Дисертації з теми "STEEL FINISHING"

Corporate entrepreneurship is examined with specific reference to the Finishing units of the Vanderbijlpark site of ArcelorMittal South Africa. The objective of the study is to assess the level of intrapreneurship within middle to upper employee levels in order to make recommendations regarding the encouragement of an entrepreneurial climate. The evaluation starts with a historic overview of ArcelorMittal South Africa, followed by an assessment of the current operational characteristics of the company. An evaluation of ArcelorMittal's interaction with its stakeholders is combined with the outcomes of two previous internal surveys of corporate culture to arrive at the causal factors to the study. A literature review is conducted to explore entrepreneurship and the attributes of an entrepreneur. Subsequently, corporate entrepreneurship is investigated in order to outline the characteristics, pivotal agents, importance and dangers of the concept. The establishment of a climate of corporate entrepreneurship was found to be dependent on the presence of 14 important constructs. If proposed steps are followed to promote corporate entrepreneurship in a company, five identified success factors will improve as a result. A questionnaire is adapted to test for the presence of the 14 constructs of a climate of corporate entrepreneurship which were identified and to verify current perceptions regarding the organisational success of the company among B to G role respondents functioning in the Finishing units of ArcelorMittal Vanderbijlpark. A target group of 325 employees was identified and questionnaires were routed to all persons in the group. A total of 180 usable responses were received on which statistical analysis was based. The validity of each construct is individually determined by calculating a Cronbach alpha coefficient and tests for both statistical and practical significance are performed to determine the effect of demographical variables on each construct. An analysis is made of perceptions regarding the presence of constructs of a climate of corporate entrepreneurship as well as constructs indicating the success of the organisation. Furthermore, the effect of demographical variables on recorded perceptions is interpreted. Recommendations, based on the analysis made as well as the literature review, are made on actions to improve the climate of corporate entrepreneurship in ArcelorMittal South Africa. The study concludes with a measurement of the achievement of objectives and suggestions for further research.
Thesis (M.B.A.)--North-West University, Vaal Triangle Campus, 2010.

Additive Manufacturing, and specifically powder bed fusion processes, have advanced rapidly in recent years. Selective Laser Melting in particular has been adopted in a variety of industries from biomedical to aerospace because of its capability to produce complex components with numerous alloys, including stainless steels, nickel superalloys, and titanium alloys. Post-processing is required to treat or solve metallurgical issues such as porosity, residual stresses, and surface roughness. Because of the geometric complexity of SLM produced parts, the reduction of surface roughness with conventional processing has proven especially challenging. In this Thesis, two processes, abrasive flow machining and ultrasonic shot peening, are evaluated as surface finishing processes for selective laser melted 316L. Results of these experiments indicate that AFM can reliably polish as-built internal passages to 1 µm Ra or better but is unsuitable for passages with rapidly expanding or contracting cross-sections. AFM can also polish relatively small passages, but lattice components may prove too complex for effective processing. USP cannot achieve such low surface roughness, but it is a versatile process with multiple advantages. Exterior surfaces were consistently processed to 1.7 to 2.5 µm Ra. Interior surfaces experienced only partial processing and demonstrated high geometric dependence. USP significantly hardened the surface, but steel media hardened the surface better than ceramic media did. Both AFM and USP are recommended processes for the surface finishing of SLM manufactured parts. Good engineering judgement is necessary to determine when to use these processes and how to design for post-processing.

The Master‘s thesis focuses on processing of hard-to-machine materials by the finishing machining methods. The first chapter comprises division and characteristics of finishing technologies in the field of machining processes. The chapter following includes division and characteristics of the hard-to-machine materials. The experimental part – another significant part of the thesis – is focused on grinding of mostly bearing rings made of hard-to-machine materials. The aim of the experimental part is to compare and subsequently assess the use of various kinds of grinding wheels in the grinding process of a given workpiece material. Several parameters are examined from the technological and economic point of view. The assessment of the experimental part provides an overview on the advantages and disadvantages of the use of the grinding wheels in the grinding process of a given material for large-scale production. The conclusion is a summary of the results obtained in the experimental part.

