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Start paving in automatic or manual?

A common question asked by paver operators is if they should have their automatic grade control system in automatic or manual when first pulling off a joint or blocks. I have seen it done both ways and I have always preferred running the first 10-20 meters in manual due to influences on the screed that change when it comes off the wood blocks and onto the asphalt. However after reviewing training materials used by different grade control manufacturers, I see that everyone's materials is training operators to have the system in auto before we start paving. Is this correct?

jblano 09.12.2015 4 4144
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  •  ebaker: 
     
    We at Roadtec, used to train how to pull off the joint in manual, primarily because this was how operators preferred to do it. We have now, probably in the last 5 to 7 years, started training people to pull off the joint in automatic. Part of this is that the crews have become more comfortable with the automated controls. The key to a nice joint, no matter whether you pull of in manual or automatic is setting up the screed and the head of material properly. I have seen many inexperienced crews check the mat thickness too often and over-correct and constantly chase for the first 10-20 yards, you can help limit this by taking off in automatic.
     
     11.12.2015 
    1 point
     
  •  jblano: 
     
    Great discussion. Assuming the operator did setup the machine correctly we can assure good results when starting a job in automatic. Perhaps the logic I and others have used for starting in manual has to do with the forces that affect the screed which are either not present or subject to change once off the blocks. For example at a stop there is no tow point force or ""P"" (in the picture below). And ""R"" is going to change when the screed leaves the wood and moves onto the asphalt. Either way in auto or manual there is going to be some changes that will have to be reacted to by either the grade control system or by an operator. The grade control system does not know it is at a joint so it will compensate all at once, where a skilled operator knows to prevent a bigger bump at the joint he will slowly make any necessary corrections manually, check for thickness, and when he is satisfied the screed is maintaining the thickness he wants he will activate the grade control to maintain smoothness (or evenness). Of course the experience of the operator is another variable not shown in the picture.
     
     09.12.2015 
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  •  mwatermann: 
     
    We know a specialized contractor with different types of pavers doing highways starting in automatic (mostly stringline) to get good results on joints/starts (going on in manual on the side with no further lane and in automatic ski sensing at side joint, talking about the surface layer).
    I think this contractor recognized that he gets better results with using automatic (stringline) mode near joints/starts, so he also starts up with automatic.
    Both ways, auto or manual you can get good results but I think Sascha's explanation makes most sense based on the assumption that operators did a proper setup and know the machine/system.
     
     09.12.2015 
    0 points
     
  •  sfeuchtinger: 
     
    Having the right settings on screed, levelling system and tow points are the deciding factors for a good paving start. This still depends on the knowledge of the operators. Bad adjustments can’t be compensate to 100% by a levelling controller (brand doesn’t matter) - that’s true.
    But for illustration: What would happen, if you start in manual mode with bad adjusted tow points at the start position? In manual mode you will follow this wrong adjustment exactly (if nobody recognize and counteract my manual corrections). If you start in automatic mode the levelling system try to compensate this wrong adjustment directly from the beginning. Of course if the pre adjustment of tow points and set point settings at the levelling system done bad you will pave a wrong thickness anyway. But in manual mode it is worse than in automatic definitely.
    That is the reason the paving team is measuring the thickness and slope in a higher frequency at the first meters of paving. A wrong pre adjustment you have to correct anyway. It doesn’t matter if the levelling system is in automatic or manual mode (or better to say it doesn’t matter if you raise or lower the screed by changing the tow point my manual driving or changing the set point).
    Also paving with Big-Ski I would recommend to start in automatic mode. Paving the base layer you do not have a good reference to follow especially for the last sensor. So here paving start should be done by using the middle sensor only at the first meters until the point the last sensor can take the new paved mat as his reference. Then quit the new set points to copy at all sensors and switch over to averaging mode.
    So my recommendation based on my experiences is: Starting in automatic mode always!
     
     09.12.2015 
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