Stackable plastic damper
BACKGROUND OF THE INVENTION 
     The present invention relates to viscous dampers, and particularly, to rotary viscous dampers for retarding the downward closing of roll down doors such as fire doors. 
     It is known to provide a viscous speed governor to the shaft of a roll-up fire door to retard the unrolling speed of the fire door after actuation during a fire. Such a known fire door such as a KINNEAR® fire door is described in FIG. 1. These governors include a housing, a disk-like rotor within the housing and a cover enclosing the rotor within the housing. The housing can include notches arranged around an outside circumference forming lugs for engagement by a rachet-like device for preventing rotation of the housing in a first rotational direction during unrolling of the door, but allowing rotation in an opposite direction during subsequent roll-up. 
     U.S. Pat. No. 4,432,254, issued Feb. 21, 1984, describes a viscous damper using the shear film mechanism to retard rotation. Such a damper utilizes a rotor disk arranged rotationally within a housing having inside walls in close conformity with the opposite side surface of the rotor disk. A gap between the inside walls and the surfaces of the rotor disk is filled with a viscous fluid which resists relative rotation between the rotor disk and the housing by a shear film mechanism. Thus when the housing is fixed for zero rotation with respect to the fire door frame and the rotor disk is fixed for rotation with an axle shaft or reel of the fire door, unrolling of the fire door by rotation of the axle is resisted by the viscous damper. 
     Prior to the present invention, the damper and rotor must be sized per the weight of the fire door, requiring a plurality of sizes and resulting increased manufacturing and inventory costs. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved structure for a viscous damping unit, particularly adaptable for retarding unrolling of a fire door after actuation. The housing of the present invention is advantageously fashioned of a composite material such as 30% glass reinforced plastic such as a fiberglass reinforced polycarbonate. The housing has integrally molded stiffening ribs to resist bending of the housing along its central axis. External engagement lugs are molded integral with the housing. 
     The housing includes features molded on side faces which allow ganging or coupling of units for additive damping. Advantageously, only one outer lug of the ganged units is required to be engageable to the framework. 
     In a preferred embodiment, the housing, rotor and cover are all made of the same material. A plurality of dampers of the present invention can be locked together in axial stacked arrangement to increase the damping influence on a shaft. Advantageously, the shaft penetrates through the coaxially aligned dampers and is keyed to the rotors of all of the dampers. The housings of the plurality of dampers are locked together via two spring pins penetrating aligned holes provided in each housing. The spring pins provide a load path to transmit the torque caused by the drag on the rotors back to a first damper engaged to the framework. The holes in the housing for receiving the spring pins are slightly elongated in a radial direction. This is to permit coupling of dampers without binding or interference due to tolerance build-up from multiple units. 
     By providing the ability to couple dampers together along a single shaft, the invention reduces the requirement to stock a variety of dampers such as dampers having rotors of large and small diameters. Proper selection of multiple dampers can increase and decrease damping influence without needing either a larger or smaller unit. Thus, an economy of spare parts and manufacturing is achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a prior art roll-down; 
     FIG. 2 is a left side view of the fire door of FIG. 1; 
     FIG. 3 is an enlarged sectional view of a stack of dampers forming a damper assembly; 
     FIG. 4 is a sectional view taken generally along line IV-IV of FIG. 3; 
     FIG. 5 is a perspective view of a housing of the damper assembly of FIG. 3; 
     FIG. 6 is an enlarged sectional view of the housing assembly of FIG. 5; 
     FIG. 7 is an elevational view of a rotor of the damper assembly of FIG. 1; and 
     FIG. 8 is an elevational view of a cover plate for the damper assembly of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show a prior art fire door assembly generally at 10 comprising a fire door 14 made up of a plurality of slats 16. The fire door is shown in a downward unrolled position. The fire door 14 is rolled around a spool assembly 18 which revolves around an axle or shaft 20. On a side of the fire door assembly 10 is mounted a case 24 in which can be assembled a damper assembly 30 of the present invention. 
