Cooling Apparatus

Abstract

Cooling apparatus for removing heat from metal removal operations or shaft bearings by the use of a jet of liquid coolant and an electrostatic field set up in the coolant, which includes a high voltage DC or AC supply connected to a probe associated with a liquid coolant nozzle.

Description

This invention relates in general to cooling apparatus, and more particularly to means for removing heat from workpieces and/or tools engaged in metal removal operations, or shaft bearings under load, and still more particularly to a combination liquid coolant nozzle and high voltage DC or AC probe for effecting cooling of a workpiece or mass.

Heretofore, it has been usual to cool workpieces being machined and other masses by use of jets or streams of a liquid coolant which absorbs the heat and carries it away. It has also been known to remove heat from a mass of material by the application of a high voltage, low amperage electrostatic field thereto, such as disclosed in U.S. Pat. No. 3,224,497. It is also known that a liquid coolant is sometimes employed for purposes of lubrication between a workpiece and a cutting tool. Similarly, shaft bearings under load have been lubricated and cooled by immersion in a liquid lubricant.

The present invention involves the combining of liquid cooling and electrostatic cooling in order to answer the cooling need in production machining where metal is removed on a production basis and in shaft bearings or the like under a high heat load.

It is known that metal removal rates, where only liquid cooling is employed, can be limited by the incipient local melting of the workpiece. Where such incipient local melting is present, it follows that "film boiling" of the liquid coolant is also present, this occurring where the heat flux at a solid surface in contact with the liquid coolant is at such a temperature level that the liquid coolant flashes into a continuous film of vapor. This vapor film acts as an insulating barrier to the solid surface, thereby driving the surface temperature up and possibly causing catastrophic failure, severe damage, or inferior surface finish to the part being machined.

By setting up an electrostatic field in the liquid coolant, according to the present invention, the film is destroyed thereby dramatically increasing the heat transfer coefficient between the workpiece and the liquid coolant by a factor of 5-20. Accordingly, the surface temperature of the workpiece is substantially reduced. All of this allows an increase in the metal removal rate, thereby decreasing production costs, and also allows obtaining a better microfinish.

While "film boiling" may not occur where friction is created between working surfaces, such as in a bearing structure, the combination liquid coolant and electrostatic field, according to the present invention, may be employed for cooling of the mass, in this case the bearing structure, which would obviously reduce the chance of failure, and enhance the working life or allow the bearing to be continuously operated at conditions heretofore too severe for extended life. It should be appreciated the liquid coolant here would be of a type that would also lubricate.

It is therefore an object of the present invention to provide a cooling apparatus especially useful for removing heat from parts involved in a machining operation and other masses experiencing a heat problem.

Another object of this invention is in the provision of a cooling apparatus including a liquid coolant stream or jet, and means for setting up an electrostatic field in the stream or jet.

Still another object of this invention resides in the provision of a cooling apparatus capable of destroying the film boiling effect of a coolant, thereby dramatically increasing the heat transfer coefficient.

A further object of the present invention is to provide a combination liquid coolant and electrostatic field arrangement for materially increasing the heat transfer coefficient of a part being machined so that the metal removal rate can be materially increased thereby reducing production costs, and so that a smoother finish can be produced.

Other objects, features and advantages of the invention will be apparent from the following detailed disclosure, taken in conjunction with the accompanying sheet of drawing, wherein like reference numerals refer to like parts, in which:

FIG. 1 is an elevational view, partly diagrammatic, of a grinding machine with the cooling apparatus of the invention applied thereto to illustrate its application in the machining of metal;

FIG. 2 is a diagrammatic, top plan view of the arrangement in FIG. 1 with some parts omitted;

FIG. 3 is an enlarged cross sectional view taken substantially along line 3--3 of FIG. 1; and

FIG. 4 is a diagrammatic, elevational view illustrating another application of the cooling apparatus according to the invention, and in particular for cooling a shaft bearing.

The cooling apparatus of the invention includes generally a nozzle or the like for discharging a stream or jet of liquid coolant, and a probe or conductor associated with the nozzle to impart an electrostatic field of high intensity in the coolant in order to materially increase the rate of heat transfer from the surface to be cooled. The cooling apparatus is applicable for removing heat from any mass, and especially for removing heat from a metal machining operation in order to permit the increase of metal removal rates to thereby lower production costs. For example, the cooling apparatus may be applied to a grinding machine set up to remove metal by grinding from a workpiece, such as a bearing part. It should be appreciated that the cooling apparatus can likewise be applied in any production machining operation where metal removal at a high rate is required.

An example of applying the cooling apparatus to other than a metal removal operation would include the operation of a shaft bearing or the drawing of metal through drawing dies. Thus, wherever cooling has heretofore been required in the form of a liquid coolant, the present invention is applicable to enhance the cooling rate, and the coolant may have lubricating properties if desired.

