BACKGROUND OF THE INVENTION Heated baths such as heated chemical baths are used for a variety of different purposes. One context in which such baths are used involves treating the surface of an object to which another part is to be attached. For example, seals such as oil seals are oftentimes comprised of a metal part and a rubber part that is molded or otherwise attached to the metal part. To ensure that the rubber part is securely attached to the metal part, it is oftentimes desirable to roughen the surface of the metal part prior to molding or attaching the rubber part.

One way of roughening the surface of the metal part involves placing the metal part in a zinc phosphate bath. The zinc phosphate reacts with the metal and dissolves some of the metal. At the same time, zinc phosphate crystals grow or form on the surface of the metal part, thus producing a somewhat roughened surface on the metal part that facilitates attachment of the rubber part.

Zinc phosphate baths are also used in a variety of other contexts. For example, prior to painting an automobile body, the metal body is placed in a zinc phosphate bath to roughen the surface of the metal body so that the paint will better attach to the metal body.

Chemical baths such as those described are typically heated. To heat the <BR> <BR> chemical bath, one or more heating elements (e. g. , heating coils) are oftentimes located in the chemical bath. In the case of metal parts such as those described above, it has been found that the metal that is dissolved by the chemical bath tends to be attracted to the heating element, thus causing sludge to form on the heating element. This sludge can build up relatively quickly and form a coating on the heating element that insulates the heating element and undesirably diminishes the ability of the heating element to heat the chemical bath. Thus, it is usually necessary to remove the heating element from the chemical bath and employ relatively expensive chemicals or mechanical mechanisms to remove this coating from the heating element.

Attempts have been made in the past to address this difficulty by applying a coating of Teflon* or other polymer to the heating element, or by polishing the heating element to impart a smooth surface to the heating element. However, these attempts have not met with much success. In the case of Teflon and polymer coatings, when the coated heating element is placed in the bath during use, water migrates through the coating and turns to steam. This creates a blister that tends to lift the coating off the heating element. This blistering of the coating requires repetitive re-coating of the heating element, which is not very cost-effective. When the heating element is polished, the polished surface tends to degrade over time, thus requiring repetitive re-polishing of the heating element.

Once again, this is not a very cost effective solution.

In light of the foregoing, a need exists for a way of preventing material in the chemical bath from collecting on the heating element while also maintaining effective heat transfer over an extended period.

SUMMARY OF THE INVENTION According to one aspect of the invention, a method of protecting a heating element in a chemical bath involves placing a heating element in an interior of a sleeve so that the heating element is surrounded by the sleeve, and immersing the heating element in a chemical bath so that the sleeve and the heating element are located in the chemical bath, with the sleeve preventing the chemical bath from coming into direct contact with the heating element. The heating element can be placed in the interior of the sleeve either before immersing the sleeve in the chemical bath or after immersing the sleeve in the chemical bath.

Another aspect of the invention involves the combination of an immersion heating element for heating a chemical bath and a protective sleeve for protecting the heating element. The heating element is loosely received within the interior of the sleeve so that the heating element is surrounded by the sleeve and is prevented from directly contacting a chemical bath when the heating element within the sleeve is immersed into the chemical bath.

Another aspect of the invention involves a device for protectively covering a heating element used to heat a liquid bath. The device includes a sleeve made of Teflons material, with the sleeve having an interior for receiving a heating element, a periphery and an opening along one portion of the periphery of the sleeve for permitting a heating element to be placed in the sleeve.

BRIEF DESCRIPTION OF THE DRAWING FIGURES Additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawing figures in which like elements are designated by like reference numerals and wherein: FIG. 1 is a front view of the sleeve that is used to cover and protect a heating element in a chemical bath according to one embodiment of the present invention;

FIG. 2A is a front view of a sleeve that is used to cover and protect a heating element in a chemical bath according to another embodiment of the present invention; FIG. 2B is a perspective view of a portion of the sleeve shown in FIG. 2A illustrating the way in which the sides of the sleeve are secured together; FIG. 3 is a front view of a sleeve covering a heating element in a chemical bath according to still another embodiment of the present invention; Figs. 4A and 4B are cross-sectional views of a portion of the sleeve according to the various embodiments of the present invention illustrated as being positioned in the chemical bath.

