GB2470075A

GB2470075A - Sieve shaker separator and weighing apparatus

Info

Publication number: GB2470075A
Application number: GB0907987A
Authority: GB
Inventors: John Stobbart
Original assignee: ENDECOTTS Ltd
Current assignee: ENDECOTTS Ltd
Priority date: 2009-05-08
Filing date: 2009-05-08
Publication date: 2010-11-10
Also published as: GB0907987D0

Abstract

An apparatus features a shaker (111, fig.2) a weighing station (108, fig.2) and one or more sieves 101 a, or sieve receiving portion. Also disclosed is a related apparatus in which stack 101 of multiple sieves 101 a is carried on the apparatus, and used to separate granular material into separate fractions, and to weight each fraction individually. The sieve aperture size decreases with each sieve, downwards to the bottom of the stack. Weighing of each fraction may involve memory comparison of individual or collective stored sieve weights, as sieves are removed from the stack in order to isolate the weight of the material in each sieve.

Description

APPARATUS AND METHOD FOR PARTICLE SIZE ANALYSIS

TECHNICAL FIELD

This invention relates to an apparatus and a method for particle size analysis.

BACKGROUND TO THE INVENTION

Particle size analysis is used to determine the particle size distribution of granular material. One method of particle size analysis uses a nested column of sieves having wire mesh screens. The sieves have apertures of different sizes. The uppermost sieve has the largest apertures and the lowermost sieve has the smallest apertures. The test material is placed in the top sieve and the entire nested column is shaken, typically by a mechanical shaker, to which the column is clamped. As the column is shaken, the material moves down the column. The material is separated by the shaking process across the sieves.

Once shaking is complete, the particle size distribution can be determined. This is typically achieved by removing the material from each sieve and weighing the samples manually. Alternatively, if the weight of each sieve is known, the weight of each sample can be determined by weighing the sieves with the samples in place.

The weight of the empty sieve is then subtracted from the measured weight of the sieve and sample. The step of determining particle size distribution is typically performed manually once the sample weights have been determined. This method of particle size analysis is time and labour intensive.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an apparatus for particle size analysis, comprises: a shaker for shaking a plurality of sieves, and a weighing station for weighing said sieves.

The shaker and the weighing station may be single unit. The shaker may include a shaker table. The weighing station may be integral to the shaker table. The weighing station may comprise a load-cell. The shaker table may be supported by a resonance system. The shaker may include a vibrator which is coupled to the shaker table. The apparatus may further comprising a securing mechanism to secure said sieves to the apparatus. The weighing station may be used to determine whether or not the sieves are correctly clamped to the apparatus.

The apparatus may further comprising: a controller adapted to control the apparatus and a memory. The memory may be adapted to store details of a plurality of sieves, said details including the weight of each sieve. The sieve weights may be determined by the weighing station. The memory may also be arranged to store the weights of said sieves and a sample material, following a shaking operation. The controller may be further adapted to determine the particle size distribution of a material based on said stored weights measurements.

The apparatus may further comprise a port for connecting the apparatus to a computer, wherein the apparatus is arranged to be controlled by a computer.

According to a further aspect, the present invention provides a method for particle size analysis, using the apparatus described above, the method comprising: loading at least one sieve with a material; placing said at least one sieve on said apparatus; shaking said at least one sieve for a predetermined period; and weighing said at least one sieve to determine the particle size distribution.

The at least one sieve may be a plurality of sieves and said step of weighing comprises: a) weighing the plurality of sieves; b) removing the uppermost sieve and weighing the remaining sieves; and c) repeating step b) until all sieves are removed.

The method may further comprise storing the weight of each sieve of said plurality of sieves prior to shaking.

According to a further aspect, the present invention may provide an apparatus for particle size analysis comprising a housing having a shaking mechanism and a weighing station, a controller for controlling the operation of the apparatus, a top surface having a sieve location in to which a stack of sieves may be positioned during use, wherein said shaking mechanism is adapted to shake a stack of sieves positioned in said sieve location and said weighing station is adapted to weigh the sieves of said stack of sieves in said sieve location.