     FIG. 3 shows the damper assembly 30 mounted to the axle 20. The damper assembly 30 comprises a plurality of damper units 34, 36, 38. Three damper units are shown, but any number from one or greater could be used. The damping components 34, 36, 38 are configured identically. Each comprise a rotor 50 having a hub 52 fixed or keyed to the axle 20 for rotation therewith and a disk 54 extending radially around the hub 52. Each damper component also comprises a housing 60 and a cover 66 which mate together capturing the disk 54 therebetween. Between an inside surface 68 of the housing and an inside surface 70 of the cover and opposite surfaces of the disk 54, a viscous fluid 71 is injected such as silicone fluid of 1,000-600,000 centistokes. The housing 60 of each of the plurality of damper components are connected together via at least one spring pin 76 and preferably two spring pins 76 which protrude through coaxially arranged bores 80 of the housings. In lieu of the spring pins a stud or other connector could be used. 
     The first inboard damper 34 closest to a back wall 82 of the door casing 24 is selectively fixed against rotation with respect to the casing 24 via a catch 86 shown more clearly in FIG. 4. 
     FIG. 4 illustrates the catch 86 mounted for rotation about an axle 88 and having a finger portion 90 abuttable with a lug 94 of the housing 60. The catch 86 is mounted for rotation with a lever 96 about the axle 88. The lever 96 has an aperture 100 at a distal end from the axle 88, the aperture connecting a spring 104. The spring 104 stretches from the lever 96 to an anchor point 108. Thus, the spring biases the finger portion 90 into a position to abut a side 94a of the lug 94. 
     As shown in FIG. 4, the housing can rotate clockwise with a trailing lug 110 rotating the catch 86 counterclockwise against the bias of the spring 104 in a ratchet fashion to pass the finger portion over the lug 110 and succeeding lugs. However, the housing 60 cannot rotate counterclockwise as the lug 94 is stopped by the catch 86. The clockwise direction of the housing 60 would correspond to an unrolling and lowering of the fire door and the clockwise direction would correspond to a rolling-up of the fire door, thus a rolling down is accomplished with a fixed housing 60 for rotation whereas the rotor 54 itself must rotate within the housing against shear forces from the viscous material. For rolling-up the door, the entire housing 60 and rotor 54 can rotate together without the necessity to overcome the shear forces of the viscous fluid. 
     FIG. 5 shows a damper assembly 34 of the present invention. The housing 60 is preferably made of 30% glass reinforced composite material, such as reinforced plastic. A fiberglass reinforced polycarbonate such as LEXAN 3413 or VALOX 553 can be used. The housing has a central hub or journal portion 120 having a bore 124 for receiving the hub 52 of the rotor 50. The hub 52 provides a keyway 128 for locking the rotor 50 to the shaft 20 to rotate therewith. Extending radially from the central hub 120 is a disk portion 130 having reinforcing gussets 134 applied around a circumference at 60° spacing. These gussets give the housing 60 structural stiffness to resist bending and flexing. Arranged around an outside circumference of the disk 130 is a ring portion 140. 
     Radially extending from the ring 140 portion, at 45° spacings are the lugs 94. The lugs 94 have an approximate rectangular shape providing approximately rectangular notches 144 between adjacent lugs 94. The lugs 94 have square channels 148 penetrating therethrough. These square channels 148 reduce the necessary materials of construction for the housing 60 and also effect weight reduction for the unit. At least one lug 94&#39; and preferably two lugs 94&#39; have the bores 80 located therethrough for attaching adjacent damper units 34, 36, 38. A viscous material fill fitting 160 is provided through one modified reinforcing gusset 134&#39;. Through this fitting, the viscous material can be injected into the space between the housing 60 and the disk 54 of the rotor 50. 
     FIG. 6 illustrates a section through the housing 60 wherein the channels 148 are shown as being rectilinear with varying width. 
     FIG. 7 shows the rotor 50 having the hub 52 and the disk 54 extending radially therefrom. The hub 52 provides the keyway 128 for locking the rotor 50 to the shaft 20. 
     FIG. 8 shows the cover 66 in more detail. The cover also comprises a plurality of reinforcing gussets 170 arranged at 60° around the circumference of the cover. Through one special reinforcing gusset 174, a viscous material fitting 178 is provided for injecting the viscous material between the cover and the disk 54. 
     As one advantage of the invention the rotor 50, the housing 60, and the cover 66 are all made of the same composite material. 
     Although the present invention has been described with reference to a specific embodiment, those of skill in the art will recognize that changes may be made thereto without departing from the scope and spirit of the invention as set forth in the appended claims.