GB2194460A

GB2194460A - Agitator assembly for a rotary mixing apparatus

Info

Publication number: GB2194460A
Application number: GB08719941A
Authority: GB
Inventors: Raolo Benvenuto Giusti
Original assignee: Guisti & Son Ltd T
Current assignee: Guisti & Son Ltd T
Priority date: 1986-08-28
Filing date: 1987-08-24
Publication date: 1988-03-09
Anticipated expiration: 2007-08-24
Also published as: GB2194460B; GB8719941D0

Abstract

The agitator assembly (14) is in the form of a substantially circular ring-shaped element (17) mounted on a shaft (11) which is intended to rotate about its own longitudinal axis, the plane of said ring shaped element being inclined at an actual angle (e.g. of 30 DEG ) to the said axis, the said axis passing substantially through the centre of said ring. The ring-shaped element (17) comprises two halves (15) each mounted by support bars (20) and clamps (16) to the shaft (11). Each half of the element may comprise a semi-circular strip (as shown) or may be tubular. Scrapers (18), which preferably may undergo limited pivotal movement, are mounted on the ring- shaped element (17) so as to lead having regard to the intended direction of shaft rotation. Scoops (19) are arranged to trail. <IMAGE>

Description

SPECIFICATION Improvements in or relating to a rotary mixing apparatus THIS INVENTION relates to a rotary mixing apparatus for use, for example, in the processing of materials in the food, phamaceutical and cosmetic industries.

One of the operations which such apparatus is required to perform is the agitation of a liquid containing pieces of a solid material and such agitation is performed by rotating an agitator within a container.

Known apparatus which employ agitators rotatable about a vertical axis, unless operated at high speed, permit settling and do not effectively distribute the solid pieces in the liquid. Moreover, such vertical axis agitators exert a considerable shearing effect on the mixture and, where the solid pieces are of a sensitive material which is easily fragmented, this strenuous shearing effect results in the degradation of the solid pieces rather than the desired even distribution of the originai solid pieces in the liquid.

UK Patent Specification No. 1539766 discloses a mixing apparatus which provides a more effective and gentle mixing action for liquids containing solid pieces, such apparatus comprising a container for receiving material to be mixed, the container having a hemispherical bottom portion; a rotary agitator drive shaft which extends horizontally through the container, the shaft being rotatably and sealingly supported where it passes through the wall of the vessel; and a circular ring type rotary agitator disposed on said drive shaft in the container for rotation with the drive shaft, the agitator lying substantially in a plane containing the axis of the drive shaft and being adapted to engage and scrape the surface of the hemispherical bottom portion of the container, the agitator comprising a pair of substantially semicircular blades each extending around a frusto-conical surface having an axis which extends radially of the agitator drive shaft and passes through the centre of the circular agitator.

Whilst the apparatus of Patent No.

1539766 provided the required mixing of the liquid product without degradation of the solid pieces therein, the operation of the agitator in practice was not always sufficiently smooth and problems with overloading of the drive motor were encountered.

It is an object of the present invention to provide a mixing vessel having an agitator which is effective in providing the required mixing action for liquids containing degradable solid pieces, yet which is smooth in operation and less susceptible to overloading of the drive motor.

According to one aspect of this invention there is provided a rotary mixing apparatus comprising a vessel for containing material to be processed, and an agitator assembly rotatable in the vessel, said agitator assembly being rotatable about a predetermined substantially horizontal axis, the agitator assembly being in the form of a substantially circular ring shaped element, the plane of said ring shaped element being inclined at an acute angle to the said axis of rotation, the said axis passing substantially through the centre of said ring.

Preferably a plurality of scraper elements are provided on the periphery of said ring, the scraper elements being located to be directed forwardly as the ring rotates in a predetermined direction.

Conveniently said ring defines one or more segment shaped webs or scoops on the trailing edge of the ring as the ring rotates in a predetermined direction, the said webs or scoops being located at portions of the ring where the tangent to the ring is substantially parallel to the axis of rotation.

Preferably said agitator assembly comprises a plurality of components which are clamped together to embrace a substantially horizontal motor driven drive shaft extending substantially diametrically across said mixing vessel.

Conveniently said agitator assembly is mounted in a substantially hemispherical lower portion of the mixing vessel.

