News

Can You Track Your Asset?


You can now with CPM Buttons!


CPM Buttons compliment your existing CMMS and as a solution to asset tracking. Never loose technical specifications again, always have technical manuals, schematics and maintenance history to hand right on an asset.


CPM’s Buttons (CPMBs) are miniature rugged coin-shaped devices packed with up to 64K bytes of non-volatile EEPROM memory, completely passive, and requiring no battery data can be read-from and written-to a CPMB virtually an unlimited number of times. Completely passive, the lack of RF emissions and need to contact to communicate assures an inherent level of security and guarantees correct identification.


Impervious to most environments each CPMB has a unique serial number and once attached to an asset or location serves as a rugged identifier and updateable logbook allowing inspection and maintenance to be tracked electronically through the asset’s life eliminating time spent on hand data entry and associated human errors. CPMBs can be updated with a momentary touch using a variety of hand held probes with USB or serial interfaces. Data stored on the button can be viewed in a variety of formats to help users in performing their job. In fact there are many applications for the CPMB, Here are just some of the uses:



The flexibility provided by CPMB technology (read, add and modify data on the asset), its durability and virtually unlimited operating life, offers Engineers the ability to dynamically access and update data on an asset at any point in the pipeline and above all this information stays with the asset. CPMBs give you the opportunity to:



For more information on how CPMB’s contact CPM Engineering on +44 161 865 6161

Do Motor Rewinds affect Efficiency?


This question has been asked of CPM by its customers when considering the whether to repair an existing electric motor or buy a new one. The drive to improve motor efficiency and reduce power consumption and the publication of the ‘Effect of Repair/Rewinding on Motor Efficiency’ study by EASA/AEMT has made the decision less straight forward.


By using the Good Practice Guide older motors can usually be returned to at least the original efficiency and on occasions improve performance by following good practice and increasing the copper content. The Good Practice Guide also explains the sources of the losses and how the motor repair and rewind process can affect them. The key steps are outlined as follows:


Initial Inspection

When a motor is received at CPM for repair/replacement the first thing is to assess the condition of the machine including its general state. Sometimes a decision can be made at this early stage dependent upon the external condition of the shaft, terminal box, cooling fins etc. The motor is photographed at this stage to record its condition.


If the external condition is good then a further, more in depth assessment can proceed. If the customer can provide history in the form of the operating temperature, current, vibration, hours of operation, stop/starts etc. Photographic evidence is invaluable.


A more accurate assessment can be made if the user can supply information such as: the motor’s operating temperatures and vibration levels; what load it has been driving; how many hours it operate per day; it approximate load; how often it starts; the type of starter used; and whether there have been any unusual incidents, such as power supply trips, lightening strikes, water damage and driven equipment failures. Also useful is any previous rewind history and how long the motor has been operating before being sent for repair.


When the motor is dismantled, an initial examination needs to identify and record the correct location of all components (so that the reassembled machine will be exactly as received. Particular attention needs to be paid to : the type, size and internal clearances of the bearings; any damage to leads and terminal arrangements; contamination; and mechanical damage.


Strip and clean stator.

Removing the old winding and cleaning the core is a critical process. Details of the original winding must be recorded, including the number of phases, slots, coils, phase connections, coil groupings, poles, turns per coil, and the number and sizes of conductor strands. The phase resistance needs to be measured and, if that is not possible, the resistance of the original winding should be calculated using the conductor cross-sectional area and the mean turn length(MTL)


Core flux testing.

To ensure stator stripping does not effect iron losses adversely, a ring flux ring should be done before and after the core has been stripped and the slots cleaned ready for rewinding. If the core loss (W/kg) increase by more than 50%, either the core needs to be replaced or the laminations reinsulated. To remove the old winding, the end winding should be cut off without damaging the core using appropriate machinery. The old winding should be burnt out in a temperature controlled oven at 360-370 c. Care must be taken to prevent the core from overheating.


When removing burned windings, damage to the lamination must be minimised – in particular to the teeth at the core end. Any splayed or displaced laminations must be re-aligned using minimum force. Care must be taken when cleaning the slots and the stator core to ensure they are not damaged because this could cause shorts. Any shorts between laminations – for example, smears resulting in impact between rotor and stator following a bearing failure – need to be removed.


Rewinding. Winding should either copy the style of the original motor of, if it’s possible to improve the performance, use a different style. When copy-winding, the same winding configuration, coil pitches, turns/coil should be maintained and cross-sectional areas increased preferably by at least 3%. End-winding straight lengths should be kept as short as practicable, and end winding lengths and coil MTL reduced where possible by cutting the projection slightly. Winding resistance should be no greater than the original and preferably lower.


