High-speed arcade hydraulic press for forming, lining, and compressing thin plastic parts

Abstract

The clamping sleeve 3 provided in each locking system for coupling the annular piston 4 of the differential cylinder 4 with the push rod 5 during the working stroke of the press has internal grooves 18 and external sets of O-rings 11, 12, and is traversed by axial channels 17 for evacuating leaking oil in order to prevent the formation of a hydrostatic oil film between the inner surface 23 and the rod 5 when clamping the sleeve 3.

Description

High-speed arcade hydraulic press for forming DOUBLE-LAYERING AND COMPRESSION OF THIN PARTS MADE FROM PLASTIC MATERIAL. The present invention relates to an improvement of a hydraulic press according to patent application no. 87 15 232 filed on November 3, 1987. The hydraulic press with a high-speed stroke according to the aforementioned patent application comprises a press table, a capital and a movable slide between the capital and the press table for shaping, doubling and compressing pieces of material of large extent and low thickness, made of plastic or of composite materials based on plastic or of fiber mats impregnated with plastic, in the form of profiled pieces, the upper half of the mold being carried by the slide which can be lowered and raised by means of a high-speed hydraulic device for the free stroke and a short-stroke hydraulic device for the working stroke. According to one embodiment of this press, the slide is raised and lowered during the free stroke by a high-speed hydraulic drive system acting centrally within the press head, and is guided slidingly by means of push rods within the press head. After the free stroke, the push rods are coupled synchronously and by clamping, via hydraulic locking devices with clamping sleeves, to the annular pistons of differential cylinders anchored in the press head. The working stroke is executed by said differential cylinders via the annular pistons and the push rods locked to these pistons, said pistons being, before locking, pre-stressed under hydraulic backpressure relative to the differential cylinders. The construction and control features of this press result in virtually shock-free and wear-free coupling through synchronous clamping of the push rods, with reduced active masses. This technical achievement is made possible by hydraulic damping and automatic compensation of the coupled masses using pre-stressed pressure cushions. Neutralizing the weight of the push rods and pistons allows for shorter braking times, a higher speed for the free stroke, and faster closing speeds. To prevent high-pressure oil from escaping from the pressure chambers in the pistons, delimited by diaphragms (e.g., nylon sleeves) surrounding the clamping bushings, into the clamping area between the bushings and the push rods, these diaphragms have two external O-rings at their ends.In the event of an O-ring leak, high-pressure oil enters the clamping area uncontrollably, resulting in reduced clamping efficiency between the clamping sleeves and the pushrods. Clamping sleeve systems of the type described in point n1 do not ensure slip-free clamping if, due to an uncontrolled lubricating oil film, a hydrostatic film forms between the pushrod and the clamping sleeve because the oil film cannot be removed—that is, the oil cannot be evacuated—during the required clamping time of approximately 0.5 to 1 second. Normally, sufficient clamping efficiency is ensured, even with lubrication, due to friction conditions.However, in the event of uncontrolled leaks, slippage can occur, namely due to the formation of a hydrostatic film. The clamping sleeve can then slide along the pushrod for a short period until this hydrostatic film is expelled. If this occurs, slippage over a stroke of approximately 20 to 30 mm causes friction temperatures so high locally that cracking (decomposition, degradation) of the oil occurs. The cracked oil adheres as a displacement on the push rods and thus enters even more uncontrolled friction conditions, which leads to a failure of the entire system, i.e. the press must be stopped and manufacturing suspended. The present invention aims to improve, on a press of the type defined above, the surface structure of the clamping bushings and the evacuation of leaking oil so as to reliably prevent the establishment of a harmful hydrostatic oil film between the push rods and the clamping bushings. According to invention 11, the clamping surface through which the clamping sleeves cooperating with the push rods is provided with lubricating oil grooves separated from each other by an interval of approximately 3.5 mm and having a width of approximately 1 to 2 mm and a depth of approximately 0.5 mm, independent of the clamping diameter of the clamping sleeves. Two first O-rings are disposed between each diaphragm and the annular piston, and two sets of second O-rings are disposed on each clamping sleeve. In addition, axial leakage oil channels are provided, between the slots of the clamping sleeves and in alignment with these slots, in the annular pistons as well as in the lower retaining rings of the clamping sleeve locking systems, these channels opening into recovery tanks. According to another feature of the invention, each time two O-rings are arranged in annular grooves on the outer perimeter of a clamping sleeve, as a barrier against oil leaking from the slots of the clamping sleeve. Preferably, each time two O-rings are arranged in annular grooves on the front sides of a clamping sleeve, as a barrier against oil leaking into the inner clamping area of ​​the sleeve. Photoelectric sensors can be advantageously placed, as level detectors, on the tanks for recovering leaking oil. In addition, oil flow grooves may be arranged on the front sides of the clamping sleeves and / or in the opposite annular surfaces of the annular pistons or the fixing rings. Finally, it is advantageous, within the framework of the invention, to use an oil having a viscosity less than or equal to that of a normal hydraulic oil of 40 cSt. The advantages obtained according to the invention consist in particular in the fact that the realization according to the invention of the surface of the clamping sleeves prevents, in combination with the realization according to the invention of the locking by clamping sleeve for the purpose of the evacuation of the leaking oil, with optimal safety the penetration of the leaking oil into the clamping area. Furthermore, during clamping, the formation of a harmful hydrostatic film from the lubricating oil film between the pushrods and the clamping sleeves is prevented. This is because, due to the high clamping pressure between the clamping surfaces, the extremely small gap between the lubricating oil drainage grooves, and the large volume of these grooves, the oil is immediately expelled from between the clamping surfaces. In other words, given the clamping time of approximately 0.5 to 1 second, the oil drainage grooves have sufficient volume to reliably expel a hydrostatic oil film 0.1 mm thick or more. This is true regardless of the clamping diameter of the clamping sleeves. The regular intervals of 3.5 mm between the grooves, regardless of the diameter of the push rods, are technically motivated by the following points. 