EP0666141A1

EP0666141A1 - Lapping machine

Info

Publication number: EP0666141A1
Application number: EP95300672A
Authority: EP
Inventors: Allan Grainger
Original assignee: Actis (UK) Ltd
Current assignee: Actis (UK) Ltd
Priority date: 1994-02-04
Filing date: 1995-02-02
Publication date: 1995-08-09
Also published as: GB9502090D0; GB2286139A; GB9402140D0

Abstract

A lapping machine comprises a rotatable lapping plate (1) and a lapping arm (6) disposed above the lapping plate (1), orthogonally to the plane of the lapping plate (1). The lapping arm (6) has a lapping head (15) at a lower end thereof and is pivotally connected by a pair of parallel connecting members (4,5) to a support column (3). The lapping plate (1) is rotated by a motor (17), which also rotates the lapping head (15), via a drive shaft (22) enclosed within the support column (3) and a driven shaft (29) enclosed within the lapping arm (6).

Description

This invention relates to a lapping machine, in particular to a lapping machine useful in the lapping of internal seal faces.
Lapping equipment is conventionally used to effect polishing and truing operations that call for a high quality precision finish, such as the faces of mechanical seals. Mechanical seals can be broadly classified as external seals, in which the seal faces are on outer end faces, and internal seals, in which the seal faces are recessed and are adjacent to an internal diameter.
Since it is relatively easy to produce external surfaces which meet the specifications for flatness, smoothness and hardness required of sealing faces, the technology of external seals is advanced. It is much more difficult to develop internal surfaces with similarly high specifications. For this reason internal seals are relatively little-used, even though they offer significant advantages of compactness and efficiency, particularly where there is a large pressure difference across the seal.
It is an object of this invention to provide a lapping machine with which internal surfaces may be produced to specifications comparable to those conventionally attainable for external surfaces.
According to the invention, there is provided a lapping machine comprising a rotatable lapping plate, a lapping arm disposed above the lapping plate, orthogonally to the plane of the lapping plate, the lapping arm having a lapping head at a lower end thereof, and the lapping arm being pivotally connected by a pair of parallel connecting members to a support, the arrangement being such that the lapping head may be introduced into a workpiece supported by the lapping plate.
The lapping arm will generally be disposed vertically and the lapping plate horizontally.
The support is conveniently in the form of a rigid column arranged orthogonally to the plane of the lapping plate. The lapping arm, the column and the pair of parallel connecting members thus define a parallelogram linkage. Though the lapping arm may, by virtue of its pivotal linkage to the support, be moved in a vertical plane passing through the support, the parallelogram arrangement ensures that it remains parallel to the support and hence orthogonal to the lapping plate. The plane of action of the lapping head will be orthogonal to the longitudinal axis of the lapping arm, and hence the internal surface of the workpiece is lapped in a plane which is parallel to the lapping plate. A high degree of parallelism is thus achieved between the internal surface of the workpiece and the datum face defined by the external surface of the workpiece which rests upon the lapping plate.
The lapping plate may be generally conventional and preferably has an abrasive surface, which may be of conventional form. The abrasive surface laps the external surface of the workpiece which rests upon the lapping plate.
The pivotal linkages between the lapping arm and the pair of parallel connecting members permit movement of the lapping arm in a single plane, which as described above is preferably a vertical plane. The connection of the parallel connecting members to the support, however, may be through universal linkages permitting movement of the lapping arm relative to the support also in a horizontal plane. This may be advantageous, for example permitting the lapping arm to be swung away from the lapping plate, thereby to facilitate positioning of a workpiece on the drive plate. The parallel connecting members may, for instance, be connected to rotatable collars mounted on the support which, in such a case, is suitably a cylindrical column.
The connecting members, or one of them, preferably the upper connecting member, is or are preferably provided with an adjustable counterweight by which the downward force exerted by the lapping arm on the workpiece may be controlled.
The lapping plate is preferably rotated by suitable drive means. The drive means may comprise a motor, eg an electric motor.
It is particularly preferred that the lapping head should also be rotated. Conveniently, the same motor is used to drive both the lapping head and the lapping plate. The motor is preferably coupled to a drive shaft disposed within the support. The drive shaft in turn is connected by suitable means, eg a belt and pulleys, to a driven shaft disposed within the lapping arm, the driven shaft being connected at its lower end to the lapping head.
The direction of rotation of the motor is preferably reversible, eg through a suitable inverter mechanism.
The invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which

Figure 1 is a schematic side view, partly cut away and in section, of a lapping machine according to the invention, and
Figure 2 is a sectional view along the line II-II in Figure 1.

