A CORE SAMPLER SYSTEM FOR TAKING SAMPLES FROM LOADS OF GRANULAR MATERIAL

Abstract: It has been found long ago that taking samples from an impure granular material by means of a simple tubular sampling spear does not provide for any representative result, and a substantial improvement has already been obtained by embodying the spear (2) with an inner suction pipe (26) and an outer blower pipe (20), said pipes being open towards one another at the spear end through an annular slot (28) for obtaining that the material which is let in through the spear tip is conveyed away by the suction air to a material separator (12) without showing any associated disturbing "vacuum cleaner effect" outside the spear mouth. With the invention, a small hole (34) is provided in the wall of the hose connection (14) between the pressure side of the blower and the spear, through which hole a weak air flow will be blown out, whereby a correspondingly weak air intake will occur through the open end of the spear, and hereby a considerable improvement of the sampling accuracy is obtained. It may even be important to arrange for a similar, but smaller hole in the suction connection to the spear in order to reduce the vacuum at this place.

Description: The present invention relates to a core sampler system for taking out samples from loads of granular material and of the type comprising a tubular sampling spear for introduction into selected areas of the material load. Samples are taken, inter alia, for measuring the degree of purity of a charge of material such as grain, seed, beans or other granular material carried by a ship or a truck, e.g. in connection with a truck being placed on a weighbridge, and hereby it is of course crucial that the samples be fully representative of the material. This may contain both relatively heavy and relatively light impurities, and by the introduction of a simple tubular spear the impurities may easily be deplaced in such a manner that they are not received by the spear in exactly the proportions in which they occur in the granular material. Normally there are only a few per cent of impurities in the material, i.e. the samples should ideally be taken with an extreme accuracy to ensure a representative distibution of the impurities in the samples. It has been found long ago that samples taken by a simple introduction of a tube spear will normally be very far from being representative with respect to the impurities in the material, and great efforts have been made to improve this circumstance. Thus, it has been endeavoured to achieve a certain improvement by carrying out a suction on the tube spear, but it has been found, however, that an associated "vacuum cleaner effect" at the insertion end of the spear has caused a suction intake of a disproportionately large amount of impurities from the surroundings of the spear tip, such that the sample result is still not fully representative. The result may even be still more inaccurate, particularly with materials having relatively large particles, e.g. beans and peas. The most accurate results so far have been obtained by using a tube spear consisting of an inner suction pipe and a surrounding pipe for supply of pressurized air, the insertion end of this spear being embodied as a short, exteriorly tapering pipe portion, which communicates axially with the mouth of the central suction pipe through an inner ring slot area wherefrom air is conveyed into the inner mouth of the suction pipe (as for example disclosed in US-A-3 580 084) from the said surrounding pressurized air pipe.The spear is connected in a closed air circulation system in which the pressure side of the blower is connected directly to the pressurized air supply of the spear, while the suction pipe of the spear, i.e. the outlet pipe for air and grain is connected to the suction side of the blower through a grain separator. It is aimed at that the static air pressure in the ring nozzle area corresponds to the ambient pressure or is very close to this, such that adjacent the ring slot no considerable over- or subpressure will occur, which might be transmitted to the material inside and outside the end of the spear. By this system strongly improved results have been obtained, probably because the material is conveyed away from the spear end without any associated "vacuum cleaner effect" and without the material in compact form being able to penetrate into the spear further than through the short distance from the tip to the ring nozzle area, hereby no long "plug " will be formed in the pipe, which through friction against the inner sides of the pipe might cause a noticable pressure against the material, which, by the insertion of the spear, is about to be introduced into the spear pipe, and it is presumed that by sample takeing with a simple pipe spear with associated closable slots it is such a pressure build-up in front of the spear tip which, by the movement of the spear and by the opening and closing of the said closeable slots thereof, contributes to the considerable inaccuracy of the sample taking. The invention relates to a sampling system of the abovementioned air circulation type, and its purpose is to provide such a modification of this type of system that a further improvement of the sample accuracy is obtainable, the previously obtained accuracy being relatively good, but not at all satisfactory, particularly when the impurities consist of seed weeds, sand, or soil particles. The invention is based on the consideration that a very weak suction effect could be established advantageously at the spear end, which would facilitate the material passage through the short "plug portion" between the outer spear tip and the ring slot area, such that a pressure build-up in front of the spear tip may be further reduced without any considerable or harmful vacuum cleaner effect. According to the invention such a weak suction effect is not provided through any changed dimensioning of the system, but through the very simple measure of a small hole being provided in the wall of the air conduit on the pressure side of the blower in the closed system, preferably close to the concerned junction between the sampling spear and an air supply hose connected thereto, and preferably a hole having an area of the magnitude 1/10 of the diameter of the suction pipe. A certain amount of air will be pressed out through this hole during the operation of the system, and as the system is otherwise closed, this air outlet must result in a corresponding suction intake effect in such a part of the system where this is possible, i.e. at the spear end as being open to the surroundings such that the said desired weak suction effect is brought about in a well-defined manner just at this place. A large number of experiments have proved that with the system according to the invention it is possible to obtain a highly improved accuracy of the sample taking, even though it must be admitted that a precise explanation of this fact cannot be given. The optimal size of the said hole will depend on the basic parameters of the air circulation system, and it can be mentioned that the hole should be of a slightly increasing size, the larger the conduit or hose connection between the blower and the spear is. Under circumstances as explained below it may even be desirable to provide a corresponding, but smaller hole in a wall portion of the suction side of the system. In the following the invention is described in more detail with reference to the drawing in which Fig. 1 is a schematic view of a sampling system according to the invention, and Fig. 2 is a detailed sectional view of the outer end of an associated sampling spear. The system shown comprises a sampling spear 2 which is suspended in a longitudinally variable outrigger arm 4 on a fixed, rotatable column 6, the arm being swingable by means of a cylinder 8. The upper end of the spear 2 is connected to a first conduit 10 which leads to a material separator 12, and to a second conduit 14, which leads to the pressure side of a blower 16, the suction side of which being connected to the separator through a suction hose 18. As indicated in Fig. 2, the spear 2 consists of an outer pipe 20 having a lower, tapering end portion 22, in which there is a central passage 24, and an inner pipe 26, which debouches somewhat above the lower, inwards thickened pipe end portion 22, such that an inner ring slot 28 is formed at this place. At its top, the inner pipe 26 is connected to the conduit 10, while the outer pipe 20 is connected to the conduit 14. During operation, air will thus be sucked up through the inner pipe 26 as well as be blown down through the outer pipe 20, whereby an air flow will occur at the lower end of the spear as indicated by full line arrows. When the spear 2 is introduced or lowered into a grain material load 30, a sample taking will hereby take place as explained, inasfar as the material, which is led into or up through the lower passage 24, will be successively caught by the air flow and thereby be led to the separator 12, wherefrom the material is separated out in a sample container 32. The so far described system with associated manner of functioning belongs to the known technique. In the system according to the invention a small hole 34 is provided at the top of the spear 2 in the wall of the outer pipe 20 or its connecting pipe stub to the hose 14. The hole 34 may for that matter be provided anywhere on the pressure side of the blower 16, only in such a manner that it is ensured that a weak air flow is pressed out through this hole. A consequence hereof will be that a correspondingly weak air flow will be sucked into the otherwise closed system wherever possible, i.e. through the lower pipe passage as indicated by a dotted arrow 36, and as mentioned a quite substential increase of the sampling accuracy is hereby obtained. It will be appreciated that with the system of the invention a considerable air flow may circulate through the system so as to give rise to but a very weak and well controlled air intake 36 through the sample intake end 24 of the spear, i.e. the sample material will be rapidly moved away from the intake area entirely independent of the added weak external suction action. In other words, despite an advantageous, powerful pneumatic conveying of the material away from the intake area there is provided for an external suction which is both weak enough to avoid the said "vacuum cleaner effect" and yet strong enough to ensure just a sufficient suction for compensating for the pressura exerted on the grain material and its impurities by the introduction of the spear end into the material. All according to the length of the spear, whereby a long spear will present an increased resistance to the introduced air flow and thus condition an increased outflow of air through the hole 34, it may be desirable to reduce the effective vacuum adjacent the spear tip, and it has been found that this is advantageously achievable by providing a still smaller hole 35 in the wall of the suction conduit 10. Thus, what is aimed at is the provision of a well controlled external suction, which should be adjusted to be in the range of 980-2450 Pa (100-250 mm water column), preferably 1470-2160 Pa (150-220 mm). The hole 34 is used for creating the suction, and if required the hole 35 somewhere on the suction side is used for limiting the suction. Such a limitation might be achievable by other means such as a throttling of the blower, but it has been found that the use of the hole 35 is preferable for achieving a high accuracy. It may be experienced that for different types of material as well as for different lengths of the hose connection 10 it can be necessary to adjust the size of the hole or holes, and though adjustable throttling means could be used it is preferable to arrange for rather large holes and for a series of different nozzle plugs for use therein.

