Overload protector for mechanical press

Details Overload protector for mechanical press Overload protector for mechanical press

2000-03-24

2002-10-01

Gerrity, Stephen F. (Department: 3721)

Presses

Safety device

Means to disable or to forestall power to the press

C100S269140, C072S021500, C072S453130

Reexamination Certificate

active

06457406

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an overload protector for a mechanical press and more particularly to an overload protector which is used in a mechanical press of multi-point type having a slide connected to a crank shaft through a plurality of connecting rods.
2. Description of Prior Art
There is a conventional overload protector recited in Japanese Utility Model Publication No. 6-18720 as an example of the overload protector of this type. The conventional overload protector is constructed as follows.
Two overload absorbing hydraulic chambers are formed within a slide. The respective hydraulic chambers have pressure receiving members vertically movably inserted thereinto. The pressure receiving members are connected to a crank shaft through connecting rods. The pressure receiving members each has a closing contact portion on its upper end surface. The closing contact portion is brought into closing contact with an under surface of an upper wall of the hydraulic chamber through pressurized oil charged into the hydraulic chamber. When the pressure receiving member descends with respect to the slide by overload imposed during a press working, the closing contact portion opens to relieve the pressurized oil of the hydraulic chamber to an oil reservoir, thereby absorbing the overload.
In order to prevent the leakage of the pressurized oil from the closing contact portion during a normal operation with no overload imposed, the closing contact portion must be precisely machined. However, being provided on the pressure receiving member of a large diameter, the closing contact portion invites a difficulty in handling and requires much labor for its precise machining. Besides, the closing contact portion has to be formed for each of a plurality of pressure receiving members provided in accordance with point number of the mechanical press. This lengthens the time necessary for machining and therefore increases the production cost of the conventional overload protector.
Further, with the conventional overload protector, when overload is imposed on one hydraulic chamber during the press working, the one hydraulic chamber immediately performs an overload operation as mentioned above. On the other hand, the other hydraulic chamber performs an overload operation through a relief valve and a plurality of pipes, which delays its overload operation. As a result, the two hydraulic chambers perform overload operations with a time lag caused therebetween to thereby incline the slide. This entails a likelihood to damage a guiding portion, a driving system or the like of the slide.
SUMMARY OF THE INVENTION
The present invention has an object to provide an overload protector which can assure a reliable operation and be manufactured at a low cost.
In order to accomplish the object, the present invention has constructed an overload protector for a mechanical press in the following manner, for example, as shown in
FIGS. 1
to
5
.
The overload protector comprises a plurality of overload absorbing hydraulic chambers
3
a
,
3
b
provided within a slide
2
of a mechanical press
1
and a plurality of relief passages
11
a
,
11
b
communicating the respective hydraulic chambers
3
a
,
3
b
with an overload protecting valve
12
. Check valves
13
a
,
13
b
and discharge valves
14
a
,
14
b
are arranged in series with each other in the respective relief passages
11
a
,
11
b
. The respective check valves
13
a
,
13
b
inhibit flow from a meeting portion (A) of the relief passages
11
a
,
11
b
to the respective hydraulic chambers
3
a
,
3
b
. The respective discharge valves
14
a
,
14
b
are arranged so as to be able to switch over to a normal condition where they communicate the respective hydraulic chambers
3
a
,
3
b
with the overload protecting valve
12
and to a discharging condition where they communicate the respective hydraulic chambers
3
a
,
3
b
with a discharge port (R). When each of the hydraulic chambers
3
a
,
3
b
has a pressure lower than a set overload pressure, the overload protecting valve
12
is kept closed and the respective discharge valves
14
a
,
14
b
are held in the normal condition. Conversely, when any one of the hydraulic chambers
3
a
,
3
b
has a pressure not less than the set overload pressure, the overload protecting valve
12
opens to relieve pressurized oil within the overloaded hydraulic chamber (
3
a
,
3
b
) to an exterior area through flow resistance applying means
78
of the corresponding discharge valve (
14
a
,
14
b
), the meeting portion (A) and the overload protecting valve
12
in order. The discharge valves
14
a
,
14
b
switch over to the discharging condition based on the fact that the meeting portion (A) reduces its pressure due to flow resistance of the pressurized oil passing through the flow resistance applying means
78
.
The present invention operates in the following manner, for example, as shown in
FIG. 1
as well as in FIGS.
5
(
a
) to
5
(
c
).
In a state where the slide
2
has returned from a bottom dead center to a top dead center, the hydraulic chambers
3
a
,
3
b
are charged with pressurized oil of a set charging pressure.
When the slide
2
descends from the top dead center to the bottom dead center and effects a press working of a work in the vicinity of the bottom dead center, a working reaction force increases the pressure of the hydraulic chambers
3
a
,
3
b.
During the press working, with no overload imposed on the respective hydraulic chambers
3
a
,
3
b
, as shown in FIG.
5
(
a
), pressure ports (Pa),(Pb) each has a pressure which is a normal operation pressure (P
0
) lower than the set overload pressure. The overload protecting valve
12
is kept closed and the two discharge valves
14
a
,
14
b
are also closed.
During the press working, when an eccentric working reaction force acts on the slide
2
to increase the pressure of one hydraulic chamber
3
a
and the pressure port (Pa), the pressurized oil of the thus increased pressure opens one check valve
13
a
to flow out to the meeting portion (A). However, the other check valve
13
b
inhibits its flow-out from the meeting portion (A) to the other hydraulic chamber
3
b
. Conversely, when the eccentric working reaction force increases the pressure of the other hydraulic chamber
3
b
and the pressure port (Pb), the pressurized oil of the thus increased pressure opens the other check valve
13
b
to flow out to the meeting portion (A). However, the one check valve
13
a
prevents its flow-out from the meeting portion (A) to the one hydraulic chamber
3
a.
During the press working, if overload is imposed on one hydraulic chamber
3
a
for any reason, as shown in FIG.
5
(
b
), one pressure port (Pa) has its pressure increased to an abnormal pressure (P
1
) not less than the set overload pressure. Then the abnormal pressure (P
1
) opens the overload protecting valve
12
to discharge the pressurized oil within the one pressure port (Pa) to an exterior area through the flow resistance applying means
78
of the discharge valve
14
a
, the meeting portion (A) and the overload protecting valve
12
. Then the meeting portion (A) rapidly reduces its pressure due to flow resistance of the pressurized oil passing through the flow resistance applying means
78
. This enlarges a differential pressure between the respective pressure ports (Pa),(Pb) and the meeting portion (A).
Therefore, as shown in FIG.
5
(
c
), both of the discharge valves
14
a
and
14
b
switch over to the discharging condition substantially at the same time, thereby discharging the pressurized oil within the respective hydraulic chambers
3
a
,
3
b
to the discharge port (R) via the pressure ports (Pa),(Pb) and the discharge valves
14
a
,
14
b
. This results in allowing the hydraulic chambers
3
a
,
3
b
to vertically contract and thereby enabling them to absorb the overload.
Also in the event overload is imposed on the other hydraulic chamber
3
b
, similarly as above, the discharge valves
14
b
,
14
a
switch over to the discharging condition substantially at

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