DE2045801B2 - PROCESS FOR THE MANUFACTURING OF DRY GRANULES FROM MELT LIQUID, THERMOPLASTIC PLASTICS - Google Patents

Description

cool only to the strengthening of its surface. The strands turn "So cut into a state because" the diameter of the cutting device M "have resistance tu overcome, namely de * surface of the Strange, while the interior is still largely in the soft state c" only relative who takes the vtsn the The granulate supplied to the cutter A # now still contains a considerable amount of heat. which is sensibly used for the trucking process of the granulate. In the granulate cooling zone G connected to the cutting device, so much heat is removed from the granulate by a coolant that the remaining residual heat is sufficient for self-drying in the drying device Tr.

As already mentioned above, the granulate cooling zone C is divided into several sections. \ n Granulatkuhl / onc ti are lumhch / VVei I nterbreilumgsaKclinuie I .j uiui (Λ turned on, in which no cooling of the continuous, granules statttmdet so that> I ίιΐ in our I nicrlVechiingsabschnnten and Ib each Obcrflachcn:.. en \ | The temperature of the individual grains is largely sewn to the internal temperature. This ensures that the subsequent cooling section lib b / v \. (iY> can develop an intense effect that otherwise with a ciranulate with only low surface temperature due to the poor thermal conductivity of plastics would be substantially reduced. Aif this way can be kept correspondingly short the cool regions of the granule cooling zone. namely, Ga. Gb and Gc.. It should be noted in this context cL'.auf that of course more or less Unterbrechunssabschniite inserted into the granule cooling zone G This depends on the temperature of the granulate in question and on its thermal conductivity The diameter of the granulate plays a role. The thinner the granules. the less important is such an interruption.

In the simplest way, the granulate is transported through the granulate cooling zone G by means of the cooling medium itself, whereby the cooling medium used in the string cooling zone S can be used. This can be, for example, water. In that case the water flow would wash the granulate through the sections Ga. Gb and Gc. at the same time it would develop its cooling effect. So that the cooling can now be interrupted in the interruption sections Ca and Lh , the granulate is transported separately from the coolant, for example via sieve drums. Sieve belts or the like.

A gas can also be used as the coolant instead of water. z. B. nitrogen or a liquid-gas mixture be used in the manner of a mist. The coolant depends on the required cooling effect and the chemical nature of the plastic to be granulated, on its sensitivity consideration must be given to certain coolants if necessary.

In the F i g. 2 shows how, for example, a cooling section of the granulate cooling zone G can be designed. This is the section Ga. This contains a pipe coil with a flange F / at its inlet (see also FIG. 1), into which the granulate with the coolant is fed from the cutting device M. The coolant washes the granulate through the pipe coil until it emerges at the exit, where it is then fed to the following interruption stage Ua. The coil is surrounded by a further cooling medium, for example water, in order to give the coolant flowing through the coil the desired temperature. So that a specific heat withdrawal can only be set in the relevant stage, stage Ga has, in addition to input I, further inputs 2, 3 and 4, which are closed

Lead taps on the pipe coil. In this way it is possible to adjust the residence time of the granulate in the Ga stage accordingly and thus to regulate the desired heat extraction, namely by optional connection to one of these inputs

in progress.

The figure? shows a diagram da <. the temperature conditions heim Purchlauf de ·· KiHi-.isto:; .- through the plant is gcmäL · 'ig. I am kidding. the The curves drawn in give the respective

ao temperature of the material. where mi:; / you core temperature. im denotes the average mpetaiur and ta denotes the surface temperature. The process begins with the still liquid plastic strands entering the \ b / ug> gerai t .

where the strands have a temperature of HX) I. While the strand is being guided through the strand cooling zone5, the material cools down. Surface strongly. and / was up to a temperature door of about 150 C. whereas the Kerpiempcru; ur only drops to about 280 C. The strands have solidified cattle on their surface and are cut by the cutter M in this state. The Granuiatkühlzor.e ο then follows. within the first in the cooling section (meters takes place a further cooling system, wherein the jewciligen temperatures, as can be seen, further lower Here, / is the difference between outdoor temperature door ta and core temperature; still large, so that decreases due to the poor thermal conductivity of plastic, the cooling intensity accordingly. . Ir subsequent L'ntertuechungsstufe ία is then added to the granules without further cooling time is a temperature compensation before / unehmen wherein depending on the duration of the interruption, the surface temperature approaches the Kerniemperatur Aährend the mean temperature in the practically constant Here remains sidewalk....: the Oberflächentemperaiur ta again considerably in. so that the cooling can affect intensively again in the following cooling step Gb. in d? r following Unterbrechunasstufe Lb then finds again an internal temperature compensation instead, which in turn increases the outside temperature ta, then in the last · ι Cooling stage Gt- the last cooling takes place first.

