KEEP FOR DOCTOR BLADE HOLDER
An injection molded keep is disclosed that includes a thermoplastic material and a reinforcement material. The keep is positioned adjacent a top plate in a doctor blade holding apparatus and provides a slot opening between the keep and the top plate for receiving an end of a doctor blade in the slot opening.
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This application claims priority to U.S. Provisional Patent Application Ser. No. 60/763,518 filed on Jan. 31, 2006.
BACKGROUND OF THE INVENTIONThis invention relates generally to doctor blade holders, and is concerned in particular with improved mounting structures (or keeps) for such holders.
A doctor blade holder generally holds a doctor blade in a desired position with respect to a rotating roll in a manufacturing process. For example, doctor blades in papermaking machines are generally employed to remove accumulated debris from a roll in the papermaking machine. In certain systems, the doctor blade may further be employed to shed a portion of a sheet of paper. Many such roll cleaning and sheet shedding applications in paper machines and other web handling applications involve blade support devices that are commonly referred to as doctor blade holders. Typically, a doctor blade holder is mounted on a heavy-duty beam, and includes a top plate with a mounting structure called a keep along its underside. Each keep coacts with the top plate to define a slot, and the rear edge of a doctor blade is received in the slot of each keep. The doctor blade then becomes captured between the top plate and the keeps.
The doctoring process often involves exposing the blade holder to high steady-state loads in combination with impact loads. It is imperative that holder components, including the keeps, be of robust design so as to safely accommodate such conditions.
In addition to the mechanical loading, the blade holder may be exposed to a wide range of caustic chemicals and high operating temperatures. For this reason, the selection of appropriate materials is of the utmost importance and often involves the use of very expensive corrosion resistant metals such as type 316 Stainless Steel.
The metal keeps are conventionally produced by a process known as investment casting whereby molten stainless steel is poured into a ceramic mold. After solidification of the stainless steel, the ceramic mold is broken apart to remove the keep. The mold is not reusable.
The casting process is labor intensive and therefore quite expensive. Since a typical blade holder requires many keeps (often several hundred), the total cost of the keeps amounts to a very significant percentage of the holder cost. Stainless steel is also difficult and costly to machine. Each keep requires the machining of two tapped holes that receives screws used to mount the keep to the top plate. This operation further adds cost to the already expensive part.
An objective of the present invention is to provide an improved keep design that addresses the major issues of structural integrity, chemical resistance, and hi-temperature endurance.
SUMMARYIn accordance with an embodiment, the invention provides an injection molded keep that includes a thermoplastic material and a reinforcement material. The keep is positioned adjacent a top plate in a doctor blade holding apparatus and provides a slot opening between the keep and the top plate for receiving an end of a doctor blade in the slot opening.
In accordance with another embodiment, the invention provides an injection molded thermoplastic keep that is positioned adjacent a top plate in a doctor blade holding apparatus and provides a slot opening between the keep and the top plate for receiving an end of a doctor blade in the slot opening. The keep includes a thermoplastic material and relief features in the thermoplastic keep. The relief features include at least one gusset that provides additional structural rigidity, at least one cavity that is positioned to provide a more uniform cross-sectional area that would exist on the keep without the cavity, and a relieve in a surface for providing that a portion of the keep adjacent a fastening screw hole maintains contact with the top plate when the keep is secured to the top plate.
In accordance with a further embodiment, the invention provides an injection molded thermoplastic keep that is positioned adjacent a top plate in a doctor blade holding apparatus and provides a slot opening between the keep and the top plate for receiving an end of a doctor blade in the slot opening. The keep includes a nut retaining and anti-rotation cavity for receiving a nut that may be fastened to a screw that passes through the top plate.
The following description may be further understood with reference to the accompanying drawings in which:
The drawings are shown for illustrative purposes only and are not to scale.
DETAILED DESCRIPTIONApplicants have discovered that a thermoplastic material may be formed by an injection molding process that is suitable for use in securing a doctor blade to a top plate in accordance with various embodiments of the invention.
With reference initially to
The keep 22 is a one piece component that is molded from a variety of thermoplastics including engineered thermoplastic materials. Such engineered plastics include, but are not limited to polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyphthalamide (PPA), polyvinyl chloride (PVC), polyethylene (PE) and polypropylene (PP).
PPA, as a base resin, combines excellent chemical and thermal resistance. When used in combination with fiber reinforcement, the mechanical properties are greatly enhanced in a variety of environments. A preferred reinforcement is discontinuous carbon fiber wherein the term discontinuous refers to the size of fibers relative to the keep. The small fibers may be injection molded resulting in random orientation. This random orientation leads to isotropic properties. The fibers may be formed of glass, carbon, aramid, ceramic and thermoplastic material. The fibers may be between about 0.25 mm and about 15 mm, and may preferably be between about 0.5 mm and about 3 mm in length. Other potential reinforcement materials may include non-fiber elements formed of glass, ceramic, or plastic as well in continuous or discontinuous size distributions. In further embodiments the reinforcement material may include a plurality of particles that are formed of glass, silicon carbide and calcium carbide, and may have a diameter of between about 1 nm to about 1 mm, and preferably may have a diameter of between about 10 nm and about 100 nm.
