Winter start-up precautions for large mining equipment

December 13, 2013  |  Best Practices

Winter start-up precautions for large mining equipmentThis article is excerpted from VISTA's Silver Series training program, Heavy Equipment - Intro & Safety

Starting up large a mining machine in cold weather can place a lot of stress on its diesel engine and hydraulic system, if not done properly. Here are some helpful tips on how to bring a machine up to operating temperature after starting it. Doing so properly will help reduce maintenance costs and extend machine life.

Pre-use inspection: A must for safety

Before starting up any piece of mining equipment, in hot or cold weather, you should always conduct a thorough pre-use walk-around inspection to make sure everything is in good working order. This is especially true of the fluid levels. Be sure there are no personnel on or around the machine before starting it. Ensure that all controls are in their neutral positions, the parking brake is applied and any energy lock-out levers are in the locked position.

Starting your mining machine

So here we go; turn the master lockout or battery disconnect switch to the "on" or "energized" position. Then, while sitting in the operator's seat, turn the on-off switch to the on position. At this time, depending upon the machine, you will see and possibly hear the machine going through an electronic self test of on-board monitoring and control electronics. If it returns a failed condition or abnormal alarms, you must not attempt to start the machine. Contact your supervisor or dispatcher and arrange for a qualified maintenance person to troubleshoot the machine and monitoring system.

If the self test is successful, initiate the engine pre-heat system. Look for and confirm that the pre-heat indicator light is illuminated. Some machines may begin the pre-heat cycle automatically. On some machines, a set of sensors may control the need for pre-heating. Be sure to consult your machine's operator manual for details on starting.

While waiting for the pre-heat indicator light to go out, sound the horn while surveying the area immediately around the machine. This is a signal to anyone in the vicinity that you are about to start the machine. Wait for 5 to 10 seconds after sounding the horn and then turn the key to the start position.

Hold the key in the start position until the machine starts, then immediately release it to the on position. You must not continue to crank the starter once the engine has started because damage will occur. If the engine has not started after 20 seconds or so of cranking the starter, you must stop and let the starter cool for a minimum of 2 minutes before attempting to start the engine again. If the engine has not started after a second attempt contact your supervisor or field maintenance person and stand by for advice or instructions.

Increase engine temperature and RPM gradually

Once the machine's engine has started, you must take care to bring the operating temperature up slowly in cold weather. During those first several minutes, you need to monitor gauges and indicators; if something is not right within the engine, it is going to reveal itself via warning lights or gauges that show values that are out of the normal operating range.

When it is very cold there needs to be a balance between increasing engine temperature and increasing engine rpm. If it's kept too low, the engine will struggle to build internal heat. If rpm is increased too quickly, there can be uneven heating of the engine block, which can stress internal components. At these temperatures, trying to push the warming process too quickly is not good for the engine.

Diesel engine health

To understand why you must take extreme care when starting and warming your machine's diesel engine in cold weather, consider this: When you first turn over the engine, the fuel and air mixture in each piston chamber will only ignite when enough heat has been generated within it. That may take several minutes, because the heat generated by compression is at first sucked up by the other nearby engine parts. Some modern diesel engines use glow plugs or pre-heaters to create the heat needed to support combustion.

The first combustion event will occur in each cylinder at different times. At first, the engine will run very rough and a large amount of unburned fuel will go up the exhaust stack as black smoke. The cylinders that are firing slowly begin to warm up the engine block around them, and eventually the other cylinders will begin firing. During this time, you must not let off on the starter too soon. If you do so, the engine won't continue cycling. But if you hold the starter down too long, you will be placing unnecessary wear on the starter motor.

A diesel engine will only run smooth and efficiently after all engine components have reached a minimum block temperature and even then it is not at its best. When a machine has been sitting at -25 degrees F it takes a lot of tender loving care to get it up to operating temperature. All components need to be properly warmed and that takes time. The engine will warm first and with it, the engine oil as it circulates. A cold running engine is doing so under duress as cold metal parts will expand as they warm. That is why the operator must keep the engine speed low to start with and then slowly increase the engine speed to about one-third of full rpm. That should take many minutes and the larger the engine the longer it should take.