1) The minimum interval between the grooves, an interval which is approximately equal to / less than 3.5 mm, is conditioned by the allowable surface pressure of the thrust rods in alloy steel type 42 Cr Mo 4. 2) By the hydraulic clamping pressure in the diaphragms, the The hydrostatic film (0.1 mm) is forced back into the gorges until the establishment of a metallic contact between the rods of thrust and clamping bushings. The material of the bushings The clamping is preferably made of bronze having resistance values ​​higher than those of push rods. 3) The discharge conditions of the liquid fluid are constant. compared to a) the thickness of the oil film approximately equal to / less than 0.1 min, b) the discharge path S12 approximately equal / less than 3.5 that is to say, with a 1 increase in the clamping diameter, the interval s should not increase in the same proportion. Only when using high-alloy, surface-hardened steels can the gap s be chosen to be less than 3.5 mm. This would result in the hydrostatic film, with a thickness approximately equal to or less than 0.1 mm, being forced back into the grooves in less than 0.5 seconds. Another important advantage of the invention is that if leak oil enters a leak oil recovery tank through the leak oil evacuation channels, level sensors provided in this tank immediately trigger an alarm, allowing the defective seal to be changed. In particular, this last feature makes it possible to prevent significant damage, i.e., a major press breakdown and therefore a prolonged production stoppage, because monitoring the oil leak recovery tanks allows for continuous verification of the oil leak seals. If photoelectric sensors are installed, this monitoring can even be automated using an electrical alarm system. Tests have demonstrated that in the case of controlled lubrication of the clamping sleeve locking system, a limited quantity of metered oil with a viscosity less than or equal to that of a normal hydraulic oil of about 40 cSt can be used, allowing the establishment of an oil film thickness of about 0.01 mm. With reference to the attached drawings, we will describe in more detail below an example of an embodiment of the invention; on the drawing Figure I is an axial section of a hydraulic locking system with clamping sleeves, schematically showing the sealing system according to the invention against leaking oil; Figure 2 is a cross-section of a high-speed stroke press according to the invention; Figure 3a represents on a larger scale detail F of figure 1; Figure 3b is a section along AA of figure 3a; Figure 4 represents on a larger scale detail E of figure 1 concerning the sealing and evacuation of leaking oil. Figure 2 shows a high-speed hydraulic press of the arch type, comprising a press frame 1, a capital or upper frame 15, and a table 14. Between the capital 15 and the table 14 is a slide 6 supporting the upper half of the mold or die and capable of being raised and lowered by means of a high-speed hydraulic drive system 9, 10. The high-speed drive system includes a pusher 9 fixed in a central position to the slide 6, and a hydraulic cylinder-piston arrangement 10 anchored in the capital 15. The slide 6 is fixed to two (or four) push rods 5 guided in the capital 15. Figure 1 is a cross-section of the arrangement of a push rod 5, a hydraulic locking device with two clamping sleeves 3, 3', and a differential hydraulic cylinder 2 with an annular piston 4 for compression pressure. By sending pressurized fluid into the inlet line, the diaphragms 7 and 7' exert pressure on the clamping sleeves 3 and 3', thus coupling the push rod 5 by friction with the annular piston 2 of the differential cylinder 4. Since the differential cylinder 4 is anchored in the cap 15, the push rod 5 is then also connected to the latter. The push-sleeve locking system 3, 3' with diaphragms 7 and 7' is fixed to the push rod 5 in the annular piston 2 by means of retaining rings 16 and 19. At locations indicated by E and F, seals and leakage oil outlets are provided. Reference numeral 17 designates a leakage oil outlet channel in the clamping sleeves 3, 3', the annular piston 2, and the retaining rings 16 and 19. Leakage oil escaping in the event of a seal failure falls or flows by gravity through the leakage oil outlet channel 17 into the recovery tank 13. Photoelectric sensors (not shown) installed on or near this tank as level detectors can serve as triggers for an electrical alarm system. Figures 3a, 3b and 4 represent in more detail the embodiment according to the invention of the clamping surface of the clamping sleeves. In order to prevent the establishment of an uncontrolled oil film of a thickness greater than / equal to 0.1 mm on the lateral surface of the push rod 5, for example in the event of uncontrolled leaks or failure of the sealing system consisting of O-rings 8 between the diaphragms 7, 7' and the annular piston 2, a blocking system against leaking oil is provided with appropriate implementation of the clamping sleeves 3 and 3'. Reference 8 designates the O-ring which, in contact with the annular piston or the fixing rings 16 and 19, applies the diaphragm 7, 7' against the clamping sleeve 3, 3'. According to the invention, two additional sets of O-rings 11 and 12 are provided in grooves 20 and 21 in the outer periphery of the front faces of the clamping sleeves 7, 7'. The O-ring 12 prevents leakage oil from entering the slots of the clamping sleeves 3, 3', so that this leakage oil cannot reach the inner surface 23 of the clamping sleeves through the slots. The O-ring 11, on the other hand, prevents the uncontrolled entry of leakage oil directly into the inner surface 23 of the clamping sleeves through one end of these sleeves. If, despite this, leakage oil does escape towards the clamping area, this oil first reaches the leakage oil drain channel 17 and from there passes into the recovery tank 13. Given the clamping system subjected to high hydraulic clamping pressure, the axial arrangement of the leakage oil drainage channels 17 is of particular importance. Indeed, due to the notching effect that radial channels would cause, especially in the annular piston 2, such radial channels could lead to failure. In view of a possible failure of the main O-rings 8, flow grooves 22 are provided frontally on the clamping sleeves 3, 3' and also in the opposite annular surfaces of the annular piston 2 or in the fixing rings 16 and 19, these grooves evacuating the leaking oil through the axial evacuation channels 17, i.e. parallel to the median axis of the clamping sleeves 3 and 3'. The oil drainage grooves 18 are designed to prevent the formation, during the tightening operation, of a hydrostatic film of lubricating oil or leaking oil that has entered the tightening area. For this purpose, the spacing or pitch s of the drainage grooves 18, which are helically formed in the tightening surface 23 of the clamping sleeves 3 and 3', is chosen to be approximately 3.5 mm, so small that the oil film is reliably torn and forced back into the grooves 18 during the tightening operation.

