DE10201869A1 - Feed system for continuous supply of loose materials to an extruder comprises a side screw feeder through which material is drawn by an air flow and then separated from the air by a screen - Google Patents

Abstract

Material to be supplied to the melt in the main extruder is sucked from a storage point into a twin screw side feeding unit (2). Air and material are separated by a screen (5) below the screws (4) and the air is extracted by a fan (8). Material to be supplied to the melt in the main extruder is sucked from a storage point into a twin screw side feeding unit (2). Air and material are separated by a screen (5) below the screws (4) and the air is extracted by a fan (8). Material on top of the screen is picked up by the screw flights and conveyed to the main extruder. A rotating paddle (3) above the screws continuously breaks up the material to prevent agglomeration. A cleaning system below the screen prevents blockage of the screen by material residues.

Description

The invention relates to a device for continuous feeding of light snippets or Short cut fibers for the production of Plastic products using extruders. The task or Feeding the light materials into the melt of one Extruders require forced feeding because of snippets or Short cut fibers with moderate to poor flow properties tend to form balls and bridges in the feed zone. This property of ball and bridge formation is u. a. by the fiber length, fiber fineness, Surface quality, fiber density and the constructive design of the screw and feed zone at the Extruder or plasticizer influenced. Especially at Snails with a shallow depth are the task of light ones Cut fibers are problematic because the sinking behavior of light cut fibers with moderate or worse Free flowing in the worm threads is insufficient.

State of the art

According to the current state of the art, light fibrous materials with moderate or worse Free-flowing properties using the darning mechanism of the plastic extruder supplied [DE 284 794 C2; DE 30 31 201 C2]. The darning for the Plastic extruders are powered by themselves tapered screw feeders, which are in one Rotate the funnel-shaped housing. The fibrous Materials are compressed and in through the stuffing screw pressed the barrel of the extruder.

Another technical variant for feeding only for fibers with poor flow properties in extruders or plasticizers is a fiber task in the form of sliver. This technical Solution is limited by the fiber length, since only fibers processed into strips with a length of more than 15 mm can be. The disadvantage here is that a more expensive textile preliminary stage for the production of the Sliver is required.

The device DE 197 54 409 for cut fibers is for the production-stable process management not suitable and knows the following disadvantages due to the structural design, Bridging and funding problems with snippets and Short cut fibers and a temporary feed process by clogging the retaining sieve with snippets and Short cut fibers, which stops the feed process brings.

The invention DE 44 28 867 a machine for direct Processing of coarsely crushed molded parts or semi-finished products is responsible for the rough materials in the hopper Beginning of the main snail with enlarged or conical Abandon snails. To improve the feeding behavior the coarse materials are supported by Air sucked in, with a defined temperature control in the catchment area is necessary for a task of Materials are not made in the melt and the Intake openings are blocked by melt. For the Dispensing of finely divided voluminous chips or Short cut fibers in the melt with shortened The extrusion path of an extruder is not the machine designed or suitable.

Object of the invention

The aim of the invention is to provide a device for continuous feeding or feeding of light voluminous snippets or short cut fibers in the melt to develop with a shortened extrusion path of an extruder. The device is specially designed for materials with a Bulk density below 0.3 kg / l and a moderate to poor Flowability designed. The invention is suitable for Feeding of textile and foil-shaped snippets and tear or short-cut fibers (e.g. aramid fibers, LCP fibers, conventional synthetic fibers such as PA, PAN, PP, PET and. a. as well as regenerated cellulose and natural fibers) with a Fiber length of 2-15 mm in the extruder for production fiber-reinforced plastics or for recycling synthetic fibers by extrusion.

The present invention differs from conventional tamping machines and machines for the extrusion technique in that the supply of Shredded and short cut fibers by means of suction conveyance into the Side conveyor of an extruder is done without that Compact material and with a loosening element (Stirrer) and with a cleaning device and Inlet pocket for a production-stable feed process reached.

This pneumatic suction conveyance of chips and Short cut fibers with the new device have compared to that described prior art the advantage that a Matting or compacting which to bridge the Material for, is prevented. Through the Cleaning device of the sieve by means of time-controlled Compressed air pulses in the counterflow principle become a production-stable material flow in the extruder guaranteed. The continuous material supply enables a constant material input, which particularly affects the Material constancy positive in the production of compounds effect.

With flexible short cut fibers of polymer and cellulosic structure causes the even Material flow with suction conveying an improved incorporation and distribution of the fiber components in the matrix material.

Especially for extruders with smaller screw diameters or thread depth is the task of the fibrous materials Using suction conveying is an advantage because of high bending moments the extruder screws, just like when working with a darning system be avoided.

The new device also has the advantage that Dust from the conveyed material through the sieve get through and thus a separation of dust and Fine parts from the fiber material for low dust Fiber dosing is possible.

The device with reference to the drawing 1 and their numbering is based on the task, snippets and Short cut fibers with moderate or poor flow properties and an average diameter or length of 2-15 mm continuously fed directly to an extruder.

