GB2467809A

GB2467809A - Flexible lining material for a furnace that measures temperature in the furnace

Info

Publication number: GB2467809A
Application number: GB0910185A
Authority: GB
Inventors: Rudolf Raber
Original assignee: ELMELIN Ltd
Current assignee: ELMELIN Ltd
Priority date: 2008-06-14
Filing date: 2009-06-12
Publication date: 2010-08-18
Also published as: GB0910185D0; GB0810942D0

Abstract

A flexible lining material (10, Figure 1) for a furnace. (e.g. coreless induction furnace 1, Figure 1) includes a laminate structure of two layers of a heat resistant material 14 having thermocouple wires 16 between them. Wires 16 may be housed in a sleeve 22, connected to a meter 56 for measuring temperature, and be moveable (slide) between layers 14 or in the sleeve 22. Layers 14 may be adhered together and to the sleeve 22 and may be made from mica paper, ceramic paper, woven glass cloth, or other supple, electrically insulating material. Lining material (10, Figure 1) may provide a slip plane layer for an induction furnace (1, Figure 1). A method of lining an induction furnace (1, Figure 1) is also provided, including a manufacturing process of the lining material (10, Figure 1). A method of installing a thermocouple in a high temperature environment is additionally provided.

Description

Furnace Lining

BACKGROUND

a. Field of the Invention

This invention relates to a lining material and method of lining an induction furnace.

b. Related Art Electrically powered induction furnaces and coreless induction furnaces in particular are widely used in foundries to provide the molten metal used to make castings.

Coreless induction furnaces typically comprise a refractory crucible inside a water-cooled induction coil. The inner face of the induction coil is usually covered by a thin layer of refractory plaster which is called the coil grout. To form the crucible, a former is placed temporarily inside the coil. Refractory sand is then rammed into the space between the coil grout and a cylindrical former and compacted to form the crucible.

It is known to provide a layer between the coil grout and the crucible to provide a slip plane between these surfaces so that movement can take place between these surfaces during the heating and cooling of the furnace, and to assist in the removal of the crucible at the end of its life. Generally this slip plane layer is : **** formed from mica or laminates of mica and other high temperature materials. S...

The interposed layer needs to be able to withstand the maximum temperatures S...

likely to be encountered in that area of a particular furnace, which could be as high . : as 550CC -950°C, as well as remaining largely unaffected by the induction field.

For optimum performance of the furnace it is desirable to measure the operating temperature at various locations. In particular, there is a need to monitor the temperature at the back of the crucible, because, amongst other things, an excessive rise in this temperature can give timely warning that the crucible is wearing thin and needs to be replaced.

SUMMARY OF THE INVENTION

Aspects of the invention are specified in the independent claims. Preferred features are specified in the dependent claims.

The invention provides both a lining material for the furnace and a built-in means for measuring the temperature in the furnace. The lining material comprises a laminate of two heat-resistant and electrically insulating layers and thermocouple wires disposed between the layers.

The lining material can be applied to a furnace wall in the form of overlapping strips, only one of which need comprise the laminate structure with the thermocouple wires. Of course, more than one strip may include thermocouple wires, and the thermocouples may be distributed around the furnace wall to allow temperature measurements at different locations.

The flexible lining material of the invention is designed to be a consumable product that can be replaced every time that a new crucible is installed into the furnace.

This is possible because the cost of the materials of the lining material of the : **** present invention is only slightly more expensive than standard slip plane materials, which do not contain a thermocouple wire, and which would otherwise be used as a consumable. S...

*.. :30 *..: In a preferred embodiment, the thermocouple wires are free to be pulled through the laminate structure. This enables a user to form a thermocouple junction at an end of the thermocouple wires, and then pull the thermocouple junction through to a desired location for measuring the furnace temperature. The other, free end of the wires can then be stripped and connected to a suitable measuring instrument.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an induction furnace, partly in section; Figure 2 is a cross-section through the furnace wall, on a larger scale; Figure 3 shows an arrangement of thermocouple wire in a sleeve for use in lining a furnace in accordance with an embodiment of the invention; Figure 4 illustrates a method of inserting thermocouple wires in a sleeve for use in manufacturing a lining for a furnace in accordance with an embodiment of the invention; Figure 5 illustrates a method of inserting thermocouple wires in a sleeve for use in manufacturing a lining for a furnace in accordance with another embodiment of the invention; *.*.

