DE2734834A1 - METHOD AND DEVICE FOR PRE-FOAMING EXTENSIBLE PLASTICS - Google Patents

Description

Method and device for prefoaming extensible

Plastics

The invention relates to a method and a device for prefoaming expandable or stretchable plastics and in particular the pre-expansion of styrene copolymers.

The molding of plastics usually involves three Operating steps namely the pre-expansion or pre-expansion of primary materials, the intermediate storage of these materials and the actual shaping.

In order to carry out the prefoaming, the primary material, which is in the form of small spheres containing a blowing agent, is subjected to heating to between 90 and 103 ^° C. by means of steam, which results in the small spheres expanding. In contrast to other gases, this vapor has the advantage that, on the one hand, a large amount of heat is given off at the moment of its condensation without a temperature drop and, on the other hand,

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that it quickly enters the interior of the balls, whereby the effect of the porogen or blowing agent is increased.

A cylinder vessel in which the material or plastic is mechanically moved and heated by the steam is used to carry out this process. At a The only such treatment is a weight change of the balls from 600 kg / nr to 20 kg / nr, with a subsequent or aftertreatment, even lighter balls can be obtained.

The spheres thus obtained cannot be used immediately for molding. The balls absorb during the heating process namely the steam and during. The cooling causes the condensation of the vapor to create a certain negative pressure in the Inside the balls, which is filled in by means of a gas and in particular by means of air. This reabsorption of gas forms what is called maturation or secondary fermentation and what is during intermediate storage takes place.

According to a. Others experience the elastic plastic is moved and heated, for example, in shape of balls located in a container with heated walls. As soon as the (small) balls reach a certain temperature reached, the inside of the container is placed under negative pressure, causing the expansion or expansion of the balls is favored. The expansion is stopped or interrupted by water atomization and the balls are under theirs Softening temperature - cooled. This procedure is

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advantageous, but reducing the post-fermentation time requires the use of specially trained and expensive expanders or expansion vessels as well as relatively long operating steps. In addition, the balls contain water ^ and the propellant, for example pentane, is present in amounts less than the above method.

5s is therefore the object of the invention while avoiding this Disadvantages of specifying a method and a device which pre-foam the small plastic balls in a simple manner.

The invention thus relates to a method for prefoaming of stretchable plastics and in particular of styrene copolymers, which consists essentially in the fact that the preheated plastics present in the form of balls or materials are moved and heated by being subject to the action of a hot gaseous fluid that rises and moves in a circular motion, the throughput and the temperature being adjusted or controlled so that the nails are lifted, that they are moved and that they are heated up to their softening temperature, and that the pre-stretched balls thus obtained directly to Forming can be used.

The invention also relates to a device for performing the method, the device being a pre-expander is, which is characterized in that it has a container made of preheated stretchable material or plastic balls is supplied, a fluid generator and a pulverizer of the fluid to the fluid

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to atomize along an increasing turbulent area, adjusting members for the inlet flow rate and the outlet flow rate the balls, the fluid throughput. and the fluid temperature and the container temperature and a puller for pulling or sucking off the pre-stretched balls at the top of the container.

The "virgin" or undeformed balls are ^{preheated to about 50 °} C. before being introduced into the expander. The steam has a heat output per kg of fluid which is considerably greater than that of a gaseous fluid such as nitrogen, carbon dioxide or air, which is why preheating is necessary in order to reduce the amount of heat in the expander itself that is necessary for expansion or stretching of the spherical shape for the same reason, in order to maintain a temperature of the gaseous fluid inside the expander which, in a much simpler way, is homogeneous and fluctuates only slightly. The most suitable gaseous fluid is carbon dioxide CO ₂ * which is an inert gas and is harmless and which _# after steam _{# is} one of the gases that most easily penetrate the expanding spheres. The fluid throughput in the expander is about 10 kg / h per kg of expanded polystyrene.

The expansion or expansion takes place in the gaseous fluid, which is kept at between 95 and 100 ^° C., in the case of polystyrene, its temperature, its throughput and the dwell time of the balls in the expander determine the tightness of the starting product.

In this device, the balls are kept in suspension and are moved by the fluid, which is a constant Ensures temperature at all points of the container. the

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Balls that have not yet expanded are the heaviest and want to remain at the bottom of the container and are lifted according to their heating and their decreasing density.

The unique feature of the device according to the invention consists essentially in that a preheating chamber of the balls is used. their introduction into the container, and that particularly effective facilities are used ^ to atomize the fluid according to an increasing turbulent path or area.

