GB2079616A

GB2079616A - Apparatus for mixing and degasifying components of synthetic resins

Info

Publication number: GB2079616A
Application number: GB8119424A
Authority: GB
Original assignee: Hedrich Wilhelm Vakuumanlagen GmbH and Co KG
Current assignee: Hedrich Wilhelm Vakuumanlagen GmbH and Co KG
Priority date: 1980-07-12
Filing date: 1981-06-24
Publication date: 1982-01-27
Also published as: ES503881A0; FR2486444A1; DE3026493A1; GB2079616B; ES8204638A1; IT1138821B; IT8122573A0; JPS5749623A

Abstract

Apparatus for mixing and degasifying components of synthetic resins comprises a container 1 having a rotatable screw conveyor 9 having a guide tube 12 located therearound, the guide tube having a discharge surface 11 at an upper end thereof. An agitating blade 14 is disposed between the guide tube 11 and container wall 1a, 1b, 1c and a baffle element 15, 16, 17, 18 is disposed in the container to hinder or prevent formation of a funnel formation in the surface of contents of the container when the contents are being agitated, thereby to ensure an adequate contents level in the region of the bottom end of the screw conveyor 9. <IMAGE>

Description

SPECIFICATION Apparatus for mixing and degasifying components of synthetic resins.

The invention relates to an apparatus for mixing and degasifying, of components of synthetic resins, more particularly thermosetting synthetic resins.

Generally such apparatus has an evacuatable cylin drical container which narrows downwardly and in which there is arranged, generally concentrically, a rotatable screw conveyor surrounded by a guide tube with a small spacing therebetween, said tube comprising at the top a discharge surface, and agita ,tion blades, preferably secured to the screw, are dis posed, radially between the lower end of the guide tube and the container.

In processing synthetic resins, an intensive mixing and degasifying is often required before the resin can be cast. This is true more particularly of ther mosetting casting resins and their components. The mixing often serves to distribute fillers uniformly in the synthetic resin. This distribution presents prob lems when the fillers are introduced in powder form, since the filler powder floats on the liquid synthetic resin mass and is difficult to stir into the liquid mass.

In a mixer of the kind specified above, the rota tional speed of the screw conveyor must be so great that the contents of the container are conveyed upwards along the screw. Relatively low rotational speeds are adequate in the case of relatively viscous compositions. The thinner the liquid contents, the higherthe rotational speed ofthe screw must be in order to convey the contents to the desired height. If the agitating blades are connected securely to the screw. The agitating blades will carry the contents of the container with them in the direction of rotation, so that the contents are rotated in the container.

Because of the rotational movement of the con tainer contents, the surface of the contents adopts what is referred to as a funnel formation. The surface shape differs in varying degrees from the form of a paraboloid of rotation as a result of the friction at the container walls and as a result of the conveying of liquid by the screw. The thinner the liquid contents are, the more marked is the funnel formation, par ticularly because ofthe high rotational speeds ofthe agitating blades connected therewith, but also due to the relatively low friction within the liquid.

If the quantity of the contents is small, the funnel formation caused by centrifugal forces may result in the screw no longer conveying any liquid upwards, since its lower end will no longer be sufficiently covered with liquid to allow the liquid to be con veyed. This may have the result that composition is no longer circulated over the discharge surface. To remedy this, some mixtures have been constructed which allow uncoupling between screw and agitat ing blades. After coupling, the agitating blades are stationary, so that funnels are no longer formed.As a result the composition can be circulated over the discharge surface, but at the cost of increased con structional outlay, complication of the task of operat ing the apparatus, with the accompanying risk of operating errors, and possible impairment ofthe standard of mixing afterthe blades are uncoupled.

The invention has as an object the construction of a mixing apparatus in such a manner that, with simple constructional means, funnel formation is reduced. The invention also aims at improving the stirring of fillers into the rest of the mixer contents.

The invention provides apparatus for mixing and degasifying components of synthetic resins, comprising a container in which there is arranged a rotatable screw conveyor having a guide tube located therearound, the guide tube having a discharge surface at an upper end thereof, at least one agitating biade disposed between the guide tube and a wall of the container, and at least one baffle element, which is adapted to hinder or to prevent the formation of a funnel formation in the surface of the contents of the container when they are being agitated.

Preferably, the guide tube of the screw conveyor is used for the arrangement of baffle elements thereupon as a result of which it is possible to provide baffle elements of many desired shapes even in mixers which have agitating arms situated near the bottom of the container. Hence, stationary baffle elements can be so arranged that they extend throughout the contents of the container. The baffle elements offer great resistance to rotational movement of the container contents, so that rapid rotation of the mixing composition is prevented or hindered.

