·Table of Contents
·Methods and Instrumentation
High productive Tightness Control of Mass Manufacturing productsS. Sazhin - Nizny Novgorod State Technical University 'Russia
In case of necessity of wide spread intensification of manufacturing production the task of high effective control of production quality can't be solved without it's automatization and mechanization. The attention to the problem automatize control of the air-tightness of products is explained with the increased requirements to the air-tightness degree of many kinds of mass manufacturing products. The urgency of this problem increased at the latest years also because of the developers
It is possible to name three main areas of application of measuring devices intended for this purpose. The first area envelops production in which 100% controls of air-tightness of items, for example, details and units of means of individual protection container, pressure transducers and other elements.
The second area of application of devices for the control of air tightness integrates those productions, where the check of items is required during the exploitation. This especially connects to unsafety explosion and fire unsafety productions. Such items are the pumps, strong units, reactor, the equipment and others. And at last, the third area of air tightness is connected to researches of new types of items of improvement existing.
If necessary broad intensification of production the problem of an effective control of quality of production can't be decided without it of automation and mechanization the attention to the a problem of the automated control of air -tightness of items is explained also by high requirements to a degree of air tightness of many kinds of industrial and household items produced by serially by the enterprises of various branches. At last the urgency of a problem was increased per the last years also that the developers of items seek to decrease of costs and improving of characteristics, use all in the greater degree materials, differing with small by air tightness, such as aluminum, plastic or materials of thin section.
In these cases the control of air tightness should implement in a rhythm of production and the test facilities being a part of a production equipment, should be high duty and automated.
We shall understand that the high duty equipment the industrial automated installations and machines intended for test of items of line production for air-tightness with productivity equal or the greater productivity of the main contribution link.
At mass manufacture of products electronic, machinery construction, chemical etc. industries one of major tasks of quality control is checking their air-tightness.
If wide intensification of industrial manufacture is required the task of highly effective quality control of production can't be solved without it's automation and mechanization. The attention to a problem of the automated control of tightness of products is explained also by increased requirements to a degree of tightness of many kinds of industrial products which are let out serially on the industrial enterprises. At last, the urgency of a problem has increased last years also because the developers of products are aiming to decrease the costs and improvement of the technical characteristics, at the greater degree using materials distinguished by low tightness, such, as aluminum, plastic or materials of thin section. In these cases the control of tightness of products should be carried out in a rhythm of manufacture, and the productive plants for the control of tightness should be a part of a complex of the process equipment, should be high-efficiency and automated.
Under the high-efficiency equipment for the control of tightness of products we shall understand the industrial automated installations, machines and stands intended for test of products of line manufacture on tightness with productivity equal or the greater productivity of the basic technological line. Further for reduction we shall name this equipment as the automated plants for the tightness control of products (APTC). The basic function APTC consists in 100% or partial control of products on tightness and in definition of products that don't appropriate to the requirements on a of tightness degree.
Test for tightness of details, units and ready products, as a rule, occurs consistently, since separating details and finishing a ready product. The necessity by-operation control is dictated first of all by economic reasons, according to which it is expedient to conduct the control of details and units air-tightness during the process.
Detection of a leakage an item at the stage of final assembly cause to conduct their disassembly, searching the unpressurized items, their repairing and replacement, additional assembly of items, and at last, final checking. For example, at detection at the final test stage of unpressurized small-sized heat exchanger there is a necessity of it's partial disassembly, replacement of unpressurized handsets, new assembly and tests. It results to the useful increase of costs on manufacturing and testing of such item, and the economic losses in this case become rather appreciable. Besides by mass production the by-operation control of items allows in time to correct industrial operations at appearance of unpressurized items. In this case there is the feedback transforming process of the control from passive (recording) in active (regulating).
Objects of the air-tightness APTC control are, as a rule, the mass production items, produced by the enterprises of many industrial fields.
The samples of controlling items manufacturing by leading fields of production shown in Table 1. There determined the tasks of air-tightness control of manufacturing items.
