## 1 Introduction
[17], it was also shown that parameters _Ssk_ and _Sku_ could be used to predict the tribological behaviour of the surface, and that the higher _Sku_ values and more negative Ssk values led to lower friction, which allows for the appropriate design of the surface condition and the selection of an appropriate treatment method and parameter finishing. The authors of works [18; 19] came to the same conclusions, additionally stating that it is also possible to predict the wear volume surfaces using several other (_Spd_, _Std_, _Sz_, _Sdq_, _Spc_, and _Sk_) roughness parameters. On the other hand, according to the authors of paper [20], a strong relationship with the amount of wear has the parameters _Vvv_, _Sok_, _Spk_, _Sku_, _Sk_, and _Sq_ and according to work [21], such parameters as _Vvv_ and _Vvc_. Similarly, in ref. [22], it was noted that low values of the height parameters, negative skewness, and kurtosis greater than three are beneficial from the point of view of lubrication of the contact surfaces. The authors of work [23] arrived at a similar conclusion by stating that the values of Ssk < 0 and Sku > 0 indicate that the surface can be considered a good bearing surface. However, in ref. [24], an increase in the values of the _Sq_, _Ssk_, and _Sku_ parameters was found to increase wear and the occurrence of scuffing. The data presented in refs. [25; 26; 27; 28] indicate that in the case of friction couples, the importance of the texture of the cooperating surfaces is increasingly appreciated, and methods of its shaping are being developed. Additionally, the above-mentioned studies on sliding friction confirm the impact of non-standard texture parameters on the wear of mating surfaces. In most cases, the parameters _Ssk_ and _Sku_ (slope and kurtosis) are considered relevant. However, several others are taken into account depending on the type of friction, co-operating materials, lubrication conditions, etc., i.e., on the specifics (construction and working conditions) of a particular friction node, and here, opinions about the impact of individual parameters are varied. These tests were generally carried out for metal-metal friction pairs operating under the condition of unidirectional sliding friction. For the 317 Ti steel-graphite gland unit of control valves operating in a reciprocating motion, no such studies have been conducted to date. In an attempt to fill this gap, studies are described in this paper to determine which surface layer properties (especially roughness parameters) are important for this friction pair and to see if they can be obtained by sliding burnishing. This research can help predict and shape the tribological properties of stems to extend the life of valves. Grinding and polishing are the most common finishing methods used in valve stem manufacturing. They make it possible to obtain a very low surface roughness, but they leave impurities (which act as abrasive particles) on the treated surface, which causes the stems-gland pair to wear faster during operation. For small diameter stems, sometimes the above methods are replaced by turning [29], drawing, cold rolling, or ultrasonic surface rolling [30]. Drawing and cold rolling are the preferred techniques owing to their high processing output. However, they result in relatively high errors in shape, which are not favourable to the high sealing efficiency of the valves. The research results presented in refs. [3, 31, 32] indicate that in the case of parts with regular shapes (particularly small-diameter shafts), slide diamond burnishing may be the preferred machining technique. The principle of burnishing the valve stem is shown in Figure 2. It is a machining method kinematically similar to turning; however, a tool with a spherical diamond tip is used here instead of a turning tool. During operation, this tool slides (with pressure) over the treated surface, causing the surface layer to cold harden and smoothing out uneven surfaces.