Figure 6 illustrates the application of layers of a lining to a furnace wall; and * ** * S S ***.

Figure 7 shows stages in making the slip lining of Figure 6.

*..: 30 S. S S * S

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DETAILED DESCRIPTION

Figure 1 shows a typical coreless induction furnace 1 comprising an outer jacket 2, with a water-cooled induction coil 4 within the jacket. The coil 4 is generally made of copper. On the inside of the coil 4, there is a thin layer of refractory plaster, usually 8-10 mm thick, called the coil grout 6 which forms a smooth surface on the inside of the furnace 1, as well as protecting the coil 4.

To form a crucible 8, a cylindrical former (not shown) typically of a diameter 200- 250 mm smaller than the coil 4 is temporarily placed inside the furnace 1 and refractory sand is rammed into the space between the coil grout 6 and the former.

The refractory sand is then compacted in a conventional manner.

A lining material 10 is provided between the coil grout 6 and the crucible 8.

Typically, the lining material 10 provides a number of functions including: * a slip plane layer, * electrical insulation, * a barrier to vapour penetration, * an aid to pushing out of the crucible from the furnace by allowing the crucible wall to slip against the furnace wall, * a temporary barrier against metal penetration, and * some heat insulation.

:. The lining material 10 of the present invention provides an improvement over ::.5 previous lining materials as it incorporates thermocouple wires 12 within its structure permitting temperature readings to be taken at desired locations around a furnace 1 lined with the material 10.

The lining material 10, illustrated in Figure 2, comprises a laminate of two heat 3*O resistant, insulating layers 14. These layersl4 may be made of any suitable heat- * resistant material such as mica, high temperature insulating paper, glassfibre web or mat (woven or non-woven), glass tissue, woven glass cloth, ceramic paper, insulating paper, high temperature cloth or any other suitable material. The two insulating layers 14 may be made of the same material or may be made from different materials. Importantly, the lining material 10 is flexible, such that it is able to be manipulated by hand, can be supplied in roll form and can be quickly and easily installed in a furnace 1.

Thermocouple wire 12 is located between the two insulating layers 14. The thermocouple wire 12 is sandwiched between the insulating layers 14 in such a way that the wire 12 is free to slide in an approximately longitudinal direction with respect to the axis of the wire 12.

Typically, the thermocouple wire 12 comprises a pair of wires 16 of dissimilar material. Each of these wires 16 are coated or surrounded by an insulating layer 18. The two insulated wires are then surrounded by and held within a common sheath 20. The insulated wires in Figure 3 have been shown spaced apart for clarity of illustration; however it will be understood that these may be tightly held within the sheath 20 in a manner well known in the art per Se. The thermocouple wires may be a type K Nc/Na material, or any other suitable materials may be employed; for example, Type J, PT100, thermistors or the like. The wires 16 may be of any suitable thickness such that they do not generate sufficient eddy currents to cause them to overheat. The wires may have a gauge of between 0.2 mm and 0.315 mm, or alternatively, the wires may have a larger cross-section, for example, 3mm mineral insu!ated stainless steel sensors are commonly used.

However, thinner gauge wire is lower cost and easier to install between the insulation layers. In addition, the wires may be single strand or multi-strand *..

: *. Preferably, the lining material 10 comprising a thermocouple wire 12 is formed in

SASS

continuous sheets and wound into rolls for ease of supply, storage and use. In this way, a continuous length of thermocouple wire 12 extends the full length of the *55* sheet of lining material 10. To enable the flexible lining material 10 to be evenly : rolled onto a reel, it is preferred that the thermocouple wire 12 traverses the width of the heat resistant material 14, as exemplified in Figures 4a and 4b. As the lining material 10 is being formed, the thermocouple wire 12 is laid between the insulating layers 14 so that it is disposed between one top corner and an opposite bottom corner of the lining material 10. In this way, when the lining material 10 is wound into a roll, the thermocouple wire 12 located in adjacent layers will not lie on top of each other.

