Dealing With Metal Wear on Construction Equipment

A Dealer’s Perspective on Repairing Construction Equipment

Holt Rental Services (HRS) of Ohio, a Caterpillar dealership with offices in several cities in that state including Toledo, Cincinnati, and Perrysburg, does structural-metal repairs in some of its facilities. According to Service Manager Ed Recker, some construction companies do regularly use their dealership for structural-metal repairs on their construction equipment, either in the field or in the shop. On the other hand, larger construction companies with good welders on staff do these repairs themselves. It is cheaper and faster that way, provided they can keep their maintenance people busy. Smaller construction companies that have minimal in-house maintenance staffs rely on either a dealership or a local welding shop.

Construction-equipment dealers, such as Caterpillar with scores of sales and service outlets around the country, do typically perform a full spectrum of maintenance on equipment. The most common maintenance problems these dealerships confront deal with engines, hydraulic systems, and pumps. But they also do much work repairing, welding, or replacing metal components. They also completely rebuild construction equipment after it has been in service 30,000-40,000 hours.

Bucket Blades and Teeth

Concerning the metal components of construction equipment, what parts wear out most quickly? Recker says that the blades and teeth on bulldozers, loader and excavator buckets, scrapers, and other construction equipment take a real beating, especially those operating in abrasive environments, such as in mining operations or in regions with sandy or high-silica soils. Mining environments are especially rough on equipment, for their operators use the buckets on excavators and loaders not only to handle abrasive soils but to lift large rocks, operations that can also place severe stresses on the boom and stick that support the excavator bucket.

But on a lot of construction equipment, Recker notes, the blades can quickly be unbolted and new blades bolted into position. Likewise, the teeth on backhoe and excavator buckets can readily be unpinned. These repairs the typical construction company can do itself without difficulty. It buys the new blades or teeth either at a construction-equipment dealer or at a third-party supplier of construction-equipment parts. A contractor might sometimes save money buying parts from such an aftermarket dealer. But, cautions Recker, he might not always be getting parts that meet original-equipment-manufacturer (OEM) standards.

Pivot-Point Holes

Another major problem concerning metal wear, Recker says, are pivot-point holes (or pin holes) – e.g., the pivot points on the arms supporting the bucket of a loader swing. These pivot holes gradually become larger and elliptical in shape, to the point where the pin becomes loose and the swing arms become wobbly. The hole widens over time as a result of the constant turning of the pin in the hole. These holes wear out much faster if the pivot holes are not frequently and adequately lubricated. When working in a dusty environment, Recker advises, it might be necessary to lube these pivot holes several times per day.

How does a maintenance person fix such a pivot-hole problem? First, the hole must be built up by adding weld material inside the hole, so that the original hole diameter is now somewhat less than the pristine hole; then the welded hole must be bored out, restoring it to its original diameter. The process of rebuilding and reboring these holes is much cheaper than the alternative: replacing, for instance, the lifting arms of the loader, a measure that could cost $100,000 on a large loader versus 1-3% of that for reboring the holes. Such repairs are most often done in the field to minimize equipment downtime, though they are sometimes done in the shop.

Buckets: High-Wear Points

As mentioned earlier, the blade and teeth of excavator buckets are high-wear points and must be unbolted or unpinned and replaced periodically. Beyond that, both the inside and outside surfaces of the bucket itself of a loader or an excavator are subjected to high abrasion because of the ceaseless sliding of earth and rock over them.

Recker says HRS frequently beefs up the abrasion resistance of a bucket by welding parallel strips or a grid pattern of 1/8-in.-high steel ridges onto both inside and outside surfaces of the bucket. This welding is done using a hard and highly abrasion-resistant steel alloy for the welding material. Called hardfacing, this grid of ridges prevents the earth from coming into direct sliding contact with the original bucket surfaces, thereby protecting those surfaces from abrasion; the earth in effect now slides over the hardfacing ridges.

How often is such hardfacing done? If a contractor is digging materials in a quarry, using a front-end loader to move large chunks of rock, he might have to rehardface the bucket surfaces at least once per year. On the other hand, if the loader is working in a much less severe environment – say moving a loamy soil, which is much less abrasive than handling either rock, aggregate, or sandy soils – the contractor might have to rehardface buckets only once every two years.

Pavement Milling Machines

Still another major maintenance problem, explains Recker, has to do with the planers or milling machines used to grind down asphaltic-concrete pavements in preparation for the laying down of a new wearing course. The key feature of such a machine is a rotating drum with scores of carbide teeth protruding from the drum surface. As the drum rotates about a horizontal axis while the paving machine moves forward at a steady pace along a pavement, these teeth engage the surface of the pavement, shaving off its surface layers.