Other features of the present invention are defined in the appended claims.

Features and advantages associated with the present invention will be apparent from the following description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are hereinafter described with reference to the accompanying diagrams where: Figure 1 is perspective view of an apparatus in accordance with an embodiment of the invention; Figure 2 is a cross-sectional view of the apparatus of Figure 1; Figure 3 is a schematic diagram of the electric circuit of the apparatus of Figure 1; Figure 4 is a flow-chart showing the process used to weigh empty sieves in accordance with an embodiment of the invention; Figure 5 is a flow-chart showing the process used to weigh a sample material in accordance with an embodiment of the invention; and Figure 6 is a flow-chart showing the process used carry out particle size analysis in accordance with an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An example of the invention includes an apparatus which is a laboratory instrument for particle size analysis. The apparatus includes a shaking table. A stack of sieves and a receiver may be placed on the shaking table. The shaking table shakes, or vibrates the sieves to bring about the separation of a sample of material. The uppermost sieve has the largest apertures and the lowermost sieve has the smallest apertures. The shaking action separates the material into different particle sizes.

The bigger particles are trapped at the top and the smaller particles fall through the sieves. The receiver may be placed at the bottom of the stack to catch particles which pass through all of the sieves. The sieves are then weighed on the apparatus.

This may be achieved by incorporating a weighing station in the shaking table. The weight of the individual sieves is stored in the apparatus. Once shaking is complete, the whole stack can be weighed to give the weight of the sieves and the material.

The uppermost sieve is removed first. The remaining stack is then weighed. From the new weight and the pre-stored weight of each sieve, the weight of material in the top sieve can be calculated. The process is continued until all of the sieves have been removed. The full particle size distribution can then be determined. The apparatus is a combined shaking machine and weighing scale for sieve based particle size analysis. An example of the apparatus will now be described in more detail.

Figure 1 shows an apparatus 100 in accordance with an embodiment of the invention. In Figure 1, the apparatus is shown with a stack of sieves in place 101.

The apparatus 100 includes an housing 102. The housing 102 includes a display 103 and a keypad 104. The display 103 is used to provide instructions to a user and to display the results of particle size analysis. The keypad 104 is used to control the apparatus 100. The housing includes a shaking table 105. The shaking table 105 is attached to a shaking mechanism (not shown in Figure 1). The shaking mechanism is arranged to cause the shaking table to shake. The shaking table includes a clamp system 106. The clamp system includes two vertical rods 106a and 106b which extend to the height of a stack of sieves 101. A clamp plate 106c is placed on top of a stack of sieves. The rods 106a and 106b pass through holes in the clamp plate 106c. Two clamps 106d and 106e are used to clamp the top plate to the rods. The clamp system 106 also includes locking handles 106f and 106g which include release buttons 106h and 106i.

Figure 2 shows a cross-section of the apparatus 100. The apparatus 100 also includes a weighing station 107. The weighing station 107 is integral to the shaking table 105. The weighing station 107 includes a load cell 108. The load cell 108 includes an inner section 108a and outer section 108b. The outer section 108b is secured to a load cell plate 109 along the lower edge of the outer section 108b. The inner section 108a is secured to a location plate 110. The movement of the inner section relative to the outer section, when items are placed on the location plate 110, enables the load cell to determine the weight of items placed on the location plate. It will be appreciated that other weighing mechanisms may be used. For example, a capacitive sensor may be used. The load cell 108 has built in end stops to prevent it being subjected to excessive force during shaking.

The shaking mechanism includes a vibrator 111 which may be a solenoid electromagnet. Alternatively, the shaking mechanism could be an electric motor with an eccentric cam, or other suitable shaking means. The shaking mechanism is arranged to shake the shaking table from 50Hz to 60Hz. The amplitude of the shaking motion can also be varied and a half sine wave input signal is used. It will be appreciated that the shaking table 105 may be shaken at other frequencies and with other waveforms. It is possible to shake the shaking table 105 with multiple frequencies, at variable frequencies and also with additional superimposed large jolts, which may be applied periodically. The shaking table 105 could also shake aperiodically, i.e. at random. The shaking table 105 may also vibrate intermittently, such as, for example, five seconds not vibrating and five seconds vibrating.

