Fly press

A fly press has a frame and a press screw rotatably mounted in said frame, and a flywheel attached for rotation with the press screw at one end, and a hydraulically driven ram rotatably attached to the other end of the press screw. An upper thrust bearing appears at one side of the frame for engagement by the flywheel, and a lower thrust bearing appears at the other side of the frame for engagement by a collar carried by the press screw. The upper and lower thrust bearings are spring biased in opposite directions. The abutment for the upper press bearing is engaged without impact when the collar disengages from the lower thrust bearing after the press blow to reduce the destructive effects on the bearing by press blows and return of the ram.

This invention relates to a fly press in which a press ram is driven by 
piston-cylinder means and constitutes a nut, which surrounds a press screw 
and has coarse screw threads in engagement with corresponding screw 
threads of the press screw, which is mounted in a cross head of the press 
frame. 
In known fly presses, a flywheel is mounted in the press frame, the press 
ram is vertically reciprocated by double-acting piston-cylinder means, and 
the energy stored in the flywheel is utilized for the press blow in that 
it is transmitted from the flywheel by the press screw and the coarse 
screw threads to the ram when the movement of the latter is reversed. 
In these fly presses in which the flywheel and the press screw are mounted 
in the press frame, the axial bearings in the cross head of the frame are 
highly loaded during the press blow. That load increases with the size and 
the cycle frequency of the press and may result in the destruction of the 
bearings. Besides, the ram is in high-friction contact with a shoulder 
stop as the press ram is returned by the piston-cylinder means and this 
friction should be reduced so that the ram can return freely. 
It is a main object of the invention to relieve the bearings of the frame 
from loads which are due to the press blow and from the frictional contact 
at the stop for the ram during the return thereof. 
In a fly press in which a press ram driven by piston-cylinder means 
constitutes a nut which is connected by coarse screw threads to a press 
screw, which carries a flywheel and is mounted in a cross head of a press 
frame, and in which said cross head is provided on one side with an upper 
thrust bearing for engagement by the flywheel and on the other side with a 
lower thrust bearing for engagement by a collar carried by the press 
screw, that object is accomplished in that the upper and lower thrust 
bearings are spring-biased in mutually opposite directions and a 
compensating ring is arranged to engage the abutment for the upper thrust 
bearing without impact when the collar disengages from the lower thrust 
bearing after the press blow. This arrangement will prevent a destruction 
of the bearings by the press blows and by the return of the ram. 
The compensating ring associated with the upper thrust bearing may rest on 
compensating springs, which are disposed in the bearing sleeve, and the 
upper thrust bearing may be engageable by stop ring, which is 
screw-threaded on mating screw threads of the press screw. 
According to a further feature of the invention a flanged bushing for 
retaining a washer and a disc spring is disposed in recess of the cross 
head and that recess contains also the lower thrust bearing, which is 
preferably provided on its other side with the collar carried by the press 
screw. As a result of this arrangement, the bearings are biased towards 
each other so that the formation of a bearing clearance, which would 
accelerate the wear of the bearing, is prevented during the press blow and 
return stroke of the press.

