AUTOMATED CEMENT LOADOUT -TECHNOLOGY AND EXPERIENCE
By:
Lon Rice, Engineering Manager, Hanson Permanente Cement
INTRODUCTION
The Permanente Cement Plant was built by Henry J. Kaiser in 1939. The original wet kilns were replaced by a dual string RSP pre-calciner in 1980. The finish mill operation was modernized in 1991 with the installation of a roll press and high efficiency separators. The bulk loadout facility remained old and inefficient. To access the loadout bins, customers had to drive through an obstacle course of old structures. In 1994 Hanson PLC (which had purchased Kaiser Cement) decided to modernize the bulk cement loadout facility. State of the art equipment would be installed to improve efficiencies and benefit our customers.
Hanson decided to build a system that would be 100% automatic. Many companies claimed to have a fully automatic system, but when asked how the hatch was located, they always had an operator with a joystick or something similar. At this point, it was found that Hanson was breaking new ground. Layouts and plans were made but the equipment that was required for the spout to locate the cement truck hatch was as yet unavailable.
Nothing further happened on the project until 1998 when a materials handling equipment manufacturer, developed a system using an electronic eye to locate the cement truck hatch. The manufacturer invited Hanson to come and look at their accomplishment. The arrangement included a spout that could move side to side, back and forth as well as up and down. The manufacturer had developed hardware and software that could process data from the electronic eye and control spout positioning accurately enough for the spout to locate and drop into a hatch opening. The prototype in their shop worked well and
Hanson’s project was back in motion.
Based on information from the spout manufacturer, goals were set. In 1998 Hanson’s Engineering Department made revised general arrangement drawings, and an engineering contractor was hired. The project was completed in 2001.
GOALS
The goals for the project were: Improve the loadout access
Reduce customer loading and waiting time Eliminate truck over and under loading Make the loadout operation more user friendly Fully automate the loading process
Reduce safety hazards
Make the facility as reliable as possible
Meet the requirements of California Division of Measurement Standards
Keep at least 2/3rds of the existing loadout operable at all times during construction Keep the existing loadout available for use after the project is complete.
The construction was to occur with customers’ trucks driving through the construction area twenty-four hours a day, six days a week
Improve the loadout access
In 1994, when Hanson first tried to modernize the facility, it was found that one of the major costs was due to unknown underground obstructions. This area had previously been the site of a lime plant and there were many buried foundations. There were also buried water lines, as well as the plant natural gas line, which ran across the middle of the site. In order to obtain economical bids for installation of the new
loadout, these unknowns had to be eliminated. As it turned out, removing the old structures not only reduced the size of the bids, but also provided better access for customers’ trucks to the loadout and reduced truck-waiting time.
ORIGINAL BULK LOADOUT SITE PLAN
Reduce customer loading and waiting time
The loadout services up to 400 trucks per 24-hour day. If it were possible to space the arrival of the trucks evenly during the day, three loadouts could handle the trucks with no waiting at all. But this is not the way it happens. The trucks come in waves. In any given hour, 16 to 20 trucks may arrive, then no trucks during the next hour. Back when loading took 10 minutes per truck with the original loadout, with three bays operating, the last truck could wait in line 50 or 60 minutes and then the additional 10 minutes while being loaded. Some customers’ trucks are loaded five or six times a day. With this kind of truck waiting and loading time, it is easy to see how Hanson could save customers considerable time and money.
Drivers tended to leave their trucks running while waiting in line. The longer the wait the more exhaust was emitted. Therefore, in addition to saving customer time and money, shortening the loading time would be good for the environment.
Make the facility more user friendly
The original loadouts that were built in 1939 had no horizontal movement capability, only up and down. Because there was a hillside and an old lime plant located in the approach to the loadout, the drivers had to make a 90-degree turn and in one length of their trucks line up with the spout. Over the years, a system of horn signals had been established so that the loadout operators could help the drivers make this alignment. Some drivers were very good and managed to line up with the spout most of the time. Other drivers quite often missed the spout and had to go around and try again. It was evident that a straighter approach and a spout that could move in all horizontal directions would help the drivers and reduce loading time.
The new system had to be easy for the drivers to understand and use. A new driver had to be able to, with only a very brief instruction from the weigh master, drive to the loadout, read and follow the signage, activate the loading sequence, and return to the shipping office for his bill of lading.