DETAILED DESCRIPTION OF THE INVENTION Referring initially to FIG. 1, a chemical bath 16 such as a zinc phosphate bath is adapted to be heated to the desired temperature by way of a heating element 14 that is immersed in the bath 16. To protect the heating element 14 from sludge build-up, the present invention involves the use of a protective cover 10. The heating element 14 is positioned in the protective cover 10, which in the illustrated embodiment of the present invention is in the form of a sleeve or bag 12. The heating element 14 could be a hot water heating element comprised of interconnected pipes 28 or other types of known heating elements used for heating a liquid bath. The size and configuration of the sleeve 12 can be varied depending upon the size and configuration of the heating element 14.

The sleeve 12 has an opening along one portion of its periphery and is closed along the remainder of its periphery. In the illustrated embodiment shown in FIG. 1, the sleeve 12 is generally rectangular in shape and is closed along the bottom 37 and two opposite sides 36,36, while being open at the top 18. In this version of the present invention, the open top 18 of the sleeve 12 is positioned above the surface of the bath 16 so that the liquid forming the bath 16 is unable to enter the sleeve 12.

The sleeve 12 can be formed of two generally rectangular sheets of material that are sealed or otherwise secured together along three sides, while being unsealed or unsecured along the fourth side to form the open top 18. In a preferred form of the present invention, the sleeve 12 is made of Teflone fluorocarbon film. In the version of the sleeve shown in FIG. 1, the sleeve 12 is made of heat-sealable Teflons (FEP-fluorinated ethylene propylene). This type of Teflon is particularly advantageous as it allows the sleeve or bag 12 to be fabricated from two generally similarly sized and configured sheets that are heat sealed together along three sides to form the sleeve 12 shown in FIG. 1. As described below, other types of Teflon material can also be used. Nevertheless, the use of heat-sealable Teflon (FEP) is quite desirable, not only from the standpoint of facilitating fabrication of the sleeve, but also from the standpoint of being more flexible than other forms of Teflon@. As a result, the heat-sealable Teflon is able to tolerate bending and kinking to a greater extent than other forms of Teflon@. Further, heat-sealable Teflon (FEP) is more slick than other forms of Teflons because it is extruded, and this provides additional advantages.

As noted above, the sleeve or bag 12 generally surrounds substantially the entire heating element 14 or heating portion of the heating element, with the open top 18 of the sleeve 12 being positioned above the surface 20 of the liquid bath 16 so that the liquid is unable to enter the sleeve 12. As shown in Fig. 4B, with the heating element 14 located in the sleeve 12, and the sleeve 12 and heating element immersed in the liquid bath 16, the pressure 22 of the liquid bath 16 presses the sleeve 12 closely against the heating element 14. Heat is thus transferred through the sleeve 12 to the chemical bath 16 so that efficient heat transfer takes place. In addition, to the extent a small amount of water may migrate through the sleeve 12, such water is able to escape through the open top 18 of the sleeve 12 as vapor.

As mentioned above, heat-sealable Teflons (FEP) is a particularly useful type of Teflons material to employ in fabricating the sleeve 12 of the present invention as it allows the sleeve 12 to be fabricated by simply sealing together two

sheets along at least a portion of their peripheries (e. g. , along three sides in the case of rectangular sheets designed to produce a rectangular-shaped sleeve).

Nevertheless, other materials can be employed. For example, Teflon materials that are not heat-sealable can be employed. One example of such a material is PTFE Teflon@. Several different types of PTFE Teflon's material can be employed, including a bondable version of PTFE Teflon material and a non-bondable version of PTFE Teflon's material.

In the case of the non-bondable version of PTFE Teflon material, two sheets of appropriately sized and configured non-bondable PTFE Teflon material can be employed. To form the sleeve, a suitable mechanism is provided to secure at least a portion of the peripheries of the sheets (e. g. , the bottom and sides of rectangular-shaped sheets) together to form the open top sleeve or bag 12. The securing mechanism can be in the form of a clamping device 30 such as illustrated in FIGS. 2A and 2B.