Referring first to Figure 1, a lapping machine comprises a revolving lapping plate 1 having an abrasive upper surface 2. The abrasive surface 2 is horizontal and thus rotates in a horizontal plane.
A vertical support column 3 stands in fixed spatial relationship to the drive plate 1 and is connected by lower and upper rigid connecting linkages (4,5 respectively) to a lapping arm 6. The lapping arm 6 is disposed perfectly parallel to the support column 3, ie vertically, and defines with the column 3 and the connecting linkages 4,5 a parallelogram.
The lower connecting linkage 4 comprises a pair of rods connected, through diametrically opposed pivots 9, to a first collar 11 which fits closely, but is freely rotatable, about the cylindrical support column 3. Likewise, the upper connecting linkage 5 comprises a pair of rods connected at pivots 10 to a second, also freely rotatable, collar 12. The pairs of rods constituting the upper and lower connecting linkages 4,5 are strengthened by rigid cross-ties 32,33.
The right hand (as viewed in Figure 1) ends of the lower and upper connecting linkages 4,5 are connected by vertical pivotal linkages 34. Similarly, the left hand ends are connected by the lapping arm 6, which is disposed centrally of the rods constituting the lower and upper connecting linkages 4,5 and connected to them at pivots 7,8.
The lapping arm 6 may be moved in a vertical plane by virtue of pivotal connection of the arm 6 to the connecting linkages 4,5 and of the rods 4,5 to the support column 3 (through the pivots 9,10). Movement of the lapping arm 6 is also permitted in a horizontal plane by virtue of the fact that the first and second collars 11,12 are freely rotatable about the cylindrical support column 3. The first and second collars 11,12 are provided with clamp mechanisms 36,37 by which rotation of the collars 11,12 can be prevented.
The vertical pivotal linkages 34 support a counterweight 13. Adjustment of the counterweight 13 alters the downward force exerted by the lapping arm 6.
The lapping arm 6 carries at its lower end a lapping head or tool 15 with an abrasive undersurface. The lapping tool 15 is disposed with its abrasive undersurface orthogonal to the longitudinal axis of the lapping arm 6, ie horizontal.
The mechanism by which the lapping tool 15 is rotated will now be described. An electric motor 17 is connected by a suitable drive coupling 19 to a drive shaft 22 disposed within the column 3 and mounted in a bottom bearing 20 and a top bearing 21. An inverter 18 is used to control the direction and speed of rotation of the drive shaft 22. The motor 17 is also used to drive the lapping plate 1.
The upper end of the drive shaft 22 is connected to a drive pulley 23 which in turn is connected by a belt 35 to a driven pulley 24 mounted on the splined end 28 of a driven shaft 29 disposed within the lapping arm 6 and mounted in top and bottom bearings 30,31. The lower end of the driven shaft 29 is fixed to the lapping tool 15. A self-adjusting belt tensioner 25 is provided which is mounted on a pulley base plate 26. The arrangement of belt 35 and pulleys 23,24 is enclosed within a safety cover 27.
In use, the lapping arm 6 is raised, and a workpiece 16 is positioned on the lapping plate 1. The lapping arm 6 is then lowered until the abrasive surface of the tool 15 contacts the internal surface of the workpiece 16. The motor 17 is then engaged to rotate the lapping plate 1 and the lapping tool 15, the workpiece 16 being held captive by the lapping tool 15 and rotating about it.
As it passes beneath the workpiece 16, the abrasive surface of the lapping plate 1 laps the external, lower surface of the workpiece 16. At the same time, the lapping tool 15 laps the internal surface of the workpiece 16. The strict orthogonality of the lapping plate 1 and the lapping arm 6 results in a high degree of parallelism between the upper and lower surfaces of the workpiece 16.

Claims

A lapping machine comprising a rotatable lapping plate, a lapping arm disposed above the lapping plate, orthogonally to the plane of the lapping plate, the lapping arm having a lapping head at a lower end thereof, and the lapping arm being pivotally connected by a pair of parallel connecting members to a support, the arrangement being such that the lapping head may be introduced into a workpiece supported by the lapping plate.
A lapping machine as claimed in Claim 1, wherein the lapping arm is disposed vertically and the lapping plate horizontally.
A lapping machine as claimed in Claim 1 or Claim 2, wherein the support is a rigid column arranged orthogonally to the plane of the lapping plate, the lapping arm, the column and the pair of parallel connecting members defining a parallelogram linkage.
A lapping machine as claimed in any preceding claim, wherein the lapping plate has an abrasive surface.
A lapping machine as claimed in any preceding claim, wherein the parallel connecting members are connected to the support through universal linkages permitting movement of the lapping arm relative to the support in a horizontal plane.
A lapping machine as claimed in Claim 5, wherein the parallel connecting members are connected to rotatable collars mounted on the support.
A lapping machine as claimed in any preceding claim, wherein the connecting members are provided with an adjustable counterweight by which the downward force exerted by the lapping arm on a workpiece may be controlled.
A lapping machine as claimed in any preceding claim, wherein the lapping head is rotated by a motor.
A lapping machine as claimed in Claim 8, wherein the motor is coupled to a drive shaft disposed within the support, the drive shaft is connected by suitable means to a driven shaft disposed within the lapping arm, and the driven shaft is connected at its lower end to the lapping head.
A lapping machine as claimed in Claim 9, wherein the motor is also used to rotate the lapping plate.