Preferably the agitator assembly is provided with scrapers to scrape the inner surface of the vessel as the agitator is rotated, each scraper comprising a mounting structure extending from the agitator substantially in the direction of rotation of the agitator and defining a pivot axis extending transversely to the direction of rotation, a scraper blade being detachably supported by the mounting structure for pivoting movement about a pivot axis, therebeing means limiting the pivoting movement of the scraper blade to a predetermined range.

Preferably the mounting structure comprises a pair of mounting posts and a pivot pin extending between the posts to define the pivot axis, and the scraper blade is detachably mounted on the pivot pin by pressing a resilient bi-furcated attachment portion of the blade onto the pivot pin so that the pin snap fits into a corresponding bore in the blade.

Conveniently pivoting movement of the blade in a first direction about the pivot axis is limited by cooperating abutment means on the mounting structure and on the blade.

Preferably the cooperating abutment means comprises a shoulder on the blade for engaging a confronting surface of a respective mounting post.

Conveniently the means for limiting the movement of scraper blade in the other direction of movement about the pivot axis comprises a stop member which depends from the mounting structure on the opposite side of the pivot axis from the agitator.

Preferably the stop member comprises a substantially rectangular frame fixed to the mounting structure and extending towards the agitator.

According to another aspect of this invention there is provided a rotatable agitator for a rotary mixing apparatus, said rotatable agitator comprising means for mounting the agitator on a drive shaft, means defining a circular ring adapted to lie in a plane which makes an accute angle with the axis of said drive shaft.

Preferably the agitator is provided with a plurality of scrapers located to be on the leading edge of said ring as said agitator is rotated in a predetermined direction by the drive shaft.

Conveniently the ring defines webs or scoops located on the trailing edge of the ring, in a region of the ring where the tangent to the ring is substantially parallel to the axis of said drive shaft.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a part sectional view of a rotary mixing apparatus embodying the invention; Figure 2 is a side view of scraper carried by an agitator ofthe mixing apparatus shown in Fig. 1; Figure 3 is a view of the scraper from the rear; Figure 4 is a plan view of the scraper shown in Fig. 2; Figure 5 is a plan view of a blade of the scraper shown in Fig. 2; and Figure 6 is a side view of the scraper blade of Fig. 5.

Referring now to the drawings, Fig. 1 shows a stainless steel mixing vessel 1 having a hemispherical lower portion 2 and a cylindrical upper portion 3. In the illustrated embodiment, a domed lid 4 is hingedly connected to the container by means of hinges 5 and can be clamped in the closed position by means of clamps 6 to form a vacuum or pressure tight seal. However, such a lid is not necessary where the product to be mixed is to be processed at atmospheric pressure.

The lower portion of the container 1 is provided with an external jacket 7 through which a heating or cooling medium may be circulated to heat or cool any material within the mixing vessel 1 during mixing. The container is supported on spaced legs 8 only two of which are visible in Fig. 1. An outlet 9 for processed material is provided which is centrally located in the lower portion of the container 1, the outlet being associated with a control valve, which is not shown.

A motor 10 is mounted, on an appropriate supporting arrangement (not shown) adjacent one side of the mixing vessel. The motor 10 drives a horizontal shaft 11 which enters the mixing vessel 1 through a first sealed bearing 12, and extends horizontally substantially dia metrically across the mixing vessel 1, the other end of the shaft 11 being received in another sealed bearing 13.

An agitator assembly 14 is mounted on the shaft 11. The agitator assembly 14 is constituted by two substantially identical agitator elements 15 which are clamped together by means of clamps 16 attached to support arms 20 of the elements 15, the clamps 16 embracing the shaft 11 and thus serving to mount the agitator assembly 14 on the shaft.

Alternatively, the agitator assembly can be secured to the shaft 11 by other means, for example by welding the support arms to the shaft.

The agitator elements together form a circular peripheral ring 17, the ring defining a plane which is off-set relative to the axis of the shaft 11. Thus the shaft 11 makes an accute angle (for example 30") with the plane defined by the ring 17, the axis of the shaft 11 passing through the centre point of the ring 17.

The ring may be formed of a strip like part, so that the ring resembles a barrel hoop, or may be tubular.

