Patent Grant
7727054
1. Technical Field
This invention relates to supplying coolant to a location of contact between a workpiece and a material removing tool, and more particularly, relates to supplying coolant to grinding operations.
2. Background Information
It is known to equip a grinding machine with a nozzle which can discharge one or more jets, sprays or streams of a suitable liquid coolant to the location of contact between a workpiece and a material removing tool, such as a rotary grinding wheel. The nozzle can be trained or aimed upon the location of contact and is connectable to a source of coolant, e.g., by a hose. Such cooling of the location of contact between a workpiece and a grinding tool beneficially affects the quality of the finished product. This is especially in a modern grinding machine wherein the tool is expected to remove large quantities of material from a workpiece, where inadequate cooling may damage the surface integrity of the workpiece material.
It is further known to design a nozzle in such a way that it can supply adequate quantities of coolant in suitable distribution to the location of contact between a relatively large surface of a workpiece and a suitably profiled working surface of a rotary grinding wheel or an analogous tool. The nozzle may satisfy the requirements regarding the delivery of adequate quantities of coolant in optimum distribution as long as the particular grinding tool remains installed in the machine and as long as such tool is in the process of removing material from a particular series of workpieces. If the particular grinding tool is replaced with another tool of differing profile, or if another profile of the same tool is moved into material removing contact with a workpiece, the nozzle may no longer ensure optimal withdrawal of heat from workpieces. Thus, it is generally necessary to replace the nozzle with a different nozzle in a time-consuming operation which may entail long periods of idleness of the machine. This situation is aggravated if several different profiles of a particular workpiece are to be treated by a set of different tools or by two or more sets of different tools. This necessitates the removal of a previously used grinding tool from the machine.
An additional factor that affects the quality of workpiece cooling is the dispersion of the coolant jet applied to the workpiece. Dispersion has been shown to be disadvantageous because it tends to increase entrained air, and air tends to exclude some coolant from the grinding zone (i.e., grinding wheel/workpiece interface). Dispersion also tends to reduce the accuracy of the aim of the coolant jet, allowing fluid to miss and/or bounce away from the grinding zone. Dispersion may be reduced by the use of relatively long straight sections of hose/tubing immediately upstream of the nozzle. This, however, is impractical in many applications due to the space limitations of many grinding machine installations. In an attempt to overcome this limitation, plenum chambers have been disposed immediately upstream of the nozzle. The relatively large cross-sectional area of the plenum was intended to slow down the coolant velocity and allow it to stabilize before accelerating from the nozzle exit aperture, to improve coherence in applications in which long, straight upstream pipe portions are impractical. However, the relatively large size of such plenum chambers makes them difficult to locate close enough to the grinding zone to provide optimal cooling in many applications.
It has also generally been found that the quality of workpiece cooling may be improved by matching the velocity of the coolant jet to that of the grinding surface of the grinding wheel. To achieve velocity matching, and to minimize dispersion and entrained air, it has generally been found that the jet should reach the grinding zone within about 12 inches (30.5 cm) from the nozzle.
A need exists for an improved coolant nozzle capable of providing coherent jets, and which is easily adjustable to provide optimal coolant flow in a variety of grinding applications and distances from the grinding zone.
According to one aspect of the invention, a nozzle assembly is provided, which includes a plenum chamber, and a modular front plate removably fastened to a downstream side of the plenum chamber. The assembly also includes at least one coherent jet nozzle disposed for transmitting fluid through the modular front plate, and a conditioner disposed within the plenum chamber.
In another aspect of the invention, a nozzle assembly includes a plenum chamber having a non-circular cross-section in a direction transverse to a downstream fluid flow direction therethrough, at least one coherent jet nozzle disposed at a downstream end of the plenum chamber, and a conditioner sized and shaped to substantially match the cross-section, which is disposed within the plenum chamber.
In yet another aspect, a nozzle assembly includes a plenum chamber configured to pass coolant in a downstream fluid flow direction therethrough, and a plurality of coherent jet nozzles disposed at a downstream end of the plenum chamber.
