Hydraulic cylinder apparatus

An improved hydraulic press having adjustable preloading or prestressing means on the cylinder body to compensate for, and neutralize, any deflection or deformation of the cylinder body under the hydraulic pressures at which the press operates. The press is designed to operate at zero clearance.

The present invention relates to an improved hydraulic press, and, in 
particular, to an improved hydraulic press wherein the piston body of the 
press is adapted to operate at zero clearance. 
The hydraulic press of this invention represents an improvement over the 
hydraulic press which is the subject matter of U.S. Pat. No. 3,592,131. In 
the operation of a hydraulic press of the type shown in the patent, the 
cylinder of large diameter at the open end of the hollow cylinder body is 
deformed or deflected slightly under load. More specifically in this 
connection, fluid pressure within the cylinder of the press causes radial 
expansion of the cylinder. In order to develop fluid pressure, load must 
be applied to the movable platen of the press which must be resisted by 
the stationary platen of the press. Under load, the diagonal distance 
across the tie rods of the press decreases, while the distance across the 
cylinder, at midpoints between the tie rods, increases. This deflection, 
while small, can result in severe overloading of the rollers which guide 
the ram extension of the piston body during its upstroke, and which are 
mounted within the large diameter of the cylinder as is the case with the 
press shown in the aforementioned patent. Overloading of the rollers can 
adversely affect their useful life. 
As disclosed in U.S. Pat. No. 3,592,131, zero clearance for the guiding of 
the ram extension of the piston body is attained by radially adjusting a 
plurality of circumferentially spaced rollers carried on roller supports 
secured directly to the cylinder body. The roller supports are vertically 
adjustable with relation to brackets which extend downwardly along the 
periphery of the large diameter cylinder at the upper, open end of the 
hollow cylinder body of the press, and the amount of vertical adjustment 
of the roller supports is determined by a shim associated with each of the 
brackets and the roller supports. By appropriate grinding, the thickness 
of the shims may be adjusted to cause the rollers to engage the ram 
extension of the piston body with a desired amount of preloading. When all 
of the rollers are thusly radially adjusted, zero clearance for the 
guiding of the ram extension of the piston body is provided. While the 
arrangement disclosed in the patent is capable of providing preloading to 
obtain zero clearance for the stated purpose, in accordance with the 
present invention, improved preloading or prestressing means has been 
evolved which more simply, effectively and efficiently enables a desired 
amount of preloading to be applied at critical areas of a hydraulic press. 
The preloading or prestressing means of this invention acts to neutralize 
and dissipate any deflection or bending of the components of a hydraulic 
press under load thereby preventing any overloading of the rollers which 
guide the ram extension of the piston body of the press. The resulting 
longer useful life of the rollers has important economic advantages both 
from the standpoint of parts replacement costs and press downtime. 
In brief, the preloading or prestressing means comprises radially 
adjustable, piston engaging guide means, and vertically adjustable, 
cylinder body engaging means. The piston engaging guide means and the 
cylinder body engaging means advantageously are supported on a plate 
member adapted to be removably secured to the cylinder body of a hydraulic 
press. The plate member is provided with a central opening, and the piston 
engaging guide means which, in a preferred embodiment of the invention, 
comprises a plurality of rollers, of the type disclosed in U.S. Pat. No. 
3,592,121, arranged in circumferentially spaced relation to one another at 
the opening in the plate member. The plate member also is provided with a 
plurality of extensions adapted to be positioned between the tubular 
columns surrounding the tie rods of a hydraulic press. The extensions 
support the vertically adjustable, cylinder body engaging means. In a 
preferred embodiment of the invention, the cylinder body engaging means 
comprises a retainer plate and a wedge-like member having interengaging 
cam surfaces. The retainer plate and the wedge-like member desirably are 
adjustably secured on an outer, overhanging margin or edge portion of the 
extensions of the plate member in a manner to enable a surface of the 
wedge-like member to engage the outer surface of the cylinder body. By 
proper adjustment of the rollers in relation to the piston body, and the 
wedge-like members along the margins of the extensions of the plate 
member, any bending and shear deflection to which the cylinder body of a 
hydraulic press is subjected under load will be effectively neutralized 
resulting in zero clearance for the guiding of the piston body. This 
arrangement prevents overloading of the guide rollers of the press, and 
provides much greater accuracy, and substantially reduces any deflection 
of the movable platen of the press when it is subjected to off center 
loading.