To achieve this, a hot air inlet nozzle is used, which is provided with openings along a helical line, the axis being arranged vertically, and the nozzle opens above the upper end of a cone part which projects from the bottom of the container} a cone part which is arranged on the bottom of the container, a plane arranged on the base of the conical part and movable about it, a horizontal wire positioned just above the plane, hot air entering at the base of the container, - and several Slits or openings provided in the wall of the container for the entry of hot air or a double supply of hot air, which enters on the one hand at the bottom of the container and through openings provided in its inner wall and which on the other hand, enters through a hot air inlet pipe, those in the supply line or feed line for the preheated balls opens.

The invention is explained in more detail with reference to the exemplary embodiments shown in the drawing. Show it:

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Flg. 1 shows a first embodiment of the device according to the invention;

2 shows a second exemplary embodiment of the device according to the invention;

3 shows a third exemplary embodiment of the device according to the invention.

According to a first exemplary embodiment of the device according to the invention shown in FIG. 1 this one expanding container 1, over which a fluid generator 12 is centered and fixed, wherein a Hot air fan 3 is provided on the side at the top of the container 1st.

The container 1 is constantly supplied at its upper part by balls made of expandable material or plastic, which are preheated in a preheating chamber 4 to about 50 ⁰ C. The wall 5 of the container 1 is heated externally by means of a jacket 6 through which a hot fluid flows. Its temperature is set or regulated to a constant value, which is chosen so that the balls can reach their softening temperature.

The fluid generator 2 is provided with a DUse 7, the The outer circumference is penetrated by openings 8, which are arranged along a helical path, and their exit is arranged exactly above the bottom 10 opposite a conical part, which has a uniform distribution of the fluid in container 1 ensures. The hot air fan 3 variable throughput promotes air in a pulsating manner by means of a

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Bladder or pore 12 opposite the top of the wall 5 of the container 1 in order to prevent certain under the effect of the negative pressure that prevails in this space Bullets do not adhere to the wall 5. The treated balls are at the top of the container 1 via a line 13 removed.

In such a device, the balls, which are constantly introduced by means of an automatic dispenser, penetrate the container 1, in which they are subject to the action of an ascending fluid ^ for example hot air, which is particularly turbulent as it comes from the bottom of the container 1 comes from each rare conical part 11 and from openings 8, which are distributed over the nozzle 7 according to a helical line. Only those balls that have achieved a certain lightness are removed from the upper end of the container 1 via the line 13, the remaining balls falling down again and being completely heated by the gas flow until they too have become sufficiently light to be discharged can.

The preferred embodiment of the device according to the invention shown in FIG. 2 essentially contains a container 20 with a cylinder-cone shape, at the bottom of which a supply line 21 for untreated balls opens and a supply nozzle 22 for hot air. A conical part 23 is attached to the bottom 27 of the container and is provided to promote the circular or rotational movement of the hot air jet when it enters the container 20. A discharge device 2k

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the pre-expanded spheres and the hot air is attached to the top of the container 20.

Before they are fed into the container 20 of the pre-expander, the unprocessed or "virgin ¹¹ balls η are heated in a can 25 which is connected to a metering device 20 that sets or controls or regulates a suitable supply of the container 20 with the unprocessed balls .

At the bottom 27 of the container 20 and in the middle of the cone part 23 is attached, which in turn is surrounded by a movable plate or plane 28 which can rotate on ball or roller bearings (not shown) under the action of the nozzle 22 incoming hot air jet. A conical part that is integral with the plane can also be used, or both components can be movable. Above the level, a wire 29, for example made of metal with a diameter of approx. 0.5 now, is held horizontally between the cone part 23 and the inlet of the nozzle 22 in order to lift the balls, which can remain on the level 28.

The hot air supply takes place not only via the nozzle 22, but also via a widening line 30 which opens into a chamber 31 next to the container 20 and is provided with passages or openings 32. The flow rate of air which is heated in a chamber 33 is, by a detector 34 monitors, controls a variable-speed motor, the opening or the closing of flaps 35 »36 and the operation or regulates, the one suction fan 38 for

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air contained in the container 20 operates. To compensate for air losses, an approach 39 in a line 40, which connects the fan 3 ^ and a fine sieve, periodically OunzugefUgt, with the fine sieve 41 at the top and is preferably provided in the groove of the container 20 in order to suck in air with the exclusion of the pre-expanded spheres, which in turn are sucked off through a discharge line, the opening of which has a rectangular cross-section through more or less approaching two elements 43, 44 controllable or can be regulated, the two elements 43, 44 being shown in broken lines and a displaceable opening form.

The mode of operation of this expander results from the description above and is only briefly explained in more detail.

