US Classes62/475, Means for discharging impurity from system62/515Evaporator, e.g., heat exchanger
Attorney, Agent or Firm
International ClassesF25B 43/00
The invention relates to a cooling device for a machine tool for cooling a heated fluid, such as cooling lubricant, with at least one refrigerating unit which receives filtered fluid from a filter means by means of a pumping means with at least one hydraulic pump, which fluid originates from at least one storage tank, with a subdivision into a clean tank and a dirty tank, the refrigerating unit returning the fluid which has been cooled in circulation to the clean tank.
In a known generic cooling device as used in practical applications, on a machine tool, for example a grinding machine, fluid emerging in the exterior in the form of a cooling lubricant is collected in a machine bed trough as a collecting station and is conveyed by means of a hydraulic pump to the dirty tank as part of a cooling lubricant storage tank. The fouled and possibly heated fluid which has been delivered to the dirty tank in this way is supplied to a filter means by another hydraulic pump, the fluid which has been filtered in this way and therefore after passing through the filter means is partially delivered to the clean tank of the storage tank via a secondary branch, and in the main branch a part of the filtered fluid travels to a refrigerating unit which returns the filtered and cooled fluid to the clean tank in circulation. From there the cleaned and cooled fluid in the form of a cooling lubricant can be transported via another hydraulic pump in the feed line of the machine tool to its parts to be cooled, such as drives, then after passing through the drives the heated cooling lubricant returning directly in backflow to the clean tank.
In the known solution, in the supply or in the main branch to the refrigerating unit there is a ball cock for adjusting the division of quantities following the indicated filter means. The purpose of this is that at a constant cooling power of the refrigerating unit it always obtains the same flow amount of liquid to be cooled from the dirty tank, in order if possible to create constant temperature conditions in the clean tank, from which via the feed line the drives of the grinding machine which are to be cooled are supplied. Since grinding machines must work very exactly and must ensure grinding-workpiece machining to within microns, even the smallest temperature deviations in the cooling circuit (feed line and return) for the drives to be supplied can entail clear and undesirable machining inaccuracies.
If at this point in the known solution the counterpressure in the filter means due to captured dirt (grinding dust, abraded particles, etc.) in the cooling lubricant is increased by the filter material used at the time, in this way the flow amount which as described should be kept constant is reduced. This change of the flow amount for the desired constant cooling power of the refrigerating unit leads to temperature changes in the clean tank; this has adverse effects on the machining accuracy of the grinder as a machine tool. Even if thorough mixing in the clean tank with the cooled fluid already located there occurs, the temperature changes resulting therefrom are still relevant such that the machining inaccuracies must be watched. Also, based on the altered mixing in the clean tank due to the changed temperatures on the discharge side of the refrigerating unit, temperature control for the machine tool is adversely affected.
On the basis of this prior art, the object of the invention is to further improve the known solution while retaining its advantages such that for a machine tool such as a grinder, fluid supply, especially with cooling lubricant, of constant temperature is ensured which enables high-precision machining with the machine tool. This object is achieved by a cooling device with the features of claim 1 in its entirety.
In that, as specified in the characterizing part of claim 1, the hydraulic pump of the pump means conveys fluid which has been filtered exclusively with the filter means from the dirty tank into the clean tank and because another independent hydraulic pump conveys the fluid which has been delivered into the clean tank to the refrigerating unit for circulation, the basic structure of the known cooling device can be maintained. The division of functions according to the invention, on the one hand filtration from the dirty tank into the clean tank, and on the other the transport of fluid from the clean tank to the refrigerating unit and back into the clean tank ensures that possible pressure losses, due to clogging of the filter of the filter means, they can no longer adversely affect the flow amounts which are to be kept constant for the refrigerating unit, with the result that altogether the temperatures on the clean tank side remain largely constant. This in turn benefits the machining accuracy of the machine tool, its parts to be supplied, such as drives, should receive a fluid of constant temperature so that the temperature control which interacts with the machine control can ensue uniform, exact machining accuracy.
The solution according to the invention is economical to produce and reliable in use. For one with average skill in the art in the field of cooling devices, it is surprising that with only a few measures and using existing components it acquires a much improved machining accuracy for a machine tool to the extent it separates the functions of filtration and cooling relative to the dirty tank and the clean tank within the sketched framework. The cooling device according to the invention need not be limited to use of cooling lubricant cooling in grinding machines, but can be used anywhere, also in hydraulic circuits, in machine tools, where a constant temperature of the supply fluid is desirable to achieve high positioning accuracies of drives or the like.
It has proven especially advantageous to undertake removal for the refrigerating unit in the so-called hot region of the clean tank, i.e., in the vicinity of the fluid return from the individual fluid consumers of the machine tool.
In another preferred embodiment of the cooling device according to the invention, provision is made such that by means of at least one other hydraulic pump fluid can be transported from the clean tank for cleaning or flushing of the machine tool. In this way for example the grinding wheel of the machine tool can be cleaned; this can also take place under high pressure. Furthermore it is preferably provided that a flow monitor inserted into the feed line triggers the pertinent hydraulic pump for the cleaning or flushing means and turns it off especially when the feed line is free of fluid. Because at this point the hydraulic pump is turned off for the cleaning and flushing means, when the machine tool is not in operation, the heat energy otherwise converted by the permanently driven hydraulic pump can no longer reach the workpiece when the cleaning or flushing nozzles are opened for the grinding wheel via the fluid; this also helps increase machining precision.
