APPARATUS FOR MEASURING IGNITION LOSS

Abstract: Disclosed is an apparatus for automatically and accurately measuring ignition loss of powder samples without the requirement of manual handling. The apparatus comprises a weighing section (1), a heating section (21) and a cooling section (31) which are integrally arranged and the weighing section (1) including a sample supply device (5) and a transporting device (3). Each of the sections are automatically operated and controlled by a controlling section (41).

Description: The present invention relates to an apparatus for measuring ignition loss in various kinds of powder samples. Ignition loss is represented by a weight percentage decrease caused by igniting a powder sample. It is one of the chemical characteristics of ceramic materials. A method of measuring the ignition loss is established by a feldspar analyzing method according to JIS (Japanese Industrial Standard) M8853 and a pyrophyllite analyzing method according to JIS M8855. Previously, the ignition loss was measured by weighing a powder sample prior to ignition by means of a balance, manually igniting the sample by using an electric furnace or a Meker burner and subsequently weighing the sample by means of the balance. This prior art measuring method mentioned above has drawbacks, for instance efficiency due to manual working is low and the safety of operators put at risk due to the high temperatures involved during the ignition. Furthermore, measurement values vary widely depending on the operator since the weighing and heating must be performed manually. An alternative apparatus, disclosed in GB-A-2116733 comprises a balance and a platter to support crucibles containing samples, each positioned within a furnace chamber. In use, the crucibles are deposited, in a predetermined sequence, on a weigh platform on the balance and weighed when empty and when loaded. As a control, an empty crucible is also included in the sequence. As they are heated in the furnace, the crucibles and samples are weighed continuously until the weights of all samples are constant. Weight loss is calculated. The present invention attempts to eliminate some of the aforementioned drawbacks and to provide an apparatus for accurately and automatically measuring the ignition loss. According to the present invention, there is provided an apparatus for measuring ignition loss in a powder sample as set out in claim 1. Preferably, the balance for weighing the gross weight of a powder sample is an electronic balance, and the preheating and igniting furnaces are electric. The crucible tray stacker preferably has a fork for transporting the tray. The use of the word powder in the specification is intended to include fine powders, coarse powders and granules. Preferably, each of the various kinds of sample are individually contained in a container with a feeder, and the sample to be measured is changed by changing the container and the feeder, so that the feeder is new and clean for every sample and the samples can be automatically selected and weighed without any contamination from the prior sample. Preferably, the container is agitated by a vibrating unit, to allow the sample to be transferred to the balance with ease. It is preferable that the container with the feeder is provided with an agitator blade. The blade enables the powder samples which have a tendency of aggregating to form lumps of powder in the container to pass easily from the container to the feeder. Furthermore it is preferable that when the powder sample is being fed from the container to the crucible by vibrating the container, a voltage applied to the vibrator unit may be varied in steps by means of the controller according to the detected weight of the powder sample already supplied to the crucible. This enables the strength of vibration to be adjusted in dependance upon the amount of powder which needs to be transferred from the container to the crucible. For example as the weight still to be transferred to the crucible decreases, the strength of vibration decreases, thus making it easier to attain the target weight. Embodiments of the invention will now be described, by way of example, and with reference to the accompanying drawings, in which: Fig. 1 is a plan view of an embodiment of the measuring apparatus in accordance with the invention; Fig. 2 is an elevational view of the apparatus shown in Fig. 1; and Figs. 3∼6 are sectional views of embodiments of a container having a feeder. Referring Figs. 1 and 2 which are an elevational view and a plan view of an embodiment of an apparatus for measuring ignition loss of a sample in accordance with the present invention. In this embodiment, the apparatus includes a weighing means 1 which is a section comprising an electronic balance 2 for measuring weight of a powder sample fed in a crucible 4 transported from a crucible tray 3, a sample supply device 5 adapted for selecting a sample to be measured from various kind of samples and feeding the selected sample into a crucible 4 mounted on the electronic balance 2 and a crucible and tray transporting device 6 for transferring the crucible 4 from the tray 3 to the balance 2 and is arranged such that the selected sample is weighed in a weighing chamber before and after ignition. The electronic balance 2 can be selected in accordance with the desired accuracy from conventional electronic balances and in the embodiment, an electronic balance having the maximum weighing value of 200 grams and a reading accuracy of 0.1 milligram may be used. The crucible 4 may be a conventional porcelain crucible or a platinum crucible. The sample supply device 5 includes a number of sample containers 8, each of which contains a different powder sample to be measured and each container 8 has a removable cap with a feeder, trays 7-1 and 7-2 for holding the sample containers 8, a sample discharging device 9 having a vibrator unit 14 for discharging the sample in the sample container 8 into a crucible 4 on the electronic balance 2 and a sample container transfer device 10 adapted for selecting a desired container 