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BOLESŁAW PRZYBYLISKI

University of Technology and Life Sciences in Bydgoszcz

CONDITIONS FOR THE RENEWAL OF USED COMPONENTS OF MACHINERY AND EQUIPMENT

Summary

The article presents the problem of operating costs of machinery and equipment associated with the cost of their use. It was shown that the main component of oper-ating costs is repair costs. One solution limiting machinery and equipment repair costs is regeneration, which, in addition to the economic aspects, should also be seen in the ecological aspect. Despite is undoubted benefits, regeneration is not suf-ficiently appreciated in the national economy. One of the reasons is the lack of support in selecting the method of regeneration with the use of computer programs. Keywords: Machine components, wear, repair, regeneration, decision support system

1. Introduction

Repair costs are an important component of operating costs of technical machinery and equipment. One solution to limit the cost of repairs is regeneration, which means restoring perfor-mance features characteristic of (typical of) new components to the old ones. This is achieved through using appropriate regeneration technologies, and, in case of units, through the application of brand new and previously regenerated components in the process of repair. Renovation (repair), in conjunction with the regeneration of worn components and replaceable units is indeed necessary with reference to machines still in use, whose production is suspended due to the fact that the lack of components is often the cause of premature elimination from the operation of machinery that could still work effectively.

2. Analysis of the need for regeneration

Financial expenditures incurred to maintain the machinery in good condition are an important group of business costs of any production company or service. Integral components of mainte-nance costs are service, inspection and repair costs.

Service and inspection are carried out in accordance with construction requirements and in conjunction with operating conditions in order to properly prepare a machine to perform its im-posed tasks and to reduce the intensity of wearing its components and units through, for example, regulations designed to maintain the pre-determined features of operational condition of an object within the admissible range of variation, without changing the physicochemical properties of an object.

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The task of repair is to restore the state of machine operational fitness, and these processes can be carried out according to pre-agreed principles, i.e. after operating for a specified number of hours, or after a specified course (plan and prevention system), or ad hoc, as per the requirements of current machine condition (condition system). The latter is often implemented in, for example, technical back-up of transport companies.

Proper machine service results in:

¾ ensuring the greatest possible durability and reliability of the use of machinery and equipment, ¾ ensuring the highest possible safety and minimal operating costs,

¾ bring the organization of work and investment in technical equipment to the technically and economically reasonable minimum,

¾ minimizing machinery operation nuisance to the environment during its operation and ecologi-cal management of exploited machines.

One of the major operational and economic indicators affecting the efficiency of a factory is the cost of repairs. The estimation of repair costs over the entire lifecycle of a machine constitutes, in practice, a significant problem. It results from the random nature and varied scope of repair according to the condition (including post-breakdown and post-accident repairs). It can be as-sumed that the actual cost of repairs Kna has a share in the cost of purchasing different types of machines Cm expressed with an indicator kna:

Kna = kna•Cm (1)

Literature data [2, 3, 5] shows that the value of indicator kna for specific machines equals from 0,4 to1,5. For example (table 1 and 2), for tractors it equals from 0,23 to 0,83, with upper values for big power tractors.

Table 1. Repair cost of tractors with various power [2] Power

(kW)

Total repair cost Kna

(PLN) Tractor price Cm (PLN) Indicator kna 66-92 151966 183843 0,83 110-125 184972 294752 0,63 147-165 297324 387848 0,77 183-198 302870 443344 0,68 217 310860 516334 0,60

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Table 2. Repair cost of Wendt tractors [3] Tractor type Power

(kW) Tractor price Cm (PLN) Repair cost Kna (PLN) Indicator k na Fendt 716 118 353 000 145560 0,41 Fendt 818 140 380 000 87960 0,23 Fendt 824 169 418000 256080 0,61 Fendt 926 199 494 000 316440 0,64

Machinery renovation issues are particularly well-described in case of farm machinery. Litera-ture data [2, 3, 5] show that an average age of tractors in Poland is approximately 18 years, and their average operation period is slightly more than 30 years, with a maximum period of more than 40 years. It can therefore be assumed that in 2020 almost all agricultural machinery and tractors purchased in the nineties will operate in agriculture. Polish farmers, taking into consideration their current impoverishment, rarely invest in expensive, new machinery and equipment, whereas often buy agricultural equipment which is usually refurbished, used, western, if only relatively cheap and useful for their farms.