The problem encountered in the machining of metal in the presence of a liquid coolant which limits the metal removal rate, such as in a grinding operation, can result in damage to the workpiece caused by incipient local melting. The incipient local melting occurs during "film boiling" of the coolant which constitutes the generation of a film of vapor at the workpiece surface acting as an insulating barrier which limits the rate of heat transfer and the maximum amount of heat that can be carried away by the coolant. Thus, the vapor barrier will cause the temperature of the workpiece surface to rise beyond that which it can tolerate and cause failure or damage to the workpiece. Application of an electrostatic field in the liquid coolant, in accordance with the present invention, destroys the vapor barrier thereby allowing a material increase in the rate of heat transfer and the amount of heat that can be removed by the liquid coolant, and also greatly improves the finish attainable.

The invention as applied to a machining operation, is illustrated in FIGS. 1 and 2, wherein a workpiece 10 is supported by jaws 11 of a chuck 12 adjacent a grinding wheel 13 carried on a shaft 14 of a motor 15. The chuck 12 may be rotatable or nonrotatable as the situation requires, and additionally movable toward and away from the grinding wheel 13. The details of the grinding machine are not a part of the invention and it may take any suitable form. Normally, wherein the workpiece 10 may be a hardened bearing part, or a part where it is necessary to apply a liquid coolant in the areas of metal removal, and the rate of metal removal is limited by the "film boiling" phenomena.

According to the present invention, the liquid coolant is applied by means of a nozzle or pipe 16 for directing the liquid coolant at the point of engagement between the grinding wheel and the workpiece. An electrostatic field is generated in the liquid coolant by means of a probe or conductor 17 that may be mounted within the nozzle, as illustrated, or therwise mounted adjacent thereto, and connected to a high voltage DC or AC supply 18. Where the liquid coolant is an electrolyte, as most coolants are, the probe or conductor 17 would be completely electrically insulated in order to prevent current movement through the electrolyte which would create an electrical short, as shown in FIG. 3 where the conductor 17 includes a wire 17a covered by insulation 17b. Where the coolant may be a dielectric, it may be necessary to have the probe or conductor bare in order to produce ions for establishing the electrostatic field. However, it should be appreciated that ions are already present in an electrolyte, and therefore none need be produced where the coolant is an electrolyte. In order to set up the electrostatic field, it is also necessary to provide a path for same by way of either connecting the workpiece and/or grinding wheel to ground potential such as indicated by the ground line 19.

In FIG. 4, the invention is illustrated in connection with the cooling of a mass where the "film boiling" phenomena is not experienced. A shaft 25 having a bearing 26 is illustrated in connection with the liquid coolant nozzle 16, the electrical probe or conductor 17 is connected to the high voltage DC or AC supply 18 wherein the coolant of a lubricating type is directed toward the bearing, and an electrostatic field is generated in the coolant. In this arrangement, a ground wire 27 is illustrated for connecting the shaft and bearing to the ground potential. Again, the electrostatic field will serve to bombard the surfaces of the bearing with ions to enhance the rate of heat transfer. With respect to this embodiment, and the illustration of FIGS. 1 and 2, a voltage level of between 10 and 60 KV would be applied, the level being slightly less than that which would cause arcing.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention, but it is understood that this application is to be limited only by the scope of the appended claims.

Claims

The invention is hereby claimed as follows:

1. In combination with a machine for cutting metal from a workpiece having a supply of liquid coolant applied to the cutting area, wherein the metal removal rate is such as to cause film boiling of the coolant at the surface of the workpiece, aparatus for eliminating the film boiling, thereby increasing the heat transfer coefficient between the workpiece and coolant, said apparatus comprising means for generating an electrostatic field in the coolant at the cutting area, said means including means setting up a ground potential adjacent the cutting area, a probe mounted adjacent to the cutting area, and a high voltage low amperage DC or AC power supply of about 10 to 60 kv connected to the probe to supply a potential just less than that which would cause arcing.

2. The combination as defined in claim 1, wherein the coolant is an electrolyte and said probe is covered with electrical insulation.

3. The combination as defined in claim 1, wherein the coolant is a dielectric and said probe is uninsulated.

4. The combination as defined in claim 1, wherein the machine is a grinder and the workpiece is a metal part.

5. The combination as defined in claim 1, wherein said ground potential setting means includes connecting the workpiece to ground potential.

6. Apparatus for removing heat from a workpiece and a metal cutting tool in a metal cutting machine comprising means directing a stream of liquid coolant onto the workpiece and metal cutting tool at the metal cutting area, and means generating an electrostatic field in the coolant, said means including means mounting a probe in the stream and terminating adjacent the metal cutting area, means connecting the probe to a source of high voltage low amperage DC or AC potential of about 10-60 kv such as to be slightly less than that which would cause arcing, and means connecting the workpiece to ground potential.