A series of double toggle jaw crushers were manufactured for a South African copper mine. The set of 4 crushers, to be installed 1250 m (4000') below the surface, were the largest jaw crushers ever manufactured in South Africa.

General arrangement for double toggle jaw crusher.

The crushers have operating capabilities from 350 to 500 m3/hr (11000 to 16000 ft3/hr) with opening dimensions of 2100 mm by 1680 mm (80" by 66"). This translates to more than 1 million tons of crushed rock per month per crusher.

Each crusher weighs approximately 250 tons and needed to be dismantled and moved underground in sections weighing less than 50 tons.

Mass of swing stock = 59 tons
Bearing size = 590 x 500 – 760 mm long (23" x 20" – 30")
2 bearings per swing jaw
Oscillation : 4 mm (0.16") @ 170 RPM

Initially the crusher manufacturer had considered bronze bearings for this application. The bronze bearings were manufactured and installed. However, during initial 24 hr tests various operational problems were identified. The bush and the shaft "picked up", the operation was noisy and there was excessive wear on the bearing.

Regular lubrication was provided to the bronze bearing by a dedicated lubrication system directly onto the bearing, but because the oscillation was so slight, the lubrication was not spread sufficiently to cover the bearing surface, resulting in high wear.

As a candidate to replace the bronze as the bearing on this crusher, Vesconite was put through a stringent evaluation process. This was necessary as the operation of the mine was critically dependent on the operation of the crusher, which in turn was dependent on its Vesconite bearings. Any stoppage of the crusher meant operation of this expensive plant came to a standstill.

The original grooving design for the bronze bearing was maintained as was the lubrication specification.

The Vesconite bearings were machined to the standard industrial specifications for Vesconite of size of interference fit and running clearance.

The bearing was installed by freezing with dry ice for 3-4 hours. This causes the bearing to shrink and overcomes the interference fit of 1.4 mm (0.06"). The bearing was then easily installed by sliding into the swing jaw.

The crusher with the Vesconite bearing was tested for 3 weeks. The following were noted when the shaft was removed for inspection after the test:

• The operation had been quiet
• There was no wear on the bush other than "bedding in" wear
• There was no wear on the shaft

The self-lubricating properties of Vesconite gave a successful operation even though the grease was not being spread across the whole bearing surface.

After more than 9 months of operation in the mine, the Vesconite bearings were still performing to requirements. Notably, even when steel that was caught in the ore fed into the crusher and damaged crusher parts, it did not damage the Vesconite bearing.

In addition to its long wear life performance advantage, the Vesconite bearings had the following advantages:

• Ease of installation - By freezing Vesconite with dry ice, installation does not require heavy equipment. Even if bearings have to be removed and replaced even on site 1250 m (4101') below the surface.
• Ease of removal (if required) without the need for heavy equipment. Bronze bearings need to be machined out of their housings. Vesconite can be removed by freezing or easy destructive methods.
• Ability to perform even if lubrication is temporarily suspended.
• The slightly larger running clearance and softer material than bronze gives the Vesconite bearing the ability to operate with a slight housing misalignment without the need to line bore the housing.

Vesconite is manufactured and stocked in the large bearing sizes required for the application.