The aim of this research work is to study the inter-relationship, under controlled industrial conditions, among skin pass reductions, surface topography characterized by 2D and 3D roughness parameters, stampability and painted surface finish quality for automotive steel sheet stampings. Different surface textures obtained from cold rolling finishing have been evaluated in terms of paint appearance (rating and spectral curve) and tentatively related to roughness parameters (2D and 3D) obtained from the cold finished sheets. Some relevant tendencies have been established amongst these parameters. The results presented here are in accordance with other recently published research showing that there is a clear relationship between these parameters, and that further detailed studies are needed.
O foco do presente trabalho é o estudo, em condições industriais, da inter-relação entre grau de redução do passe de acabamento, topografia superficial caracterizada pelos parâmetros de rugosidade 2D e 3D, estampabilidade e aparência de pintura de chapas de aço para painéis automotivos. Diferentes texturas superficiais de chapas de aço foram analisadas em termos de aparência de pintura (rating e curvas espectrais) e tentativamente relacionadas com os parâmetros de rugosidades (2D e 3D) obtidos na chapa antes de estampar. Algumas tendências relevantes foram estabelecidas entre estes parâmetros. Os resultados presentes aqui estão de acordo com publicações recentes mostrando uma clara relação entre estes parâmetros e que trabalhos futuros ainda são necessários.