In a still further aspect, a nozzle assembly includes a plenum chamber, a modular card removably fastenable to a downstream side of the plenum chamber, at least one coherent jet nozzle disposed within the card for transmitting fluid from the plenum chamber therethrough, and a conditioner disposed within the plenum chamber.
Another aspect of the invention involves a method for delivering a coherent jet of grinding coolant to a grinding wheel. The method includes determining a desired flowrate of coolant for a grinding operation, and obtaining a grinding wheel speed at an interface of a grinding wheel with a workpiece. The method further includes determining coolant pressure required to generate a coolant jet speed that matches the grinding wheel speed, determining a nozzle discharge area capable of achieving the flowrate at the pressure, and determining a nozzle configuration.
In another aspect of the present invention, a grinding tool kit includes a dressing roller sized and shaped to impart a profile to a grinding wheel, and a dressing module sized and shaped for being coupled to a plenum chamber. The dressing module includes a plurality of coherent jet dressing nozzles which are sized and shaped for supplying coolant from the plenum chamber to a dressing zone of the grinding wheel. The kit also includes a grinding module sized and shaped for being coupled to another plenum chamber. The grinding module includes a plurality of coherent jet grinding nozzles which are sized and shaped for supplying coolant from the other plenum to a grinding zone of the grinding wheel.
The above and other features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings, in which:
Referring to the figures set forth in the accompanying drawings, the illustrative embodiments of the present invention will be described in detail hereinbelow. For clarity of exposition, like features shown in the accompanying drawings shall be indicated with like reference numerals and similar features as shown in alternate embodiments in the drawings shall be indicated with similar reference numerals.
Embodiments of the present invention are provided with a range of modular nozzle configurations to apply coherent jets of coolant in a nominally tangential direction (e.g.,
Where used in this disclosure, the term “coherent jet” refers to a spray that increases in thickness (e.g., diameter) by no more than 4 times over a distance of about 12 inches (30.5 cm) from the nozzle exit. The term “axial” when used in connection with an element described herein, unless otherwise defined, shall refer to a direction relative to the element, which is substantially parallel to the downstream flow direction therethrough, such as axis 23 of nozzle 22 shown in
The present invention may be used with nominally any grinding machine, provided that the pressure applied to deliver coolant through the nozzles can be adapted to achieve the desired levels taught herein. Advantageously, various embodiments of the present invention may provide savings in set-up time needed to adjust the grinding machine, grinding wheel, workpiece, dressing wheel and coolant to run a grinding operation, and reduction in workpiece burn, improvement in part quality, and an increase in grinding wheel life by improved dressing wheel efficiency.
Potential advantages of various embodiments of the present invention include enabling the nozzle assembly to be located further away (i.e., greater than 12 inches or 30.5 cm) from the grinding zone, to reduce mechanical interference with the workpiece and fixture. Some embodiments permit the grinding wheel to be dressed less frequently, or by smaller amounts, than those using conventional coolant assemblies, to increase grinding wheel life and/or generate less downtime due to less frequent wheel changing. Improved application of coolant tends to generate less thermal damage to workpieces, and/or may generate higher yield than attainable using conventional coolant assemblies. Embodiments of the invention also tend to reduce entrained air in the coolant spray to reduce creation of foam when using water-based coolants. The relatively low dispersion of the coolant spray generated by these embodiments tends to improve the aim of the coolant into the grinding zone for improved utilization of the applied flow. This improved dispersion also generally reduces misting of the coolant spray. Moreover, these embodiments include modular nozzles which may be quickly changed, to reduce grinding machine downtime during changeover.
Referring now to
Another coherent jet nozzle suitable for use with the present invention is rectangular nozzle 20′ shown in
Turning now to
Chamber 30 also includes a flow conditioner 40, which extends transversely therein. Conditioner 40 will be discussed in greater detail hereinbelow with respect to
The skilled artisan will recognize that the coolant supply pipes 32 typically used in grinding machines are generally chosen with as small a diameter/cross-sectional area as possible, based upon both the coolant flow rate requirements of a particular grinding application, and the capacity of the coolant supply pump.