Fully automate the loading process
Not only did the loadout need to be 100% automatic, it needed to be faster than the old system and prevent over and under loading of customers’ trucks. With the old system each loadout bay had an operator and still averaged 10% over/under loads.
Reduce safety hazards
While waiting to be loaded, although Hanson tried to prevent it, drivers would exit their trucks, walk around the staging area, and visit with other drivers. The drivers not being in their trucks caused
additional delays. When the truck finally reached the loadout the driver had to exit his truck and carry his load papers up a flight of steps to give them to the operator. Drivers walking around moving trucks, for whatever reason are a potential safety hazard. The goal was to keep the drivers in their trucks and out of harms way.
Make the facility as reliable as possible
There were to be back up systems for the controls and data storage. If a programmable controller broke down, a second unit had to be ready to take over immediately. Also if the server broke down, sales transaction data stored in a back up server could immediately take over the task of feeding order information to the loadout, processing transaction data and sending it on to Hanson’s mainframe.
California Division of Measurement Standards
Early in the design stage of the project a set of drawings and an outline of the software was presented to the California Division of Measurement Standards in Sacramento. Hanson was told that the State could not approve any drawings, software or systems until they could actually see and test the system.
Some of the items that the State required:
The weigh master must be able to see where and which trucks were being loaded. There had to be assurance that all of the truck wheels were on the scales during loading. There must not be a way for personnel to tamper with the transaction data.
The scales must be type approved
The shipping office is located 400 feet from loadout. Because Hanson had faced a similar problem several years earlier while modernizing another area of the plant, video cameras had to be installed at the loadout and monitors in the shipping office. The cameras were placed such that the truck number, the scale and the spout could be vi ewed during loading.
To be sure that the truck is fully on the scale, two light beams were mounted at the end of the scales. The first beam tells the computer to turn on a red light to signal the driver to stop the truck because his front wheels are nearing the end of the scale. The second light beam informs the computer if the front wheels of the truck have actually rolled off of the scale. When a truck rolls off the scale, a red light flashes, letting the driver know that he must back up before the loading process will be permitted to proceed. As soon as the truck has backed up far enough to reestablish the light beam, the flashing light stops. This feature has been especially useful in dealing with truckers that tend to go a little too fast and cannot stop quickly enough to stay on the scale.
All of the data transfer from the shipping office to the loadout and back again is done electronically. The weigh master waves an ID card before the antenna on his desk. This action creates a computer file specifically for this sales transaction. This allows the data to be sent to and from the loadout as a
complete transaction package. The weigh master then gives the ID card to the driver. During loading, the data can be viewed but not changed by a loadout operator.
Once the facility was up and running, Hanson called for State inspection and approval. Prior to receiving approval Hanson could fill the trucks but could not use the new facility data for sale of cement. The state inspector tested the system and approved it without any changes.
While waiting for State approval of the new loadout, Hanson tested and proved the data transfer
hardware and software. To test it, we had to run parallel systems, i.e. the bills of lading printed up in the old manner using the remote scale data, and the new bill of lading system using data from the new loadout. When 100% accuracy and State approval was attained, Hanson stopped using the old bills of lading and the shipping office personnel’s workload was significantly reduced.
During construction at least 2/3rds of the loadout facility must be operable at all times
The old loadout loss-in-weight scales and spouts were located directly below the cement bins. In order to feed cement to the new facility, airslides had to be installed into the existing cement bins and only one of the three loadouts could be shut down at any given time. The other two loadouts were required to service the customers.
The old loadouts remain operable after the project is complete
The old loadouts, even though not state of the art, could still be used if there was a failure in the new loadout facility. Another reason to keep the old loadout was that the old and new loadout facilities are fed electrical power from separate sources. If one power source failed the other could still operate.
The construction must be done with hundreds of trucks driving through the construction area
During the construction, sales volumes were good and every day there were hundreds of trucks passing through the heart of the construction. Due to traffic 24 hours a day, six days a week, tunnels were built to protect the customers and their trucks from falling materials. Even with the tunnels, lifts had to be timed to prevent passing loads over trucks and personnel. As a result of the effort put forth by Hanson, the contractors and Hanson’s customers, work was accomplished with no injuries or truck damage. However, accommodating the customer’s trucks caused delays and therefore increased the construction time.
