C. M. Consulting
P.O. Box 407
Odell, Oregon 97044
C. M. CONSULTING
A Division of Cliff Mansfield Incorporated
Winter Maintenance Checklist
Winter's coming. And with it comes
time to perform needed maintenance chores at the asphalt plant. When setting up
a plan of attack some people find it helpful to use a checklist to determine
which items need special attention and which ones need only regular servicing.
What follows is the author's inspection protocol, used to formulate a schedule
for a plant maintenance and repair regimen.
In Part 1 we talked about drum-mix plants, and the equipment common
to both drum and batch plants. This article will concentrate on the batching
tower and its specific requirements. As you perform these inspections keep a
clipboard handy to note any needed repairs. Marking paint is also useful to
highlight units in need of attention.
As stated in Part 1, the author is not familiar with every conceivable
combination of equipment in our rapidly changing industry. Omissions are bound
to happen. Keep in mind that this article is intended as a guideline and in no
way professes to be the last word on the subject. Feel free to delete or add
sections as needed to suit your particular application.
Remember to follow OSHA lock-out, tag-out regulations during these inspections.
HOT STONE ELEVATOR:
Hot elevator chains operate in a very hostile environment. Heat,
dust and stress all work together to promote wear. Unless we track that wear and
address it at the appropriate time, things can come shuddering to a halt. As we
all know, when the bucket-line breaks digging out the 300 degree rock,
untangling the piled up chain and making the needed repairs is a time consuming
chore. One most of us would rather avoid, if at all possible. An inspection,
using a critical eye, can go a long way towards dodging the proverbial bullet.
Begin by removing all access and inspection doors.
1- An external inspection is first. Look for thin metal, dust leaks and
obvious structural damage.
2- Remove the guard and inspect the hot stone elevator's drive system.
Chain drives are common. If your unit use this method of propulsion it is
important that you inspect the chain for excessive wear and both sprockets for
any signs of damage. Look for a condition called 'fish eyeing', or cupping on
the load side of the teeth. Mark any abnormalities you find.
If your unit is belt driven you need to look for cracked or glazed belts,
excessively worn sheaves and a loose condition which requires adjustment.
3- Examine the motor and gearbox for any abnormalities. Mark for
attention anything that raises doubts.
4- Inspect both upper bearings. Use a bar to pry the shaft around. With
the weight of the chain on the shaft, this operation will require considerable
5- Look through the access door and examine the top sheave. On friction
drives look for irregular wear patterns, breakage or looseness. For toothed
sprockets look for excessive wear, fish-eyeing and obvious damage.
6- Some elevators use idlers. It is essential that each one of these
receive an exacting examination. Idler shafts have been known to break, and
under certain conditions stall the elevator. On sprocket driven units the bucket
chains have broken as a result of the impact with the idler shaft.
NOT A PRETTY SIGHT!
Look at each idler. Bent or grooved shafts and worn wheels must be scheduled for
7- Look at the tail shaft and traction wheel. Is the wheel egg shaped? Is
it worn out or loose? Are the bearings in good condition? Do the adjusters work?
How about the shaft's dust seals, are they working? Mark anything that needs
8- Look at the individual chain links. If they are worn to the pins and
the side bars abraded to knife edges do you really want to head into a paving
season with them?
When ordering hot stone elevator chain, get the best you can afford. I know of
no other situation where the adage 'you get what you pay for' applies as well.
9- Lastly, examine each and every bucket. Look for excessive wear, cracks
or missing bolts. Any severely distorted bucket is a liability and should be
GENERAL MAINTENANCE section
near the end of this article.
The screens are very important to the operation of a batch plant.
In fact, they are the only reason to own a batch plant as opposed to a drummer.
Any examination of this unit should be done with an eye toward efficiency.
1- Start with an external inspection. Look for missing parts, such as lid
hold-downs, and for signs of dust leaks. Look at the skirting seals under the
units. Are they there or long gone? Examine the top covers. Are they worn out
where they rest on the frame or other lids? All these conditions should be
addressed. Check to see that the screens move freely. If they don't, look for a
buildup of aggregate under the drive end. Check the size of the material. If
it's a useable size that normally goes into a hot bin the accumulation could
point to leaks in the oversize discharge, exacerbated by screen flooding and
Often, this condition can be addressed by repairing the leaks and reversing the
screens so that they throw the material back toward the hot elevator. This makes
the material stay on the screens a bit longer, giving it time to work through
the screen cloth. This same approach can sometimes solve sampling problems which
are caused by carry-over at higher production rates. It's not uncommon for a
plant operator who has his machine calibrated and in 'spec' at a certain
tons-per-hour rate to find he is being forced to run his plant ever faster in
order to meet production demands. As production rates increase, so does the
carry-over rate. Under the right conditions the finished product can go out of
'spec', leading to hair pulling and a midnight recalibration session. If you've
experienced this scenario, try reversing the screens. This should produce a more
consistent mix through a wider range of feed rates.