Maintenance of such machines involves unscrewing the worn carbide teeth and screwing in new ones. Such maintenance, Recker notes, is most often done in the field. And either the contractor or maintenance staff from the local dealership performs the maintenance.

Backhoe and Excavator Booms and Sticks

Another common structural problem with construction equipment, Recker explains, relates to the boom and stick (i.e., the bucket-support arms) of backhoes and excavators. Since backhoe and excavator buckets are constantly lifting heavy loads, the supporting arms are subjected to constant stresses. It is not uncommon for these arms to be overstressed and damaged, to the point where they need major structural repair. In most cases, damage to booms and sticks, Recker says, is the result of operator abuse: attempting to lift rocks or other loads heavier than the equipment can handle. This often happens with smaller equipment. Rather than bringing in a larger piece of equipment, an operator may overload a smaller excavator, lifting rocks heavier than what the equipment normally handles. Such repeated abuse eventually results in boom failure.

Repair of damaged booms, Recker notes, involves cutting out damaged portions of the steel and welding new steel in place. Equipment dealers, such as Caterpillar and John Deere, can provide specific engineering guidance on how to do these repairs – even if the contractor decides to do the actual repairs in-house or have them done by an independent welding shop.

How Contractors Can Improve Their PM Programs

How important is preventative maintenance (PM) of construction equipment? Recker believes a good PM program can greatly reduce the need to make repairs. Most important, he believes, is keeping pivot-point holes well greased. Depending on the particular environment one operates in, it might be necessary to grease such pin holes several times per day. As part of their equipment-maintenance staff, many construction companies have a greaser, he says, who does nothing but goes around to the equipment on job sites and greases it. Other companies require the equipment operators themselves to take care of such routine PM.

Many equipment dealers, including Caterpillar, also provide PM programs, sometimes as part of the initial purchase price of the equipment. Typically equipment dealers have a staff of maintenance people who travel to a customer’s construction sites, inspect each piece of equipment once every 250 hours, do any necessary repairs, replace parts, lubricate equipment, and so on. Recker believes that a high percentage of construction companies give top priority to equipment maintenance and have effective PM programs, for they realize that, when equipment is broken, downtime can be very costly. Further, they realize that ordering certain parts can sometimes take weeks – all the more reason to have a well-organized PM program in which equipment regularly receives inspection by qualified maintenance staff and problems are spotted early.

Harold Sulfridge, service manager for Whayne Supply Company, a Caterpillar dealer in Corbin, KY, with eight other branches across the state, says smaller construction companies (12 pieces of construction equipment in their fleet) do only light routine maintenance in-house (e.g., lubrication) and rely on equipment dealers to do major repairs. Large construction companies, though, with large equipment fleets, have their own maintenance and repair staffs and shops and do significant repair work in-house, such as hardsurfacing of buckets and dozer and scraper blades and replacing bucket and dozer blades and bucket teeth.

But for major repair work, such as rebuilding an excavator bucket or overhauling the undercarriage of a tracked vehicle, Sulfridge says even large construction companies often rely on equipment dealers. In rebuilding a bucket, for instance, Whayne Supply will weld T1 protective steel plate onto the walls of the old bucket. In some cases, where there is extensive wear on the original bucket walls, this Caterpillar dealer might even disassemble the old bucket and weld in new steel-plate bucket walls.

Shook Brothers Inc. (SB) is a medium-size construction company in Berlin Center, OH, that performs bridge and highway work for the county and state government and construction-equipment repair for other contractors. Partner Rick Shook says the number-one construction-equipment maintenance problem is pivot-point holes. The pin holes that are especially subject to wear are the ones on front-end loaders, where the bucket arms connect to the equipment body; the ones on backhoes and excavators, especially the stick-bucket pivot point; and ones on small bulldozers, where the blade arms fasten to the dozer body.

If these pivot-hole points are well maintained, Shook states, the holes might never widen and demand repair. In some working environments, it might be necessary to grease these pivot-point holes three times per day. Wear can be at least twice as fast when working in sandy as opposed to clay soils. SB does repair work for other construction companies. Based on the firm’s experience, Shook maintains that 50% of construction companies have good PM programs, lubricating equipment frequently; another 25% have really bad PM programs, never greasing pivot-point holes and thereby facing frequent failure of these pin holes.