Claims: A sampling system for taking samples from loads of granular material and of the type comprising a pipe-shaped sampling spear (2) for introduction or lowering into or down into selected areas of the material load (30), said sampling spear (2) comprising a central pipe (26) and an outer pipe (20) and having at one end connection means for connection of the outer pipe (20) with the pressure side of a blower (16) and of the central pipe (26) with the suction side of the blower (16) through a sample separator (12), the spear (2) at its other, free end having an inlet nozzle consisting of the open outer pipe end (22), in which the mouth of said central pipe (26) is situated, an annular slot (28) occurring between the mouth of the central pipe (26) and the open outer pipe end (22) at an axial distance therefrom, said annular slot being connected to the pressure side of the blower (16) through said outer pipe (20), characterized in that a small-sized exhaust hole (34) is provided in the wall of the pipe or hose connection (14) between the pressure side of the blower (16) and the outer pipe (20) of the spear (2). A system according to claim 1, characterized in that the area of the hole (34) is of the magnitude 50-200 mm² for a cross sectional area of the inner suction pipe (26) of the magnitude 500-1000 mm². A system according to claim 1, characterized in that the hole (34) is provided near the hose connection end of the sampling spear (2). A system according to claim 1, in which another, but smaller hole (35) is provided in the wall of the suction conduit (10) between the spear (2) and the sample separator (12). A system according to claim 1 or 4, in which the parameters of the air circulation system are adjusted such that at the free intake end of the spear (2) a sub-pressure of 980-2450 pascals (100-250 mm water column) is created, preferably 1470-2160 pascals (150-220 mm).

Inventors: KLIT, KNUD KRISTIAN BORG
Applicants: KLIT, KNUD KRISTIAN BORG
Application year: 1987
Main classification: G01N1
IPC codes: G01N33, G01N1