Application of PID Control Unit for System Stabilization in Process-integrated Powder Coating by Radial Axial Rolling of Rings

The process integrated powder coating by radial axial rolling of rings represents a new hybrid production technique in order to apply the functional layers on ring-shaped work pieces. Since the layer is produced in a powder metallurgical way [1], the ring volume decreases during the compaction of the layer material. In conventional ring rolling processes an isochoric plastic deformation of the ring is exploited in order to control the process. However this is not true any more for a ring exhibiting a compressible layer [2]. Consequently different control mechanisms have to be developed for the new considered process. One major aspect is the stability of the process which is governed by a stable position of the ring as well as the roundness of the ring. Therefore the finite element (FE) model has been coupled with a PID-controller unit and it will be shown that a stable process can be reached in this way. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of powder metallurgical coating by radial axial ring rolling

The process integrated powder coating by radial axial rolling of rings is expected to provide a new hybrid production technique to apply different kinds of powder metallurgical functional surfaces to ring–shaped work pieces. The main advantages compared with conventional manufacturing processes in this field can be found in lower costs, shorter process cycles and larger producible work pieces. In order to meet the requirements for an industrial application of this new process it is important to proof its capability particularly with regard to reproducibility and to investigate its boundaries. A reliable process simulation will provide a deeper insight into the governing parameters and reduce the money and time consuming experimental tests. Considering a numerical simulation using the FE method two challenges can be named. First one requires a material model to describe the compaction of metal powder at different elevated temperatures. As second the simulation of the ring rolling process itself is still very time consuming. A fine spatial discretization due to large deformations in the rolling gap and contact interaction between workpiece and rollers are the most prevailing factors in this context. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of heat treatment on the phase transformation in powder metallurgical multi-functional coating

Heat treatment is an important part of the manufacturing of metallic products, especially in powder coating processes. It provides an efficient way to improve the properties of the metal as e.g. hardness by controlling the rate of diffusion and the rate of cooling within the microstructure. The process-integrated powder coating by radial axial rolling of rings is a new hybrid production technique which is introduced in [1]. The applied temperatures in hot rolling are within the range of austenitizing temperatures for the investigated steels [2]. Therefore, reasonably controlling the temperature is an important task [3]. The paper is concerned with the integration of heat treatment of the rolled ring into the subsequent cooling process. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finite element simulation for dynamic large elastoplastic deformation in metal powder forming

In this paper, a transient dynamic analysis of the powder compaction process is simulated by a large displacement finite element method based on a total and updated Lagrangian formulation. A combination of the Mohr–Coulomb and elliptical yield cap model, which reflects the stress state and degree of densification, is applied to describe the constitutive model of powder materials. A Coulomb friction law and a plasticity theory of friction in the context of an interface element formulation are employed in the constitutive modelling of the frictional behaviour between the die and powder. Finally, the powder behaviour during the compaction of a plain bush, a rotational flanged and a shaped tip component are analysed numerically. It is shown that the updated Lagrangian formulation, using a combination of the Mohr–Coulomb and elliptical cap model, can be effective in simulating metal powder compaction.     

Development of a finite element model of metal powder compaction process at elevated temperature

This paper presents the finite element modelling of metal powder compaction process at elevated temperature. In the modelling, the behaviour of powder is assumed to be rate independent thermo-elastoplastic material where the material constitutive laws are derived based on a continuum mechanics approach. The deformation process of metal powder has been described by a large displacement based finite element formulation. The Elliptical Cap yield model has been used to represent the deformation behaviour of the powder mass during the compaction process. This yield model was tested and found to be appropriate to represent the compaction process. The staggered-incremental-iterative solution strategy has been established to solve the non-linearity in the systems of equations. Some numerical simulation results were validated through experimentation, where a good agreement was found between the numerical simulation results and the experimental data.     

A review of planning and scheduling systems and methods for integrated steel production

Iron and steel industry is an essential and sizable sector for industrialized economies. Since it is capital and energy extensive, companies have been putting consistent emphasis on technology advances in the production process to increase productivity and to save energy. The modern integrated process of steelmaking, continuous casting and hot rolling (SM–CC–HR) directly connects the steelmaking furnace, the continuous caster and the hot rolling mill with hot metal flow and makes a synchronized production. Such a process has many advantages over the traditional cold charge process. However, it also brings new challenges for production planning and scheduling. In this paper we first give a comparative analysis of the production processes and production management problems for the SM–CC–HR and the traditional cold charge process. We then review planning and scheduling systems developed and methods used for SM–CC–HR production. Finally some key issues for further research in this field are discussed.     