A soldagem altera as propriedades mecânicas dos aços ligados ao níquel, em especial seu desempenho em aplicações criogênicas. Assim, este trabalho apresenta um estudo sobre a soldabilidade metalúrgica do aço com 9% níquel e tem como objetivos: identificar se a fragilização em temperatura abaixo da temperatura Ac3 ocorre em ZACs com dois e três ciclos térmicos simulados fisicamente; analisar as características da junta soldada pelo processo de soldagem por atrito linear com mistura e os efeitos da soldagem multipasse; e analisar a influência dos passes de enchimento e acabamento sobre o comportamento mecânico da ZAC da raiz de uma junta soldada pelo processo de soldagem MIG/MAG. Destacam-se entre os resultados da simulação física da ZAC: as amostras que tiveram a temperatura máxima abaixo da temperatura Ac1, no terceiro ciclo térmico, não apresentaram o efeito de redução da energia absorvida no ensaio Charpy V; a fração volumétrica de austenita retida não aumenta a quantidade de energia absorvida no ensaio Charpy V para as amostras que tiveram a temperatura máxima do segundo ciclo térmico abaixo da temperatura Ac3 (723°C); e a correlação linear múltipla sugere um modelo empírico, baseado nos dados deste trabalho, onde os fatores de fração volumétrica do microconstituinte martensita-austenita, fração volumétrica de austenita retida e tamanho de grão são mais relevantes para a quantidade de energia absorvida no ensaio Charpy V. Destacam-se entre os resultados da soldagem por atrito linear: a energia absorvida no ensaio Charpy V da zona misturada do primeiro cordão (CP1) é menor que o metal de base; o segundo cordão gera duas regiões na zona misturada do primeiro cordão, que tendem a aumentar a energia absorvida no ensaio Charpy V; os valores de energia absorvida no ensaio Charpy V apresentam correlações lineares simples com a microdureza, a fração volumétrica do microconstituinte martensita-austenita e com o tamanho de grão. Destacam-se entre os resultados da soldagem com MIG/MAG: A soldagem do aço com 9% de níquel com a liga Inconel 625 gera uma zona não misturada entre o metal de solda e a ZAC; a amostra com todos os passes de solda (CP3) apresenta a menor energia absorvida no ensaio Charpy V entre todos os experimentos; e a trinca, no ensaio Charpy V, propaga na zona não misturada no CP1 e no CP2, que tiveram as maiores energias absorvidas no ensaio Charpy. O CP3 apresenta propagação de trinca na linha de fusão e possui a menor energia absorvida no ensaio Charpy V.
Welding modify the mechanical properties of nickel steels, especially their performance in cryogenic applications. Thus, this work presents a study on the metallurgical weldability of 9% nickel steel and its objectives are: identify if the embrittlement in temperature below the Ac3 temperature occurs in HAZs with two and three thermal cycles simulated physically; analyze the characteristics of the joint welded by friction stir welding process and the effects of multipass welding; and analyze the influence of the filling and finishing passes on the mechanical behavior of HAZ from the root of a joint welded by the GMAW welding process. The results of the physical simulation of the HAZ were: the samples that had the maximum temperature below the temperature Ac1, in the third thermal cycle, did not present the effect of reduction of the energy absorbed in the Charpy V test; the retained austenite volumetric fraction does not increase the amount of energy absorbed in the Charpy V test for the samples having the maximum temperature of the second thermal cycle below the Ac3 temperature (723 °C); and the multiple linear correlation suggests an empirical model, based on the data of this work, where the volumetric fraction factors of the martensite-austenite microconstituent, retained austenite volumetric fraction and grain size are more relevant for the amount of energy absorbed in the Charpy V test. The FSW welding highlights results: the energy absorbed in the Charpy V test of the mixed zone of the first pass (CP1) is smaller than the base metal; the second pass generates two regions in the mixed zone of the first pass, which tend to increase the energy absorbed in the Charpy V test; the values of energy absorbed in the Charpy V test show simple linear correlations with the microhardness, the volumetric fraction of the martensite-austenite microconstituent and with the grain size. The GMAW welding highlights results: welding of the steel with 9% nickel with the Inconel 625 alloy makes an unmixed zone between the weld metal and the HAZ; the sample with all weld passes (CP3) shows the lowest energy absorbed in the Charpy V test among all the experiments; and the crack, in the Charpy V test, propagates in the unmixed zone in CP1 and CP2, which had the highest energies absorbed in the Charpy test. The CP3 shows crack propagation in the melting line and has the lowest energy absorbed in the Charpy V test.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
In machining processes the main functions of cutting fluids (FC) are cooling and lubrication of the tribological system comprised of the workpiece, the chip and the cutting tool. When adequately chosen and correctly applyed they may raise tool lives, reduce machining forces and improve the surface finishing of the workpiece. However, during their use, research has demonstrated that water based cutting fluids (emulsions and solutions) become suceptible to microbiological contamination (by bacterias) that uses nutrients encountered in their composition to grow and reproduce. According to the specialised literature, the metabolic activities of these microorganisms degrade the cutting fluids, altering their chemical and phisycal properties. However, the study of this theme is limited and there is no research work that quantitatively indicates the influence of these contaminants in the machinability parameters. Therefore, the present work has the main objetctive of quantifying three machinability parameters (cutting force, surface roughness and tool life) when turning V304UF stainless steel using two water based cutting fluids (emulsion of vegetable base and semi-syntetic of mineral base). These two cutting fluids were intentionaly contaminated in an induced manner by periodic inoculations up to a mean contamination of 105 UFC/mL. With this procedure it was possible to compare the eficiency of new and contminated cutting fluids during the turning process. The results showed that the contaminated cutting fluids with 105 UFC/mL changed the pH, destabilized the emulsions and caused small changes in the machinability parameters (maching force, surface roughness and tool life), mainly under low cutting speeds and feed rates. Thus, the contamination of the cutting fluids, particularly the vegetable base ones, can promote small influences in important machinability parameters.
Em processos de usinagem as principais funções dos fluidos de corte (FC) são refrigerar e lubrificar o sistema tribológico constituído pela peça, cavaco e ferramenta. Quando escolhidos e aplicados corretamente, eles podem aumentar a vida da ferramenta, diminuir as forças de usinagem e melhorar o acabamento da peça fabricada. No entanto ao longo de sua utilização, pesquisas apontam que os FC s à base de água (emulsões e soluções) tornam-se susceptíveis a contaminação microbiológica (bactérias) que usam nutrientes encontrados em sua composição para crescerem e se reproduzirem. Segundo a literatura especializada, as atividades metabólicas destes microrganismos degradam os FC s, alterando suas propriedades físicas e químicas. Entretanto, o estudo desse assunto é limitado, e não há trabalhos que indicam quantitativamente a influência desses fluidos contaminados nos parâmetros de usinagem. Deste modo, este trabalho teve como principal objetivo quantificar três índices de usinabilidade (forças de usinagem, acabamento superficial e vida da ferramenta) no processo de torneamento do Aço Inoxidável Austenítico V304UF, utilizando dois FC s aquosos (emulsionável de base vegetal e semissintético mineral). Esses FC s foram contaminados de forma induzida através de inoculações periódicas até alcançarem o nível de contaminação média igual a 105 UFC/mL. Deste modo, foi possível comparar a eficiência dos FC s novos com os contaminados no processo de torneamento. Os resultados mostraram que as contaminações dos FC s com 105 UFC/mL, alteraram o pH do meio, desestabilizaram as emulsões e causaram pequenas mudanças nos parâmetros de forças de usinagem, rugosidade e vida da ferramenta, principalmente nas condições com baixa velocidade de corte e taxas de avanço. Assim, para baixas velocidades de corte, os fluidos de corte contaminados, principalmente de base vegetal, podem causar pequenas influências em importantes parâmetros de usinabilidade do processo.
Mestre em Engenharia Mecânica

