pierre van Rooyen, David Brown, south Africa, presents a case study

Refusing to
compromise
Pierre van Rooyen, David Brown,
South Africa, presents a case
study about the development of a
new gearbox series for conveyor
drive systems.
D
avid Brown, a global manufacturer and designer of gears
and gear systems, was approached by one of the US’s
largest power utility companies to assist at a major coal
mining complex in Pennsylvania. The contract was to
become a significant moment in the company’s business.
The customer’s specific requirements had been unfulfilled by previous
manufacturers, whose conveyor drive systems in operation at the site had
become troublingly unreliable. Given their critical role in powering the
conveyor belt systems used to transport raw coal from underground
mining operations to the preparation plant, this presented a major problem.
Repeated issues had required more and more scheduled and unscheduled
maintenance, together with the loss of valuable production time.
January 2013 | World Coal | 61
Figure 1. The CX series gearbox, which can be supplied individually or as a complete
conveyor drive unit comprising some or all of the following parts:
1. CX series gearbox.
6. Cooling fan.
2. Low-speed output couplings.
7. Safety guards.
3. Conventional and fluid-type input couplings. 8. Flywheel and support bearings.
4. Holdback/backstop.
9. Electrical motors (HV or LV).
5. Disc or drum brakes.
10. Base frame or torque arm.
Characteristics of the gearbox are also described in Table 1.
Table 1. CX series range characteristics
Housing material
Grey iron or high tensile ductile iron
Housing design/construction
Split case along shaft centres, symmetrical
flippable housing
Speed range (input speeds)
To suit standard motors 50 and 60 Hz, 4 and 6 pole
Ambient temperature range
-10˚C to 45˚C (14 – 113˚F)
Nominal rated sump temperature
80˚C (176˚F)
Warranty
Optional 3 year warranty with 3X assurance
Mechanical ratings
55 – 3000 kW (90 – 4000 hp.)
Thermal ratings
140 – 3000 kW (185 – 4000 hp.)
Lantern housing options
Numerous configurations to suit requirements
Output shaft options
All combinations available
62 | World Coal | January 2013
In a situation where continuous
operations are the primary goal, any
unscheduled shutdowns due to
equipment failure can result in
significant cost increases. After
assessing the situation, the
customer’s own engineering experts
determined they did not want to
spend any more money or man hours
trying to keep up with the failing belt
drive system. The customer
presented David Brown with a clear
challenge: fix the problem once and
for all – and fast.
To fulfill the sheer range of
requirements, which included the
ability to operate at ambient
temperatures ranging from
-10˚C to 45˚C without any external
lubrication or cooling system,
David Brown had to develop a very
specific solution. The biggest
challenge was to ensure adequate
lubricant flow to the high-speed
bearings without a pump. The
company introduced a reducer to
manage operating speeds between
10 – 100% of motor speed under full
load (without a forced lubricating
system) and a bespoke low speed oil
collection system. This approach was
then tested in South Africa as
David Brown simulated the worst
conditions possible using a slow
speed drive and extremely high
viscosity oil. The field test was
successful, so the customer in
Pennsylvania had the assurance of a
proven technology for a lasting fix.
A customer-led innovation
The Pennsylvania project was
unique, requiring a specific approach
and solution, representing an
exciting challenge for David Brown:
a complex, critical and unusual
problem requiring the most skilled
expertise to develop a solution –
quickly and reliably. This project
marked a turning point for the
company and the beginning of a
steady increase in customer concern
over gearing units being thermally
underrated for the temperatures in
which they operate. The company
began to receive increasing numbers
of technical specifications from
mining clients, particularly in
conveyor drive applications,
specifying bearing lives in excess of
50,000 hours, with some as high as
100,000 hours. The company
continued to deliver tailored
solutions for its mining customers to
meet their exacting requirements,
but also began to explore the idea of
a standard but adaptable range to
improve efficiencies while also
driving down cost.
With competitors already offering
some smaller product ranges, the
company needed to be able to offer a
significant increase in product
performance to make pursuing the
concept worthwhile. However, it did
not take long to validate the idea.
