Method of manufacturing double-chambered infusion bags by folding

A method of pleating and folding a succession of instances of an elongatedly shaped tubular blank of filter paper having two ends and containing measured and separate quantities of an infusionable substance so as to obtain from each tubular blank a filter bag having two envelopes containing the infusible substance, comprising the steps of:

• conveying plurality of tubular blanks of filter paper singly and in succession along a feed direction extending substantially tangential to a rotatable wheel which is equipped with a plurality of radial grippers providing respective arms by which each filter bag is taken up, compacted and conveyed further in said feed direction;
• taking up each tubular blank in succession, when that blank is in a position located above at least three bearing elements which are ordered along said feed direction, of which two are stationary, shaped in such a way as to converge toward said rotatable wheel and offered to opposite end of the respective tubular blank, while the third said bearing element is capable of movement transverse to said feed direction;
• forming a pleat in an intermediate portion (10c) of each tubular blank in succession, using said third bearing element in succession;
• folding each tubular blank in succession double in such a way as to draw two respective envelopes thereof together, by inducing a movement that commences in the position at which the respective said tubular blank is taken up and terminates at a position in which the respective said tubular blank, guided by second two stationary bearing elements, comes to rest between said arms of a respective said gripper with said two ends thereof located close together;
• and
• between said steps of forming and folding pinching said ends of each blank by action of respective movable pressure elements operating against said two stationary bearing elements so as to prevent the contents of the envelopes from escaping during the movement of the respective resulting bag toward said rotatable wheel.