Method of construction for density screening outer transport walls

Abstract

A method for combining three different means of constructing the concentric layers of the outer collecting wall for industrial size centrifuges, whereby treating the inward-facing elements of easily cast or stamped materials using processes such as Physical Vapor Deposition, Chemical Vapor Deposition or metal plating, transforms them into an innermost member with superior hardness and durability, and whereby said wear surface member or deposited layer is physically supported by a middle composition layer made up of one or more investment castings designed to optimally transfer centrifugally-induced compression loads from the innermost wear surface toward the outer surface of the composite wall, such castings being of ceramic, metals or other materials, and whereby the outer surface of said composite wall is comprised of a filament-wound hoop strength reinforcement layer, using aramid, graphic, carbon or such fibers mixed and embedded in resin, such that all highly desirable characteristics for a centrifuge outer, heavies-collecting wall are provided, including interior hardness and wear abrasion, incompressibility and intrinsic dynamic balance, and substantially higher hoop or bursting strength, than can be attained through any metal-crafted centrifuge outer wall, and, model for model, for substantially lower design and fabrication costs.

Description

.Iadd.BACKGROUND--CROSS REFERENCES TO INVENTORS' ADDITIONAL PATENTSThis application is a reissue patent application of U.S. patent application Ser. No. 09 / 156,171 filed Sep. 17, 1998, now U.S. Pat. No. 6,033,564; which is a continuation-in-part application of U.S. patent application Ser. No. 09 / 115,527 filed Jul. 13, 1998, now U.S. Pat. No. 6,312,610. .Iaddend.BACKGROUND--FIELD OF INVENTIONThe pertinent field of the invention is the "imperforate bowl," related to prior art under "fluid separation," especially "Disk Centrifuges," "Nozzle Centrifuges," and "Split Bowl Centrifuges"BACKGROUND--DESCRIPTION OF PRIOR ARTWithin the scope of this application, prior art is taken to mean conventional methods of construction for the outer walls of centrifuges. One such method for such design, fabrication and assembly predominates for all major types or classes of imperforate bowl centrifugal devices, including notably: (1) those used to separate small volumes of materials, such as Test Tube, Tu...

AI Technical Summary

Benefits of technology

When the inventors committed their researches to the re-thinking of the basic material, or materials, used to fabricate centrifuge outer walls, they also became freed up to consider using multiple materials, in a hybrid sandwich, with each layer of material being chosen to do a specific indicated job in the strongest, least expensive way possible.

The researchers chose to emulate or model the sequential trajectory of heavy particles being thrown from the core of a rotating centrifuge, out to and as it developed, through the outer wall of a centrifuge. This intellectual process of following a hypothetical thrown particle, along its journey from the inside of the outer wall to the outside, and assessing the materiel requirements of an ideal centrifuge outer wall at each point of this trajectory, led to the following sequential or layered analysis of the ideal characteristics for each point or layer of this journey.

The primary, explicit job of a centrifuge is to throw heavies outward, thus sorting them away from the lighter fluid flow of the device's center core. The ejecting heavies, the densest and often most abrasive materials in a given fluid flow, thus constantly bombard the innermost or facing surface of the outer wall of a centrifuge. The inventors' review of old and new manufacturing materials and of their related fabricated processes, as available in the late 1990's, led through the manufacturing taxonomy to "non-shaping", and then to "surface finishing" and then to "surface-coating" (see FIG. 3, a reproduction of page 8, Dodd, Allen & Alting, op.cit.).

In-depth review of many different types of "high-tech" surface coatings revealed how, among many lat

Problems solved by technology

In manufacturing, the actual materials and equipment used are costly, but these costs are substantially determined by those responsible for product design before manufacturing even begins.

First, regarding wear surfaces, centrifuge interiors in general and particularly the interior surface of the outer wall of a centrifuge, are an extremely punishing and hostile environment for any chosen construction materials.

To put this yet another way, a centrifuge outer wall of a given outer diameter ("x" inches) operating at its maximum burst strength RPM's will likely experience structural failure if that centrifuge's rotational speed is further increased.

And, conversely, a given centrifuge operating at its maximum outer wall burst strength at a fixed RPM will also likely fail at that RPM if its design diameter is further increased.

The well-documented strength ceilings for steel, titanium and alloy metal used in centrifuge outer walls, and the well-known ratios of rotational speed / centrifugal force times diameter which are governed by those limitations, have created widely accepted limitations for the use of centrifuges.

