It’s time to get serious about belt and chain alignment.Belt and Chain alignment is not something new. It’s a fact that early industrial machines were all belt driven i.e. Cotton mills. We don’t actually align the belts or chains, we align the pulley or the sprocket. If you look at some of the ways that we try and align these Sheaves (Pulleys) and Sprockets you would think that we were still in the dark ages. Some of the traditional methods leave a lot to be desired!

It’s time to get serious about belt and chain alignment.

Use just one eye for a more accurate alignment!

I have seen a tradesman quite literally eye balling a belt into alignment. I guess this is called the calibrated eyeball method.

Tradesmen laugh when I show this slide because they know that this is done more often than you think.

A Maintenance Technology magazine published the traditional methods for belt and chain alignment showing the correct and incorrect ways of using string or a straightedge.

Look at the advances we have made in the maintenance world and yet we are still using a string or straightedge to do alignment. I would say this is still the common form of belt alignment today.

The above is from MT magazine and the string is red so maybe it’s laser string?

Using a piece of string to align two sheaves should be left in the past. It belongs in the dark ages. I know that the Egyptians built some wonderful and accurate things with knotted rope but I think that day has past for us. If you are serious about machinery installation, you have to use a laser.

The old traditional methods were time consuming and inaccurate and if you had to measure a long span it became a two-man job. You had to measure, make an adjustment and then re-measure.

In one technical paper, published by Carlisle belt manufacturer – one of the better articles I have read on the subject – they say you can use a straightedge but you have to measure on the outside surface of the sheave andinside of the surface. Why is that?

Going back and forth so many times led to the term, “That’s close enough.”

I believe it is so that you can see if you have a mismatched sheave. Do you think that on your belt drives you can get a straightedge between the sheave and the machines casing? Not likely, so this is not done.

The fact of the matter is that the differences between the wall thickness of sheaves has been ignored in, I would guess, over 90% of the time. How would you do this if you were using a string? The reality is that when using a string or straightedge you are only measuring in the horizontal plane and the vertical is ignored aswell as the difference in the sheave wall.

Welcome to the New Millennium.Easy Laser developed the first ever laser belt and chain alignment system called the BTA D100 (Belt transmission alignment), takingthe hit and miss out of this work process. But even with this tool there is still a lot that is missed in the installation of our belt and chain driven machine units.

What we are trying to do is to correct the offset and angular misalignment in both the horizontal and vertical planes.

Angular misalignment in the horizontal plane. (Toe-out and toe-in)

Parallel misalignment (offset) in the horizontal and vertical planes.

Angular and parallel misalignment in both planes.

The reason why we do this is to reduce the wear on sheaves, belts, seals, bearings, etc. You want to increase efficiency, lower energy consumption as well as decreasing vibration and noise. Misaligned belts also create unwanted heat (see right).

They took amp readings before and after using the BTA laser system and the results showed a 3.5% decrease in power consumption.

The company runs 24/7 but they used a conservative number of 800 operating hours per year and 40HP as the average motor. We used 0.07 cents per kilowatt so you could see the power savings in Canadian dollars.

53 40HP motors40HP = 30KW30KW x 53 = 1.590KW1,590KW x 800 hrs = 1,272,000KW$0.07 x 1,272,000 = $89,040.00Less 3.5% equals a power saving of $3,116.40

To give you some idea of the power saving, a study was conducted by a Steel (SSAB) Mill in Sweden. They have 200 fans, however, they only used 53 of them for the study.

A fan with a 1hp motor that is running 24/7 for all 365 days of the year should get a minimum of 3 years of operation. Industrial experts like Terry Wireman say you should get 7 years. Generally, I think you should be in the 3 to 5 year range.

The installation process.Many tradesmen start with removing the old belts and installing the new ones. But there is a lot more that has to be done before you get to this point of the process. One of our goals must be to remove any unwanted stress from the machine units. This is why we should start with the base.

Check that it is anchored securely and that the machines mounting pads are flat. A twisted base will distort the machine and create vibration. Machine units are designed to be mounted on a flat surface. Are the bases in your plant flat? How would you know? We just make the assumption that it is flat, don’t we?

Another issue that is often overlooked is checking for distortedmachinery feet (Softfoot). Why is it that we will check for softfoot on a coupled driven unit but not on a belt driven unit?We have to correct softfoot when aligning coupled shaft because if we don’t we will not get the results we need in order to achieve an accurate alignment that is within the tolerance that we need.

Softfoot measurement with feeler gauge.

