A new shaft mucker design developed by Cementation and Mining Technologies International (MTI, now Joy Global) substantially reduced maintenance costs for Cementation and performed well on a shaft-sinking project at Resolution Copper, completed in 2014.

The new design, dubbed VSM 14, is an improvement on previously existing technology. Vertical shaft muckers have long, extendable booms that reach down to the shaft floor, with jaws on the end that pick up material and drop it in separate containers for removal. By strengthening the boom and downsizing the jaws, the new design reduces the stresses on the boom without losing operating speed.

Shaft muckers

The original vertical shaft mucking machine was invented in the late 1940s and began to be widespread in North American mines starting in the 1950s. Known as the Cryderman mucker, it was distinguished from other shaft muckers by its pneumatic cylinders and pneumatic telescoping boom. The boom is anchored to a galloway – a multi-stage platform in the shaft that supports equipment and personnel – and can reach down into the extremities of the shaft.

The original Cryderman design was adapted in different sizes. The largest version of this design quickly became popular in both Canada and the United States, but it was not used in Cementation’s work until 2005. (Cementation had used the original Cryderman design and another type of shaft mucker, called the cactus grab, usually more popular in South Africa.)

The machine that Cementation used while sinking the Main and Vent shafts at Xstrata’s (now Glencore’s) Nickel Rim South project in 2005 racked up enormous maintenance expenses for an otherwise successful project, according to Ryan Gough, manager of project services at Cementation Canada. “We spent an astronomical amount of money on spare parts,” he said. “It was in excess of $1 million.”

The biggest problems centred on the extendable boom. Several booms failed at the same spot, a transition zone where the inside diameter of the boom changed. If they did not fail, the booms had a tendency to bend, which prevented them from being retracted and required them to be replaced before mucking could resume.

“Generally the bent booms could be placed on a press and straightened,” said Gough, “but it obviously took considerable time to repair a boom and caused significant delays in the shaft.”

There were other problems as well: cracked jaws, centre pipe failures and dirt accumulating in the jaw cylinder shroud, which then damaged the cap and seals on the stationary boom.

In 2006 Gough approached the equipment manufacturer MTI about collaborating on a redesign. MTI had not built shaft muckers of this type but was willing to help find solutions. A design team met with Cementation’s project services engineers, as well as site operations and maintenance, with the objective of building a machine with higher reliability, lower maintenance costs and performance changes that would better suit Cementation’s requirements.

Most critically, the Cementation team proposed reducing the size of the jaws from about 70 centimetres to about 45 centimetres. That “would reduce the stress on the boom and hopefully reduce or eliminate bending of the extendable booms, failure of the extendable booms and cracking of the jaws,” Gough said.

VSM 14 design

From this process emerged the VSM 14. This machine has 45-centimetre jaws and the booms are made of higher-strength steel that can resist bending and breaking. The extendible boom tube was redesigned to have a constant cross section in the failure-prone area, thus eliminating the stress caused by the change in wall thickness. A new centre pipe design eliminates failures, a new jaw cylinder shroud prevents the buildup of debris and new leather cylinder packings are more tolerant of contamination in the air.

The VSM 14 also has an additional 24 inches of reach, which Gough explained is useful for two reasons: it can be used in larger-diameter shafts, and it can allow the boom to operate less than fully extended, which reduces likelihood of damage.

Two complete machines and two spare boom assemblies were delivered in spring 2007 and tested in the Inco (now Vale) Coleman exhaust shaft sinking project, which involved sinking a 21-foot diameter shaft to a depth of 4,371 feet. The machines performed beyond expectations.

“We did not have a single bent boom or boom failure,” said Gough. “Downtime on the machines was limited to the same operator-induced problems that accompany all of the various vertical shaft muckers, broken hoses and jaws cylinders damaged due to contact with the shaft wall.”

Despite the reduced jaw size, the actual mucking capacity of the VSM 14 was unchanged. Studies showed that the larger jaws were only half-full on average, so their size could be reduced while maintaining a capacity that would not affect production cycle times.

Cementation’s cost data proved that the new VSM had paid off. At the Coleman exhaust shaft, where the VSM 14 was first used, all items charged to the shaft mucker’s cost code totalled $204,507.95, which breaks down to $181.30 per metre or $1.30 per tonne. In contrast, the costs attributed to the mucker at the Nickel Rim vent shaft came to $460.50 per metre and $3.80 per tonne. The Nickel Rim main shaft had a cost per metre of $769.16 and a cost per tonne of $4.78. These figures include parts and rebuilds, but not labour or downtime losses.

The new design has become the standard shaft mucker for Cementation and has found other customers. MTI/Joy Global has sold 22 of the machines since they were developed. They have been used on shaft-sinking projects at the Resolution Copper mine in Arizona and the Lucky Friday mine in Idaho.