GB2345655A

GB2345655A - Centrufugal evaporator

Info

Publication number: GB2345655A
Application number: GB9925999A
Authority: GB
Inventors: Michael Cole
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-11-12
Filing date: 1999-11-04
Publication date: 2000-07-19
Also published as: WO2000029122A1; GB9824702D0; GB9925999D0

Abstract

A centrifugal evaporator (vacuum butyrometer) features an automatic balancing device 16 (see also Figure 2) which is enclosed in a housing 18(36 in Figure 3, 50 in Figure 4) made from eg: anodised aluminium, stainless steel, Hastelloy (RTM) or polypropylene which protects said device from physical or chemical damage. Solvent vapours emitted by samples during the course of centrifugal evaporation could harm the automatic balance device (which is an incompletely packed ball bearing race), so the inert housing offers protection from corrosion <I>etc</I>.

Description

2345655 C1101/c Title: Improvements in or relating to Cgntrifugal

Evaporators

Field of the Inventio

This invention relates to the protection of automatic balancing devices for reducing vibration of rotating sample holders in centrifugal evaporators. The invention is particularly concerned with protecting the said automatic balancing devices from chemical damage by liquids or vapours during operation of centrifugal evaporators.

Background tg the Invention

A centrifugal evaporator, for drying samples which comprise solid material dissolved or suspended in a liquid, is described in W099/33538 and comprises a sealable chamber in which samples are mounted in rotating gimbaled sample holders which are spun at high speed to subject Ehe samples to centrifugal force, thereby inhibiting loss of sample material due EO spitting and/or frothing of the liquid as evaporation takes place, and means to accelerate evaporation, including a pump whereby the chamber is substantially evacuated, and a heater.

An automatic balancing device comprising an annular race incompletely filled with steel ball bearings and associated with a rotating assembly to reduce vibration due to imbalance of the assembly, is described in W098/01733.

When samples dry at different rates, as e.g. when some contain a more volatile liquid than others, imbalance of the rotating sample holders can arise, with consequent vibration.

It has been proposed to fit an imbalance sensor to a centrifugal evaporator to brake the rotating sample holders before the vibration becomes sufficient to damage the evaporator and/or samples therein. It is also known to prevent imbalance of the rotating sample 2 holders by careful positioning of the samples in the holders or by periodically interrupting the evaporation and rebalancing the sample holders by adding solvent to dry samples or repositioning the samples in the sample holders. Both methods are tedious and time consurning.

It is therefore an object of the invention to enable continued operation of a centrifugal evaporator, in the event of imbalance of the rotating sample holders, e.g. due to differential rates of drying of samples.

Summaa of the Inventio According to one aspect of the present invention, apparatus for drying samples which comprise solid material dissolved or suspended in a liquid, comprises a sealable chamber, a shaft therein for rotation in use about a generally vertical axis, a rotor attached to the shaft, sample holders pivotally suspended from the rotor in which sample holders the samples are contained, drive means for rotating the shaft, rotor and sample holders relative to the chamber, heating means and pumping means whereby the sealable chamber is substantially evacuated, to facilitate drying of the samples, and an automatic balancing device associated with the shaft and/or rotor for counteracting any imbalance of the rotating sample holders arising during operation which would otherwise result in vibration, wherein the automatic balancing device is enclosed in a housing to protect it against physical and/or chemical damage.

It may be advantageous for the housing to seal (i.e. hermetically) the automatic balancing device from its external environment to prevent solvent vapour and/or other contaminants from entering the automatic balancing device.

Where corrosive solvents or vapours are likely to be present, it is advantageous for the housing material to be inert at least with respect to the solvents or vapours present.

Preferred materials for the housing are polypropylene, glass filled polytetrafluoroethylene, (RTM) stainless steel, hard anodised aluminium, or Hastelloy k, 3 Stainless steel has the advantage that it will not be attacked by most solvents used in a centrifugal evaporator.

However, it may be advantageous to use a low density material such as polypropylene so as to minimise the overall mass of the balancing device.

In a particular embodiment, apparatus for drying samples as aforesaid is such that the automatic balancing device comprises an annufar bearing race incompletely filled with ball bearings and arranged so that in use the ball bearings therein are distributed around the race to counteract any imbalance of the rotating sample holders.

It is advantageous for the ball bearings to be formed from a material having a density substantially greater than that of steel. Preferably the ball bearings are formed from high density materials such as tungsten or depleted uranium since, for a given counteracting effect, the overall size of the race may be reduced both in depth and diameter, as compared with using e.g. steel ball bearings.

