Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Positioning of a mold part to form a cavity or controlling...
Reexamination Certificate
2002-07-09
2004-11-23
Heitbrink, Jill L. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Positioning of a mold part to form a cavity or controlling...
C264S328100, C425S150000, C425S589000, C425S595000, C425S451700, C425S451900
Reexamination Certificate
active
06821463
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention refers to injection molding machines for plastic materials, and in particular relates to a method and to a mold clamping press according to which use is made of a clamping device for clamping a mold, by which it is possible to operate with precision and at high speed.
STATE OF THE ART
In the plastic material injection molding, use is substantially made of two types of clamping presses for the closure of a mold, that is to say clamping presses having two platens, and presses having three platens provided with two or more peripheral tie-rods which extend longitudinally to the press.
In the case of clamping presses having three platens, these comprise a first stationary platen for supporting a half mold, a second movable platen for supporting the other one of the half molds, sliding along guide rods, and a third stationary platen forming part of a reaction structure, to which a toggle system is connected to control the sliding of the movable platen between an open condition and a closed condition of the mold, and the clamping of the same mold.
Presses of this kind require an expensive and bulky structure, and highly complex control systems necessary to generate the high clamping forces for tightly closing the mold, with mold closing and opening times compatible with the length of the entire operative cycle of the machine.
An alternative configuration to reduce costs and overall dimensions, contemplates the use of only two platens, including a stationary platen to support a first half mold, and a movable platen to support a second half mold, which is made to slide along horizontal guides by means of hydraulical actuators or other types of control systems.
A two platen press also comprises tie-rods which extend from one platen to the other one, and engage with mechanical clamping devices operated at the end of the working stroke during which the movable platen approaches the stationary platen, before exerting the high clamping force for closing the mold, or at the time of reopening of the mold at the end of each injection cycle.
Examples of injection molding machines with two platen clamping presses, and mechanical closing and clamping systems, are found in DE 1.159.137, U.S. Pat. No. 2,916,768, U.S. Pat. No. 5,188,850; U.S. Pat. No. 5,192,557 and in WO 98/51468.
Usually, in clamping presses of this type the tie-rods are rigidly fastened and protrude jutting out from one of the platens, in such a way that their extremities engage with clamping jaws or other clamping devices disposed on the other platen of the press; the clamping jaws must be operated beforehand to engage the tie-rods which subsequently are drawn by means of hydraulic actuators capable of exerting the necessary clamping force or tonnage for closing the mold.
The injection molding presses of the aforementioned type, present the drawback of requiring long rest times between different mold opening and closing operations, which increases the working cycle of the press.
In particular, pauses are required for operating the clamping devices; such pauses have significant repercussions on the output of this type of machine.
In fact, considering that in presses of this kind it is possible to operate with molding cycles in the range of 10-15 seconds, or times even less, it is clear that resting times in the range of 0.5÷3 seconds can prove to be unacceptable or of such length as to greatly conditioning the output of the machine. This depends mainly upon the mechanical and structural characteristics of the clamping devices, as well as upon the use of complex safety systems which must come into operation each time the press is to be open and closed.
U.S. Pat. No. 5,066,217, U.S. Pat. No. 5,417,913 and U.S. Pat. No. 6,186,770 show other types of two platen clamping presses.
In particular, U.S. Pat. No. 5,066,217 and U.S. Pat. No. 5,417,913 show a two platen presses whose tie-rods are axially movable with respect to the platens supporting the half molds, and in which use is also made of mechanical systems for locking the platens to the tie-rods, which substantially comprise radially movable half nuts, or angularly rotatable coupling members which engage with corresponding screw threads or annular ribs on the tie-rods of the press. Presses of this kind again present the same drawbacks inherent in the clamping and closing devices of the patents previously referred to; in particular, they present a greater complexity of the system for locking the platens to the tie-rods and intercycle times which are still considered high for this kind of press.
U.S. Pat. No. 6,186,770, which represents the closest prior art in respect to the present invention, also shows a two platen press in which the tie-rods are axially secured to one of the platens, and in which the other platen of the press is provided with a mechanical connection with each tie-rod, substantially comprising an internally threaded bush member which engages by screwing onto a screw threaded portion of the corresponding tie-rod, both in order to cause the sliding of the movable platen, and in order to generate the tonnage necessary for the tight clamping of the mold. A belt system is provided to synchronize the rotation of all the bush members.
According to a possible embodiment, the press comprises a first control means to cause the rotation of the bushes whenever the movable platen must be moved forward or backward, and second independent control means to rotate the bushes themselves, or alternatively the same tie-rods, whenever the tonnage for clamping the mold must be exerted. In both the solutions, in addition to generation of the tonnage for clamping the mold, the threaded bushes also serve to cause the sliding displacement of the movable platen, thereby resulting in frictional forces and stress between the screw threads.
OBJECTS OF THE INVENTION
It is therefore necessary to seek new and alternative solutions whereby it is possible to obviate the aforementioned drawbacks, for closing and securing the tie-rods to the platens supporting the molds, in two platen presses for injection molding machines.
Consequently, the main object of the present invention is to provide a method and a two platen press for injection molding, which make use of a locking device for the closure and locking of the platens to the tie-bars of a press, which is capable of obviating the aforementioned drawbacks.
In particular, one object of the present invention is to provide a method for clamping a two platen press, as referred to above, allowing extremely short clamping times, suitable for fast cycle machines, and which does not require any particular or complex safety system, thereby ensuring the utmost speed and precision during the closing and tight clamping steps of a mold.
A further object of the present invention is to provide an injection molding press of two platens type, provided with a clamping system for clamping the mold and securing the platens to the tie-rods which, in addition to possessing extremely short resting times, is also extremely functionally simplified in that the locking of the platens to the tie-rods and the tight clamping of the mold, take place simultaneously and in synchronism on all the rods of the press, without causing frictional forces.
A still further object of the present invention is to provide a clamping device of the type referred to above, by which it is possible to use separate control systems for the displacement of the movable platen and for locking at the same time the platens to the tie-rods, ensuring in all cases a fast and immediate clamping action whatever the final position of the movable platen with respect to the stationary one.
BRIEF DESCRIPTION OF THE INVENTION
According to a general feature of the present invention, a method is thus provided for clamping a mold of an injection molding press of the type comprising:
a first platen for supporting a first half mold;
a second platen for supporting a second half mold, at least one of said platens being slidably movable with respect to the other one
Di Dio Leonardo
Vignale Anselmo
Davidson Berquist Jackson & Gowdey LLP
Heitbrink Jill L.
Sandretto Industrie S.p.A.
LandOfFree
Method and mold clamping press for injection molding machines does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and mold clamping press for injection molding machines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and mold clamping press for injection molding machines will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3298557