Device for strand guiding

Abstract

Device for guiding strands in a cutting head for producing uniformly cut granule sections from strands of brittle and / or fracture-sensitive material, characterized in that the strands are guided from region A to region D without deflection (change of direction). The angles α, β, γ are approximately 0.

Description

[0001] In the plastics processing and manufacturing industry, strands of molten plastic or rheologically similar products are produced using a continuous casting head in the rod pelletizing process. This continuous casting head has a material inlet and an outlet, which consists of at least one hole. The material emerges from this hole. The hole shapes the strand into the desired shape.

[0002] The formed strand is then transferred to a strand guide that depends on the process and product.

[0003] After strand conveying, further processing steps may follow until the strands enter the strand granulator. This cuts the strands into regular sections, called granules or pellets.

[0004] Within the strand granulator, the strands are conveyed by a conveyor, usually 2 rollers ( Fig. 1 1+3), which are arranged one above the other, are captured in the roller gap and passed to the cutting element ( Fig. 1 2), usually a rotating rotor with at least 1 knife cut off.

[0005] The cut is usually made by a pair of knives, which consists of a rotating knife 8Fig. 1 2) and a stationary knife ( Fig. 1 5). The stationary counter knife also serves as the support for the strands before cutting.

[0006] The position of the feed rollers in relation to the cutting rotor, or the angle of the strand run in the distance between the feed rollers and the intersection point on the cutting rotor, is given. State of the art

[0007] In order to be able to process a wide range of products with the strand pelletizers available on the market today, the following geometry in the cutting head has become established.

[0008] The state of the art is that an angle alpha (α) between the horizontal inlet of the strand ( Fig. 1 4) and the strand path after the feed rollers is necessary to deliver the strands in optimal shape to the intersection point a on the cutting rotor ( Fig. 1 2). In addition, an angle Beta (β) can be set between the path of the strand running towards the cutting rotor and the angle of the counter knife ( Fig. 1 5) be cheap.

[0009] Basically, the height of the strand when cut is different from the height of the strand before cut.

[0010] This means that, in the state of the art, the strand is deflected at least once between entering the strand pelletizer and the cut. Typically, after leaving the clamping area (α) of the feed rollers ( Fig. 1 1+3). Usually also a second time (β) and especially often a third time (γ). Disadvantage of the known methods

[0011] Plastic strands or strands made of a molded material that is fragile will break at the deflection point or be so damaged that they then break uncontrollably at a later point. This is particularly problematic because the strand pieces that break before the cut are cut in an undefined manner by the cutting rotor.

[0012] This means that you get irregular granules with varying lengths. In addition, a break, unlike a cut, creates a lot of dust, especially with the brittle materials used here.

[0013] This leads to excessive waste or makes it impossible to produce the material type using this process, especially if, after cutting, the resulting granules are sorted by length into fractions such as overlength, good length, and underlength / dust. This creates an uneconomical pass / fail ratio. At a low feed speed (strand speed) of 50 m / min and, for example, 10 strands entering the cutting area in parallel, approximately 160,000 granules per minute are produced. If, for example, 30% of the cuts are defective, this results in a reject rate of 1,440 kg / day.

[0014] This problem is solved by the features listed in the claims.

[0015] It has been shown that it is advantageous for the strand to run in a straight line between the points AD without any deflection. ( Fig.1) The course does not have to be horizontal or straight, but can also be tilted relative to the horizontal.

[0016] Since this is particularly difficult to implement in areas AB and AC due to the machine setup conditions, as the strand forming point (strand source) is usually positioned significantly below A, this was solved by a special inlet shape so that the strand is brought into area C in a particularly gentle manner, so that it can then again lead in a line from CD. Thus, even in such cases, an angle of α approximately 0 and β approximately 0 can be achieved. The kink at B (γ) is then mitigated by the special inlet shape.

[0017] Especially when the strand path between BCs is changed from horizontal to tilted, this allows this special strand guide to be retrofitted into existing systems without modifying significant parts of the cutting head. This allows existing systems to be conveniently adapted to the material type being processed.

Claims

[1] Device for strand guidance in a cutting head for the production of uniformly cut granulate sections from strands of brittle and / or fragile material, characterized by that the strands are guided from area A to area D without deflection (change of direction). Where the angles α, β, γ are approximately 0. [2] Device for strand guidance in a cutting head for producing uniformly cut granulate sections from strands of brittle and / or fragile material according to one of the preceding claims, characterized by that the strands are guided from area B to area D without deflection (change of direction). The angles α, β are approximately 0. However, the strand guide does not necessarily run horizontally. [3] Device for strand guidance in a cutting head for producing uniformly cut granulate sections from strands of brittle and / or fragile material according to one of the preceding claims, characterized by that the strands are guided from region C to region D without deflection (change of direction), the feed to region C being equipped with an arcuate feed device (6). The angles α, β are approximately 0. [4] Device for strand guidance in a cutting head for producing uniformly cut granulate sections from strands of brittle and / or fragile material according to one of the preceding claims, characterized by that the components for achieving claims 1 to 3 are designed in such a way that a simple conversion of the existing cutting heads is possible.

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