Alternatively, the shaking mechanism may run continuously. The apparatus 100 will normally be used to shake at a fixed amplitude and fixed frequency.

The load cell plate 109 which supports the load cell 108 is connected to the housing 101 via a set of springs 112a -d or other resonance system. The vibrator 111 is also fixed to the housing 101.

The stack of sieves 101 are separate from the apparatus 100 and are loaded onto it with the material samples when required. The stack 101 includes a plurality of sieves lOla, a receiver lOib and the lid 106c. The receiver lOlb is placed at the bottom of the stack 101 and is for catching any material having a particle size smaller than the aperture of the bottom sieve. The sieve with the smallest apertures is placed on top of the receiver 101 b. The remaining sieves are placed on top of the lowermost sieve in order of ever increasing aperture size. Finally, the clamp plate 106c is placed on top of the uppermost sieve.

Figure 3 is a schematic diagram of the electric circuit of the apparatus 100. The apparatus includes a controller 113. The controller 113 is coupled to the display 103, keypad 104, the vibrator 111 and the load cell 108. Also shown is a memory 114. The memory 114 is for storing instructions which are carried out by the controller 113 to perform a shaking and weighing operation. The memory 114 also stores details of sieves and of particle analysis results. The apparatus 100 also includes a power supply 115 to power the apparatus 100. The apparatus also includes circuit protectors (not shown) such as fuses, switches and EMC filters. The apparatus 100 also includes an AC driven phase angle controller 121 for driving the vibrator 111.

In an alternative embodiment, the load cell 108 is not integral to the shaking table 105. Instead, the shaking table 105 includes an opening (not shown). The load cell 108 has a smaller diameter than the receiver 101 b. The opening in the shaking table is larger than the load celllO8 but smaller than the receiver lOib. Therefore, the receiver lOlb can rest on the shaking table 105 without falling through the opening.

The load cell 108 is positioned beneath the opening and is attached to the housing 102. The load cell 108 is connected to the housing 102 by a lift mechanism (not shown) which is adapted to raise the load cell 108 up through the shaking table 105.

When shaking is complete, the lifting mechanism raises the load cell 108 into engagement with the receiver bib. The lifting mechanism lifts the stack 101 off the shaking mechanism so that weighing can begin. Alternatively, the load celllO8 is fixed to the housing 102. A lowering mechanism (not shown) may be attached to the shaking table 105 in order to lower the shaking table 105 below the load cell 108 so that weighing can commence. The shaking mechanism can be integral with the lifting mechanism. The input signal to the shaking mechanism could be set to lower the shaking table 105 below the load cell 108. An alternative to a single opening would be to have a series of openings in the shaking table 105. A series of corresponding prongs or plates (not shown) could be attached to the load cell 108.

These would come through the bottom of the shaking table 105 once the sieves have been unclamped. The sieves stack 101 would be lifted up and its full weight applied to the load cell 108 prongs. Thus, in this embodiment, the load cell 108 is not integrated into the shaking table 105, but is only engaged when required.

In a further alternative embodiment, the stack 101 could be mounted to a shaking mechanism at the top of the apparatus 100. When shaking is complete, the sieves could be unclamped and, through the action of gravity, have their mass applied to the weighing station mounted beneath the sieves.

A further alternative embodiment may use a hydraulics system. The hydraulic (or pneumatic) system shakes the stack of sieves in a first mode. Once shaking is complete, the hydraulic system is used to measure the weight of the sieves in a second mode. In effect, the hydraulic system is operated in reverse to weigh the stack. Alternatively, a mechanism to measure the displacement of the shaking table with the sieves loaded on it (such as laser inteferometry), using springs, to convert load to displacement may be used.

It will be appreciated that other mechanism exist for weighing and shaking and that the invention is not intended to be limited to any particular mechanism or combination of mechanisms.