Years ago, SB repaired these pin holes by welding the hole in the field using stick electric-arc welding and the ubiquitous 7018 welding rod. Typically it would take about four hours to weld around a pivot-point hole and another few days to actually bore a new hole through the welded area. In recent years, Shook purchased devices that automatically weld the pin hole and then bore a new hole – the entire process taking a day’s work or less. There are several companies that make automatic welding and boring machines for construction-equipment applications, among them: Bore Repair Systems Inc., Alstead, NH (www.borewelder.com); Bortech Corporation, Keene, NH (www.bortech.com); and York Portable Machines, Campbell River, BC, Canada (www.yorkmachine.com).

Repairing Bulldozer Blades

Another major construction-equipment problem for SB is bulldozer blades: the wearing out of the cutting edge along the bottom of the blade. The cutting edges (about 6 in. high), Shook points out, are usually bolted onto the bottom of the blade. Shook usually buys a new carbide-tipped cutting edge from an equipment dealer for about $1,800 and bolts it on. In most cases, it is difficult to unbolt the old cutting edge because abrasive soils have worn away the old bolts and threads. (In this respect, sandy soils are much more abrasive than clay or loamy soils.) Accordingly, the old bolts must be removed using a cutting torch.

Shook says many problems with construction equipment develop during cold weather, especially when temperatures plunge below 10ºF. In such cold weather, the steel becomes much more brittle, especially during the first hour of operation in the morning, when equipment is still cold. At such times, it is not uncommon for an excavator boom to fracture, the blade on a loader or a dozer to break, or the ripper tooth (or spike) on the back of a dozer to snap off.

To help prevent such cold-weather problems from developing, Shook recommends that an operator “warm up” construction equipment before subjecting it to normal workloads. For instance, he could drag around the loader or excavator bucket on the ground for 10 or 15 minutes through loose material, avoiding any hard digging. The friction will warm up the metal, making it far less susceptible to fracture. The same sort of warm-up ritual can be used with dozer blades and ripper teeth (spikes), reducing the probability of cold-weather fractures.

Shook says another major problem with construction equipment is boom failures on backhoes and excavators. For instance, one backhoe recently developed a major fracture on the boom, breaking near the pivot-point hole that joins the boom and stick. The fracture was mainly the result of backhoe-operator abuse: he was swinging the bucket from side to side, in effect using it as a hammer to widen the walls of a ditch. Such hammering placed excessive lateral forces on the boom and stick, resulting in boom fracture. Some manufacturers make their booms from a medium-carbon steel, rather than from a higher-strength low-alloy steel, thereby making them more susceptible to failures.

SB was able to repair the boom in the field using stick-electrode electric-arc welding. Old metal was cut out and new steel plate welded into position. Shook says they used a 7018 welding rod, a mild steel with a tensile strength of 70,000 psi. For SB this is an all-purpose welding rod used for a wide range of welding tasks – except for hardfacing of buckets and dozer blades. The company also uses gas-shielded electric-arc welding with solid wire, but only in shop settings where the staff doesn’t have to be concerned about the shielding argon gas blowing away.

Tracked-Vehicle Undercarriage Repairs

Still another major construction-equipment maintenance problem is undercarriage repair for tracked vehicles. SB does such repair work in-house. A significant step involves replacing worn rollers (typically five to seven rollers on each side of the dozer) with new ones. Instead of buying rollers at the construction-equipment dealer, Shook purchases them from a third-party aftermarket dealer, saving 30-50%. A roller for a small dozer typically costs $200; for a larger dozer, $500. The quality of aftermarket parts, he believes, has improved considerably over the past 15 years, brought about by the growth of the global economy and the consequent availability of construction-equipment parts from overseas, especially Italy.

Another important part of undercarriage repair has to do with the grouser bars, the 1.5- to 3-in.-long protrusions from the track surface, placed there to greatly enhance the traction of the track.

When operating in sandy soils, which are highly abrasive, new grouser bars need to be welded onto the track (usually using stick electric-arc welding) about every 2,500 hours.

Do Repairs In-House or Outside?

Concerning the issue of whether a contractor should have its construction-equipment repair done in-house or outside, Shook says the key consideration is the quality of the maintenance staff. If a company has good mechanics and welders on staff, then it makes sense to do many repairs in-house. If not, a construction company can take its equipment to a dealer or an independent construction-equipment repair shop such as SB. The advantage of using an independent over a dealer, Shook argues, is that independents often work on a wide variety of equipment brand names, whereas many dealerships repair only their own brand-name equipment. Further, independents often charge less for repairs because they have lower overhead.