DESIGN History
The 1994 layout was revised in 1998 to accommodate the automated spout. This required only minor structural design changes however, the complexity of the sensors and control functions increased greatly.
What was to be modernized
Three of the four existing loadout bays would be modernized. Because the fourth loadout bay holds specialty cements that amount to only 5% of sales the expenditure could not be justified. The design was to reuse the existing cement feed system and three of the four existing loadout bins for the modernization.
Cement transport
To allow the spout to reach all of the possible locations of the various trailer hatches and to meet the loading time requirements, the loadouts were designed to have articulating airslides with instantaneous flow rates of 1000 ton/hour. The top airslide leading from the cement storage bin is stationary. The second airslide is connected on both ends with swivel joints. The third airslide is supported on the
discharge end by the swivel joint on the carriage. To make the assembly reliable, every swivel joint had to be supported. That meant that the lower joint of the second airslide required a movable support. To accommodate this, a circular monorail with a trolley was designed.
OLD SPOUT ASSEMBLY CEMENT LOADOUT BIN CURVED MONORAIL AUTOMATIC FEED SPOUT CARTRIDGE TYPE DUST COLLECTOR SWIVEL CONNECTIONS DUST RETURN PIPE VENTILATION DUCT BAG HOUSE DUST COLLECTOR FLOW CONTROL GATE SAFETY GATE AIR SLIDE AIR SLIDE AIR SLIDE SHUT OFF GATE
MATERIAL FLOW DIAGRAM
Flow control
To facilitate accurate flow control, airslides were designed with computer controlled flow control gates. One was installed at the discharge of the cement bin to control the flow rate and the other at the discharge end of the third airslide section to instantaneously stop the flow when the desired weight is attained. The operation is as follows: first the gate at the discharge end of the airslide opens allowing cement to flow from the airslide into the spout. Next the flow control gate at the upper end of the airslides opens to allow the desired flow rate (say 90% open). When the trailer is 85% full the flow control gate closes from 90% to 30%. Finally, at about 300lbs short of the full load, both gates close. This offset was necessary since the suspended dust contained in the spout and spout dust collector will come to rest in the trailer. Since the cement flow rate changes with gate settings, temperature, moisture content and flow characteristics, the point at which the gates close must be adjustable.
On-scale loading
Before the modernization, Hanson filled the trucks at the loadout and weighed the trucks in and out 400 feet away at the old shipping office. If the load was incorrect, the truck had return to the loadout to adjust the load. With on-scale loading it was known exactly how much cement was in the truck as it was being placed.
On-scale loading requires that the truck be completely on the scale and stopped before and during the loading operation. Although the scale could be made long enough to facilitate the longest truck, with different truck shapes there was a problem accommodating all of the possible configurations. The truck would be stopped if the electronic eye detected the hatch, or the front tires broke the light beam – whichever came first.
A scale was selected that had side rails. Side rails prevent the truck from driving off the sides of the scale and keep the truck within the two-foot side travel range of the spout. If the driver can align his truck with the scale, the spout can locate and enter the hatch opening.
Data flow
Cement orders are taken by the shipping office personnel and entered into the server. When the
customer arrives to take the cement, the order data is sent from the server to the computer at the loadout. The loadout computers wait for the antennae to receive the indication that the customer is waiting to be loaded. When this occurs, the computer file associated with the sales transaction is brought up and the truck is told to enter the scale. Once the truck has stopped on the scale, the spout computer is told by the loadout computer what type of truck and how many hatches are to be filled. Transaction data is stored in the loadout computer until the loading is complete and then is sent to the shipping office server. When the customer drops the ID card into the slot outside the shipping office the card reader antenna tells the server to print out the bill of lading.
DATA FLOW DIAGRAM
HANSON'S MAIN AS 400 SERVER #1 SERVER #2 PCS DESK ORDER SHIPPING OFFICE SCALE TRUCK DRIVER PCS TRUCK CUSTOMER'S OFFICE SHIPPING READERS CARD I.D. PRINTERS LADING BILL OF SPOUT COMPUTERS LOADOUT COMPUTER MACHINE INTERFACE LOADOUT MAN SCALE LIGHT LIGHTS TRAFFIC BAR DROP SCALES TRUCK BEAMS FRAME
EQUIPMENT
The final design included the following equipment.