This also applies to vehicles. Approximately 22 million registered vehicles use Polish roads, including approximately 16.5 million passenger cars (which constitutes 75% of all motor vehicles) and about 2.7 million trucks (which constitutes 12.7%), with an estimation that an average age of these vehicles in Poland exceeds 11, and 79% are vehicles more than five years old [4].

Significant exploitation of machines and technical equipment entails increased frequency, ex-tent and cost of repairs. In the structure of repair costs, the cost of spare parts occupies a significant position – these parts may constitute up to 70% of the total cost of repairs.

One solution to limit the cost of repairs is regeneration, which means restoring performance features characteristic of (typical of) new components to the old ones. This is achieved through using appropriate regeneration technologies, and, in case of units, through the application of brand new and previously regenerated components in the process of repair. Renovation (repair), in conjunction with the regeneration of worn components and replaceable units is indeed necessary with reference to machines still in use, whose production is suspended due to the fact that the lack of components is often the cause of premature elimination from the operation of machinery that could still work effectively.

The problem of the regeneration of components was noticed in Poland in the years 1965– 1970, mainly due to the needs of agriculture. The organization of regeneration of components and renewal of the replaceable units was based on a system of command economy and was subordinate to the central economy management by the Central Planning Office and relevant departmental ministries. In accordance with recommendations of superior units (Central Planning Office, departmental ministries etc.) a network (system) of units responsible for regeneration of compo-nents and restoration of damaged units was created. This system was highly uneconomical and unprofitable for the parties involved, and it finally shut down its operations at the end of the eighties.

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In the system of market economy, the problem of regeneration of components and units is rarely mentioned in literature worldwide, which does not mean that other countries do not deal with issues of recovery of components and units for regeneration. The reason is that the aim of manufacturers in these countries is to high quality of manufactured machinery and equipment, low operating costs and environmentally friendly methods of managing used (scrapped) objects pro-duced by them [5.10].

Functioning systems of repair and regeneration Organization in Western Europe based on ex-isting objects (manufacturer, trade, etc.) that are owned by private entities, acting in market economy, and carry out regeneration as something quite natural and viable from an economic point of view. In Western countries, problems related to regeneration of components and renewal of machinery and equipment are dealt with on an ongoing basis by original equipment manufacturers, for whom the most important issue is the low price of products, full range of spare parts (including cheaper – regenerated), low operating costs (including repairs), high quality, reliability, functional-ity and aesthetics of their products.

Original equipment manufacturers organize and supervise the operation of a system based mainly on a well equipped network with professional service, factory service repair points and a network of commercial dealers.

Constant development of various regeneration methods and organization forms of the renova-tion process leads to:

¾ the reduction of the level of expenditure incurred on machinery repairs, and, simultaneously, the reduction of their operating costs,

¾ the extension of durability and reliability of regenerated components,

¾ the reduction of demand for expensive new replacement components and units,

¾ saving drastically decreasing raw materials, and thus recycling damaged components, which has a beneficial effect on the environment.

The cost of regeneration of machine parts [2, 3, 5] constitutes 30–60% of the cost of produc-ing new components, especially when the renewal process is carried out with industrial methods in specialized renovation plants.

This stems from the essence of the regeneration process because the technologies used in this process require much smaller volumes of material and energy as compared to technologies of production of new components.

In addition to the economic aspect, the regeneration of vehicles, machinery and equipment should also be considered in terms of compliance with EU standards for environmental protection, since regeneration positively influences the protection of natural resources (metal ores, energy, etc.), environmental degradation during their extraction (mining damage) and processing into finished products and consumer products.

