Rapid expansion of expandable rock bolts from Virsbo

SSAB’s expandable rock bolts (SSAB ERB) consist of a folded steel tube with an upper bushing and inflation bushing welded at each end of the tube.

This year there will be over 2 million rock bolts produced in Virsbo, which means a volume of some 14,000 tonnes of steel. The SSAB unit in Virsbo gets its coils from SSAB in Borlänge. Virsbo has its own slitting line to slit the coils. “We form a tube that at the same time is folded into an ERB profile. The next step is to cut the profiles to customized length and send them to the ERB machines to put on the bushings and weld the ERB bolt,” explains Production manager Jonas Löfberg at SSAB Special Steels.

Rapid growth

“We have seen very positive development and our products are winning a growing share of the market. More and more customers are seeing the benefits of our products. And it is great to see positive development here in Virsbo, where we developed and started producing these expandable rock bolts some 40 years ago,” says Virsbo Unit manager Hans Åkerblom at SSAB Special Steels.

 “There is still great potential in our sales of these products. One clear advantage over competitors is that our delivery performance is above 95%, clearly the highest in the market. Another clear advantage is sustainability. With SSAB’s environmentally friendly products, customers use only high pressure water to inflate, whereas competitors also use concrete or chemicals, etc.,” continues Åkerblom.

“Since we use SSAB steels to produce expandable rock bolts we know how our steel behaves and how to use it. We can be proud also of the best quality on the market. The main markets for the products are in North America, although there has recently been more and more activity, sales and interest in South America and Southern Europe. We have also major Finnish customers,” states Åkerblom.

FACT BOX

Reinforcement with ERB arrests crack formation and propagation. Reinforcing occurs by expanding i.e. hydroforming the bolt in the drilled hole with high water pressure against the drill hole wall. The expansion of the bolt creates a friction and interlocking anchor. There is immediate full-length support for faster excavation, no waiting for grouting to set and no chemicals needed, only water.

After drilling the hole, installation of expandable rock bolts requires a water pump to expand the bolt into the shape of the hole to create instant support. Installation is flexible to variations in drill hole diameter and other irregularities. Installation is clean and easy.

ERB requires extremely good elongation i.e. formability performance of the bolt. SSAB steels make it possible and make a huge difference for the end-user. This enables fast and reliable reinforcement, which is required as safety criteria increase.

Customer benefits using SSAB produced ERB

• Clean composition
• High quality raw material
• Consistent properties
• Energy-efficient steel production 
• QA systems and certificates
• Full chain customization possible
• Traceability through all processes