GB2131311A - Stirrer - Google Patents

Abstract

A stirrer, particularly for laboratory use, which comprises a shaft (1) on which is non-fixedly mounted a blade (2) through a hole (3) therein which is close fitting on the mount, the centre of gravity of the stirrer lying along the shaft axis. The blade can be rotated between its operative position (as shown) to an inoperative position (by rotation through 90 DEG ) which allows the stirrer to pass through the narrow neck of a flask. Preferably the shaft has a lower, loop portion (1A) which mounts the blade (2). <IMAGE>

Description

SPECIFICATION Stirrer This invention relates to stirrers and to their manufacture and use.

The invention provides a stirrer comprising a shaft on which is mounted a blade, the blade being mounted through a hole therein and being close fitting on the mount, the centre of gravity of the stirrer lying along the longitudinal axis of the shaft.

The invention also provides a method of stirring a medium, which method comprises stirring it with the stirrer.

Known stirrers comprising a shaft on which is mounted a blade have disadvantages. A very widely used stirrer is of the type shown in Figures 1 and 2 of the accompanying drawings, which Figures are side views perpendicular to each other. This stirrer comprises a glass shaft 1 on which is mounted a detachable polytetrafluoroethylene blade 2. The shaft 1 has a shoulder 1A so that the blade 2 is in line with the longitudinal axis of the shaft 1 (see Figure 2). The blade 2 is mounted through an asymmetric hole 3 in the blade 2, so that the blade 2 can be attached by passing it over a stop member 4 onto the mount 5 and rotating the blade 2 into the working position shown in Figures 1 and 2. The blade 2 is thus loose fitting on the mount 5, and with repeated attaching and detaching of the blade 2 the hole 3 becomes enlarged so that the blade 2 fits even more loosely.Consequently, in use, there tends to be play of the blade 2 about the mount 5, resulting in uneven stirring of the medium, usually a liquid medium, being stirred. The play also means that relatively thick areas of the medium, e.g. lumps in a liquid medium, can be passed over by the blade 2, the thick areas merely rotating the blade 2 about the mount 5 rather than the blade 2 passing through the thick areas. Finally the play means that the blade can become detached whilst stirring. Stirring is also uneven, and a tendency for vibration present (which tends to lead to breakage), by reason of the offcentre effect due to the centre of gravity of the stirrer being off-set from the longitudinal axis of the shaft 1.

It can be seen that the stirrer of the invention, having its blade close fitting on the mount and having its centre of gravity along the longitudinal axis of the shaft, overcomes these problems. Hence, more even stirring can be achieved, a tendency for vibration is removed, and there is less chance of the blade becoming detached while in use. In addition, since the blade is close fitting, there is less space to get clogged with material being stirred.

Another very widely used stirrer is the link stirrer type shown in Figure 3 of the accompanying drawings, which is a side view. This stirrer comprises a glass shaft 1 at the end of which is a closed glass loop 1A, the arm of the loop 1A passing through glass links 2. The links 2 are loose fitting on the arm and flail about in use. The stirrer is very vulnerable to breakage, and has a tendency for uneven stirring, e.g. by the links not passing through, but being displaced over or under, relatively thick areas in the medium, usually liquid, being stirred. In addition, abrasion of the container containing the medium being stirred tends to occur, resulting in serious wear for instance of round-bottom flasks. The stirrer of the invention in contrast is more robust and gives more even stirring.

In the stirrer of the invention, the blade is close fitting on the mount, i.e. the clearance in the hole is small. Preferably there is contact fit between the blade and the mount, so that there is substantially no clearance between them. Usually the maximum clearance between the mount and the edge of the hole is less than one-fifth the height of the blade. The smallerthe maximum clearance, the less play there can be of the blade on the mount.

So that the blade can be inserted into the neck of a flask or other container whose neck is narrower than the length of the blade, the present stirrer preferably has, like the stirrer shown in Figures 1 and 2, a blade which can be rotated, preferably 90 , about the mount to decrease the major dimension of the stirrer perpendicular to the longitudinal axis of the shaft.

To achieve even greater evenness of stirring, it is preferred that the present stirrer in the working position is symmetrical about each of 2 perpendicular planes in which the longitudinal axis of the shaft lies.

The blade is preferably mounted on the shaft of the present stirrer by having the arm of a loop at the end of the shaft passing through the hole in the blade. The loop is preferably a closed loop, so that the blade cannot become detached. When the shaft and loop are of glass, the presence of the loop, especially a closed loop, makes the stirrer particularly robust compared to the known types of stirrer illustrated in Figures 1-3, and when the stirrer illustrated in Figures 1 and 2 breaks at the stop member, as often happens when the blade is being attached or detached, the damage is too serious to be worth repairing. The arms of the present loop preferably contact the sides of the blade; this helps to hold the blade more rigidly.

