Compactor Redesign for Mining Applications

Rockford Engineering works closely with clients in the mining industry. One such client approached us with an issue regarding their hydraulic compactors which compress the mineral fines into sheets for further processing. Rockford designed and tested a solution at their Regina location, then delivered the units to the client’s site. The goal was to introduce an automated system focusing on increasing reliability, improving maintainability, and achieving a tighter, more accurate control of the operating pressure.

The Problem

Each compactor has (2) two rolls -one fixed and one floating. The floating roll has (2) two hydraulic cylinders that exert a force to compress the product as it passes between the rolls. Two different systems currently provide hydraulic pressure to the system, however, there are known reliability issues and relatively poor control of the operating pressure.

Existing System 1:

A pneumatically driven hydraulic pump is used to generate cylinder pressure –this allows compressed air to produce high-pressure hydraulic fluid. The hydraulic pressure is adjusted by setting a conventional knob-style pneumatic pressure regulator. There are also hydraulic relief valves and accumulators that protect the system in case of over-pressure spikes created from lumps of debris passing between the rolls.

Existing System 2:

An electric fixed displacement pump, submerged in a reservoir, is used to generate cylinder pressure. There are (2) two solenoid valves in the system – one functions as an orifice to bleed downstream pressure and the other functions as a dump valve which allows the system pressure to be rapidly lowered. A combination of both is used to control the system pressure. There is also a kick-down relief valve located near the cylinders to protect the system in the case of a significant overpressure condition.
The client approached Rockford Engineering to develop a practical solution that would accomplish the following:

1. Allow the pressure set-point to be maintained within a predictable and repeatable tolerance and be adjusted by the PLC control system.
2. Address the maintenance issue of increased wear on the electric motor and starter components caused by frequent motor starts.
3. Generate minimal heat, as the ambient conditions can be quite hot and reliable heat rejection is difficult in a potash mill environment.
4. Allow the system to reduce the pressure when no product is present, referred to as “park pressure”.
5. Develop a hydraulic system that is suitable in a mill environment in regards to cleanliness, maintainability, and ruggedness.

The Solution

For this solution, we considered the benefits of each existing system and coupled that with the latest technology in order to provide a practical solution. The high points of the new system design are as follows:

• Utilize the same pneumatic-over-hydraulic pumps due to their ability to maintain a constant pressure without generating heat.
• Incorporate an additional proportional pressure reducing / relieving valve with an integral pressure transducer to allow the downstream pressure to the compactor cylinders to be set from the PLC. The closed-loop PID operation allows for extremely accurate performance.
• Two additional accumulators will be added and set at a higher pre-charge pressure which will minimize pressure fluctuations during cylinder movement.
• A pressure filter would be located downstream of the hydraulic pump to protect the system against contaminants. The filter has a pressure switch so that a plugged filter condition will be visible in the PLC control system.
• A particulate and coalescing filter on the compressed air supply to protect the pneumatic-over-hydraulic pump will be added. These both have pressure switches to detect a plugged filter condition in the PLC control system.
• Incorporate a kick-down relief valve on the pump side to protect the circuit from over-pressure conditions. There is also a lockable ball valve to allow for maintenance operations and manual pull valves to bleed the pressure down.
• Add oil level and temperature monitors to detect low oil level or high-temperature conditions in the PLC control system.

Rockford worked closely with the client thought the design process, obtaining the concept and design approvals at key stages of the project life cycle. Final design & detailed production drawings were completed including general arrangements, detailed schematics, and weldments.

Eight units were completed and tested at Rockford’s facility in Regina.

Representatives from the client company were present during the factory acceptance testing and provided excellent feedback on the testing parameters, their expectations, and provided sign off prior to shipment.
The first unit has been put into production and the client is very pleased with the performance. It has allowed for a significant increase in stability and steady control of the operating pressure. The new system maintains the pressure within a tolerance approximately 20 times tighter than the previous system.

Work with Rockford

Rockford Engineering has specific expertise regarding custom hydraulic system design. Our engineers’ combination of both practical in-the-field experience and high-level hydraulics training makes us a perfect candidate for projects such as this.

Our in-depth understanding of complex hydraulic systems can be an asset in both greenfield and brownfield initiatives. Whether designing a new system for your specific application or analyzing an existing system for improvement and optimization, Rockford can help.

We cater to all industries in both mobile and plant environments – contact us today!