Cass Construction Company (CCC) is a large local contractor based in El Cajon, CA, involved mainly in the installation of water and sewer lines and storm drains. It has more than 300 pieces of construction equipment in its fleet, including 15 rubber-tired loaders, 16 track-mounted excavators, six backhoes, 11 scrapers, nine track-mounted dozers, four rubber-tired dozers, and numerous dump trucks.

Cass’s equipment superintendent, Steve Johnson, says they do virtually all their maintenance and repair of construction equipment in-house. They have a four-bay garage for doing mechanical repairs, a component rebuilding shop, and a welding and machine shop. In all, there are 13 people working in the equipment-maintenance department.

Wear on Frontloader Buckets:
#1 Maintenance Problem

CCC’s number-one maintenance problem is wear on the buckets of its front-end loaders – especially on the leading edge of the bucket just beyond where the blade is bolted to the bucket. On the larger loaders, these blades are usually bolted on. Larger loaders are subjected to heavier earth loads, and the blades need to be replaced more often (typically once per month). The smaller loaders are subjected to lighter loads; their blades don’t have to be replaced very often, and accordingly the blades are often welded on. For a typical 4-yd.³ loader, with 10-ft. bucket width, a new blade costs about $800. When one edge of the blade wears out, the blade can be rotated and the rear edge now used as the cutting edge.

Regarding the bucket surfaces themselves, Johnson says they protect them by hardfacing. Specifically, they hardface the bottom inside surface of the bucket, from the inside edge of the blade into the bucket about 4 in. To do this, a welder using stick electric-arc welding, usually in the field, lays down a continuous bead of welding material along a line parallel to the blade edge. When completed, there will be several of these parallel ridges of hardfacing, each about 1/2 in. apart, each running the full width of the bucket, and each 1/8 in. high. These parallel ridges constitute a matrix that will trap soil, the trapped soil serving to protect the bucket surface from further abrasion. An alternative explanation is that the ridges prevent the soil from coming into direct contact with the bucket surface, the earth in effect sliding over the tops of the ridges. In addition to hardfacing the bottom inside surface of the bucket, CCC also hardfaces the sidewalls (toward the front end) both on the inside and outside surfaces. For the hardfacing, CCC uses a Stoody 3031 welding rod, a hard low-alloy steel with good abrasion and impact resistance. Given the highly abrasive silica soils in San Diego County, it is necessary, says Johnson, for CCC to redo the hardfacing every four to five months. The wire approach is preferable in many cases because it is much faster. In the field, the company uses either stick or wire electric-arc welding.

CCC also makes use of quick couplers on its loaders, so the bucket can quickly be attached or removed from the loader. These devices allow equipment to in effect be quickly changed from a loader to a forklift for lifting and transporting pipe on the job site. The company also uses quick couplers on its excavators so that, in the digging of trenches, they can quickly switch from a bigger bucket to a smaller one, or vice versa. Such couplers are areas of high wear, and accordingly CCC protects coupler surfaces with hardfacing, an operation that must be repeated every for or five months.

Wear on Excavator Buckets:
#2 Maintenance Problem

As with other construction companies, CCC finds excavator buckets an item of very major wear, especially when such equipment is operating in the highly abrasive silica soils of southern California or handling a lot of abrasive aggregate in the excavation of trenches.

Johnson proclaims that he is not a strong advocate of hardfacing for excavator and backhoe buckets. First, hardfacing requires considerable labor. Second, all the heating done during the welding process, he claims, places stresses in the original bucket metal, ultimately creating cracks in the bucket. Third, the welded-on hardfacing ridges don’t really penetrate into the base metal, thus making for a less secure weld. Finally, Johnson likes to keep interior surfaces of the bucket smooth and free of obstructions, such as hardfacing ridges, so that soil can flow into and out of the bucket readily.

Instead, CCC deals with bucket abrasion by welding 1-in.-thick x 4-in.-wide AR 500 abrasion-resistant alloy-steel (high in carbon and nickel) plate strips onto the bottom surface of the bucket (strip length varies from 24 to 72 in., depending on the bucket width). Company maintenance people actually weld a series of parallel steel-plate strips, set 2 in. apart, transversely across the exterior bottom surface of the bucket. Sometimes, CCC welds hardfacing ridges on top of the steel strips, to extend the life of the strips. The matrix of steel-plate strips helps trap soil on the bucket underside; the trapped soil then helps protect the original metal surface of the bucket.

In summary, CCC is in favor of hardfacing loader buckets but not excavator buckets. On excavator buckets, the company believes it is far better to weld abrasion-resistant strips on the outside bottom surface. Why this difference of approach? Johnson states that wear on loader buckets is much less severe than on excavator buckets because loaders usually handle loose material, while excavators mainly dig into virgin soils, where abrasions of bucket metal will often be far more severe.