A finite strain viscoplasticitymodel for cold compaction processes ofmetal powders

The production of metal parts by powder metallurgical methods is of increasing interest due to energy and material efficiency of the processes. However, there is still a lack of reliable numerical methods and constitutive models to describe the compaction process from the loose powder to the green (un-sintered) compact via die-compaction or cold isostatic pressing. A new phenomenological constitutive model within the framework of viscoplasticity with internal variables is developed. A central part of the model is a unique and smooth single surface yield function. The applied evolution equations together with the assumed associated flow rule and the convexity of the yield function guarantee thermodynamic consistency of the model. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Powder compaction. Experiments,modeling and simulation

Field-assisted sintering technology (FAST) is a combined thermal and mechanical loading process to compact and sinter a powder material within one process step. In this short essay a constitutive model of thermo-viscoplasticity is proposed representing most of the phenomena observed in the experiments. The constitutive model is calibrated to the experimental data and some predicted experiments are compared with constitutive model showing appropriate results. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Remarks on Centers of Rings

It is proved that for matrices A,B in the n by n upper triangular matrix ring Tn(R) over a domain R,if AB is nonzero and central in Tn(R) then AB =BA.The n by n full matrix rings over right Noetherian domains are also shown to have this property.In this article we treat a ring property that is a generalization of this result,and a ring with such a property is said to be weakly reversible-over-center.The class of weakly reversible-over-center rings contains both full matrix rings over right Noetherian domains and upper triangular matrix rings over domains.The structure of various sorts of weakly reversible-over-center rings is studied in relation to the questions raised in the process naturally.We also consider the connection between the property of being weakly reversible-over-center and the related ring properties.     

Investigation of discrete stress distribution for dry powder compaction using Discrete Element Method and weighted Voronoi tesselation

Powder compaction of granular material plays a substantial role in the manufacturing process of ceramics industry and powder metallurgy industry. The compaction behaviour is ruled by granular flow and densification of deformable particles. Discrete element method (DEM) allows to investigate the powder compaction process numerically on the microscale by modeling the forces on the particle level and simulating the particle motion. Three-dimensional data about particle size distribution and spatial structure of the particle packing can be extracted from micro-computed tomography (µCT). An average stress tensor can be computed from DEM results, evaluating the contact forces and the distances from the particle center to the contact point with respect to an average cell volume. A weighted Voronoi tesselation of the polydisperse particle assembly is proposed for mapping a cell volume to each individual particle. With this approach all structural information of the particle system can be transferred from a discrete particle model to a heterogeneous volume model of micro-structure. Discrete stress distributions for uniaxial powder compaction are presented. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Formation of Vortex Rings

The production of a vortex ring formed by using a piston to drive fluid through an orifice is considered. A cylindrical vortex sheet is supposed to be formed initially which rolls up into a vortex ring. Energy and momentum are conserved during rollup and determine the speed and size of the ring. It is shown that these quantities are independent of the vorticity distribution in the core of the ring. Reasonable agreement with experimental observations is found. A speculation is made about the criterion for the rings to be laminar or turbulent.     

Ideal-Symmetric and Semiprime Rings

Lambek extended the usual commutative ideal theory to ideals in noncommutative rings, calling an ideal A of a ring R symmetric if rst ∈ A implies rts ∈ A for r, s, t ∈ R. R is usually called symmetric if 0 is a symmetric ideal. This naturally gives rise to extending the study of symmetric ring property to the lattice of ideals. In the process, we introduce the concept of an ideal-symmetric ring. We first characterize the class of ideal-symmetric rings and show that this ideal-symmetric property is Morita invariant. We provide a method of constructing an ideal-symmetric ring (but not semiprime) from any given semiprime ring, noting that semiprime rings are ideal-symmetric. We investigate the structure of minimal ideal-symmetric rings completely, finding two kinds of basic forms of finite ideal-symmetric rings. It is also shown that the ideal-symmetric property can go up to right quotient rings in relation with regular elements. The polynomial ring R[x] over an ideal-symmetric ring R need not be ideal-symmetric, but it is shown that the factor ring R[x]/xⁿR[x] is ideal-symmetric over a semiprime ring R.     