Claims

DEMANDS 1. A high-speed hydraulic press comprising a press table, a dome, and a sliding block between the dome and the press table for shaping, doubling, and compressing large-format, thin-walled parts of plastic or plastic-based composite materials or plastic-impregnated fiber mats, into profiled parts. The upper mold half is supported by the sliding block, which can be raised and lowered by means of a high-speed hydraulic device for the free stroke and a short-stroke hydraulic device for the working stroke. The sliding block is raised and lowered during the free stroke by a high-speed hydraulic drive system acting centrally in the dome and guided by push rods in the dome. After the free stroke, the push rods are...coupled synchronously and by clamping via hydraulic locking sleeves, with the annular pistons of differential cylinders anchored in the cap, and the working stroke being executed by said differential cylinders via the annular pistons and pushrods locked with these pistons, said pistons being, before locking, pre-stressed under hydraulic backpressure relative to the differential cylinders, according to any one of claims 2 to 7 of patent application No. 87 15232 of November 2, 1987, each clamping sleeve (3, 3') being surrounded by a membrane (7, 7') delimiting a pressure chamber for clamping the sleeve with pressurized oil, characterized in that a) lubricating oil grooves (18) are provided in the, inner clamping surface (23) of the clamping sleeves (3, 3') with an interval (s) of approximately 3.5 mm between the grooves, with a groove width between 1 and 2 mm and with a depth of the gorges of approximately 0.5 min, regardless of the clamping diameter of the clamping sleeves (3, 3'), b) the first two O-rings (8) are arranged, for each clamping sleeve (3, 3'), between the membrane (7, 7') and the annular piston (2) and two sets of second O-rings (11 and 12) are arranged on each clamping sleeve (3, 3'), and c) leakage oil channels (17) are arranged axially between the slots of the clamping sleeves (3, 3'), in alignment with said slots, in the annular piston (2) as well as in the lower fixing rings (16) of the clamping sleeves, these channels opening into recovery tanks (13).

2. Press according to claim 1, characterized in that two second O-rings (12) arranged in annular grooves (20) on the outer perimeter of a clamping sleeve (3, 3') are provided as a barrier to leakage oil with respect to the slots of the clamping sleeve (3, 3').

3. Press according to claim 1 or 2, characterized in that two second O-rings (11) are arranged in annular grooves (21) formed in the front faces of a clamping sleeve (3, 3') as a barrier to oil leakage towards the inner clamping area.

4. Press according to any one of the preceding claims, characterized in that photoelectric sensors are arranged, as level detectors, on the leaking oil recovery tanks (13).

5. Press according to any one of the preceding claims, characterized in that oil flow grooves (22) are provided in the front faces of the clamping sleeves (3, 3') and / or in the opposite annular surfaces of the annular piston (2) or of the fixing rings (16, 19).

6. Press according to any one of the preceding claims, characterized by the use of an oil having a viscosity less than or equal to that of a normal hydraulic oil of 40 cSt.