Bag And Belt Cleaner
Reduces Employee Dust Exposure

handle 50- or 100-b bags.

by Andrew B. Cecala,
Robert J. Timko, and
Alexander D. Prokop

ag loading and stacking process-
es are the highest dust-exposure
job categories in the metal/non-
metal mining industry.’ ‘To cost-effec

tively decrease respirable dust leve

the Pittsburgh Research Center of

National Institute for Occupational
Safety and Health (NIOSH), former-
ly of the U.S. Bureau of Mines, ¢
signed and tested a system called th:
Bag and Belt Cleaner Device
(B&BCD). The B&BCD is capable of
cleaning the surfaces of either 50- or
00-Ib bags. A combination of dust

control techniques leave the bag sur-
face and conveyor essentially dust free
The B&BCD can be placed in the

conveyor line anywhere between the
bag-loading and the bag-stacking
process. Although the original design

of the system was to handle 50- or
100-Ib bags, it can handle most bag
sizes with minor modifications
Cleaning the surfaces of the bags and

the conveyor belt greatly reduces dust

and Belt Cleaner Device (shown with access panels removed) can

liberate bei

{ while the bags ai
transported to the bag-stacking loca-
tion, Ultimately, this reduces the dust
exposure for bag stackers, other
workers in and around the area
the end users of the bagged material

The B&BCD uses a
of stationary brushes, rotating brush:

and

ombin:

es, and air nozzles to clean product
material from the surfaces of the bags
re 1). The
) ft long and is installed
As a bag
enters the device, it travels through a

and conveyor belt (F
B&BCD is 1

as a part of the canveyor lin

flexible plastic door where a station
ary brush on a swing arm starts the
cleaning process on the front and top
of each bag.

The bag then travels through a sec-
ond plastic door and enters the main
section of the device where a rotating
circular brush cleans the top of each
This brush r

bag
bag travel direction, creating addi

ates opposite to the

tional friction to improve bag clean
The sides «

each bag are then

ionary brush posi-

tioned each side of the chamber.

An airjet nozzle is located at the end

of each of these brushes.

Each bag should travel through
with the valve aligned on the same
side of the device for proper clean
ing because the valve side of the bag
normally is much more contaminat
ed with product than the opposite
side. A plastic airjet nozzle deliver
ing 20 cfm of air is used to clean the

valve side of the bag. On the non

valve side, a flat fan airjet nozzle de

livering 3.0 cfm is used because it is
not necessary, nor cost effective, to
use a high-volume airjet nozzle on
this side.

The bag then travels over a rotat

beneath

ing circular brush locate

the bag to clean the bottom of each
The brush rotates in the sa

ction as the bag moves because

bag.
dir

reverse rota

me

‘ion would cause

hang up due to the length of the
open span, especially with 50-Ib bags.
The cleaning process is efficient,
brush rotation in the

even with the

same direction as the necause

the weight of cach bag forces it

onto the bristles of the brush

The bag then exits the device
through anc chamber, again hav
ing two sets of flexible plastic doors. A
chain conveyor is use
le
removed from the bags to fall into a
hopper located beneath the B& BCD.
Product collected in the hopper is pe

riodically recy

dj for the entire

th of the device to allow product

led back into the

process via a screw conveyor
The B& BC

at only requires hookups

D is a self-contained

system

electricity, compressed air, and ex
ntilation. Electrical needs in

clude 440 volts, three-phase p

haust v

drawing approximately 14 amps dur

ing ne

operatic
Compressed air requirements in
clude supplying the two air nozzles
with approximately 40 ps
In addition,

fm

a minimurr
iodically change the
spacing of the stationary side brushes

ntity of air

is necessary to

to accomodate 50- or 100-lb bag sizes.
An exhaust-air vol

mately 1,200 cfm is

me of approxi

ceded to keep the


system at negative pressure relative to
the surrounding atmosphere. This
prevents dust generated within the
B&BCD from flowing out of the unit
and contaminating the work environ-
ment. Because of the quantity of dust
being removed, it is recommended
that this exhaust air be ventilated into

a baghouse.

Put to the test on silica sand
The B&BCD was evaluated at two sil-
ica sand plants, both uct
sized between 120 and 325 mesh in
50- and 100-Ib paper bags. The pri-
mary goal of each evaluation was to
compare respirable dust concentra-
tions with and without the B&BCD.
At the first evaluation site, two bag
stackers manually loaded pallets, At the
second site, this process was automated

"io rocyee product

Figure 1: Schematic drawing shows the major components of the Bag and Belt Cleaner Device.

using a palletizing machine. The dust-
plants, Real-time aerosol dust monitors
(RAM-1) were used at various locations
around the conveying and bag-stacking
process and were considered the pri-
mary dust-monitoring instruments.
The RAM-1 device uses a 10-mm
(0.39-in.) Dorr-Oliver cyclone to clas-
sify the respirable dust fraction—parti-
cles having an aerodynamic diameter of
10 microns or less.