8 from the sample containers retained in the sample container trays 7-1 and 7-2 and transporting the selected container to the vibrator unit 14 of the sample discharging device 9. Each of the container trays 7-1 and 7-2 can be transported to the position of the sample container transfer device 10 by means of a sample container tray slide mechanism 11 and further can be transferred in a direction perpendicular to the transport direction from the position of the transfer device 10. After the container 8 containing the next sample to be weighed has reached the position of the container transfer device 10 by means of the container tray slide mechanism 11, the container is transported to a container clamping mechanism 12 of the sample discharging device 9 inclined as shown by a phantom line in Fig. 2 and is fixed. If a sample container which has been weighed is still clamped to the container clamping mechanism, after the tray slide mechanism 11 is driven to position the sample container trays 7-1 and 7-2 for the used container 8 to be returned at the position of the sample container transfer device 10, the sample container transfer device 10 is driven from the position to return the sample container 8 to the predetermined position and then the sample container 8 is transferred and fixed as mentioned above. The sample discharging device 9 is returned to a position as shown by a solid line after the sample container 8 to be weighed is fixedly mounted by means of the container clamping mechanism 12. The sample in the container 8 is then fed into the crucible 4 on the electronic balance 2 by means of the vibrator unit 14. The vibration caused by the vibrator unit 14 may be constant until the target weight is reached, or, alternatively a voltage applied to the vibrator unit is varied in stages by means of a controller in depedence upon the amount of powder which needs to be transferred from the container 8 to the crucible, taking the detected weight into concideration. The strength of vibration may be varied so as to attenuate the vibration and accurately attain the target weight. In the embodiment, the crucible and tray transporting device 6 comprises a first crucible transfer device 15 adapted for transferring the crucible 4 from the crucible tray 3 to the electronic balance 2 and returning the crucible 4 containing the weighed sample to the crucible tray 3, a crucible tray slide table 16 adapted for intermittently transferring the crucible tray and a second crucible transferring device 17 adapted for transferring the crucible tray 3 loaded with the crucible 4. Furthermore, in this embodiment, in order to maintain the atmosphere within all of the weighing section 1 at a dry air condition, the weighing section 1 is provided with a drying device 18 for drying the atmosphere within the weighing section 1. Also, the drying device is arranged to discharge air through exhaust ports 19-1 and 19-2. Any conventional moisture absorbents or humidifiers may be used for the drying device 18. It is preferable to feed dry air from the outside into the weighing section. A heating means 21 comprises a section having a preheating electric furnace 22 adapted for preheating the weighed sample in the crucible 4 retained on the crucible tray 3 to remove volatile matters at a low temperature, an igniting electric furnace 23 for igniting the preheated crucible 4 retained on the crucible tray 3 to a predetermined high temperature and a crucible tray stacker 25 including a fork 24 for transporting the crucible tray 3 loaded with the crucible 4 within the heating section 21. The preheating electric furnace 22, igniting electric furnace 23 and crucible tray stacker 25 are arranged within a heating chamber. The preheating electric furnace 22 is preferably a muffle furnace which can heat the sample at about 500°C by means of a Nichrome heater and the igniting electric furnace 23 is preferably a muffle furnace which can ignite the sample at about 1,000°C by means of a Cantal heater. An electric furnace may, of course, be used for both preheating and igniting. The crucible tray stacker 25 serves for receiving a crucible tray 3 from the preceding step and for delivering it to the following step and for charging and discharging the crucible tray 3 in and out of the preheating electric furnace 22 and the igniting electric furnace 23, respectively. The heating section 21 includes exhaust pipes 26-1 and 26-2 for discharging hot gas from the preheating electric furnace 22 and the igniting electric furnace 23 and an exhaust port 27 for discharging the atmosphere out of the heating chamber. A cooling means 31 is a section arranged between the weighing section 1 and the heating section 21 to transfer the crucible tray 3 retaining the crucible 4 with the sample weighed at the weighing section 1 to the heating section 21 for the following heating step and to receive the crucible 4 retained by the crucible tray 3 after ignition of the sample and to cool it in water or air by means of a cooling device 32. The cooling section 31 is located within a cooling chamber which is airtightly sealed from the weighing section 1 and the heating section 21 by means of openable shutters 33-1 and 33-2, respectively. An elevator 35 for transporting the crucible tray 3 is also arranged in the cooling chamber. The cooling section 31 may be supplied with dry air from the drying device 18 in the weighing section 1 and is provided with an exhaust port 34 for discharging the atmosphere out of the cooling section. All the operations of the weighing section 1, the heating section 21 and the cooling section 31 are controlled by a control section 41. Figs. 3∼6 are sectional views of various embodiments of the sample container 8 with a feeder usable in the present invention. The sample container 8 shown in Fig. 3 comprises a container body 51 which may comprise a conventional glass weighing bottle and a cap 53 which is attached to the container body 51. The cap 53 has a feeder 52 integrally formed with the cap 53. When the sample container 8 is settled on a vibrator unit 14 and is vibrated by the vibrator