EP2995422A1

EP2995422A1 - Anchoring for the head of a regulating wheel in a centerless grinding machine

Info

Publication number: EP2995422A1
Application number: EP15380037.0A
Authority: EP
Inventors: David Barrenechea Azpeitia; Modesto Larrañaga Murgoitio
Original assignee: Danobat SCL
Current assignee: Danobat SCL
Priority date: 2014-09-15
Filing date: 2015-09-15
Publication date: 2016-03-16
Also published as: ES2521965B1; ES2521965A1

Abstract

The present invention relates to an anchoring for the head of a regulating wheel in a centerless grinding machine, wherein the grinding machine has a regulating wheel (2) arranged in a head (6) projecting in a cantilever manner, in the lower portion of which there is at least one additional fastener (8) establishing an attachment aimed at eliminating the cantilevering of said head (6) to prevent vibrations thereof.

Description

Field of the Art

The present invention relates to centerless grinding machines for grinding cylindrical parts, proposing an anchoring for the head of a regulating wheel of said machines, aimed at eliminating the cantilevering of said head and making it rigid, with the main objective or benefit of reducing cycle time and improving roundness; in addiction to aiding in efficiently reducing instabilities that give rise to vibrations known as chatter effect, improving machine precision and productivity conditions.

Prior Art

A centerless grinding process is known for grinding cylindrical parts, performed by means of machines made up of a grinding wheel, a regulating wheel and a guide rod on which the part to be ground is supported, one or both wheels being incorporated in a supporting carriage, which allows a separation and approximation movement to adapt the relative position of the wheels as needed.
Said centerless grinding process allows obtaining very precise finishes and high productivity ratios, high productivity ratios being achieved as the result of the possibility of using wheels having a large width and the elimination of the need for operations for centering and fastening the part to be ground, which entails a considerable reduction in operating times and the possibility of automating the grinding process.
However, grinding process precision and productivity are critically affected by the ease with which dynamic instabilities occur, giving rise during the work process to vibrations known as chatter effect, which are more likely to occur as the width of the wheels increases. The analysis of those instabilities causing the chatter effect and studies aimed at preventing or minimizing their effects have been the object of many works carried out by universities, research centers and machine manufacturers, from different technical/technological fields.
In the case of the regulating wheel, there are machines with a supporting head that projects in a cantilever manner with respect to the carriage or portion bearing this head, which aids in the occurrence of instabilities causing the chatter effect.
Patent number JP H06246634 belonging to Toshin Technical KK proposes a system that aims to prevent vibration of the assembly supporting the regulating wheel of a centerless grinding machine, establishing a supporting head of said regulating wheel in the form of a cylindrical block, in conjunction with a cylindrical shape of the carriage of the regulating wheel, to establish a rigid fixing, in which the head does not project in a cantilever manner with respect to the carriage. For wheels of excessive width, this solution requires a large machine since the cylindrical configuration of the supporting head of the regulating wheel must be coaxial with the cylindrical shape of the carriage. Furthermore, the manufacture of this solution is very complex.
German Patent number DE 19839185 belonging to Mikrosa discloses a solution for fixing the grinding wheel by means of a hydraulic system which allows releasing and fastening the grinding wheel quickly. This solution bears no relation to the assembly of the regulating wheel and to the objective of eliminating the cantilevering of its head and of making it rigid. In fact, this solution arises because the wear of the grinding wheel requires it be replaced from time to time, the time for changing said wheel being a critical factor in some cases due to the short lifetime of said wheel; solution which reduce said grinding wheel replacement time have been sought.
In addition, the parts to be ground in centerless grinding machines can be loaded from the upper portion by means of a gantry solution, such that the part to be ground moves down until it is located between the grinding wheel and the regulating wheel, the axles of both wheels in this case being able to be parallel when they receive between them the part to be ground. This working mode is known as plunge grinding.
However, in through-feed grinding the parts to be ground are introduced in the machine in an axial direction passing between the grinding wheel and the regulating wheel. In this case, the regulating wheel is arranged with a certain inclination to cause the forward introduction movement of the part, such that the greater the inclination of the wheel, the higher the speed achieved for introducing the part. To that end, the regulating wheel is arranged in a head which is fixed in its rear portion with respect to the carriage of said regulating wheel by means of fasteners which can be loosened to change the inclination of the head with respect to the carriage, said fasteners being able to be formed by screws going through elongated holes, or said fasteners being able to be hydraulic fasteners which allow quicker locking and unlocking of the head with respect to the carriage. This solution establishes the fixing of the head of the regulating wheel with possibility of changing its position in inclination with respect to the carriage, but it is not efficient in eliminating the vibrations of said head of the regulating wheel, since the head is still arranged in a cantilever manner with respect to its fixing.
There is therefore a need to identify and modify in the mentioned machines structural parts the arrangement of which on one hand allows improving static rigidity and on the other improving dynamic behavior to prevent the damaging effect of vibrations and favor attainable productive capacity and precision.