As a result, funnel formation is very greatly reduced, so that even with small amounts of contents the lower end of the screw may still be covered with enough liquid to allow the composition to be conveyed upwards to the discharge surface. By having baffle elements which project upwards from the lower region of the container, the stirring-in of fillers, more particularly light pulverulent fillers, is facilitated, more especially if the baffle elements project through the surface of the contents of the container.

For the baffle elements which project out of the surface of the composition form turbulent regions in the surface ofthe liquid composition, and even material in powder form, is quickly drawn into such regions.

However, even with baffle elements of lower height the composition may be given such considerable turbulence that fillers are stirred-in relatively quickly.

The invention can be constructionally very simple, since baffle elements and their supports may be stationary, in other words rotary bearing arrangements and balancing may both be necessary. There is no need for agitating arms which can be uncoupled, thus also obviating the aforesaid disadvantages with any uncoupling of the agitating arms.

The baffle elements can be each secured individually on the guide tube, preferably so as to be secured at a point below the surface level of the contents.

The baffle elements may also be secured on the guide tube above the surface level, and so formed that they project into the contents. Preferably the baffle elements comprise radiaily projecting supports having baffle plates arranged on them, such that with only one fixing point on the guide tube, or very few such fixing points, the container interior can be occupied by baffle elements in such a way that all of the rotating mass will come into contact with baffle elements.

The invention can be carried out with a single support. However, it is preferable to use symmetrical arrangement, for example a pair of supports arranged diametrically opposite one another and secured on the guide tube. More particularly in the event of containers of relatively large diameter, more than two supports may also be advantageous.

The number of supports and the number of baffle elements will depend on the intended use to which the mixer is to be put.

Preferably, the agitated arms are adjacent a wall of the container, spaced a short distance therefrom, the baffle supports may then be arranged to lie close to the agitation arms, so that the baffle plates may be disposed across the entire cross-section of the container, i.e. the baffle elements may extend from a region very near to the bottom of the container to the outer regions of the container interior.

One constructional example of the invention is shown in the drawings, wherein: Fig. 1 shows a vertical sectional view through a mixer, and Fig. 2 shows a horizontal section taken on the line ll-ll of Fig. 1.

The mixer comprises a container 1, comprising a cylindrical portion la, a frustoconical portion ib, which tapers downwardly, and a horizontal bottom portion IC. In the centre of the bottom portion there is provided an aperture 2 closable with a valve 3.

Below the valve 3 is a conduit 4 for transporting contents discharged from the container 1.

The container is closed at the top in vacuum-tight manner by a cover 5. Filling unions 6 and 7 for introduction of mixer components are situated in the cover 5. A drive device 8 for a screw conveyor 9 is arranged in the cover 5. Afrustoconical discharge plate 11 is secured by the cover by means of bars 10.

The upper edge 1 la of the discharge plate is connected fast to a screw guide tube 12.

The axis of rotation of the screw 9 is coincident with the axis of the container 1. The lower end of the screw projects into a tubular neck 13 of the container bottom portion 1c. The guide tube 12 surrounds the screw in such a way that the outer edge of the screw helix 9a is spaced only a short distance from the internal wall of the guide tube 12.

Agitating arms, given the general reference numeral 14, are secured on the lower end of the screw 9.

Each agitating arm 14 has a horizontal portion 14a situated at a short spacing from the container bottom portion ic, an upwardly sloping portion 14b situated at a short distance from the frustoconical portion 1b of the container, and a vertical portion 14c situated at a short distance from the cylindrical portion la of the container 1. The upper end 14d of each agitating arm is situated at a level which corresponds approximately to the level of the lower edge 1 1b of the discharge plate 11.

Supports 15 situated diametrically opposite one another are secured on the lower end of the guide tube 12. These supports have a lower horizontal por tion 15a which is disposed at a short distance from the horizontal portion 14a of the agitating arms, and an upwardly inclined portion 15b disposed at a short spacing from the portion 14b of the agitating arms.

Three vertical bars 16, 17,18 are secured on each support. The outer bar 18 extends at a short distance from the vertical portion 14c of the agitating arms.

The bars 16 and 17 are arranged so that there is substantially equal spacing between the guide tubes 12 and the bar 16, between bars 16 and 17, and between the bars 17 and 18. The upper ends 16a, 17a, and 1 8a of the bars are situated at the same level as the upper ends 14d of the agitating arms.

