Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Mold motion or position control
Reexamination Certificate
1998-04-27
2001-03-13
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Mold motion or position control
C425S556000, C425S589000, C425S595000, C425S451900
Reexamination Certificate
active
06200123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic closing unit such as used, for instance, in injection molding machines.
2. Related Art
The closing unit of an injection molding machine receives the injection mold. It carries out the movements necessary for the closing and opening of the injection mold and produces the forces necessary for the locking and opening of the injection mold. The main components of each closing unit are a stationary plate on the injection side (hereinafter referred to as the injection plate), a movable closure plate, as well as a locking device. One part of the injection mold is clamped on the stationary injection plate while the complementary part of the injection mold is clamped on the movable closure plate. By locking device there is to be understood the device which, upon the injection, produces the necessary closing force for keeping the injection mold closed. Both mechanical locking devices with lever mechanisms and hydraulic locking devices with hydraulic cylinders are known. The present invention relates to a closing unit with hydraulic locking.
From International Patent Application WO-A-93/16828, a closing unit for an injection molding machine is known in which the movable closure plate can be displaced between the stationary injection plate and an end plate which is also stationary by two displacement cylinders. The movable closure plate is provided with a central push rod which is guided in an annular insert in the stationary end plate. On this end plate a force cylinder is arranged which has a single-acting annular piston passed through axially by the push rod. A locking ring is guided in a cylindrical guide tube which is screwed onto the end plate. If the force cylinder is acted on by pressure, the annular piston of the force cylinder is advanced in the direction towards the movable closure plate. The front surface of the annular piston thereby comes against the facing end surface of the locking ring, the latter being pushed axially in its cylindrical guide tube in the direction towards the movable closure plate. In order to lock the locking ring on the push rod, the push rod has an outer toothing and the locking ring has a complementary inner toothing. The inner toothing and the outer toothing are divided into several rows of teeth by longitudinal grooves. The locking ring can be turned into first and second angular positions by means of a positioning cylinder. In the first angular position, the rows of teeth of the outer toothing can be passed through axially by longitudinal grooves of the inner toothing and the rows of teeth of the inner toothing by longitudinal grooves of the outer toothing, so that the push rod slides without substantial resistance through the locking ring. In the second angular position, the tooth of the outer toothing, on the other hand, can engage behind the teeth of the inner toothing. In this position, the locking ring is locked on the push rod. The annular piston of the force cylinder can exert a pressing force on the push rod via the locking ring and thus transmit the necessary closing force to the movable closure plate.
Upon the opening of the mold, the locking ring initially remains locked to the push rod. The two displacement cylinders produce a short rearward stroke in order to open the mold. By this short rearward stroke, the locking ring and the annular piston are moved backward simultaneously. Thereupon, the lock between the push rod and the locking ring is opened so that the push rod can slide through the locking ring when the closure plate is pulled back at high speed by the two displacement cylinders.
It may be emphasized that it would be desirable to produce the opening force for the opening of the injection mold also by the force cylinder. However, this is not possible in a closing unit in accordance with WO-A-93/16828 since the force cylinder is designed as a single-acting cylinder and furthermore it cannot be seen how a pulling force can be transferred in a simple manner from the piston via the turnable locking ring to the push rod.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to create a closing unit in which the closing and opening forces are produced by the sane hydraulic cylinder. This object is achieved by a closing unit in accordance with claim
1
.
The solution in accordance with the invention consists essentially therein that the force cylinder is developed as a doubling annular pressure cylinder having a first pressure chamber for producing an closing force and a second pressure chamber for producing an opening force, the piston of this hydraulic force cylinder being secured against turning and coupled by a screw thread to the locking bushing. In this way, both a pressing force and a pulling force can be transmitted from the piston which is fixed against rotation via the rotatable locking bushing to the push rod, and thus to the closure plate. The screw thread is a simple, extremely compact, and low-stress solution for turnably connecting together the piston and the locking bushing. By turning the locking bushing from the first angular position into the second angular position, the locking bushing naturally experiences an advance X relative to the piston. However, this is not disturbing since this advance can even be used in an extremely advantageous manner in order to distribute the axial play between the inner toothing and the outer toothing which is necessary for their engagement in such a manner that inner toothing and outer toothing already lie substantially without play against each other prior to the transmission of the force.
In order to assure a dependable engagement of the inner toothing into the outer toothing, a relatively large axial flank clearance should actually be present upon the engagement. A large flank clearance, however, also has substantial disadvantages. Thus, for instance, the operating stroke of the force cylinder is increased, and thus the consumption of energy of the closing unit. The flows through the force cylinder are considerably greater, so that the hydraulic system of the closing unit must also be designed larger. Furthermore, the locking bushing is relatively strongly accelerated upon overcoming a large flank clearance, so that the teeth of the inner toothing strike with great momentum against the outer toothing.
WO-A-93/16828 proposes developing the outer toothing on the push rod and the inner toothings in the locking ring as a thread, the disturbing flank clearance, in accordance with WO-A-93/16828, being eliminated by the turning of the locking ring. However, this means that the toothing necessarily has, in the direction of rotation of the locking ring, a negative pitch in the direction of the force to be transmitted, and that furthermore, the pitch of this thread is necessarily determined by the flank clearance and the angle of rotation of the locking ring. In this way, the designer, however, is subjected to substantial constraints in development with respect to the toothings, which constraints, for instance, prevent functionally correct, load-resistant optimizing of the toothings in many cases.
In accordance with the present invention, it is unimportant whether the teeth of the inner and outer toothings are arranged annularly, or helically with positive pitch or helically with negative pitch. The advance produced by the screw thread upon the turning of the locking bushing permits in each case the axial flank clearance S to be distributed between inner toothing and outer toothing in such a manner that, in the locked position between the tooth flanks which are to transmit the force, no substantial axial flank clearance is present any longer. If, furthermore, the actuator for the turning of the locking bushing is so designed that it can place the locking bushing into a second angular position both by counterclockwise rotation and by clockwise rotation, then the flank clearance S between the inner and outer toothings is distributed on the one hand on the left side and on th
Mailliet Marc
Mailliet Monique
Mailliet Pierre
Fitzpatrick ,Cella, Harper & Scinto
Husky Injection Molding Systems Ltd.
Mackey James P.
Mailliet Marc
Mailliet Monique
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