Object of the Invention

In relation to said centerless grinding machines, the invention proposes an assembly of the head of a regulating wheel which eliminates the cantilevering of said head and makes it rigid, keeping it in an arrangement which aids in effectively reducing vibrations, during operational work of the machine.
The head of the regulating wheel is fixed on its supporting carriage in a conventional manner by means of rear fasteners, which can be screws or hydraulic devices, that can allow placing the head in an adjustable inclined position, keeping the head in a cantilever manner with respect to the fixing on the supporting carriage.
According to the invention, the fixing of said head of the regulating wheel is complemented with at least one additional fastening device arranged in the carriage, in relation to the lower and preferably front portion of the head. This fastening device acts in relation to a respective formation of the head, establishing an anchoring thereof which eliminates its cantilevering.
An anchoring for the head of a regulating wheel is thus obtained with a fixing reinforcement in the vertical direction of the cantilever arrangement, so vertical rigidity is achieved and horizontal rigidity is complemented, greatly reducing vibrations of said head due to stresses it receives during operational work of the machine.
If the additional fastening device is one in number, this device will preferably take up a lower arrangement, centered with respect to the head of the regulating wheel. Nevertheless and according to a preferred solution of a practical embodiment of the invention, arranging two additional fastening devices located close to the sides of the head has been envisaged, but obviously the number of additional fastening devices can vary without altering the essence of the invention.
The additional fastening devices can be with screws going through elongated holes or can be formed by pressure pistons pressing on corresponding formations of the head of the regulating wheel, said pistons being able to be hydraulic or pneumatic pistons; but also without it altering the object of the invention, said additional fasteners can be formed by any manually- or automatically-operated mechanical pressure device which allows establishing the corresponding anchoring.
In this same sense, an arrangement contrary to that already described in terms of the position of the elements forming each additional fastening device, i.e., the pistons being placed in the head and acting against the formations of the carriage, for example, would not alter the essence of the invention.
The proposed anchoring therefore has very advantageous features for eliminating work vibrations in centerless grinding machines, acquiring its own identity and preferred character of application with respect to conventional assemblies for said function.

Description of the Drawings

Figure 1 shows a schematic side elevational view of a conventional centerless grinding machine.
Figure 2 is a schematic perspective view of the assembly of the head of the regulating wheel on its supporting carriage, in a centerless grinding machine, according to the object of the invention.
Figure 3 is a side view of the assembly of the preceding figure with the additional fasteners of the lower portion of the head of the regulating wheel made with screws.
Figure 3.1 is a view such as that of Figure 3, but with the additional fasteners of the lower portion of the head of the regulating wheel arranged more towards the front.
Figure 4 is a view such as that of Figure 3, but with the additional fasteners of the lower portion of the head of the regulating wheel made with hydraulic devices.
Figure 5 is an enlarged detail of zone V of the preceding figure.