Restoring characteristic performance features characteristic of new components to the used ones is achieved through the application of appropriate regeneration technologies, and in case of units, through the use of the brand new and previously regenerated parts in the repair process.

The study in terms of cost of regeneration of components with division into costs of material, electricity and labour shows that these costs are as follows [4,10,11]:

– indicator of material consumption = 1 – 3%, – indicator of electricity consumption = 4 – 10%, – indicator of labour cost = 23 – 40%.

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Despite its undoubted benefits, the regeneration of components and renewal of units has never been sufficiently appreciated in the national economy, although the demand for such services continues to grow.

According to the research conducted by NOT Czestochowa on the demand for services related to regeneration in equipment and transport companies, textile factories, food management compa-nies and cooperatives, approximately 43 thousand components with cylindrical surfaces and 16 thousand components requiring the regeneration of their surfaces have to be regenerated each year [9]. In the shipbuilding industry, it is estimated that the annual need for regeneration includes over 8.000 various items of machinery and equipment with a total weight of approximately 3 thousand tons, and the execution of this regeneration program requires an effort of approximately 500 thousand hours of labour. As an example, the savings thanks to the regeneration of a single bush of ship's engine are approximately 7 thousand dollars, which represents 35% of the value of a new bush, and the regeneration of a polymerization vessel for the production of polyvinyl chloride in the company Anwil Wloclawek represents 10% of the cost of purchasing a brand new tank [4]. The use of regenerated components and renewed units in other sectors of economy, such as min-ing, transportation, communication, etc. can pose a significant challenge.

Low utilization of regeneration stems mainly from:

– ineffectiveness of buying up used components suitable for regeneration,

– regeneration of components is a more complex and complicated activity area than their produc-tion,

– the lack of preference distinguishing it from other business activities causes its reduction, with preference on production,

– the lack of a steady flow of highly qualified professional staff in the field of regeneration, – deficiencies of fully operating and expensive moulders, machines for applying a regenerated

layer, equipment for metalworking etc.,

– improper supply of materials for the conduct of regeneration,

– the lack of support in selecting the regeneration method with the help of computer programs. In order to change the situation, the following should be undertaken:

– increasing the effectiveness of regeneration,

– extending the assortment of components for regeneration,

– implementing new, hitherto unfamiliar methods and technologies of regeneration, – using virtual technique to choose the most appropriate regeneration method, – automation and mechanization of technological processes of regeneration, – development of other forms of regeneration organization,

– introducing proper economic mechanisms stimulating regeneration development to enterprises. The working conditions of both the automotive and machinery parts are very diverse; materi-als, of which they are manufactured, as well, hence the practical need for diversity of regeneration technology. In addition, even in many cases there is a possibility of regeneration of two or more times [8], and every subsequent regeneration does not necessarily have to be carried out in the same manner as the previous one. Its conduct, from the technical point of view, is possible, but a prerequisite is that the elements after the regeneration keep their original functionality, unless there has been a re-classification of an item or product after the regeneration (i.e. a higher or lower class), or some changes have been introduced to the original function.

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life. Fatigue life of a new structural element NCmust at least correspond to the period of operation of an object to the first overhaul

1 p

N

: 1 p c

N

N ≥

(2) Primary regeneration of a structural element, for obvious reasons, makes sense if the supply of fatigue life

N

p

2 after regeneration enables element operation in the whole second repair-to-repair

period NMN: MN p

N

N

2

(3) so 1 2 C p p

N

N

N

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Assuming that the object operation periods between major repairs are the same, one can speci-fy the overall dependence on the supply of endurance for more than one regeneration:

1 1 C p p

N

nN

N

n+

(5) where: n – times of regeneration

Regeneration processes generally affect the durability of the regenerated part. This impact may be taken into account by inserting to the relationship Np2 constituent

N

R1:

1 1

2 C p R

p

N

N

N

N

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Extensive literature on the subject regarding the value of NR in relation to the overall durabil-ity of an element allows to describe the following:

NR= kNC (7)

where:

k – coefficient depending on the method of regeneration, k > 0 – for regeneration methods reducing the fatigue life,

k = 0 – for regeneration methods not influencing fatigue properties of an element, k < 0 – for methods of technological processes of regeneration increasing fatigue

properties of an element. After insertion, we obtain:

C p C p

N

N

k

N

N

1 1 2

(8) C C p p C p

N

N

N

k

N

k

N

N

1 2 2 1 3

(9) where:

k1, k2 – coefficients for subsequent regeneration.