Another analysis technique per-
formed at both evaluation sites in-
volved removing surface dust from a
specific number of bags with a vacu-
um-cleaning device. This was done to
determine the reduction in the
amount of product on the outside of
the bags using the BK BCD. Ten, 100-
Ib bags and 20, 50-Ib bags were ran-

domly removed from the conveyor
line and thoroughly vacuumed. By
pre- and post-weighing the vacuum
bags on an analytical balance, the
amount of product removed from the
bags was determined. The effective-
ness of the B&BCD was determined
by comparing identical product mesh
and bag sizes at each site.

The first evaluation was per-
formed by measuring dust levels be-
fore (Phase 1) and after (Phase 2) in-
stallation of the B&BCD. The entire
conveying and bag-stacking area was
enclosed with transparent plastic ma-
terial to minimize the effects of back-
ground dust sources. Each phase was
performed for five, 8-hr days and
measured respirable dust liberated by
the movement and handling of bags
during the palletizing process.


7 Product Gi, mesh i

25

Figure 2: Amount of product removed from the exterior of S01b bags by vacuum-
ing, with and without the cleaner device in operation, at evaluation site #2.

Average respirable dust concen-
trations in Phase | ranged from 0.99
to 2.02 milligrams per cu meter
(mg/m'). In Phase 2, they averaged
0.63 to 1.89 mg/m’. The perfor-
mance of the B& BCD was adversely
impacted by an insufficient quantity
of exhaust air. As previously stated,
the device was designed to operate
with an exhaust volume of approxi-
mately 1,200 cfm. When the device
was originally started, the facility was
only able to provide about 475 cfm.
An additional fan was installed that
increased the exhaust volume to 725
cfm; however, the system was still
only operating at 60% of the de-
signed air volume. This deficiency
caused the unit to have insufficient
negative pressure which resulted in
some dust leaking from the device
into the work environment

Bag-surface vacuuming provided
the best indication of the B&BCD's
effectiveness at the first evaluation
site. For Phase 1, the weight gain of
the vacuum bag per test ranged from
46 to 171 grams (g). This compared
with a weight gain of between 9 and
17 g per run during Phase 2. The re-
ductions in the amount of product on

the outside of the bags with the
B&BCD were 77.6%, 81.2%, and
89.9% for 200-mesh/100-Ib bags,
325-mesh/100-Ib bags, and 200-
mesh/50-Ib bags, respectively. These
results were not significantly influ-
enced by the lack of exhaust air vol-
ume to the B&BCD and provide a
good indication of the reduction in
product on the exterior of the bags.

‘The second evaluation site was at
an operation that was making a num-
ber of modifications to modernize its
ground silica bagging and stacking
process. Along with the B&BCD, a
new bag-filling machine, a bag flat-
tener, a bag-weighing and printing sta-
tion, and an automated bag palletizer
also were installed. It was not possible
to perform pre- and post-installation
testing of B& BCD due to these mod-
ifications. Because of this, dust con-
centrations were recorded with and
without the B&BCD operating dur-
ing similar time periods for each spe-
cific mesh and bag size.

‘Testing at this field evaluation site
again provided results showing the ef-
fectiveness of the B& BCD at reduc-
ing respirable dust concentrations.
There were three dust-samphing loca-

tions in the mill area around the
B&BCD to evaluate respirable dust
levels with and without the device in
operation. These three dust-sampling
locations averaged a 24% reduction in
respirable dust over the entire evalu-
ation period

Results obtained by vacuuming the
exterior surfaces of the bags also pro-
vided a good indication of the effec-
tiveness of the B& BCD. The average
weight gain of the vacuum bag per run
of product bags before going through
the B&BCD was between 43.7 and
72.8 g. This compares to an average
weight gain of between 5.3 and 10.7 g
per run after going through the
B&BCD (Figure 2).

At the second field evaluation site,
dust concentration measurements also
were taken inside the B&BCD, with
and without the device operating. Dust
levels were higher with the device in op-
eration because of the dust and product
being removed from each bag as it trav-
eled through the device. The increase
in dust levels ranged from 180% to
1,000% during operation of the
B&BCD. Dust cleaned from the bags
within the device means less dust gen-
eration and contamination of mill work-
ers after exiting the device

Throughout this research project,
modifications were made to improve
the operational effectiveness and safety
of the B& BCD. The system has shown
itself to be a practical, reliable, and ef-
fective technique to clean product bags
and the belt at mineral-processing
plants, thereby improving worker
health. To date, the B&BCD has been
in operation for more than three years
without significant problems. 3

Andrew B. Cecala is a mining engineer,
Robert J. Timko is 3 physical scientist
and Alexander D. Prokop is a mechan)
cal engineer technician, ali with NIOSH’s
Pittsburgh Research Center

Noted Reference

Warts Jr., W.F,. and D.R. Parker,
Quartz exposure trends in metal and
nonmetal mining, Applied Occupation-
al & Environmental Hygiene, Dec
1995, vol. 10, no. 12, pp 1009-1018.