Maintenance/Management: Getting the right bite
| May 28, 2009 |
Anybody who has ever struggled to push a dull saw blade through a thick piece of wood knows how much more muscle power it takes when your tools aren’t sharp.
The same principle holds true for excavator and wheel loader bucket teeth. The wrong tooth or a blunt tooth forces you to burn more fuel and robs you of many buckets over the course of a day. When you have the power of a diesel engine and robust hydraulics providing the muscle for the digging you may not notice it much, but over time the wrong tooth hurts your productivity and profitability.
In their quest to continually improve the performance of machines, manufacturers are developing new tooth systems that penetrate well, stay sharper longer and offer tooth-to-adapter locking systems in which the retaining pins are installed from the top rather than the side, making them easier to change and more secure. Although the goals of these new tooth systems are similar, the design details vary considerably. So it behooves you to learn specifically how teeth affect productivity and how each of these new systems may meet your needs.
The impact of teeth
“If it doesn’t take as much force to push a bucket into the pile, then the loader or excavator doesn’t use as much fuel,” says Bob Klobnak, senior product consultant, Caterpillar marketing and product support division, ground engaging tools. “Those two things are directly related. It varies a lot depending on the material and in easy digging it may not make much difference, but in harder digging our customers have verified productivity and wear life increases with teeth that have a lower profile for easier penetration.”
In assessing different teeth you want to consider the balance between wear life and penetration, says Kirk Yoresen, marketing communications manager, engineered products, Esco. “You can make a tooth that will wear for a long time, but it may not be easy to push through the material. Some customers may have a material that is difficult to load and opt for penetration over wear life. Then another customer digging in the same material, but with a different machine or some other variable, may find wear life more important than penetration.” Wear life is often the most important trait in mines and big quarries when downtime is limited, he says.
New locking systems
With the advent of top-locking tooth systems, however, manufacturers were able to partially break free from this penetration vs. wear-life dilemma. Before the top-locking systems, most teeth were secured to the adapters with a thick steel pin hammered into the side of the tooth and adapter. Since this pin and the holes it went through were the weakest point on the tooth/ adapter assembly, manufacturers had to beef up the metal around it – creating a tall, thick tooth with steeply angled top and bottom surfaces. These teeth were strong, but massive, more like molars than incisors.
With the top-locking mechanisms, the need for all the metal bulk supporting the side pins went away. Tooth profiles slimmed down considerably, the top and bottom angles flattened out and the wear metal was pushed to the front, creating a more knife-like blade with better penetration and improved wear life.
The basic principles of these top-locking systems are the same, but most manufacturers have a slightly different retaining pin system. Some are tapped in and tapped out, some can be pressed in by hand, others use pry bars or special tools. Some are held in place with spring-tensioned steel, others use compressible rubber or polyurethane retainers. The locking pins themselves take little of the load, so to take the stresses that used to be transmitted to the side pins, manufacturers have added more contact surface between the tooth and the adapters. Some of these are just large mating surfaces, others use a twist-on assembly that secures and provides more contact area.
The top-pin systems also make it easier and safer to change teeth. On side-pin designs, whacking away at a punch with a sledge hammer can be a chore. Trying to center a punch on the tightly spaced teeth of a narrow excavator bucket is also difficult. And this metal-to-metal contact will occasionally create shrapnel or errant hammer blows that can smash fingers or damage components. Top-pin systems can eliminate these issues.
In addition to being longer, many of today’s bucket teeth are self-sharpening. “Self sharpening is a matter of shape and geometry,” Klobnak says. “You put ribs and pockets in the shape of the tooth so that as the material flows past it doesn’t become blunt in the front but wears equally along the length.”
“There are some applications, such as limestone quarries, where you just can’t fight it, ” Yoresen says. “”But in most applications – dirt, sand and gravel – you’re going to get certain wear patterns. We analyze those wear patterns and then design the steel such that in areas of high wear we have more metal or so that the tooth diverts the flow of material to maintain a constant cutting edge. In many cases the teeth will continue to get sharper throughout their life.”
