CA2301390A1

CA2301390A1 - Colloid mill

Info

Publication number: CA2301390A1
Application number: CA002301390A
Authority: CA
Inventors: Arnold S. Carter
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-03-20
Filing date: 2000-03-20
Publication date: 2001-09-20

Abstract

A colloid mill has a cylindrical processing chamber with an inlet end, a discharge end and a rotor mounted in the chamber between the two ends. The inlets to the inlet end are radial, while the discharge from the discharge end of the mill is tangential. This provides a good mixing of the materials introduced at the inlet before they are subjected to milling by the rotor and minimizes the back pressure on the material being discharged at the discharge end. The rotor assembly in the mill has two rotors spaced axially apart. Beaters project from the rotor assembly into the mixing chamber at the inlets and through the mixing chamber between the two rotors.
The rotor assembly is mounted on the rotor shaft to prevent axial migration of the rotor assembly on the shaft. At one end, the shaft is mounted in thrust bearings while at the opposite end it is mounted in a self-aligning spherical bearing that allows axial expansion and contraction of the shaft due to thermal effects. The mill may be made with two rotor assemblies arranged back-to-back, with a centre inlet and discharges at opposite ends.

Description

COLLOID MILL
The present invention relates to a stirrer mill, primarily a colloid mill for mixing and forming colloidal mixtures of immiscible materials.
Various colloid mills are known in the prior art. A typical use of such machines is forming aqueous hydrocarbon emulsions. Typically, such a mill will include a rotor rotating in the housing with porting to direct the materials being processed through a narrow gap between the rotor and the housing. This causes a shearing and intimate mixing of the materials being processed. The present invention relates to certain improvements in a mill of this type, as will be discussed in the following.
According to the present invention there is provided a stirrer mill comprising:
a housing including:
a substantially cylindrical processing chamber that is symmetrical about a mill axis;
an inlet including at least one inlet port that opens laterally into the processing chamber substantially toward the mill axis;
a discharge including a discharge port that opens into the processing chamber substantially tangentially; and a rotor assembly mounted in the processing chamber between the inlet and discharge for rotation about the mill axis.
Prior art mills use axial inlet and outlet ports. The lateral inlet port or ports of the present invention inject the materials being processed into the mill laterally of the movement through the mill. This creates a good mixing of the materials prior to their entering the milling zone between the rotor assembly and the housing. This reduces the amount of preliminary mixing that must otherwise be carried out in the milling zone and dwell time in the milling zone, resulting in improved productivity of the mill.
The prior art use of axial discharge ports requires a redirection of the flow after the mixing zone. This increases back pressure and the power required to operate the mill.
These improvements contribute to a significant improvement in the output of a mill consuming the same power as a prior art mill.
In preferred embodiments, the mill has a set of beater bars extending axially into the housing upstream of the rotor to augment the mixing of the materials being injected. The rotor assembly may include two spaced rotors so as to provide an intermediate mixing or stirring zone between two milling zones. Beater bars may extend through this intermediate mixing zone for more effective stirring and mixing of the processed materials.
The mill's output can be increased by arranging two mills back-to-back, with an inlet in the centre and outlets at opposite ends. Two rotor assemblies are used, mounted on a common shaft.
Colloid mills wear and must be refurbished from time to time. This may require reboring of the processing chamber. Because the end caps or covers of the housing are generally centred on the bore of the processing chamber, the end caps must be replaced to match the rebored chamber. In the present invention it is preferred that the annular main body of the housing has a counter bore at each end and the two end covers have centring disks on their inner faces for centring engagement in the counter bores. These centring disks serve to maintain the proper alignment of the end caps on the housing main body. The main bore of the processing chamber can be bored out oversize without affecting this arrangement.
It is also preferred that the rotor assembly includes a rotor mounting arrangement that secures the rotor assembly to the rotor shaft to prevent axial movement of the rotor on the shaft. This eliminates migration of the rotor on the shaft, a problem that can arise with the prior art.
The rotor shaft may be mounted at one end, preferably the drive end, in a fixed thrust bearing and at the opposite end in an axially floating, self aligning bearing. This arrangement allows the thermal expansion and contraction of the shaft without losing the precision of the shaft alignment and without effect on the drive coupling to the shaft.
Another preferred feature of the present invention is the configuration of the teeth on the periphery of the rotor. These are preferably axial teeth, with each having a thickness that tapers radially inwardly. The most preferred configuration has the confronting faces of adjacent teeth parallel. This tooth configuration has been found to provide improved milling performance while being relatively easy to produce and maintain.
In the accompanying drawings, which illustrate exemplary embodiments of the present invention:
Figure 1 is a side view of a mill according to the present invention;
Figure 2 is an axial cross-section of the mill;
Figure 3 is a section along line 3-3 of Figure 2;
Figure 4 is a section along line 4-4 of Figure 2;
Figure 5 is detail V of Figure 2 showing the end cap mounting;
Figure 6 is detail VI of Figure 2 showing the mounting of the rotor shaft through the end cap;
Figure 7 is detail VII of Figure 2 showing a shaft bearing;
Figure 8 is an axial cross-section of an alternative embodiment of the present invention; and Figure 9 is detail IX of Figure 3 showing the configuration of the rotor teeth.
Referring to the accompanying drawings, there is illustrated a colloid mill with a housing 12. The housing has two mounting pedestals 14. At each end, the 5 housing is closed with an end cap or cover 16. Mounted on the end cap is a packing housing 18. On one end of the mill the packing housing carries a bearing housing 20 with a closed outer end. On the other end of the mill is a bearing housing 22 through which the rotor shaft 24 extends for connection to the mill drive.
On the drive end of the mill are two inlet ports 26 and 28. These are 10 diametrically opposed ports on opposite sides of the housing. These discharge towards the axis of the mill. At the opposite end of the housing is a tangential discharge port 30. This is located at the bottom of the housing and on one side.
As illustrated most particularly in Figure 2, the housing 12 includes a cylindrical processing chamber 32. At its outer ends, the housing main body has counter bores 34 that accommodate centring disks 36 on the inner faces of the end caps 16. The end caps are fixed in place using bolts 38.
Inside the processing chamber 32 is a rotor assembly 40. This includes the rotor shaft 24 which extends axially through the processing chamber. A key 42 is set into the shaft. This is a relatively long key with a centre section 44 that is deeper than the remainder of the key. A spacer 46 is fitted onto the shaft and is keyed to the centre section 44 of the key 42. The spacer is held in place by a set screw 48. At opposite ends of the spacer 46 are two rotors 50. Each has a hub 52 that is keyed to the shaft 24 by a respective end section of the key 42. The keyways in the rotor hubs are smaller than the centre section 44 of the key, so that the movement of each rotor along the shaft towards the centre is prevented. Set screws 54 secure the rotor hubs in place on the shaft.