Assuming that k1 = k2 = k and

2 1 p p

N

N

=

C p C p

N

N

kN

N

2

2

1 3

(10) and generally: C p C p

N

nN

nkN

N

n+1

1

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after transformation C p p C

kN

N

N

N

n

+

1 1 (12) where n is an acceptable number of regeneration times due to the fatigue life of an item. The above-mentioned formula determines how many times a given component can be regenerated, despite the restrictions resulting from the action of dynamic loads, maintaining the required re-serve of durability. If the value n is lower than 1, the regeneration of components should not be performed.

The fatigue life is determined by material properties and the nature of operation loads. The analysis of the structure in terms of fatigue life is important in solving the possibility of regenera-tion in general, and, in particular, the possibility of multiple regeneraregenera-tion. If you know the "history" of a component and its conditions of loading, and, in case of many technical objects such is the case, most of the components designed for regeneration are targeted at well-defined repair (usually the main one), and after a specific course (hours of work, expectancy, km course, etc.). The nature of the load depends on a variety of operating conditions, and its value (i.e. in units of stress) depends on the construction of an element (geometry, materials, dynamic). Knowing the history of operation of a component and its loading conditions, in the analysis one can apply classical methods with the use of the Wöhler, Smith and Haigh diagrams, taking advantage of the possibility to replace the existing load amplitudes during the operation period with one amplitude value called replacing Saz determined on the basis of operational load spectrum in conjunction with the fatigue curve or equivalent Sar designated on the basis of the equation of the fatigue curve and fatigue damage summation hypothesis. Statistical descriptions of the distribution of average values and amplitudes of random loads for various technical objects known from literature can be used here.

3. Basic assumptions of the advisory program for the selection of method of machine component regeneration

The purposefulness of regeneration use does not require justification. One problem, however, is to establish a reasonable scope for its application (Fig. 1). The decision to regenerate should be based on a profound analysis of the economic, operational, technical, technological, organization-al, and accidental (specific) criteria.

Each of these criteria contains many specific features which affect its limit value. One should aim at ensuring that all criteria features are described with nominal values. This is of course difficult and requires significant effort, but in terms of overall benefits, the creation of a data bank is most reasonable. A data bank with open structure of an open (permanently supplemented) may serve as a basis for a computer program supporting the decision on regeneration, but also identify-ing specific technical and technological regeneration solution..

In the process of making a decision about the method of regeneration of a machine element, it is important for the decision to be optimal. Determining an optimal decision is based on the selection, from a set of feasible solutions using a specific algorithm, of such a decision which takes an extreme value. Considerations are carried out on the basis of knowledge about an object and way to control it in the form of tasks defining object properties. If such a set of tasks is accurate

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and complies with certain rules, it can be used to build a computer program imitating an expert action that is a decision support system (DSS).

Where it is necessary to quickly process large amounts of data or a decision problem is associ-ated with the use of complex computational models, the computer prompts possible solution options to the decision maker (man), so that he could make a final decision.

The term "expert system" can be applied to any system that on the basis of detailed knowledge can draw conclusions and make decisions, acting in a manner similar to the human reasoning process. At this "stage of technological development", an expert system is a computer program that performs complex tasks of high intellectual requirements and does it so well as a man who is an expert in this area (Table 3). They are unique since they use extensive knowledge in the form of facts and practices (Fig. 2) acquired from a real expert [6].

Expert systems with their origin go back to the first artificial intelligence systems created in the sixties and seventies to tackle problems from a variety of fields. An overall objective of these systems is to collect and use their own knowledge (factual and procedural) for solving decision problems poorly structured or unstructured [7].