Certain features of the embodiment which will be described more fully 
hereinafter are apparent from U.S. Pat. No. 3,595,163, the disclosure of 
which is explicitly referred to and considered part of the present 
application. In that known fly press, the press screw carries two 
oppositely handed screw threads, which are in threaded engagement with a 
nut carried by the traverse of the press frame, particularly a nut which 
is rigid with said traverse and with the press ram so that the latter 
moves up and down at twice the speed of the screw. This arrangement 
enables a given number of press cycles to be performed per unit of time 
with a lower input power than was required before. 
The piston-cylinder units which at one end thereof engage the traverse and 
preferably extend through the same may engage at their other end a 
screw-mounting bridge member disposed between the oppositely handed screw 
threads. Alternatively, the piston-cylinder units bear at one end on the 
traverse of the press and at the other hand on a screw-mounting bridge 
disposed over the flywheel. In both cases, the piston-cylinder units move 
only at one-half of the speed of the vertically reciprocating ram of the 
press. Because the stroke of the piston is only one-half of the stroke of 
the ram, lower oil flow rates are sufficient so that the space requirement 
and structural expenditure are reduced and an overheating of the control 
valves is avoided. 
The press ram 29 of the fly press which is shown is driven by 
piston-cylinder means and constitutes a nut, which has coarse screw 
threads, which engage mating screw threads of a press screw 1, which is 
mounted in a cross head 3 of the press frame and carries a flywheel 2. 
This arrangement is known per se. It is apparent from the drawing that an 
upper thrust bearing 4 provided on the cross head 3 is engageable by the 
flywheel 2 and a lower thrust bearing 5 is engageable by a collar 6 
carried by the press screw when the latter rotates during the return 
stroke of the ram. The upper thrust bearing 4 for supporting the flywheel 
2 is supported in a bearing sleeve 7 on a compensating ring 8, which is 
disposed in a recess of the sleeve 7 and which rests on compensating 
springs 9 also disposed in said recess. The press screw 1 has a portion 11 
in screw-threaded engagement with a stop ring 10, which is engageable with 
the top of the bearing 4. The cross head 3 has on its underside a recess 
12, which contains a washer 15, a flanged bushing 13, and a disc spring 14 
between the washer 15 and the underlying flange of the flanged bushing 15. 
The recess 12 contains also the lower thrust bearing 5, which bears at its 
top on the flanged bushing 13 and is provided at its bottom with a 
pressed-on backing ring 16, which rests on the collar 6 carried by the 
press screw so that the bearings are urged toward each other. A stop ring 
10 associated with the upper thrust bearing 4 is screw-threaded on a 
portion 11 of the press screw and is enclosed by a centering ring 17, 
which supports the flywheel 2, which is fitted on the tapered end portion 
18 of the press screw 1. Screws 19 are fitted in the flywheel and extend 
through the centering ring 17 and are screw-threaded in peripherally 
spaced apart, tapped bores formed in the stop ring 10 to hold down the 
flywheel 2 and the centering ring 17 on the stop ring 10. 
The backing ring 16 associated with the lower thrust bearing 5 is 
surrounded by a stop ring 20, which is disposed in an annular recess 21 
formed in the cross head 3 around the recess 12. The stop ring 20 is 
formed with angularly spaced apart oil bores 22, which extend radially 
through the stop ring 20 and are open at opposite ends, and is spaced by a 
clearance S above the collar 6 carried by the press screw. The stop ring 
20 serves to take up the force (arrow P), which is due to the main blow of 
the press. 
An oil bath B is held between the stop ring 10 and a sealing ring 23 fitted 
on the stop ring 10 and in the upper bearing sleeve 7, and the collar 6 
carried by the press screw and a sealing ring 24 fitted on said collar and 
in a carrying ring 25. The oil is forced up through helical grooves 26 on 
the backing ring 16 into the clearance space defined by the stop ring 20 
during the upward movement of the press ram 29 and can escape through 
bores 22 without a pressure peak during the force (arrow P) which is due 
to the press blow. In conjunction with the other features which have been 
described, the arrangement of all axial and radial bearings for the press 
screw 1 in an oil bath B in the cross head 3 results in a substantial 
decrease of the load on the bearings during the press blows and of the 
stop for the ram 29 during the upstroke. 
During the downstroke of the ram 29, the weight of the moving masses 
results in rolling friction in the thrust bearings 4 and 5, which consist 
of axial roller bearings. The entire press screw 1 runs in an oil bath. 
During the press blow, the oil volume disposed in the clearance space S 
defined by the stop ring 20 is displaced toward the press screw and the 
collar 6 then bears on the stop ring 20, which is made from a bronze alloy 
hardened steel. The thrust bearings 4 and 5 are thus relieved. The upper 
bearing sleeve 7 is lined by a sliding surface bearing bushing 27. The 
shaft of the press screw 1 is surrounded by a sliding surface bearing 
bushing 28 above the lower supporting bearing 5. 
During its return stroke, the ram 29 is pushed against the press screw so 
that the collar 6 is forced against the stop ring 20 and thus tends to 
displace the oil film. This could block the rotational movement if such 
blockage were not prevented by the provision of the flanged bushing 13, 
which is associated with the lower thrust bearing 5 and biased by an 
oppositely acting spring 14. In this way, rolling friction in the lower 
thrust bearing is eliminated during the press blow so that damage to the 
bearing is prevented.