2- Next, remove all the lids and side covers. It's a good idea to take a
fire hose and clean the accumulated fines off the screen frames and springs. It
makes it much easier to find damaged and cracked components. Caution: Remember
to open all the gates below and provide a way for the water to escape from under
the plant. Once the unit is clean you should inspect it for broken springs and
cracks in the framework.
3- Closely inspect each screen cloth. Look for excessive wear and broken
wire. Check the screen trays. Are they all tight? Is the screen cloth secure?
It's good insurance to stock a complete change of screens. When stored in a
custom built rack on the screen deck, they are ready for installation with a
minimum of fuss. Don't forget to keep a supply of the appropriate bolts handy.
4- Examine the screen drive and eccentric. Follow the manufacturer's
recommendations as to periodic maintenance. In general, you should look for
damaged components, worn sheaves or belts and broken motor mounts.
1- Inspect the inside of each bin. Look for thin metal, missing
partitions and any structural damage. Check the overflow chutes and hats, if
used, for leaks. Schedule maintenance on anything amiss. Look at the bin
dividers. Do they go up close enough to the bottom of the screens to prevent
2- Check the gates and their pivots/rails. Do they work freely? Are they
3- Examine the air cylinders. Check for leaks or loose rod and pivot
4- Schedule the air solenoids for kits and cleaning. The same for the air
oilers. This is cheap insurance and could possibly avert a problem at a later
Spare solenoids, air lines, a cylinder and an oiler might possibly shorten
'downtime' in the event of a component failure.
AGGREGATE WEIGH HOPPER:
The examination of this unit is essentially the same as for the hot
bins with the exception of the weigh system.
1- Check the basic iron for thin spots.
2- Check the gate and its pivots/rails.
3- Check the air system. Again, schedule the solenoid and oiler for kits
1- Begin by cleaning all the knives/pivots. Use compressed air. Do not
lubricate them once they are clean.
2- Inspect all knives and pivots. Look for loose, missing or misaligned
components. If you find anything wrong contact a reputable company that
specializes in scales. Have the scales repaired and calibrated.
It's best to schedule this activity for a time when all other repairs to related
equipment have been completed. The addition or deletion of metal in the weigh
hopper can drastically affect calibration.
OIL INJECTION SYSTEM:
types of oil injection systems are in use: Gravity feed and forced feed. The
checklist for the weigh system and for the asphalt oil bucket is nearly the same
for both systems. The gravity system has a clapper valve and some associated air
controls. The forced feed system uses an injection pump which we will address
1- Examine the exterior of the unit. Is it covered in asphalt? If so,
from where? Is it caused by overflows which could be pointing to a problem with
the scale read-out and its signal to the blending computer, or possibly from a
sticky fill valve that occasionally fails to shut off when told to do so?
2- Check the heat transfer oil system for the bucket. Does it leak? Does
it work? Check to see if the hot oil lines are binding the bucket, possibly
resulting in inaccurate readings. If so, schedule repairs.
3- Examine the clapper valve on the gravity system. Does it fit properly
and seal? Are the pins worn out? How about the air cylinder, is it worn out? Air
lines in good shape? As with all the other solenoids and oilers, it's a good
idea to schedule those on the oil injection system for a cleaning session and
then install tune-up kits.
4- Check the spray bar where it enters the side of the pugmill. Is it
free or does it bind? Under the right conditions a binding spray bar can lead to
abnormally high oil contents. You should look for an accumulation of material
between the bottom of the spray bar and the side the pugmill. This material can
restrict the downward movement of the oil bucket as it fills and cause the
scales to read lighter than the amount actually in the bucket. Any build-up here
should be scheduled for removal.
For additional information on this subject
or help with any problems encountered
contact Cliff Mansfield,
7:30am to 9:00pm Pacific Standard Time.
bucket fill system:
1- Check the overall condition of the valve. Is it leaking? How about its
connections? Does the heat transfer oil system work? Does it leak?
2- Examine the air actuation system. Use the same criteria to evaluate it
as we've used throughout this inspection.
This procedure is the same as the one for the aggregate weigh
1- Clean all the knives/pivots. Use compressed air. Don't lubricate them.
2- Inspect all knives and pivots. Again, look for loose, missing or
misaligned components. If you find anything wrong contact a reputable company
that specializes in scales. Have them repaired and calibrated.
As with the aggregate scales, it's best to schedule this activity for a time
when all other repairs to related equipment have been completed.
1- Check the pump and all its lines. Schedule any leaks for repairs.
2- Check the drive system. Some pumps use couplers and a direct drive
motor, others use a belt drive while still others are driven by a chain off the
pugmill itself. Whatever method yours uses examine it for the same flaws we've
discussed on other units, such as fish-eyeing, worn sheaves/belts and couplers.