Each rotor has a disk-like web 56 and an annular peripheral head 58 carrying axially oriented teeth 60. As illustrated most particularly in Figure 9, the teeth are generally "square" in profile. The thickness of 62 of the tooth is not however, uniform. The tooth profile tapers radially inwardly from the periphery of the rotor. The side faces of adjacent teeth are parallel.
The two rotors are joined by axially oriented tie rods 66. These pass through the two rotors at circumferentially spaced positions. At the discharge end of the processing chamber, nuts 68 are threaded onto the tie rods. At the opposite end, deep nuts 70 are threaded onto the tie rods. These project axially from the rotor into the mixing chamber. Tension on the tie rods clamps the rotors to opposite ends of the spacer 46. The deep nuts 70 act as beater bars in the upstream mixing chamber and the tie rods act as beater bars in the intermediate mixing chamber between the two rotors.
Each of the end caps 16 has a central opening 72 through which the shaft 24 passes. The packing housing 18 extends into that opening and carries a bushing 74 that serves to support the shaft and prevent damage to the rotor and the housing in the event of a bearing failure. The packing housing carries mechanical packing 76 and a packing gland 77. At the drive end of the rotor shaft, the bearing housing 22 carries a thrust bearing assembly including two tapered roller bearings 78 to support the rotor shaft. The bearings are held in place using retainers 80 of conventional form. This bearing assembly prevents axial movement of the shaft in the bearing housing.
A keyway 82 is formed at the end of the rotor shaft to provide for the coupling of a drive pulley, sprocket or gear to the shaft.
At the opposite end of the mill the bearing housing 20 houses a self aligning spherical bearing 84 which is mounted to provide some end play 86 within the bearing housing. This accommodates the thermal expansion and contraction of the rotor shaft during operation.
In a typical operation of the mill, a long chain hydrocarbon may be introduced into one of the inlet ports 26 and 28 while water and an emulsifier is injected into the other. These materials will be mixed thoroughly by the beaters 70 as soon as they are introduced. The mixture is then forced through the gap between the upstream rotor 50 and the cylindrical surface of the processing chamber 32, with the teeth of the rotor producing a shearing action on the mixture. Between the two rotors, the tie rods 66 act as beaters producing a further mixing action before the mixture once more passes through a milling zone between the second rotor and the inner surface of the processing chamber. After passing through the milling zone between the second rotor and the processing chamber the material is swirling circumferentially within the processing chamber. This swirling movement leads the processed material from the mill through the tangential discharge without a change in the flow direction.
A second embodiment of the invention is illustrated in Figure 8. In that embodiment, the mill 90 includes two rotor assemblies 92. Each rotor assembly includes a spacer 94 between two rotors 96 and the two rotor assemblies are separated by a centre spacer 98. In this case, the tie rods 100 extend through all four rotors to hold the doubled rotor assembly together. The inlets to this embodiment open laterally into the centre section between the two rotor assemblies where the tie rods serve as beaters to mix the materials introduced before they pass axially through the milling zones to spaced tangential discharges 102 at opposite ends of the housing.
While particular embodiments of the present invention have been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention and are intended to be included herein. The invention is to be considered limited solely by the scope of the appended claims.