unit, the sample contained in the container body 51 is fed from the tip of the feeder 52 through an outlet 54 formed in the cap 53 to the crucible 4 set on the electronic balance 2 in response to the vibration by the vibrator unit. Fig. 4 shows a modification of the sample container 8 with the feeder 52. This container has a blade 55 extending inside the container body 51 for breaking up lumps in the powder sample, caused by the vibration in order to weigh sample more accurately. Fig. 5 shows a modification of the sample container 8 having a modified feeder 52 which is preferably used for accurately weighing powder samples which generate static electricity under vibration. Such a feeder 52 is in the form of a tapered trough having a shape section and which is provided with a projection 56 extending downwardly from the front end 52a thereof. The projection 56 thus prevents the charged powder from adhering on and along the under surface 52b over the front end 52a of the feeder 52. Such an adhered powder when it drops on the balance, affects the weight measurement of the sample. Fig. 6 shows another modification of the sample container 8 which is preferably used for samples having a tendency of aggregating powder to form lumps of powder sample in the container. In this embodiment, a baffle plate 57 in the form of a spider radially extending from the central portion thereof is arranged within the container body 51 to prevent a large particle 58 from feeding out the container 8. In operation of the above mentioned ignition loss measuring apparatus, firstly, predetermined empty crucibles 4 are set on the crucible tray 3. Meanwhile, sample containers 8, which are filled with different samples respectively, are set at the predetermined positions in the sample container trays 7-1 and 7-2. The position and the nature of the powder are input to the controller 41 together with the weighing sequence. Then, the first crucible transfer device 15 of the crucible and tray transporting device 6 is driven to transport a crucible 4 from the crucible tray 3 to the electronic balance 2. The predetermined sample container 8 on the sample tray 7-1 or 7-2 is transferred by means of the sample container transfer device 10 and secured to the tip of the tilted sample feeding device 9 by means of the container clamp mechanism 12. After the sample feeding device 9 is returned to the initial position, the vibrator unit 14 begins to vibrate so as to feed a predetermined weight of sample to the crucible 4. Then, the weighed crucible 4 is returned to the given position on the crucible tray 3 by means of the crucible transfer device 15 to complete the weighing step for one sample. When the crucible tray 3 is filled with the weighed crucibles 4, the crucible tray 3 is transferred to the cooling section 31 from the weighing section 1 through the shutter 33-1 by means of the crucible tray slide table 16 and the second crucible transferring device 17. The crucible tray 3 on the elevator 35 is transferred to the heating section 21 through the shutter 33-2 by means of the crucible tray stacker 25. In the heating section the crucible tray 3 retaining crucibles loaded with the sample is preheated at about 500°C in the preheating electric furnace 22 and then transferred to the igniting electric furnace 23 by means of the crucible tray stacker 25 and ignited at about 1,000°C. After the igniting stage, the crucible tray 3 is taken out of the igniting electric furnace 23 by means of the crucible tray stacker 25 and transferred to the cooling device 32 in the cooling section 31 through the shutter 33-2. In the cooling device 32 the crucibles on the crucible tray 3 are cooled in water and then in air by means of the cooling device 32. After cooling, the crucible tray 3 is returned to the initial position shown in fig. 1 by means of the second crucible transferring device 17 and the crucible slide table 16 in the weighing section 1. Subsequently, each crucible 4 is again transported by means of the crucible transfer device 15 to the electronic balance 2 for weighing the ignited and cooled sample. Finally, the ignition loss is determined by the initial weight and the weight after ignition at the controlling section 41. The results of measuring the ignition loss of clay and mixture by use of the automatic ignition loss measuring apparatus according to the present invention are shown in the following Tables 1 and 2 in comparing with prior art, respectively. In carrying out the above measurements, platinum crucibles were used. Invention Prior art Ignition loss (wt%) 1 12.74 12.61 2 12.76 12.78 3 12.69 12.86 4 12.58 12.85 5 12.63 12.77 6 12.70 12.71 7 12.76 - 8 12.73 - Mean (wt%) 12.70 12.76 Range (wt%) 0.18 0.25 Standard deviation (wt%) 0.060 0.085 Relative standard deviation (%) 0.47 0.67 Examples of Measurement of Ignition Invention Prior art Ignition loss (wt%) 1 4.68 4.69 2 4.69 4.63 3 4.72 4.62 4 4.70 4.65 5 4.63 4.63 6 4.67 4.71 7 4.70 4.62 8 4.71 4.64 Mean (wt%) 4.69 4.65 Range (wt%) 0.09 0.09 Standard deviation (wt%) 0.028 0.033 Relative standard deviation (%) 0.60 0.71 It is understood from the results shown in the Tables 1 and 2, the ignition loss can be automatically weighed more accurately in use of the ignition loss measuring apparatus according to the invention than in the prior art. Obviously, the invention is not limited to the embodiments described above and is possible to variously modify or change within the scope of the invention. For example, number of sample containers and trays is not limited to the embodiment described above. It is understood from the above that in the ignition loss measuring apparatus according to the present invention, the weighing section, the heating section and the cooling section are integrally arranged and controlled by the controlling section, therefore it is possible to measure automatically the ignition loss without manual operation in a safe manner and with high efficiency. Furthermore, it can be used to accomplish accurate measurement and faculty of the measuring apparatus regardless of the technical skill of operators.

