Jewels in the crown: high-reach demolition excavators

Twenty years ago, high reach demolition excavators were a rare sight. Today they are almost commonplace in Europe and are growing in popularity around the world.

This is especially true in urban environments where space is at a premium and demolition has to be carried out in a controlled manner, often with tight restrictions on noise, dust emission and other nuisances.

Until just a few years ago, the primary driver for these machines was height but this has changed. Some contractors still want the highest, but many others would ideally opt for a balance of height against performance.

By this, they mean the biggest, most powerful possible tool at the optimum height - usually said to be a reach of between 25 and 30 with tool weights from 4 to
7 tonnes.

Most original equipment manufacturers (OEMs) offer a range of high reach demolition excavators in their product line using their base carriers modified for the role with, usually, an extending undercarriage to increase stability, heavy duty guarding on the cab and undercarriage, and, especially where the larger machines are concerned, a tilting cab that allows a clearer view of the business end of the machine - the tool at the end of the boom.

Frequently they also feature a coupling system that allows relatively quick boom change-overs to allow for flexibility in use. However, the one common limiting factor most of these machines feature are tool weights seldom over 2.5 tonnes, including any quick tool coupling system fitted on the end of the boom.

Given the current economic climate, allied to the latest engine emissions, the OEMs in recent months have been concentrating more on their standard models, re-engining them to meet Stage IIIB/Tier 4 Interim emission requirements.

Given also the fact that many had only recently completed their full line of high reaches, things have been quiet in recent months where OEM produced demolition machines are concerned.

The main exception to this is Caterpillar, who has teamed up with boom specialists on both sides of the Atlantic to produce its next generation high reaches.

In Europe, a Vensys Group subsidiary company has been formed that takes standard Cat carriers and modifies them for the demolition role.

The Dem 50 introduced in 2010 was followed by the 33 m Demlone 70 introduced at the beginning of 2011, with the final 43 m Demlone 100 expected to appear by the end of this year.

In mid-2011, the first North American equivalent, the 70 tonne Apex 70, made its first appearance in mid-year. For North America, Caterpillar has teamed up with Jewell Equipment, the leading North American boom specialist, to form a similar arrangement as in Europe.

The Apex 70 will be followed by the 100 tonne Apex 100 and then, depending on demand, the 50 tonne Apex 50, with the first two models expected to be the most popular in the North American marketplace. These three machines will offer working heights broadly similar to their European counterparts.

Blending the best

One new machine introduced in recent months stand out from the crowd. Decked out in Rusch Special Products' company livery of black and purple, the RS 4500-H is the latest in a line of five very special demolition machines that have emerged from this Dutch company's fabrication facilities.

First, the RS 4500 cannot be called a demolition excavator! True, it may have started life as a Hitachi 870 carrier (hence the -H designation), but the final result has been modified to a point that this is almost meaningless and it incorporates design features that you do not see on even the largest demolition machines.

Incidentally, should a future customer order an RS 4500 based around a different OEM's carrier, say for example a Caterpillar machine, the -H designation will change to reflect that fact.

It is the new machine's designation that gives the first clue to the fact that while it may look like the high reach demolition excavators we are used to seeing on site, whether high reach or straight boomed, there is more to the RS 4500-H.

Almost without exception, an excavator designation has some connection to the weight of the machine, or in some demolition excavators' cases, the weight and height they can work at.

In the case of the RS 4500-H, the designation reflects something unfamiliar to most in the demolition industry but very familiar to the crane sector - the maximum front tipping load moment, usually taken over the front idler on the track set that in this machine's case is 4500 kilogramme Newton metres or 450 tonne metres.

In its very simplest form, this number is derived from the weight on the boom multiplied by the distance of the load away from the carrier, but of course there is a lot more to it than that. Suffice it to say, it is a complex calculation, especially for a machine like the RS 4500-H.

The machine has numerous operating configurations for its three boom options, and this is where maximum front tipping load moment comes in. The weight of the machine will vary according to the configuration adopted for the task in hand - hence a designation based on weight would not be a sensible one.

However, the maximum tipping load moment remains constant irrespective of the configuration, hence the decision to adopt this as the designation.

A major design driver for the machine was the need to make transport as simple as possible and Rusch researched the varying regulations around Europe.

Germany proved to have the most restrictive (maximums of 100 tonne weight, 28 m long, 3.5 m wide and 4.2 m tall) and designed accordingly, hence the selection of the ZX870 as a base rather than the Hitachi ZX1200, a popular choice among demolition contractors.

Provision of a hydraulically extending undercarriage to provide an additional 1 m on each side in working configuration results in a square footprint that allows the machine to operate with full 360° rotation.

So far, only the four stage articulated boom has been produced. Its transport will require at least four special trailers: one for the body excluding counterweight but including the lower cylinders and boom element (although these can be removed and transported separately if required), one for the lower (main) and second (auxiliary) boom, a third for the third (main stick) and fourth (auxiliary stick) and a fourth for the two track elements.

The counterweight can be transported by a standard truck.

Once these reach the work site, the RS-4500-H body jacks itself up, allowing the trailer to be removed, and then acts as a crane to lift the two track elements into place where they are hydraulically secured.

Once this is done, the counterweight is secured to arms that then hydraulically lift it into place on the back of the carrier superstructure.

The two section main boom is then connected to the carrier body, followed by the two upper elements, all of which are securely locked into place by hydraulically activated locking pins.

The telescopic boom, when fabricated, is likely to have similar transport requirements, and the dig boom will naturally require less.

With its number of configurations, operating such a machine as the RS 4500-H safely and efficiently is a challenge, and here another element has been brought over the crane industry - an extensive load monitoring and control system that can accommodate the 15 separate configurations that are possible.

Separate working range diagrams have been developed for each.An IQAN system controls all the movements of the machines, with the safety features controlled by a separate system developed specifically for the machine by Rusch working together with system provider PAT.

The latter software monitors input from a number of different sensors that monitor factors such as wind speed, counterweight position, boom configuration and angles, pressure in luffing cylinders, telescopic boom positions and locking, and hydraulic cylinder end of stroke.

Should the system record a 90% approach to the established safe limits, an audible warning will sound, with all further movement cut if the 100% limit is reached.

The operator can always retract from the limit position, even in the latter situation.

The danger of reach

Like almost every other sector of the construction industry, the demolition sector is finding it difficult to attract suitable young personnel to follow on from the ageing workforce currently carrying out the bulk of the work.

This particularly applies to demolition high reach operators. They require skills other than just the ability to use an excavator efficiently and safely.

A basic understanding of structures and how to bring them down safely with their machine in the appropriate position is required. Fortunately, accidents are relatively few but when they happen they are often highly visible and spectacular.

An accident that occurred in Detroit, US, in July illustrates the point. Caterpillar's brand new Apex 70 machine made its first appearance on site during the demolition of the Ford Auditorium in the city.

Within days, it was lying on its side on the site. Since the location had two live roads running alongside, it was highly visible to the public and as a result, featured heavily on the Internet - in fact, had the machine gone over on its other side, the boom could well have ended up lying across one of these roads.

The cause of the incident is still under investigation but Caterpillar and Jewell are no longer part of this, suggesting that the cause of the accident was not connected to design, engineering of fabrication issues on the machine.

Recognising this shortage of skilled operatives, the UK's National Federation of Demolition Contractors has introduced what it believes to be the world's first high reach excavator training programme for machines with a reach of up to 30m.

It is important to note that before operators can take the training, they already have to be UK certified operators of excavators with a boom of up to 15m.

This recognises the fact that high reach demolition excavators are not tools for amateurs, no matter how easy the manufacturers make them to operate.