Air damper with graphite coated lip seal

Abstract: The air damper includes a piston reciprocating within a cylindrical housing. The piston includes a lip seal which is coated with a minimum of 0.5% / seal part weight graphite powder/molybdenum disulfide. This provides for increased smoothness of operation of the air damper, particularly at low speeds.

Description: BACKGROUND OF THE INVENTION This invention pertains to an air damper comprising a cylindrical body and a reciprocating piston according to the preamble of claim 1. Such an air damper is known from EP-A-0 658 611. Description of the Prior Art In the prior art, an air damper of the type with a piston shaft and a lip seal reciprocating within a body or cylinder is well-known. However, a typical rubber seal may slide roughly, particularly at low speeds, resulting in a rough operation of the air damper. Many coatings may attract dust or plug the air orifice thereby impairing the function of the air damper. Moreover, the use of grease or silicone may cause the seal to stick in place and not open. Moreover, the viscosity of grease increases under cold conditions which slows down the damping rate. An elastomeric coating for a lip seal is disclosed in U.S. Patent No. 4,818,620 entitled "Elastomer Coated Lip Seal", issued on April 4, 1989 to Pilkington, but does not adequately address the above deficiency. Graphite powder for lubrication purposes is likewise old in the prior art, such as is disclosed in U.S. Patent No. 5,702,769 entitled "Method for Coating a Substrate with a Sliding Abrasion-Resistant Layer Utilizing Graphite Lubricant Particles", issued on December 30, 1997 to Peters but does not address the above deficiency with regard to smoothness of operation. OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of this invention to provide for increased smoothness of operation of an air damper, particularly at low speeds. It is therefore a further object of this invention to achieve the above object without any impairment of the function of the air damper, such as attracting dust or plugging the air orifice. It is therefore a further object of this invention to achieve the above objects without unduly increased manufacturing expenses or other deficiencies. These and other objects are achieved by the features of claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein: Figure 1 is a plan view of an air damper which is adaptable to the present invention. Figure 2 is a cross-sectional view of the housing of the air damper which is adaptable to the present invention, illustrating the film of graphite powder spread within the interior of the housing by the movement of the piston. Figure 3 is a plan view of the piston and shaft of an air damper which is adaptable to the present invention. Figure 4 is a plan view of the piston of an air damper which is adaptable to the present invention, with the two positions of the lip seal shown in phantom. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings in detail wherein like numerals refer to like elements throughout the several views, one sees that Figure 1 is a plan view of an air damper 10 which is adaptable to the present invention. This air damper 10 is disclosed in more detail in U.S. patent application serial no. 09/177,029, entitled "Silent Damper with Anti-Rattle Shaft", filed on October 22, 1998. Air damper 10 typically comprises a cylindrical housing 12 with a closed end 14 and an open end 16 (see Figure 2), along with a piston 18 attached to a shaft 20 with an attachment head 22 (see Figure 3). Selective air communication groove 24 is formed between disks 26, 28 of piston 18 (see Figure 4). The vertical portion (in the orientation shown in Figure 4) of selective air communication groove 24 formed on disk 28 has substantially greater area than the vertical portion of selective air communication groove 24 formed on disk 26. Lip seal 30 urges radially outward against the interior of cylindrical housing 12 to form a relatively airtight seal. As piston 18 is extended or withdrawn from cylindrical housing 12, lip seal 30 urges against disk 26 thereby restricting the passage of air through selective air communication groove 24 thereby effecting damping. However, as piston 18 is retracted into housing 12, lip seal 30 urges against disk 28 thereby allowing increased passage of air through selective air communication groove 24 thereby diminishing damping. It is important to the operation of air damper 10 that selective air communication groove 24 not become plugged or blocked. As evidenced by film 32 shown on the interior of housing 12 on Figure 2, lip seal 30 is coated with a minimum of 0.5% / seal part weight graphite powder or molybdenum disulfide. Moreover, typically, lip seal 30 is made of rubber or thermoplastic elastomer impregnated with a minimum of 3% molybdenum / seal part weight, or a minimum of 2% TEFLON® (polytetrafluoroethylene) or silicone / seal part weight. Cylindrical housing 12 is typically made with a minimum of 2% silicone impregnated thermoplastic. This graphite powder as evidenced by film 32 allows for smoother operation of piston 18 within housing 12 without the risk of attracting dust or plugging selective air communication groove 24. Thus the several aforementioned objects and advantages are most effectively attained. Although a single preferred embodiment of the invention has been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by that of the appended claims.

Claims: An air damper comprising a cylindrical body (12) and a reciprocating piston (18) including a lip seal (30) reciprocating within the cylindrical body (12), having a coating of graphite powder or molybdenum disulfide on said lip seal (30) in order to increase smoothness of operation of said reciprocating piston (18), characterized in that said lip seal (30) includes rubber or thermoplastic elastomer impregnated with one of the following: a minimum of 3% molybdenum/seal part weight or a minimum of 2% polytetrafluorethylene/seal part weight or a minimum of 2% silicone/seal part weight or a minimum of 2% wax/seal part weight. An air damper according to claim 1 wherein said lip seal (30) is coated with graphite powder or molybdenum disulfide with a minimum of 0,5%/seat part weight.

Inventors: BIVENS STEVEN L, BIVENS, STEVEN L.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 2000
Main classification: F16J15
IPC codes: F16F9, F16J15