Claims: An apparatus for measuring ignition loss in a powder sample comprising: (i) a weighing means (1) having a weighing device (2) comprising a balance and a sample supply device (5) for selecting and feeding a predetermined sample to a crucible (4) on the weighing device (2); and (ii) a crucible and tray transporting device (6) for transferring the crucible (4) from a tray (3) to the weighing device (2) to receive the sample, returning the crucible (4) containing the weighed sample to the tray (3), transferring the tray (3) retaining the crucible (4) containing the weighed sample to a heating means (21) and from a cooling means (31) and finally transferring the crucible (4) from the tray (3) to the weighing device (2); (iii) said heating means (21) having a preheating furnace (22) for preheating the crucible (4) containing the weighed sample on the tray (3) to remove volatile matters at a low temperature, an igniting furnace (23) for igniting the sample in the preheated crucible (4) on the tray to a predetermined high temperature and a crucible tray stacker (25) for transporting the tray (3) within the heating means (21); (iv) said cooling means (31) being for cooling the sample and the heated crucible (4) on the tray (3); and (v) controlling means (41) for controlling operations of the weighing means (1), the heating means (21) and the cooling means (31). An apparatus according to claim 1, wherein said sample supply device (5) comprises: (i) a plurality of sample containers (8) each containing a powder sample to be measured, the containers being retained on a sample container tray (7-1, 7-2) and each having a detachable cap (53) with a feeder (52) integrally formed with the cap (53); (ii) a sample discharging device (9) having a vibrator unit (14) for feeding the sample from the sample container (8) to the crucible (4) on the weighing device (2); and (iii) a sample container transfer device (10) for selecting a predetermined sample container (8) from sample containers retained on the sample container tray (7-1, 7-2) and transporting the selected sample container (8) to the vibrator unit (14) of the sample discharging device (9). An apparatus according to claim 2, wherein said sample container (8) has a blade (55) extending from the inner wall of the container for preventing the powder sample aggregating in the interior of the container. An apparatus according to claim 2, wherein said feeder has a projection (56) which extends downwardly from the front end of the feeder. An apparatus according to claim 2, wherein each said sample container has a baffle plate (57) arranged within the container to prevent large particles of the sample from feeding out of the container. An apparatus according to any of claims 2 to 5, wherein said weighing device (2) is arranged to continuously detect the combined weight of the crucible (4) and the sample as the crucible (4) receives the sample from the sample container (8) which is agitated by the vibrator unit (14), the strength of vibration of the vibrator unit (14) being adjusted in dependence upon the amount of powder which needs to be transferred from the container (8) to the crucible (4). An apparatus according to any one of the preceding claims, wherein said crucible and tray transporting device comprises: (i) a first crucible transfer device (15) to transfer a crucible (4) from the tray (3) to the weighing device (2) and return the crucible (4) containing the weighed sample to the tray (3); (ii) a crucible tray slide table (16) to intermittently transport the crucible tray (3) and the crucible (4) from the weighing device (2) to the heating section (21); and (iii) a second crucible transferring device (17) to transfer the crucible (4) on the crucible tray (3) between the cooling section (31) and the crucible slide table (16).

Inventors: NARUKAWA, AKIRA
Applicants: NGK INSULATORS, LTD.
Application year: 1988
Main classification: G01N5
IPC codes: G01N5, G01G17, G01N31