However, a diesel engine will not warm properly even at one third throttle without a bit of work to continue the process. Move the machine slowly forward and backward in a straight line, but don't perform any work yet. When you move the machine, it must be done with care as every other part of the machine is still at the frigid ambient temperature; the transmission, final drives and drive shafts, bearings, various oils and lubricants, seals, and so on must also be slowly warmed through movement

One thing to remember about diesel engines: They do not take kindly to running slow and cold. An engine running slow and cold does not burn fuel cleanly. Not only does this cause high levels of emissions from unburned fuel, but it can also cause carbon deposits in the engine and an accumulation of moisture and sludge in the engine oil. Neither condition bodes well for engine economy or long-term health.

Warming the rest of the machine

No matter what the ambient temperature was when you started the engine, the coolant temperature gauge will soon begin to move up. Generally, the gauge will stay below the operating range, unless the machine gets a bit of work to do. So now is the time to increase the engine rpm to about 50 percent and begin warming the rest of the machine. Start by warming the hydraulic and drive systems; doing so will speed the warming of the engine and prepare the rest of the machine for work.

Warming up the hydraulics

When warming hydraulics, always start with the smallest cylinder or lowest-volume function first. There is usually less stress when working with smaller components. When it comes to warming hydraulic oil, one device that can help is the overpressure relief valve. Hydraulic pumps are capable of generating enormous pressure, enough to break cylinder components. When pump pressure is applied to a hydraulic cylinder and the cylinder rod travels to the end of its stroke, something has to give. The overpressure relief valve provides a way to release that built-up pressure.

On larger machines, you will probably find relief valves that are set to by-pass at pressures of 2,500 psi to 3,500 psi. When that amount of pressure by-passes through an orifice there is a lot of heat generated. The downside is that the heat generated stays quite local; it does not circulate to any great extent.

Warm the hydraulic oil carefully

Use this technique to warm hydraulic oil quickly, but be careful on two fronts: First, bypassing the overpressure relief valve requires the cylinder rod to be moved to the end of its stroke. If that is not done with care, serious damage to the rod end and piston can result. Second, oil forced through the relief valve gets very hot very quickly.

To properly use this technique, do not slam the cylinder rod and piston against either end of its stroke. Also, the cylinder must not be held in an overpressure bypass condition for more than 3 seconds, or damage may occur. Hold the cylinder in bypass for 3 seconds at one end of its stroke. Then move the cylinder rod move to the other end of its stroke and hold it there for 3 seconds. Repeat these steps several times, which will warm and circulate oil in the general vicinity of the cylinders and in the hoses going to them.

Move to the hydraulic circuit that controls the next largest set of cylinders and perform the same set of warming exercises. As cylinders get larger, the volume of oil increases and the time required to warm that circuit also increases. Continue the process until the largest cylinders have been warmed. A large face shovel like the ones used in mining has 13,000 liters (approximately 3,400 gallons) of hydraulic oil in its system. Warming this machine in the coldest temperatures may take hours.

Warm the hydraulic motors

Once all of the hydraulic cylinders have been exercised and warmed, it's time to turn your attention to warming the hydraulic motors that are used for swing and ground travel. The hydraulic motors on a typical face shovel have the task of moving an enormous mass of very cold metal. At extremely cold temperatures even metal becomes brittle and can break if subjected to too much strain. That's why you should proceed slowly and avoid hard or abrupt motions.

Slowly work up to full operating mode

When you feel that the machine is ready to be put to work, start out slow and easy and work up to a fully operational mode. Take it a bit easy at first. Listen and feel for the signals that the machine sends you. It will let you know when it is ready to work hard and to its full potential.

Related: Winter shut-down precautions for large mining equipment

Tags: mining

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