Cartridge heater having resilient retaining means

DETAILED DESCRIPTION Referring now to the drawing, FIG.
1 illustrates a fragmentary portion of a plastic molding machine, indicated generally at 10, having a mold support plate 12 which supports a plurality of molds 14.
In the illustrated embodiment, the molds 14 are tubular and extend through a header plate 16 which has a plurality of cylindrical heater bore-holes or cavities 18 formed generally transverse to the longitudinal axes of the molds 14.
The heater bore-holes or cavities 18 are cylindrical and have generally the same nominal diameter.
However, due to relatively broad tolerance ranges, the diameters of the individual bore-holes or cavities 18 may vary by a few hundredths of an inch.
Under this condition, if a cylindrical cartridge heater, such as indicated generally at 20, having an outer diameter on the low side of its dimensional tolerance range is inserted into a bore-hole or cavity having a diameter formed on the high end of its dimensional tolerance range, a slight clearance may result between the outer peripheral surface of the cartridge heater and the annular surface 18a of the bore-hole or cavity.
Such clearance may lead to longitudinal displacement of a cartridge heater from its corresponding bore-hole or cavity if subjected to longitudinal vibrations during operation of the molding machine, with resulting overheating and potential burnout and premature failure of the cartridge heater unless restrained against such displacement.
Referring now to FIGS.
2 and 3, a cartridge heater 20 constructed in accordance with one embodiment of the present invention includes an elongated outer metallic sheath 22 having a cylindrical outer peripheral surface 22a.
The cartridge sheath 22 is preferably made of corrosion resistant stainless steel and houses an inner heater core having an electrical resistance wire element 24 which is helically coiled or wound on a generally cylindrical elongated insulating core 26.
The resistance wire element 24 has insulated lead ends 24a and 24b which extend from an open rear or lead-wire end of the sheath 22 and are adapted for connection to a suitable electrical power supply