EP0956924A1

EP0956924A1 - Tool carrier for a double-spindle grinding machine

Info

Publication number: EP0956924A1
Application number: EP98107087A
Authority: EP
Inventors: c/o Officina Meccanica Domaso SpA Gibezzi
Original assignee: OMD Officina Meccanica Domaso SpA
Current assignee: OMD Officina Meccanica Domaso SpA
Priority date: 1998-04-17
Filing date: 1998-04-17
Publication date: 1999-11-17

Abstract

A tool carrier is provided preferably for a grinding disc such as used in a double-spindle grinding machine. The carrier comprises at least one channel (2) extending through its interior and lying parallel to a plane surface (6) of the carrier (1). A cooling medium inlet (21) located at an inner radial portion of the carrier connects the channel (2) to an outlet (20) located at the circumference of the carrier. The channel arrangement allows the cooling medium to circulate through the tool carrier (1) when rotated on a drive spindle (12).

Description

The present invention relates to a tool carrier for use in a double-spindle grinding machine. More particularly, the invention relates to a carrier for support of a grinding disc by which the carrier can be cooled.
Double-spindle grinding machines are known in the art by which two grinding discs are mounted on respective carriers spaced at a distance. The object to be ground (for example a coil spring) is placed between the discs where grinding takes place on two opposing surfaces. In the case of coils springs, a revolver plate carries the springs between the opposing rotating discs whereby the ends of the coil spring are ground plane with high precision. The grinding discs normally have an abrasive material (BNC) or diamonds adhered to their surface. The grinding material is heat sensitive and in long term operation, heat builts up in the disc, which is also transferred to the carrier support of the disc.
The surfaces of the abrasive disc can be cooled by circulating air. Arrangements are known in the art by which air is forced to circulate over the disc surfaces for the purpose of cooling. However, when high performance grinding is required, air cooling is not sufficient and overheating of the disc can lead to early deterioration.
An object of the present invention is to provide a tool carrier suitable for support of a disc-shaped tool, particularly a grinding disc, by which heat built-up in the disc caused by the grinding process can be minimized.
According to the present invention, a tool carrier is provided which is suitable for mounting a disc-shaped grinding tool and which is mountable on a drive spindle. The carrier comprises at least one channel extending through the carrier and lying parallel to a plane surface thereof. The channel is connected to a cooling medium inlet and outlet in such a matter that the cooling medium can circulate through the tool carrier.
Preferably, the carrier is circular and suitable for supporting a grinding disc. The cooling medium, such as water, is supplied to an inlet disposed at a radially inward portion of the circular carrier. From there, the channel is formed as a spiral outwardly and terminates at a cooling medium outlet located at an outer peripheral portion of the circular carrier.
The present arrangement has the advantage that rotation of the carrier combined with the spiral form of the channel provides a pumping effect on the cooling liquid due to the centrifugal forces.
In another embodiment, the cooling channel is formed by the series of intersecting bores provided in the carrier plate. The openings of the bores are closed off, whereby intersecting segments on the bores then form the cooling channel.
Also provided according to the present invention is a douple-spindle grinding machine which makes use of the tool carriers of the preferred embodiments.
Further objects and advantages of the present invention will become apparent from the following description of embodiments taken in conjunction with the drawings.

Fig. 1: shows a double-spindle grinding machine according to one embodiment of the present invention.
Fig. 2a and 2b: show a top view of the spiral channel in the carrier plate according to one embodiment.
Fig. 3: shows another embodiment of the tool carrier with the cooling channel formed as plurality of segments.