3D printing, also known as additive manufacturing (AM), has got rapidly developed since 1987. Compared with conventional manufacturing methods, 3D printing provides some advantages such as increasing material utilization and less waste of material. Maraging steel provides good strength and toughness without losing ductility, which has been used for the 3D printing technique. Selective laser melting (SLM) is one of the 3D printing methods, which is mostly used for metal and alloy powder. In this thesis, selective laser melting will be used for maraging steel. 3D printing maraging steel is a new material, the research about the properties of 3D printing maraging steel is still ongoing. Corrosion resistance is one of the most important properties of maraging steel due to the high cost of corrosion. So this thesis will focus on the corrosion behavior of 3D printing maraging steel. The purpose of this thesis was to find the best heat treatment condition for high corrosion resistance and to find the relationship between microstructure and corrosion behavior of maraging steel. In this thesis, several kinds of maraging steel samples with different heat treatment conditions were used. SLM, SLM austenized&quenched, SLM aged, conventional austenized&quenched, and conventional aged. Besides, two kinds of solutions were produced, NaOH (pH=11.5) and Na2SO4 (pH=6.5). To observe the microstructure, an optical microscope was used. The grain size is different between SLM and conventional samples, and also different between the samples with different heat treatment conditions. The potentiodynamic polarization method was used to measuring the corrosion behavior. SLM samples have much lower current density, and the passivation potential and the corrosion rate are similar compared with conventional samples. But due to the lack of further experiments, the relationship between corrosion behavior could be affected by the combined effect of several factors.

碩士
國立中山大學
機械與機電工程學系研究所
107
In this study, a horizontal magnetic brush tool composed of iron powders was used to investigate the effects of the load (0.5 N~1.05 N), the iron powder weight (0.1 g~0.2 g) and the magnetic brush shaping (natural forming, pre-shaping) on the contact area and height after the contact between the magnetic brush and the workpiece. When the workpiece and the tool were not rotating, the contact area and the height of the magnetic brush increased along with the weight of the iron powders. In addition, as the load increased, the contact area also increased, while the magnetic brush height decreased and then approached a saturation value. The contact area of the pre-shaped magnetic brush was smaller than that of the naturally formed magnetic brush; and the height of the pre-shaped magnetic brush was greater than that of the naturally formed magnetic brush. When the workpiece is rotated and the tool is not rotating, the contact area was slightly increased and the magnetic brush height was slightly decreased. The magnetic brush shifted in the direction of rotation of the workpiece, and some of the magnetic brush links was broken. When both the workpiece and the tool were rotated, the contact area was greatly increased, and the height of the magnetic brush was greatly reduced. Finally, the 304 stainless steel cylindrical workpiece was polished using circulating cutting fluid mixed alumina abrasive grains and iron powders to observe the variation of the surface roughness of the workpiece at the weight 0.2 g of the iron powders, the load of 0.65 N, the pre-shaping magnetic brush, and the rotating tool. Results showed that the surface roughness could decreases from Ra =0.257 µm、Rmax = 1.025 µm to Rmax = 0.091 μm、Ra = 0.021 μm after a polishing time of 8 minutes at the rotating speed 400 rpm of workpiece, and the rotating speed 60 rpm of the tool.

