DESCRIPTION

The present invention relates to a method and apparatus for thermally insulating a data logging device configured to log data during a heat treatment and oil quench process. Within an integrated oil quench furnace, problems can occur where parts situated in different areas of the product basket suffer distortion due to uneven temperature distribution in the process. It is therefore desirable to monitor ambient or part temperatures throughout the duration of the heat treatment cycle in the furnace and oil quench. In this way the ambient furnace temperature and the rate of quench in all areas of the product basket can be monitored.

The usual method of monitoring the temperatures in a product basket is to connect thermocouples to parts in specified positions within the basket to an accurate temperature data logging device. The data logger is protected from high furnace temperatures by a thermal barrier which travels together with the parts in the furnace basket. However if an oil quench is involved then the system has to be completely sealed (oil / air tight ) as well as being designed to withstand temperatures in excess of 850°C in the furnace over several hours.

A fully sealed system presents the problem of air, sealed within the thermal barrier, expanding due to elevated temperature within the furnace and over several cycles distorting the casing, or thermal stress distorting the casing, to an extent where oil will enter and destroy the data logger. The oil quench therefore represents a risk of damage to the measurements system and a potential safety risk due to ignition of retained oil. It is known to provide a thermal barrier for a data logging device used for logging data during a heat treatment and salt bath quench process. The thermal barrier consists of a sealed inner container and an unsealed outer container. The two-container construction helps to reduce the volume of air sealed within the sealed thermal barrier, thereby reducing expansion stresses introduced during heating and quenching cycles, and reduces the temperature of the inner thermal barrier reducing the thermal stress during heating and quenching cycles. However, the salt bath quench is maintained at a significantly higher temperature than an oil quench, and therefore imposes considerably less thermal stress on the thermal barrier than an oil quench. Also, the salt bath quench is non-flammable, unlike the oil quench which is volatile and highly flammable.

In accordance with a first aspect of the present invention, there is provided apparatus for thermally insulating a data logging device configured to log data during a heat treatment and oil quench process, comprising: a first container configured to house the data logging device whilst connected to at least one external thermocouple, the first container being sealed in use to prevent ingress of oil when oil quenching; and a second container which is configured to house the first container and which is unsealed in use to permit egress of air when heat treating, the second container comprising at least one disposable insulation member defining a chamber for receiving the first container, the at least one disposable insulation member being substantially non-absorbent to oil.

The second (hereinafter "outer") container helps to keep the temperature within the first (hereinafter "inner") container relatively low during the thermal treatment. Being air permeable, the outer container is not subject to problems caused by trapped air expanding during thermal treatment. During the quenching operation, the inner container prevents the data logging device from coming into contact with oil when oil quenching. However, the at least one disposable insulation member is sacrificed when oil quenching because it becomes contaminated following ingress of oil and will need to be replaced before the apparatus is re- used. Due to the fact that the at least one absorbent member is substantially non-absorbent to oil, there is minimal oil retention in the outer container, meaning the risk of fire is reduced. The at least one disposable insulation member may have a microporous or nanoporous structure.

The inner container may have a body comprising a first part, a second part, a high temperature gasket and a clamp for clamping the high temperature gasket between the first and second parts when sealed together. The first and second parts may be metal, and one part may be configured as an open-topped box and the other as a lid for the open-topped box. The high temperature gasket may have a flat profile and may be configured to operate at temperatures in excess of 300°C. Releasing the clamp allows the first and second parts to be separated for access to the data logging device when housed in the inner container. One part of the body may comprise at least one compression fitting (e.g. a metal compression fitting) for receiving at least one external thermocouple connected to the data logging device when housed in the inner container. The inner container may be lined with a thermal insulator (e.g. an insulator with a microporous or nanoporous structure). The thermal insulator lining may include thermal break openings therein. The thermal insulator may itself be lined with a thermal conductor (e.g. a metal sheet such as stainless steel sheet). The inner container may also comprise a phase change heat sink. The phase change heat sink may be configured to be thermally coupled to the data logging device when housed in the inner container. For example, the phase change heat sink and data logging device when housed in the inner container may be mounted on the thermal conductor lining the thermal insulator.

The apparatus may be configured such that in use a data logging device housed in the inner container may operate at a temperature below 80°C even when the apparatus is exposed to a temperature in excess of 850°C for at least 30 minutes, and perhaps even for 2 hours or more, and possibly up to about 5 hours. During such high temperature exposure, the apparatus may be configured to maintain a temperature of an interior surface of one part of the body of the inner container below about 300°C which may correspond to a flash point of the oil quenchant.

The outer container may comprise two parts, at least one of which may comprise an open support frame and a removable sheet metal insert. The open support frame may be configured to resist distortion when heated and quenched. The removable sheet metal insert may be readily replaceable. The removable sheet metal insert may be a single component or may comprise multiple components configured or arranged to form a box-like structure. One part of the outer container may define an open-topped box and the other part may be configured as a lid for the open-topped box. The lid may be secured to the open-top box when the inner container is housed in the outer container.

In accordance with a second aspect of the invention, there is provided a method of monitoring temperature of an object throughout a heat treatment and oil quenching process, comprising thermally insulating a data logging device with apparatus according to the first aspect of the invention, with at least one external thermocouple connected to the thermally insulated data logging device; coupling the at least one thermocouple to the object to be monitored; heat treating and then oil quenching the object together with the thermally insulated data logging device; and removing the first container from the second container.