Other advantageous embodiments of the cooling device according to the invention are the subject matter of the other dependent claims.
The cooling device according to the invention will be explained below for one embodiment with reference to the drawings. In this connection, the figures are schematic and not to scale, drawn in the manner of hydraulic diagrams.
FIG. 1 shows a solution as in the prior art and
FIG. 2 shows a representation corresponding to FIG. 1 with the inclusion of the cooling device according to the invention.
Before the cooling device according to the invention is explained using FIG. 2, the known structure as shown in FIG. 1 will be detailed first.
FIG. 1 shows the known cooling device for a machine tool designated as a whole as 10 in the form of a grinding machine. The grinding machine 10 has three linear motors 12 and two axial motors 14 and a grinding spindle motor 16 for driving a grinding wheel which is not shown. The other indicated motors 12 and 14 allow five-axle grinding operation with which turbine blades or the like can also be ground with high precision. Via a distributor 18 the indicated motors 12, 14 and 16 are supplied with a fluid in the form of a cooling lubricant via a feed line 20 in the form of a fluid line by means of the hydraulic pump P4 from the clean tank 22. The possible level of the cooling lubricant in the clean tank 22 is symbolized with a level display 24. The cooling lubricant supplied to the distributor 18 by means of the hydraulic pump P4 via the feed line 20 is supplied for cooling the motors 12, 14 and 16 accordingly to them via fluid lines and the heated cooling lubricant is in turn discharged on fluid lines and supplied to a collecting site 26 which returns the fluid which has then been heated in the operation of the machine tool via a fluid line in the form of a return 28 to the clean tank 22. In this way an inherently closed cooling lubricant circuit for the motors of the machine tool 10 is implemented. The level displays used in each case can also be used for triggering of the fluid level in the pertinent containers (tanks).
Cooling lubricant can be supplied via another hydraulic pump P3 from the clean tank 22 to a flushing gun which is not detailed and which can be connected to a triggerable 2/2-way valve 30. The working grinding wheel can on the one hand be cooled and on the other cleaned by way of this flushing gun as part of a cleaning and flushing means. Optionally there can also be a high pressure cleaning means 32 which has a pressure booster in order to be able to clean the indicated grinding wheel with high pressure. The individual cleaning nozzles are then blocked via solenoid valves or supplied with the cooling lubricant.
As FIG. 1 furthermore shows, in the region of the machine tool 10 fluid emerging into the exterior in the form of a cooling lubricant which occurs especially when the grinding wheel is supplied from the outside, is collected in a collecting station 34, which can constitute a type of machine bed trough for the machine tool 10, the fluid level in the collecting station 34 being shown symbolically with a level display 24'. A hydraulic pump P1 transports the fluid which has been fouled in this respect and possibly heated into the dirty tank 36, an overflow from the dirty tank 36 which is not shown to the machine bed trough as the collecting station 34 ensuring that the dirty tank 36 is not unintentionally overfilled. The possible fill level in the dirty tank 36 is shown by way of example with the level display symbol 24''. Both the clean tank 22 and also the dirty tank 36 are a common component of a storage tank 38; but it would also be conceivable here to locate the clean tank 22 and the dirty tank 36 spatially separate from one another on the machine tool 10. In addition, several tank units (not shown) could form the respective individual tank. Furthermore, all hydraulic pumps are driven by conventional electric motors M which release heat in operation.
The dirty tank 36 which is separated from the clean tank 22 via a partition has another hydraulic pump P2 which supplies the dirty fluid from the dirty tank to a filter means 40. Following the filter means 40, the pertinent fluid line is divided into a main branch 42 and a secondary branch 44. The indication main branch and secondary branch is arbitrarily chosen and need not necessarily be related to the respective main flow amount of fluid following the filter means 40. An adjustable ball cock 46 with pressure gauge monitoring is connected to the main branch 42. The main branch 42 on the input side discharges into a refrigerating unit designated as a whole 48, conversely the secondary branch 44 discharges into the clean tank 22. On the input side, the refrigerating unit 48 has a heat exchanger 50 which made for example as a plate heat exchanger acts as an evaporator. The refrigerating unit 48 furthermore has a compressor 52 and a condenser 54. The refrigerating unit 48 is therefore made as a compressor-refrigerating unit and consists in this respect of a closed refrigerating circuit 56 with a sealed compressor 52. A conventional refrigerant is added to the refrigerating circuit. Furthermore a drain line 58 which discharges into the clean tank 22 and which is a component of a cooling circuit which is open in this respect is connected to the evaporator or heat exchanger 50, in addition to the main branch 42.