As shown in
For example, in the embodiment of
Nozzles 20, 20′ may be fabricated using any number of well-known techniques, such as machining, casting, or forming. For example, nozzles 20 may be conveniently fabricated using a specially shaped milling tool.
Referring now to
Flow conditioner 40, of appropriate dimensions as discussed herein, may be used to condition flow through a rectangular chamber 30 upstream of either round nozzle 20 or a rectangular nozzle 20′. The foregoing embodiments have been shown to yield a coherent jet at more than 12 inches (30.5 cm) away from the nozzles 20, 20′. These nozzle assemblies are thus capable of satisfying the cooling requirements of many distinct grinding applications, while being placed further away from the grinding wheel/workpiece interface than similar assemblies of the prior art.
Moreover, although chamber 30 and conditioner 40 are shown & described having rectangular transverse dimensions, they may be configured in other shapes, e.g. circular or non-circular geometries, such as oval, pentagonal, or other polygonal shapes, in various embodiments. Turning now to
Advantageously, a laser pointer or other suitable pointing device, may be projected from the plate 38′ towards the profile of the grinding wheel to identify which of the holes 42 are to be selected for a given grinding operation. A card 46 may then be machined with corresponding nozzles 20, 20′. In this manner, a discrete card may be provided for each profile being ground. Advantageously, the coolant nozzle configuration may be adjusted for various distinct grinding operations simply by replacing cards 46 within plate 38′, (i.e., without the need to change other coolant system components such as the plenum chamber 30 or piping, etc.). This aspect of the invention thus facilitates quick and highly repeatable set up of the coolant nozzles for each grinding operation, which is thus particularly suitable for small production batches.
In a variation of this embodiment, the front plate 38′ may be produced with an open front portion 48 as shown in phantom in
Thus, as described herein, plates 38 and 38′ serve as means for removably fastening a plurality of coherent jet nozzles to a downstream side of said plenum chamber. Moreover, although plate 38′ has been described as having bores 42, and the cards 46 as having nozzles 20, 20′, the skilled artisan should recognize that the bores and nozzles may be reversed without departing from the spirit and scope of this invention. For example, plate 38′ may be provided with an array of nozzles, while the card is provided with a desired pattern of bores. During use, upon insertion the card would effectively close some of the nozzles, and open only those required to generate a desired jet spray pattern.
In the embodiments described hereinabove, nozzles 20, 20′ associated with a single plenum chamber 30 may be disposed to form a profile. These nozzles may be of the same size (e.g., diameter), or may be of distinct sizes. (In the embodiments of
As mentioned hereinabove, embodiments of the present invention may be used for substantially any grinding application, such as creep-feed, surface, slotting, cylindrical grinding. In the cases of internal grinding and flat grinding, if desired the jet may be directed towards the grinding zone at an angle to the surface being ground.
Moreover, although the nozzle assemblies of the present invention have been shown and described for cooling a grinding zone of a grinding operation, the skilled artisan will recognize that embodiments of the invention may similarly be used to supply coolant to a dressing zone of a conventional dressing operation, without departing from the spirit and scope of the present invention. The ‘dressing zone’ refers to the interface between the grinding wheel and a conventional dressing tool used in conventional grinding wheel dressing operations.
Briefly described, dressing generally involves applying a desired profile to a grinding wheel by engaging the grinding face of the rotating wheel with a plunge or traversing diamond dresser, or with a rotary diamond truer. Since the dressing zone is distinct from the grinding zone (e.g., typically on the opposite side of the wheel from that of the grinding zone) a separate nozzle(s) is utilized. When deep and/or otherwise complex wheel profiles are to be formed by such a dressing/truing operation, it is common for a straight coolant nozzle to be used as an approximation of the actual desired profile. Disadvantageously, this may lead to insufficient coolant application in portions of the dressing zone, and may generate excessive dresser/truer wear, especially in the event the wheel includes sintered sol gel ceramic aluminum oxide abrasives. The various embodiments of the present invention, however, may be used as described herein, to provide a nozzle assembly that matches the desired profile (e.g., by using a matching array of nozzles 20, 20′ in a plate 38 or card 46) in the dressing zone, but which is sized for supplying a lower flowrate suitable for dressing operations. (For convenience, the term ‘module’ may be used herein to refer to either plate 38 or card 46.) For example, a plenum chamber 30 (e.g., with a plate 38′) may be provided at both the grinding and dressing zones. A kit may then be provided, which includes a first module (e.g., a card 46), having a pattern of nozzles or bores pre-configured to apply a desired flow pattern at the grinding zone; another module (e.g., card 46), having a pattern of nozzles or bores pre-configured to apply a desired flow pattern at the dressing zone; and optionally, a dressing roller configured to impart a particular desired profile (which corresponds to the pattern of the cards) to the grinding wheel. Use of the modules enables the coolant nozzle configuration at both the grinding zone and the dressing zone to be adjusted for various distinct grinding operations simply by installing the modules, e.g., by disposing cards 46 or plates 38 on their respective plenum chambers, and optionally, installing the dressing roller.