3- On units that use a vacuum breaking valve to control emptying the
weigh bucket you should check it and its operating system for any problems. For
air operated systems start by checking the air cylinder. Is it worn out? Are the
air lines in good shape? As with all the other solenoids and oilers, it's a good
idea to schedule these for a cleaning session and then install tune-up kits.
Follow OSHA Lockout-Tag out regulations before inspecting this
potentially lethal unit.
1- Remove the inspection doors and examine the interior of the unit. Look
for excessively worn shanks, tips and liners. Cracked or broken components
should be slated for immediate replacement.
2- Check the asphalt injection spray bar. Are all the spray nozzles in
place? (see note 1) Is the bar worn thin on the top where the aggregate from the
weigh hopper cascades over it? (see note 2)
3- Examine the mainshaft bearings. Again, use a bar to pry the shafts
around. Mark for replacement any bearing you are in doubt about.
4- Inspect the drive assembly. With chains, look for 'fish-eyeing' and
excessive wear. For belt drives look for glazed or loose belts and worn sheaves.
Special attention should be given to those units that use shaft couplers. Check
for any signs of damage or movement. Again, when in doubt replace them. Failure
of one of these devices on certain pugmills can throw the timing off, resulting
in catastrophic damage to the machine.
Several oil related problems plaguing hot mix manufacturers can be traced back
to the spray bar. One, sluggish emptying of the weigh bucket, can result in
slowed production rates. Which usually leads to the removal of some of the spray
nozzles in an attempt to speed things up. This, in turn, leads to the second,
potentially more damaging issue: Spray nozzles control the distribution of oil
in the mixer. If adjusted and sized properly the oil is uniformly distributed
throughout the pugmill. If set-up incorrectly, or removed altogether, the
resulting spray pattern can produce lean/rich spots in a particular batch of
mix. If the state's sample person gets mix from a lean spot and his results
reflect a low oil content, the operator adjusts the oil upward to avoid going
out of spec. If, on his next test, the inspector pulls the sample from a rich
spot the resulting jump in oil percentage could easily put a plant out of spec
and into penalty territory. If the swing is bad enough it could result in a
mandatory shut-down and plant recalibration. Put quite simply, all of this could
be due to an easily addressed oil distribution problem in the pugmill. Using a
slat conveyor, batcher and holding silo usually eliminates this problem.
However, for those plants that operate without a silo the problem can easily put
you into a adversarial situation with the state DOT since all the data you have
(tank stickings and quantities used over time) shows that you are, in fact,
putting in the correct percentage of asphalt oil. Unfortunately, both you and
the state would be right under these conditions. But the state has the final
say, making it best to avoid the situation from the start.
A word of advice: Remove or modify spray bar nozzles only when you thoroughly
understand what result that action will have. If you are experiencing
distribution problems like those discussed earlier, analyze the issue. Once you
see what's going on don't be afraid to experiment. In general, you want to be
sure that oil comes out the farthest end of the spray bar from the weigh bucket.
If you must plug nozzles to get the oil to the far side, start with the one
closest to the weigh bucket since it gets oil first and has it last.
The addition of a trough on top of
the oil spray bar to catch and hold a quantity of aggregate can go a long way
toward eliminating wear on this item. Try a 6" x 1" x 1/8" channel iron. Have it
welded to the top of the bar, the uprights pointing skyward.
All gearboxes and speed reducers should be examined for oil leaks
and noted for repair if needed. It is a good idea to schedule each box for an
oil change during the winter months. Collect properly marked samples from each
box and give them to a reputable oil analysis company, they will be able to
detect any abnormalities and perhaps avert a surprise breakdown at a later date.
A thorough greasing regimen should be completed prior to plant
restart. For electric motors, follow the manufacturer's recommendations. Each
year numerous motors fail because uninformed service personnel pump them full of
grease like they would a troughing roller. Some motors vent excess grease
internally, so once enough of the stuff is pumped in failure is bound to follow.
Most motor manufacturers recommend a yearly greasing schedule consisting of one
or maybe two pumps of the gun. Read and follow their guidelines.
You should check all wiring and junction boxes for any condition
that could render the workplace unsafe. Mark anything that is substandard.
This is a safety issue. A clean place to work, statistically, has
fewer accidents than one covered in grease and oil, and the accumulated debris
of years of maintenance.
Another issue is that a clean, neat, squared-away facility is
looked upon more favorably and less critically by state plant inspectors and
officials from the DEQ than one which appears to have been resurrected from the
briny depths of the ocean for the sole purpose of blundering through the
upcoming job. Think about it.
Good luck on your repairs, and in the coming season. Pave on men,
turn 'er black and don't look back!
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