GB2089597A

GB2089597A - Drive Arrangements for Machines Working Plastic State Materials

Info

Publication number: GB2089597A
Application number: GB8039596A
Authority: GB
Original assignee: Simon Rosedowns Ltd
Current assignee: Simon Rosedowns Ltd
Priority date: 1980-12-10
Filing date: 1980-12-10
Publication date: 1982-06-23
Also published as: GB2089597B

Abstract

A machine such as a screw press for working materials in a plastic state, having a main drive motor and material working means driven thereby, characterised by an auxiliary drive motor connected or ready to be connected via an over-running clutch or freewheel device, to said working means, and automatic means which causes said auxiliary motor to be energised and to commence driving said working means in the event of failure of said main drive motor and before the working means has completely lost motion, and to discontinue operation of the device for feeding material to said working means. The motors may be electrical and the auxiliary motor supplied from a battery.

Description

SPECIFICATION A Machine for Working Materials This invention relates to a machine for working materials in a plastic state, and particularly to a drive system therefore.

Many machines used in industry and powered by electric motors have the undesirable characteristic that if a power failure occurs the machine stops during an operating process, and in some cases cannot be restarted even if the interruption in supply is only momentary. With many power supples, direct on-line starting of high powered motors is not permitted by the power supply authority. Consequently starters have to be used to limit the starting current taken by the motor and this in turn limits the maximum torque available to levels below that obtainable in direct on-line starting conditions.

In the case of certain machines used for working materials in a plastic state this problem is particularly felt since many such materials are thixotropic, thermoplastic or thermosetting or have more than one of these characteristics.

Thixotropic materials set solid if not kept in motion.

Thermoplastic materials become more fluid when heated and in some cases the energy required to keep them hot may be provided in the form of mechanical work. Thermosetting compounds will set hard if kept hot for more than a limited time. Materials having any of these characteristics may be processed in a continuously operating machine of a given power, but if the machine is allowed to stop the torque required to restart it is much greater than that required to maintain it at operating speed.

One way of avoiding this difficulty is to use over-sized motors, but this causes further problems in that starting currents are increased above the level permitted, and when the machine is running, the lightly loaded motor has a poor power factor and consequently the installation is inefficient.

Typical machines showing these characteristics are screw presses, extruders, expanders and mixers, used in the food industry and in the rubber and plastics industries.

An object of the present invention is to provide for a machine of this general kind, a drive system which will at least substantially avoid the aforementioned difficulties.

According to the present invention there is provided a machine for working materials in a plastic state, having a main drive motor and material working means driven thereby, characterised by an auxiliary drive motor connected or ready to be connected to said working means, and automatic means which causes said auxiliary motor to be energised and to commence driving said working means in the event of failure of said main drive motor and before the working means has completely lost motion.

The invention will now be described, by way of example only, with reference to a screw press which comprises one or more shafts which carry helical screw flights rotating within a perforated barrel. The press is so arranged that material fed in at one end is subjected to increasing pressure as it passes along the barrel and thus is pressed and de-liquified. Many such presses are used for removing the oil content of vegetable oil seeds and typically are driven by electric motors of up to 300 kilo-watts.

It is necessary during operating of the machine to ensure that roation of the screw shafts is continuous in the event of a power failure thus preventing the material in the barrel from becoming hard.

In accordance with the invention a small auxiliary motor is coupled to the main motor shaft either directly or, for example, through a chain drive. An over-running clutch or freewheel device is interposed between the auxiliary motor and the main motor shaft so that during normal running of the main motor, the auxiliary motor is not rotating.

In one example, the auxiliary motor may be a D.C. electric motor powered by a battery. During operation, if the main power supply is discontinued, a contactor between the supply and the main motor opens which causes a switch to be closed to connect the auxiliary motor to the battery. Rotation of the auxiliary motor engages the over-running clutch or freewheel device and commences driving the shaft of the press to continue the process. The auxiliary motor is preferably of lower power then the main motor so that the speed of rotation of the press is reduced in order that the auxiliary motor may supply the necessary driving torque. Of course, the time taken for the screw press to clear the material from its barrel will be increased, and the performance of the battery must be selected accordingly.

Preferably, also, the device employed to feed fresh material to the press, which usually is continuously operating, is arrested by the opening contactor which stops the main motor, and restarted only when the main motor re-starts or when the barrel becomes empty.

If the main power supply fails for only a short period the press could be re-started by the main motor starter without waiting for the barrel to be completely emptied of material by the auxiliary motor since the re-starting action of the main motor would be effected against the dynamic frictional load of the press rather than a much higher static load, should the press have stopped.

As alternatives to the use of a D.C. electric motor powered by a battery, other kinds of motor could be used such as an air motor operated by a stored compressed air supply, a stream motor operated from a boiler or steam accumulator, or still a hydraulic motor operated by a hydraulic accumulator. In any event, the auxiliary motor must be capable of taking over the driving motion from the main motor before the screw shaft or other material working means has completely lost its motion. Thus sensing means such as the opening of a contactor is necessary to cause immediate energisation of the auxiliary motor.

Claims

1. A machine for working materials in a plastic state, having a main drive motor and material working means driven thereby, characterised by auxiliary drive motor connected or ready to be connected to said working means, and automatic means which causes said auxiliary motor to be energised and to commence driving said working means in the event of a failure of said main drive motor, and before the working means has completely lost motion.

2. A machine according to claim 1, wherein said auxiliary drive motor is drivingly coupled to the driving shaft of said main drive motor, transmission from said auxiliary motor to said shaft being through an over-running clutch or freewheel device whereby during normal running of the main drive motor, the auxiliary motor does not rotate.

3. A machine according to claim 1, or claim 2, wherein said motors are electrically powered and said auxiliary motor is supplied from a battery, said automatic means comprising a contactor between the main drive motor and the electrical power supply thereto which when the latter is discontinued, opens and causes a switch to be closed to connect the auxiliary motor to the battery.

4. A machine according to claim 1, or claim 2, wherein said auxiliary motor is an air motor operated by a stored compressed air supply.

5. A machine according to claim 1 or claim 2, wherein said auxiliary motor is a steam motor operated from a boiler or steam accumulator.

6. A machine according to claim 1 or claim 2, wherein said auxiliary motor is an hydraulic motor operated by an hydraulic accumulator.

7. A machine according to any one of the preceding claims wherein said automatic means is operatively connected to a device feeding material to the working means thus to discontinue operation of said device in the event of failure of said main drive motor.