The standard tooth profile is just a ramp with flat sides, says Jason Simmons, ground engagement tools engineer for John Deere. And after just a few hours of use the nose on these types of teeth will begin to round. “On Fanggs (Deere’s proprietary tooth design) the top and bottom are curved and the sides are curved like the shape of a moldboard on a grader. With all four sides angled, you’re able to keep that sharp point,” he says.
And keeping a sharp point throughout a tooth’s life cuts down on replacement costs as well. “Often a tooth is replaced even when there is wear material still left, because the penetration is affected,” Klobnak says. “The operator can feel the penetration change or the bucket doesn’t dig as well as it should.” So by making the tooth longer and lower you get more hours out of a set of teeth before it gets blunt.
Each manufacturer has its own proprietary steel alloys from which they make their teeth and adapters. And while it’s impossible just from looking to determine the quality or suitability of a particular alloy, there are some things you should observe and keep in mind.
Steel can be formulated to be hard and abrasion resistant or soft and tough. A hard steel won’t wear out as quickly, but a hard, quick hit may cause it to crack. Soft steel wears faster but can take shocks without breaking or developing cracks. To cover a wide variety of applications and soil conditions, most manufacturers strike a balance between the two properties. But the best way to know if you’ve got the right type of steel in your teeth is to observe how they perform over time.
For particularly tough, abrasive applications some manufacturers weld carbide strips onto the tooth in high-friction areas. These are expensive, and usually make sense only for the large quarries and mines. “Those are really for applications where the customer can’t afford the downtime,” Simmons says.
But what manufacturers don’t recommend is hardfacing the teeth yourself. “It will void the warranty if you hardface, and the tooth will probably break,” Yoresen says. The reason is that manufacturers put the carbide wear strips on before the tooth goes through its final heat treating process. The heat generated by welding a finished tooth will ruin the temper of the steel and cause that area to be subject to breakage.
And keep in mind that teeth get hot – too hot to touch during some operations, especially the teeth on bigger loaders or excavators working in abrasive materials. This can degrade the temper of cheaper steel, so in choosing a tooth design it can’t hurt to find out its temperature rating.
Tooth breakage is another consideration. “When we talk to our end users their number one concern is tooth breakage,” says Nil Vallve, marketing and operations manager for MTG. And a loose fit between the tooth and the adapter can quickly lead to breakage or damage. “When all the parts are new everything fits tight, but the key to a good tooth system is one that stays tight over time,” he says. To do this the design has to avoid concentrated areas of stress and spread out the impact forces and mating surfaces to as wide an area as possible.
And a broken tooth can sometimes be more than just a problem for that machine. “The costs of a lost tooth can snowball, especially if you’re working around any kind of crusher,” Yoresen says. “If you have a big chunk of hard steel like a tooth fall into a $200,000 crusher you’re going to damage the motor or other major component.”
What’s best for you?
With all these complex shapes and proprietary steels how can you determine what’s the best tooth system for your needs? Vallve recommends trial and error. Experiment with different systems under conditions that are as equal as you can manage and compare the results. “Customers in the United States are very good about this,” he says. “They’re more quality oriented, especially in big quarries and mines.” You can simply observe which tooth lasts longer, but you can also check fuel used and even weigh the teeth at the end of the field test.
Word of mouth can also help, Yoresen says. “Ask around. The people who work in quarries are fairly knowledgeable. Ask them if they have tried a particular tooth and what they thought about it.”
Investing the time to select the best tooth system for your needs will deliver good payback, but only if you and your operators treat the systems properly.
The number one rule is to do the preventive maintenance, Yoresen says. “People don’t like to shut the machine down; they don’t like to spend the money. But when there are days off or weekends, check the fit of the components. Make sure they’re tight. Most manufacturers have literature that explains how to maintain fit surfaces and keep them up to par.”