The clamping device 30 can include plates that engage the outer periphery of the sheets on opposite sides. Thus, as shown in FIGS. 2A and 2B, a pair of plates 34 is positioned along the bottom 18 of the two sheets 24', 24', and a pair of plates 34 is positioned along each of the sides 16 of the sheets 24', 24'. In addition, a plurality of bolts 31 are provided to hold the plates 34 together, with the edges of the two sheets thus being held between the two plates 34. Also, to ensure a liquid-tight seal between the two sheets 24', 24'of PTFE Teflon material, a suitable gasket 33 can be positioned between the two sheets 24', 24' along the bottom 18 and opposite sides 16 of the sheets. Thus, when the bolts 31 <BR> <BR> are appropriately tightened (e. g. , by nuts), the plates 34 will firmly press together the two sheets 24', 24'of non-bondable PTFE Teflon material with the interposed gaskets 33.

The gaskets 33 can be made of a suitable sealing material such as silicone foam rubber. Other materials capable of withstanding the temperature of the liquid bath and the chemicals in the bath can also be employed. Thus, the material

selected should not be susceptible to degradation over an extended period of time from the heat and chemicals associated with the bath.

The plates 34 can be made of plastic while the bolts 31 can be fabricated from stainless steel. Once again, other materials capable of withstanding the heat and chemicals existing in the bath can be employed. Also, although the embodiment shown in FIG. 2A involves bolts 31 passing through the edges of the sheets 24', 24', it is to be understood that the bolts could be positioned outside the edges of the PTFE Teflon sheets 24', 24'.

As mentioned above, it is also possible to employ a bondable version of PTFE Teflon material to form the sleeve or bag 12. The sleeve or bag 12 can be formed by utilizing two sheets of the bondable PTFE Teflone material. The use of bondable PTFE Teflon material provides the advantage that suitable adhesives can be employed. That is, bondable PTFE Teflon material is typically manufactured by etching the surface of the material with hydrofluoric acid.

Adhesives can then adhere to the etched surface of the bondable PTFE Teflon material. In this way, gaskets 33 such as described above can be adhered to the surfaces of the sheets to help facilitate a liquid-tight seal in the resulting sleeve.

With the gaskets adhered to the surfaces of the sheets, the sheets can once again be clamped together using a suitable clamping mechanism such as that described above. The selected adhesive should desirably possess characteristics capable of being used in the environment of the liquid bath (e. g. , possessing appropriate chemical and heat resistant characteristics).

In addition to the various materials described above, it is to be understood that other plastic materials can be employed to form the sleeve 12. Appropriate material should be capable of withstanding the conditions existing in the fluid bath during use.

The sleeve 12 preferably has a slick surface 26 which inhibits material in the chemical bath 16 from attaching to the sleeve 12 itself. The enclosure of the heating element in the sleeve protects the heating element 14. Teflon

fluorocarbon materials such as those discussed above have superior antistick and low frictional properties. Additionally, Teflons fluorocarbon materials are chemically inert and solvent-resistant to virtually all chemicals except molten alkali metals, gaseous fluorine, and certain complex halogenated compounds such as chlorine trifluoride at elevated temperatures and pressures. Other types of materials may also exhibit sufficient antistick and protective properties depending upon the nature of the materials in the chemical bath 16.

The sleeve 12 preferably has a melt point in a temperature range higher than the temperature range of operation for the heating element 14 in the chemical bath 16 so that the sleeve 12 is not melted by the heating element 14. Teflon fluorocarbon films can have a melt point in a temperature range from about 500° F to about 600° F measured according to ASTM D-3418 (DTA). Many chemical baths are operated at much lower temperatures, thus making such films highly useful in this environment. For example, a zinc phosphate bath and heating element could operate at about 190° F to about 200° F. Of course, other baths 16 and heating elements 14 may operate at lower or higher temperature ranges. Also, other films may operate sufficiently if they have a melt point in a temperature range that is higher than a temperature range of operation for a particular heating element 14 in a particular chemical bath 16. The sleeve 12 is preferably useful in connection with heating elements comprised of hot water coils and steam coils, as well as electric heater coils.

Another advantage associated with the use of Teflon fluorocarbon materials for the sleeve 12 is that such materials advantageously possess a relatively high folding endurance so that the sleeve 12 is less likely to tear or break when it is pressed against the heating element 14 under the pressure of the liquid in the bath 16. Teflon fluorocarbon films can have a folding endurance (MIT) in a range from about 10,000 cycles to about 100,000 cycles measured according to ASTM D-2176. Accordingly, Teflons fluorocarbon films can tolerate at least about 10,000 folding cycles, and up to about 100,000 folding cycles, before a

break forms in the film. Other films having relatively lower folding endurance may still operate sufficiently to be used in the context of the present invention.