Since the present invention represents an improvement in the hydraulic 
cylinder apparatus disclosed in U.S. Pat. No. 3,592,131, the invention 
will be described in relation to its use in such apparatus. However, it 
should be understood that the invention may be used in other forms of the 
apparatus, including a hydraulic press employing three instead of four tie 
rods, for example, as shown in said patent. Referring, now, in particular, 
to FIGS. 1, 2 and 3 of the drawings, the press structure diagrammatically 
illustrated, and designated generally by reference numeral 10, includes a 
supporting base 12 suitably secured to a foundation 14. A bed member 16 is 
secured to the base 12, and a plurality of tubular columns 18 extend 
upwardly from the bed member 16 to support a crown member 20. As shown, 
the crown member 20 is provided with a downwardly facing stationary platen 
22. The press structure 10 advantageously is prestressed by means of 
threaded tie rods 24 which extend through the bed member 16, the column 18 
and the crown member 20 upon which tie rod nuts 24a and 24b are threadly 
mounted for prestressing purposes. 
The bed member 16 is in the form of a hydraulic cylinder body 16a which is 
open at the top and closed at the bottom. The cylinder body 16a has a 
cylinder 26 of large diameter at the open end thereof, and a cylinder 28 
of small diameter at the closed end communicating with the cylinder 26 
substantially midway between the open and closed end of the cylinder body 
16a. A piston body 30 is longitudinally movably received in the cylinder 
body 16a, and intermediate its ends is provided with a piston 30a of large 
diameter which is received in the large diameter cylinder 26. The piston 
body 30 also includes a piston extension 30b of small diameter which is 
received in the small diameter cylinder 28, and a ram extension 32 of 
intermediate diameter which extends through the open end of the cylinder 
26. A platen 34 is secured to the top of the ram extension 32, and 
constitutes the movable platen of the hydraulic press structure 10. The 
piston 30a is provided with annular hydraulic packing 36 which is held in 
place by a shouldered bushing 38 engaging a shoulder on the piston 30a and 
a shouldered bushing 40 having an upwardly facing shoulder. A retainer 
ring 42 is suitably secured to the piston 30a, and engages the shoulder on 
the bushing 40 for maintaining the bushings 38 and 40 and the hydraulic 
packing 36 in place on the piston 30a. 
As best illustrated in FIGS. 2, 3 and 5 of the drawings, the preloading or 
prestressing means of the present invention comprises a plate member 50 
secured to the cylinder body 16a by screws 52 and nuts 54. The plate 
member 50 is provided with a central opening 56 through which the upper 
portion of the ram extension 32 and the platen 34 extend. Radiating 
outwardly from the opening 56 are a plurality of spaced extensions 58 
which, as shown in FIG. 2, are positioned substantially midway between the 
tubular columns 18, and their associated tie rods 24, of the press 10. 
While the plate member 50 is illustrated as having two pairs of opposed 
extensions, the number of extensions on the member 50 will be determined 
by the number of tie rods comprising the press. Thus, in a three tie rod 
press, the plate member will have a corresponding number of extensions, 
each extension being positioned substantially midway between the tie rods. 