The motor 10 is adapted to drive the shaft 11 in an anti-clockwise direction when viewed from the motor looking towards the mixing vessel 1. Thus the agitator elements rotate with the shaft, causing the off-set ring to rotate about the shaft.

The leading edge of the ring is provided with a plurality of scraper elements 18 which will be described hereinafter in greater detail, and thus as the shaft 11 rotates the scraper elements 18 advance through the material to be mixed.

The trailing edge of each of the two semicircular ring forming parts of the agitator elements is provided, at points where the tangents to the ring are substantially parallel to the axis of the shaft 11, with scoops or webs 19.

In operation of the mixer, the material to be mixed in the form of a liquid containing degradable solid pieces is introduced into the mixing vessel 1 and the motor is operated. The agitator elements rotate about the axis of the shaft 11, and the scrapers serve to scrape material off the interior of the mixing vessel.

The scoops 19 tend to lift the solid pieces of the product, such as pieces of fruit as the agitator rotates, thus providing a thorough mixing effect and a homogeneous mixture without destroying the degradation solid pieces.

If the ring is formed as a strip the strip may be inclined so as to provide a lifting effect as the strip passes through the material to be mixed.

It has been found that a mixer in accordance with the present invention provides a more thorough mixing in a shorter period of time than corresponding prior proposed mixers, and suprisingly utilises less power to perform the same degree of mixing.

It has also been found that mixer in accordance with the invention may mix dry mixtures with only a minimum amount of jamming or with no jamming at all.

It is believed that the fact that the plane defined by the agitator makes an acute angle with the axis of the drive shaft facilitates the mixing action effected by the mixer.

A scraper 18 of the apparatus is illustrated in more detail in Figs. 2 to 6 of the drawings and will now be described with reference to such Figures.

Scraper 18 comprises a stainless steel mounting structure 30, a scraper blade 31 detachably carried by the mounting structure and a back-up or stop frame 32 secured to the mounting structure.

The mounting structure comprises a pair of spaced apart steel posts 33 and 34 welded to the agitator member 15 (which is shown here as being tubular) and supporting therebetween a pivot pin 35 whose ends 38 and 39 project through aligned bores 36 and 37 in the ends of the posts 33 and 34 remote from the agitator member. The projecting ends 38 and 39 of the pin 35 are welded to the respective posts 33 and 34 so that the pin is non-rotatable.

As shown in Figs. 5 and 6, the scraper blade 31, which may be formed from a suitable plastics material, such as polytetra fluoro ethylene as sold under the Registered Trade Mark TEFLON, has leading and trailing surfaces 40 and 41 connected by a bevel surface 42 which extends at an angle of, for example, 35 degrees to the trailing surface 41. A bifurcated attachment portion 43 of the blade 31 is formed with a slot 44 leading to a bore 45 into which the pivot pin is introduced in order to mount the scraper blade 31 on the mounting structure 30. The slot 44 of the blade has a width which is smaller than the diameter of the pivot pin 35, so that the walls of the slot 45 are resiliently forced apart as the blade is pushed onto the pivot pin so that the pin enters the bore 45 with a snap action and is resiliently retained in the bore 45.

The scraper blade is notched at each end adjacent the attachment portion 43 to form two shoulders presenting respective inclined abutment surfaces 46 and 47 which make an angle of, for example, 40 degrees with the trailing surface 41 of the scraper blade and which are positioned in conforming relationship to corresponding surfaces 48, 49 (see Fig. 3) of the mounting pillars 33 and 34 when the scraper blade is mounted on the pivot pin 35.

The back-up frame 32 of the scraper comprises a substantially U-shaped frame made, for example, from a steel rod and having end portions 50 and 51 welded to end surfaces 52 and 53 of the mounting posts 33 and 34.

The plane of the frame 32 lies substantially parallel to the trailing surface of the scraper blade and lies within the outline of the surface of the blade.

The direction of movement of the agitator member during use of the mixing vessel is indicated by the arrow X in Fig. 2. From this, it will be seen that, during a period when the scraper blade 31 is in contact with the surface of the vessel 1, forces acting on the scraper blade 31 tend retain it in position on the pivot pin 35. Pivoting movement of the blade 31 is also limited in the clockwise direction about the pivot pin 35 by the abutments 46 and 47 coming into contact with the mounting pillars 33 and 34 and, in the anticlockwise direction, by the blade coming into contact with the back-up frame 32, so that the pivoting movement of the blade 31 is confined to a predetermined range, and the blade is supported during periods when there is no contact with the vessel surface and, when re-engaging the vessel surface, is presented at a suitable angle to avoid detachment or jamming of the scraper blade.

