Piston, cartridge and method of venting a cartridge

A method of forming a two-component piston, the method comprising:

• injecting a material into a mold having a first mold and a second mold to form a piston cover, the second mold being rotatable along a longitudinal axis relative to the first mold;
• rotating the second mold relative to the first mold to expose an opening in a surface of the second mold;
• removing the piston cover by passing an undercut portion of the piston cover through the opening;
• and
• attaching the piston cover to a piston body and overmolding the piston body to the undercut portion of the piston cover,
• the undercut portion being an attachment portion that extends longitudinally in a direction of a rear side of the piston body and a radially extending portion of the attachment portion extends is a substantially perpendicular direction to a longitudinal direction.

A two-component piston for a cartridge, the two-component piston comprising:

• a piston cover having a radially extending attachment portion, a rear side and a front side;
• and
• a piston body including a front side and a rear side,
• the rear side of the piston cover arranged adjacent to at least a part of the front side of the piston body and comprising a valve member configured and arranged to be received within the piston body and to extend into the piston body towards the rear side of the piston body, the piston cover configured to move relative to the piston body upon actuation of the valve member, and the piston cover being non-releasably connected to the piston body by a part of the piston body being overmolded to the radially extending portion of the attachment portion of the piston cover,
• the piston body comprising an annular groove at the front side, the piston cover extending into the annular groove and up to a base of the annular groove, and the attachment portion projecting from the piston cover at the base of the annular groove into the piston body.

A two-component piston for a cartridge, the two-component piston comprising:

• a piston cover having a radially extending attachment portion, a rear side and a front side;
• and
• a piston body including a front side and a rear side,
• the rear side of the piston cover arranged adjacent to at least a part of the front side of the piston body and comprising a valve member configured and arranged to be received within the piston body and to extend into the piston body towards the rear side of the piston body, the piston cover configured to move relative to the piston body upon actuation of the valve member, and the piston cover being non-releasably connected to the piston body by a part of the piston body being overmolded to the radially extending portion of the attachment portion of the piston cover,
• the radially extending attachment portion being a first attachment portion,
• a second attachment portion radially opposed to the first attachment portion, and
• the plurality of attachment portions including at least four attachment portions evenly disposed about a perimeter of the piston cover.