Loadout
Structures
Two structural steel buildings to house the three loadouts Computers and control equipment
Six computers with three monitors Four programmable controllers
Miles of interacting data and control cables Communications
A complete intercom system interconnected with the plant phone system Software
Five different data transfer and processing packages
Two totally customized software packages for equipment and process control as well as the man machine interface.
Process equipment
Three bag houses to vent the airslides.
Three cartridge type dust collectors to vent the spouts Thirteen airslides each with blowers
Three spout assemblies on carriages Three truck scales
Three truck traffic control lighting systems Three product sampling devices
Two compressors with air dryers Electrical gear
A complete MCC with transformer Over head power lines
Staging areas
60,000 sqft. of asphalt
600 feet of area drainage culvert
Shipping office
Styrofoam and concrete structure Five computers with five monitors Two bill of lading printers
One cluster server Phones and modems
All of the equipment and piping required for creature comfort in the new office One remote truck scale
COMPUTER ROOM
GRADE ELEV VARIES TRUCK APPROACH SCREEN SILO PENETRATION ADAPTER (N) SUPPORTS AIRSLIDE AIR CONN. TYP. (TYP) 8 ° GATE (AIR) SHUT OFF 24" AIR SLIDE CHUNK TRAP VALVE TRICKLE
(W/SIDE BAG REMOVAL) DUST COLLECTOR DC-12,13 12 2 C SILOS S-28,29L GA-28,29 AIR BLOWER AIR BLOWER TIPPING VALVES AIR BLOWER AIR BLOWER FAN VENTILATION FLOW CONTROL GATE FV-28,29 "POP TOP" INSPECTION (TYP) FA-28 & FA-29
TV-28,29 AIR BLOWER MT-28, 29 TV-12,13 SAMPLER TOP OF SILO
SPOUT IN 'UP' POSITION
LOAD SPOUT
SENSOR 3 TON TROLLEY W/YOKE W/CURVED MONORAIL (BY 'DCL') (BY 'DCL')
ELEV 80'-0"
AIRSLIDE SUPPORTS TYP
AERATED AIRSLIDE (TROUGH) SECTION
LIGHT BEAMS
TEMPERATURE SENSORS
SPOUT COMPUTER
SIDE ELEVATION BULK SILO 28, 29
(source: ESI Drawing)
ROOM COMPUTER COLLECTOR DUST VENT. FAN SHUT OFF GATE FSV-28 8° 8°
END ELEVATION BULK SILO 28, 29
CONSTRUCTION
Construction started in February 1999 and was completed in January 2001. Ordinarily it would not take so long to construct a few buildings and three spouts. However in this case the construction had to occur without stopping cement shipments and building permits were difficult to obtain. Both problems helped to extend the construction time.
Hanson acted as the general contractor. The Engineering Department was staffed up to handle the workload. The team consisted of a project manager, three mechanical contractors, two electrical contractors, an independent inspector, and an engineering firm.
Construction inspections were made and reported to the County by a third party inspector. Although a third party inspector costs additional money, it worked well because Hanson was able to get the
inspections when needed rather than when the county inspector was available. Once a week the county inspector looked over the project and collected the third party inspection reports.
To promote the use of concrete construction and reduce the noise level in the office, Hanson wanted to use Styrofoam formed (ICF) concrete construction. Because it was a different method of construction than most local contractors were used to, it was difficult to get bids. However an acceptable contractor was found, the building was erected and well finished. This type of construction makes a very strong and quiet building. Just what is needed when an office is placed between two continuous lines of truck traffic.
PERMITS
Although the Santa Clara County Building Department tries to grant building permits as quickly as possible, their thoroughness causes problems whenever someone wants to build something out of the ordinary. In Hanson’s case, it appears that everything being built was out of the ordinary.
Building codes require, among other things, shear walls in all buildings. Hanson’s engineers put in angle iron diagonal braces rather than solid walls with plywood sides. The shear wall requirement was easily overcome, but when the County engineers wanted to treat the airslides as if they were chimneys or water pipes, a lot of educating of the Building Department on cement handling equipment was needed. After six months and a lot of money, Hanson finally received a building permit for the new loadout.