During the oil quench, oil will penetrate the second container and contaminate the at least one disposable insulation member thereof. The method may further comprise replacing the contaminated at least one disposable insulation member before re-using the apparatus. Heat treating may comprise exposing the object together with the thermally insulated data logging device to a temperature in excess of 850°C for at least 30 minutes, and perhaps even for 2 hours or more, and possibly up to about 5 hours. When heat treating, the temperature at which the data logging device operates within the first container may be configured to remain below 80°C. Oil quenching may comprise immersing the object together with the thermally insulated data logging device in oil at a temperature below 250°C, such as about 70°C.

An embodiment of the invention will now be described by way of example, with reference to the following drawings, in which:

Figure 1 is a cutaway perspective view of apparatus for thermally insulating a data logging device configured to log data during a heat treatment and oil quench process; and Figure 2 is a cutaway view showing detail of the apparatus shown in Figure 1. Figure 1 shows apparatus 10 embodying the present invention which comprises a first ("inner") container 12 and a second ("outer") container 14 configured to house the first container 12. The first container 12 is configured to house a data logging device 20 whilst connected to at least one external thermocouple 22. The first container 12 is sealed in use to prevent ingress of oil during an oil quench of a thermal treatment process. The second container 14 is intentionally unsealed to allow egress of air when the apparatus 10 is heated during the thermal treatment process. This means that oil will penetrate the second container 14 during the oil quench of the thermal treatment process. The second container 14 comprises at least one disposable insulation member 30 defining a chamber 32 for accommodating the first container 12. The at least one disposable insulation member 30 is substantially non-absorbent to oil, meaning that oil retention and consequential fire risk will be minimised when the apparatus 10 is opened to access the data logging device 10 after the oil quench of the thermal treatment process. The at least one disposable insulation member 30 preferably has a microporous or nanoporous structure. The second ("outer") container 14 comprises two body parts: a lower part 40 configured as an open-topped box; and an upper part 42 configured as a lid for the lower part 40. Each body part 40, 42 comprises an open support frame 44 and a removable sheet metal insert 46. The open support frame 44 is configured to resist distortion caused by thermal

expansion/contraction during the thermal treatment process, and comprises metal rods or tubes (e.g. stainless steel bars). The removable sheet metal insert 46 is readily replaceable if distorted by thermal expansion/contraction during the thermal treatment process. In one configuration, the or each removable metal sheet insert 46 may be a single component (e.g. formed from a single metal sheet); in another configuration, the or each removable metal sheet insert 46 may be formed from separate components (e.g. five separate components which together form two sides, front, back and base of the open-topped box). The latter

configuration may even help to reduce distortion and improve fitting of the at least one insulation member 30 into the second container 14 which has been previously used and the side panels subjected to distortion due to thermal cycling. The lower and upper parts 40, 42 define an enclosure for the at least one disposable insulation member 30 arranged around the inner periphery of the second container 14.

The first ("inner") container 12 comprises two body parts: a rigid casing 50 with an opening 52; and a face plate 54 for covering the opening 52. The first container also comprises a high temperature gasket 56 which in use is disposed around the opening 52, and clamping bolts 58 for trapping the high temperature gasket 56 between the plate 54 and the rigid casing 50 to effect an air tight seal. Compression glands 60 are provided in the face plate 54 for the at least one external thermocouple 22 to pass through the first container 12 when connected to the data logging device 20 whilst maintaining the air tight seal.

The rigid casing 50 is lined interiorly with a thermal insulator 62 (e.g. blocks of microporous or nanoporous insulation) and includes thermal break openings 64. The thermal insulator lining 62 is itself lined interiorly with a metal liner 66 (e.g. stainless steel sheet) and defines a chamber 68 for housing the data logging device 20. The chamber 68 also houses a phase change heat sink 70. The phase change heat sink 70 is thermally coupled to the data logging device 20 when housed in the chamber 68 via the metal liner 66.

The data logging device 20 is thermally insulated with the apparatus 10, with at least one external thermocouple 22 connected to the thermally insulated data logging device 10. Prior to starting a thermal treatment process, the at least one external thermocouple 22 is coupled to an object (not shown) to be thermally treated. The object and the thermally insulated data logging device are together heat treated and then oil quenched as part of the thermal treatment process. During the oil quench, oil penetrates the second ("outer") container 14, but not the first ("inner") container 12. Once the oil quench is completed, the thermally insulated data logging device is recovered, and the first container 12 is removed from the second container 14 following separation of the lower part 40 from the upper part 42. Thereafter, the data logging device 20 is removed from the first container 12 through the opening 52 following separation of the face plate 54 from the rigid casing 50. The at least one disposable insulation member 30 arranged around the inner periphery of the second container 14 will be

contaminated with oil from the oil quench, although due to its minimal absorption of oil there will be little risk of fire from contact with any localised hotspot within the apparatus 10.

Before reusing the apparatus, oil-contaminated insulation member(s) 30 are disposed of and replaced with replacement insulation member(s) arranged around the inner periphery of the second container 14.