Molding machine for producing plastic hollow bodies

Details Molding machine for producing plastic hollow bodies Molding machine for producing plastic hollow bodies

1999-03-24

2001-05-08

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Control means responsive to or actuated by means sensing or...

Control means responsive to product weight or dimension

C425S145000, C425S149000, C425S527000, C425S532000

Reexamination Certificate

active

06227838

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a molding machine for producing plastic hollow bodies and including at least one extrusion die for producing a preform, injection plunger means for delivering plasticized plastic material to the at least one extrusion die, a triggering device displaceable toward and away from the at least one extrusion die, two blow mold halves arranged between the extrusion die and the triggering device and displaceable toward each other for forming a blow mold in which the preform produced by the extrusion die is received and a hollow body is formed upon gas being blown in by the triggering device, a computerized control means, a weight-measuring device for determining weight of the hollow bodies and further control means.
2. Description of the Prior Art
A molding machine of the above-described type, but without a weight-measuring device and other measuring means is disclosed in European patent No. 535,254. Generally, it is known to provide a molding machine, which is disclosed in this European Patent, with a weight-measuring device. The control of produced hollow bodies is effected in a following manner. A hollow body is cut up, according to its length, in three sections, and the thickness is measured at the edges of the cuts. Also, transitional regions at sharp bends of the hollow body profile or at the cuts as well as the end regions of the hollow body and adjoining them middle regions are examined. However, one cannot exclude a possibility of an error during a mass production of hollow bodies, which leads to undesired deviations of the wall thickness. A wall thickness error leads to a premature breaking of a hollow body when it is subjected to a certain stress. A wall thickness error also results in too thick or too thin regions in a hollow body or in formation of a hole in the hollow body. At present, the control of the quality of hollow body is effected manually, which is expensive. The cuts made in a hollow body make it defective and results in a loss of the hollow body. Because not all of the formed hollow bodies are subjected to cut-up, the testing of the non cut-up hollow bodies is incomplete. However, in many cases, e.g., in manufacturing of motor vehicles it is desired that each separate hollow body be subjected to a precise control.
Accordingly, an object of the present invention is to provide a molding machine of the type described above in which each hollow body is automatically tested as to whether it has a uniform wall thickness.
SUMMARY OF THE INVENTION
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a molding machine of the above-described type and including a pressure-measuring device for determining pressure of the plasticized plastic material, a weight-measuring device for determining weight of produced hollow bodies; a height-measuring device for determining the height of the produced hollow bodies, data-transmitting lines connecting the pressure-measuring, weight-measuring, and height-measuring devices with the control means, control lines connecting the control means with respective measuring devices, and transfer gripping means for transferring a formed hollow body to the weight-measuring body device and the height-measuring device.
In the molding machine according to the present invention, the control of the hollow bodies is effected automatically, without any loss of the hollow bodies resulting from their testing. Testing of each produced hollow body is insured. The testing or control of the hollow bodies is effected in the machine itself. The pressure of the plasticized plastic material is monitored before the material enters the extrusion die. It is monitored in the injection plunger. According to the present invention, the molding machine is equipped with a transfer gripping device, with the weight and height being measured within the operational region of the transfer gripping device. There is a two-way connection between the three measuring devices and the control means. Through the data transmitting lines, the measured data are communicated to the control means, and the control means monitors the operation of the measuring devices via control lines. The present invention is based on the determination that when predetermined relationships exist between the three measurements, pressure, weight and height for a hollow body, the hollow body would have predetermined ratios of the wall thickness and would be capable of performing a predetermined function. Generally, the predetermined pressure of the plasticized plastic material and a predetermined height of the hollow body, together with a predetermined weight, indicate that the predetermined wall thickness ratios of the hollow body have been obtained.
As a result of the measurements, defective hollow bodies, i.e., hollow bodies for which at least one measurement is outside of a predetermined range, are discarded. Good hollow bodies are delivered to a counter. A hollow body is considered to be good when the measured pressure, the measured weight, and the measured height are within their respective predetermined ranges, and the cutting off of the end region has been registered by the sensor associated with the cutting-off means.
It is possible to measure the pressure of the plasticized plastic material on its way from the injection plunger to the extrusion die. However, it is particularly advantageous when the injection plunger has an actuation hydraulic system, and the pressure-measuring means comprises means for measuring the hydraulic pressure in the actuation hydraulic system of the injection plunger. This indirect measurement of the pressure of the plasticized plastic material reliably predicts the consistency of the plasticized plastic materials and can be easily implemented technically.
In many cases, a hollow body is produced with an end region, e.g., a bottom which is not necessary for the designated function of the hollow body and is, therefore, lately cut off. It is possible to carry out pressure and height measurements of the hollow body with the end region without being yet cut. However, it is preferable and advantageous when a cutting-off device is provided in the operational region of a transfer gripping device which transfers hollow bodies between the preform blow mold station and the weight-and/or height measuring device. This improves the measurement results as an error can occur in the end region.
It is particular preferable and advantageous when the cutting-off device is associated with a sensor for monitoring the cutting-off process. In this way, only cut-off hollow bodies reach the weight-and height measuring devices.
According to a preferred and advantageous embodiment of the present invention, the hollow bodies are elastically compressible in the height direction, and during the height measurement, the measuring piston, which forms part of the height-measuring device, is displaced a predetermined length against a hollow body compressing the same, and a force-measuring device, which registers the force corresponding to the compression of the hollow body, displays a value corresponding to the hollow body height. At that, the measuring piston is displaced downward a predetermined length amount and compresses the hollow body to a greater or lesser degree dependent on the hollow body height. The force, which is necessary for compression of the hollow body, represents a measure of the hollow body height. Such a force-measuring device is simpler to develop than a measuring device which measures the height of a hollow body directly.
The force-measuring device can be supported on the drive rod of the measuring piston or against a support for the hollow body. It is particularly preferable and advantageous when the measuring piston itself is used as a force-measuring element. This eliminates the need in transferring the hollow body between the weight-measuring device and the height measurement device, with the weight-measuring device being used for e

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