A first embodiment of the tool carrier according to the present invention is shown in Fig. 1. The tool carrier 1 shown in the lower portion of the figure will be discussed in detail. As will be understood, the upper and lower tool carriers disposed in opposite to one another form a double-spindle grinding machine. The tool carrier comprises an abrasive support 3 mounted on a carrier plate 5. The carrier plate 5 is mounted on a spindle head 8, which is secured to the drive spindle 12.
The abrasive plate 3 defines the plane surface 6 for support of a grinding disc. The illustration in Fig. 1 also shows the conventional air cooling of the grinding disc. Air is supplied along the axis X of the spindle 12 through an opening 16 in the carrier plate 5. The air discharge from the opening 16 is forced outwardly to form an air current A shown in Fig. 1. The outflowing air passes over the surface of the grinding disc to provide cooling.
According to the first embodiment, the tool carrier 1 is also cooled by means of circulation of a cooling medium, preferably water. As shown in Figs. 1 and 2, a spiral channel 2 is provided between the abrasive support 3 and the carrier plate 5. A cooling medium inlet 21 is provided at a radially inward location of the circular carrier, while the cooling medium outlet 20 is provided at the outer circumference of the carrier. As shwon in Fig. 2a, the spiral channel 2 comprises a number of turns from the inlet 21 to the outlet 20. In the present embodiment 3 1/2 turns are used. Preferably the spiral should have three to six turns depending on the dimensions of the carrier and the heat load in the particular grinding process.
Returning to Fig. 1, the spiral channel 2 is disposed predominantly in the outer area of the circular plate. It is this position where the rotational speed of the grinding disc would be greatest and it is here where the object to be ground would be placed between the two grinding discs.
It will also be appreciated from Fig. 1 that the spiral channel 2 is located within a plane with is substantially parallal to the plane surface 6 of the abrasive support 3. The arrangement ensures that heat generated in the disc tool will be uniformly dissipated into the cooling medium flowing through the spiral channel 2.
The dashed line B shown in Fig. 1 illustrates the cooling medium flow in the carrier 1. The cooling medium enters a port 7 in the spindle head 8 and passes to a supply line 15a, which runs perpendicurlar to the plane surface 6 or parallel to the spindle axis x. A supply bore 15, best seen in Fig. 2a, is formed in the carrier plate 5. The supply bore 15 intersects supply line 15a to allow communication there between. The outer opening of the supply bore 15 is closed with a stop 4. The supply bore 15 also communicates with the inlet 21 of the channel 2 at the radially inward start position of the spiral channel 2.
Having circulated through the spiral channel 2 out to the outlet 20 (as seen in Fig. 2a) the cooling medium enters a discharge bore 14, which also extends radially into the carrier plate 5. The discharge bore 14 is also provided with a stop 4 such that discharge fluid flows toward the center of the carrier. The fluid then enters the discharge line 14a, which is also perpendicular to the plane surface 6. The fluid moves to the discharge port 11 for circulation to a heat exchanger for dissipation of the accumulated thermal energy. The cooling circulation system will normally be closed and the cooling medium preferably is water.
The arrangement of the cooling channel 2 in spiral form from the inlet 21 to the outlet 20 provides a pumping effect to circulate the cooling medium. The centrifugal force generated on the cooling medium during rotation of the carrier plate urges flow through the channel 2. The pumping effect generated is normally sufficient that no further pump need to be supplied in the cooling medium circulation system. The cool medium circulates at a relatively low pressure, although for higher heat dissipation at higher grinding performance, the pressure can be increased with additional mechanical pumping means.
As shown in Fig. 1, the double-spindle grinding machine according to this embodiment comprises first and second tool carriers 1 and 1' disposed opposite to one another such that the respective spindles 16 and 16' are arranged coaxially. The plane surfaces 6 and 6' oppose one another, each surface intended for support of a grinding disc. As mentioned above, cooling air can be supplied from the interior of the respective spindles 12 and 12'. As shown in Fig. 2b, a channel 22 can be provided in the spindle which communicates via the opening 16 to the space between the two grinding discs. In the double-spindle arrangement, the two air flows from each spindle collide with one another or intersect in a manner such that the resulting combined air flow is directed radially outwardly. Thus a combined system is achieved whereby the grinding disc would be cooled at its outer surface by cooling air and cooled on its inner surface adjacent to the abrasive support 3 is dissapated by the cooling medium in the spiral channel 2.
A second embodiment of the tool carrier according to the present invention is shown in Fig. 3. Instead of being spiral, the cooling channel 302 is formed by a number of intersecting bores. The bores are formed by drilling into the outer circumference of the carrier plate 300 so as to form a plurality of straight interconnected segments 302a, 302b, 302c. The bores are closed at the outer circumference of the plate 300 by means of stops 304. The intersections of the bores then define segments of the cooling channel 302. Cooling medium inlet 321 and outlet 320 are arranged near the center of the plate 300. The location of the bores which define the segments of the cooling channel 302 are designed to provide the most uniform heat dissipation, while at the same time providing a simple means for manufacturing the cooling channel. In addition, the amount of material removed from the carrier plate 300 by means of the bores should be as uniform as possible so as not to disturb the balance of the carrier 300 which will rotate at high speed. Counterbalance weights can be applied in the form of the size and weight of the stops 304 if necessary.

Claims

Tool carrier suitable for a disc-shaped tool and mountable on a drive spindle (12), comprising

at least one channel (2) extending through and lying parallel to a plane surface (6) of the carrier (1) with a cooling medium inlet (21) and a cooling medium outlet (20) connected to the channel (2) such that the cooling medium can circulate through the tool carrier (1).
Tool carrier of claim 1, wherein the carrier is circular and the cooling medium inlet (21) is disposed at a radially inward portion of the circle, the channel being arranged to spiral outwardly from the cooling medium inlet (21) to the cooling medium outlet (20) located at an outer radial portion of the circle.
Tool carrier of claim 2, wherein the spiral-shaped cooling channel (2) includes three to six turns from the cooling medium inlet (21) to the outlet (20).
Tool carrier of claim 2 or 3, wherein a supply bore (15) and a discharge bore (14) are formed radially in the circular carrier (1) parallel to said plane surface (6), the supply and discharge bores
(15, 14) communicating with the cooling medium inlet (21) and outlet (20), respectively.
Tool carrier of claim 4, wherein the supply and discharge bores (15, 14) connect at their inner radial ends to cooling medium supply and discharge lines (15a, 14a), the supply and discharge lines (15a, 14a) disposed substantially perpendicular to said plane surface (6).
Tool carrier of claim 1, wherein the carrier is circular and the cooling medium inlet (321) and outlet (320) are disposed at a radially inward portion of the circle, the channel (302) being formed of plural straight interconnected segments (302a, 302b, 302c).
Tool carrier of claim 6, wherein the plural straight segments (302a, 302b, 302c) are formed from intersecting bores into the circular carrier (1), the outer openings of the bores being closed with stops (304) to form said channel (302) of interconnected segments.
Tool carrier of any of the claims 1 to 7, wherein the carrier (1) comprises a central opening (16) adapted to supply cooling air to the plane surface (6).
A double spindle grinding machine comprising a first tool carrier (1) according to any of the claims 1 to 8, mounted on a first spindle (12) and a second tool carrier (1') according to any one of the claims 1 to 8 mounted on a second spindle (12'), the spindles (12, 12') being disposed coaxially and the carriers (1, 1') mounted such that their respective plane surfaces (6, 6') oppose one another at a distance to form a space therebetween.
Grinding machine of claim 9, wherein cooling air supplied from the central opening (16) of the first carrier (1) intersects with cooling air supplied from the central opening (16') of the second carrier (1') so as to urge the combined air flow outwardly in the space between the respective plane surfaces.