Textile mills can save energy by maintaining ring frame tin roller bearings with specialty grease, says Ashok Sethuraman.

 

In any industrial equipment, the motor is coupled to the machine by the belt and couplings involving a couple of bearings. But the ring frame needs 40 to 50 bearings set in a tin roller to transmit power from motor to load.

 

What are the savings in the mill's electricity consumption?

The empirical thumb rule for any textile spinning mill is that ring frames consume around half the mill's monthly electricity bill. If we save around 6 per cent on existing running frames, this works out to 3 per cent saving in mill's monthly electricity bill at no cost except spending on specialty grease. This can be implemented by zero and low cost measures to achieve the savings in ring frames. This will create scope for savings and motor loading and can be used to improve ring frame productivity.

 

45 NPPB tin roller bearings after removing the dried and caked grease lump, result of repeated re-greasing of MP3 grease

 

How can this energy be saved in the ring frame?

Mills frequently record the relative condition KWH (Kilo Watt Hour) of ring frames for the same count show >10 per cent variation. One major reason for excess consumption in a frame is the tin roller bearings which consume too much power. Actually, the tin roller bearing is the starting point of power distribution to each batch of 24 spindles x 50 or 1200 spindles. The grease in the tin roller bearing dries out and hardens in a few months and consumes more power. The tin roller system consumes around 12 per cent power of the ring frame first, and then allows the power to reach the spindles.

 

The root cause of the problem is tin roller bearings come to the mill with factory- sealed multipurpose grease. Later, we re-grease the same multipurpose grease once in six months. That amounts to a lot of grease over the years as the earlier grease is not removed from the drain plug. With time, the grease supply tubing gets choked and the bearing's grease dries. Suitable replacements include Polyuria-based Lithium grease, under brand names like Mobil PolyrexEM, SKF LGHP2 or ONWO Polytek grease priced at 800/kg. The specialty of this grease is shear stress stability, longer grease consistency and extended re-greasing intervals.

 

To decide which machine to re-grease first, take a look at your log book. The ring frame that is gobbling up more electricity needs a planned for one eight-hour shift. Two days before the shutdown, record the cumulative KWH of the frame with basic and power parameters. Measure the KW (Kilo Watt) of machine with empty doff, remove the motor belt and measure the KW of the hot motor without the belt and with no load.

 

Re-grease all tin roller bearings and replace only if required, using only spare bearings enriched with the recommended specialty grease. Remove motor bearings at the Drive End (DE) and Non Drive End (NDE). Clean them, re-grease with most suitable specialty grease. Check and take photo of bearings with hard grease lumps caused by oil that dried out early. In fact, specialty grease needs to be applied not just to tin roller bearings, but all higher HP motor bearings.

 

Motor manufacturer Baldor greases motors and can thus give longer intervals between re-greasing, even under severe conditions. When this suits hot motor bearing for better shear resistance and grease consistency, this will also suit tin roller.

 

Remove the tubing supplying grease, clear the choke and ensure that the new grease seeps out slowly through the input tubing.

 

When you start the machine after this routine maintenance, measure the motor again to confirm the difference in energy consumption by noting KWH readings for two days. To sustain the savings thus obtained, this exercise needs to be repeated annually when the machine is switched off. If the bearing greasing is in good condition, check for the need for online re-greasing every six months. The only expenditure incurred in this is the cost of specialty grease.

 

Once the bearings are removed from the frame, those that are worn out should be eliminated. These can be treated with specialty grease and kept aside as spares, in case you should require some. Buy only low-cost tin roller bearings to replace them and to start in one frame. This is practical and convenient. Swap the newly greased bearings in the next frames. Remember to check the grease type with the Original Equipment Manufacturer (OEM).

 

Why have ring frames been losing energy all these years?

In mills, capacity utilisation is self-imposed, rigorous and often unhealthy. So, machines, especially the ring frame, may run almost 24 hours a day. There is no time for preventive maintenance schedules. So the alternative is regular on-line and in-site lubrication of bearings. The worker pumps in extra grease on tin roller bearing sets. In 8 out of 10 mills, after greasing a frame, the machine trips when it is started due to over greasing and has to be re-started. After a few kick-starts to the machine, the ring frame limps to normal.

 

Why should a mill correct energy losses?

The prevailing crisis in many mills is caused by a hike of over 30 per cent in raw material cost. Cutting energy losses reflects lean manufacturing practices and is one way the mill can reduce power costs. On off days, maintenance is like timely first aid to ageing machines. Mills need to plan to take each ring frame off for one shift to grease the bearings.