In a preferred embodiment, the thermocouple wire 12 is housed within a sleeve 22 fixed between the insulating layers 14. In one embodiment, shown in Figure 3, the sleeve 22 is sandwiched between a pair of heat resistant layers 14, in this example formed from mica. The layers 14 are laminated together using a suitable adhesive and pressure, securing the sleeve 22 in place between the layers 14. No adhesive is present within the sleeve 22 so that the thermocouple wire 12 remains free to be pulled through the sleeve 22 within the laminate structure.

One method of manufacturing the sleeve 22 within which the thermocouple wire 12 is housed is illustrated in Figure 4. A web 24 of heat-sealable material, for example PVC or polyethylene, is provided with a longitudinal fold 26 so as to divide the web 24 into a first half 28 and a second half 30. In this example the fold 26 is central, but could alternatively be provided off-centre. The web 24 is initially folded diagonally along a second fold line 32 and then troughed or folded inwardly along this same fold line 32 to divert the web 24 travel through a nonzero angle, in a manner which will be familiar to practitioners of origami. In this example the angle is 90 but other angles could be used. *...

As the web 24 is advanced in a longitudinal direction 34, the central fold line 32 and the direction of travel are diverted through 90°. The thermocouple wire 12 is : *. fed through the troughed web 24 along the diverted central fold line. The sleeve 22 is formed by heat sealing one side of the web material 24 to the other along a line 36 parallel to the diverted central fold line 26. The sleeved thermocouple wire 12 is *S* then cut free of the remainder of the web 24 along a cutting line 38 and is used in : the manufacture of this laminated lining material 10. The remaining cut part of the web 24 is discarded.

Another method to manufacture a sleeved thermocouple wire 12 is to place the wires 16 (in this example contained in sheath 20) centrally between two strips of sleeving material 40a, 40b, for example 10-20 mm wide, and seal both edges 42 by crimping or heat fusing them together, as illustrated in Figure 5.

Alternatively, the sleeve may be manufactured in set lengths, for example 100 m lengths. In this case, in order to insert the thermocouple wire within the sleeve, the sleeve is concertinaed or bunched-up and placed over and around a thin-walled hollow tube. The thermocouple wire is then pushed along the bore of the tube, and drawn through the tube as the sleeve is pulled off the end, thereby inserting the thermocouple wire along the length of the sleeve.

The thermocouple wire 12 may alternatively be shrouded in a bag. In another embodiment, the wire 12 may be fed into a tube, for example a length of silicone tubing. The tubing may be slit lengthways by a blade, with the wire 12 being fed in behind the blade.

In alternative embodiments, the lining material 10 may be constructed in such a way as to allow the thermocouple wire 12 to remain free to be pulled through the lining material 10 by techniques such as adhesive suppression (use of powder or tape on the wires to stop them sticking), or adhesive obviation (removal of the adhesive from the proximity of the thermocoup!e wire). In this case, the lining material 10 incorporating the thermocouple wire 12 may be formed such that the ::: two heat resistant layersl4 are joined together, preferably by adhesive, in regions at a distance from the thermocouple wire 12, but are riot stuck together close to : * the thermocouple wire 12, thereby forming a continuous pocket or passage * between the insulating layers 14 in which the thermocouple wire 12 is located, and within which the thermocouple wire 12 is free to slide. S...

*..: One advantage of supplying a thermocouple wire 12 pre-inserted within the lining material 10 as described, is that the thermocouple wire 12 may be easily installed and located within the furnace 1. Because the thermocouple wires 12 are typically low-cost, the lining material 10 is only slightly more expensive than the conventional slip plane material which would otherwise be used and so can also be used as a consumable, with a new lining and therefore new thermocouples installed each time a new crucible 8 is formed. Preferab'y the construction of the lining material 10 incorporating the thermocouple wire 12 is such that the material is flexible so that the lining material 10 is able to be manipulated by hand and will substantially conform to the shape of the furnace walls when used to line an induction furnace 1.