The invention provides a method of making the present stirrer having a closed loop at the end of the shaft, which method comprises placing the blade through its hole onto the arm of an open loop, moving the blade round the loop away from the opening in the loop, and then closing the loop. This is particularly useful when the blade would not resist heat used to close the loop when the opening is adjacent to the blade, e.g. when the loop is glass and the blade is polytetrafluoroethylene. An open glass loop can be closed by fusing glass across the opening, or by fusing in a separate link of glass to close the opening. The open loop can already be on the end of the shaft when placing the blade on the arm.Alternatively, the loop can be separate from the shaft, and then be fixed to the shaft after the blade has been placed on the arm; the loop is then attached to the shaft before, or preferably after, closing the loop. A glass loop is preferably fixed to a glass shaft by fusing glass together.

The present stirrers with loops are more quickly and more easily manufactured than the known ones illustrated in Figures 1-3.

In a particularly preferred and surprising embodi ment, the blade in the present stirrer with a loop is prevented in use from sliding round the loop by the loop and blade being so dimensioned and shaped that in use the blade cannot slide round the loop, but in a different rotational position of the blade about the mount, the blade can slide round the loop. This enables the stirrer to be made readily and yet the blade does not get displaced in use.

The blade of the present stirrer is preferably glass, stainless steel, plastic e.g. polytetrafluoroethylene or polyvinyl chloride, or plastic (e.g. polyvinyl chloride) covered metal (e.g. stainless steel). In laboratory stirrers, the blade is preferably polytetrafluoroethylene. In larger stirrers, the blade is preferably stainless steel of polytetrafluoroethylene. A low friction material such as polytetrafluoroethylene is advantageous.

The shaft is preferably glass, brass, stainless steel or plastic (e.g. polyvinyl chloride) covered metal (e.g.

stainless steel). In laboratory stirrers, the shaft is preferably glass. In larger stirrers, the shaft may be glass, or may be for instance stainless steel or brass so that it is less fragile.

When the stirrer has a loop, the loop is usually made of the same material as the shaft.

The present stirrers are usually employed to stir liquid media. The stirrers can be used in conjunction with conventional apparatus, e.g. stirrer guides and flasks. The stirrers, depending on their size, can be used to stir for instance flasks of 0.1-40, e.g. 0.1-20, litres capacity.

The stirrers can be for instance of length 20-60 cm.

The shaft can be for instance of diameter 5-20 mm.

The blade can be for instance 4-15 cm in length. The blade can be for instance 1-4 cm in height. The blade can be for instance 0.1-2 cm thick.

The blades are usually curved at the bottom, desirably to match the curvature of the container in which they are used.

The invention is illustrated by the accompanying drawings (not entirely to scale), in which: Figures 1-3 show known stirrers as already described; Figures 4-6 show a stirrer according to the invention; Figure 7shows a shaft and open loop which can be used to manufacture a stirrer shown in Figures 4-6; and Figures B 1, 81, BZB3,B4, B5 and B6 show blades for astirrershown in Figures 4-6.

Figures 4 and 5 show the stirrer with the blade in the working position, and Figure 6 the stirrer with the blade rotated for insertion through the neck of a flask. Figure 6 is the same view as that of Figure 4 but with the blade rotated 90". Figure 7 corresponds to the stirrer position shown in Figure 5.

Figure 4 is a side view and Figure 5 an end view perpendicular to the side view shown in Figure 4. It can be seen that the centre of gravity of the stirrer lies along the longitudinal axis of the shaft and that the stirrer is symmetrical about each of 2 perpendicular planes in which the longitudinal axis of the shaft lies. Figures B1, B2, B3, B4, B5 and B6 are side views corresponding to that in Figure 4.

Referring to Figures 4-6, the stirrer comprises a shaft 1 on which is mounted a blade 2. The blade 2 has a hole 3 through which passes the arm of a closed loop 1A at the end of the shaft 1. The hole 3 is sufficiently small that the blade 2 is close fitting on the mount 1 B; the maximum clearance X between the mount and the edge of the hole 3 in the blade 2 is less than one-fifth the height H of the blade 2. The arms of the loop 1A contact the sides of the blade 2.

The internal height Y of the loop 1A is not less than half the length L of the blade 2, so that the blade can be rotated 90" from its working position and pass through the loop. The internal width Wofthe loop 1A is equal to or greater than the distance W' between the edge of the hole in the blade 2 and the curved side of the blade 2, so that the blade 2 can slide up the arms of the loop 1A.

The hole is sufficiently low in the blade 2 that the blade 2 cannot slide up the side of the loop 1A in the working position shown in Figures 4 and 5, since the top of the blade 2 would be restrained by the side of the loop 1A. When the blade 2 is rotated 1800 about the mount (so that the flat top of blade 2 in Figure 4 would now be at the bottom), the blade 2 can be pushed up the side of the loop 1A.