The cost of power is eating directing into the Operating Profit Margin (OPM) of the mill. In a running textile mill, instead of running 10 frames daily at 16000 rpm as spindle speed, rest one frame daily and operate 9 of 10 frames at 18000 rpm. The tenth frame can be taken for overhauling for the day and night maintenance work schedule. This gives it compulsory rest once in 10 days or two weeks. The exercise has to be repeated with other frames.

 

Energy consumption of ring frame

 

How can this loss be prevented?

Most mills ignore greasing the tin roller bearing for years. The mill decides to replace tin roller bearings once in eight years but does not consider taking out the tin roller bearings to overhaul them in those eight years. When the mill maintenance department wants to take up the overhaul of the ring frame, the management postpones the same citing market demand.

 

On every annual re-greasing with specialty grease, old grease should be allowed to ooze out of the drain cup. This confirms the new grease has taken its place and offers mechanical shear stability, stiffer grease consistency, rust inhibition and deposit control and delivers exceptional protection even under the most demanding conditions, such as high temperatures and high speeds. This is suitable for ring frame motor bearings which face tangential shear stress and therefore, to tin roller bearings.

 

What are the parameters to monitor the ring frame energy?

Approximately 8 of 10 mills of Indian Texpreneurs Forum, Coimbatore have procured the thermal imager in their 25,000 spindle mill segment. We understand each mill is using it innovatively to find hotspots in machines due to friction and misalignment in all sub-systems.

 

It was once believed that the thermal imager is useful only to spot electrical loose joint hotspots, but these mills are wisely engaging the thermal imager daily to find fresh hotspots and take immediate steps the next day to reduce their intensity. The same is to be followed in tin roller bearings in each frame. Relative condition monitoring of hotspots across the bearings, set in a frame, will yield more inputs to arrest hotspots.

Thermal Imaging shows hotter motor bearing and dried & caked MP 3 grease inside the bearing.

 

How can OEMS support textile mills to reduce running losses?

OEMs of the ring frame machine, tin roller bearing, motor, belt and grease have to adapt to latest monitoring techniques including thermal imager and vibration by SPM (Shock Pulse Monitoring). They need to transfer the knowledge to train the user to reduce daily running power losses from equipment. The tin roller bearing OEM should share the name of the grease they are using, re-greasing intervals, and possibility of using Polyurea-based specialty grease to increase re-greasing intervals to a year instead of every three to six months. They need to share the idea that bearings can be removed, cleaned and re-greased with specialty grease.

 

General guidelines

Lubrication of bearings and machine internals yield both tangible and intangible results. Tangible results include gradual fall in power consumption. Visual symptoms are localised hotspots that gradually disappear with the right quality and quantity of lubrication at the right time. The intangible benefit is that the machine sustains its rated efficiency when operated at its best operating point and works at its comfort level even after a decade of severe usage.

 

The textile spinning mill is alignment-oriented. Many of our loads are tangentially coupled to motors. The production comes down due to misalignment inside the machines. Lubrication lets the machine tolerate poor alignment and friction and make it run smoothly.

 

This lubrication with grease starts from motor end bearings to the transmission gears and to the load side. So to start with, the power of 55 KW at 1500 RPM (Revolution per Minute) is first applied to the drive end bearing and then gets transmitted to the load. So even a thermal imager can point out the deviation by more than 10oC difference from DE to NDE bearing.

 

Now, the mills use standard multipurpose grease for motor bearings. Some mills pump more grease every three to six months into each motor bearing and increase power consumption and man-hours for re-lubrication. They also add to their grease inventory.

 

Many mills confirm that heat on their motor skins has reduced by 20oC and more from changing from conventional grease to specialty grease. For healthy running of motors, the ambient 20oC is the allowable skin temperature and once the temperature rises over that, it indicates more losses.

 

In a motor, bearing malfunction is one of the causes of motor burnout, on an average in seven out of ten cases. Hence, the greasing and condition monitoring of machines have become critical.

 

This step has to be taken right away to reduce power loss due to wrong grease. Why should we allow excess consumption of 6 per cent because of poorly lubricated and incorrectly greased tin rollers? With one set of spare bearings to start with, the mill may be surprised to see the power loss over eight years that it has ignored unwittingly.

 

After removing the hard cake in bearing, the mill finds relief. Tomorrow, it will be a delight to the mill, as it has reduced energy losses by overhauling tin roller bearings within the mill premises and improved motor loadings. Mills have even reduced friction losses from tin rollers through the spindle tape of the spindles and the ring frame optimised unit per kg at higher spindle speeds. Loss from using the wrong grease can happen in Simplex with multiple bearings and carding. The time to act on it is now.

 

Image courtesy:

1. Salona Cotspin Ltd, Coimbatore

2. SITRA study

3. Lubrication Guide - Excerpt from GEK-72836E

 

About the author:

Ashok. S is a BEE Accredited Energy Auditor from Coimbatore