The apparatus the includes a user interface in the form of the display 103 and keypad 104. The display may be a liquid crystal display which able to display text and graphics in one more languages. The display 103 may include a backlight. The keypad 104 may be illuminated. The electric circuit also includes a piezo sounder 116 which is adapted to make a beeping sound to prompt the user at various stages of the particle analysis process. It will be appreciated that that there are many user interface arrangements, such as touch screens, speech synthesis, track balls, etc. The present invention is not intended to be limited to any particular user interface.

The apparatus 100 may also include a link 117 to an external computer, such as a serial link. Other links such as Ethernet may also be used. The apparatus 100 may also include a USB link through which data can be transferred to a USB memory stick. In an alternative embodiment, a remote computer could be used as the user interface. Such a computer could also control the apparatus 100, thereby allowing fewer components to be present in the apparatus 100 itself. The user interface could, therefore, be run on a remote computer via a communication link. This could consist of a series of web pages, provided by the apparatus 100, which are viewed and interacted with by the remote computer.

The user interface allows the user to select a range of operational parameters, such as the length of time to shake the sieves, the sequential number of the experiment, the amplitude of the shaking, whether the shaking is intermittent or continuous and if intermittent, what the respective on and off periods are. Other operational parameters could be set. In addition to operational parameters, the user interface allows a user to set system parameters. System parameters includes operational frequency, time and date, US/UK formatting, languages etc.. There is potential for other system parameters.

The apparatus 100 may also include a printer (not shown). This may be provided as an integral printer or as an external peripheral device. The apparatus 100 may also include a port (not shown) to accept removable data storage media such as floppy disk, USB memory stick or digital memory card (such as an SD card).

The operation of the apparatus 100 will now be described. Firstly, a calibration process will be described.

The apparatus may be calibrated prior to carrying out particle size analysis. There are a number of ways to calibrate the apparatus. The process described here is one example of how the apparatus may be calibrated. This method uses two calibrated standard weights. A first calibrated standard weight (not shown) has a weight which is towards the maximum weight that the apparatus can measure. A second calibrated standard weight (not shown) may be at 25% of the maximum weight.

These weights are processed against known standard weights to allow linear scaling and zero compensation of the scale. Calibration is only done periodically, but could be done as often as the user wishes.

A method of operating the apparatus will now be described with reference to Figure 4. The following example will be described in the context of a stack of sieves including five sieves and a receiver. The sieves are labelled one to five, with sieve one having the largest apertures and sieve five having the smallest apertures.

Before particle size analysis can begin, the stack of sieves needs to be weighed.

This is done by defining a stack using the keypad 104, and storing the stack details in the memory 114. Firstly, the user enters a reference number for the stack. The user then enters a reference number for each sieve in the stack (step 201). The controller 113 then instructs the user, via the display 103, to place each sieve on the load cell 108 in turn. Each sieve is weighed by itself (step 202) and its weight is recorded in memory 114 together with that sieves particular reference number (step 203). For simplicity, in this case, the sieves are all determined to weigh 1000g.

For example, the entry could take the form: STACK 1111; Sieve: 5Oum, weight 1000g.

The sieves weight's can be recorded individually and in any order. Alternatively, the sieves weight's can be typed in to the apparatus from calibration certificates.

As a further alternative to weighing the sieves individually, the sieve's weights could be calculated by weighing the whole stack and removing each sieve, one by one.

For example, the weight of the whole stack might be 5000g. The top sieve is then removed. The remaining stack weighs 4000g. Therefore the top sieve weighs 1000g. This is continued until only the receiver lOlb is left, Therefore, the weight of each sieve, and the receiver, can be calculated.

As with all measurements, further accuracy can be obtained by carrying out multiple repeated measurements and taking an average. Alternatively, further statistical techniques can be used, such as excluding upper and lower bounds etc.. Sieves could be weighed prior to shaking before every experiment. However, more commonly, the sieves are only weighed periodically.

Once the sieve weights are recorded in memory 114 the user can proceed to analyse a sample of granular material. This will be described with reference to Figure 5.

In this embodiment, the weight of the sample material is calculated first. This is achieved by taking various measurements prior to shaking the stack. The sieves are first placed together in the stack together with the receiver lOib. The user then presses a key on the keypad 104 to start a pre-shake weighing process (step 301).