What appears not to be possible using the decades-old metal based methods of construction and assumptions inherent to all conventional centrifuges is the processing of comparatively large volumes of fluid at centrifugal forces well above approximately 2,500 to 3,000 gravities.

This cannot presently be done because metals cannot provide sufficient hoop or bursting strength to contain the heavier, high volumes, in large diameters, at higher gravities.

Many of today's most pressing environmental problems present very high processing volumes combined with extremely fine, light (and often very dangerous, i.e., cryptosporidium cysts in water supply) particles requiring separation.

However the very high initial cost of and extensive ongoing maintenance required by each of these centrifuges has so far inhibited their use in large arrays of many of such devices, as would be required, for example, to continuously treat all the drinking water for a large metropolitan area.

In addition, more and more long-term health disadvantages of the use of chemicals in water, both individually and from the side-effects of their combinations, are coming to light.

These widespread and intractable disadvantages further underscore the desirability of cost, strength, volume and operating breakthroughs in centrifuge design generally, as dictated by centrifuge outer wall design specifically.

Those disk centrifuges which use stacked disk cores to amplify gravitational separation can separate quite small particles from fluids, in industrial size quantities, due to that amplification technique allowing the use of rotational forces below 3,000 gravities; however, such extremely complex, and maintenance-intensive devices cost many hundreds of thousands of dollars each.

Again, they have not been adopted for large scale fluid separation such as water treatment, most likely because they are not cost-effective for such mass use.

Finally, commercial decanting centrifuges' upper centrifugal limits in the 2,500 gravity range, lacking the amplifier effect of stacked disks, cannot remove particles below approximately 3 to 5 microns.

And, large volume Decanters are also extremely expensive, approaching one million dollars apiece.

First, the thin wear layer would need incompressible physical support by means of the layer immediately outside or behind it.

This is the case because the wear layer is not only being bombarded with many extremely heavy, abrasive individual particles being thrown from the centrifuge, but also because it is being subjected to immense, deforming, centrifugal force.

As stated previously in this application, centrifuges spinning at high speed have extremely low tolerance for weight or density imbalances across the axis of spin.

In addition, for some applications, such middle-layer members can be made of extremely incompressible but comparatively lightweight materials such as cast ceramic.

Until now, the limitations of metal-fabricated wall strength available in commercial centrifuges has drawn a line in the sand regarding how large they can be, and how fast they can spin.

And, as stated above, until now their limitations have governed centrifuge development.

In those parts of such devices having high-strength requirements, such as all parts to be high-speed rotated out away from the axis of spin where centrifugal force is the highest, metal parts is the final assembly of conventional centrifuge walls are often laboriously x-rayed to uncover metal crystal and / or welding flaws which would compromise bursting strength and lead to catastrophic failure at speed.

The extremely high cost of steel and alloyed raw materials certified to have predictable, uniform crystal structure, strength and other qualities, and the equally high cost of casting, turning, finishing, testing and documenting such parts, is well known in the metal trades.

In large part because of the costs of raw materials and fabricating, a single large decanting centrifuge can cost a million dollars or more.

A single conventional disk centrifuge, also metal fabricated, can cost a quarter million dollars or more.

Smaller tubal centrifuges, again made of cast and carved metals, but of lesser cost because of their smaller sizes, can spin much faster and produce much higher gravities than the other devices, but only because of their deliberately small diameters, which keep the centrifugal forces produced within the available strength of the metals used, but also limit their use to fluids in test or extremely small production quantities.

In centrifugal devices designed to attain comparatively higher rotational speeds, another problem must be addressed, which is harmonics.

In a centrifugal device, spinning so as to produce 2,000 or 3,000 multiples of gravity, and filled with extremely heavy fluid whose heavier components are being thrown outwards at greatly increased weights due to gravitational force, harmonics or out-of-phase vibrational forces can quickly cause structural failures.

Centrifuge device assemblies for high-speed operation must therefore achieve precise dynamic balance, and they must also be torsionally rigid, since twisting forces in a device, particularly during acceleration, can also induce destructive harmonics.

Carbon fibers, although strongest, are also brittle; Kevlar fibers, less strong, are far more flexible.

However, the use of filament winding to dramatically strengthen centrifuge outer collecting walls is herein claimed as both novel and non-obvious to experts in the imperforate bowl field.

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