As soon as the preheated unprocessed balls penetrate into the container 20, they are set in rotation the level 28, which in turn is caused by the entry of the hot air stream is rotated by the nozzle 22. The wire 29 is used to detach balls that are moved by the hot air stream then around the cone part 23 and finally in an ascending circular motion to the top of the Container 20. The entry of hot air through the openings contributes to the intensification of the effect of the hot air flow. The most expanded balls are pushed to the top of the container 20, while the others are still heavier The balls want to sink downwards and again the effect of the rising hot air flow until they are complete exposed sIna °

Vorexpansionji The pre-expanded balls are over the Opening 42 conveyed or sucked into a discharge line.

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In particular, the polystyrene balls are ^{heated to between 95 and 100 °} C., which corresponds to their softening point. At this temperature the propellant, for example pentane, expands and causes the spheres to expand. In a single operating step, expanded spheres are obtained which have a density of 16 kg / nr.

In order to set this density, three parameters are essentially changed, namely

the supply throughput of the balls, the throughput of the expansion fluid, the passage time or residence time of the balls in the fluid.

This achieves a uniform expansion of the ball, which is much shinier and also at the same density are mechanically more resistant than spheres expanded by means of steam.

In this case, however, the expansion time is in a gaseous form Fluid a little longer than with an expansion by means of steam, whereby on the other hand the spheres have the considerable advantage, that they can be used directly for molding. This allows the pre-expander to work directly on a molding machine and can also be a .. plastic or Loss of material through refilling can be avoided, which can reach 2% by weight of the plastic.

Sin in the Fig. 3 illustrated third embodiment the device according to the invention has a double-walled frustoconical container 50 with two Walls 51, 52, above which a hot air ventilation is arranged is, which has a first fan 53, circular Resistors 54 for air heating, the above and between the both walls 51, 52 are arranged, discharge window 55 for

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expanded balls, with the discharge window 55 in their Height adjustable, and has a filter 56 withstanding the throughput of the balls.

The air is ^{heated to about 100 °} C. by means of the resistors 54 and is set in rotation or circulated by rotating the impeller 57 of the fan 53, as a result of which the air flowing between the two walls 5I, 52 is given a circular movement. This Baft penetrates in the center of the container 50 via openings (not shown) in the inner wall 5I which are tangential to the wall open in such a way that the circular and ascending movement of the hot air introduced is initiated.

These openings in a number of over 20,000 are over the straight lower part 58 of the container 50, where the openings are at. Largest (approximately 3 mm), over the entire conical surface and over about 10 cm in a straight part of an area 59 (about 1.5 mm) and over the whole Height of the container 50 above the window 55, in order to possibly detach the balls that are on the fine sieve or Filters sticking.

The air temperature is precisely regulated by an electronic system (not shown) which is a voltage regulator controls.

The base of the container 50 is formed by a plate 60 which is attached to the body of the container 50, for example by means of brackets 61, which enable the soil to be quickly dismantled during emptying.

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The plate 6θ is from a vault 62 in a conical shape built over, which is covered by small openings 63. Part of the air contained in the double wall penetrates below the vault 62 via openings 64, 65.

A special second fan 66 for low throughput and high pressure sucks in ambient air, which it in a line 67 and then into a heater 68 promotes. Inside a chamber 69 is a container or reservoir 70 provided, which has two perforated walls 71 and 72, between which the balls sink through each conduit occur during operation of the device.

The store 70 is therefore penetrated radially by hot air, which dries the balls and which escapes through a central path formed by the wall. The lower end of the chamber 69 is provided with an electrode J ^ which is connected to a detector 75 which controls or sets the air temperature at the outlet of the heater 68 and a control flap 76 for the air throughput to the storage tank 70.

The preheated balls coming from the store 70 sink down and flow through a conduit 77 which is curved near the bottom of the container 50 so that there a horizontal line 78 is formed which opens radially in the container 50.

A hot air inlet line 79 which is provided with a control valve 80 and is connected to the heater 68, is extended by a straight nozzle 81, which is more or less displaceable in the interior of the horizontal line 78 by acting on the steering wheel 82 of an Archimedean worm or screw 83

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The control valve 8θ and the Archimedean screw 83 allow the amount of primary plastic or material introduced into the expander to be adjusted.

Closing a flap 84 enables the supply of material or plastic to be completely halted or interrupted.

The operation of the device according to the invention results from the description made, which is why only a few comments follow.

The balls are generally continuously over the line 73 is introduced and after it has been heated in the container or in the chamber 69, they penetrate the bottom of the Container 50 at a more or less high speed which is adjustable by acting on the control wheel 82.