The controller 113 then weighs the unloaded load cell to obtain a zero measurement (step 302). The controller 113 then instructs the user, via display 103, to place the stack on the load cell 108. The weight of the stack of sieves is then measured and stored in memory 114 (step 303). This measurement is called STACKWEIGHTPRESHAKE and in this case is 6000g. The user then places the sample in the top sieve and the apparatus weighs the stack with the sample (step 304). This measurement is called MEASUREDWEIGHTPRESHAKE. From these measurements we can calculate the weight of the sample (step 305) using the following equation: SAMPLEWEIGHTPRESHAKE =

MEASUREDWEIGHTPRESHAKE -STACKWEIGHTPRESHAKE

The STACKWEIGHTPRESHAKE can be compared with that recorded in the apparatus. This may be used to compensate the value recorded in the apparatus.

In the above embodiments, we have ignored weight of lid 106c, as the lid is applied to the whole stack after weighing of the individual sieves of the stack. The lid I 06c is removed after shaking. Therefore, the weight of the lid is not processed. The lid may be included in alternative embodiments.

The process of shaking and weighing the sieves will now be described with reference to Figure 6. Once the weight of the sample is determined, the stack of sieves is clamped to the shaking table 105 using the clamp system 106 to secure the stack to the table (step 401). This is to prevent loss of the sample. The user then presses a key on the keypad 10 to start the shaking process (step 402). The sieves are then shaken as defined by the operational parameters of the apparatus, as previously described.

It will be appreciated that there are a number of ways to initiate shaking. For example, the user may begin shaking by pressing a key on the keypad 104. The keypad may also be used to pause and resume shaking.

In one embodiment, the apparatus 100 has a mechanism for detecting whether or not the sieves are clamped in place properly. This mechanism uses the output of the load cell 108. When the stack is properly clamped on the shaking table 105, the load cell 108 produces a very high reading which is higher than the maximum range of loads the machine is specified to weigh. This reading is checked and compared to a set threshold. If the reading is below the threshold, it implies that the stack of sieves is not correctly clamped. The apparatus 100 will not start shaking and will indicate to the user that the stack must be properly clamped. If the reading is over the threshold, the apparatus 100 will enable the operator to begin the shaking operation.

This monitoring can be done at the start of the process prior to shaking or could be carried out during shaking. In the latter case, the system will stop shaking if the load drops below the threshold.

The above describe clamp detector will operate with the embodiment in which the load cell 108 is fixed to the shaking table 105. Where the load cell is separate to the shaking table 105, and is arranged to be raised up in use, it may not be possible to use the load cell 108 to assess clamping. In this case, this function could be provided using other sensors (not shown).

Once shaking is complete, the user is prompted by the controller 113. The prompt may be in the form of an audible or visual warning. The user then releases the clamp system 106 and removes the lid 106c (step 403). The process of weighing the sieves, post shaking, then begins.

In a first embodiment, the weight of each sieve, post shaking, is determined by recording the weight of the stack as each sieve is removed. This may be done using a pie-stored algorithm which instructs as user to remove each size, in turn, at the end of a timed period (for example, every eight seconds). Each time the user removes a sieve, the weighing station 107 weighs the remaining stack, and calculates the weight of the sieve which has been removed.

The weighing algorithm starts when a user selects the appropriate options using the keypad 104 (step 404). The controller 113 then instructs the load cell 108 to weigh the stack (step 405). This weight is MEASUREDWEIGHT 1. The controller 113 instructs the user to remove the top sieve (sieve 1) (step 406). The controller 113 then instructs load cell 108 to weigh the remaining stack. The process returns to step 405 and the process is repeated. The apparatus determines the weight of the stack without sieve 1. This is MEASUREDWEIGHT 2. This process continues to determine MEASUREDWEIGHTS 3 to 7. In the present case the measured weights are as follows: MEASUREDWEIGHT I (all sieves and receiver): 6600g MEASUREDWEIGHT 2: (sieves 2 to 5 and receiver): 5500g MEASUREDWEIGHT 3 (sieves 3 to 5 and receiver): 4400g MEASUREDWEIGHT 4 (sieves 4 and 5 and receiver): 3300g MEASUREDWEIGHT 5 (sieve 5 and receiver): 2200g MEASUREDWEIGHT 6 (receiver): ilOOg MEASUREDWEIGHT 7 (nothing): Og From this information, the weight of each sieve together with its portion of the sample can be calculated (step 407). For example, the weight of sieve 1 and sample is MEASUREDWEIGHT I -MEASUREDWEIGHT 2 = 1100g. This is referred to as SIEVE1PLUSFRACTION1. The other weights are SIEVE2PLUSFRACTION2 = ilOOg, SIEVE3PLUSFRACTION3 = ilOOg, SIEVE4PLUSFRACTION4 = 11009, SIEVE5PLUSFRACTION5 = 11 OOg, RECEIVERPLUSFRACTION6 = 1100g.

