From meeting safety and production goals to selecting the right machines, transfer station managers and operator should consider each piece of the equation.
By Clay Layne
We all know that transfer station applications are harsh and challenging. Trying to meet safety, production and efficiency goals while keeping costs low, confronts transfer station managers and operators every day. Not only do operators need to use efficient best practices, but selecting the right machine will also allow transfer station managers and operators to achieve these goals.
Safety
As one of the harshest environments people and machines can work in, waste applications have inherent safety risks. For transfer stations, it is all about garbage in and garbage out. To put it in context, a transfer station is extremely busy, with very little margin for error. Most transfer stations are inside buildings that are cramped, have poor lighting, slick floors, and do not forget all the inbound/outbound vehicles and foot traffic. Therefore, safety is the most important thought process from beginning to end of shift.
Machine Selection
Selecting the right machine is just as important as efficient best practices. Knowing the answers to the following questions will point us in the right direction to select the right machine for the transfer station:
1. What type of work cycles will be performed/percent of time at each work cycle?
- Unloading
- Stockpiling
- Sorting/separating
- Loading
- Cleaning
2. What type of material will be handled/percent of time?
- MSW (Municipal solid waste)
- C & D (Construction and demolition)
- Green waste
3. How much inbound tonnage is handled per hour/day/week?
4. How much outbound tonnage is handled per hour/day/week?
5. How is the outbound material loaded?
- Same level—truck sideboard height? Is tamping required?
- Half separation—reach required? Tamping required?
- Full separation or below grade—Hole size? Tamping required?
6. What are the peak times and how much tonnage is moved during that time?
7. Does the floor need to be cleared of materials at the end of the shift/day?
8. Are there building restrictions (low ceilings, pillars, etc.)?
9. What are the underfoot conditions (level, sloped, slick, dry, etc.)?
10. Do you anticipate growing your production over the next several years? If so, how much?
11. What are the biggest safety concerns?
Photos courtesy of Caterpillar.
Tire Spin
Let’s get right to the point. One of the highest costs in these applications, besides operator and fuel, is tire cost. With the combination of slick floor, rough floor, bucket contact with the floor, and loads of different materials that cause friction, you cannot help but sometimes spin the tires. Depending on the tire, especially the hard rubber that most transfer station customers use, they can be upwards of $40,000+ per set. I have seen tires being wore down to replacement level in 900 hours. What are best practices that can get us from 900 hours to 3,000+ hours before having to buy another set? Purchase machines that have either a computer-aided traction control, manual traction control or computer-aided rim pull control for the wheels. These systems help the operator lower tire spin and keep traction. Train your operators that once they start to spin, adding more power does not help them. Adding more power is a common fallacy and adds more spin. Experienced operators will back off power to gain traction and keep themselves engaged with the waste they are handling. Some operators will take a mattress or green waste and ‘sweep’ the floor to try to dry the floor out. Other operators will make ‘cleaning’ runs with their buckets (flat as possible) about every third or fourth push. (Note: tilting the bucket at a 30 to 45-degree angle to clean the floor or push might get desired results, but it adds friction to the floor, spins tires, uses more fuel, wears floors and the cutting edge quickly.)
Pushing Material
Best practices in pushing material are simple. Take as much as you can without spinning tires or losing material around the edges. This is not easy with floors that get really slick after the many types of garbage and liquids that are dumped on the floor. Some of the best operators engage the pile of waste to be pushed with a flat bucket on the ground. Once they make good contact, they will raise their bucket about a half to one inch to clear the floor and “slide” the load. This technique helps prevent friction, wheel spin and lowers fuel burn. Pushing in straight lines is a must since the wheels and tractive capability of the machine are in line, which is the strongest power to the ground. Trying to push something while arced only adds to fuel burn, tire spin and damage to the machine with less production.
One last item—have your operators be aware of what we call favorite side turns or ‘forced’ turns. In transfer stations, sometimes operators must always turn a certain direction to stockpile or load haul vehicles, or they prefer to turn a specific way. This practice wears out tires, cutting edges, center pins in wheel loaders. Push straight, slide the load, govern your wheel spin, taking only as much as the bucket can push without losing material—these are all part of efficient push techniques. In excavators/wheeled excavators, favorite sides keep the machine turning through the same arc, which could wear swing bearings unevenly.