The use of Teflons fluorocarbon films is further advantageous in that they have a relatively high elongation at break so that the sleeve 12 is more likely to stretch to generally conform to the shape of the heating element 14 without breaking. Teflon fluorocarbon films generally possess an elongation at break of about 300% measured according to ASTM D-882. Accordingly, Teflon fluorocarbon films may stretch around the members or coils 28 of the heating element 14 to closely conform to the shape of the heating element 14, thereby promoting more effective and efficient heat transfer to the bath 16. Of course, other films having relatively lower elongation at break may still operate sufficiently to be used in forming the sleeve of the present invention.

It is also preferable that the sleeve 12 possesses a relatively high coefficient of thermal conductivity so that the heat from the heating element 14 can be efficiently transferred to the bath 16. Teflon fluorocarbon films can have a coefficient of thermal conductivity of about 0.195 W/m*K measured according to the Cenco-Fitch test method. The efficiency of heat transfer is also dependent upon the thickness of the sleeve 12 as well as the temperature of the heating element 14. Other films having a relatively lower coefficient of thermal conductivity may nevertheless be suitable for use in the present invention.

The sleeve 12 also preferably has a relatively low permeability of water vapor so that the amount of water vapor seeping into the sleeve 12 is minimized.

Teflon fluorocarbon films can have a permeability of water vapor of from about 2.0 to 7.0 g/m2*d measured according to ASTM E-96. To the extent water vapor seeps through the sleeve 12, and assuming the sleeve is provided with an opening 18, the water vapor is heated by the heating element 14 and is able to escape through the opening 18 in the sleeve 12. Other films having relatively higher permeability of water vapor may still operate sufficiently in the content of the present invention.

As shown in FIG. 3, the sleeve 12 is adapted to receive the heating element 14 by inserting the heating element 14 from above through an opening that is provided in the sleeve 12. The sleeve 12 is sized such that the heating element 14 is loosely received in the interior of the sleeve. The heating element 14 is positioned so that the heating coils or members 28 forming the heating element are positioned below the top edge of the sleeve 12. As generally shown in FIG. 1, the heating element 14 enclosed within the sleeve 12 is positioned in the liquid bath 16 (e. g. , chemical bath such as a zinc phosphate bath) contained within a tank 15.

The heating element 14 in the sleeve 12 can be positioned in the tank 15 that is filled with the liquid, although it is possible to place the heating element 14 in the sleeve 12 into a tank that is empty or only partially filled, followed by filling of the tank to the desired level. FIG. 3 illustrates supports 40 which can be used to support and suspend the heating element 14 within the tank. Also, the heating element can be positioned in the sleeve, with the heating element and sleeve then being immersed in the bath, or the sleeve can be at least partially placed in the bath followed by insertion of the heating element into the sleeve.

As illustrated in FIG. 4B, when the heating element enclosed within the sleeve 12 is immersed in the liquid bath 16, the liquid pressure 22 of the bath 16 presses the sleeve 12 against the heating element 14. The sleeve is thus sufficiently flexible that the fluid pressure can press the sleeve against the heating element thereby allowing effective heat transfer. In the illustrated embodiments, the heating element 14 has multiple coils 28 that are spaced apart. The liquid pressure 22 of the chemical bath 16 forces the sides 12 of the sleeve into contact and at least partial surrounding relationship with the coils 28, thus causing the sleeve to generally conform to the heating element 14 and the coils 28. This advantageously facilitates an effective and efficient heat transfer from the heating coils 28 to the liquid bath 16. At the same time, because the heating element 14 is surrounded by the sleeve and, in the case of an open-ended sleeve, the open end of the sleeve is positioned above the level of the liquid bath 16, the liquid forming the

bath 16 (e. g. , chemical bath) does not contact the heating element, except possibly for small amounts of liquid that may migrate through the sleeve. Consequently, sludge or other coatings are inhibited from accumulating on the heating element 14. To the extent a small amount of liquid from the bath migrates through the sleeve 12, the water can escape as vapor through the open portion of the sleeve 12.

Although the above described embodiments of the sleeve 12 include an opening along one portion of the periphery of the sleeve 12, the sleeve can be sealed along substantially its entire outer periphery (except where portions of the heating element enter the sleeve 12) so that the heating element is substantially entirely sealed within the sleeve 12. This alternative can reduce heat loss and possibly increase heat transfer to the liquid bath.

