Drum Wood Chippers vs Disc wood chippers: Which is better?

The history of drum wood chippers vs disc wood chippers

1970s and 1980s

Going back a good number of years, the differences between the two designs were more distinct and this was predominantly due to the lower levels of development of the systems in place: many manufactures were still relatively new to the game and household names now on the market did not even exist.  The tree care market in Europe and the USA was also undergoing a rapid development and the market needs were very much in flux as was the financial status of the average customer and also the type of work they were doing.  Back in the 70s and 80s, the drum chipper was quite prevalent (though generally simple in concept and design) and the disc chipper was just starting to make itself felt on larger scale, with the capacity generally being limited to the smaller dimensions in Europe.  That being said, in the world of very large log and tree processing, the situation was reversed and the big machines were principally disc, with forced infeed.

1980s and 1990s

As the tree care market advanced through the 80s and 90s (directly accelerated in the UK to the industry it is now due to the storm of 1987),  customer needs became more focused and specific and the design of chippers became more mature and tailored to specific niches and capacities that has lead now to a blurring between the two generally accepted forms of cutting (lets ignore screw feed here due to the very low volume use in Europe of this type in tree care work).  Processing lower volumes of brashy/leafy material, whilst delivering an increasingly higher quality of chip on a compact footprint became the new norm, and then came cost of ownership, maintenance et al.  The disc chipper surged in Europe, driven predominantly by the UK market influence and in the USA by the simplicity of the larger 12 capacity disc chippers with a letter box style infeed.

Nowadays

Now, as the technology matures and manufacturing cost can be reduced due to the use of CAD/CAM and FEA analysis, combined with the ever-higher demand for more capacity on a reduced footprint, drum chippers are working their way back into mainstream tree care: they are definitely now the dominating design in the sub 6-inch domestic use class, that previously was the playground of discs.

So, with that all being said, what are the pros and cons of disc and drum style cutters in today’s market?  It’s best to look at the market need itself, rather than a predetermined machine capacity - the customer does not want the chipper, but requires the material disposed of efficiently, so let’s tailor the opinion based on the need (UK oriented, but this is essentially the same for much of Europe).

Application 1: Small scale, medium-light tree work, formative pruning, dead wooding, remedial work, crown lifting, thinning, crown reduction and occasional section felling) ;  chip to waste or limited scope to transport chip in volume long distances; small crew/company size

Disc chipper pros:

• Generally compact design that allows engine location to be either in line (narrow trailer/tracked machine) or to side (suited for zero tail swing turntables) for wide stance and stability
• Disc design is relatively simple and robust and cheap to manufacture, thus reducing purchase price
• Disc design combines cutting and discharge in one compact item, for good chip throw for reduced system complexity
• Current state of the art design disc do not require shear-bar adjustment when cutter knives are changed
• Disc design when cutting vertically down produces generally very good chip quality in most species
• Vertical down cut design (between rear bearing and outside of disc) allows feed roller very close to disc to significantly lower occurrences of oversize chips and infeed blockages
• Simple cutter housing design lends itself to good access for changing cutter knives
• Smaller disc designs can be made to have tight clearances between shear-bar and cutter knives for effective leaf cutting and reduced discharge blockage in larger leaf species

Disc chipper cons:

• Disc design requires relatively large cutter housing that will make up a significant percentage of machine size, weight and cost (could have been used for other systems in an alternative design)
• Infeed capacity (height x width- i.e. max. letter box size possible)) is greatly limited by disc diameter in vertical down cut designs
• The opening in the cutter housing (between feed roller and cutter disc) can sometimes be limited due to housing design and bearing location, leading to potential blockage issues
• Wide letter box designs (cutting horizontally) have a strong tendency to create poor chip quality, especially when knives are no longer sharp and processing species such as willow. Elm, Leyland Cypress., etc.
• Wide letter box designs (cutting horizontally) place the cutter disc rear bearing in the infeed and this forces the infeed rollers further away from the cutter disc, creating higher occurrences of oversized chips (due to sudden feed surge when end block is grabbed) and potential blocking
• Energy consumption by the discharge air paddles is generally lower than discs
• Disc cutters will generally perform poorly in chip quality and production once the knives have become dull
• Cutter disc bearings are heavily loaded axially and this can have a very negative impact on reliability and service life, especially if correct greasing is not carried out

Drum chipper pros:

• Drum design (and associated cutter housing) is generally significantly more compact than a disc design for the same nominal capacity-leading to more space and weight being available for other systems
• Drum design lends itself extremely well for a very wide infeed capacity making it ideal for wide brashy material
• Drums require a generally higher rpm compared to discs (for effective discharge and cutting speed due to the smaller diameters), but this produces better chip ejection and less re-cutting of material and less fines
• Drum chippers have the bearings at the side and have limited axial loads leading to generally higher reliability and service life
• Drum designs lend themselves very well to locating the feed roller very close and also providing a very large opening between infeed and drum - this significantly reduces the occurrences of infeed blockages
• Drum cutter housing and infeed housing designs can be very compact and simple, thus relatively cheap compared to disc designs
• Drum designs can provide very good chip quality, when the shear-bar is located closer to the centre line of the drum (creates a down cut motion basically identical to discs)
• Drum designs are very suitable for large volumes of large diameter material due to the heavy robust drum design
• Drum chippers will still be able to process reasonable volumes of material with dull knives, with acceptance that chip quality will suffer and in wet material the occurrences of discharge blocking will increase

Drum chipper cons:

• Engine location needs to be parallel to cutter drum rotation, thus in general has to be inline – excepting compact petrol engines, it is not practical to have the engine at the side for turntable use
• Drum designs tend to be more complex and thus more expensive than equivalent disc designs resulting in a more expensive machine
• Smaller drums designs required additional air paddles and high rpms to effectively discharge material resulting in higher noise and energy use compared to similar capacity discs
• Compact drum designs can be more susceptible to discharge chute blockages with wet leafy material such as Leyland Cypress and London Plane
• Changing knives (to sharpened set with smaller dimensions) requires adjustment of shear bar – this can be time consuming for the customer and access might be limited due to the general drum/infeed design
• Larger drum chippers tend to be heavier and longer than their disc equivalents

Application 2: Larger scale, medium-heavy tree work (dead wooding, remedial work, crown lifting, crown reduction, frequent section felling, powerline/road/rail clearance); chip to waste or transport chip in volume long distances; big crew/company size/ dedicated chipper teams

The above pros and cons also apply here, but as the scale of work dictates volume processed and efficiency (and serviceability/reliability/robustness) over compactness and purchase cost, the advantages and disadvantages are skewed heavily in the drum chippers favour.

Disc chipper pros:

• Disc designs lend themselves to larger turntable chippers that can be used in street tree applications
• Large disc designs are generally cheaper compared to equivalent capacity drum machines
• Disc chippers have very good discharge for relatively lower sound output

Disc chipper cons:

• Large letter box infeed dictates large disc and cutter housing.  A practical upper limit is around 12 inches capacity, after which the machine is generally too big for its capacity
• Large diameter discs have high energy requirements due to the discharge air paddles
• Disc chippers are not as suitable as drums for large volumes of large diameter material due to chip processing through the disc and overall infeed opening dimensions possible
• Axial loads on cutter disc bearings become significant dictating their size which increases costs and reduces space available for infeed opening, feed roller location, etc.
• Not really suitable for grapple feeding large logs and trees due to overall throughput and aforementioned bearing considerations
• Very difficult to include any form of chip size control (screens, etc.) without significantly reducing overall performance and energy efficiency

Drum chipper pros:

• Large infeed capacity relatively simple without compromising cutter and cutter housing size leading to relatively compact machine (for its class) compared to disc equivalent
• Generally above 12 inches capacity, drum design are the only practical option due to machine size
• Due to infeed roller location and opening between roller and drum, ideally suited for processing large material with minimal infeed blockages
• Relatively straightforward to add chip quality control systems, although additional discharge blowers may be required, depending on size of system
• Bearings see relatively little axial loads and the design is ideally suited for grapple feeding large branches and trees.
• Cutter and infeed housing is relatively simple in design and thus easier and cheaper to make in robust form to suit the larger material being processed

Drum chipper cons:

• Chip quality control systems generally require addition blower (disc with paddles or equivalent) that adds additional cost, weight, system complexity, energy consumption and noise compared to a similar capacity disc chipper
• Generally, more expensive than the equivalent capacity disc chipper
• Not suited for turntable design due to overall engine and system length

Why not explore Vermeer’s full range of wood chippers?  If you would like more information on our products or servicing, contact our expert team on 01933 274400, email us at sales@vermeeruk.co.uk, or complete an enquiry form where our team will be able to help you out.

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