A method of lining a furnace 1 using a lining material 10 in accordance with the invention will now be described with particular reference to Figures 6 and 7. The lining material 10 is provided in strips 44, which may be cut from a longer roll of material (not shown). The lining material 10 is located on the inner surface of the coil grout 6, and is typically fixed in place using suitable means such as adhesive.

Each strip 44 of lining material 10 is typically laid vertically up the inner surface of the furnace wall in contact with the coil grout 6. As each subsequent strip 44 is laid, it is positioned so that it overlaps the previous adjacent strip 44. Because the lining material 10 is relatively thin, typically less than 5mm thick, the strips 44 may be cut to length using a knife or scissors. As the strips 44 are cut, the thermocouple wire 12 within the lining material 10 is also cut, leaving a length of thermocouple wire 12 extending between the top 46 and bottom 48 edges of the strip 44. I...

Alternatively, and depending on specific requirements, a furnace 1 may be lined I...

*** with a traditional slip plane material for the majority of its circumference, with only : *..* one or two sections lined with lining material 10 incorporating a thermocouple 12.

In this example, each strip 44 except for strip 45 is of conventional slip material construction. Strip 45 is formed in accordance with an embodiment of the invention **** :30 and has thermocouple wires 16 held in a common sheath 20 and contained in a *:*. sleeve 22 which is sandwiched between the heat resistant layers 14. If temperature measurements are desired in other locations within the furnace 1, other strips 44 may also be provided with thermocouple wires 12 at appropriate locations in accordance with the invention. The laminate 10 may be provided with a self-adhesive backing (not shown) to aid its fixing at a desired point in a furnace 1.

Figure 7 illustrates the method used to form a thermocouple junction 50 at a desired location in the lining material 10. A user firstly frees a few cm, typically about 15 mm, of the wire at the bottom 48 of the strip 44 at point A. This may be done by peeling or scraping one of the insulating layers 14 away from the thermocouple wire 12. Alternatively, a first, lower end 52 of the thermocouple wire 12 could be pulled through the lining material 10 so that a short length of the wire extends from a first, lower edge 48 of the lining material 10. The user then removes the sheath 20 and the insulation 18 from an end portion of the wires 16, twists the exposed wires 16 together and forms a thermocouple junction 50 by any suitable method and as is well known in the art. The thermocouple junction 50 may be formed by melting or fusing the tips using a high temperature flame, or they may be joined by brazing or soldering. The thermocouple junction may also be formed by simply twisting the wires together.

In order to position the thermocouple junction 50 in the desired location corresponding to a location where temperature will be measured in the furnace 1, for example a point halfway up the side of the furnace as illustrated in Figure 6, the thermocouple wire 12 is drawn back through the sleeve 22 in the lining material 10. As described hereinbefore, the thermocouple wire 12 is free to be pulled 2'5 through the laminate 10 because it is secured in such a way that it is free to slide " between the insulating layers 14. Sliding the thermocouple wire 12 back through : **, the lining material 10 in this way causes the second, upper end 54 of the wire to b.I protrude from the second, top edge 46 of the lining material 10. This second end 54 of the thermocouple wire 12 can be connected to a meter 56, optionally via a *.*S :30 suitable electrical connector (not shown), in such a way as is well known in the art.

I * S I.

The lining material 10 of the present invention therefore provides a means of measuring the temperature at the back of the crucible through the inclusion of pre-inserted thermocouple wires 12 within the structure of the lining material 10. In this way, thermocouples 12 may be quickly and easily installed in different locations around the circumference of the furnace 1, giving a user the flexibility as to how many thermocouples 12 are installed and where they are placed.

