Opposed endless belt grinding apparatus

Grinding apparatus for retaining and grinding workpieces comprises two endless abrasive belts guided to move in a direction opposed to the direction of movement of the workpieces. An angularly adjustable support biasses each abrasive belt to converge towards the direction of movement of the workpieces and the spacing of one or both abrasive belts is adjustable in response to the workpiece size. A disc having apertures therearound and rotatable so that workpieces in the apertures pass between the endless belts to grind the exposed ends of the workpieces.

BACKGROUND OF THE INVENTION 
This invention relates to grinding apparatus and particularly though not 
exclusively to apparatus for the grinding of the ends of helical springs. 
Heretofore it has been customary to sandwich grind, i.e. grind the opposed 
ends of a helical spring or other workpiece simultaneously, by passing the 
spring between two spaced, co-axial, rotating abrasive wheels. For this 
purpose the spring is held in a rotary magazine and is traversed about an 
axis lying parallel with the abrasive wheel axis into and out of the space 
between the two abrasive wheels, the axis of the spring also being 
parallel with the aforementioned axes. The material is ground from the 
ends of the spring progressively by reducing the spacing between the 
abrasive wheels. This type of arrangement has certain disadvantages. If 
production rates are to be maximised it is necessary for the material 
removal rate by the abrasive wheels to be high. In consequence, 
considerable heat is generated which can alter the temper and mechanical 
qualities of the springs. In addition the abrasive wheels are subject to 
considerable wear, and require frequent dressing, for example every half 
hour, involving machine `down-time` and subsequent machine resetting in 
order to produce springs of predetermined dimensions. Replacement of 
excessively worn abrasive wheels is also a time consuming and therefore 
costly operation in terms of lost production. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide apparatus for use in 
the grinding of the ends of springs or other workpieces, which enables 
high rates of material removal without heat degradation of modification of 
the spring or workpiece, and with which less machine down-time is required 
due to dressing, adjusting or replacement of grinding means than was 
necessary with apparatus used heretofore. 
The invention provides grinding apparatus for grinding workpieces 
comprising holding means adapted to retain a workpiece with opposed ends 
thereof extending therefrom, a pair of endless abrasive belts disposed on 
opposed sides of said holding means, each belt having a run thereof guided 
in spaced relationship with said holding means along a path adjacent and 
diverging from a path of relative movement between said run and the 
holding means. Preferably a surface of each belt run opposed to an 
abrasive surface thereof is in contact with respective support means 
operable to bias said abrasive surface into contact with the respective 
end of a workpiece. Each support means may have a belt support which 
converges towards the holding means in the relative direction of motion 
between the holding means and the abrasive belt. 
Moving means may be provided to move the holding means into a space between 
the two endless abrasive belts, such space being defined by a repective 
one run of each of the belts. 
The grinding apparatus may comprise fluid supply means operable to supply 
cooling fluid thereto, and also may comprise a coolant clarifier operable 
to collect and dispose of debri cut from the workpiece. 
Preferably one abrasive belt is positionally adjustable towards and away 
from the other, or both are adjustable, to adjust the overall length of 
the ground workpiece. The apparatus may comprise workpiece gauging means 
operable to gauge the length of a ground workpiece and to cause movement 
of the adjustable abrasive belt towards or away from the other in 
accordance with a difference in the length gauged by said gauging means 
and a predetermined length. Preferably said gauging means is a non-contact 
gauging means. 
The holding means may comprise a disc shaped member having a plurality of 
apertures therein adjacent the periphery thereof, each aperture being 
adapted to retain a workpiece therein with the opposed ends thereof 
protruding from said aperture at opposed sides of said disc shaped member. 
The disc shaped member may be mounted so as to be rotatable about an axis 
substantially perpendicular to the direction of travel of said one runs of 
said abrasive belts with said periphery extending between said one runs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1 to 3 there is shown a twin belt grinding machine 
30. The machine 30 comprises a magazine 31 having apertures 32 in which 
springs or other workpieces 33 are received for grinding. The machine 30 
also comprises lower and upper grinding units 34, 35 respectively, each 
having an endless abrasive belt 36 driven in the direction shown by the 
arrows by respective driving pulleys 37 and passing round two idler 
pulleys 38. The pulleys 38 provide substantially horizontal runs 39 of the 
belts 36, each of which passes in contact with a respective supporting 
platen 40. The magazine 31 is mounted in the machine 30 for rotation in 
the direction shown by the arrow about a vertical axis 41 laterally spaced 
from the plane of movement of belts 36 so that the springs 33 pass in 
succession into the space between the runs 39 of belts 36. The lower 
grinding unit 34 is fixed in the machine 30 whereas the upper grinding 
unit 35 is mounted on a slide 43 which is movable vertically by means of 
control unit 42 so as to adjust the relative spacing of runs 39 of belts 
36 for differing required machined lengths of springs 33. The control unit 
42 comprises a ball screw 44 and DC electric servo-motor (not shown) 
equipped with a positional feed back transducer to determine the machined 
length of springs 33. A non-contact gauging device 61 of only conventional 
type may be coupled to the servo-motor to adjust the position of grinding 
unit 35 to provide the desired machined length of springs 33. The speed of 
rotation of magazine 31 may be varied to adjust the rate of feed of 
springs 33 between the belt runs 39. The guide platens 40 have 
belt-contacting faces converging in the direction of feed of the springs 
33 so that material is progressively ground from the ends of each spring 
33 as it is fed between the belts 36. The angular disposition of the guide 
platens 40 relative to each other may be varied by adjustment means 60 of 
any conventional type to vary the angle of convergence and thereby control 
the rate of progressive depth of grinding cut applied to the springs 33. 
