Patent Application
20220275989
Embodiments of the present invention relate generally to apparatus involved in cryogenic and deep cryogenic treatment of materials and, more particularly, to deep cryogenic treatment of large size and large volume items for industrial applications.
Deep cryogenic treatment (DCT) of metal articles to enhance wear life has been performed since the 1940's. Early experiments involved quick immersion of die sets directly in a liquid nitrogen (LN2) bath. Those items that did not immediately thermal crack from the 400° temperature differential survived and many exhibited significantly longer life and resistance to fatigue, impact and wear. It was later discovered that a slow ramp down in temperature and a prolonged exposure to dry liquid nitrogen vapors is preferable over direct wet immersion.
DCT is a cold, diffusionless-thermal process that takes 20-50 hours to complete and permanently imparts wear, corrosion and fatigue resistance to metals and metal-matrix items.
Over the last 70 years, improvements to low temperature cryogen delivery systems, PID controllers and thermal processing techniques have made the process reliable, however, DCT has only received limited commercial acceptance due to:
The largest available commercial DC treatment chambers are approximately 3′×3′×6′ rectangular or 3.5′×5′ round. The maximum recommended load weight is approx. 5,000 pounds. None of the machines, service providers or treatment facilities perform or provide test, measurement, validation and/or certification services on-site, or at time of DC treatment, for items so treated.
None of the current equipment provides authentication of treatment or standards-based traceability for treated parts, nor do the equipment or service providers supply engineering test data to customers seeking actual confirmation of treatment or proof of levels of performance improvement. A simple anecdotal statement or a payment receipt for services rendered is all that is supplied, in lieu of any formalized testing, authentication or certification against ASTM or industry-accepted standards.
The rectangular machine designs (see 0005) employ either direct immersion of a part in liquid nitrogen, partial dry gaseous exchange or surface exposure via liquid droplets from adjacent spray bars or a combination of these techniques (U.S. Pat. No. 5,865,913 issued February 1999 to Paulin et al; U.S. Pat. No. 5,259,200 issued Nov. 1993 to Karmody). These methods promote quick treatment of parts via rapid exposure of parts to a −320° F. liquid—a condition and technique that can induce thermal shock and metallurgical stress and can also result in subsurface cracking, shortened item life and corrosion formation. These machine designs are not capable of needed post-DCT tempering in-situ and, therefore, users of these equipment designs must perform tempering heat treatment using additional apparatus.
The round chamber (tank) design employs a dry vapor liquid nitrogen atmosphere, contained in a vacuum insulated round chamber, for non-stress inducing thermal exchange (U.S. Pat. No. 5,174,122 issued December 1992 to Levine).
However, both the round and rectangular designs only permit limited weight and volumetric capacity per lot treatment—essentially precluding widespread use of this technology in industrial or commercial applications, or in any scalable application such as is required in the mining, oil and gas, power generation, locomotive or automotive industries. Currently, the available equipment primarily serves the hobbyist, academic, research or small volume markets such as machine tooling, firearms, motor sports or electronics.
Another obstacle to large scale DC application is the volume of supplied liquid nitrogen (LN2) required for treatment of large lots. Most DCT service providers purchase small volumes of LN2 (sufficient to perform a single DC treatment) in 230 litre easily transportable containers. provided by such commercial gas suppliers as Linde, Air Liquide, Praxair or General Air. LN2 delivered in this manner is a low cost, variable expense that requires no large physical space, storage requirement or dedicated flow control equipment. A large chamber for industrial applications could require 10,000 litres or more of liquid nitrogen to perform a single treatment. This type of operation requires significant physical space, material handling capability, cryogen production and/or storage—beyond the financial and operational ability of small DCT service providers.
The lack of a large size DCT chamber with in-situ tempering capability, integrated part authentication and validation equipment, scaled specifically for industrial use, is a key obstacle to widespread adoption of deep cryogenic technology to address wear, corrosion and fracture issues in metal and metal-matrix parts.
Among other things, embodiments herein provide apparatus and methods to deep cryogenically treat large size and weight metallic items in a fixed or portable location; above, in-ground or at ground level.
Embodiments describe cold temperature thermal apparatus that is directly linked to a Programmable logic controller (PLC) or computer with active feedback software and hardware
Embodiments also describe one or more LN2 storage tanks, an on-site or remote liquid nitrogen generator and flow control equipment to deliver LN2.
The present disclosure is described in conjunction with the appended figures:
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, one having ordinary skill in the art should recognize that the invention may be practiced without employing one or more specific details. In some instances, geometry, configuration, techniques and manufacturing details have not been shown to avoid obscuring the present invention.