Each SIEVExPLUSFRACTIONx then has the pre-recorded empty sieve weight deducted from it to determine the final sample weight in that sieve (408). In the present case, there are six samples, one in each of the five sieves and one in the receiver. Each sample weighs 100g. Once the results are recorded and stored in memory 114 they can be processed. For example, a user can: a) view the raw data; b) view the raw data with cumulative weights; c) view the data as a series of percentages of the whole sample; d) compare the data with a pre-recorded master stack, which is a stack that consists of the same sieves but with the weight post shaking of the "desired' sample distribution recorded. In effect it is a reference for what is desired by way of results; e) produce graphical information; and f) view statistical information.

It will be appreciated that many more options for viewing data are possible.

The data can also be transferred to a remote computer via the serial link mentioned above. Here it can be saved as a file, processed by a dedicated software application or imported and processed by a standard software application such as EXCEL�.

This data can also include operational and system parameters such duration of shaking. is

As noted above, the results data may be stored in memory 114. From here it can be transferred at a later date, deleted or processed further.

In the above described embodiments, the sample weight distribution is calculated by removing a sieve, one at a time, from the stack, with the stack being weighed after each removal. In an alternative embodiment, the user removes the stack from the apparatus 100 after shaking. The sieves are then re-applied and weighed individually.

This method could record the ZERO WEIGHT (unloaded weighing station 106) and the MEASURED WEIGHT and through subtraction infer the SIEVE WEIGHT WITH SAMPLE. Using further subtraction of the pie-recorded empty SIEVE WEIGHT produce the WEIGHT OF SAMPLE IN THAT SIEVE.

In other words, MEASURED WEIGHT -ZERO WEIGHT -PRERECORDED EMPTY SIEVE WIEGHT = WEIGHT OF SAMPLE IN THAT SIEVE.

Alternatively, the ZERO WEIGHT could be used for the whole stack of sieves (assuming the ZERO WEIGHT does not change during the weighing of all sieves in the stack). A further alternative is to use the ZERO WEIGHT taken prior to shaking.

As noted above, it is possible in all weighing operations to take multiple measurements to reduce errors through averaging. In addition, it is possible that the controller 113 could monitor the measured weight over a period of time and only allow the measurement if the weight recorded is stable within defined parameters.

This is so as to prevent bounce from the sieve being removed or applied too aggressively. In effect, allowing more time to settle if the reading has poor stability to ensure accurate results and not results influenced by the manual handling of the sieves. There are a range of statistical means that are widely known to achieve both enhanced accuracy and to detect stability and to ensure correct measurement, these are not detailed here.

It will be appreciated that any numbers of sieves or receivers can be shaken with any load.

As a further option, the apparatus 100 may be adapted to shake a stack of sieves an dependent on its weight. The heavier a stack, the less effect a particular shaking motion has on the stack. Therefore, the apparatus can change the shaking motion to compensate for heavier sieves stacks. The apparatus 100 records the total loaded mass of the entire sieve stack, before shaking. This recorded total mass is then summed with the mass of the shaking table unloaded. This enables the total shaken mass to be determined.

As noted above, the shaking table is supported on a resonance system and this is driven by a solenoid whose magnetic field varies the amplitude of the shaking table depending on the voltage, current and/or the point at which a triac is triggered (in effect the phase angle is controlled).