According to the invention, the object is achieved by the fact that the fibers are sucked by suction from the discharge opening of a metering device or the storage container through a downpipe ( 1 ) into the screw housing ( 2 ) of the side feeding device or side extruder by suction by means of air flow. The upper end of the downpipe is open so that the pipe opening serves to equalize the pressure for the suction promotion. The downpipe is connected to the worm housing in an airtight manner, a viewing window in the cover of the worm housing being advantageous for controlling the fiber transport. There is an agitator ( 3 ) in the screw housing or hopper to loosen and distribute the material and to avoid bridging of the material in the screw housing. The screw housing can be equipped with one or two screw conveyors ( 4 ). Below the screw surface, the material air flow is separated by a sieve ( 5 ) and the air is sucked out of the housing. The sieve width below the screw should be between 20-80% of the screw diameter. The mesh size of the sieve through which the air is drawn depends on the size of the material and the vacuum required for the suction. This air flow causes the chips to be drawn into the screw flights of the screw conveyors or onto the sieve. Due to the rotary movement of the screws, the snippets are combed off the sieve and conveyed in the screw passage in the direction of the extruder opening ( 11 ), a gradual tapering to the screw tube diameter (inlet pocket) ( 12 ) in the screw housing promoting the material transport to the extruder.

The sieve for separating the material air flow is fixed by a holder (hereinafter referred to as an open housing insert) ( 6 ) and can be replaced when worn.

The counter pressure device for cleaning the sieve with compressed air supply ( 7 ) and a non-return flap or slide ( 8 ) are integrated in the open housing insert. In the event of a cleaning pulse, compressed air is blown into the interior of the open housing insert, the non-return valve closes and the air flow only escapes through the sieve in the opposite direction of flow. There is no reversal of the material flow into the downpipe, since the adhering material is gripped by the sieve through the rotating screw conveyors and is transported away in the direction of the extruder opening. If a non-return valve is used, it must be set so that the mechanical non-return valve does not close during normal suction operation of the air and only closes it with the cleaning impulse that has a significantly higher air pressure. If the flap or slide is electrically controlled, this can be controlled together with the signal for the pressure pulse. This time-limited procedure of 0.2-5 s causes the sieve to be cleaned using compressed air in the counterflow principle and ensures that the material feed is stable. As an alternative to the counterpressure device, the screen can also be cleaned from below with rotating brushes in the open housing insert in order to avoid clogging of the screen in the long term.

The air is extracted from the housing using a fan ( 9 ). The amount of air extracted is regulated via a flap ( 10 ). A negative pressure of max. 0.5 bar is sufficient.

The main advantage of the device described is light Scraps or short cut fibers with poor Flowability and an average diameter or length of 2-15 mm to feed the extruder continuously.

For conventional material feed, the open Housing insert replaced by a closed housing insert conventional fillers, glass fibers or Granules can be abandoned and the Side conveyor or side extruder flexible can be used. A retrofit from conventional Side conveyor or side extruder or conversion thus possible.

example

embodiment

On a plant, the device described (drawing 1) is used to feed natural fibers (flax) to a twin-screw extruder ZE 25 via a twin-screw side feeder.

Flat short cut fibers with an average cutting length of 4 mm were used for the fiber feed. The blower for the forced conveyance of the synthetic fibers by means of air flow had a max. free flow rate of 800 m ³ / h and a max. Air pressure of 0.2 bar. The tests were carried out with fiber quantities of 10 kg / h, the speed for combing or feeding the fibers into the extruder of the twin-screw side conveyor being 350 rpm. The mesh size of the screen as a parting plane for flat short cut fibers (6 mm) in continuous operation was 750 µm in this application example.

Claims (4)

1. Device for production-stable continuous Feeding light, voluminous materials (snippets or short cut fibers) with moderate to poor Flowability for indirect feeding via Twin-screw side feeding devices or Twin-screw side extruder with shortened extrusion path in the melt of an extruder, in which by means of negative pressure the material snippets below the screw conveyors or short cut fibers (synthetic fibers such as PA, PAN, PP, PET u. a. as well as cellulose regenerate and natural fibers) in the Snail flights are sucked. Below the The material and air flow is sucked into the screw surface separated on a sieve and from the screw housing the airflow is sucked out below the sieve. On the sieve the material is gripped by the screw flanks and conveyed in the conveying direction by the screws. Above the snail is an agitator, the one ensures continuous loosening of the material. For continuous production-stable process control a cleaning element integrated underneath the sieve clogging of the sieves (separation plane of material and Airflow) to prevent material residues. 2. Device according to claim 1, characterized in that to clean the mesh or holes, the parting line from Material and air flow (sieve) by means of a counterflow device or rotating brushes at intervals. 3. Device according to claim 1, characterized in that a stirrer for feeding or Dissolution of material agglomerates is. 4. The device according to claim 1, characterized in that a closed one for conventional material feed Housing insert is used alternatively.