The balls are now subject to several air currents starting from the openings 63, the nozzle 81 and the openings of the Inner wall 51 of the container 50. The air rises in a vortex-like upwardly rising movement while being sucked in by the impeller 57, whereby the air is returned to the interior of the double wall. In this way there are .the balls are floating, like on a rising fluid bed, without touching the walls 51 of the expander.

The double wall is also perforated at the level of the container 50 above the window 55 and through the perforations penetrating air loosens the balls that would otherwise stick to the fine sieve or filter.

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Because the balls cannot pass through the fine sieve or the filter 56, they are passed through the window 55 removed prior to their use for molding.

The density of the spheres is controlled by changing three parameters, namely the height of the window 55, the throughput of the introduced air by means of the tap 88 and the forward or backward movement of the nozzle 8l by turning the control wheel 82.

By using the device according to the invention, balls of excellent quality can be obtained because they can have a weight of about 8 to 25 kg / nr and because they do not adhere to one another or to components of the device. Moreover, the throughput in their manufacture can reach 12 to 25 kg / h with an accuracy of the order of 1 % .

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Claims (12)

Expectations .J Process for the pre-expansion or pre-expansion of expandable plastics, in particular of styrene copolymers, dad; u r c h characterized in that the previously preheated plastics in the form of balls are moved and heated by, that they are exposed to the action of a rising and circulating gaseous hot fluid, its throughput and temperature can be adjusted so that the balls are raised, that they are moved and that they are heated up to their softening temperature, and that the pre-expanded spheres thus obtained immediately can be used for shaping. 2. The method according to claim l, characterized in that the balls are preheated in a container on the a temperature of about 50 ° C is brought. 3. The method according to claim 1 or 2, characterized in that that carbon dioxide gas, air, nitrogen, freon or, in particular, freon 114 is used as the gaseous fluid. 4. The method according to any one of claims 1 to 3, characterized in that the balls are heated to near their softening temperature, which is about 95 to 100 ⁰ C for polystyrene. 5. Device for carrying out the pre-expansion process according to claim 1, marked by a container (1, 20, 50) which is supplied with balls made of preheated expandable plastic, 709886/0879 ORIGINAL INSPECTED a fluid generator (2) and an atomizing device for atomizing the fluid according to an increasing turbulent course, Sin adjusting elements for adjusting the inlet flow rate and the exit flow rate of the balls, the fluid flow rate, the fluid temperature and the container temperature, and a discharge device (13, 42, 45) for the pre-expanded Balls at the top of the container (21, 50). 6. Apparatus according to claim 5, characterized in that the atomizing device for atomizing the fluid has a hot-air kinetic shower (7) according to an increasing turbulent course, which is provided with openings (S) which are arranged along a helical line, wherein the axis of the DUse (7) is arranged vertically and the DUse (7) opens above the upper end of a conical part (11) which protrudes from the bottom (10) of the container (1) (Fig.l). 7. The device according to claim 5, characterized in that the atomizing device of the fluid has a conical part (23) according to a turbulent course, which is provided on the bottom (27) of the container (20), and a movable plane (28) _; around and at the base of the cone part (28), a horizontal wire (29), which is arranged exactly above the plane (28), a hot air inlet at the base of the container (20 Y / several openings (32) for hot air inlet which are provided in the wall of the container (20) (Fig. 2). 8. Apparatus according to claim 5, characterized in that the atomizing device of the fluid according to a turbulent course has a double entry of hot air, the on the one hand through the bottom of the container (50) and through openings provided in its inner wall (5I) and on the other hand 709886/0879 273483 * penetrates through an inlet line (79) for hot air, which is preheated in the supply line (77, 78) for Balls opens (Fig. 3). 9. Apparatus according to claim 8, characterized in that that the hot air inlet line (79) is designed so that it can be displaced inside the feed line (77, 78) and thereby enables the feed rate of the balls to be changed. 10. Apparatus according to claim 8 or 9, characterized by a first fan (53) for sucking air upwards in the container (50) and leading it into the Double wall (51, 52) of the container (50), υηα a second Fan (66) for drawing in ambient air to one Heater (68) which directs the hot air to the bottom of the container (50). 11. The device according to claim 10, characterized in that that the inner wall (5I) of the container (50) is perforated at least on its frustoconical part. 12. Apparatus according to claim 10 or 11, characterized in that the inner wall (5I) of the container (50) is perforated is on its upper part above the discharge openings (55) of the balls in order to promote a detachment of the balls stick to the sieve or filter (56) and clog it.