Scrapers come in two forms: motorised wheel tractor or drawn/towed scrapers. Drawn scrapers are attached through a tow mechanism usually to an Articulated Dump Truck (ADT) or a tractor/dozer, but in Earthmoving applications, nearly all scrapers are so called wheel tractor-scrapers (or motorised) Caterpillar machines.
Why use a Scraper?
Scrapers are a cost effective investment. In many applications, one scraper can replace an excavator, 1-2 haul trucks, and possibly a compactor and/or dozer. With a good operator, the machine never stops for loading or dumping, which is why scrapers can achieve the lowest cost per cubic meter of dirt to move.
Like all machinery, it is important to match the requirements of job to the type and specification of the machine. Whilst scrapers are known to be very efficient in dirt, scrapers are used in all industry types: road construction, mining (coal stock piling for example), quarry and aggregates.
Scrapers come into their own on jobs with short hauls where the cut and fill areas are close together and have sufficient length to fill the hopper.
How much is a scraper and how do operating costs compare?
Scrapers are often seen as a big investment, and if looked at in the context of how much you are spending to get just one machine, it is easy to fall into the trap that scrapers are expensive. However, considering a scraper may mean you don’t require the other machines at all, then the equation quickly changes. The trick is to look at what the total running cost is of your entire fleet for the project.
Fuel and labour is a significant cost when running earth moving machinery. Because a scraper can replace several machines and doesn’t sit still (like a haul truck being loaded by an excavator), the only engine running is on the scraper, thereby reducing total fuel burn for your project. And you’re only paying for one operator.
This also means that owners can often do more work with fewer pieces of equipment and less operators, thereby increasing the profit on each job.
Scrapers have a very good service life. Whilst some customers rotate machines at 6-10,000 hours, a well maintained scraper can stay in service for 30-40,000 hours. Customers who buy a good machine with a comprehensive service history and continue with preventative maintenance can thereby depreciate the cost of the machine over a considerable period of time, meaning that the cost per hour is reduced. This means that the higher initial investment cost can be written off over a longer time period than many other types of machines.
What’s the difference between a single and twin engine scraper?
A single engine scraper has an engine only in the front tractor section, whilst a twin engine scraper obviously has an engine also in the rear section. One engine burns less fuel than two (during for instance the transport leg), however it’s about matching the machine to the job. Twin engine scrapers are designed for steep grade or high rolling resistance underfoot conditions, and are also effective in push pull combinations (where more than one scraper is hooked up in tandem).
How do I improve the efficiency of my scraper?
Having a good operator is more important with scrapers than many other types of machines. The operator needs to find the balance of how to effectively load the machine within its design capabilities (for example use the optimum cut depth for the surface). Productivity is also maximised by making sure the machine never stops, that is, it uses the design advantage of being able to load and dump whilst still on the move.
Consideration also needs to be given to the site layout, for example making sure that you run the loaded machine on the short haul road and take the empty machine back on the longer section of the loop. It is also important to load downhill and avoid rocks any bigger than about 50-60 centimeters in diameter. However, whilst scrapers can handle occasional rocks, this is not their primary purpose, as it will reduce flight and chain life and cause wear to the ejector, as well as potentially jam the auger or elevator mechanisms.
Keeping the haul road well maintained reduces wear on the hitch and drive train and allows for higher transport section speeds.
What’s the difference between an open bowl/elevator/auger scraper?
All scrapers use the sharp front horizontal cutting edge for loading, with the cutting edge lowered or raised to determine the penetration depth. As the material fills the hopper, the bowl is raised to transport the material to the dump section, where the back panel of the hopper (commonly known as the ejector) hydraulically pushes the load forward and the load tumbles out.
In order to increase the fill rate (both volume and speed) of the bowl, scrapers are fitted with an elevator. This is a metal conveyor chain with horizontal flights that helps lift the material from the cutting edge towards the back of the bowl. An elevating scraper is therefore better on finer finishing grades and in softer materials (such as fine clay, sand, topsoil and other fine materials with poor cohesive characteristics).
There are also models that use an Auger instead of a conveyor. This design raises less dust than a conveyor design and suits and suits chunkier style materials better.
The other consideration when choosing scraper design is the fill factor. Open bowl scrapers fill rates vary from about 50% (single engine self loading) to 95/110% (push/pull with the first scraper achieving 95% fill and the second 110%). An auger and elevator scraper can achieve 100% fill factors.
What to look for when buying a scraper?
Like all types of machinery, having a good history of preventative maintenance is a very good indicator of the quality of the scraper you are buying, so start by getting a qualified diesel fitter to look at the machine, checking out the condition of the drive train etc. Another potentially costly repair is if the hitch has not been maintained, so check the pins and bearing clearances and for signs of wear. It is much better to replace these before line boring of the king and queen posts is required. Wear items, like the cutting edges, tyres and even replacing flights are reasonably straight forward and minor to replace by comparison.
Another aspect often underestimated is to consider who you are buying the machine from, and why it is for sale. Buying from auction or direct from an owner is a much greater risk than buying from a reputable dealer, who will be mindful of their reputation and building a loyal customer base. As a result, the standard of the machines they buy to onsell will be higher, and they will also have checked over the machine and fixed potential issues (or at a minimum notify the buyer of upcoming issues), and can also help ensure the machine is configured to the requirements of your job site.
Still need help?
Choosing the right machine for your job is very important and can be confusing. The above covers some of the application considerations and site concepts. In order to ensure you get the right machine to meet your requirements, call RDW Machinery on 07 3875 1358 to discuss.