Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Reexamination Certificate
2000-06-28
2002-03-26
Wilson, Gregory (Department: 3749)
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
Reexamination Certificate
active
06361312
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an automated materials processing furnace that is capable of high temperature operation. In particular, this invention enables the processing of material samples under both terrestrial and microgravity conditions and provides for the monitoring of process parameters.
BACKGROUND OF THE INVENTION
The ability to more accurately predict and/or control the behavior of materials processed at high temperatures allows researchers and industry to develop commercial processing conditions which optimize the manufacture of these materials. Such processes involve areas that deal with:
Coefficients of liquid diffusion
High temperature semiconductor crystal growth
High efficiency infra-red glass processing
Travelling liquid-solid interface characterization
The information attained from current terrestrial experiments involved in such investigations, have generated wide and varying results. The primary source of these variations is the effect of convection at high temperatures when the material is in a liquid state. The removal of convective influences provides a significantly improved determination of the underlying processing characteristics. This can be attained through the reduction of gravity.
Earth bound “near-zero” gravity (&mgr;g) can be attained for short intervals of up to 25 seconds. However, these high temperature processes normally require extended periods of &mgr;g in order to complete a particular investigation. Currently, the only viable environment capable of attaining these conditions is the NASA Space Shuttle and the International Space Station (ISS). Unfortunately, the design and operation of any hardware on the Space Shuttle or ISS are restricted by standard predefined safety criteria, physical size, power consumption and available crew time.
The safety criteria imposed by NASA on a particular flight qualified payload (facility) is directly related to the standard set of design specifications established to protect the crew and the Space Shuttle systems. Of these, the most applicable to materials processing facilities are:
Containment of toxic and/or molten specimen materials
Limitation of surface touch temperatures to below 49° C.
Control of electromagnetic interference
The size restriction is related to the need to conform to the standard payload dimensions specified for locating and mounting hardware to the Shuttle or ISS structure. The two types of standard units are a locker and a rack.
Power consumption limitations are a capacity limit for the Shuttle and ISS. A payload has a maximum allocated energy consumption per day that has a specified peak and average power limit. It is therefore desirable to design the payload for operation at the lowest possible power level since this will allow longer daily operations.
Crew time restrictions are imposed by NASA in that experiments are allocated a certain amount of weekly crew time. Since initiating the construction of the ISS in 1998, the time allocations of the crew for the operation of experiments on the Shuttle is becoming more restricted and it is predicted that it will be even more so on the ISS. Facility space is always at a premium since there is limited working space on both the Shuttle and the ISS. These restrictions indicate that for a payload to be productive in this environment, the design needs to maximize the utility of the available working space and to include components that minimize the crew time associated with conducting the experiment.
Previous designs for high temperature experimental hardware have generally been single function furnaces that required a significant amount of crew time to support the operation. One such facility is the QUELD furnace which flew in 1992. This was a single zone furnace that was designed for the processing of samples for liquid metal diffusion studies. The unit's performance allowed for the isothermal processing of materials at temperatures up to 940° C. The unit required significant astronaut intervention for process initiation, sample insertion, sample removal and quenching. The system also required the sample to move with respect to the furnace which could cause unwanted disturbances of the specimen material prior to sample cooling. As the furnace relied on astronaut interventions for processing the samples, there was a risk that the samples were not processed correctly. The requirement for astronaut interventions also limited the number of samples that could be processed based on the available crew time.
Another single function facility is the CFZF facility which is a float/travelling zone facility that utilizes focused movable halogen lamps to create a molten zone in a sample. The furnace accomplishes a travelling melt zone by slowly moving the lamp focal point along the length of the sample. The CFZF is configured only as a float zone furnace and processes one sample before requiring sample replacement by an astronaut. Manual sample insertion by an astronaut runs the risk of potential error in sample installation resulting in incorrect processing. Astronaut time limitations also restrict the number of samples that can be processed.
The AGHF facility is a Bridgeman furnace used as a single processing mode furnace for directional solidification and crystal growth. The system uses a mobile liquid cooling ring to create a moving temperature gradient. The AGHF is operated as a gradient furnace and utilizes one sample per process run and requires astronaut intervention for sample replacement. The risks for astronaut error are again present during the sample installation and the available crew time limits the number of samples in a given mission.
Another facility that was designed for use in limited studies is the LIF facility which is a single zone isothermal furnace capable of processing materials to 1600° C. The unit uses only a single sample and requires astronaut intervention for replacement. This limits the number of samples that can be processed and is also prone to astronaut error in operator procedures. The LIF employs an internal limited capacity helium gas cooling system for the sample which also limits the number of samples that can be processed.
The AADSF is another directional solidification furnace that achieves a moving temperature gradient across the sample by moving the sample over a stationary heating zone. The motion of the sample over the heating element during processing may induce unwanted vibrations in the specimen material.
The TEMPUS facility uses a degree of automation to reduce crew time but still has limitations with respect to scientific versatility. The TEMPUS is an electromagnetic levitation furnace that employs the heating of spherical samples using radio waves. The sample is stabilized in the middle of a magnetic field while the material is processed. The TEMPUS has a capacity of 22 samples contained in a carousel that automatically rotates each sample into position for processing. The unit is limited to those materials that can be contained in a magnetic field, heated by radio waves and have a sufficiently low vapour pressure when molten so as not to contaminate the processing vessel. The unit also provides only simple uniform heating.
The QUELD II facility attempted to address the design issues of process flexibility and reduced crew time. The facility is a 3 zone multi-purpose facility that was initially designed to be used on the MIR space station for processing several different types of materials (liquid metals, semiconductors and infra-red glasses) during a two year period. The sample automation of the unit was limited to two samples per astronaut intervention. There was also the requirement for the astronaut to input into the facility the correct process program number and therefore was prone to processing error. The processing of the samples involved a stationary furnace and movable samples and again the movement of the sample from the furnace to the cooling quench blocks could cause unwanted disturbances in the specimen material. The unit was also limited to the processing of m
Misener D. Lowell
Pugh Sydney M.
Smith Reginald W.
Smith Timothy J. N.
Alston & Bird LLP
Millenium Biologix Inc
Wilson Gregory
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