Periodic jordan rings and order structure

The aim of this paper is to obtain information about a periodic Jordan ring by using only properties of its idempotent elements. Osborn proves that a power-associative periodic ring having only one nonzero idempotent element is a division ring. so associative. He also proves that a periodic Jordan ring is a subdirect product of simple periodic Jordan rings and that a simple periodic Jordan ring is either a periodic field or a Jordan ring of capacity 2. Using these results we obtain some necessary and suficient conditions for a periodic Jordan ring to be associative, and these conditions are only given in terms of the idempotent elements. We also characterize the periodic Jordan ring which are a direct product of periodic fields and simple periodic Jordan rings of capacity two.     

关于实Hilbert环

通过引进“强实Hilbert环”这一概念,本文证明了,一个环A是强实Hilbert环,当且仅当多项式环A[X]是实Hilbert环,当且仅当A[X]的每个实极大理想在A上的局限是实极大的,从而文献[1]中两个主要结果被否定.此外,本文还研究了所谓的“严格的实Hilbert环”,这类环对于半代数零点定理等方面的探讨更具应用意义.     

环的Armendariz性

研究了一个环何时具有Armendariz性．使用环论的一般方法,证明了在一定条件下商环、具有一对零同态的Morita Context环以及映射环是Armendariz环,推广了已有的某些结果．     

Doset Hibi rings with an application to invariant theory

We define the concept of a doset Hibi ring and a generalized doset Hibi ring which are subrings of a Hibi ring and are normal a?ne semigroup rings. We apply the theory of (generalized) doset Hibi rings to analyze the rings of absolute orthogonal invariants and absolute special orthogonal invariants and show that these rings are normal and Cohen-Macaulay and has rational singularities if the characteristic of the base field is zero and is F-rational otherwise. We also state criteria of Gorenstein property of these rings.     

Possible mechanism of creep under internal pressure in laminated rings made of composite material

The authors discuss the deformative susceptibility of a ring made of spirally arranged armature layers and a polymer binder. They show that in prolonged stress on these rings by internal pressure under conditions of a highly pliable matrix additional deformation may occur, caused by sliding of the coils.     

A mathematical model and two-stage heuristic for hot rolling scheduling in compact strip production

This paper addresses a new hot rolling scheduling problem from the compact strip production process, which is the mainstream production technology that is used worldwide for sheet strips. The problem is modeled as a combination of two coupled sub-problems. One sub-problem is a sheet strip assignment problem that assigns sheet strips to rolling turns with the constraints of safe values of different gauge levels, and the other is a sheet strip sequencing problem that decides the rolling sequence for all of the sheet strips in a rolling turn to form a particular parabolic shape in thickness. To solve this hot rolling scheduling problem, we present a novel approach that consists of a sheet strip assignment heuristic and a sheet strip sequencing heuristic. The sheet strip assignment heuristic minimizes the number of virtual sheet strips by generating rolling turns according to the ordered sheet strips with maximum gauge level and their safe values. The sheet strip sequencing heuristic minimizes the average change of the thickness of adjacent sheet strips by arranging a certain number of duplicate sheet strips to the increasing stage of a rolling turn. Extensive experiments based on both synthetic and real-world instances from a compact strip production process show the effectiveness of the proposed two-stage heuristic in solving the hot rolling scheduling problem.     

Reflexivity with maximal ideal axes

The reflexive property for ideals was introduced by Mason and has important roles in noncommutative ring theory. We in this note study rings with the reflexivity whose axis is given by maximal ideals (simply, an RM ring) which are a generalization of symmetric rings. It is first shown that the reflexivity of a ring and the RM ring property are independent of each other, noting that both of them are generalizations of ideal-symmetric rings. We connect RM rings with reflexive rings in various situations raised naturally in the procedure. As a generalization of RM rings, we also study the structure of the reflexivity with the maximal ideal axis on idempotents (simply, an RMI ring) and then investigate the structure of minimal non-Abelian RMI rings (with or without identity) up to isomorphism.     

Applying an edit distance to the matching of tree ring sequences in dendrochronology

In dendrochronology wood samples are dated according to the tree rings they contain. The dating process consists of comparing the sequence of tree ring widths in the sample to a dated master sequence. Assuming that a tree forms exactly one ring per year a simple sliding algorithm solves this matching task.

But sometimes a tree produces no ring or even two rings in a year. If a sample sequence contains this kind of inconsistencies it cannot be dated correctly by the simple sliding algorithm. We therefore introduce a algorithm for dating such a sample sequence against an error-free master sequence, where n and m are the lengths of the sequences. Our algorithm takes into account that the sample might contain up to missing or double rings and suggests possible positions for these kind of inconsistencies. This is done by employing an edit distance as the distance measure.