Detailed Description of the Invention

The Object of the invention relates to a centerless grinding machine for grinding cylindrical parts (5), which is made up of a grinding wheel (1), a regulating wheel (2) and a guide rod (13) on which the part (5) to be ground is supported, as seen in Figure 1. The aforementioned wheels (1 and 2) are incorporated in respective supporting carriages (3 and 4) allowing an approximation and separation movement for placing the wheels (1 and 2) a distance from one another, as needed depending on the part (5) to be ground.
As seen in Figure 1, the regulating wheel (2) is arranged in a head (6) which is fixed on the respective supporting carriage (4) by means of conventional rear fasteners (7), the head (6) is arranged in a cantilever manner with respect to said fixing, causing it to experience vibrations due to grinding stresses during operational work of the machine.
The conventional rear fasteners (7) can be four in number, said rear fasteners (7) establishing a fixing capable of allowing placement of the head (6) in an adjustable inclined position to facilitate loading the parts (5) to be ground by means of axial introduction in the machine. For that purpose, those rear fasteners (7) can be screws going through elongated holes, but they can also be hydraulic pressure devices, for quicker locking and unlocking of the fixing. The inclination of the head (6) can be changed by loosening the rear fasteners (7), tilting it with respect to the axis indicated with reference number (14) in Figure 2.
According to the invention, in order to prevent vibrations of the head (6) of the regulating wheel (2) in the position in which it is assembled in a cantilever manner on the supporting carriage (4), there is arranged in relation to the lower portion of the head (6) at least one additional fastener (8) complementing the fixing of said head (6) of the regulating wheel (2) in the vertical direction. According to a preferred embodiment depicted in Figure 2, the existence of two additional fasteners (8) is envisaged, one on each side of the head (6), but the number of such additional fasteners (8) can vary, without it altering the object of the invention.
Said additional fasteners (8) are devices acting in relation to corresponding formations (9) of the head (6); these devices can be formed by screws (10) going through elongated holes of the formations (9), as depicted in Figures 3 and 3.1, or they can be devices formed by pistons (11), preferably hydraulic pistons, acting in counter position on the formations (9) of the head (6), as depicted in Figures 4 and 5.
Nevertheless, for the function of holding on the formations (9) in order to secure the attachment of the head (6), the mentioned additional fasteners (8) can be formed by any manually- or automatically-operated hydraulic device, pneumatic device, mechanical device, etc., which allows applying pressure through one or both sides on the corresponding formations (9) to determine a fixing which secures the attachment of the head (6).
Figure 3 depicts the solution in which the additional fasteners (8) are formed by screws (10) going through elongated holes of the formations (9), as in the solution depicted in Figure 3.1, the difference between both solutions being the arrangement of the additional fasteners (8) being more or less towards the front. Logically, each machine configuration and morphology will establish which should be the best placement of the additional fasteners (8), but they will provide better anchoring when they are arranged more towards the front.
Similarly, when a single additional fastener (8) is chosen, its most logical arrangement is in the central lower portion of the head (6), whereas if there are two additional fasteners (8) their most logical arrangement will be symmetrical to the theoretical vertical midplane, transverse to the head (6) and, preferably as close as possible to the side ends of the head (6). If there are more than two additional fasteners (8), their most logical distribution would be to keep that symmetry, both aligned and not aligned with one another. Obviously, the different possible arrangements of the additional fasteners (8) do not alter the essence of the invention. Furthermore, although the logical arrangement of the additional fasteners (8) is in relation to the lower portion of the head (6), it would even be possible to consider a solution in which they act in relation to the upper portion of the head (6).
According to the present invention, the head (6) is thus fixed by means of the combination of the conventional rear fasteners (7) and the additional fastener or fasteners (8), with a horizontal and vertical attachment, which prevents or at least considerably reduces the production of vibrations due to grinding stresses during operational work of the machine, which allows achieving a much more precise grinding.
On the other hand, the arrangement of the additional fasteners (8) does not interfere with the freedom of positioning the head (6) in an adjustable inclination to facilitate loading parts (5) by means of axial introduction in the machine, since it is only necessary to loosen both the rear fasteners (7) and the additional fasteners (8) for that purpose, the head (6) therefore having freedom of movement for being placed with the desired inclination, once this has been done, the attachment again being secured by tightening the rear fasteners (7) and the additional fasteners (8) again, in the same conditions as before changing the positioning.
To facilitate assembling the additional fasteners (8) when they are hydraulic devices, the arrangement of a detachable part (12) fastened in a removable manner on the supporting carriage (4) of the head (6) is envisaged, but any other solution for assembling the mentioned additional fastening devices (8), for example, in housings defined by the actual structure of the supporting carriage (4), without detachable parts establishing said housings, the latter being closed by means of corresponding covers, does not alter the essence of the invention.
Logically and in a machine configuration in which the head (6) of the regulating wheel is not assembled on a carriage (4) but instead on another portion of the machine, this portion will incorporate the corresponding component of each additional fasteners (8) which would in turn be located in the carriage (4).

Claims

An anchoring for the head of a regulating wheel in a centerless grinding machine, the machine comprising a grinding wheel (1) and a regulating wheel (2), the regulating wheel (2) being arranged in a head (6) projecting in a cantilever manner, characterized in that there is at least one additional fastener (8) in the lower portion of the head (6) establishing an attachment aimed at eliminating the cantilevering of the head (6).
The anchoring for the head of a regulating wheel in a centerless grinding machine according to claim 1, characterized in that there are at least two additional fasteners (8), one on each side of the head (6).
The anchoring for the head of a regulating wheel in a centerless grinding machine according to claims 1 and 2, characterized in that the additional fasteners (8) consist of screws (10) going through elongated holes of formations (9) of the head (6).
The anchoring for the head of a regulating wheel in a centerless grinding machines according to claims 1 and 2, characterized in that the additional fasteners (8) consist of pistons (11) acting under back pressure on the formations (9) of the head (6).