System and method for the continuous feeding of an extruder

Abstract

A system for the continuous feeding of an extruder with a mixture containing a plastic granulate and one or more additives, comprising a cylindrical, vertical mixing apparatus (1) equipped with a stirrer, with filling openings for the plastic granulate and the one or more additives at the upper end of the cylindrical, vertical mixing apparatus (1), and a first discharge pipe (2) at the lower end of the mixing apparatus (1) which has a shut-off device and which is connected to a feed hopper (3) from which the extruder is fed, characterized in that a second discharge pipe (4) with a shut-off device is provided at the lower end of the mixing apparatus (1), through which rinsing water can be completely drained from the mixing apparatus (1).

Description

[0001] The invention relates to a plant for the continuous feeding of an extruder and a method.

[0002] When preparing mixtures containing plastic granules for injection molding or extrusion applications, the components of the mixture are usually weighed into a mixer according to the recipe, mixed, and discharged into a feed hopper for the extruder. While the extruder is being fed from this hopper, the next batch of mixture can be prepared in the same recipe after the mixer has been completely emptied.

[0003] However, if a mix with a different formulation needs to be prepared, the mixing equipment must be cleaned before producing the second mix with a different formulation than the previous one. This can be done manually, semi-automatically, or fully automatically and is usually achieved by rinsing with water, especially under high pressure, if necessary with the use of cleaning aids.

[0004] If there is a fixed connection between the mixing device and the feed hopper, the flushing process in the mixing device can only be started after the feed hopper has been completely emptied, which can take a long time, for example one to two hours, depending on the extruder throughput and the size of the feed hopper.

[0005] The rinsing process of the mixing apparatus then proceeds in such a way that the rinsing liquid, usually rinse water, flows through the mixing apparatus and through the feed hopper for the extruder. This removes any encrustations of additives, especially dye residues, from the mixing apparatus.

[0006] A disadvantage of the above-mentioned operating mode is that the extruder must be shut down when changing the recipe to clean the mixing apparatus for preparing the mixture. This is time-consuming, especially for extruders with high throughputs, and leads to production losses due to downtime. Further prior art can be found in the publications DE 20 2004 015 743 U1, WO 2007 / 045 529 A1, WO 2009 / 037 118 A1, DE 40 27 319 A1, and AT 411 161 B. In contrast, the object of the invention was to provide a system and a method for the continuous feeding of an extruder, according to which downtimes during a recipe change can be minimized or avoided.

[0007] The solution consists in a plant for the continuous feeding of an extruder with a mixture containing a plastic granulate and one or more additives, comprising a cylindrical, vertical mixing apparatus which is equipped with a stirrer, with filling openings for the plastic granulate and the one or more additives at the upper end of the cylindrical, vertical mixing apparatus and a first outlet pipe at the lower end of the mixing apparatus which has a shut-off device and which is connected to a feed hopper from which the extruder is fed, which is characterized in that a second outlet pipe with a shut-off device is provided at the lower end of the mixing apparatus, via which rinsing water from the mixing apparatus can be completely drained directly, bypassing the feed hopper.

[0008] It was found that it is possible to design a system for feeding an extruder in a simple manner so that no or minimal downtime of the extruder occurs when the recipe is changed.

[0009] According to the invention, a system is provided comprising a cylindrical, vertical mixing apparatus equipped with a stirrer. The stirrer is driven, as is conventional, by a motor, which is usually arranged above the mixing apparatus. The mixing apparatus is equipped with filling openings for the plastic granules and the one or more additives at its upper end.

[0010] In another embodiment, the individual components, i.e. the plastic granulate and the one or more additives, are weighed individually and filled through a filling opening.

[0011] In this context, plastic granulate is understood to mean a uniform granulate of plastics, but also a mixture of plastic granules with different molecular weights, different chemical compositions or different geometries.

[0012] As additive or additives, one or more substances selected from the following list are used: Waxes, plasticizers, lubricants and mold-release agents, pigments, dyes, matting agents, flame retardants, antioxidants, stabilizers against light and thermal damage, fibrous and powdered fillers and reinforcing agents and antistatic agents in the amounts customary for these agents.

[0013] The additives can be in pure form (solid, liquid, or gaseous), or used as a mixture of the pure substances. They can also be used in a formulation that facilitates dosing, such as a solution or a dispersion (emulsion or suspension). A formulation as a masterbatch, i.e., a concentrated mixture with a compatible thermoplastic polymer, is also suitable and, in some cases, preferred.

[0014] In principle, all thermoplastically processable plastics (polymers) can be used as plastic granules, either in pure form as individual components or already impact-modified as a mixture with other thermoplastics or with rubber components.

