4 is driven, and using a pressure block 10, a load is applied to the cap 12 through the top surface 12b thereof to maintain the rubber plug 4 compressed. Under this condition, a tightening roller 14 folds a skirt (lower end 12c of a cylindrical portion 12a) of the cap 12 inwardly to perform a tightening operation. Subsequently, the load applied to the top surface 12b of the cap is once released, and then a load is applied again starting from a value FB which is less than the load FA applied during the tightening operation, gradually increasing to a higher value. In the course of increasing the load, a load FC at the instant when a displacement in the elevation of the top surface of the cap is detected, and this load FC is determined to be a seal load upon completion of the tightening operation. By detecting the load FC upon completion of the tightening operation, a seal capacity of the rubber plug 14 can be confirmed.