As the weight is changed on the shaking table, so does the resonance of the system.

As such, the amplitude of the shaken stacks will vary from that originally set and delivered by the solenoid. However, in this embodiment, as an addition, it is possible to take the total shaken mass and to carry out calculation whereby the amplitude of the solenoid oscillation is increased or decreased from the norm on the basis of the measured weight. Thus, the amplitude of the resonance system is kept constant irrespective of weight.

The apparatus described above requires less time and labour than prior art devices.

The shaking and weighing processes are both carried out, on the same device, with the sieves remaining in situ (subject to final removal during the weighing process).

It will be appreciated that the features recited in the claims may be used in combinations other than those recited in the claims.

Various modifications, changes, and/or alterations may be made to the above described embodiments to provide further embodiments which use the underlying inventive concept, falling within the spirit and/or scope of the invention. Any such further embodiments are intended to be encompassed by the appended claims.

Claims

Claims: 1. An apparatus for particle size analysis, comprising: a shaker for shaking a plurality of sieves, and a weighing station for weighing said sieves.
2. An apparatus according to claim 1, wherein said shaker and said weighing station are a single unit.
3. An apparatus according to claims 1 or 2, wherein said shaker includes ashaker table.
4. An apparatus according to claims 1, 2 or 3, wherein said weighing station is integral to the shaker table.
5. An apparatus according to any preceding claim, wherein said weighing station comprises a load-cell.
6. An apparatus according to any claim 3, wherein said shaker table is supported by a resonance system.
7. An apparatus according to claim 6, wherein said shaker includes a vibrator which is coupled to the shaker table.
8. An apparatus according to any preceding claim, further comprising a securing mechanism to secure said sieves to the apparatus.
9. An apparatus according to claim 8, wherein said weighing station is used to determine whether or not the sieves are correctly clamped to the apparatus.
10. An apparatus according to claim 1, further comprising: a controller adapted to control the apparatus and a memory.
11. An apparatus according to claim 10, wherein said memory is adapted to store details of a plurality of sieves, said details including the weight of each sieve.
12. An apparatus according to claim ii, wherein said sieve weights may be determined by the weighing station.
13. An apparatus according to claim 12, wherein said memory is also arranged to store the weights of said sieves and a sample material, following a shaking operation.
14. An apparatus according to claim 13, wherein said controller is further adapted to determine the particle size distribution of a material based on said stored weights measurements.
15. An apparatus according to any preceding claim, further comprising a port for connecting the apparatus to a computer, wherein the apparatus is arranged to be controlled by a computer.
16. An apparatus according to claim 14, wherein said controller is adapted to cause said shaker to produce an intermittent larger amplitude shaking motion, during said shaking process.
17. An apparatus according to claim 1, wherein said weighing station and shaker are vertically moveable in relation to each other and said weighing station can be moved in to engagement with a stack of sieves.
18. An apparatus according to claim 1, wherein said weighing station is used to vary the output of the shaker, depending on the weight of a stack of sieves.
19, A method for particle size analysis, using an apparatus according to any of claims ito 18, the method comprising: loading at least one sieve with a material; placing said at least one sieve on said apparatus; shaking said at least one sieve for a predetermined period; and weighing said at least one sieve to determine the particle size distribution.
20. A method according to claim 19, wherein said at least one sieve is a plurality of sieves and said step of weighing comprises: a) weighing the plurality of sieves; b) removing the uppermost sieve and weighing the remaining sieves; and C) repeating step b) until all sieves are removed.
21. A method according to claim 20, further comprising storing the weight of each sieve of said plurality of sieves prior to shaking.
22. An apparatus for particle size analysis comprising a housing having a shaking mechanism and a weighing station, a controller for controlling the operation of the apparatus, a top surface having a sieve location in to which a stack of sieves may be positioned during use, wherein said shaking mechanism is adapted to shake a stack of sieves positioned in said sieve location and said weighing station is adapted to weigh the sieves of said stack of sieves in said sieve location.
23. An apparatus substantially as described hereinbefore and as shown in Figures 1 to 6.