This invention relates generally to filter-driers for refrigeration systems and particularly to a casing and a molded filter-drier core having superior structural characteristics of attrition resistance, strength and permeability while being held firmly in place by structural cooperation between the casing and the core.
Filter-driers are used in refrigeration systems to filter solid contaminants and to remove soluble contaminants from the refrigerant and lubricant. The three general types of construction of filter-driers are loose fill, compacted bead, and molded core.
In a loose fill design, the desiccant is captured within mesh screens to prevent the desiccant beads from escaping into the system. The beads form a desiccant bed trapped between the shell and mesh screens, however, within the desiccant bed the beads are only loosely held. Flow of refrigerant through the desiccant bed or vibration of the filter-drier shell from other sources results in undesirable movement of the individual beads within the bed. Contact of the desiccant beads with the shell, mesh screens, or other desiccant beads can lead to attrition of the desiccant beads. As attrition of the beads progresses, the desiccant fines escape the mesh screens and circulate in the refrigerating system.
Compacted bead designs use desiccant beads similar to the loose fill design but incorporates perforated metal and mesh screens, filter pads, and springs to compact the desiccant bed. The compaction of the desiccant bed restricts the movement of the individual beads compared to a loose fill design and reduces the risk of attrition, however, this design does not eliminate attrition.
A molded core unit consists of a molded desiccant block held in place with support screens, filter pads, and springs. The molded core is made of smaller granules of desiccant than the loose fill or compacted bead design. The desiccant granules are bonded together using an organic or inorganic binder to form a solid shape. This design prevents attrition of the desiccants by not allowing movement of the granules.
Typically, shells to contain the desiccants in a filter-drier are either welded steel shell consisting of steel tubing and/or stamped pieces welded together to form a sealed shell. Alternatively, copper spun shells may be used in which copper tubing is reduced to a specific fitting size. Prior to welding a steel shell or spinning to reduce the diameter of the copper tubing, the internal parts consisting components such as perforated screens, mesh screens, filter pads, desiccant, and springs are assembled. The purpose of the screens and springs is to contain the desiccant beads or desiccant core.
Known filter-drier units having molded cores are disclosed in U.S. Pat. Nos. 2,556,292, 5,440,898, 5,562,427 and 2,551,426. 2,556,892 discloses a core formed from molded discs and U.S. Pat. No. 5,440,898 disclosed a molded core which is strengthened by the use of fibers. In both cases, the core is spaced from an outer metal casing and held in place by a lateral support system at each end. U.S. Pat. No. 5,562,427 discloses a copper casing with longitudinally spaced grooves formed to hold a preformed solid core. The grooves are formed by the drawing process but are at each end of the core. U.S. Pat. No. 2,551,426 discloses a preformed block of drying agent which is supported by longitudinally spaced internal protrusions.
The present system overcomes the need for support systems for holding the core in place in a manner not disclosed in the known prior art.