Ask yourself the question, what is softfoot? We know that it is the distortion of the foot or the bases mounting pad that twist the machines casing and deflects the shaft. Right!

Now do you think that a belt driven system could have distorted feet or base pads? Do you think that it would run better with this stress removed? The obvious answer is yes.

Sheave inspectionUse a sheave gauge to check that the side wall has not become concave. You usually see the most wear in the small sheave because it obviously has the most contact with the belt. The wall becomes concave or dished out and the belt loses the wedging action that it needs to create torque. Then it starts toslip creating heat which is the beginning of the end of the belt.

The rule of thumb for this is 1/32 (0.031 thou), if it’s over this, replace it. You have to be careful with worn sheaves if you are using a laser that sits in the v-groves. A small amount of wear can put the beam off over the distance between the sheaves. The way to check this is to do an alignment and than reverse the laser units to make sure that it is the same.

Picture courtesy of Carlisle Power Transmission

Picture courtesy of TB Woods Incorporated.

Like this Not like this

You should also use a dial indicator to measure that the Rim run out of each sheave is no greater than 0.002” thou. This can happen with straight bored hubs that have been oversized. Also, use a dial indicator to check Face run out of each sheave.

If you have ever stood at the side of a belt drive and can see the sheave appears to be wobbling, it’s usually because the sheave is skewed, however, it can also be a bent shaft. High readings are common with taper lock bushings that have been installed incorrectly (Skewed by the air gun).

The rule of thumb for this is to adjust bushing mounting screws to a tolerance 0.001” thou per inch of sheave diameter. Spend some time on sheave inspection, it is important.

We spend money buying balanced sheaves but create an imbalance by installing the wrong sized key. Measure the length of the hub. Then measure the length of the keyway that’s cut in the shaft. Add them together and divide by two. This should be the length of the key.

A quick way to check the sheave run out is to put the laser transmitter on the sheave and point the beam down onto the floor position. Put your boot up against the beam and hold it there. Remove the laser and rotate the sheave 180 degrees. Re-attach the laser and if the beam hits the edge of your boot or the same position as before its OK. If the beam is off re-check with the dial indicator to see if it’s a bent shaft or skewed sheave.

It does not have to be on the floor you can point it across the room to a position on the wall. Obviously the greater the distance, the more you will see the beam move.

Always mount the laser transmitter on the stationary machine and the detector or targets on the moveable.

Now check the belts, even the new ones. Make sure there are no defects and that it is the right size for the sheave. Never use a combination of new and old. If all looks well you are now ready to start your alignment procedure.

The alignment procedure is simple.1. Start with the vertical plane and correct the angle by shimming the motor. 2. Adjust the toe-in or toe-out again until the value reads zero. (Remove all the angular misalignment first in both planes.)3. Now slide the sheave forward or back in order to correct the parallel offset.

Then slide the sheave forward or back in order to correct the parallel offset.

The correction procedure is simple.

Vertical

Offset

Horizontal

Start with the vertical plane and correct the angle by shimming the motor.

Adjust the toe-in or toe-out again until the value reads zero.

In other words remove the angular misalignment.

Shim

12

6

9

3

If you don’t want to mark the wall pull your tool box over or something else that’s portable and line up the beam. Many new fan bases are light weight and flexible so you may want to add stiffeners or gussets.

Fix the stationary machineMount the laser transmitter on the stationary machine unit and point the beam backwards away from the moveable machine. Locate the beam on a fixed position, i.e. a wall or a pipe, and mark the position with a marker at the top and bottom. Now point the laser beam forward past the moveable machine and again mark the position, top and bottom.What you have done is marked the position of the stationary machine unit. I call them anchor points. This means that when you tension the belt later, if the beam is off the mark more than what is deemed acceptable, you have probably distorted the base when you tightened the belt.

Measure the wall widths of both sheaves. If they have different face widths, just add or subtract the difference from the zero value of the target or if you are using a digital system, adjust the offset to the value you want for perfect alignment.

Now the trick is to keep it in this position while you tension the belt. I must admit that this is not easy especially when using the base that just has the one adjusting bolt but this is why we useskilled tradesmen. Tension the belts to the manufacturer’s specifications and keep your eye on the laser marks on your toolbox to make sure that the base is not being distorted during thetensioning. And most importantly you must re-tension the belt and check the alignment within the next 24 to 48 hours of operation. If you are using a digital system you should record the finished results in the machines history file.

Now sit back and plan on checking the belts in three years and replacing them in five.

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