Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Mold motion or position control
Patent
1988-10-27
1991-01-01
Heitbrink, Timothy
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Mold motion or position control
91392, 92162R, 100269B, 100273, 425419, 4254512, 4254519, 425590, 425595, B29C 4580
Patent
active
049814265
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a clamping mechanism for use within an injection molding machine for molding synthetic resins.
2. Description of the Related Art
A clamping mechanism for opening and closing a mold is disclosed in Japanese patent application Laid-Open No. 60-143915. The mechanism includes means for reducing hydraulic resistance during the opening and closing of the mold. In particular, an internal diameter of a front chamber of a cylinder is larger than an internal diameter of a rear chamber of the cylinder, and a clearance is formed between the peripheral wall of the rear chamber of the cylinder and a piston.
In the above-described clamping mechanism, hydraulic resistance within the cylinder is reduced because oil can flow through the clearance around the periphery of the piston. But a large quantity of oil is required when a clamping ram is moved at high speed. Conventional pipes for receiving and supplying oil have small inlets and outlets. Hence, flowing-in-and-out of oil during operation of a large clamping mechanism is not smooth, and high-speed opening and closing cannot be carried out.
In view of the foregoing, the present inventor has developed means, as disclosed in Japanese Patent Application No. 61-276185, in which a front chamber of a cylinder and a rear chamber of the cylinder communicate with each other through a large diameter passage which can be opened and closed by a valve, whereby oil from the front chamber can be moved to the rear chamber through the passage during opening and closing of the mold. Thus, the flowability of oil within a large clamping mechanism is not impaired by pipe resistance and high-speed opening and closing can be carried out smoothly. However, cavitation tends to occur in the back of the piston because of a shortage of oil within the cylinder. Such cavitation increases the amount of time needed to establish the final clamping pressure.
A supply tank has been used in the prior art to supply oil to a cylinder as a piston moves out of the cylinder. But such a tank requires a valve and means for coordinating the operation of the valve with the movement of the piston. Such an arrangement is complicated and difficult to operate.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an uncomplicated clamping mechanism which can accumulate and charge oil into a cylinder according to the movement of a piston without requiring valve operation.
The present invention relates to a clamping mechanism for use within an injection molding machine. The mechanism includes: a clamping cylinder with a front chamber and a rear chamber, the internal diameter of the rear chamber being greater than the internal diameter of the front chamber; and a main piston which is movable within the cylinder. The diameter of the outermost periphery of the piston is less than the internal diameter of the rear chamber of the cylinder such that fluid flows around the piston when the piston moves from an open position to an intermediate position. The diameter of the outermost periphery of the piston is equal to the internal diameter of the front chamber so that fluid cannot flow around the piston when the piston moves from the intermediate position to a closed position. The mechanism further includes a clamping ram which is fixed with respect to the main piston; and a booster ram which is coaxial with the clamping ram. The mechanism further includes charging means for supplying fluid to and for receiving fluid from the clamping cylinder. The charging means includes a charge cylinder, a charge piston which is movable within the charge cylinder and a charge piston rod. The charge piston rod is connected to the clamping ram such that movement of the main piston toward the closed position causes the charge piston to discharge fluid from the charge cylinder into the clamping cylinder. The dimensions of the clamping piston, the clamping ram, the booster ram and the charge piston are such that pressure within the clampi
REFERENCES:
patent: 4861259 (1989-08-01), Takada
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