FIG. 4A illustrates a further variation on the present invention. Ideally, it is preferable that 100% of the surface of the coils be used to transfer heat to the liquid. As mentioned above, the fluid pressure of the liquid bath advantageously presses the sleeve 12 against the coils 28 of the heating element 14 and thus facilitates achievement of this goal. However, if the spacing of the coils 28 of the heating element 14 is relatively small, the sleeve may not be able to contact 100% of the surface of the coils. Thus, in the variation shown in FIG. 4A, a heat transfer liquid 42 is provided in the sleeve 12. This heat transfer fluid helps facilitate heat transfer from the coils to the liquid bath.

The heat transfer fluid can be water or another known form of heat transfer solution. Also, using a heat transfer liquid, the sleeve 12 can be open along one portion as shown in, for example, FIG. 1. Alternatively, the sleeve 12 can be sealed along substantially its entire outer periphery (except where portions of the heating element enter the sleeve 12) so that the heating element is substantially entirely sealed within the sleeve 12. The heat transfer fluid should be selected based on the maximum temperature to which the coils are heated. For example, assuming the heating element is of the type in which hot water at a temperature of about 260°F flows through the coils, a heat transfer solution having a boiling point

above 260°F could be employed. In this way, approximately 100% of the surface area of the coils and 100% of the surface area of the sleeve would be used to transfer heat.

The thickness of the material forming the sleeve 12 will also have an effect on the efficiency of heat transfer and the durability of the protective cover 10. A thicker sheet material will typically be more durable but might also insulate the heating element 14 somewhat and reduce heat transfer efficiency. A thinner material, on the other hand, is likely to allow for more efficient heat transfer, but may not be quite as durable and resistant to cracking and/or rupture. Many factors may effect the selection of the thickness, including, the physical properties of the material used, the nature of the chemical bath, and the desired duration of use.

For example, a sleeve made of Teflon FEP fluorocarbon film for use in a zinc phosphate bath for an extended period of time, may have a thickness of between about 3 mil and 30 mil, preferably between about 5 mil and 20 mil, and most preferably about 10 mil. Other combinations of chemical baths 16, materials, and desired results may result in the use of thicker or thinner material for the sleeve 12.

Other variations may include sealing the sleeve 12 around its entire periphery, including sealing around the portion of the heating element extending into the sleeve interior, and providing a vent tube or the like through which water vapors can escape. Such a configuration may be advantageous, for example, for use in a bath that is relatively deep, wherein the heating element 14 is to be placed near the bottom of the bath 16. This configuration may also be useful with electric heating elements.

In still other configurations, the sleeve 12 may have more than one opening 18. For example, a sleeve 12 could be cylindrical, having an opening 18 on each side. The sleeve 12 could be placed over a heating element 14 having components that extend out of the bath 16 at two locations. The cylindrical sleeve 12 could fit over and generally enclose the heating element 14 and extend out of the bath 16 at

both locations where components of the heating element 14 extend out of the bath 16, whereby liquid pressure 22 of the chemical bath 16 presses the sleeve 12 against the heating element 14 thereby allowing effective heat transfer while also protectively covering the heating element 14 from the liquid bath 16.

Generally, the aspects and uses of the present invention may extend to various kinds of covers, sleeves, and materials having characteristics suitable for the uses and functions contemplated by the present invention. Additionally, the aspects of the present invention may extend to many different kinds of baths, including chemical baths, that have the materials or characteristics that negatively effect heating elements used therein. Likewise, the aspects of the present invention may extend to various kinds of heating elements including, but not limited to, hot water, steam, and electric immersion heating elements, including heating elements of different shapes and sizes and which are supported and operated in many configurations in a chemical bath.

As mentioned above, the present invention has particular application to zinc phosphate baths. However, the invention could also be used in other types of chemical baths as mentioned above. For example, heaters are used in alkaline cleaners or alkaline stripper tanks that strip off water-borne adhesive. The stripped off water-borne adhesive tends to come out of solution and attach to the heaters, thus forming a hard coating on the heaters that must be cleaned off. Also, the surfactant in the cleaners also tends to attach to the heaters and form a hard coating. Using the sleeve of the present invention can prevent these difficulties.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments described. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the invention be embraced thereby.