SWD systems facilitate the individual or group decision making process (Fig. 3), at the same time showing a rapid response to user queries, considerable content-related flexibility, adaptation to the individual style of decision-making by the user and the ability to adapt to changing internal and external conditions. An important issue is the fact that the SWDs only support and not replace the user in the decision-making process.

To begin creating an advisory system (SD), first answers to at least two questions have to be found: whether the construction of SD is well founded? and whether it is at all possible? If the answers to the questions are positive – you can proceed to the next creative stage that is to define what the task system. It then proceeds to build knowledge bases, i.e. the acquisition of knowledge from experts in the field. At this stage the method of knowledge management and tools to build the system are selected.

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Figure 1. Factors conditioning the effectiveness of machine component regeneration Source: Elaborated based upon [10].

Table 3. Types of export systems depending on conducted tasks

Category Tasks conducted by export systems

INTERPRETATIVE deduce situation description on the basis of observation or sensor condition, i.e. speech, image and data structure recognition.

PREDICTIVE conclude about the future on the basis of a given situation, such as weather forecast, disease development.

DIAGNOSTIC determine system failures on the basis of observation, i.e. medicine, electronics, mechanics.

COMPLETION configure objects in limitation conditions, i.e. computer system configuration. PLANNING start actions in order to achieve their objectives, i.e. robot actions. MONITORING compare observations with limitations, i.e. in nuclear power plants, medicine, traffic.

CONTROL control system behaviour; include interpretation, predication, repair and monitoring of object behaviour.

IMPROVEMENT give action guidelines in case of bad object functioning. REPAIR make schedules of actions while repairing damaged objects.

INSTRUCTION training system for students.

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Figure 2. Export system structure Source: Elaborated based upon [13].

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Figure 3. Scheme of knowledge management in SD Source: Elaborated based upon [1].

The analysis of the state of knowledge conducted above indicates that the construction of an advisory system is a time-consuming process, but from the benefit perspective essential in support-ing the decision-maksupport-ing process by a technologist.

Actually, the realization of an algorithm to create an information and decision-making system intended to assist a technologist in selecting the method of regeneration of machine parts, both in industry and scientific research, will help achieve the assumed objective of the work.

The objectives of this system are as follows: ¾ expertise in diagnosing component wear, ¾ expertise in regeneration technology,

¾ indication of literature sources on regeneration, ¾ marketing of regenerated elements (in the future).

System architecture should be open architecture. It will include a group of subsystems dynam-ically merging with each other in a kind of specific structure. They include the following:

¾ databases,

¾ information on cases, ¾ collections of rules, ¾ expert systems.

Databases including the following will be created: ¾ information collection embracing:

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- quantitative and qualitative wear of machine components (vehicles in particular) - directories of physicochemical and technological properties of machinery parts, - directories of physicochemical and technological properties of regenerative materials, - machine component regeneration techniques and methods,

- directories of machines and equipment applied in regeneration, - directories of supportive equipment,

- research methods of regenerated elements, - supplementary materials.

¾ summaries of articles from Polish and foreign journals on the renovation of machine compo-nents.

To build a knowledge base, it is proposed to use software package for the construction of ex-pert systems PC-Shell by AITECH.

4. Conclusions

Widely conducted operational tests show that while using the equipment intensive processes, mainly of tribological wear, affect approximately 20% of the range of all parts of a final product. It is technically and economically justified to conduct regeneration of approximately 65% of these parts, which constitutes approximately 15% of all components of a final product.

The analysis of organizational systems of repair and regeneration of spare parts shows that: – there is an indisputable need for a new model of system for the organization of regeneration and renewal of components and replaceable units,

– designed model of the system must be strictly based on the principles of market economy, taking into account the economic viability of each cell of the system (manufacturer, operator, retailer, etc.),

– in order to minimize expenditures related to the organization of individual objects of the sys-tem – the designed syssys-tem should make full use of existing and emerging infrastructure (repair shops, commercial distribution network, the Internet, etc.).