Steel finishing operations such as pickling, galvanizing, plating, etc., involve a process of removing scale, rust and dust from the surface of stainless steel. In this, sheets of steel are immersed in hot acidic solution resulting in waste liquor which contains heavy metals like Fe, Cr, Ni, etc. When treated with lime, these heavy metals get settled as metal hydroxides in form of sludge. As per the Act of Hazardous Waste (Management and Handling) Rules, 1989, the disposal of lime treated spent pickling sludge should be done with consideration and is not easy. In normal practice, this sludge is being stored in leak proof bags and no proper disposal technique is being employed by small and medium industries. An attempt has therefore been made to utilize the lime treated pickling sludge in cement concrete mix in the presence of fly-ash as a binder agent. The main objective is to immobilize heavy metals in the concrete matrix and studying its leaching characteristics and compressive strength. Sludge is characterized for the heavy metal content using AAS, EDX and XRD. Other physical and chemical properties are also analysed. Test cubes of nominal mix M20 were prepared and these were tested for its 7 and 28 days compressive strength. Toxicity characteristics leaching procedure (TCLP) test as per USEPA was carried out on these cubes to study the extent of immobilization and stabilization of heavy metals in the concrete matrix. For this, Four factors were varied on three levels i.e. Percentage of cement replaced by sludge (5%, 7.5% & 10%) and Percentage of fly-ash (0%, 15% & 20%), type of cement used and particle size grading of sludge, to assess the effect of these factors on compressive strength and heavy metal concentrations in leachate. Taguchi methodology (L9 orthogonal array) was used for optimizing the design of experiments and for further analysis. Experimental results show that the lime treated pickling sludge can be utilized with cement/concrete with some binding materials like fly-ash. By Analysis of Mean (ANOM) method, it was found that 7.5% addition of sludge and 20% fly-ash as partial replacement of cement with 43 grade OPC and sludge particle size ranging between 0.3 to 2.36mm produced the optimal performance for compressive strength and heavy metal immobilization values of the cement-sludge-flyash concrete cubes. By Analysis of Variance (ANOVA) method, it was found that particle size grading of sludge and percent of sludge added as cement replacement contributed 46% and 41% respectively to the optimal performance. Formation of C2H, C3H and gypsum (C-S-H gel) may be contributing in the better performance of concrete.

碩士
健行科技大學
機械工程所
101
The finishing of #304 stainless steel in the market is mostly by electropolished to get smoothy and shine surface. However, these finishing methods must undergo longer time and environmental pollution. Magnetic abrasive finishing is a fast and high precision approach, but the magnetism of magnetic abrasive is reduced when finishing #304 stainless steel, and because the centrifugal force generated tends to throw abrasive away from the processing area, the efficency of finishing is thus decreased. This study mainly focuses on the effect of the magnetic gel abrasives at stainless steel surface, and experiment the finishing efficiency of single factor. We used high polymer material gels as binders and restrained magnetic and hard abrasive grains in the gels to form magnetic gel abrasives. Since the gel abrasives are viscous, they can not only wrap around the abrasive grains to prevent from spreading, but also attach tightly onto the surface of stainless surface. We placed the magnetic gel abrasives on stainless steel surface to conduct finishing, and experiments using the Taguchi method and L18 orthogonal array are performed based on different abrasives rata to investigate the changes in surface roughness and material removal rate…The results showed that after 35min of stainless steel finishing choose right abrasive rata and steel grit, the surface roughness can be decreased from Ra0.2936μm to Ra0.0136μm, and the roughness improvement rate of this process would reach 95% and resistance repellency can be improved with surface smoothing. This proves that the magnetic gel abrasive finishing developed in this study has outstanding finishing effect on stainless steel.

碩士
東南科技大學
機械工程研究所
101
In this study, mold steel SKD 11 is machined using magnetorheological (MR) fluid under an external magnetic field. The MR fluid comprises silicone oil with pure water as the based fluid for alumina, ferric ferrous oxide, carbonyl iron powder and silane coupling agent. The external magnetic field whose force is controlled by a permanent magnet changes the viscosity of the MR fluid. The grinding mechanism installed on a machine table is under computer numerical control and the surface quality of the workpiece is measured by a 3D surface roughness profilometer. The effects of various machining parameters on surface roughness are examined to determine the optimal machining conditions. Experimental results show that the optimal machining conditions are spindle rotational speed, 100 rpm; axial loading, 14 kg; magnetic flux, 199 mT; and processing time, 11 min, which yielded mirror surface quality with surface roughness of 0.03 μm.Experimental results show that the optimal machining conditions are spindle rotational speed, 100 rpm; axial loading, 14 kg; magnetic flux, 199 mT; and processing time, 11 min, which yielded mirror surface quality with surface roughness of 0.03 μm.

