Screening grids. Grilles with movable filter screen XGC

Screening grating (synonym: hood, Bucca blend, Potter-Bucca blend - are not currently used) is a device designed to increase the contrast of an X-ray image by absorbing X-ray radiation scattered by the human body.
Sifting lattice consists of a housing, a raster mounted inside it, a raster movement mechanism, a control and signaling system (Fig. 1). Raster is a set of thin (0.02-0.3 mm) narrow lead plates, separated by layers of wood or cardboard, and currently plastic or aluminum.

Rice. 1. Flat movable screening lattice: 1 - bell; 2 - cocking handle; 3 - cassette holder.

Rice. 2. X-ray with a screening grating: 1 - X-ray film; 2 - raster of the lattice; 3 - the object under study.

In a directional raster, the plates are oriented towards the focus of the X-ray tube, so the bulk of the direct X-ray radiation passes between the plates. Most of the scattered radiation does not coincide in direction with the direct beam and is absorbed by the lead raster plates (Fig. 2). This reduces the haze due to the scattered radiation and increases the image contrast. Rasters in which the plates are arranged in parallel are called flat, but the most common screening grids with directional rasters for certain focal lengths (90 to 150 cm). If the raster is used not at the specified distance, then there is a sharp attenuation of the intensity at the edges of the field. The most important characteristic of the screening lattice is its ratio (the ratio of the width of the gap between the plates to their height). With a decrease in the ratio, the intensity of the total (primary and secondary) radiation transmitted through the screening grating decreases, which can be compensated by an increase in the exposure time or the generation voltage.
At voltages up to 100 kV, a screening grid with a ratio of 1: 6 is used, which slightly absorbs the primary radiation and filters out 70-80% of the secondary, at high voltages, a sifting lattice with a ratio of 1:12 or less. Distinguish between fixed screening grids (Lisholm grids) and movable. The Lysholm screen has a flat screen with very thin (0.02-0.03 mm) lead plates and narrow (0.2-0.3 mm) gaps. Such a screening grid is placed on the cassette (or in the cassette) and allows the study to be carried out in any position of the patient. It leaves fine streaks on the X-ray that do not interfere with the perception of the X-ray image. Its disadvantages include the lack of directivity, strong absorption of primary radiation, and the permeability of thin plates for scattered radiation. In a photograph with a movable screening grid, the image of the lead plates is blurred and does not interfere with the reading of X-ray images. Raster driven by a spring or motor. To avoid streaky shadows from the plates, the raster motion time should be slightly longer than the shutter speed. However, at short shutter speeds, shadows appear when the raster moves uniformly due to the so-called stroboscopic effect. To combat it, an uneven raster movement slowing down according to a certain law is used, or vibration screening grids are used. For very short exposures, screening grids with a large number of plates per centimeter of raster length are used. The minimum exposure for a raster is indicated in its passport (for domestic screening grids - 0.04 sec.). Modern screening grids are equipped with several replaceable screens designed for specific voltages and holding times.

The grill is a series of filter elements equipped with specially designed teeth and attached to drive chains. The elements form the filter screen of the grill. Thanks to the geared motor, the elements on the outside of the grate move upward and, thanks to the teeth, lift the trapped debris from the water. In the upper part of the lattice, thanks to the guide vane, the direction of movement of the elements changes, and on the back side of the lattice they begin to move downward. The bulk of the debris is separated from the filter elements by gravity when the direction of travel changes. The adhered debris is removed with a cleaning device. Also, the grid elements, moving downward from the back of the grid, are washed with a stream of treated water. After separation of the retained substances, the shape of the elements ensures a low resistance to water movement. The grid opening depends on the selected filter elements and is selected depending on the cleaning process or is determined by the customer. The work of the grate is automated and the movement of the web can occur both continuously and periodically, depending on the amount of retained contaminants.

