New Holland are gearing up to celebrate the 50th anniversary of its rotary combines, which first appeared in the form of the TR70 in 1975.

Up until that time, combine harvesters had all worked on the well-proven and robust drum and straw walker principle that had been the mainstay of combine harvesters since their early years.

Yet, in what is regarded as the very first combine harvester, developed by Hiram Moore in the mid 1800s, separation of the grain was undertaken by a rotary sieve lying in a longitudinal position behind the drum, so the idea was not completely novel.

Hiram Moore combine — The very first combine built by Hiram Moore relied on a longitudinally mounted sieve for separation

The rotary concept may well have enjoyed a brief flame of life right at the start, yet it was soon forgotten, so what advantages did New Holland see in resurrecting the idea and devoting ten years and a good deal of money in developing it further?

Advantages of type

There are several features associated with rotary type combines which are said to make them superior to conventional straw walker types – the chief of which is increased capacity.

New Holland brochure — Twin rotors were promoted as taking farming into the future as illustrated by that old marketing favourite, the father and son motif.

To understand why this is, we need to remind ourselves that there are two stages to separating the grain from the straw.

The first is the threshing operation in which the seeds are dislodged from the ears. This leaves an admix of straw grains and chaff that needs to be separated, which is the second function of a combine harvester.

Legacy mechanism

With a conventional set-up, the crop is fed to the drum which then rubs it against the rasp bars to separate the grain. This is how mechanical separation has worked since threshers were invented, but it has limitations.

The first problem is that this method can damage the grains, while the second is that the crop only passes through the threshing mechanism once, so any grain that is not dislodged at this stage stands the risk of passing out through the rear of the machine.

Straw walker combine — The layout of a typical straw walker combine with a threshing drum feeding the crop onto the walkers for separation. Source: Estes Concaves

There is also a limit at which the crop can be processed, for the rate is dictated by the speed at which it can fall from the drum. This function is entirely dependent upon gravity – a force which, unfortunately, cannot be adjusted to suit conditions.

There are three variations that can be built into the combine to increase the rate of processing, the first two being the width and diameter of the drum while the third is to install an extra drum.

However, these fixes are limited by the space available within the combine and the expense of building a larger machine to accommodate them.

Once threshed, the crop then passes on to the separation stage, which consists of a series of long, narrow boxes moving relative to one another, shaking the remaining grains from the straw which in turn moves it to the rear of the combine in doing so. These are the straw walkers.

Rethinking the wheel

New Holland rotary combines address the two functions of threshing and separation in a somewhat different way.

The standard threshing drum is removed completely and, in its place, two long rotors run fore and aft along the axis of the machine at a slight incline.

Combine diagram — The two longitudinal rotors can be clearly seen in this brochure from the seventies

This slope serves to lift the crop away from the header and raise it above the sieves before depositing the straw from the rear.

These rotors are enclosed in circular grates that form a tube around them, the first half of which is designed for threshing while the second half is responsible for separation.

It is claimed that as the crop passes through the system, it rotates three times around the rotor before being ejected from the rear end, the great benefit being that its separation is a less brutal affair that results in fewer damaged grains.

Thin rotor diagram — An explanation of the twin rotor system for the TR70

It can also process more crop, for the grain is ejected through the sieves by centrifugal force rather than gravity, thus it is the speed of the rotors that is the primary adjustment rather than the setting of the concave.

In its early combines, New Holland stated that the crop took only three seconds to pass through the machine rather than nine in a conventional type.

It was also claimed that the thinner but larger mat between the rotors and grates provided a greater separation throughout the crops’ passage through the rotor.

Rival design

Being able to process more crop means rotary combines tend to have a higher work rate, although there is great debate as to whether they are suitable for all conditions.

New Holland’s sister company, Case, also has a rotary system known as the axial flow. However, this has just the one larger rotor rather than a pair of contra rotating units.

Clayson Combine — The new twin rotor combines would be pitched against such machines as the Clayson 1545 with 120hp on tap.

New Holland state that the smaller twin rotors encourage the grain to separate quicker because the tighter turning radius increases the centrifugal force experienced.

The company claimed in its early sales literature that twin rotors also smoothed out the power demand and gave a more equal distribution of grain over the sieves, factors which are still important today.

First rotary on the market

The first development machine, adapted from a 985 straw-walker model from the Claeys factory in Belgium, which it acquired in 1964, was trialled in maize in 1968, and wheat the following year.

By 1969, a totally new combine design with these internal elements was under test, and in 1975 the first production model, the TR70 with a 145hp engine and 5,550L/158-bushel grain tank, was launched, which also happened to be the first New Holland combine built in the US.

Dockside loading — The Twin Rotor machines enjoyed success around the world

For the 1979 season, it was replaced by the upgraded TR75, and joined by a larger companion, the TR85. The range evolved over the next two decades, with the 25,000^th TR combine produced in 1997.

Over 70,000 TR and CR Twin Rotor combines have been produced globally since the introduction of the concept.

Tangential rotary

In Europe, there was some concern about straw quality, for this was considered as much a part of the crop as the grain, especially in livestock areas, and the twin rotor machines had been developed primarily for the American market.

There was now a considerable gap between the capacity of the traditional straw walker machines and the new way of doing things, a gap that was filled by hybrid combines rather than dropping straw walkers altogether.

Straw walkers remained fairly basic machines that may have been slower but had simplicity and price and the preservation of the straw on their side.

And they were still being developed – the introduction of variable speed walkers to accommodate slopes is an example of another step forward in their design.

Hybrids

However, the higher capacity of rotary combines could not be completely ignored. Work rate is the driving force of machinery design and so it was that the hybrid combine was developed for the European market.

Known as Twin-Flow combines, this combination of technologies was introduced in 1983 and utilised a conventional drum and concave followed by a large beater and rotary separator in place of the straw walkers.

The rotary separators were still placed across the combine parallel to the drum, and this remained the case until the introduction of the Crossover Harvesting System, which scaled down twin rotors in the fore and aft configuration to perform the separation function.

New Holland CR — The culmination of 50 years development is seen in the flagship CR 11

The evolution of New Holland’s approach to harvesting has culminated in the CR series of machines which are the company’s largest combines yet, being topped by the CR10 and CR11.

The advent of the rotary technology has allowed far greater throughput and, to make the most of this potential, these two models are powered by 775hp and 634hp engines respectively, encouraging work rates that may consume a lot of diesel but cover a lot of ground in doing so.

Advantages of type

Legacy mechanism

Rethinking the wheel

Rival design

First rotary on the market

Tangential rotary

Hybrids

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