碩士
國立成功大學
工程科學系碩士在職專班
104
Based on the finishing mills in Chung Hung hot rolling plant, the thesis is to study the effects of the flow rate of hot rolling lubricant and the cooling-water pressure on the qualities of roller and steel strip surfaces. The experimental study is conducted by combining the application of rolling lubrication and cooling related technologies with the site conditions. The effect of rolling oil on the roller surface can be learned from the visual and touch inspections. However, to analyze the influence of the cooling-water pressure needs to use electronic instruments to detect the surface roughness of the steel strip. The research result indicates that the amount of the rolling oil has the interaction relationship with the front-end finish rolling, whose judge criterion is subject to the rolling force magnitude and stability.The result also illustrates that the larger cooling water pressure has the smaller average roughness. However, the higher pressure water would cause the deeper depressions in some sporadic sites.Since the average roughness for the pressure range used in the work all fits the product requirement, the steel strips with shallower depressions (caused by the lower pressure water) are chosen, which could be used for electroplating products with obvious economic benefits.

碩士
國立臺灣科技大學
機械工程系
89
The Objective of this study is to develop a non-contact surface roughness measuring system for the steel with good surface finishing (Ra=0.04~0.8µm). The system consists of four major parts, namely the line projector, a X-Y stage to move the specimen, CCD camera, and image analysis software. The measuring principle of the developed system based on the scattering characteristics of the laser beam projected on a workpiece surface with homogenous surface roughness. The larger the surface roughness value the larger the correspondent line width. The line width of the image was determined by the so-called edge detection method through calculating the first derivative of the smoothed image filtered by average filter and then finding the maximum slope position. A back propagation neural network was also developed in this study to predict the unknown surface roughness of the specimen via the measured line width by training the experimental surface roughness and line width data. According to the experimental results, the predicted surface roughness through back propagation neural network method was more accurate than that of the second order, third order, and fourth order polynomial curve fitting of the experimental surface roughness and line width data.

碩士
國立成功大學
工程管理碩士在職專班
105
The management and improvement of cost are the basic tools for business competition. Usually, a traditional cost system may be acceptable to evaluate the products cost of raw material level products, but it could not fulfill the requirement of rigorous distribution cost for the individual product. It will distort the cost structure and mislead the wrong decision making. However, the incorrect information will bring the improper price strategies which would impact the marketing strategies and whole business competitive advantages as well. Regarding to the steel industry, it is integrated downstream products with small quantity and various grades. It leads more significantly to the distortion of products cost and causes the strategies of product- mix unhealthy. Activity-based costing approach is a proper tool for evaluating the product cost. It is an effective method for managing the business performance and resource consumption. We can figure out the product cost by linking the productive operation activities and the resource consumption by the ABC approach. It seems that the evaluated product cost is more accurate than the traditional average cost method. Since the ABC approach takes all resources consumption for each product actually uses. We conduct the ABC approach to clarify the diversity product cost on cold-finished steel products. Furthermore, we combine it with the activity-based management (ABM) to improve the process flow for assessing the product cost. To gain diversity production line limitations and product margins, we establish a productive mathematical model with linear programming technology on the case for accomplishing the optimization productivity. Finally, proper product strategies have been evaluated by the linear programming technology. It has been solved the optimization product-mix with an effective resource planning, and mathematical models to verify the product strategies. The proposed decision support system will be established for preparing activities of marketing strategy. As a result, it has been improved the quality of decision making and influenced the business operation thinking of product price and sale. It seems to install a foundation of intelligent management as well as industry 4.0.

D. Tech. Chemical, Metallurgical and Materials Engineering
Discusses the objective of this present study is to manufacture particulate-strengthening Zn-Al-SnO2-TiO2 composite alloy on mild steel from chloride and sulphate baths with the target of improving mechanical and anti-corrosion, wear properties for automotive and decorative applications. Sub-Objectives:To study the effect of Zn-Al-SnO2-TiO2 composite properties on mild steel substrate To investigate the novel multifunctional thin films evolution formed on mild steel and their tribological properties. To investigate thermo-mechanical recrystallization behaviour and its thermal instability.To study the anti-corrosion resistance performance of the electrofabricated quaternary Zn-Al-SnO2-TiO2 coatings.To draw attention to the functional processing parameters of Zn-Al-SnO2-TiO2 produced coatings for high durability.