Although the foregoing discussion describes nozzle assemblies associated with a single plenum chamber, it should be recognized that a single plenum chamber may be partitioned, or otherwise divided into two or more sub-chambers without departing from the spirit and scope of the invention. For example, a plenum chamber may be divided into two parallel, side-by-side portions, which may be selectively actuated or closed, depending on the configuration of the nozzles in a card 46 or plate 38 coupled thereto.
Having described various embodiments of the invention, the following is a description of the set-up and operation thereof. This method is described in connection with Table 1 below.
The flowrate of coolant applied to a grinding zone may be determined 100 either using 102 the width of the grinding zone or by using 104 the power being consumed by the grinding process. For example, 25 GPM per inch (4 liters per minute per mm) of grinding wheel contact width is generally effective in many grinding applications. Alternatively, a power-based model of 1.5 to 2 GPM per spindle horsepower (8-10 liters per min per KW) may be more accurate in many applications, since it corresponds to the severity of the grinding operation.
As discussed hereinabove, the coolant jet may optimally be adjusted to reach the grinding zone at a velocity that approximates that of the grinding surface of the grinding wheel. This grinding wheel speed may be determined 106 empirically, i.e., by direct measurement, or by simple calculation using the rotational speed of the wheel and the wheel diameter.
The pressure required to create a jet of known velocity may be determined 108 using an approximation of Bernoulli's equation shown as Eq. 1:
where SG=Specific Gravity of the coolant, and vj=velocity of the coolant in meters/second or surface feet/minute (i.e., the wheel speed determined at 106).
Using Table 2 below, the total area of nozzle(s) outlet may be determined 110, using the flowrate and pressure determined at 100 and 108. As shown, Table 2 is an example (in English and Metric versions) of an optimization chart which correlates pressure and coolant jet speed, to exit aperture size based on either the exit diameter d of a single round nozzle 20, or the combined exit area of a rectangular nozzle 20′ or array of nozzles.
Knowing the total area of nozzle(s) outlet, the configuration of the nozzle(s) may be determined 112. For example, a single round nozzle 20 or rectangular nozzle 20′ may be used 116, or an array/matrix of nozzles 20 may be used 114.
In the event a matrix of nozzles 20 is used, the flowrate of coolant from such a matrix may be described as a function of exit diameter d and linear pitch of the nozzles. (As used herein, the term ‘linear pitch’ refers to the distance between the center axes of adjacent nozzles 20.) For purposes of the following calculations, it is assumed that the nozzles 20 are closely-packed, i.e., adjacent nozzles 20 are disposed so that a distance of less than about ¼ D separates their outer diameters D, such as shown in
The flowrates for a matrix of Y nozzles having an outer diameter D, (and thus a pitch of D,) and an outlet/exit diameter d, may be determined using Eq. 2. (In many applications, a reasonably coherent jet is formed by using a value of d that is less than or equal to about ½ D.) For example, in a grinding operation in which the grinding wheel has a surface velocity in the grinding zone (vs) of 30 m/s, and a plenum pressure of 4.5 bar is used, the flowrates for a plurality of nozzles having an outer diameter D of 6 mm, (and thus a pitch of 6 mm,) and d of 3 mm, may be determined as follows:
where Cd=discharge coefficient of the nozzle, which is approximately 0.9 for the nozzles 20, 20′, described herein.