MAIN ADVANTAGES

The grids have good separation of coarse impurities, high level automation, low power consumption and noise. All materials of construction have good corrosion resistance and ensure stable operation of the grating.

The grate design ensures good removal of trapped debris and cleaning of the grate. Therefore, the effects of clogging and overgrowing are absent and the grating requires minimal maintenance.

Automation of the grate at the customer's option provides for both cleaning at a certain time interval, and automatic cleaning according to the difference in levels before and after the grate.

TECHNICAL SPECIFICATIONS AND DIMENSIONS

The grilles are produced in a wide range of sizes, depending on the customer's requirements. Grilles (model) from XGC300 to XGC 3600. Grilles over 1800 mm wide are available on request. The gap width is 1 mm, 3 mm, 5 mm, 10 mm, 15 mm, 20 mm, 30 mm, 40 mm, 50 mm, depending on the characteristics of the suspended suspension and the cleaning process. The depth of the channel can also be selected in accordance with the existing situation in the range from 0.8 to 15 m. The grating specification also indicates the height of the unloading of the retained waste and the angle of inclination.

In general terms, the grating designation is written as XGC-500, where

XGC - model of a lattice with a moving leaf (DIAGRAM - DRAWING), 500 - width of the lattice in mm.

The complete specification of the lattice is written as:

XGC - 500 X1000 X800 X5 X70 ,

500 lattice width (mm),

1000 - channel depth (mm),

800 - unloading height (mm),

5 grille gap (mm),

70 - tilt angle (°).

SCHEME - DRAWING

PARAMETERS OF STANDARD GRILLES

For a water depth of 1 meter, are presented in table 1.
Table 1.

model			XGC-300	XGC-400	XGC-500	XGC-600	XGC-700	XGC-800	XGC-900	XGC-1000	XGC-1100	XGC-1200	XGC-1300		XGC-1400	XGC-1500
Filter element size (mm)			100 or 150
Screen movement speed (m / min)			2
Motor power (kw)			0.37-0.75							1.1-2.2
Water depth m			1.0
Water speed (m / s)			0.8
Grille gap (mm)	1	Production capacity m 3 / day	1780	3090	4390	5650	6960	8270	9470	10830	12140	13390		14700	16010	17260
	3		3650	6030	8510	11290	13770	16240	18710	21340	23820	26290		28920	31400	34030
	5		4450	7850	10720	14120	17260	20600	23800	26940	30080	33480		36620	40020	42900
	10		5230	8890	12560	16220	19880	23020	27200	30870	34530	38190		41850	45510	49180
	15		6975	12290	17615	22935	26750	33310	38015	43335	48625	53970		59290	64605	69060
	20		8720	15690	22670	29640	36620	43600	48830	55800	62780	69750		76730	83700	88940
	25							45640	51880	57980	65395	72805		80215	86320	92860
	30							47080	54930	60160	68010	75860		83700	88940	96780
	35							47955	55365	61470	72290	72290		85450	59810	98960
	40							48830	55800	62780	76730	76730		87200	90680	90680
	50							52320	56670	65390	78470	78470		91550	95910	95910

AUTOMATION SYSTEM

The grilles are supplied with their own control cabinet. They can also be equipped with a customer-designed automation cabinet. As standard, the grilles are supplied with their own control cabinet. Both single-phase and three-phase power supply of the cabinet is used. The cabinet is designed according to the customer's requirements and, as a rule, includes buttons "start", "stop" located in place, engine protection and control lamps - "start", "stop" and "emergency".

Also, the grid automation system can be equipped with a programmable logic controller and communication with a dispatching center for remote control. In these cases, a "grate key" is additionally provided in place to prevent automatic start-up during grate maintenance, repair work and other similar situations.

