Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1998-07-01
2001-01-23
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C428S068000, C428S071000, C428S075000, C360S097010, C360S097020, C181S207000, C181S208000, C156S253000, C156S256000, C156S261000, C156S250000, C156S308400, C228S174000, C228S170000
Reexamination Certificate
active
06177173
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to vibration damped laminate articles having improved force (torque and/or pressure and/or stress) retention, decreased or eliminated potential for spring back, methods of making the articles and fastening assemblies. An attachment device, such as a screw or clamp, that provides a mechanical force to hold a laminate article of the invention in a location has improved force retention compared to systems using known laminates.
BACKGROUND OF THE INVENTION
Periodic or random vibrations or shocks can excite the resonant frequencies in various structures, such as disk drive covers, disk drive bases, automobile oil pans, valve covers, etc., which can be problematic due to the resultant formation of undesirable stresses, displacements, fatigue, and even sound radiation or high levels of sound transmission. In addition, these various components (disk drive covers, automobile valve covers, etc.) may also be used as part of an enclosure to prevent acoustical noise from transmitting through the enclosure and are designed to reduce the level of noise passing through. Such undesirable vibrations, shocks or noise sources are typically induced by external or internal forces or noise generators and can be experienced by a wide variety of articles and under a variety of conditions. For example, resonant vibrations can cause significant levels of acoustical noise in a disk drive assembly. This noise can be easily transmittable through a typical monolithic material cover or base casting of the disk drive allowing excessive noise to pass through the material which is undesirable to the operator of the disk drive. The resonant vibrations in the cover or base may also lead to excessive vertical or horizontal displacement of the key mechanical attachment points in the disk drive leading to poor overall disk drive performance and even potential reliability problems. Control of the resonant vibrations and shock in a disk drive are key to optimum performance in the read/write process and quiet operation plus high disk drive reliability.
The preferred known method to reduce resonant vibrations, shock effects and noise transmission or generation is by using viscoelastic damping materials in a design. The viscoelastic damping materials will dissipate the vibrational energy generated by the resonant vibrations thus reducing the negative effects of the excitation source. The viscoelastic materials when used in a design can also reduce the transmitted or generated noise in an article. The viscoelastic materials can be used as an add-on item to the article or more optimally as an inner layer of a laminate structure used to make the article.
One of the largest uses of viscoelastic laminates is in the automobile industry for oil pans, valve covers, and other viscoelastic laminate formed parts or panels. The laminates in these applications offer significant reductions in the acoustical noise transmission and generation escaping from the engine and also reduce the acoustical noise that can enter the passenger compartment in addition to reducing the resonant frequency amplitudes in the articles. These laminates typically have an attachment area by which the laminate part is attached to a base, housing or other structure. The method of attachment of the laminates could be by screws, bolts, nails, rivets, clamps, or other mechanical attachment devices.
One potential problematic area in using the viscoelastic laminates is in the attachment of the laminates. The viscoelastic damping material will stress relax following attachment of the laminate(s) to the structure or base using the screws, bolts, nails, rivets, clamps or other mechanical attachment devices. The attachment devices are used to securely hold the laminates in a specific alignment and under a specific stress or pressure or torque or fastening force. The torque, pressure, stress, or fastening force will tend to relax somewhat normally even in non-laminate structures due to stress relaxation in the fastener material, substrate material, or fastener attachment point to the structure. Thus, in a laminated article, stress relaxation occurs in the fastening system, the laminate, and also to a smaller degree the higher modulus layers of the laminate. The dominate area of stress relaxation is typically the viscoelastic material part of the laminate. Furthermore, variations in temperature above the application temperature of the laminate using the attachments devices can allow the attachment system to stress relax in a shorter period of time.
The stress, torque, pressure, or fastening force in the attachment device prevents the attachment device from loosening during use of the structure the laminate is attached to. If the attachment device is allowed to fall below a critical attachment force, the laminate could become loose allowing the laminate to shift from the desired location. The loose laminate could interfere with other items near it and/or induce misalignment in items attached to the laminate. Furthermore, the fastener devices could loosen to the point where they would no longer support the laminate in a proper alignment leading to a catastrophic failure of the unit to which the laminate is attached.
Methods that have been used to prevent failure of the attachment of the laminate due to the stress relaxation in the viscoelastic layer are discussed below. Certain methods can add cost, processing time, design complexity, etc., or combinations of each which may not be desirable. Operations or designs to reduce the viscoelastic layers stress relaxation after application of the fastener device include those which are disclosed in PCX-9 POLYCORE COMPOSITES® Physical Properties Sheet, Pre Finish Metals Inc., Polycore Composites®, Elk Grove Village, Ill., such as:
1) The use of automatic Bolt Torque equipment should allow for the entire laminate construction. This fastener attachment method provides for an increased attachment force (torque or pressure) (as compared to a non-laminate material) via the attachment device to the laminate in the attachment area such that after the damping material layer stress relaxes the minimum force required for the application is maintained. The increased torque required initially when attaching the cover to achieve the minimum torque in the screw following stress relaxation can exceed the strength of the screw head-shaft interface, the screw head features (Phillips, Torx, slotted, etc.) that the driver uses to engage the screw and through which the force is applied. In addition, the screw hole tapping or screw features can be stripped in the base or combinations thereof.
2) Another method involves use of a thin input viscoelastic layer in the construction of the laminate to lessen the amount the viscoelastic layer can stress relax. (PCX-9 discloses a layer which is only 0.0254 mm (0.001″) thick.) This approach is undesirable as the optimum design of the laminate viscoelastic thickness to reduce resonant vibrations (and reduce acoustical noise generated or transmission) may not be the optimum for the viscoelastic layer thickness in regard to force retention after viscoelastic relaxation.
3) Another method involves retorquing or applying a secondary (or more) re-application of attachment force once the viscoelastic layer has stress relaxed to achieve the desired attachment force. This method is disadvantageous in that it adds cost to the attachment process and is not acceptable in most applications, especially high volume applications where added work in process or secondary operations can significantly increase manufacturing costs.
4) Another method involves the application of heat to the laminate during the attachment device application process. This method to reduce stress relaxation is disadvantageous in that the use of heat during the laminate article attachment is often not practical for a manufacturing process as it will add cost, application complexity, safety concerns if the temperature required is high, and difficulty in monitoring the process. In addition, compon
3M Innovative Properties Company
Watkins III William P.
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