In order to be able to ensure the desired setpoint temperature by means of the refrigerating unit 48 which has an almost constant cooling power, a definable flow amount is tapped by means of the ball cock 46 via the main branch 42 following the filter means 40 and is supplied to the refrigerating unit 48 with its heat exchanger 50. The cooling power of the refrigerating unit is controlled within certain limits by an expansion valve, depending on the cooling power which prevails via the cooling circuit 60 on the evaporator 50. The required cooling power, viewed over a shorter time interval, is then almost constant due to the operating mode of the machine tool. An excess partial amount which may be present following the filter means 40 in the secondary branch 44 is delivered directly to the clean tank 22 as an excess amount. As fouling of the filter means 40 increases however, a counterpressure builds up and the desired flow amount of cooling lubricant which is to be kept constant in the main branch 42 is reduced. This change of the flow amount at the indicated constant cooling power leads to a change of temperatures in the return to the clean tank 22 via the drain line 58. At the same time this leads to altered mixing of the cooled fluid which has been delivered via the drain line 58 and of the fluid which remained in the clean tank 22.
But the altered mixing then again adversely affects the temperature control and it is not possible to supply cooling lubricant with a constantly given temperature (setpoint temperature) via the feed line 20 of the machine tool 10 with its parts to be cooled. Since in this regard especially an altered temperature situation which deviates from the setpoints arises on the motors 12, 14, and 16, in this respect high-precision machining with the machine tool 10, especially with its grinding wheel, is not possible. This is further supported in that via the hydraulic pump P3, whether with normal pressure or whether with high pressure, cooling lubricant with an altered temperature is supplied to the grinding wheel (not shown) and therefore to the workpiece via a cleaning or flushing means. Furthermore, matching of the current cooling power demand of the entire machine tool 10 takes place by the compressor-refrigerating unit 48 being turned on or off. Turning on takes place when the upper boundary of a setpoint temperature is reached, and turning off takes place when the lower boundary of the setpoint temperature is reached. As a result of the unwanted temperature changes in the clean tank 22, switching hysteresis then occurs which likewise causes a temperature fluctuation in the feed line 20 of the parts of the machine tool 10 to be cooled; this in turn has an adverse effect on accuracy in machining.
To avoid the aforementioned disadvantages in a known cooling device for a conventional machine tool 10 in the form of a grinding machine, the solution according to the invention with an altered cooling device is used, as follows in detail from FIG. 2. With respect to the representation of the machine tool 10, it has the same structure as the known solution and likewise a compressor-refrigerating unit 48. Furthermore, the clean tank 22 has been preserved, likewise the dirty tank 36 and the collection station 34 in the form of a machine bed trough. Furthermore, as before, a hydraulic pump P4 supplies the machine tool components to be cooled and by means of a hydraulic pump P1 fouled fluid in the form of cooling lubricants travels from the collecting station 34 into the dirty tank 36. Likewise the hydraulic pump P3, as already described, supplies the cleaning and flushing means for the grinding wheel of the machine tool 10. In this regard reference is made to the aforementioned statements for the known solution as shown in FIG. 1.
The cooling device according to the invention at this point has an independent filter circuit 62 in which by means of the hydraulic pump P the fouled and possibly heated fluid from the filter means 40 travels cleaned to the clean side with the clean tank 22. From there, then by means of a further independent hydraulic pump P5 in the closed cooling circuit 60, the fluid is relayed to the evaporator or heat exchanger 50 of the refrigerating unit 48 and the fluid which has been cooled in this way (lubricating coolant) then travels via the drain line 58 back into the clean tank 22 for recirculation by means of the hydraulic pump P5. In this way a very uniform temperature distribution within the clean tank 22 at a constant level relative to the given setpoint temperature can be achieved. Preferably removal of the fluid takes place via the hydraulic pump P5 in the hot region of the clean tank 22 which faces away from the drain line 58 with the cooled cooling lubricant and in the vicinity has the input of the return 28 via which the heated cooling lubricant coming from the machine tool 10 is returned to the clean tank 22. An internal, closed cooling circuit 60 thus is obtained via the clean tank 22, even if the clean tank 22 can be made open to the exterior.
By decoupling of the filter circuit 62 to the cooling circuit 60, in any case the pressure losses in the cooling circuit 60 are kept constant; this in turn leads to the flow amounts and thus the temperature being able to be kept constant. A special controller function of the refrigerating circuit 56 in the compressor-refrigerating unit (continuous running with bypass control) additionally enables an improvement of the constancy of the feed line temperature, i.e., hysteresis of 1 K, that is, . -.0.5 K in the feed line 20 to the parts of the machine tool 10 which are to be supplied is achieved. With the cooling device according to the invention therefore the temperature of the fluid in the clean tank 22 can be kept constant and thus supply of the machine tool 10 with fluid of a definable setpoint temperature which is not changed by the supply of fluid from the filter circuit 62 is possible; this leads to high-precision machining with the machine tool 10. The cooling device according to the invention need not be limited to the use of cooling lubricants, but can be used wherever fluids, also hydraulic media, are to have a temperature as constant as possible in machine tools and from which particle dirt has been removed via a filter means 40. When reference is made to hydraulic pumps in the application, their use is not limited to oil hydraulics, but designed as a fluid or media pump also other fluids, such as cooling lubricants or the like, can be transported.