It will be appreciated that the scraper construction described above provides a simple yet reliable scraper structure in which scraper blades may be conveniently and readily assembled or exchanged without the use of tools and in which cleaning of the mixing vessel and the scrapers is facilitated.

Claims

1. A rotary mixing apparatus comprising a vessel for containing material to be processed, and an agitator assembly rotatable in the vessel, said agitator assembly being rotatable about a predetermined substantially horizontal axis, the agitator assembly being in the form of a substantially circular ring shaped element, the plane of said ring shaped element being inclined at an acute angle to the said axis of rotation, the said axis passing substantially through the centre of said ring.

2. A rotary mixing apparatus according to claim 1 wherein a plurality of scraper elements are provided on the periphery of said ring, the scraper elements being located to be directed forwardly as the ring rotates in a predetermined direction.

3. A rotary mixing apparatus according to claim 1 or claim 2 wherein said ring defines one or more webs or scoops on the trailing edge of the ring as the ring rotates in a predetermined direction, the said webs or scoops being located at portions of the ring where the tangent to the ring is substantially parallel to the axis of rotation.

4. A rotary mixing apparatus according to any one of the preceding claims wherein said agitator assembly comprises a plurality of components which are clamped together to embrace a substantially horizontal motor driven drive shaft extending substantially diametrically across said mixing vessel.

5. A rotary mixing apparatus according to any one of claims -1 to 4 wherein said agitator assembly is mounted in a substantially hemispherical lower portion of the mixing vessel.

6. A rotary mixing apparatus according to any one of the preceding claims wherein the agitator assembly is provided with scrapers to scrape the inner surface of the vessel as the agitator is rotated, each scraper comprising a mounting structure extending from the agitator substantially in the direction of rotation of the agitator and defining a pivot axis extending transversely to the direction of rotation, a scraper blade being detachably supported by the mounting structure for pivoting movement about a pivot axis, therebeing means limiting the pivoting movement of the scraper blade to a predetermined range.

7. A rotary mixing apparatus according to claim 6 in which the mounting structure comprises a pair of mounting posts and a pivot pin extending between the posts to define the pivot axis, and the scraper blade is detachably mounted on the pivot pin by pressing a resilient bi-furcated attachment portion of the blade onto the pivot pin so that the pin snap fits into a corresponding bore in the blade.

8. A rotary mixing apparatus according to claim 6 or 7 in which pivoting movement of the blade in a first direction about the pivot axis is limited by cooperating abutment means on the mounting structure and on the blade.

9. A rotary mixing apparatus according to claim 8 as appendent to claim 7 in which the cooperating abutment means comprises a shoulder on the blade for engaging a confronting surface of a respective mounting post.

10. A rotary mixing apparatus according to claim 8 or 9 in which the means for limiting the movement of scraper blade in the other direction of movement about the pivot axis comprises a stop member which depends from the mounting structure on the opposite side of the pivot axis from the agitator.

11. A rotary mixing apparatus according to claim 10 in which the stop member comprises a substantially rectangular frame fixed to the mounting structure and extending towards the agitator.

12. A rotatable agitator for a rotary mixing apparatus, said rotatable agitator comprising means for mounting the agitator on a drive shaft, means defining a circular ring adapted to lie in a plane which makes an accute angle with the axis of said drive shaft.

13. A rotatable agitator according to claim 12 wherein the agitator is provided with a plurality of scrapers located to be on the leading edge of said ring as said agitator is rotated in a predetermined direction by the drive shaft.

14. A rotatable agitator according to claim or wherein the ring defines webs or scoops located on the trailing edge of the ring, in a region of the ring where the tangent to the ring is substantially parallel to the axis of said drive shaft.

15. A rotary mixing apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

16. A rotatable agitator substantially as herein described with reference to and as shown in the accompanying drawings.

17. Any novel feature or combination of features disclosed herein.