In abrasive materials reloading can also accelerate wear and should be avoided, Yoresen says. This happens when the operator gets an incomplete bucket, dumps it back on the pile and then tries for a bigger bucket load. “Now you’ve doubled the tooth wear for that cycle but only gotten 50 percent more material.”
Backdragging with loader buckets and chopping out asphalt and other hard materials with excavator buckets are also best avoided. These particular operations can also lead to damaged adapters. And replacing an adapter can cost 10 times as much as replacing a tooth.
And you need to choose the style of tooth carefully as well. The best way to do this is to discuss your needs with an equipment dealer, says John Taaffe, marketing manager, Customer Support, Volvo Construction Equipment. If a loader is being used in a concrete recycling application which is abrasive it requires a tooth with extra material on the bottom and an effective penetration design to get into the pile easily, he says. An excavator digging a basement in clay will benefit from correctly sized and spaced “spade nose” teeth being fitted to achieve a smooth and clean floor, ready for concrete to be poured.
Cat K Series tooth system
The new tooth system from Cat is actually two systems. Both are top-locking designs. The “hammerless” system is designed for bigger machines (988 to 992 wheel loaders and 330 to 385 excavators) and uses a retaining pin that pushes in and pops out with a pry bar. The retaining pin on the “drive-through” system (950 to 980 wheel loaders, 315 to 325 excavators and 953 to 973 track loaders) is tapped in and tapped out minimal force using a hammer and punch. With both designs, the teeth twist onto the adapter guided by two opposing rails. This enables the tooth to grip the adapter even tighter under load, reducing tip vibration and loosening. And the rails hold the tooth securely even after the retainer is removed making tooth changes easier and safer.
The curved top profile of Deere’s self-sharpening, self-cleaning Fanggs teeth slice through material to improve penetration and also help the material break up and roll more easily into the bucket resulting in better bucket fill characteristics. And the curved bottom profile of Fanggs excavator teeth follow the bottom profile of your bucket, so there is less friction as you curl your bucket coming out of the trench. Fanggs are the standard factory tooth from the company but you can also get them as replacement teeth to fit the designs of a variety of top-or side-locking adapters.
ESCO Super V system
A culmination of five decades of tooth design, the ESCO Super V has evolved from the company’s Helilok and Vertalok systems. The low-profile, self-sharpening Super V system has a tap-in/tap-out top retaining pin and a twist-on design for faster, easier and safer tooth tip changes. The locking pin works in two axis; one that resists twisting and the other resists forward thrust off the adapter and keeps the tooth tight on the adapter to minimize nose wear. The design allows more metal-to-metal contact area between the tooth and adapter and spreads out impact stress to improve durability.
Volvo tooth system
A self-sharpening design with strategically positioned wear material, the new Volvo tooth system offers a vertical locking device and a reinforced area on the heel of the tooth that protects the adapter and guide lugs from early wear. The edge where the adapter meets the tooth is angled, which better resists frontal forces and reduces the risk of the tooth box opening up. The inverted trapezoidal shape of the adapter nose provides a snug fit between the adapter and tooth even when the teeth are well worn. The tap-in/tap-out retainer pin has a reusable steel pin and a smaller, replaceable polyurethane retainer impregnated with carbon dioxide to provide the required elasticity for easy installation and removal.
MTG KingMet and StarMet
These two systems have similar, self-sharpening tooth designs but different retaining pin systems. The KingMet system is designed for the construction market and machines in the 5- to 200-ton classes. It uses a top-loading retaining pin that can be hammered in and out with low effort. The StarMet system, designed primarily for big machines in quarries and mines, is hammerless, which is what mines and quarries are pushing for to avoid injuries It uses a unique side-retaining pin installed and removed with a key that looks like a large, square-ended Allen wrench for fast assembly and disassembly. A wear cap on the top of the StarMet system protects the top of the adapter from wear and its narrow legs help protect the welds on the bottom of the adapters from abrasion and increase the wearlife of the parts.