Claims

1. A stirrer mill comprising:
a housing including:
a substantially cylindrical processing chamber that is symmetrical about a mill axis;
an inlet including at least one inlet port that opens laterally into the processing chamber towards the mill axis;
a discharge including a discharge port that opens into the processing chamber substantially tangentially; and a rotor assembly mounted in the processing chamber between the inlet and discharge for rotation about the mill axis.

2. A mill according to Claim 1 wherein the rotor assembly includes:
at least one rotor; and a plurality of beaters projecting axially from the rotor towards the inlet.

3. A mill according to Claim 1 or 2 wherein the rotor assembly includes two rotors spaced apart along the processing chamber.

4. A mill according to Claim 3 wherein the rotor assembly includes a plurality of beater bars extending between the two rotors.

5. A mill according to any one of Claims 1 to 4 wherein the inlet includes two inlet ports that open laterally into the processing chamber to the mill axis.

6. A mill according to Claim 5 wherein the two inlet ports are diametrically opposed.

7. A mill according to any one of Claims 1 to 6 wherein:
the housing includes two axially spaced discharges;
the inlet is positioned axially between the axially spaced discharges; and two rotor assemblies are mounted in the processing chamber between the inlet and the respective axially spaced discharges.

8. A mill according to any one of Claims 1 to 7 wherein the housing comprises an annular body with axially spaced open ends with a counterbore at each end, and two end covers closing the respective ends, each cover having a centring disc on an inner face thereof for centring engagement in the respective counterbore.

9. A mill according to any one of Claims 1 to 8 including a rotor shaft extending axially through the housing and a rotor mount securing the rotor assembly to the rotor shaft and preventing axial and rotational movement of the rotor assembly relative to the rotor shaft.

10. A mill according to Claim 9 including:
a first bearing mount on a first end of the housing, the rotor shaft projecting from the housing through the first bearing mount;
bearings in the first bearing mount supporting the shaft for rotation and preventing axial displacement of the shaft in the first bearing mount;
a second bearing mount on a second end of the housing opposite the first end, the rotor shaft projecting from the housing into the second bearing mount;
and a self-aligning bearing in the second bearing mount supporting the shaft for rotation and axial displacement of the shaft in the second bearing mount.

11. A mill according to Claim 10 including shaft drive means coupled to the rotor shaft adjacent the first end of the housing for connecting the rotor shaft to a drive motor.

12. A mill according to any one of Claims 2, 3 and 4 wherein the rotor assembly includes an annular periphery comprising a plurality of axial milling teeth, each tooth having a thickness in a direction circumferentially of the rotor that tapers radially inwardly.

13. A mill according to Claim 12 wherein confronting faces of adjacent teeth are substantially parallel.