[0015] Examples, but not limitations, include polystyrene, high-impact polystyrene (HIPS), SAN, impact-modified SAN (ABS, ASA, MABS), poly-α-methylstyrene-AN copolymer, polymethyl methacrylate, polyamide, polyesters (PBT, PET, etc.), polysulfones, polycarbonates, polyolefins (PE, PP, PIB), polylactic acid, and others, in various proportions. The production of such polymers is known to those skilled in the art and can be found in the relevant literature.

[0016] The invention relates in particular to a plant for feeding an extruder with a mixture containing one or more dyes as additive(s).

[0017] At its lower end, the mixing apparatus has a first outlet pipe for the mixture, which is equipped with a shut-off device. The outlet pipe is arranged vertically or at an angle, whereby it is essential that the mixture produced in the mixing apparatus can be completely drained.

[0018] The mixture falls through the outlet pipe with the shut-off valve open into a feed hopper, from which the extruder is fed. It is also possible to serve multiple extruders via the feed hopper.

[0019] In particular, the first outlet pipe can be connected to a conveying device, preferably a discharge screw, to assist in conveying the mixture produced in the mixing apparatus into the feed hopper. Precise dosing is made possible, for example, by a suitable gravimetric dosing device.

[0020] According to the invention, a second outlet pipe is provided at the lower end of the mixing apparatus, which is also provided with a shut-off device.

[0021] The second outlet pipe must be positioned in such a way that the contents of the mixing device can be completely drained through the second outlet pipe.

[0022] According to the invention, a method is also provided for the continuous feeding of an extruder during a recipe change, in which firstly a first mixture containing a plastic granulate and one or more additives is provided in a cylindrical, vertical mixing apparatus equipped with a stirrer, to which the plastic granulate and the one or more additives are fed via filling openings at the upper end of the same, after which the mixture falls via a first outlet pipe with a shut-off device at the lower end of the mixing apparatus into a feed hopper for the extruder, which is characterized in thatthat after emptying the mixing apparatus into the feed hopper and shutting off the first outlet pipe, the mixing apparatus is rinsed with a rinsing liquid and then the rinsing liquid with any residues of the mixture contained therein is discharged from the mixing apparatus via a second outlet pipe by opening a shut-off device in the second outlet pipe, whereby the feeding of the extruder with the mixture from the feed hopper is not interrupted, and after which a second mixture of a plastic granulate and one or more additives is produced in the mixing apparatus with a different recipe from the first mixture and, after emptying the first mixture from the feed hopper, is fed into the feed hopper and from there to the extruder.

[0023] Similarly, after the second mixture has been completely drained from the mixing apparatus, the mixing apparatus can be rinsed in the same manner as described above, followed by emptying of the rinsing liquid containing any residues of the second mixture, whereby the extruder does not have to be switched off during this further rinsing process.

[0024] The mixing apparatus is rinsed primarily with water as the rinsing fluid, optionally with the addition of cleaning agents. Rinsing with high-pressure water is preferred.

[0025] The flushing water is preferably drained directly into the sewer via the second outlet pipe.

[0026] The plant and the process according to the invention are particularly suitable for extruders with high throughputs, particularly preferably for extruders with throughputs in the range of 500 to 10,000 kg / h.

[0027] By using the system according to the invention and the method according to the invention, the costly shutdown of extruders, in particular extruders with high throughputs, and corresponding downtimes and thus production losses can be avoided. Example 1 (comparison)

[0028] In a cylindrical mixer with a volume of 1500 l, equipped with an overhead stirring motor and a two-stage paddle mixer, the following components were added one after the other via a filling opening: 400 kg of ABS granules containing approximately 50% graft rubber based on polybutadiene-g-SAN, 600 kg of α-methylstyrene-acrylonitrile copolymer, 0.6 kg of a phenolic antioxidant, 0.6 kg of a sulfur synergist, 1.2 kg of a liquid antistatic agent, 5 kg of magnesium stearate, and 10 kg of carbon black. The mixer was closed, and the stirrer was started and operated at 50 rpm for 6 minutes until the mixture was homogenized. The batch was then discharged into a storage hopper via a bottom outlet valve and fed to the extrusion line via a gravimetric dosing device at a rate of 1200 kg / h. After emptying the mixer, the same recipe was prepared two more times. After the last batch, the mixer and storage hopper were emptied, and the extruder was shut down. The mixer and storage bunker were thoroughly rinsed with a high-pressure cleaner.The rinse water was discharged from the mixer and the storage bunker into the wastewater system for treatment. The dosing system was cleaned separately.

[0029] The extruder shutdown phase lasted approximately 90 minutes.

