Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With means to cause relative movement between mold and charger
Reexamination Certificate
2002-04-17
2004-04-20
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With means to cause relative movement between mold and charger
C425S589000, C425S595000
Reexamination Certificate
active
06722875
ABSTRACT:
This invention relates generally to injection molding machines and more particularly to injection molding machines having vertically oriented clamp systems.
BACKGROUND
“Vertical” injection molding machines consist of an injection unit mounted either with a horizontal or vertical orientation and a clamp system oriented vertically to hold the two mold halves together under force sufficient to resist the pressure exerted by the molten plastic. Orientation of the clamp system vertically allows for operational ease as compared with horizontal clamp systems for certain applications including, but not limited to, insert molding and cable connectors.
The clamp systems commercially used in today's vertical injection molding machine generally comprise either a three platen (or plate) or “C”-frame systems.
Tie bar type machines typically use three main plates conventionally known as a stationary platen, an end platen, and a movable platen. In these designs, the stationary platen mounts the stationary mold half and the movable platen mounts the movable mold half. The end platen is used to mount the traverse actuators and the tonnage actuators. In a straight hydraulic clamp, the end platen houses the tonnage cylinder. In a toggle clamp, the end platen mounts the tonnage cylinder and the toggle linkage mechanism employed as a force multiplier. In either system, the end platen is used to react the forces when tonnage is developed to hold the two mold halves together. This is a general description of tie-bar or tie rod type machines present in the commercial marketplace. Within the patent literature, a number of variations are present.
In C-frame machines there are no tie bars and a large frame acts as both the stationary platen and the end platen. The stationary half of the mold mounts to the lower C-frame and the movable mold half mounts to the movable platen. The movable platen is again driven by actuators mounted on the upper C-frame and may be either straight hydraulic or incorporate a toggle linkage to develop tonnage. In either system, the C-frame upper and lower halves act to react against the force generated during tonnage application. This is a general description of C-frames in the commercial marketplace today. Within the patent literature, variations probably exist.
The overall height of the conventional vertical machines is therefore higher than what is otherwise required because of the presence of the end plate or the top leg of the “C”-frame. It is to be appreciated that, because the stationary platen of a vertical injection machine is mounted to ground, vertical molding machines are inherently suited to large, heavy mold applications requiring high mold tonnage. Conventional, large vertical machines thus require massive mold frames which raise height clearance concerns. In contrast, horizontal machines have length concerns but such concerns can be addressed, in most instances, by plant layout techniques.
More recently, the injection molding machine industry has begun commercializing two-platen mold clamping systems which have reduced the length of horizontal machines. Reference can be had to assignee's U.S. Pat. No. 5,776,516 to Armbruster et al., issued Jul. 7, 1998, for an example of a two-platen mold assembly.
In the patent literature, reference can be had to U.S. Pat. No. 5,338,171 to Hayakawa et al., issued Aug. 16, 1994, for a description of a number of mold clamp systems, including a two-platen system for a vertical machine. The two-platen mold systems under discussion are characterized by high tonnage, hydraulic piston-cylinder units with small piston travel displacing little hydraulic fluid because a smaller driving cylinder, pneumatic or hydraulic, is used to move the mold halves into and out of molding engagement. The movable platen moves into and out of molding engagement and is maintained in molding engagement under high tonnage by tie rods or by bushings for guide bars and the like. For the horizontal machine, this mounting/guiding arrangement is acceptable because the weight of the platen can be supported by rollers (indirectly in contact with ground) which can also assure alignment. For the vertical machine, the guide bars must closely control and guide the movable platen to assure consistently repeatable cycles necessary for the mold guide pins to properly align the mold halves. Bushings wear and require constant maintenance to assure lubrication of clean surfaces.
Additionally, the high tonnage lock rods must be positively locked for clamp tonnage and unlocked. Also, there are safety requirements that require the mold position to be locked in event of power failure, emergency stop, intrusion into the clamp zone, etc. The requirements are especially pertinent for vertical injection molding machines because they require that the movable platen be prevented from dropping vertically. Typically, the safety requirements for a positional lock are met by a locking rod which is usually located out of the center of acting forces. In the case of an emergency lock, a conventional locking rod could create significant damage to the system because of disproportional distribution of inertia forces. In one of the inventors' earlier patents, U.S. Pat. No. 5,035,606, issued Jul. 30, 1991, a fail safe locking arrangement is disclosed which overcomes many of the problems present in conventional locking arrangements. This invention improves on the locking arrangement disclosed in the '606 patent which is incorporated herein by reference.
A particular advantage that vertical injection molding machines possess is the ability for the machines to be equipped with a rotating table overlying the stationary platen. The table is equipped with a plurality of stationary mold halves that are rotated by the table through successive work stations to reduce the overall process time. For example, after molding, the stationary mold half with the molded part is rotated to an ejector station where ejector pins dislodge the molded part from the mold cavity. The transfer to an ejection station while another mold half is simultaneously rotated into a molding relationship with the movable platen, reduces the cycle time otherwise required in a horizontal machine to eject the part, or alternatively, employ complicated mold transfer mechanisms to shuttle mold halves into and out of the clamp. Other stations on the rotating table may be dedicated to robotic part removal, insert placing, etc.
Typically, the table is rotated in sliding contact with the stationary platen and the station position is determined by limit or proximity switches. The sliding table motion requires lubrication and maintenance and also limits the mold weight of a machine otherwise inherently suited for executing large clamping forces.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide an improved vertical type injection molding machine which addresses the concerns discussed in the Background.
This general object along with other features of the invention is achieved in a vertical injection molding machine which includes a lower stationary platen upon which a lower mold half is mounted and an upper vertically movable platen on the bottom side of which is mounted an upper mold half in confronting relation to the lower mold half. An advance mechanism is provided for raising and lowering the movable platen relative to the stationary platen and the machine has an injection unit for injecting molding material into one of the mold halves when the mold halves have been moved into a molding relationship. A plurality of vertically extending locking rods positioned to straddle the mold halves is provided with each locking rod being attached at one end thereof to the stationary platen (for example, by being connected to a high tonnage clamp piston of a cylinder mounted to the stationary platen). Each locking rod extends through a locking rod opening in the movable platen and has a plurality of longitudinally spaced annular grooves extending over a rod length adjacent the opposite
Ralph Brian J.
Zakich Paul
Heitbrink Tim
Van Dorn Demag Corporation
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