Warranty and service maintenance after sale

1. The company adheres to the principle of "priority of quality and user-centered service" to provide you high quality services and impeccable service.
2. The standard warranty covers the product for one year from the date of sale. The company has an after-sales service team and has been consistently improving its quality, striving to provide service in a fast and convenient manner.
3. The company sends a specialist to guide the installation and debugging according to the actual situation and conducts training for the customer's personnel to familiarize 2-3 workers with the operating principles and Maintenance equipment.
4. The engine and other spare parts selected by the company from other manufacturers are well-known products both in China and abroad, in order to ensure quality and reliability.

8.8. Methods for reducing scattered radiation 8.8.1. The use of a screening array is a proven effective means of reducing scattered radiation, which does not carry useful information and increases the patient's radiation dose. The use of the grating also allows you to increase the contrast and resolution of the image. 8.8.2. Screening grids are of three types: with parallel, focused and with a cross arrangement of plates (lamellas). The efficiency of the grids is evaluated in terms of the ratio of the height of the plates to the distance between them (raster - R). The larger the raster, the more effective the lattice. The most commonly used gratings are 6: 1 and 12: 1. For "hard" technology (> 100 kV), a lattice with a large grid must be used. 8.8.3. Screening gratings are designed for a certain focal length, most often 70 - 100 cm. Gratings with a focused arrangement of lamellas are used only at large focal lengths. In this case, to reduce the absorption of radiation, it is advisable to set the focal length with an accuracy of up to several percent. 8.8.4. For effective work the grating must comply with the correct centering - the direction of the central beam should be strictly in the center of the grating perpendicular to its surface. 8.8.5. Cross bars are the most effective. Their effectiveness is 1.5 times higher than those commonly used. In order to further increase the efficiency, it is necessary to use moving gratings, which improves contrast and reduces the radiation dose. 8.8.6. The efficiency of a lattice depends not only on its type and raster, but also on the material from which it is made. For example, a tantalum cross lattice is much more efficient than conventional material lattices. The efficiency of the lattice also increases when the spaces between the lamellas are filled with fibrous filler. 8.8.7. When using a screening lattice, the following data must be indicated on it: whether it is focused or not, if it is focused - the radius, as well as the size of the tube. In a focused grating, special accuracy is required when aligning the central axis of the grating with the central beam of the radiation beam. The distance between the grating and the focal point of the tube should be close to the grating radius. The grating should also indicate the side facing the X-ray tube. 8.8.8. The use of a screening grating leads to the absorption of part of the radiation; therefore, to compensate for it, one should, first, increase the voltage (by an average of 25%) and, second, reduce the irradiation field. 8.8.9. The use of a screening grid is necessary when examining large parts of the body (large organs) such as the skull, pelvis, gastrointestinal tract, etc. 8.8.10. When examining children, it is advisable to use moving gratings, which improve the information content of the image and make it possible to reduce the patient's radiation dose due to the use of a short exposure. The speed of the grating should be fast enough. If this cannot be achieved, thin lamellas are used with small gaps. 8.8.11. For fluoroscopy and neonatal examinations, the use of a screening grid is not necessary because Irradiation of small volumes, such as small children, is accompanied by a slight scattering of radiation. Refusal to use the grate in this case can reduce the child's radiation dose by 2 - 4 times. 8.8.12. When studying children of preschool and school age, the 8: 1 lattice is most effective. The minimum shutter speed when using a screening grid should be 0.04 s. When using complex gratings, it is necessary to increase the voltage and exposure. 8.8.13. The most effective is the scanning array: a synchronously moving (or rotating) screening array with one or more lamellas located in front of and behind the patient. One of the gratings is fixed on the collimator (light diaphragm), the other on the table. The optimal lattice raster is 12: 1. Their size is determined by the aspect ratio. This method suitable for use with highly sensitive X-ray film (or screen-to-film system). It requires an increase in exposure. The use of a scanning grating instead of a screening grating allows to reduce the scattered radiation and, accordingly, the patient's radiation dose by 20 - 50%, as well as to improve the image contrast. The disadvantages of this method include its high cost.