Combines Drum belt slip

[JHEnt]

Generally a belt should not be slipping. Any slippage of a belt leads to glazing of the drive surface. Maybe your belt is already glazed someIJ An older belt can also have streching problems when they get hot. This will make them run loose. Usually if they strech then some of the cords inside are broken. They will often run so that the backing is not lavel across the pully then. How exactly is a TF set upIJ Is it something like a JD CTS with threshing cylinder up front and longitudinal rotory separators behindIJ

 

[John_W]

The rotor is transverse, or cross ways like a Gleaner. They split the flow in the middle and route half the straw each way. Must not have been the best idea as the TF's are long gone. There is a picture of one in the combines of the world at the bottom of the page. It is about 1_2 way down on the right side. It is a TF78 in the picture.

 

[Shane_IN]

Sounds normal to me. I know the manual for my TR86 says to run at full capacity you should not exceed 10% drop in rotor speed from empty to full. I usually run at around 7% drop. So if they are set at say 1000 empty I try to stay near 930 or somewhere near that. And fan speed hardly changes with the drop in rotor speed so that isn't a good gauge really.

 

[Shane_IN]

I did some lookin and surprisingly these TF's were popular somewhere! Check out the link, it appears the machine isn't too old and in a few sites I found some of these TF that were built as last as or even later than 1998. Interesting, never heard of the things.

 

[kiwi]

Thanks Shane and JHEnt for your replies. Your views differ and warrant dsicussion. I have been around long enough to have started on chain driven threshing drums (or cylinders depending on what part of the world you are in). They did not slip. Bit of a hassle changing drum sped when conditions changed though so the first belt driven drums were welcomed but also treated with scepticism because they would not be as positive a drive as a chain. Rubber is a whole lot different to steel and it deforms under load. Thats why tractor tyres must have some slip if they are going to transmit tractive power efficiently. Drum belts are a whole lot stiffer than tyres and seem to be more cord than rubber. However where the belt meets the pulley it is the rubber that transfers the power. Being rubber it must flex to some extent and this means it must slip to some degree. My question is, How much is normalIJ Shanes comment that the TR86 manual says the rotor should not drop more than 10% between load and no load interests me. Particularly when he goes on to say that, like our machine, his fan speed hardly changes. It is my contention that as the fan requires minimal power to drive and as the power required to drive the fan does not change under different harvesting loads, in the absence of an engine tachometer, the fan speed is a reasonable guide to engine rpm and changes in engine rpm. It therefore seems to me that, in Shanes case, his fan speed hardly changes so engine rpm is not changing much say a reduction of 3%. However his rotor speed is dropping by 7% with NH saying up to 10% is acceptable. Actual rotor belt slip would therefore be the difference between fan and rotor speed changes or around 4% for Shane with up to 7% acceptable to NH. Do we regard this as the normal slip for a belt under loadIJ In my years of farming I have often seen discussion on normal wheel slip but never about normal belt slip. Should we be giving more consideration to slip as a factor with belt drives given the effect it has on threshing efficiency and that, as JHEnt comments, it can lead to glazed pulleys and overheating beltsIJ I will make some comments on TF combines under a separate post. Kiwi

 

[JHEnt]

Your comment that rubber deforms under a load, I think is the reason why there is a larger drop in rotor speed than in fan speed. That would be the belt being pulled tighter by the extra load. If I'm thinking it out correctly the load will cause the belt to try to move inward on the drive pulley more than the driven. So it would be pulling itself toward a smaller diameter on the drive side. The smaller the drive diameter the slower the speed.

 

[Shane_IN]

You have to take into consideration our sensors too. They only read in 10 rpm incriments so they are not terribly accurate. I don't recall exactly how much the fan speed drops nor the engine rpm's from full to empty but it does seem that the rotors show the most loss. But if you look at it in percentages it may not be so much. Just thought for a moment and think maybe, maybe, if I have the fan set at 1000 it drops to about 960 full so that is about 4-5% drop and 6-7% drop on rotors so that is close. And I think that the engine high idles at 2310 and runs about 2190 full which is about 5% drop. So yeah, something like that. Have a good one!