Referring, now, in greater detail to FIGS. 2 and 5 of the drawings, the 
plate member 50, at the opening 56 therein, has an annular, downwardly 
facing flange 50a which is received in an annular recess 16b provided at 
the open end of the cylinder body 16a. The ram extension 32 of the piston 
body 30 is guided for longitudinal movement by a plurality of 
circumferentially spaced guide rollers 60, rotatably mounted on roller 
supports 62, secured, as by screws 64 and 66, to the plate member 50 along 
an annular recess 50b formed at the periphery of the opening 56 therein. A 
plurality of brackets 68 are adjustably secured to the plate member 50 by 
screws 70. Each bracket 68 includes a downwardly extending leg 68a which 
is received in the recess 50b and which is provided with a cam surface 
68b. The cam surface 68b engages a cam surface 62a on the roller supports 
62. The roller supports 62 are bifurcated as illustrated in FIG. 4 for 
receiving the guide rollers 60. A pin 72 having a head 72a extends through 
the bifurcated end of each of the roller supports 60, and is provided with 
a reduced threaded portion for receiving a nut 74 for securing the pin 72 
in place on the support 62. As best illustrated in FIG. 5, the guide 
rollers 60 preferably are in the form of a roller bearing having an inner 
race 60a carried by the pin 72, a plurality of rollers 60b, and an outer 
race 60c which engages, and guides, the ram extension 32 of the piston 
body 30. The ram extension 32 advantageously is provided with a plurality 
of flat inserts 76 which present flat surfaces against which the outer 
race 60c rolls as the ram extension 32 is moved upwardly and downwardly. 
These surfaces provide a sound base for preloading the guide rollers 60, 
as will be described below, and also tend to prevent rotation of the 
piston body 30 with respect to the cylinder body 16a. In this same 
connection, as shown in FIG. 4, a bracket 78 desirably is secured as by 
screws 80 to the plate member 50, and supports a key 82 received in a 
keyway 84 formed in the ram extension 32 of the piston body 30. The key 82 
and the keyway 84 operate to prevent rotation of the piston body with 
relation to the cylinder body as the piston body is longitudinally moved. 
Each of the extensions 58 of the plate member 50 has an end portion 58a 
which overhangs and extends beyond a wide flange 16c formed at the upper 
edge of the cylinder body 16a. A retainer plate 86, having a cam surface 
86a, is secured to the end of the portion 58a by screws 88. A wedge-like 
cam member 90, having a cam surface 90a, is secured, as by screws 92, to 
the underside of the end portion 58a. The cam surface 90a of the member 90 
engages the cam surface 86a of the retainer plate 86, while the inner 
surface 90b of the member 90 engages the outer surface of the flange 16c 
of the cylinder body 16a. 
In utilizing the preloading or prestressing means of the present invention 
to achieve zero clearance for the guiding of the ram extension 32, and to 
neutralize any deflection or deformation of the cylinder body 16a under 
load, the guide rollers 60 are radially adjusted with relation to the ram 
extension 32 by vertical adjustment of the leg 68a of each bracket 68 with 
respect to the cam surface 62a on the roller supports 62. When all of the 
guide rollers 60 are thus appropriately radially adjusted with the desired 
amount of preloading, zero clearance for the guiding of the ram extension 
32 of the piston body 30 is provided. Since the guide rollers 60 are in 
the form of ball bearings, there is minimum resistance to the longitudinal 
movement of the ram extension 32 even though it is guided at zero 
clearance. As in the case of the press disclosed in U.S. Pat. No. 
3,592,131, fluid pressure within the cylinder 26 of the press 10 of the 
present invention causes radial expansion of the cylinder. Fluid pressure 
is developed by applying load to the movable platen 34 which must be 
resisted by the stationary platen 22. Under load, the diagonal distance 
across the tie rods 24 decreases, while the distance across the cylinder 
26 at the midpoints between the tie rods 24 increases. The plate member 
50, due to its unique mounting in relation to the cylinder 24, does not 
experience any stresses, and, therefore, any deformation due to fluid 
pressure within the cylinder 24. In order to compensate for any radical 
expansion of the cylinder 26 under load, the cam surface 90a of each 
wedge-like cam member 90 is preselectedly vertically adjusted with respect 
to the cam surface 86a of each of the retainer plates 86. By thus 
appropriately prestressing this area of the cylinder body 16a, any radial 
expansion of the cylinder 26 at the positions where the retainer plate 86 
and the wedge-like cam member 90 are located is effectively absorbed or 
neutralized by the retainer plate 86. The guiding accuracy of the 
arrangement thereby is maintained during the complete upstroke of the 
piston body, and no overloading of the rollers 60 occurs. 
While for purposes of illustration, one embodiment of this invention has 
been described, other forms thereof may become apparent to those skilled 
in the art upon reference to this disclosure, and therefore, this 
invention is to be limited only by the scope of the appended claims.