With reference additionally to
The keep also includes a plurality of engineered relief features. For example, mutually spaced parallel strengthening gussets or ribs 46 are located between the recesses 44 and extend rearwardly from the ledge 38 along the underside of the base 34. The gussets provide additional structural rigidity. The relief features also include at least one cavity 52 that is positioned to provide a more uniform cross-sectional area that would exist on the keep without the cavity, and a relieve 54 (as also shown in
The keep also provides that the slot opening is partially defined by a slot flat portion 56 that has a flatness tolerance of at least 0.250 inches per inch. The keep further provides a top plate flat portion 58 that contacts the tope plate, and the top plate flat portion has a flatness tolerance of at least 0.250 inches per inch.
As shown in
With this arrangement, there is no need to drill and tap holes in the keep. The use of mass produced threaded nuts as an alternate to a machining operation further reduces cost.
The nuts 50 are prevented from rotating by the matching molded recesses 44 in the keep. Thus, when the two screws are tightened, there is no need to use a wrench to hold the nuts at the underside of the keep. This simplifies the assembly operation further reducing the overall cost of the blade holder.
Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the invention.
Claims
1. An injection molded keep comprising a thermoplastic material and a
- reinforcement material, said keep being positioned adjacent a top plate in a doctor blade holding apparatus and providing a slot opening between said keep and said top plate for receiving an end of a doctor blade in said slot opening.
2. The keep as claimed in claim 1, wherein said thermoplastic material includes at least one of a polyetheretherketone, polyphenylene sulfide, polyphthalamide polyvinyl chloride, polyethylene and polypropylene.
3. The keep as claimed in claim 1, wherein said reinforcement material includes a plurality of fibers.
4. The keep as claimed in claim 3, wherein each of said fibers is formed of at least one of glass, carbon, aramid, ceramic and a thermoplastic material.
5. The keep as claimed in claim 3, wherein each of said fibers has a largest dimension of between about 0.25 mm and about 15 mm.
6. The keep as claimed in claim 3, wherein each of said fibers has a largest dimension of between about 0.5 mm and about 3 mm.
7. The keep as claimed in claim 1, wherein said reinforcement material includes a plurality of particles.
8. The keep as claimed in claim 7, wherein each of said particles is formed of at least one of glass, silicon, carbide and calcium carbide.
9. The keep as claimed in claim 7, wherein each of said particles has a diameter of between about 1 nm to about 1 mm.
10. The keep as claimed in claim 7, wherein each of said particles has a diameter of between about 10 nm to about 100 nm.
11. The keep as claimed in claim 1, wherein said keep includes at least one gusset for providing additional structural rigidity.
12. The keep as claimed in claim 1, wherein said keep includes cavities that are positioned to provide a more uniform cross-sectional area that would exist on the keep without the cavities.
13. The keep as claimed in claim 1, wherein said keep includes a relieve in a surface for providing that a portion of the keep adjacent a fastening screw hole maintains contact with the top plate when the keep is secured to the top plate.
14. An injection molded thermoplastic keep that is positioned adjacent a top plate in a doctor blade holding apparatus and provides a slot opening between said keep and said top plate for receiving an end of a doctor blade in the slot opening, said keep comprising a thermoplastic material and relief features in said thermoplastic keep, said relief features including at least one gusset that provides additional structural rigidity, at least one cavity that is positioned to provide a more uniform cross-sectional area that would exist on the keep without the cavity, and a relieve in a surface for providing that a portion of the keep adjacent a fastening screw hole maintains contact with the top plate when the keep is secured to the top plate.
15. The keep as claimed in claim 14, wherein said keep provides a flat portion of a surface that contacts the top plate, wherein said flat portion has a flatness tolerance of at least 0.250 inches per inch.
16. The keep as claimed in claim 14, wherein said keep provides the slot opening with a flat portion having a flatness tolerance of at least 0.250 inches per inch.
17. The keep as claimed in claim 14, wherein said thermoplastic material includes at least one of a polyetheretherketone, polyphenylene sulfide, polyphthalamide polyvinyl chloride, polyethylene and polypropylene.
18. The keep as claimed in claim 14, wherein said keep further includes a plurality of reinforcement fibers formed of at least one of glass, carbon, aramid, ceramic and a thermoplastic material.
19. The keep as claimed in claim 14, wherein said keep further includes a plurality of reinforcement particles formed of at least one of glass, silicon, carbide and calcium carbide.
20. An injection molded thermoplastic keep that is positioned adjacent a top plate in a doctor blade holding apparatus and provides a slot opening between said keep and said top plate for receiving an end of a doctor blade in the slot opening, said keep comprising a nut retaining and anti-rotation cavity for receiving a nut that may be fastened to a screw that passes through the top plate.
21. The keep as claimed in claim 20, wherein nut is received with said cavity in a snap-fit arrangement.
22. The keep as claimed in claim 20, wherein said nut is adhered to the keep within the cavity.
Type: Application
Filed: Jan 26, 2007
Publication Date: Aug 2, 2007
Applicant: Kadant Web Systems (Auburn, MA)
Inventors: Michael DeJesus (Charlton, MA), Robert Reid (Charlton City, MA), David Gardiner (Paxton, MA), Christopher Borradaile (Medway, MA)
Application Number: 11/627,440