At the end of this stage, the core temperature // and the surface temperature ta have largely approximated. In this state of the granulate, the separation of the coolant takes place in the separator B. to which the drying device Tr is located.

closes. At this point the granulate still has a residual heat that is sufficient for self-drying at this stage. The core temperature // and the surface temperature ta continue to approach each other. The granulate then leaves the drying device dried, but at a relatively high temperature level, which here still requires dry cooling, which takes place in the subsequent dry cooling device Tk , in the

2

the granulate is cooled to the desired final temperature. This can be, for example act as a cooling drum or a cooling screw.

In the example of use on which the diagram is based, it is provided that the surface temperature ta never falls below 100 ° C. until the end of drying in the drying device Tr. It is assumed here that water is used as the coolant. This measure has the advantage that the coolant boils immediately when it comes into contact with the plastic, which counteracts diffusion or sorption of water into the plastic.

By optionally setting the residence time in the individual sections of the granulate cooling zone G, namely Ga, Gb and Gc, as well as in the interruption stages Ua, Ub , a certain temperature level of the granulate can be set in the desired manner, which can be important for various purposes. The process engineer thus has the ability to adapt the method according to the invention to different operating and material conditions. In particular, he can set a certain temperature level in the drying device Tr by setting the interruption duration.

1 sheet of drawings

Claims (3)

to give the granulate the possibility that patent claims: s ° .a surface temperature before being passed on to the next stage approximates the internal temperature 1. Process for the preparation of dry equals, so that for cooling in each one fol granules from molten, thermoplastic 5 lowing stage again a relatively high temperature Plastics in which the surface of the granulate is drawn from the melt. As a result gene strands through a coolant flowing around them, the full effectiveness of the tel solidified only on their surface and unfold in the coolant. Because the drying of the be cut in this state, whereupon the granulate goes faster, the higher the Granulate also by means of a coolant so much temperature is on the surface of the granulate, Heat is withdrawn so that it remains in it, and that which sets in again after the interruption has an effect Residual heat is extracted particularly intensively for subsequent self-igniting cooling. Drying is sufficient, as a result of which a liquid can be used as a coolant shows that the cooling of the granulate in gas or a mixture of liquid and gas is provided in several successive stages (mist). When using liquid, the coolant is expediently kept in each stage Granulate surface and coolant, nor plastics with a scopic effect, are not able to cool down at a favorable value and then absorb the coolant in themselves.
Surface and internal temperature of the granulate The invention is illustrated by an embodiment before passing on to the next level, explained in more detail using the drawing. It shirt can be balanced. shows 2. The method according to claim 1, characterized in Fig. 1 a device which, according to the invented, that the cooling works with a liquid process according to the invention, 2 a cooling device in the area of the gradient follows. bulk cooling zone, 3. The method according to claim 2, characterized in Fig. 3 is a temperature diagram for the pre-characterizes that when cooling with a liquid direction according to F i g. 1 continuous plastic.
Coolant the surface temperature of the art 30 According to FIG. 1, the system shown has material above the boiling point of the coolant an autoclave A , in which liquid plastic is kept means. is located. Instead of the autoclave, a continuous polymerization tube or r kick an extruder. This is on autoclave A. 35 main valve H connected, which leads to the distributor V. The distributor directs the melt to the individual The invention relates to a method for producing nozzles which can be shut off individually or together. · Production of dry granules from melts. From the nozzles the liquid, thermoplastic plastics then pass, in the case of the melt, to a so-called withdrawal device £, strands withdrawn from the melt by a coolant flowing around them within which the coolant exiting from the nozzles only on their surface, plastic strands are solidified by a cooling medium and be cut in this state. This can also be done by injecting the granulate through a coolant. So much heat is withdrawn below the injectors of the extraction device that the E remaining in it emerge from this pipe R , which is sufficient for the plastic strands supplied by the remaining heat to the subsequent self-drying injectors and the voltage. pass this circulating coolant downwards. Such a method is known from the USA patent. Discharge device E and pipes R form a script 2,975,483. The cooling of the straight strand cooling zone S. Below the tubes /? If the cut granulate is located, a known cutting device M with rotating is carried out with water along a water-permeable 50-generating knife, which turns the supplied strands into gra-Tian sports tape. This cooling is not very internally cut. The granulate produced in this way becomes sive, so that only a small throughput of gradients is passed on from the flow of the coolant and results in granulate. reaches a granulate cooling zone G, which is The invention is based on the object that dene parts are divided into more detail below To make the cooling process particularly intensive. 55 is received. To the granulate cooling zone G According to the invention, this object is then followed by a separator B which, for example, achieves the cooling of the granulate in several stages by centrifugal action, the coolant being carried out in successive stages, the granulate being separated. The latter then reaches a surface temperature of the drying device Tr in each stage, to which a dry cooling granulate is not connected below a certain device Tk for the 60. The dry cooling heat transfer between the surface of the granulate and the device Tk is only required if the coolant still cools at a favorable value and a granulate at a low temperature, which determines the surface and internal temperature, is desired as a result of the process,
of the granulate before being passed on to the next stage can be approximately compensated. 65 certain temperature of the coolant and one In the method according to the invention, the corresponding length of this zone as well as Bec ^! A gradual cooling of the granulate takes place, taking into account the speed of passage of each stage, the cooling is interrupted in order to remove so much heat from the strands that they separate