Classic Machines: Caterpillar's 641 scraper

Описание: The Cat 641 scraper by Richard Campbell

Rated at 28 cubic yards struck and 38 cubic yards heaped the Caterpillar 641 was a quantum leap in Cat scraper design. Released in 1962 along with the models 630A, 631A, 632, 650, 651, 657, 660 and 666 the 641 sat roughly in the middle of the range capacity-wise.

In order to take best advantage of the new machine’s capabilities, Caterpillar had also developed a new range of engines and transmissions to cope with the higher horsepower requirements that had become necessary to move these big beasts around.

The power plant chosen for the 641 was the Caterpillar D346. This was a 60 degree, V8 turbocharged diesel engine, rated at 450 horsepower at 1900 rpm. This was mated to a nine-speed Caterpillar full powershift, barrel type, planetary transmission that incorporated a downshift inhibitor to prevent the engine over speeding.

In top range the 641 could get along at almost 30 miles per hour (50 km/h), which was a very reasonable speed for such a large machine.

In 1965 engine output was increased to 500 flywheel horsepower.

For stopping the Cat 641 used air operated shoe type brakes, supplemented by a hydraulic retarder to extend brake shoe life. This was a standard factory fitted item.

Steering was via two double acting cylinders connected to torque multiplying linkages mounted high on the gooseneck hitch.

A deeply padded seat was positioned over the top of the left wheel well, and was provided with a hydraulic snubber. This however did little to iron out the rough riding characteristics of a two axle scraper.

A comprehensive set of instruments (including a rev. counter with a tell-tale) were provided on a split instrument panel on either side of the steering column.

A steering brake was provided to assist in controlling wheel slippage should the machine become stuck. (Later series machines had a foot operated differential lock to control unwanted wheel spin.)

Scraper operation was by three separate levers – one to raise and lower the bowl, one for raise and lower the apron, and the other controlled the ejector.

An optional attachment on earlier production machines was a synchronization switch, which lowered the apron when the bowl was raised to carrying height, thus saving the operator quite a few hand movements during an operating shift. This attachment later became standard equipment.

Optional equipment included a cab and full heating for colder climates.

As was stated previously, the 600 series was a completely new design for Caterpillar and nowhere was this more noticeable than in the design of the bowl.

This was all-hydraulically operated – not a hint of cable – and drew upon research and experience gained from the previous cable operated “lowbowl” scrapers. It was very modern in appearance.

Two double acting lift cylinders provided penetration force for the cutting edge and were fitted with check valves to prevent sudden bowl dropping in the event of a hose failure in the hydraulic circuit.

Also incorporated into the bowl cylinders was a quick drop function that allowed pump loading in difficult loading material, such as sand. It also worked very effectively as an emergency brake.

The apron was connected via a solid link to a lever arm which was operated by a double acting hydraulic cylinder buried in the gooseneck. This gave the apron some power to force its way through material in closing and was not dependant on weight of material carried in the apron to effect closure.

The ejector was powered by a single double acting cylinder and was fitted with a gate type spillguard.

In late 1963 Caterpillar offered an “extreme service” bowl for the 641 (and selected others in the 600 family) for use in severe loading conditions. This featured considerably more high analysis steel in all the wearing areas and, in the 641s case, added an extra 4000 pounds to the weight of the machine.

Along with the extra steel, thicker, heavier duty cutting edges were also supplied.

It is not known how many of the severe service machines were built. The ‘extreme service’ option appears to have been dropped around 1971.

Mention must be made of Caterpillar’s cushion hitch. This was not offered on the early 641s but was available as an optional extra from 1968.

When the upgraded 641B was introduced cushion hitch was still an option and was not made a standard fit item until around 1974.

Due to the hard riding nature of these scrapers, most purchasers opted for the cushion hitch.