Additionally, as the lining 10 is not permanently installed in the furnace 1, maintenance costs are reduced compared to thermocouples that are permanently incorporated in the structure of a furnace. Furthermore, the lining material 10 can be applied to any size or shape of furnace, and the lining does not have to be io specially machined or shaped to fit in a particular furnace.

Although the invention has for illustration been described with reference to the installation of thermocouple wires in an induction furnace, it will be understood that the invention is not limited to this embodiment. The invention provides a way of easily installing a thermocouple in any high temperature environment, for example engines or boilers. * *** * . * ** * * *** * * * ** * S * I.e. **** S. I

I I S * S.

Claims

Claims 1. A flexible lining material for a furnace, the lining material comprising a laminate structure of two layers of a heat resistant material having thermocouple wires disposed between them.
2. A flexible lining material as claimed in Claim 1, wherein the thermocouple wires are sUdable between the layers of heat resistant material.
3. A flexible lining material as claimed in Claim 1, wherein the thermocouple wires are housed in a sleeve between the layers and wherein the thermocouple wires are slidable within the sleeve.
4. A flexible lining material as claimed in any of claims 1 to 3, wherein the heat resistant material is selected from the group comprising mica paper, glass tissue, woven glass cloth, ceramic paper, insulating paper, high temperature cloth.
5. A flexible lining material as claimed in any preceding claim, wherein the lining material further comprises an adhesive layer.
6. A method of lining an induction furnace, the furnace having a crucible and a coil grout layer, the method comprising the step of placing a flexible lining material between the coil grout and the crucible, wherein the hr. ing material comprises a : * laminate structure of two heat-resistant layers and thermocouple wires disposed between the layers. * .** * I **.I

: ***,
7. A method as claimed in Claim 6, wherein the thermocouple wires are ***.formed into a thermocouple junction after the lining material has been formed and prior to placing the lining material in the furnace. *
S. 11:30 I.

: 8. A method as claimed in Claim 7, wherein the method comprises the steps of: -cutting a strip of lining material to a desired length, the thermocouple wires extending the full length of the strip of lining material between a first and a second end of the strip of lining material; -forming a thermocouple junction at a first end of the thermocouple wires; and -sliding the thermocouple wires between the heat resistant layers so as to locate the thermocouple junction between the first and second ends of the lining material.
9. A method as claimed in Claim 8, wherein after the thermocouple junction has been located between the first and second ends of the lining material, the second end of the thermocouple wires is connected to a suitable meter for measuring temperature.
10. A method as claimed in any of claims 6 to 9, wherein the thermocouple wires are housed within a sleeve within the lining material.
11. A method as claimed in Claim 10, wherein the thermocouple wires are free to move within the sleeve prior to being heated in the furnace.
12. A method according to claim 10, wherein the wires are placed in the sleeve prior to disposing the sleeve between the heat resistant layers by a process comprising: -providing a moving web of a heat-sealable material having a longitudinal fold therein; -troughing the web inwardly so as to divert the direction of movement of the : .. web through a nonzero angle; -feeding the thermocouple wires into the troughed portion of the web adjacent to the longitudinal fold as the web is advanced; : 30 -forming a heat seal between portions of the web either side of and in a line : substantially parallel to the longitudinal fold; and -slitting the web to leave a sleeve of heat-sealable material housing the -13-wires along its length.
13. A method according to claim 12, wherein the nonzero angle is substantially 900.
14. A method according to claim 10, wherein the wires are formed in the sleeve prior to disposing the sleeve between the layers of the laminate by a process comprising: locating the thermocouple wires between two strips of sleeving material and sealing opposite edges of the sleeving material by crimping or heat fusing them together.
15. A method of installing a thermocouple in a high temperature environment, the method comprising locating a heat-resistant material in said environment; at least some of the material comprising a laminate structure of two heat-resistant layers and thermocouple wires disposed between the layers.
16. A flexible lining material for a furnace substantially as herein described with reference to the drawings.
17. A method of lining an induction furnace substantially as herein described with reference to the drawings. * * * * * **** * S **S. * ** * S S S... S'S.SS S * S S S *S