Repairers using hand winding techniques can usually reduce copper losses. Care is needed when changing winding styles. A change must ensure that the flux per pole is unchanged and that the winding resistance is at least the same, but preferably reduced.


Providing the conversion is performed correctly – preferably using EASA’s AC Motor Redesign and Verification program – there are no disadvantages in changing to a two layer lap winding. Most repairers prefer this form of winding because all coils are the same. Two layer lap winding coils can be made with the MTL the same of lower than the original. Replacing a two layer winding with a single layer will certainly reduce efficiency.


Assembly.

When reassembling the motor, it is critical that any replacement bearings are fitted correctly and that the motor has the same internal clearances as the original and contains the manufacturers specified volume of lubricant. Service engineers need to liaise with the customer to ensure that the lubricant is the same as, or compatible with, that used by the customer. Seal seatings must have the specified surface finish and must be lubricated. Replacement fans must be identical; changes can increase windage losses or reduce airflow and increase temperature rise.


Source : Electrical Apparatus Service Association – European & World Chapter

Gearbox & Gear System problems


Summary


Gears and gearboxes are generally reliable devices. However, problems do occur, and many are caused by the application and operation, rather than gear faults. A prime observation is that gearbox failures frequently initiate in the bearings rather than the gears themselves. Examples include misalignment caused by deflections, vibration, thermal expansion effects during start-up, external contamination due to orientation, and breathing / sealing arrangements.


Introduction


A review of all gear and gearbox failures shows that the failure sequence frequently starts with a bearing, rather than a gear. Bearings being the apparent root of about half of all the failures.


This may at first sight seem surprising, since rolling element bearings (used in the majority of gearboxes) seem to have a relatively easy job compared to the gears. The gears have substantial sliding in the tooth contact, and substantial bending stresses in the teeth. Rolling bearings have neither, just (nominally) pure rolling.


However, rolling bearings operate under high contact stresses, and are susceptible to the effects of small debris particles in the lubricant. These may well be the reasons why the bearings frequently suffer before the gears.


A more detailed analysis divides the failures into further categories, as shown in the graph. For some failures, there are multiple causes, (ie. no prime cause), and so this analysis has to be treated cautiously. (For example, we cannot conclude that 19% of all gear failures are caused by gear misalignment - in some cases this was only a partial cause.)


The major categories shown in graph 2 are discussed in more detail below. It is appropriate to comment here on the minor categories.


Starting torque related failures (3%) are quite small, indicating that starting torque effects are in general well understood and allowed for by designers.


Manufacturing errors (excluding design errors!) are also quite small, at 6%. There are many cases where a minor manufacturing error or deficiency has been found, investigations have shown that this was of minor or zero significance in the failure. There is a tendency for users, repairers and manufacturers alike to identify a small manufacturing error and then correct it. Any subsequent improvement in life may then be attributed to the correction of this error, whereas the truth may be that the cure was due to some other aspect, of design, set-up, or operation, which happened to change at the same time.


Generally, the gear design standards are conservative, and a manufacturing error has to be quite severe to be the prime cause of failure.


CPM & Gearbox Services


Whilst CPM offers a 24 hour repair and rebuilds service they also investigate the root cause for the failure and offer a service to:

         
  • Avoid reoccurrence      
  • Engineer out the problem      
  • CBM services to detect faults before they cause damage


More Information

For further information on how CPM can help you reduce your costs and for a full copy of the report call +44 161 865 6161


Source: Gears Conference - London

Why Mechanical Seals Fail

(5/03/2010)


Mechanical Seal failures seem to fall into four broad categories:

         
  • The seal motion was restricted and the faces opened.      
  • Heat caused the 0-rings to deteriorate.      
  • The seal materials were attacked by the fluid sealed.      
  • The seal was installed incorrectly.


Mechanical Seals motion restricted:


The spring-loaded (dynamic) seal face constantly moves to maintain full face contact with the stationary seal face. The main reasons for this movement are

         
  • 1. The stationary face is not perpendicular to the pump shaft.      
  • 2. The pump has bearing end play. This means that the shaft moves back and forth a few thousandths     of an inch at frequent but random intervals.      
  • 3. There is some impeller unbalance causing shaft whip.      
  • 4. The pump is operated away from its BEP, causing side loads on the shaft.      
  • 5. There is thermal shaft growth and Pump vibration that affects the seal.


Here are the major conditions that can restrict..
Movement of the spring loaded mechanical seals face:

         
  • 1. Solids have collected in the seal or around the dynamic seal ring.      
  • 2. The fluid sealed has caused the dynamic 0-ring to swell.      
  • 3. The temperature limit of the dynamic 0-ring has been exceeded and the 0-ring has lost its elasticity (compression set) or become hard.      
  • 4. Spring compression is inadequate because of incorrect installation.      
  • 5. Solids in the stuffing box, gasket protrusion or other foreign material restrict the motion of the dynamic seal ring.


