As part of the work, the error level of simulations of uniform optical-fibre Bragg gratings was determined using the transitionmatrixmethod. The errorswere established by comparing the transmission characteristics of the structures obtained by simulation with the corresponding characteristics arrived at experimentally. To compile these objects, elementary properties of the characteristics were specified, also affecting the applications of Bragg gratings, and compared with each other. The level of error in determining each of these features was estimated. Relationships were also found between the size of the physical properties of Bragg gratings and the level of errors obtained. Based on the findings, the correctness of the simulation of structures with the said method was verified, giving satisfying results.
By the very nature of their work, castings used in furnaces for heat treatment and thermo-chemical treatment are exposed to the effect of many unfavorable factors causing their deformation and cracking, significantly shortening the lifetime. The main source of damage are the micro- and macro-thermal stresses appearing in each cycle. As the cost of furnace instrumentation forms a significant part of the total furnace cost, in designing this type of tooling it is important to develop solutions that delay the damage formation process and thus extend the casting operation time. In this article, two structural modifications introduced to pallets castings to reduce thermal stresses arising at various stages of the cooling process are proposed. The essence of the first modification consists in making technological recesses in the wall connections, while the aim of the second one is to reduce the stiffness of the pallet by placing expanders in the external walls. Using the results of simulation analyses carried out by the finite element method, the impact of both proposed solutions on the level of thermal stresses was evaluated.
Examples of cast grates whose construction was based on previously used "old" patterns of the technological equipment for heat treatment furnaces (TEq) are presented. Manufacturers of this type of castings have at their disposal numerous earlier designs of the applied TEq. Their adaptation for the needs of a new order, i.e. the creation of a new design or modification of the already existing one, significantly reduces both cost and time of the implementation. It also allows making new grate constructions of various shapes and sizes, reducing in this way the number of patterns stored by the manufacturer of castings. The examples of cast grates shown and discussed in this study document the variety of ways that can be used when making them from the already existing patterns or castings. The presented grates were made using master patterns, entire castings or their fragments, and modular segments.
The results of research on the effect of the type of cooling agent used during heat treatment and thermal-chemical treatment on the formation of temperature gradient and stress-deformation distribution in cast pallets, which are part of furnace accessories used in this treatment, are disclosed. During operation, pallets are exposed to the effect of the same conditions as the charge they are carrying. Cyclic thermal loads are the main cause of excessive deformations or cracks, which after some time of the cast pallet operation result in its withdrawal due to damage. One of the major causes of this damage are stresses formed under the effect of temperature gradient in the unevenly cooled pallet construction. Studies focused on the analysis of heat flow in a charge-loaded pallet, cooled by various cooling agents characterized by different heat transfer coefficients and temperature. Based on the obtained temperature distribution, the stress distribution and the resulting deformation were examined. The results enabled drawing relevant conclusions about the effect of cooling conditions on stresses formed in the direction of the largest temperature gradient.
The main aim of this study was to examine the compression-induced state of stress arising in castings of the guide grates during operation
in pusher-type furnaces for heat treatment. The effect of grate compression is caused by its forced movement in the furnace. The
introduction of flexible segments to the grate structure changes in a significant way the stress distribution, mainly by decreasing its value,
and consequently considerably extends the lifetime of the grates. The stress distribution was examined in the grates with flexible segments
arranged crosswise (normal to the direction of the grate compression) and lengthwise (following the direction of force). A regression
equation was derived to describe the relationship between the stress level in a row of ribs in the grate and the number of flexible segments
of a lengthwise orientation placed in this row. It was found that, regardless of the distribution of the flexible segments in a row, the stress
values were similar in all the ribs included in this row, and in a given row of the ribs/flexible segments a similar state of stress prevailed,
irrespective of the position of this row in the whole structure of the grate and of the number of the ribs/flexible segments introduced
therein. Parts of the grate responsible for the stress transfer were indicated and also parts which play the role of an element bonding the
structure.
