The ShearTube^TM ShearDamper^TM for Precision Machine Tools

Winner of a 1994 R&D 100 Award as being one of the 100 most technologically significant new products of the year.

A ShearTube^TM ShearDamper^TM allows an engineer to highly damp a structure without imposing strict limits on the structure's geometry or materials. As shown above, the ShearTube^TM damper is incorporated into a structure in the following manner:

1. The structure has rough holes formed in it (casting, drilling, or welding in a pipe).
• The holes may be any shape, but should maximize the cross-section perimeter (e.g., a square).
• The neutral axes of the holes must be as far away as possible from the neutral axis of the structure.
• Ideally, the holes almost fill the structure (e.g., four squares inside of a large square beam).
2. Modestly smooth-surfaced tubes (0.5 mm R_a) that are 3-5 mm smaller than the hole are covered with a high loss damping material (e.g., Scotchdamp^TM).
3. The tubes are suspended into the hole, and an epoxy replicant (e.g., Vibradamp^TM from Philadelphia Resins) is injected (poured) around the tubes.
4. After the epoxy hardens, the component is ready to be used.
5. To achieve excellent temperature control of the machine, the ShearTubes^TM are used like heat exchanger tubes to channel temperature-controlled fluid inside the machine.

Good stiffness and damping are necessary, but not individually sufficient, requirements of a precision machine. Typically, damping in a machine is obtained from the materials and microslip in the joints. The net result is that cast-iron structures have amplification-at-resonance factors on the order of 200. Polymer concrete structures can have 5-10 times more damping than cast- iron structures.

However, many advanced materials (e.g., ceramics) have very poor damping and require an additional damping mechanism. The ShearTube^TM ShearDamper^TM is a viscous shear damper that can be readily incorporated into machine structures. Applications include all types of machines where vibration needs to be damped.

This design is fundamentally different from earlier constrained layer damper designs (e.g., exterior plates which had a tendency to delaminate or require tight manufacturing tolerances) in that the dampers are in the internal shear of a thin film of viscoelastic material. Since the neutral axes of the tubes are displaced from the neutral axis of the structure, bending of the structure causes relative motion to occur between the two surfaces. This motion shears the viscous fluid and dissipates vibration energy at a rate orders of magnitude higher than would normally occur in the material of the structure or in its joints.

In addition, the tubes make excellent heat exchanger tubes in which temperature controlled fluid can be circulated. This allows machines to achieve virtually isothermal performance which greatly minimizes errors, as opposed to other vibration mitigation systems based on solid poured materials.

This concept allows machine tool builders to design a machine with integrally cast longitudinal holes which can have ShearTube^TM dampers installed if the customer requests a high damping option on the machine order form. Thus the concept facilitates modular construction of machine tools.

For questions of a technical nature, contact Prof. Alexander Slocum, and for questions of a commercial nature, contact Mr. Richard Slocum. Please send your inquiries in writing to:

Dr. Alexander Slocum
Aesop, Inc.
PO Box 2126
Concord, NH 03302-2126
Fax: (603) 224-5369