Stockpiling Material
Stockpiling material effectively is an art that many operators have a hard time mastering. Most of the time they are under pressure to get the material in, stockpiled and back out again. They either do not have time to handle the material correctly or do not take the time to do it correctly. Sometimes the building configuration or capacity does not lend to adequate storage of material especially if something goes wrong with outbound haul vehicles. Operators must stack the material as high and as safely as they can. Climbing the pile with the machine is not an option. This leads to incorporation of material into the machine no matter how well it is guarded and could eventually lead to a possible rollover. Operators that know and use best practices will leave one or two loads at the foot of the stockpile and then push them up with the next load sliding material higher on to the stockpile. Another method would be to push up as high as the machine can and as the operator dumps the load, they will make a slight indention in the waste with their bucket to push the next load into. Operators do need to be careful when pushing with lift arms extended as high as they can with a full bucket. No matter whose machine or bucket, material could fall over the waste rack and crawl down the lift arms and cylinder, and make contact the cab and glass.
Loading: Haul Vehicles, Conveyors
All of the previously mentioned brings us to the inevitable—stockpiled material must go back out the door and travel to the landfill. First, let’s start with sorting before loading. Having the right tool on the end of the wheel loader or excavator/wheeled excavator to sort reject material is vital. Sorting grapples and grapple buckets are the best for machines to quickly grab, pull, carry and reject unwanted material. Whether it is sorting cardboard or metals prior to loadout in a transfer station, operators need to be alert and understand how to use the tools at their disposal.
Best practices for loading outbound haul vehicles in a transfer station depend on the type of load out for which the building is designed. Below grade or tunnel loading means that the haul vehicle is below the grade the machine is on. Pushing in straight lines, sliding the load, pre-staging material in front of the pit prior to the next haul vehicle—are all efficient practices. For a haul vehicle that is half above/half below the level of the load machine, having the pile close by, loading the bucket as full as possible without spillage, (the bucket can only hold so much) running short distances, making as few turns and wheel revolutions are all good practices. For haul vehicles on the same level as the loadout machine, (this is the most inefficient) operators need to make sure that their stockpile is close, keep distances short, do not overfill buckets and keep straight when approaching the haul vehicle.
Tamping
Every transfer station operator wants to achieve “full rated loads” with outbound haul vehicles. To achieve a fully rated load, most
operators will ‘tamp’ the load for two reasons: 1) To gain as much weight outbound a possible, and 2) To keep the load top flat/level so that the load can be tarped safely. The bottom line is if you must tamp, be square with the haul vehicle so you do not put side loads into your machine or haul vehicle. Do not raise tires or track off the floor. By using that much hydraulic power, you add pressure past the design point of the structures of any machine. Eventually, something will fail. Observe how long you are tamping. Keep tamp time short. With an excavator or wheeled excavator, tamp in layers. This will help you gain max load weight. Try to leave the haul vehicle in one piece. Be cognizant of the amount of pressure you are putting downward into the haul vehicle (do not flex, push or pull sides). One last point, if you have the material and capacity to achieve fully rated loads without tamping, then perform a test of weights with tamping or not tamping loads. You might be surprised at the slight amount of weight you gain for the fuel and stress on the machine you use.
At the End of the Day
Best practices for transfer station operations are simple:
1. Safety first. Include the whole team and make everyone accountable.
2. One of your highest costs is tires. Monitor tire spin and train your operators on machine systems and ways to keep spin to a minimum.
3. Proper push and stockpiling techniques will increase production and efficiencies while keeping maintenance, fuel and floor costs low.
4. Whether loading haul vehicles, hoppers or conveyors, using proper sorting, fluffing and outbound loading techniques assures lower costs and helps meet production goals.
5. Use proper tamping techniques without raising the machine off the ground. Most of all, find out if the amount of time you tamp justifies the slight amount of weight increase that might take place. | WA
Clay Layne is the Waste Application Specialist with Caterpillar (Peoria, IL). He started working for Caterpillar in 2008 as an
operator at the Peoria Proving Grounds working with engineers on the Research and Development of Caterpillar Machinery. In 2011, Clay moved to the Edwards Demonstration and Learning Center. It was here that Clay started working in the Waste Industry, conducting onsite operator training for Caterpillar customers all over the world. Clay can be reached at (309) 675-8486 or e-mail l[email protected].