Brief Description of the Draw'

The invention will now be described, by way of illustrative example, with reference to the accompanying drawings in which:

Figure I is a schematic sectional view of a centrifugal evaporator comprising a rotor with test tubes pivotally suspended therefrom and an enclosed automatic balancing device in accordance with the invention; Figure 2 is a perspective view of the disassembled automatic balancing device associated with the rotating sample holder shown in Figure 1; Figure 3 is a schematic sectional view of an automatic balancing means enclosed in a hard (RTM) anodised aluminium., stainless steel or Hastelloy/ housing suitable for use in apparatus in accordance with the invention.

4 Figure 4 is a schematic sectional view of an automatic balancing means enclosed in a polypropylene housing suitable for use in apparatus in accordance with the invention.

Detailed Description

The centrifugal evaporator shown in Figure I comprises a plurality of test tubes 10, of which two are shown, wherein samples (not shown) are located. The test tubes are pivotally suspended from a rotor 12 that is attached to a vertical shaft 14. An automatic balancing device 16 is enclosed in a housing 18 in accordance with the invention. Both are located around the vertical shaft 14 as close as possible to the rotor 12 and secured by a locking ring 20. A motor 15 rotates the assembly of the vertical shaft 14, automatic balancing device 16, housing 18, rotor 12 and test tubes 10. A heater 22 supplies heat to the rotating test tubes and samples therein. The aforesaid apparatus is contained in a sealable chamber 24 connected to a pump 17 for evacuating the chamber and removing vapour given off as the samples are dried.

The test tubes 10 are pivotally suspended from the rotor 12 such that when the rotating assembly is stationary the test tubes hang vertically as shown in Figure 1. When the assembly is rotated the closed ends of the test tubes swing outwardly and upwardly until they are approximately horizontal, and the centrifugal forces acting upon the sample material (not shown) in the test tubes 10 tend to restrain sample material in the test tubes.

The automatic balancing device 16 is shown in detail in Figure 2. it consists of outer and inner circular cups, 26 and 28 respectively, and a plurality of ball bearings 30.

The outer circular cup 26 has a central frustrurn 32 formed inside it. The inner circular cup 28 has an outer diameter that makes a snug fit inside the outer cup 26. With the inner cup 28 inside the outer cup 26 an enclosed annular bearing race is formed, bounded axially by the bases of the inner and outer cups and radially by the curved surface of the frustrum 32 and the curved inner surface of the inner cup 28. The plurality of loose ball bearings 30 have equal diameters that enable them to roll freely around the race. The ball bearings incompletely circumferentially fill the race.

Both inner and outer cups have central circular holes 34 of equal diameters. With the inner cup inside the outer cup and the ball bearings in place to form the assembled automatic balancing device, there is a circular hole through the device, the centre of which hole coincides with the centre of the annular race. The balancing device is by virtue of said central hole located around the vertical shaft 14 of the centrifugal evaporator and rigidly secured thereto, so that the centre of the annular bearing race coincides with the axis of rotation of the vertical shaft, and relative movement between the race and the shaft is .. sed. When the vertical shaft and hence the balancing device are rotated the ball bearings, become distributed around the annular race in a manner tending to counteract imbalances of the rotating assembly, such as may arise due to uneven loading of the test tubes or uneven evaporation of liquid from the samples.

Typically the ball bearings 30 are of Tungsten or depleted Uranium. The balancing effect produced by a ball bearing used in this manner is proportional to the product of its mass and its radial displacement from the axis about which it rotates. It is therefore possible, using high density materials such as Tungsten or depleted Uranium to produce a balancing device capable of providing a particular imbalance counteracting force, which is physically smaller in radius or depth or both, than an equivalent balancing device using less dense material for the ball bearings, such as steel.

An automatic balancing means that has been used to advantage has been produced and is commercially available in the UK from SKF AutoBalance Systems AB under the name DynaSpin (trade mark).

Figure 3 shows one preferred embodiment of the invention. A housing 36, formed from (RTM) hard anodised aluminium, stainless steel or Hastelloyi partially encloses an automatic balancing means 38. The balancing means is held against the underside of a first flange projecting radially from the upper end of a vertical shaft 40 by the housing 36. A rotor 42 6 is mounted on the upper surface of said first flange and with its centre coinciding with the axis of rotation of the vertical shaft 40.