The new shipping office building permit had its problems as well. The County engineers had not been exposed to Styrofoam formed concrete construction and this bogged down the permit process. It took four months to get the shipping office building permit. Since then, this type of construction has become more commonplace in this area.
Dust collector permits from the Bay Area Air Quality Management District were more easily obtained. Hanson hired an agency that specialized in dust collector permits.
TRAINING
Although airslides, spouts and dust collectors are normal cement plant process equipment, the use of computers and automation necessitated training for everyone. Initially Hanson trained all employees on the flow of material, general arrangement and data transmission, so the layout and how the system would operate would be understood. Prior to this, the loadout operators had not used computers, and were at first apprehensive in using them.
Hanson had to train the operators for each phase of the equipment startup: manual, semi-auto and full automatic modes, that way if and when something failed the operators would know exactly what to do. Yes, it failed many times during startup and the operators came through.
The shipping office personnel also had to be trained. They had to learn to make all of the transactions through the computer rather than manually inputting data and typing out bills of lading, they had to look up the customer/order on the computer via the CRT, use the ID card to initiate files and start the loading process. This training was also done in stages. The shipping office training went well.
STARTUP
The first stage of the startup was in as manual a mode as possible. The scale controlled the cement flow but the operator controlled everything else: spout movement, input of the ID card and checking truck weight before loading.
The second stage of the startup was to use the automated spout. This was the primary purpose of the new loadout system, therefore this stage was critical. After nearly a year of continuous work, the
automatic spout vendor was able to reach a satisfactory success rate. Until this time the operators had to take over the operation and manually direct the spout into the hatch whenever the system failed. Full automatic mode was the last stage of the startup. To reach this level everything had to work. While the bugs were being worked out, loadout operators had to stand by in case problems were encountered. Trucks still had to weigh in and out on the remote scale located adjacent to the shipping office, and the bills of lading were still being hand typed by the shipping office because the system had not yet been certified by the State.
Hanson knew the project was getting close to completion when a driver advised that he had not seen much of swing shift operator lately.
PROBLEMS AND SOLUTIONS
The electronic eye did not work 100%
The first problem to become apparent was that the electronic eye would malfunction about 30% of the time. This was quite hard to understand in that the system that Hanson had tested in the manufacturer's shop worked 100% of the time. The manufacturer tried numerous modifications of hardware and software to overcome the problem. Radar was added to eliminate the elevation changes. Since the prototype system was tested in their shop and not in the sunlight, it was thought that perhaps the glare from sunlight was causing the photocells to malfunction. To reduce the light, additional siding was added to the building. Finally it was discovered that malfunctions occurred more as a function of the shape of the trailer, rather than of light intensity. Torpedo shaped trailers caused more malfunctions than straight trailers. Since the electronic eye was looking for a shadow line 22 inches long, the eye interpreted a shadow line on the side of the trailer as the hatch opening. The manufacturer added additional lights to eliminate side shadows. This reduced the malfunctions to 10%. After months of additional trial and error, the manufacturer improved the operation of the eye to scan in multiple directions. With that change the system worked as desired.
Testing the system without holding up the flow of customer trucks
To solve the electronic eye’s operational problems it was necessary to test fill trailers. The problem was that customers were not happy about having to wait while the computer program was researched when the eye would malfunction. During the heavy shipping time of the day, the time spent looking for the source of the problem would slow the loading operation, and when shipping was slow there were no trailers to load. Hanson rented a bulk truck so that the testing could continue during the slow times of the day.
Cement flow rates were not consistent
Right away it was apparent that cement flow rates were not always the same for a given flow control gate setting. After a few false starts it was found that the flow rate varied with temperature. Temperature sensors were installed at the feed end of the airslides for each loadout. Software was then written to change the flow gate settings, based on temperature, to control the cement flow rate. This turned out to be a very acceptable solution for the problem.
Making sure that the trailers were not over or under filled
Finding an acceptable cement flow rate was not easy. If the cement flowed too fast, it was difficult to stop the flow at the correct time or the trailer would fill with aerated cement before the correct weight was achieved. If the flow was too slow it took too long to fill the trailer. To overcome the problem, a software program was written to vary flow gate settling during the loading process. At the start of the loading process the flow gate opens quickly to a maximum setting and stays there until the trailer is 85% full.
Then the flow gate closes to 30% open. The idea is to maximize the flow rate as long as possible and then reduce the flow rate just before stopping it altogether.