As shown in FIG. 3 the belt-contacting, converging surface of guide 
platens 40 are flat, but alternative profiles of platen may be used if 
desired. These surfaces are hardened to prevent pick up of abrasive belt 
backing material and have radiussed leading and trailing edges. The idler 
pulley 38 disposed between the drive pulley 37 and the run 39 of each belt 
is positionally adjustable on the respective grinding unit 34 or 35 by 
hydraulic means (not shown) so as to tension the abrasive belt 36. In 
addition the provision of three pulleys 37, 38, 38 for each belt 36 
enables a longer belt 36 to be used in comparison with a two-pulley 
arrangement. 
In this way the life of belt 36 is prolonged, it runs at a lower 
temperature and is less prone to becoming "clogged" with material cut from 
springs 33 than with a two pulley arrangement. The grinding belts 36 are 
driven by an electric motor (not shown). 
To exploit the high metal removal rate possible with the machine 30 it is 
provided with means for supplying coolant fluid to the grinding region. 
This prevents or substantially reduces the generation of heat which could 
alter the temper and mechanical qualities of the ground springs whilst 
enabling high feed rates of springs through the machine. As shown in FIG. 
3 coolant nozzles 45 are mounted on the respective grinding unit 34, 35 to 
supply coolant fluid at the level of each abrasive belt run 39 in the 
grinding region. To maintain the coolant fluid in the grinding region 
resiliently flexible curtains 46, preferably of rubber, are provided on 
each grinding unit 34, 35 around this region, the curtains 46 overlapping 
to sufficient an extent to provide an effective shield throughout the 
range of vertical adjustment of grinding unit 35. At the locations of 
entry to and exit from the grinding region of the springs 33 in the 
magazine 31 the curtains 46 may be cut into strips or brushes or other 
suitable space sealing means may be provided. 
The machine 30 may be provided with a coolant clarifier pumping system (not 
shown) which automatically collects and disposes of the metal debris in a 
chute remote from the machine 30. 
A suitable control system for the machine 30 is shown diagrammatically in 
FIG. 4. The microprocessor control unit 47 is programmed to control the 
motors of machine 30 in response to instructions entered therein on 
keyboard 48. Controllable items are machine on/off 49, magazine rotational 
speed 50 and position 51, positional adjustment 52 of support platens 40, 
belt tensioning 53, belt drive on/off 54 and speed 55 and non-contact 
gauge setting 56. Data relating to the abovementioned items may be 
displayed on screen 57 or presented digitally at 58. The machined spring 
size as determined by the gauge is displayed digitally at 59 and can be 
compared with the gauge setting information supplied to the control unit 
47. Other controls incorporated into the control system may be; abrasive 
belt drive initiated before magazine drive initiated; abrasive belt speed 
and support platen position adjusted in accordance with data relative to 
the type of spring being ground; automatic upward movement of slide 43 if 
non-standard operation of machine 30 occurs; coolant fluid feed rate 
dependent upon the prevailing grinding conditions and push-button override 
of the automatic operation of the machine if required. 
By means of the invention the production rate of the sandwich grinding of 
springs or the like workpieces may be increased by a factor of up to 30 by 
comparison with the twin abrasive wheel machines presently used. In 
addition the cost of grinding the workpieces can be reduced by a factor of 
up to 12. A further advantage of the machine of the present invention lies 
in the aspect of machine down-time, it taking approximately 5 minutes to 
change the abrasive belts when worn or damaged and approximately 21/2 
hours to change worn or damaged abrasive wheels. Furthermore the frequent 
dressing of the abrasive wheels and readjustment of the machine necessary 
with the twin abrasive wheel machines is avoided. 
The apparatus described herein has the springs disposed vertically and 
travelling in a horizontal plane to be ground, the belt or belts lying in 
a vertical plane. If desired the springs may be mounted so as to be 
disposed horizontally and to travel in a vertical plane to be ground. 
Workpieces other than springs may be ground with the apparatus herein 
described, particularly if such other workpieces are to be duplex or 
sandwich ground to accurate dimensions. 
In the apparatus of FIGS. 1 to 3 both of the abrasive belts 36 may be 
movable towards or away from each other if desired, i.e. the lower 
grinding unit 34 may have a position control unit 42 associated therewith. 
Also the movement of one or both grinding units may be controlled by a cam 
device instead of the ball screw as hereinbefore described.