## 1 Introduction  
Maintenance, defined as the sum of activities to maintain and restore a technical system to specific qualitative conditions [1, 2], has a major influence on the profitability of production units, which has a significant impact on costs and operational safety. The importance of maintenance has increased with the achievement of high productivity through the development and implementation of strategies adapted to operating conditions, in particular those of technological equipment. The final objective of maintenance is to maintain and return to the initial operating conditions of the equipment in order to fulfill the functions for which it was created [3, 4]. At the same time, availability [5, 6] represents the degree or probability that a product can be used and is in good working order whenever it is required in time and space. It depends on two factors, namely reliability (being a function of uptime) and maintainability (being a function of downtime or repair). In view of the above, availability is considered to be the ability of equipment to perform its specified function at a given time or within a given time interval under the combined aspects of reliability, maintainability, and the organization of maintenance actions. In the concrete case of quarry technological equipment [7], for example, those from Bata, Arad, the analysis of the production flow regarding the critical areas from the point of view of maintenance revealed frequent production bottlenecks; the design of the maintenance program must respect both the interventions in accordance with the technical specifications of the manufacturers, as well as the conclusions of the analyses regarding the nature and cause of the interruptions in the production activity. The disadvantages of the method consist of maintaining, with high costs, stocks of parts with a high frequency of replacement due to wear [8,9]. In the Bata quarry, Arad County, basaltic rocks are extracted, processed, and sold, mainly intended for the construction of highways and railways but also for other civil works. The physical-petrographic characteristics of the basalt are presented in Table 1.  
The production process of the Bata quarry is carried out with mobile, semimobile, and fixed machinery, corresponding to the three production flows, as follows:  
* The primary rock crushing flow, composed of Sandvik CM1208i primary jaw crusher, Stockholm, Sweden (Figure 1), Liebherr 944 L excavator, Bulle, Switzerland (Figure 1), Volvo L220 E front loader, Gothenburg, Sweden (Figure 2);
* Secondary and tertiary rock crushing-sorting flow, consisting of Sandvik H4800 Secondary Crusher, Sandvik UH420 Tertiary Crusher, Chieftain 2100 Sorting Station, Volvo L220 E Front Loader;
* The rock loading-transport flow, consisting of excavator Caterpillar 345 CL and dumper Volvo A35D. The activity on the primary flow allows the crushing of raw stone at a size of 0-300 mm; a hydraulic back cup excavator and wheel loader carry out the loading and unloading of the crushed material, which is then transported to the secondary-tertiary crushing-sorting flow for temporary storage or loading into trucks for delivery. The machines that make up the primary crushing flow are mobile, a fact that requires the presence of a worker at each machine, both for their operation and for the execution of maintenance works, which are planned to be executed at the same time. The activity carried out on the secondary and tertiary crushing-sorting stream consists of crushing the broken stone of 0-200 mm to the size of 0-63 mm; a new crushing follows, as a result of which the sieves with dimensions of 0-25 mm are obtained, grouped into sizes of 0-4 mm, 4-8 mm, 8-16 mm, 16-25 mm. The Volvo L220 E wheeled front loader from the primary crushing stream is used to load the 0-200 mm crushed stone, and another front loader of the same type is used to load the finished products into trucks.