The above gate controls worked fine except for accounting for the cement that was still falling through the spout when the shut off gate closed. With the flow reduced at the end of each filling cycle it was possible to make a very close estimate of the amount of cement falling through the spout. A variable was added to the software program to accommodate this estimate.
The communication between the truck drivers and the computer had to be reliable.
A reliable method of communication between the customer’s truck driver and the automated loadout had to be found. Using keypads would require that the drivers have all the transaction data and know how to use the pad. Having the drivers call the weigh master was too cumbersome. ID cards would work if the drivers did not have to get out of their trucks. However, cards with magnetic strips are subject to damage by magnets and weather. Radio frequency cards appeared to be the answer. The RF chips are totally encapsulated in the plastic card and therefore not subject to weather and are not affected by a magnet. Additionally, the cards do not have to be swiped. RF transmission allows the card to communicate if brought within three feet of the antenna.
Equipment incompatibility
There were three major electrical problems: proximity sensors which were adversely affected by temperature, incompatibility between circuit boards, and power feed back.
It seems that the proximity sensors were heat sensitive and if the air temperature reached 100 degrees they would fail, but as soon as the temperature dropped below 100 degrees they start to work again. It was difficult to find the problem, because the failures were intermittent. Once the problem was isolated, the manufacturer provided replacement sensors.
Some of the cards, even though designed to work together, would not. Memory cards would overload and erroneous signals would send the carriage to the end of the track at full speed. At other times the carriage would get lost and could not find its way back to home position. The manufacturer found the problem and replaced the cards free of charge.
There was also a problem with cards being damaged due to stray electrical currents inside the spout carriage control cabinet. The manufacturer determined that when power was cut off the carriage drive motor, the motor acted as a brake thus generating and sending electrical power back into the control cabinet. A simple resistor bank used to absorb the electrical current solved the problem.
STEP BY STEP DESCRIPTION OF LOADING OPERATION
The cement truck pulls up to the weigh master’s window. The driver tells the weigh master what type of cement, his truck number, for whom he is hauling and where the load is going. The weigh master locates the order in the computer, pulls the order up and by waving an ID card over an antenna at his desk creates a file in the computer for the transaction. The operator then gives the ID card to the driver and tells him to proceed to the loadout area. Each card has a number and for this discussion, it is assumed the ID card number is 397. The computer downloads all the order data for this transaction into file 397. It even downloads truck history data, based on the truck number, from the server.
In the loadout area there are signs that tell the driver which bay dispenses the desired type of cement. There are three automated loadout bays, numbered 28, 29 and 1. Number 28 is used in this example. The driver pulls up to the entrance of the correct bay, stops short of entering the scale and waves the ID card at the antenna. When an ID card is within three feet of an antenna the transmitter is activated. The antenna tells the computer that the truck holding ID card number 397 is waiting to be loaded at bulk loadout bay number 28. If the driver had gone to the wrong bay, the computer would not allow the truck onto the scale. The drivers have been provided with phones at each antenna site so that they can call the weigh master and get further instructions. If the driver is at the correct bay, the computer will turn on green lights at both ends of the scale. The drop bar at the exit of the scale is lowered. The driver
the light to turn red. First, which is normally the case; the electronic eye on the spout sees the open hole in the top of the trailer. Second, which is the case when the first hatch opening is a long way back, the front wheels of the tractor breaks the first light beam at the exit end of the scale.
When the truck has stopped and the scale senses no movement for at least a second, a tare weigh is taken. The tare weight is compared with that recorded the last time the truck weighed in. If the new tare weight is more than 200 pounds greater than the previous weight the computer will not load the truck. If this happens the driver must call the weigh master and explain the difference (e.g. fuel fill-up). The weigh master can override the system and allow the loading to proceed.
When the scale senses that the truck has stopped, the spout starts its travel towards the entrance end of the scale. It will continue until it locates the first hatch opening. The spout computer then lowers the spout into the open hatch, starts the dust collector and takes a second tare weight. This tare weigh includes the weight of the spout and the suction effect of the dust collector on the scale reading.
The computer combines the second tare weight, the type of truck (semi or dual), the number of hatches that were filled the last time that this truck was loaded and calculates how much cement should be placed into each hatch. The computer knows, from the truck history transmitted in file 397, if the truck is a semi or a dual, if it has one two or three hatches, and the desired percentage of the load to be put into each hatch.
