Story and drawings by David Hatch
During the slip operation, the ground was an exciting place to be. The viewing experience would be a little like watching Devil’s Tower rise out of the earth to its finished height in seven days–or the lights going on at the Field of Dreams. “If you build it they will come.” Especially at night, the farmers came. They stood, they watched. Without trying, we stepped out of their cornfields, and they beheld a sight they would never forget.
At night, the gatherers saw lights, heard a roaring winch engine, and saw concrete trucks lined up. They heard shouts from the deck to the ground: “More vertical rebar!” They could see concrete finishers go around and around the structure, lit with strings of incandescent bulbs. But silent to them were the jacks, lifting the whole unit several inches a minute.
Out in the flatlands, night travelers who were miles away could see a slip going up.
Ground support was by means of various components.
The Steel Pile–There was a steel pile on the ground. The guy running the steel gin pole called down for vertical or horizontal re-rod. He also called down for jack rods or a large drinking-water container with cups. Perhaps he sent up parts or hydraulic oil. Mostly, he sent up steel using a cable choker.
The Concrete Truck and Driver–Here is an important guy, the concrete-truck driver. He filled the concrete bucket as fast as he could, got out of the way, and watched it go up. As the gin pole operator pulled the bucket in for dumping, it went out of sight of the driver below. Then it reappeared in free fall to the ground and the cycle repeated.
I believe concrete-truck drivers had a dangerous job for many reasons. What if the winch operator did not stop the free fall in time? What if a pulley failed or snapped at its axle? What if someone dropped something from above, like the finisher’s bucket or brush? What if a Georgia buggy driver overfilled the form just above the concrete truck?
There were always one or two trucks lined up when the current one was out of mud. Sometimes we had to ask the driver to add more water to the mix as it was too thick. Sometimes we asked them for more calcium to have it set quicker, perhaps if the mud was too thin. Tricky business. They have come out with trucks that unload the concrete from the front. I believe that it is easier for the driver to control his parking and dumping. Those were not legal in Iowa back then as they were too heavy. No clue about the law today.
The Boom Truck–What a cool old truck! Resembling a tow truck, this cob-job lifter moved things around the job site. It was as fun to drive as it was deadly. Every driver was warned, “Don’t drive under low hanging power lines, you will snag them, and it will kill you!”
The Job Superintendent’s Office–This was often a large mobile home. There were blueprints everywhere and concrete dust all over. It couldn’t be helped. That is where you got your new hardhat if you needed one.
The Townspeople–Putting up an elevator in a small town made for a big gathering. This would be their elevator. Their grain would go into it. Their bread and butter depended on this concrete and steel. And so they came and watched. Seeing a slip-form operation working at night is better than visiting the midway at the state fair. The sights, the sounds, the whole event–wow!
The Winch–The winch that lifted the concrete bucket was powered by a Ford industrial engine. I had always thought it was a six-cylinder inline engine, but it may have been a four. The winch was anchored into the ground, several hundred feet away from the base of the elevator. I never studied the anchoring into the earth, but it must’ve been substantial.
The engine shroud was red. The operator stood up while running the winch. The throttle was a small wire with a piece of wood as the handle running through the shroud to the carburetor. There was a large foot-brake for the operator’s right foot. It had a hand clutch for the right arm. The hand clutch was tall, like a walking cane or taller, bent over to the right at the top. There were no gears, just single speed. There was no tachometer visible. It would’ve been fun to have a tachometer.
The winch operator had to be alert at all times. He had to have good eyesight for distance. The goal was to get the concrete bucket filled with mud and send it up to the gin-pole operator at the hopper. That gin pole operator would swing the bucket in, dump it as fast as he could into the hopper, and push it back out in the open air. Then the winch operator would begin to free fall the bucket to the ground. Obviously everything I just described cannot be done from at 10 feet off the ground. Once you hit 20 feet and up, things got exciting.
The winch operator had a lot of responsibility, because if he wasn’t being careful, he could run the bucket up into the top gin pole at full speed, knocking the hopper guy off. If he wasn’t careful, when free-falling the bucket to ground and braking late, he could injure folks on the ground–especially the concrete truck driver.
The winch operator had to keep an eye on the cable winding (spool wrap) so that it did not overlap and pinch itself, causing a frayed cable.
For myself, this job was so intense that when I was not working, I would sit up in bed and run the winch in my sleep. The guys working with me got the biggest kick out of that. We were all piled up in motel rooms as we moved from town to town.
In conclusion, it was a blast! I absolutely loved this job–especially the roar of that engine at full speed under load.
David Hatch was born and raised in Ames, Iowa. Prior to college studies, Pastor Dave worked construction and had hopes of serving in law enforcement until his partial color-blindness prevented that. He did not know what to do with his life. Through God’s Providence and a phone call from his sister, who was a kindergarten teacher in Milwaukee, he enrolled in a college where, unknown to him, many of his future classmates were studying to be pastors. He received his education at Concordia College in Milwaukee; Concordia Teacher’s College, River Forest, Ill.; and Concordia Theological Seminary, Fort Wayne, Ind. His pastoral career began in 1982, following seminary, when he served as an admissions counselor at Concordia College in Bronxville, N.Y. and parish pastor at Love Lutheran Church outside of Albany, N.Y.
David is doing a great job bringing information, context and narrative to work that many see but only a few know and understand. One area I can help bring clarity to for David is the pace or speed at which the form advances. There are many factors that must remain in balance for a slip form to properly function and yield an acceptable appearance. This would be an entire separate article to properly cover content. However, assuming all relevant factors are in balance, when preparing a cost estimate for a proposal to build the a slip form grain elevator, typically an advancement rate of 10”-12” per hour was used. This rate was based on historical performance of field crews. The limiting factor of the hydraulic jacking system was the rate at which the hydraulic oil would fully return to the reservoir under the pump at the end of a cycle. On a typical grain elevator slip that used 3 and 6 ton jacks, the 6 ton jack farthest from the reservoir as measured by the oil line distance, was always the last to “return” as it was called, meaning return the oil to the reservoir and be ready for another stroke. As deck foreman, I was responsible for determining the advancement rate on many slips. Normally I would tell the jack man the cycle rate I wanted in minutes and seconds. He would then energize the pump at that cycle rate starting another lift. Sometimes I would tell the jack man to “jack on returns” meaning watch the farthest 6 ton jack, and as soon as it was ready for another stroke, start another lift cycle. The hydraulic jacks were manufactured in Sweden so all dimensions were metric. Converting to imperial, each stroke advanced the form approximately 7/8”.
Very interesting, thanks!