For the Love of DD Washers

– The title best describes the relationship between me and DD washers, Vajala says about his interest in this demanding area of expertise.

His special expertise includes material development for seals, high-quality seal installations, developing operating conditions for seals, and solving operational problems with DD washers. In a pulp mill’s production process, the DD washer seal is a small component, but its importance to production reliability is significantly greater than its size. Juha Vajala simplifies the matter by stating that a DD washer lives or dies with its seals.

– If a seal is badly damaged, it can cause the DD washer to stop due to high torque, leading to an unplanned production shutdown. Therefore, seals are not just about the price of an individual wear part, but about the operational reliability of the entire pulp mill, he says.

High Demands on Seals

From the perspective of the seals, the operating principle of a DD washer involves a specific challenge: the drum rotates, but the seal remains stationary. This subjects the seal to continuous abrasive wear at temperatures near 100 degrees Celsius, and the friction itself generates heat. In addition, the seal must withstand the strong chemicals used in pulp manufacturing. Therefore, the seal must be extremely wear-resistant and chemical-resistant, but at the same time flexible enough to keep process chemicals and pulp fiber inside the DD washer under all operating conditions.

– The requirements placed on seals are quite fierce. That is the main reason why I originally got excited about the product development of DD washer seals, as I enjoy tough challenges.

Juha Vajala moved to working with DD washers in February 1997. Before that, he worked at the Olkiluoto nuclear power plant for a total of about 3 years, where he also completed his Master’s thesis on developing valve maintenance for the nuclear power plant.

– The time I started working with DD washers was really challenging. The production capacity of pulp mills had been increased, and much more was required from both DD washers and their seals. The seals should have developed at the same pace as the rest of the technology, or preferably been one step ahead, but that was not the case. Seal failures occurred monthly back then, causing extra production shutdowns for pulp mills. Fortunately, during the first couple of years when I was responsible for seal development, the situation was brought to a tolerable level quite rapidly through very quick measures and changes to the seals, their installation, and their operation in pulp mills.

Deep Expertise is Built Over a Long Time

The early experiences taught Vajala a principle he has followed ever since: seals should not be developed just for today's conditions; they must meet the requirements of the next developmental step. If a solution works today, it does not mean that development work can stop there.

PR Rolls’ experience with DD washers dates back to the 1980s with its predecessor, Pikoteknik Oy. Juha Vajala emphasizes PR Rolls' long history in DD washer services and product development, as deep expertise in a specific field is only born over years and decades. With Vajala joining, PR Rolls' expertise is strengthened across all stages of the seal lifecycle: material development, seal solution development, installation methods, personnel training, customer consultation, and analyzing and eliminating problems—often before they even arise.

In addition to strong expertise, Vajala was attracted to PR Rolls by the size of the company. According to him, PR Rolls is just the right size to be flexible and fast in decision-making, while being widely networked internationally. As a young man, Vajala feared that moving to this field would mean he could no longer travel abroad. This fear turned out to be groundless, as his duties have taken him and continue to take him to different parts of the world—everywhere where pulp mills exist.

– Seals cannot be developed just at an office desk. Working at the mills is an essential part of maintaining and developing expertise, allowing one to see, for example, how seals are installed and how they behave in real conditions, Juha Vajala emphasizes.

Juha Vajala brings decades of experience to PR Rolls in managing the entire lifecycle of DD washer seals.
Photo: Jorma Uusitalo