A second flange of smaller diameter than, and adjoining, the first flange projects radially from the vertical shaft 40 below the first flange. The vertical surfaces formed by the circumferences of the first and second flanges have formed in each a single groove to accommodate O-rings 44 and 46 respectively. The housing 36 is in the form of an annular trough sized to accommodate the balancing device and having radially outward projecting lips upon its inner and outer walls. The inner surface of the outer wall and the outer surface of the inner lip abut the vertical surfaces of the first and second flanges respectively and form an interference fit with the O-rings retained in the grooves therein. The enclosure of the automatic balancing unit formed by the housing and first and second flanges, seals the automatic balancing unit from inter alia solvent vapours produced during operation of the centrifugal evaporator or liquids spilt during negligent loading of the evaporator. Clamps such as 48 retain the housing 36 against the lower surface of the rotor 42 and the first flange, and thereby retain the balancing device against the lower surface of the upper first flange. The clamps are secured to the lower surface of the second flange by bolts.

It is preferable during manufacture of the particular embodiment set out above to grind the first and second flanges at the same time as the rest of the vertical shaft is ground to size. This ensures the required degree of concentricity between the axis of rotation of the shaft and the race within the automatic balancing device.

Figure 4 shows a second preferred embodiment of the invention, wherein a housing 50 of polypropylene partially encloses an automatic balancing device 52. The housing 50 is generally annular and includes cylindrical axial extensions 54 and 56 from the inner edges of the upper and lower openings. The inner surfaces of the two extensions are each grooved to accommodate O-rings 58 and 60.

A vertical shaft 62 is formed at its upper end with a radially projecting flange to which a rotor 64 is attached. The automatic balancing device 52 is secured against the lower 7 horizontal surface of the flange by a clamp 66, against which a locking ring 68 bears. The locking ring 68 is tightened against the clamp 66 on a threaded section 70 of the vertical shaft 62. The inner cylindrical surface of the clamp 66 has a groove therein to accommodate an annular seal 72 of generally triangular cross-section, arranged so that the radially inner region of the seal is thicker than the radially outer region thereof. The inwardly protruding portion of the seal 72 is trapped between the shaft 62 and the inner face of the clamp 66 thereby, sealing inner surfaces of the clamp to the shaft.

The two O-rings in the upper and lower extensions 54, 56 of the housing engage the shaft 62 and seal the housing to the shaft. The automatic balancing device is therefore completely sealed from the external environment within the centrifugal evaporator chamber by the housing 50, vertical shaft 62, clamp 66 and the three seals 58, 60 and 72.

In this embodiment a sufficient degree of concentricity between the axis of rotation of the vertical shaft and the race within the automatic balancing device is achieved by precision grinding the shaft and flange and mounting the automatic balancing means thereto as described above.

8 C1101/c

Claims

1. Apparatus for drying samples that comprise non-volatile material dissolved or otherwise mixed in a liquid, comprising a sealable chamber and pumping means to evacuate the said chamber, a shaft therein for rotation in use about a generally vertical axis, a rotating sample holder attached to the shaft, in which sample holder the samples are contained, drive means for rotating the shaft and sample holder relative to the chamber, heating means for accelerating the evaporation of liquid from the samples, and an automatic balancing means associated with the shaft rotating sample holder and/or sample holder for counteracting any imbalance of the rotating sample holding arising during operation which would otherwise result in vibration characterise"b: a housing enclosing the automatic balancing means for protecting it against physical and/or chemical damage.

2. Apparatus according to the previous claim wherein the housing that encloses the automatic balancing means seals the said means from its hermetically external environment.

3. Apparatus according to either of the previous claims wherein the housing is formed from a material that is chemically inert at least in so far as concerns solvents or vapour present in the chamber.

4. Apparatus according to any of the previous claims wherein the housing is formed from polypropylene.

5. Apparatus according to any of claims I to 3 wherein the housing is formed from stainless steel.

9

6. Apparatus according to any of claims I to 4 wherein the housing is formed from a low density material e.g. polypropylene to minimise the overall mass of the balancing means.

7. A method of protecting an automatic balancing means for use in a centrifugal evaporator wherein the said balancing means is enclosed in a housing to inhibit or prevent chemical and/or physical damage to the balancing means.

1

8. A method of making a centrifugal evaporator comprising the steps of including in the said evaporator an automatic balancing means and a protective housing therefor.

9. Apparatus wherein a housing protects the automatic balancing means associated with a centrifugal evaporator, substantially as herein described with reference to, and as shown in, the accompanying drawings.

10.

A method of protecting an automatic balancing means for use in a centrifugal evaporator, substantially as herein described with reference to, and as shown in, the accompanying drawings.