In particular embodiments, the stirrer shown in Figures 4-6 is made using glass for the shaft 1 and loop 1A, and polytetrafluoroethylene for the blade 2.

This stirrer can be made by placing the blade 2 onto an arm of the open loop at the end of shaft 1 in Figure 7, with the curved side of the blade 2 towards the inside of the loop; the blade 2 is then moved round the loop away from the opening; and the glass on both sides of the opening is then heated to fuse them together to close the opening. Alternatively, a separate link of glass rod is fused by heating to each arm of the open loop to close the opening. In either case, the blade 2 can then be moved round the loop into position where the opening was. Rotation of the blade 2 in this position so that the stirrer becomes as in Figure 6 enables itto be inserted through the neck of a flask, which neck is narrower than the length L of the blade 2 (but not wider than the height H of the blade 2).Rotation of the blade 2 in the flask, e.g. by pressing the stirrer against the bottom of the flask, enables the stirrer to take up the working position shown in Figures 4 and 5, in which the blade 2 cannot slide up the side of the loop 1A.

In particular embodiments of the stirrer shown in Figures 4-6 the blade 2 is of polytetrafluoroethylene and the shaft 1 and the loop 1A of glass. Figure B1 of the accompanying drawings shows a blade suitable for use in such a stirrer in a 100 ml round-bottom flask, B2 for a 250 ml round-bottom flask, B3 for a 500 ml round-bottom flask, and B4 for a 1 litre round-bottom flask, in each case 6 mm diameter stirrer rod 45-50 cm long being used to make the shaft 1, 5 mm diameter stirrer rod being used to make the loop 1A, the hole in the blade 2 being drilled to a diameter of 5.6 mm on a centre 6 mm from the curved side of the blade 2 (so that the distance W' is 3.2 mm), and the blade being 3.2 mm thick. Figure B5 shows a blade suitable for use in such a stirrer in a 5 litre round-bottom flask and B6 a blade suitable for use in such a stirrer in a 10 litre round-bottom flask, in each case 11 mm diameter stirrer rod about 55 cm long being used to make the shaft 1,7 mm diameter stirrer rod being used to make the loop 1A, the hole in the blade 2 being drilled to a diameter of 7.1 mm on a centre 9.5 mm from the curved side of the blade 2 (so that the distance W' is 5.95 mm), and the blade being 6.4 mm thick.

CLAIMS (Filed on 27 Oct. 83) 1. A stirrer which comprises a shaft on which is non-fixedly mounted a blade through a hole therein which is close fitting on the mount, the centre of gravity of the stirrer lying along the shaft axis.

2. A stirrer according to claim 1 wherein the blade is mounted rotatably so as to vary a dimension of the stirrer perpendicular to the shaft axis.

3. A stirrer according to claim 1 or claim 2 wherein the mount comprises a closed loop at the end of the shaft.

4. A stirrer according to claim 3 wherein the loop and blade are formed such that in one orientation the blade cannot be displaced round the loop.

5. A stirrer according to claim 4 wherein the loop and blade are formed such that in a second orientation the blade can be displaced round the loop.

6. A stirrer according to claim 5 wherein the loop is an elongate loop having substantially parallel side members spaced apart by approximately the width of the blade in the direction of the hole therein, and the hole in the blade is located asymmetrically therein such that its distance from the nearest edge only of the blade is less than the spacing between the side members.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. stirrer rod about 55 cm long being used to make the shaft 1,7 mm diameter stirrer rod being used to make the loop 1A, the hole in the blade 2 being drilled to a diameter of 7.1 mm on a centre 9.5 mm from the curved side of the blade 2 (so that the distance W' is 5.95 mm), and the blade being 6.4 mm thick. CLAIMS (Filed on 27 Oct. 83)

1. A stirrer which comprises a shaft on which is non-fixedly mounted a blade through a hole therein which is close fitting on the mount, the centre of gravity of the stirrer lying along the shaft axis.

2. A stirrer according to claim 1 wherein the blade is mounted rotatably so as to vary a dimension of the stirrer perpendicular to the shaft axis.

3. A stirrer according to claim 1 or claim 2 wherein the mount comprises a closed loop at the end of the shaft.

4. A stirrer according to claim 3 wherein the loop and blade are formed such that in one orientation the blade cannot be displaced round the loop.

5. A stirrer according to claim 4 wherein the loop and blade are formed such that in a second orientation the blade can be displaced round the loop.

6. A stirrer according to claim 5 wherein the loop is an elongate loop having substantially parallel side members spaced apart by approximately the width of the blade in the direction of the hole therein, and the hole in the blade is located asymmetrically therein such that its distance from the nearest edge only of the blade is less than the spacing between the side members.