After an extensive survey across its
entire customer base, which spans
all major mining regions, including
Australasia, the Americas and
Africa, the company quickly moved
beyond informal feedback. Increased
bearing life, increased thermal
ratings, reduced noise and easier
maintenance were confirmed to be
customers’ top priorities. These
system requirements were not a
huge surprise, but the company
became very interested in another
finding from the survey. Many
customers seemed resigned to not
being able to realistically meet all
these requirements in a single
gearing unit. A gap in the market
was evident and this became the
starting point and the backbone for
the development of the CX series
gearbox – David Brown’s
standardised range with a
difference.
The company drew on its
150 years in business and
established credentials in the mining
sector. It was able to assemble a
project team from North America,
India, Australia, South Africa and
the UK whose collective expertise
had been proven in the world’s most
extreme mining environments.
David Brown is driven by customer
need, so while developing the
advanced technologies of the CX
series was exciting, it was also a
very natural route for the business.
Pennsylvania became just one of
a number of projects this team drew
upon in developing the advanced
technologies of the CX series, which
Bearing the brunt
The CX series is designed specifically to address the requirements of conveyor drive
applications. The power capacity of conveyor drives is often constrained by bearing
life limitation. David Brown provides optimised systems to balance mechanical
power, thermal ratings and bearing life.
nn Bearing life minimum: 60,000 hours L10a @ 1.5 SF rated power.
nn Adequate bearing life for shaft mount units utilising ISO bearings.
nn Focus on bearing life during design is a major contributor to overall system
reliability and operating cost.
Figure 2. Maximised bearing life for enhanced performance.
Figure 3. David Brown’s CX525R2 ready for dispatch in Australia.
Figure 4. Modular, flippable case design with enhanced thermals.
January 2013 | World Coal | 63
the company field-verified in one of
the world’s most remote locations:
Australia’s Pilbara iron ore region,
operating in ports and mines with
ambient temperatures exceeding
45˚C. All field and rig test
experience, which has been in
operation for more than five years,
has been further verified by state-ofthe-art analysis.
Benefits
The resulting CX series is a
customised conveyor drive system
that represents a new model
specifically designed for the mining
industry where performance, bearing
reliability and thermal life are
primary concerns. It represents
optimised capabilities for conveying
drives on the market today and has
already been proven to be reliable
and low in maintenance. The
company’s driving philosophy has
been to deliver a custom solution
that adds value to the customer
process and not supply a fixed
standard, which may compromise
performance. David Brown believes
it stands to make a significant and
positive impact in mining operations
worldwide. Regional engineering
facilities allow the units to be
adapted to suit specific customer
requirements.
Crucially, the CX series delivers a
number of key product solutions
without the need to use a larger unit
– enabling the customer to select
units similar in size to those in place
but with the added advantages of
improved bearing life and increased
thermal capacity. The statistics are
impressive: the CX series delivers up
to four times longer bearing life and
up to 20% greater thermal capacity,
which reduces the need for ancillary
cooling equipment. Not having to
upsize just to achieve desired thermal
ratings is especially relevant in very
high ambient temperatures. The CX
series has thermal ratings in excess of
50% better than competitors’ drives
that give similar mechanical power.
What is exciting about that is that it is
relatively easy to optimise one
feature, but here the company has
optimised across the range of features
customers most want without making
concessions. Others talk about low
mass units or very compact designs
but all carry a distinct thermal
disadvantage.
Customers require relatively quiet
units to meet stringent industry
standards. David Brown introduced
precision gear tooth profiles to reduce
noise, while maximising power
transfer so there is no compromise in
performance. The CX series can carry
very high loads. An optimised rugged
cast housing also gives a superior
power-to-weight ratio and there is a
unique flippable design with modular
mounting options to maximise fitting
flexibility.
Throughout the design process,
the company’s teams have
undertaken study analysis on the
whole system – looking at gears,
bearings, the shaft and the case
design. David Brown has made use
of computational fluid dynamics
(CFD) modelling in the case design,
as well as noise, vibration and
harshness (NVH) modelling for the
gear train and has been able to
achieve an optimised product that
gives the best performance possible.
The CX series is a total system that
has been optimised for overall
system reliability and operating
cost.
Customer interest levels since the
launch of the CX series last year at
MINExpo INTERNATIONAL® 2012 in
Las Vegas reflect excitement in the
marketplace, with a dramatic increase
in the number of enquiries.