Johansson gauge blocks (‘Jo blocks’) are made of steel and used for precision length measurement. Their surface is very smooth, and two blocks can adhere to each other; however, strong adhesion occurs only after sliding (wringing). Various hypotheses explaining wringing and adhesion mechanisms in the blocks have been suggested in the literature, including the role of intermolecular forces, oil surface tension and air pressure. The authors study the frictional sliding of two Jo blocks against each other to obtain insights into the mechanisms of wringing. The results show an increase in the friction force with the sliding distance, which is consistent with the removal of the oxide film from the steel surface by wringing. This is likely the dominant mechanism of Jo block adhesion.

中文翻译：

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Johansson 量块的摩擦和粘附

Johansson 量块（“Jo 块”）由钢制成，用于精确长度测量。它们的表面非常光滑，两块可以相互粘附；但是，只有在滑动（拧干）后才会发生强粘附。文献中提出了各种解释块中挤压和粘附机制的假设，包括分子间力、油表面张力和气压的作用。作者研究了两个 Jo 块相互之间的摩擦滑动，以深入了解拧干的机制。结果表明摩擦力随着滑动距离的增加而增加，这与通过拧干从钢表面去除氧化膜是一致的。这可能是 Jo 块粘附的主要机制。