The purposefulness of regeneration is evident – it only requires to establish its rational appli-cation. Each regenerated element has different requirements as to quality, properties and technical parameters, which causes trouble with the selection of an optimal method of regeneration. It is therefore necessary to use computer technologies that enable rapid and accurate analysis of multi-ple data.

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[1] Bałuch H., Konieczno budowy systemu monitorowania szyn, Materiały Seminarium: „Diagnostyka nawierzchni szynowych”, Politechnika Gdaska, Gdask-Jurata, 2004.

[2] Grze Z., Metoda aktualizacji wska nika kosztów napraw maszyn rolniczych nowej genera-cji, Problemy Inynierii Rolniczej, nr 3 (2005).

[3] Grze Z., Rze nik C., Badania porównawcze metod szacowania wartoci eksploatowanych maszyn rolniczych, Inynieria Rolnicza, nr 13 (2001) s. 156–160.

[4] Jazdon A., Przybyliski B., Wybrane zagadnienia z zakresu recyrkulacji i regeneracji ele-mentów samochodów wykonanych z tworzyw sztucznych, Materiały V Midzynarodowej Konferencji Naukowo-Technicznej „PROBLEMY RECYKLINGU”. Wydział Inynierii Produkcji Szkoły Głównej Gospodarstwa Wiejskiego, Polskie Towarzystwo Recyklingu, Warszawa, wrzesie 2007, s. 180–187.

[5] Muzalewski A., Koszty eksploatacji maszyn, IBMER, Warszawa 2000.

[6] Ociepka P., wider J., Współczesne systemy doradcze do wspomagania projektowania maszyn, Wydawnictwa Politechniki l skiej, 2007.

[7] Pokojski J., Systemy doradcze w projektowaniu maszyn, WNT, Warszawa, 2005.

[8] Przybyliski B.: Regeneracja wielokrotna a trwało  zmczeniowa. Materiały Konferencji „REGENERACJA ‘98”. OW SIMP Bydgoszcz, Wydział Mechaniczny ATR, Borów-no/Bydgoszczy, czerwiec, 1998, s. 179–187.

[9] Tomczyk W., System regeneracji – tak, ale jak go zorganizowa? Technika Rolnicza-Ogrodnicza-Le na, nr 2 (2004).

[10] Tomczyk W., Efektywno regeneracji czci maszyn w aspekcie ochrony rodowiska, Jour-nal of Research and Applications in Agricultural Engineering, Vol. 52(2) (2007)

[11] Wojdak J., Sdłak P., Oszczdno energii w procesach regeneracji czci maszyn, Inynieria Rolnicza, nr 5 (1999).

[12] Wójcicki Z., Szeptycki A., Prognoza przemian w motoryzacji polskiego rolnictwa, Technika Rolnicza-Ogrodnicza-Le na, nr 1 (2003).

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UWARUNKOWANIA ODNOWY ZUĩYTYCH ELEMENTÓW MASZYN I URZĄDZEē

Streszczenie

W artykule przedstawiono problem kosztów eksploatacji maszyn i urzdze zwizany z kosztami ich obsługiwania. Wykazano, i głównym składnikiem kosztów eksploatacji s koszty napraw. Jednym z rozwiza ograniczajcym koszty napraw maszyn i urzdze jest regeneracja, któr oprócz aspektów ekonomicznych naley rozpatrywa take w aspekcie ekologicznym. Mimo niewtpliwych korzyci, regene-racja czci nie jest dostatecznie doceniana w gospodarce narodowej. Jedn z przyczyn jest brak wsparcia wyboru metody regeneracji za pomoc programów komputerowych.

Słowa kluczowe: elementy maszyn, zuycie, naprawa, regeneracja, system wspomagania decyzji

Bolesław Przybyliski

Department of Working Machines and Vehicles Machine Exploitation and Transport Institute Faculty of Mechanical Engineering

Cytaty

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