[0030] After the cleaning process, a different recipe was prepared: 400 kg of ABS with approximately 50% graft rubber, 600 kg of α-methylstyrene-acrylonitrile copolymer, 0.6 kg of a phenolic antioxidant, 0.6 kg of a sulfur synergist, 1.2 kg of a liquid antistatic agent, 10 kg of montan wax, and 30 kg of titanium dioxide. Several batches of this mixture were run until the next product change and cleaning process. Embodiment 2 (invention)

[0031] In a cylindrical mixer with a volume of 1500 l, equipped with an overhead stirring motor and a two-stage paddle mixer and the 2 outlet pipes according to the invention, corresponding Fig. 1, the following components were added one after the other via a filling opening: 400 kg of ABS granules containing approximately 50% graft rubber based on polybutadiene-g-SAN, 600 kg of α-methylstyrene-acrylonitrile copolymer, 0.6 kg of a phenolic antioxidant, 0.6 kg of a sulfur synergist, 1.2 kg of a liquid antistatic agent, 5 kg of magnesium stearate, and 10 kg of carbon black. The mixer was closed, and the stirrer was started and operated at 50 rpm for 6 minutes until the mixture was homogenized. The mixture was then discharged into a storage hopper via a bottom outlet valve and discharged via the first outlet pipe into a storage hopper. It was fed to the extrusion line via a gravimetric dosing device at a rate of 1200 kg / h. After emptying the mixer, the same recipe was prepared two more times. After the last batch, the mixer was emptied and the first outlet pipe was closed. While the storage hopper was being emptied, the mixer was thoroughly rinsed with a high-pressure cleaner.The rinse water was fed into the wastewater system for treatment through the second outlet pipe designed according to the invention. While the storage hopper and the dosing system were subsequently cleaned separately, the next formulation could be prepared in the mixer without having to shut down the extruder.

[0032] After the cleaning process, a different recipe was prepared: 400 kg of ABS with approximately 50% graft rubber, 600 kg of α-methylstyrene-acrylonitrile copolymer, 0.6 kg of a phenolic antioxidant, 0.6 kg of a sulfur synergist, 1.2 kg of a liquid antistatic agent, 10 kg of montan wax, and 30 kg of titanium dioxide. Several batches of this mixture were run until the next product change and cleaning process.

[0033] A production downtime of the extruder of approximately 90 minutes was avoided compared to the state of the art.

[0034] The invention is explained in more detail below with reference to a drawing: The only Fig. 1 shows schematically a horizontal section through a system according to the invention.

[0035] A cylindrical, vertical mixing apparatus 1 has a first outlet pipe 2 into a feed hopper 3 for an extruder, as well as a second outlet pipe 4 for a rinsing liquid, in particular rinsing water.

Claims

[1] Plant for the continuous feeding of an extruder with a mixture containing a plastic granulate and one or more additives, comprising a cylindrical, vertical mixing apparatus (1) equipped with a stirrer, with filling openings for the plastic granulate and the one or more additives at the upper end of the cylindrical, vertical mixing apparatus (1) and a first outlet pipe (2) at the lower end of the mixing apparatus (1), which has a shut-off device and which is connected to a feed hopper (3) from which the extruder is fed, characterized by that a second outlet pipe (4) with a shut-off device is provided at the lower end of the mixing apparatus (1), through which the rinsing water can be completely drained from the mixing apparatus (1). [2] Plant according to claim 1, characterized by that the first outlet pipe (2) is connected to a conveying element, in particular to a discharge screw. [3] A method for continuously feeding an extruder during a recipe change, in which a first mixture containing a plastic granulate and one or more additives is first provided in a cylindrical, vertical mixing apparatus (1) equipped with a stirrer, to which the plastic granulate and the one or more additives are fed via filling openings at the upper end thereof, after which the mixture falls via a first outlet pipe (2) with a shut-off device at the lower end of the mixing apparatus (1) into a feed hopper (3) for the extruder, characterized by , that after emptying the mixing apparatus (1) into the feed hopper (3) and shutting off the first outlet pipe (2), the mixing apparatus (1) is rinsed with a rinsing liquid and then the rinsing liquid with residues of the mixture contained therein is discharged from the mixing apparatus (1) via a second outlet pipe (4) by opening a shut-off device in the second outlet pipe (4), whereby the feeding of the extruder with the mixture from the feed hopper (3) is not interrupted, and after which a second mixture of a plastic granulate and one or more additives is produced in the mixing apparatus (1) with a recipe different from the first mixture and, after emptying the first mixture from the feed hopper (3), is fed into the same and from there to the extruder. [4] Method according to claim 3, characterized by that an extruder is fed with a throughput in the range of 500 to 10,000 kg / h. [5] Method according to claim 3 or 4, characterized by that the mixing apparatus (1) is rinsed under high pressure, the rinsing liquid being water. [6] Method according to one of claims 3 to 5, characterized by that the first and second mixtures contain one or more colorants as additive(s).

Images