At this point cement can be put into the trailer. The computer opens the gate at the discharge end of the airslide. Normally there are two tons of cement left in the airslide from the previous loading operation. The two tons of cement will drop into the hatch and within seconds the flow control gate located at the feed end of the airslide will open to 95% and cement will flow down the airslide at 1000 tons/hr and into the hatch. The dust collector cleans the cement from the displaced air and returns the cement to the trailer. When the scale senses 85% of the calculated weight for that hatch has been delivered, the flow control gate closes down to 30%, reducing the flow rate to 150tons/hr. This is done to decrease the amount of cement falling through the spout and make it easier for the shut off gate to stop the flow at the right moment. The final weight is normally within 200 pounds of the desired weight.
% FLOW CONTROL GATE OPENING
TIME in SECONDS 0 0 80 40 30 20 10 50 60 70 100 50 60 70 80 90 40 30 20 10
CEMENT FLOW DIAGRAM
SHUT OFF GATE OPENS
SHUT OFF GATE CLOSES
When the desired weight for that hatch is attained, the scale tells the computer that the correct weight has been reached and the computer tells the spout to move to the next hatch.
The process for moving the hatch is as follows:
The computer tells the spout lift motor to raise the spout. The spout continues to rise until it reaches the full-up sensor
Then the computer tells the carriage to travel towards the entrance end of the scale The carriage continues to travel until the electronic eye sees the next hatch opening The spout is lowered into the hatch
When the last hatch has been filled, the spout is told to lift and return to its home position at the exit end of the scale. As soon as the spout lifts far enough to make the full-up limit switch, the carriage starts traveling back to the home position. The scale takes a gross weight. The signal to the computer that the full-up position has been made also tells the computer to turn the light at the exit end of the scale from red to green and to raise the drop bar to allow the truck to exit the scale.
All of the loading data including weights, times and type of cement are sent electronically from the loadout computer to the shipping office server in file number 397.
The driver then proceeds back to the shipping office and deposits his ID card into a slot on the outside of the building. An antenna in the chute reads the ID card and tells the shipping office computer the truck that was loaded in accordance with the data in file number 397 is at the window and waiting for a bill of lading.
The computer then prints out three copies of the bill of lading for the driver and a copy of the bill of lading for Hanson. The driver signs one copy and leaves it at the plant gate when he exits the plant site. The data from file 397 is then stored in the shipping office server memory. The sale data is sent via modem to Hanson’s mainframe computer in Pleasanton, California. No one at the shipping office has to handle, transmit, or even see the transaction data. The mainframe computer then generates an invoice and sends it to the customer.
CONCLUSION Success or failure?
The purpose of this project was primarily to improve efficiencies and customer service. The objectives were to make loading more accurate, easier, quicker, cleaner and safer.
Hanson received favorable comments from customers when the access to the loadouts was improved. Loading was made easier in that the drivers no longer had to thread their way between structures to reach the loadout bays. The loading spout finds the truck rather than vice versa. All the driver has to do is follow the lights and stop as directed. It is not possible to park incorrectly so long as the truck is on the scale. And if the truck is not on the scale the computer tells the driver how to correct the problem.
The original loadout took at least 10 minutes if the driver was able to align his truck with the spout.
For those that had trouble with alignment, the loading took 15 to 20 minutes. Loading time has now been reduced to five minutes. With the reduction in loading time the time spent waiting in line has dropped to 15 minutes.
Originally over and under loads averaged 10%. When this occurred, the driver had to go back to the loadout and get more cement or worse yet blow off cement. This could take up to 30 minutes. Of the trucks that load in the automated system there are no over and under loads.
The loadout systems were built with dust collectors right at the spouts. The only dust that escapes occurs after the spout has lifted from the hatch. Waiting for all of the air trapped in the cement to escape before lifting the spout would not be acceptable to the customer.
The trucks do not have to wait as long to be loaded, so there is less engine exhaust being generated -causing less pollution.
Normally the waiting time is so short that there is no reason or desire on the part of the drivers to exit their trucks. This keeps the drivers safer.
The objectives of Hanson’s automated loadout project were met and by all accounts the customers are satisfied with the new system.