|Field||Samples of control items||The tasks of manufacturing control|
|Chemical and oil mechanical engineering||Seals, hardware, valves, pumps, pipe lines, Guar vessels and etc. items||1. Hermetic detection of a production equipment|
2. Gas penetration into working premises
3. Increasing of operation general equipment failsafety
|Chemical industry||Details, units and assembly of means of individual protection. Aerosol packings for varnishes, paints and other products. Polymeric items and etc.||1.Guarantee of air-tightness of devices for individual person protection 2.Maintenance of specific air-tightness of packings for products storage during guaranty period|
|Automobile industry||Valves and reinforcement, tanks of distributors, elements and units of systems of an oblate air||Maintenance of reliable activity of automobile units|
|Food-processing industry||1. Container for products|
3. Polymeric packings
|Maintenance of products safety during warranty period|
|Production of household aggregates||Details, units of refrigerators assembly and other items||Maintenance of reliable activity of the aggregate during warranty period|
|Gas industry||1. Details and units of gas cookers|
2. Details and units of devices of a gas automation
3. The gas reinforcement
|Maintenance of demanded air-tightness Maintenance of reliable activity of devices of a gas automation|
|Air industry||Details and units of systems of fuel, oblate air, oil. Bodies, compartments etc.||1. Maintenance of high reliability of airplanes units and assemblage|
2. Maintenance of the guaranteed life of activity of units
|Ship building||The reinforcement, pipelines, elements and units||Maintenance of reliable activity of instrumental systems, units, engines of courts and ships|
Most of APTC are designed on the basis of synthesis of units identifying functionality test automated systems. In a fig. 1 the scheme with basic connections between standard units is shown.
|Fig 1: Block-diagram of automated air-tightness control plants (APTC)|
The trial functions of APTC consist of 100% or selective control of items on air-tightness and in detection of items not conforming the requirements specifications. The degree of air-tightness is determined with the help of indirect parameters, such as the consumption, gas concentration or pressure, which, penetrating through an open defect, promotes formation the one of parameters.
As visible, from the analysis of the block-diagram, APTC consists of a unit supplying items on a test item for their fixing and hermetic sealing (1), test unit (2), in which there is hermetic sealing of an item (3), unit of measuring of items by results of the control (4) is placed also. The test chamber is connected to the unit of primary transformation of leakage size (5), forming unequivocally dependent from size of leakage signal and used hereinafter for information processing and effect on additional bodies. The correlation of activity of all units is provided with the microprocessor controller (6), in which structure enter in a number of cases the unit of information processing, including system of compensation of a background signal. Determining units of APTC is the test unit and unit of transformation of leakage size.
The study of the domestic and foreign plants and devices for the high-duty control of air-tightness of items allows to reveal their general features and to classify them.
First of all APTC is intended, as a rule, for the 100% control of air-tightness of items of line production. In this connection they should have high efficiency. By the form of inspected parameter APTC is concerned to number high-duty microconsumption measuring, rather sensing gas analyzer or accelerometers of pressure. The plants, as a rule, multicomposite with a complex cycle of the control, discrete or continuous.
In circuits of equipment production APTC usually finish process of manufacturing and tests of items. This provides the special responsibility of the air-tightness control operation of items, and refer to the control of items on APTC attribute to number of major parameters of the installations.
The other basic parameters of APTC are productivity and the sensitivity. In many cases arises necessity of a simultaneous combination of high values of productivity, sensitivity and reliability of the control. The adduced features distinguish APTC from the other measuring test complexes and confirm a conclusion about development of an independent kind of technological machines.
The consideration basic structural scheme APTC, correlation and sequence of operations at the air-tightness high-duty control of items allows to determine the following design modules:
The modules of primary transformation of gas leakage size are intended for registration of a flow of gas through open defects of an inspected item and transformations to a threshold or continuous signal.
As shown higher, all modules of primary leakage transformation are subdivided into two large groups: gas analyzer modules and modules of general pressure. The operational analysis of modules is expedient to conduct in aggregate with auxiliary elements ensuring operation of modules. On fig. 2 the conception of halogen module with protection of latest input channel against external environment is adduced.
|Fig 2: Principle scheme of halogen module|
|Fig 3: Example of signal record of module on a fillet of the recording instrument|
The module actuates halogen a sensing element (4), supply unit (19), amplifier (6), and recorder (20). The sensing element (4) with the purpose of an elimination of a poisoning of electrodes at large concentration of a freon is purged by gas - carrier, which consumption is supported to constants. Arrangement of a sensing element in a flow of gas - carrier promotes full isolation of element's electrodes from external environment, in which structure there can be tracks of a freon. It is provided with an auxiliary system including regulators of the consumption 12, 14, 16, valves 3, 7, 8, 9, 15, 17, unit of clearing of gas 13 and rotameter 5. On fig. 3 the record of a signal of a module on the automatic potentiometer KCP-4 is adduced. The record describes actual test specifications and shows, that the general time of the control of air-tightness of items including respond and recovery time doesn't exceed 30 sec. Because of halogen of a module there are automated devices for air-tightness control of aerosol packings, refrigerating aggregates etc. items.
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