Therefore, specific flowrate Q′f=1.9 l/min per mm at 30 m/s, regardless of the number of nozzles.
The specific flowrate results, using Eq. 2, for four discrete nozzle pitches (i.e., diameters D) are shown in Table 3 below, for different coolant jet speeds.
Where the pump fitted to a grinding machine is incapable of supplying sufficient pressure to match the jet speed to the wheel speed, then the apertures of the nozzle(s) may be made (e.g., using Table 1) to support the required flowrate at that lower pressure.
The following illustrative examples are intended to demonstrate certain aspects of the present invention. It is to be understood that these examples should not be construed as limiting.
Gas turbine components were ground at two locations (Cut A and Cut B), using a conventional grinding machine equipped with a 100 mm wide BLOHM® coolant nozzle having a tapered exit height h which varies from 0.75 mm to 1.5 mm, fed by a conventional 25 mm vertical BLOHM® pipe with an elbow upstream of the nozzle. The coolant pump was rated at 400 liters/min, at 8 bar. Additional grinding conditions were as follows:
Cut A
Cut B
Conditions were substantially identical to those of Example 1, except the BLOHM® nozzles were replaced with two coherent nozzles 20 each placed at the end of relatively long (greater than 12 inches or 30.5 cm) and straight 1 inch (2.5 cm) diameter coolant supply hose. The nozzles 20 were directed towards the grinding zone from a point further from the grinding zone than the BLOHM® nozzles. The desired flowrate for Cut A was determined, using the Tables hereinabove, based on matching the wheel speed at 5 bar pressure, to be about 136 liters/minute. The desired flowrate for Cut B was similarly determined to be about 49 liters/minute. Based on the flowrate, the nozzle 20 chosen for Cut A had a diameter d of 10 mm, for an exit area of 79 mm2. The nozzle 20 chosen for Cut B had a diameter d of 6 mm, for an exit area of 28 mm2.
The grinding wheel of this Example 2 required approximately 50 percent less dressing than the grinding wheel of Example 1, for a corresponding increase in useful life of the grinding wheel, reduced cycle time, and minimal wasted coolant flow.
A nozzle assembly was fabricated substantially and shown and described hereinabove with respect to
The assembly of Example 3 was provided with a conditioner 40 having an array of holes 42 of 0.125 inch (0.32 cm) diameter, and a center-to-center spacing of 0.19 inch (0.48 cm) substantially as shown. The conditioner was placed approximately 1.5 inches (3.8 cm) upstream of the downstream face 36 of chamber 30. Dispersion of the coolant jet was measured in the manner described with respect to Example 3.
As shown in
Although the various embodiments shown and described herein refer to round or rectangular nozzles 20, 20′, the skilled artisan should recognize that nozzles of substantially any transverse geometry may be utilized, using suitable approximations of the various dimensional parameters included herein, provided they produce coherent jets as defined herein, without departing from the spirit and scope of the present invention.
Moreover, the skilled artisan should recognize that any suitable means may be utilized to replace the modules (i.e., plates or cards) of the present invention. For example, the modules may be replaced manually, or alternatively, may be replaced automatically, such as by a modified version of a conventional manipulator commonly used to automatically exchange grinding tools between successive treatments of a workpiece in a grinding machine.
In the preceding specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.
This application claims priority, and is a divisional of U.S. patent application Ser. No. 10/669,817, entitled Coherent Jet Nozzles for Grinding Applications, filed on Sep. 24, 2003, now U.S. Pat. No. 7,086,930 the contents of which are incorporated herein by reference in their entirety for all purposes, and which claims priority, and is a divisional of U.S. application Ser. No. 10/206,029, now U.S. Pat. No. 6,669,118 entitled Coherent Jet Nozzles for Grinding Applications, filed on Jul. 26, 2002.
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| Number | Date | Country | |
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| Number | Date | Country | |
|---|---|---|---|
| Parent | 10669817 | Sep 2003 | US |
| Child | 11483288 | US | |
| Parent | 10206029 | Jul 2002 | US |
| Child | 10669817 | US |