In the comparatively mild-abrasion environment that loader buckets experience, Johnson explains, hardfacing can stand up for some time, the labor-intensive field hardfacing operation not having to be done all that often. But in the severe-abrasion environment encountered by excavator buckets, hardfacing doesn’t last all that long and must be repeated fairly often – a procedure that can be time-consuming and costly, especially if done in the field where slower stick electric-arc welding must be used.

Johnson claims that welding abrasion-resistant strips on the bottom outside surface of the excavator bucket is far more effective than hardfacing because it lasts much longer in abrasion-resistant soils. And the closely spaced, parallel steel strips are far more effective in trapping soil on the bucket surface, which serves to protect the original bucket surface. And since excavator buckets don’t have to have new strips added very often, repair work can be done in the shop. And there, Johnson says, CCC fabricators usually use gas-shielded electric-arc welding with large-diameter (7/16-in.) automatic feed. This welding method enables them to lay down 50 lb./hr. of weld material, which is more rapid than with stick welding.

Usually such a solution is good for about six months in these abrasive soils, then new alloy-steel strips must be again welded to the bottom of the excavator bucket. It is not true, he says, that adding steel plate to the bucket significantly reduces the load-carrying capacity of the bucket, for the weight of the steel-plate strips is only a small fraction of the load-carrying capacity of the bucket. After about four years, the inside of the bucket is badly worn. Accordingly, the bottom of the bucket is cut out and replaced with new steel plate, welding it into position.

Wear on Blades of Scrapers:
#3 Maintenance Problem

Another major equipment maintenance problem for CCC is scrapers. The blade that does the actual grading work on a typical scraper is 13 in. high and 12.5 ft. wide. In the high-silica soils of southern California, Johnson says, a blade needs to be replaced every week; but in clay-type soils with not too many rocks, every two to two-and-a-half weeks is sufficient.

Johnson usually buys replacement blades through an aftermarket dealer, typically saving 30% compared with the price paid from the original-equipment dealer. A typical 13.-in.-high, 12.5-ft.-long blade is made of heat-treated T1 alloy steel and sells for about $1,000. But Johnson has the supplier tip both top and bottom edges of the blade with a tungsten carbide coating (extending about 2 in.), a procedure that adds another $1,000 to the price but that triples the blade’s life. When the leading edge (making direct contact with the ground) of the blade wears out, the blade can be inverted and the top edge now used as the leading edge.

Still another important maintenance problem for CCC is the ripper tooth (or spike) on the back of tractor dozers, used for gouging into and ripping up soil and old pavements. Such an 18-in.-tall spike is made of a very high-carbon steel and has both its tip and leading edge coated with tungsten carbide. Typically this spike needs to be replaced once per day – sometimes twice – at a price in the $100-$170 range.

Tracked-Vehicle Undercarriage Repair:
#4 Maintenance Problem

The undercarriages of tracked vehicles – whether bulldozers, loaders, or excavators – are yet another major maintenance dilemma. These need to be overhauled every 3,500-4,500 hours, says Johnson. Given that CCC puts about 1,800-2,000 hr./yr. on such equipment, that amounts to an overhaul of the undercarriage about once every two years.

Such overhauls are often done in the field, Johnson explains, because it would typically cost $700-$1,000 merely to transport a tractor back to the shop. In doing an overhaul, the two mechanics performing the work will first elevate the tracks off the ground using the dozer’s rear spike. They then remove the track, track chains, sprocket, idler, and rollers. The worn rollers (typically 14) are replaced, each typically costing $700-$1,000. On average, such an undercarriage overhaul will take about three days.

The steel grouser bars protruding perpendicularly about 3 in. from the surface of a dozer’s track pads are a high-wear item. These bars are especially important on bulldozers and, to a lesser extent, on tracked loaders and excavators. They dig into the soil, giving the tracked vehicle adequate traction; when the grouser bars get too worn down, traction will become insufficient and the track will begin to slip. Once a grouser bar has been worn down to a height of only 1-1.5 in., it is time to weld a new 3-in.-high grouser bar onto the leading edge of the old grouser bar. CCC has to replace grouser bars every 1,000-1,500 hours – roughly twice per year.

A Large Construction Company’s Approach to Preventative Maintenance and Repairs

Johnson maintains that there are things a construction company can do to extend the life of a tracked vehicle’s undercarriage so that overhauls don’t have to occur too frequently. Most important is that operators avoid driving at high speeds in reverse – nothing over second gear – to avoid excessive wear to track bushings. Another important gu