Depending on the course of the processes of heat treatment and thermo-chemical treatment, the technological equipment of heat treatment furnaces is exposed to different operating conditions, as the said processes differ among themselves in the temperature of annealing and atmosphere prevailing in the furnace chamber, in the duration of a single work cycle and in the type and temperature of the coolant. These differences affect the magnitude of stresses occurring in each cycle of the operation of furnace accessories, and thus play an important role in fatigue processes leading to the destruction of these accessories. The kinetics of temperature changes during each cooling process plays an important role in the formation of thermal stresses on the cross-section of the cooled parts. It depends on many factors, including the initial cooling temperature, the type and temperature of the cooling medium, or the dimensions and shape of the object. This article presents a numerical analysis of the effect of the initial temperature on the distribution of stresses on the cross-section of the grate ribs, generated in the first few seconds of the cooling process carried out in two cooling media, i.e. hardening oil and water. The analysis was carried out by the finite element method, based on the results of experimental testes of temperature changes in the rib during its cooling.
The purpose of this study was to establish a relationship between the type of wall connection used in the cast grates, which are part of the
equipment operating in furnaces for heat treatment and thermal-chemical treatment, and stresses generated in these grates during the
process of rapid cooling. The places where the grate walls are connected to each other are usually characterized by the thickness larger
than the remaining parts of walls. Temperature variations in those places are responsible for the formation of hot spots, and in the hot spots
temperature changes much more slowly. The type of wall connection shapes the temperature gradient in the joint cross-section, and hence
also the value of thermal stresses generated during cooling. In this study, five different designs of the grates were compared; the difference
in them was the type of the designed wall connection. The following design variants were adopted in the studies: X connections with and
without holes, T connections with and without technological recesses, and R (ring) connection. Numerical analysis was performed to
examine how the distribution of temperature changes in the initial phases of the cooling process. The obtained results served next as a tool
in studies of the stress distribution in individual structures. The analysis were carried out by FEM in Midas NFX 2014 software. Based on
the results obtained, the conclusions were drawn about the impact of different types of wall connections on the formation of thermal
stresses in cast grates.
The lifetime of guide grates in pusher furnaces for heat treatment could be increased by raising the flexibility of their structure through, for
example, the replacement of straight ribs, parallel to the direction of grate movement, with more flexible segments. The deformability of
grates with flexible segments arranged in two orientations, i.e. crosswise (perpendicular to the direction of compression) and lengthwise
(parallel to the direction of compression), was examined. The compression process was simulated using SolidWorks Simulation program.
Relevant regression equations were also derived describing the dependence of force inducing the grate deformation by 0.25 mm ‒ modulus
of grate elasticity ‒ on the number of flexible segments in established orientations. These calculations were made in Statistica and Scilab
programs. It has been demonstrated that, with the same number of segments, the crosswise orientation of flexible segments increases the
grate structure flexibility in a more efficient way than the lengthwise orientation. It has also been proved that a crucial effect on the grate
flexibility has only the quantity and orientation of segments (crosswise / lengthwise), while the exact position of segments changes the
grate flexibility by less than 1%.
Various examples of the design of cast elements of the equipment used in furnaces for the heat treatment of machine parts are given.
Shortcomings in their performance are indicated. Reasons for required stability of equipment are briefly discussed. Elements of equipment
illustrate the possibilities of using a charge-carrying pallet with dimensions of 900×600×45 mm as a basis for multi-component
technological equipment. Introducing additional elements, such as metal baskets, intermediate pallets or crossbars to the main pallet, it
becomes possible to create different configurations of this equipment. The technological equipment presented and discussed here is offered
to different plants which heat-treat a wide variety of produced parts. It was found that the reliability and durability of new designed
equipment can be checked only during practical use. For large plants dealing with the heat treatment of bulk quantities of parts
homogeneous or similar in shape is recommended to use the dedicated tooling.