Numerous DCT chamber designs exist in prior art. All are single chamber, rectangular, square or round in shape. They use simple programmable logic controllers (PLC) and are not system linked to any means of authentication, test, validation or certification apparatus. Some of these designs are described in U.S. Pat. No. 3,891,477 issued June 1975 to Lance and U.S. Pat. No. 4,739,622 issued April 1988 to Smith.
None of the present designs utilize treatment information acquired from a test-based, scientific materials database and archive, compare or contrast results against prior material treatments. None of the designs, current or otherwise, known to this inventor, utilize parametric software that combines dynamic treatment, test and engineering analysis to upgrade improvement modifications in treatment protocols.
None of the commercially available deep cryogenic machines, known to this author, are able to treat a part or items larger than 4′×4′×6′, or treat any loads or single parts exceeding 5,000 pound weight. None of the current manufactured DC equipment is able to authenticate, test, validate or certify part treatment in accordance with ASTM or qualification standards for 3rd party certification.
Liquid Nitrogen is supplied to one or more LN2 storage tanks, via an on-site or off site liquid nitrogen generator, directly linked to the DCT chamber. Normally, such storage tanks are dual wall, vacuum jacketed and supply LN2 between 125-250 psi. They can be vertical or horizontally mounted and are usually placed on a concrete pad, engineered to support tank weight when full.
The term ‘facing skins’ may refer to any stainless steel, galvanized, aluminum, metal-matrix or metallic sheet metal—welded, brazed, riveted, lapped, screwed, bolted, assembled or fabricated—that is used to provide either or both a sealing surface and an additional reflective and/or insulating layer to reduce thermal exchange and inhibit thermal transport.
The chamber may rest on one or more vapor barriers, leveling pads and/or insulation mats which can prevent thermal loss, condensation, moisture wicking and damage to the floor or concrete underlayment.
The entire deep cryogenic chamber is capable of handling up to 60,000 lbs total aggregate weight and may be sub-dividable into one or more chambers—each independently controlled and capable of staggered or simultaneous cryogenic and/or tempering, treatment or processing cycles—with respect to the treatment cycle operating in an adjacent (subdivided) tank chamber.
The loading and unloading of large components into the chamber may be accomplished by hand, robot-assisted, roller rail or crane/hoist assist, while small components may be loaded as described above or off-line pre-loaded into custom built containment cages that facilitate more orderly and rapid logistics flow. The use of custom containment cages also simplify lot authentication, RFID tracking and verification and assist in segregating and processing quantities that require specific contract-stated control of material.
Regardless of loading method, all DC treatment described by this invention may utilize procedures outlining authentication, material control, validation, test, measurement and certification of materials. Such methods and procedures may include one or more of the following: transducer and thermocouple-based direct part temperature sampling, active feedback and protocol recalibration at flow controls, sensor-based data acquisition, time/date stamping for authentication, use of part-affixed strain gages for part/lot treatment authentication, archival data storage, use of statistically valid baseline and witness proxy artifacts for destructive testing and non-destructive residual stress and/or retained austenite testing using X ray diffraction for validation and certification.
The chamber operates using solenoid-activated, gravity fed cryogen delivery via distribution hubs with individual distribution flow tubes running along the side or back walls—either having percolation holes running along some portion of the tube length or unperforated walls until termination at open ends or a combination thereof. Fabricated heating ducts, to channel on-demand propane or natural gas supplied tempering heat, are mounted to the tank structure. Cryogenically-rated hardware and hose link the solenoid-controlled LN2 distribution hubs to the LN2 source and permits rapid connect/disconnect.
As seen in one embodiment in
Following the dwell phase, LN2 flow is halted and the payload temperature slowly returns to ambient temperature due to a combination of a) thermal exchange from temperature differential between internal and external chamber temperatures, and b) the introduction of heat through ducted plenums by external forced-air propane or natural gas-fired torpedo heaters. The chamber temperature slowly increases the payload temperature over an 8-16 hour period until it reaches equilibrium by matching the external chamber ambient temperature. This portion of deep cryogenic treatment is called the ‘ramp up’ phase.
By conducting the ‘ramp up’ or warming phase in a semi-sealed chamber without introducing external, moisture-laden air, condensation and corrosion formation at dew point exchange is avoided. When the payload reaches ambient temperature, the heat cycle continues and between 1-3 tempering cycles to a maximum of 350° F. are conducted. These 2-8 hour tempering cycles are necessary to remove hydrogen embrittlement from certain materials and to increase post-DCT ductility. This portion of the DCT cycle is called the ‘tempering’ phase.
The flow control device illustrated in
| Number | Date | Country | |
|---|---|---|---|
| 63149370 | Feb 2021 | US |
