(1) Field of the Invention
This invention relates generally to draft inducers for furnaces.  More particularly, the present invention relates to blower housings and the assembly of such housings. 
(2) Description of Related Art
Prior methods used to join blower housings have included everything from spot welding, seam welding, joining with mechanical fasteners or retainer clips.  More recent methods have been made possible by the advent of plastics engineered to withstand forces such as impact or more relevantly, the force imparted to a plastic blower housing by an inducer. 
For example, U.S. Pat.  No.  3,627,442 to Brandt discloses a blower housing made from three pieces of preformed sheet metal.  Two end walls are provided along with a scroll-shaped wall that is situated between the end walls.  The three pieces are joined by mechanical fasteners that are inserted into apertures in the end walls that align with threaded, thread-engaging apertures formed in the scroll-shaped wall.  This type of housing structure requires a significant amount of machining as well as a considerable number of steps to assemble or disassemble the blower housing to service the blower.  Moreover, it is easy to impart an uneven pressure to the seal at various points along the seal due to variations in the tightening of the fasteners. 
An improvement to the blower housing assembly disclosed in the '442 patent is taught in U.S. Pat.  No.  5,158,432 to Cox.  The '432 patent teaches a tab and slot sheet metal joining technique wherein tabs situated on the scroll-shaped wall are inserted into apertures in the end walls.  Thereafter, the tabs are rolled or folded to interlock the parts.  Although a secure joint can be established, the parts cannot be easily disassembled without considerable effort.  Furthermore, the parts cannot be repeatedly cycled through assembly, disassembly and re-assembly without damaging the tabs through the process of metal fatigue. 
A further improvement made possible by the advent of durable plastic materials is disclosed in U.S. Pat.  No.  4,865,517 to Beehler.  In the '517 patent, a blower housing is assembled from two mating clam shell-like halves.  Each half has a circumferential groove situated on an exterior surface adjacent to the half's periphery.  The shell halves are held together with preformed spring steel clips that engage the circumferential grooves of the shell halves.  The clips coupled with a tongue and groove joint and optional gasket provide an air tight seal along with the ability to readily disassemble the housing to service the enclosed impeller.  However, due to the use of the steel clips, corrosion is still a factor especially when the blower is used in a heating furnace in which moisture develops. 
Apart from using any type of mechanical fasteners, some manufacturers have used adhesives to secure an end wall cover to a blower housing.  This eliminates the ability to service the enclosed impeller by removing the cover.  Inevitably, some damage will occur if the cover is forcibly removed from the blower housing. 
Another approach used to secure parts of a blower housing is disclosed in U.S. Pat.  No.  5,443,364 to Mistry et al.  The '364 patent teaches a blower housing with the scroll-shaped wall and one end wall being fabricated as one piece.  The other end wall is separate and serves the function of a housing cover.  The housing cover is secured to the blower housing with a series of unique tab-aperture combinations.  A series of radially extending tabs are formed on the cover.  Flexible arms that extend from the blower housing are formed with barbed detents at the distal ends.  To secure the cover to the housing, the cover and housing are aligned so that the flexible arms match up with the apertures.  The two parts are then compressed together so that the barbed arms snap into the apertures.  A seal is created between the parts by virtue of a top circumferential edge of the housing that is mated to a circumferential channel in an interior side of the cover.  Although this design provides a snap-on type seal, the design of the flexible arms are prone to deformation or breaking and are relatively fragile due to their small size.  Inevitably, the same pressure cannot be imparted at every point along the seal due to the spacing of the flexible arms. 
Although numerous designs have been developed to seal blower housings none to date have the capability to provide a corrosion-free housing that is easy and cost-effective to manufacture such that a strong even pressure seal is provided along with the ability to provide ease of assembly and disassembly as well as the ability to withstand cycles of assembly and re-assembly without any appreciable damage to the joining surfaces.  A way to provide all these advantages has now been developed.