Dynamic angle measurement (DAM) plays an important role in precision machining, aerospace, military and artificial intelligence. Because of its advantages including high sensitivity, solid state and miniaturization, fibre-optic gyroscope (FOG) has great application prospects in the field of DAM. In this paper, we propose a dynamic angle metrology method based on FOG and a rotary table to evaluate the DAMaccuracy with FOG. The system synchronously collects data from the FOG and rotary table, and analyses the DAM accuracy of the FOG for different sway conditions compared with that of the angle obtained from the rotary table. An angle encoder in the rotary table provides absolute or incremental angular displacement output with angular displacement measurement accuracy of 10′′ (0:0028◦) and angular displacement repeat positioning accuracy of 3′′ (0:00083◦), and can be used as an angle reference. The experimental results show that the DAM accuracy of the FOG is better than 0:0028◦ obtained with the angular encoder, and the absolute DAM accuracy of the FOG is better than 0:0048◦ for given conditions. At the same time, for the multi-path signal synchronization problem in the metrology field, this paper proposes a signal delay measurement method combining test and algorithm procedures, which can control a delay within 25 μs.
In this article, we study tilted fiber Bragg gratings (TFBGs) with tilt angles of 6◦ and 8◦, their transmission spectra, and spectral parameters that have a linear dependence on the refractive index of the environment. It is shown that there can be several such characteristics, such as the minimum, width and energy of the spectrum. The linear dependence of the spectrum width on the refractive index does not depend on the tilt angle. The linear dependence of the spectrum minimum is only observed for a tilt angle of 8◦. The results of this work can be used to create a sensor system based on an optical fiber.
In this work, an electrically tunable long-period fiber grating (LPFG) coated with liquid crystal layer (LC) is presented. As a LC layer, a prototype low-birefringence 1550A LC mixture was chosen. As a LPFG host, two types of gratings were studied: the LPFGs based on a standard telecommunication fiber, produced by an electric arc technique with a period of 222 μm, and the LPFGs based on a boron co-doped fiber written by a UV technique with a period of 226.8 μm. The relatively short period of these gratings allowed exploiting unique sensing properties of the attenuation bands associated with modes close to the turn-around point. Experiments carried out showed that for the UV-induced LPFG with a LC layer, on the powered state the attenuation band could be offset from the attenuation band measured in the unpowered state by almost 130 nm. When the arc-induced LPFG was coated with the LC, the depth of the attenuation band could be efficiently controlled by applying an external E-field. Additionally, all experimental results obtained in this work were supported by the theoretical analysis based on a model developed with Optigrating v.4.2 software.
This paper presents the implementation of a thinned fibre Bragg grating as a fuel adulteration sensor for volatile organic compounds. The proposed sensor can detect upto 10% adulteration of benzene, toluene and xylene: hydrocarbons precisely, whereas traditional methods can detect only upto 20% adulteration. The results obtained from the experiments are verified using Finite Difference Time Domain method. It is found that experimental results have very less deviation from simulation results. The proposed sensor provides us with the new possibility that may have commercial application, as well.
The contradiction between the restriction of grating manufacturing technology and high-resolution measurement requirements has been the focus of attention. The precision requirement of angle calculation during the digital subdivision processing of a Moiré signal is focused on, the causes of errors in the solution of arcsine function are analysed, and an improved coordinate rotation digital computer (CORDIC)with double-rotation iteration is proposed by discussing the principle of the conventional CORDIC in detail herein. Because the iterative number and data width of the improved CORDIC are limited by the finite digital circuit resources and thus determine the calculation accuracy directly, subsequently the overall quantization error (OQE) of the improved CORDIC is analysed. The approximate error and rounding error of the algorithm are deduced, and the error models of iterative number and data width are established. The validity and application value of the improved CORDIC are proved through simulations and experiments involving a subdividing circuit. The corresponding relation between the approximate error, rounding error and iteration number, as well as the bit width are proved by quantization. The error of subdivision with the improved CORDIC, obtained through a calibration experiment, is within ±0.5′′ and the mean variance is 0.2′′. The results of the research can be applied directly to a digital subdivision system to guide the parameter setting in the iterative process, which is of crucial importance in the quantitative analysis of error separation and error synthesis.
Spectral characteristics and amplitude tunability of a long period grating with a dual- resonance inside fiber loop mirror are studied in terms of applied stress caused by elongation. Inserting the polarization controller between grating and part of polarization maintaining fiber in the loop structure enables tuning of resonance and interferometric peaks. The maximum sensitivity of demonstrated sensor is of 1.943 dB/mε for the range of 1.1–4.4 mε. Combination of these two optical components allows to measure strain in a wider range comparing with sensors based on standard long period grating.