The mixer operates as follows. During the preparation of a composition 19 the container is connected via a suction union 20 to a vacuum pump. Casting resin components and any fillers necessary are introduced through the unions 6 and 7. When the +, screw 9 is stationary the surface ofthe contents will be horizontal and generally located at level 19a. In the illustrated constructional form the length of the agitating arms 14 and of the bars 16,17, 18 acting as baffle plates is made such that in the event of the maximum preferred quantity of contents being used the agitating arms and the bars will still project somewhat above the surface 19a.

When the screw 9 rotates (the direction of rotation is indicated in Fig. 1 by the arrow 21) the agitating arms also rotate at the same rotational speed. The agitating arms tend to carry the container contents 19 with them, resulting in a rotational movement of the contents 19. The baffle plates 16, 17, 18 cause a considerable braking of this rotational movement and in addition considerable turbulence action in the liquid, whereby the mixing is intensified. The rotational movement also results in a so-called funnel formation tendency i.e. the centrifugal forces tend to drive the contents 19 against the container wall. This phenomenon is limited by the strong braking action ofthe bars 16,17,18.

The bars 16, 17, 18 projecting through the surface 19a, and also the projecting agitating arms 14, break up the surface of the contents (which, however, is generally not uniformly horizontal during the operation if the mixer), so that even fillers in powder form are stirred quickly into the mass 19.

Even if the amount of the contents is small, the mass is influenced by the baffle elements since the supports, which in fact themselves also act as baffle plates, are so shaped that they reach as close as possible to the container without interfering with the agitating arms. As already indicated, the baffle ele ments reduce funnel formation phenomena, so that even with a small amount of contents and relatively high screw speeds of rotational movement, and thus high agitating arms speeds, there is still sufficient liquid over the lower end of the screw for the screw to transport the liquid upwards.

Claims

1. Apparatus for mixing and degasifying compo nents of synthetic resins, comprising a container in which there is arranged a rotatable screw conveyor having a guide tube located therearound, the guide tube having a discharge surface at an upper end thereof, at least one agitating blade disposed between the guide tube and a wall of the container, and at least one baffle element, which is adapted to hin der or to prevent the formation of a funnel formation in the surface of the contents of the container when they are being agitated.

2. Apparatus as claimed in claim 1 wherein a baffle element comprises a baffle plate affixed to a supporting arm which projects from the guide tube.

3. Apparatus as claimed in daim 2, wherein the support members project radially from a lower end of the guide tube, and the baffle plate projects upwardly from a supporting arm.

4. Apparatus as claimed in claim 2 or 3, wherein the baffle plate is a substantially vertical bar.

5. Apparatus as claimed in claim 2,3 or 4, wherein at least one part of the said at least one agitating blade is arranged adjacent to the wall of the container, and the supporting arm of the baffle ele anent is adjacent to and inward of an agitating blade.

5. Apparatus as claimed in any one of claims 2 to 5 wherein two baffle elements are provided, the supporting arms thereof being secured to the guide tube and located diametrically opposite one another.

7. Apparatus as claimed in any one of the preced- ing claims, wherein a said baffle element is adapted to project through the surface of contents of the apparatus.

8. Apparatus as claimed in claim 7, wherein the said baffle element has an uppermost portion at the same revel as a lowermost portion ofthe discharge surface.

3. Apparatus as claimed in any one Df the preced- ing claims, wherein the container is a substantially ght circular cylinder having a frustum shaped bst- tom portion.

10. Apparatus as claimed in claim 19, when dependent upon claim 5, wherein a portion of the atating blade is adjacent to the wail of the frustum shaped portion and the blade projects upwardly therefrom adjacent to the wall of the right cylindrical region.

II. F tparahls 1or mLxing a nd degasifying synth- etic resins, substantially as hereinbefore described with relerence to the accompanying drawings.

12. Synthetic resin when degasified by an apparatus as claimed in any one of the preceding claims.

13. Apparatus for the mixing and degasilyins of components of synthetic resins, more particularly thermosetting synthetic resins, comprising an evacuatabie cylindrical container which narrows downwardly and in which there is arranged, concentrically, a rotatable screw conveyor surrounded by a guide tube with a small spacing therebetween, said t7be comprising at the top a discharge surface, and agitating blades secured preferably to the screw are disposed, with a radial component, between the lower end of the guide tube andthe container characterised in that baffle elements project from the guide tube, said baffle elements being situated at least partly below the contents surface level.