Thermal degradation of Mechanical Seal 0-rings:


0-rings are the one part of a mechanical seal that are sensitive to heat because of the way they are manufactured. The ingredients are mixed together, put in a mould and cured at high temperature for a specific time. The compound will then assume the shape of the mould and its hardness, or durometer, will increase. When the 0-ring is placed in an 0-ring groove in a seal and heated to a temperature beyond its recommended limit, the curing process will continue and the 0-ring will take a compression set. This means that the 0-ring has lost some of its resilience and squeeze, and fluid may leak past the 0-ring. The higher the temperature, the shorter the time before the 0-ring takes a compression set. When an 0-ring is exposed to high temperature for a long period, it will become hard and brittle, causing mechanical seals failure.


Since heat is often a problem and seldom helps the mechanical seal application, what can be done about it?

         
  • 1. Use a balanced seal to minimize the heat generated by the seal.      
  • 2. Use low-friction face materials. Carbon vs silicon carbide is the best choice.      
  • 3. Use a clean liquid flush or product recirculation to carry away heat.


Mechanical Seal materials attacked:


When the correct materials are not selected,

         
  • 1. The 0-rings may swell locking up the mechanical seal,      
  • 2. The mechanical seal faces may deteriorate rapidly, and      
  • 3. The metal seal components may corrode.

All can cause the mechanical seals to fail.


Mechanical seals installed incorrectly:


Many mechanical seals fail at initial start-up or prematurely because they were not installed correctly. Cartridge seals eliminate all measurement, protect the seal faces from contamination and are easy to install. With these seals, installation problems are minimized. The Outside seal is preset and requires no installation measurement. Only in-line seals require careful measurement to insure correct installation. By following the mechanical seals installation instructions, step-by-step correct seal installation is easily achieved.


Source: Mechanical Seals.Net

SIEMENS CHOOSES CPM AS A DRIVES TECHNOLOGY PARTNER

(16/02/2010)


Siemens Drives Technology (DT) has linked up with a number of industry suppliers and distributors in a drive train partnership that will directly benefit end users.


The aim of the partnership is to promote Siemens capability and to deliver products and systems faster to customers. Siemens drive train products, include


         
  • Variable speed drives      
  • Induction motors      
  • Geared motors and gearboxes

The partnership allows CPM to stock Siemens and offer a 24-hour, 7-day-a-week call out service for all of its products including the wide range of EFF1 industrial motors up to 200 kW. Additionally, the agreement gives CPM access to the technical and application expertise of Siemens products including motor and drive installations, and manufacturer warranted motor repair facilities.


Paul Dudley, Siemens Channel Manager (Drives Technology), said: “This new partnership enables Siemens to deliver its DT products and services through a strong national and regional parts network to its large and varied customer base. Siemens customers will see an immediate and long-term benefit from this move.”


For more information email us at info@cpm-uk.com or call +44 161 865 6161

Core Testing Motors without stripping the Stator

(05/02/2010)

Fact or myth?


Imagine the scenario. A motor is showing signs of overheating and all the normal onsite tests for load and application have been exhausted. You send it to your motor repair company for investigation. The static and dynamic tests all show the motor to be within specification and so more in depth investigations need to be performed.


One consideration is a breakdown of the laminated core which can cause hot spots and result in the stator windings overheating and ‘burning out’ prematurely. So, how is this diagnosed or eliminated from the investigations?


Misconception


There is a misconception that you have to strip the stator of its windings before you can core test the stator. The magnetic flux path in a core test is a ‘ring flux’ around the back iron of the stator. This flux does not magnetically couple to the windings. Because of this whether the stator windings are in good condition or failed, it does not affect the core test. Thus, it is a myth that the stator windings need to be removed in order to perform a core test and so eliminate the core from your investigations.


Another Misconception


Is that the damage to the core is always visually evident once you remove the rotor. The individual laminations are insulated with a very thin coating between them. This insulatation layer can therefore be degraded without any outward signs on the surface of the stator core. It is good practice however to core test the stator before and once the windings have been removed (if you make the decision to rewind the stator) and as part of your motor repair procedure for motors undergoing overhauls in order to detect core damage and so avoid premature winding failures.


For further in-depth testing of stator cores lamination testers can be used particularly when ensuring lamination degradation in energy efficient motors.


This procedure can also be used on wound rotating components including rotors and armatures.


Final Test Run


The final load test and ‘heat run’ run should be performed on all energy efficient motors to ensure their compliance to the Original Manufacturers specification. All tests at CPM are performed in accordance with OPN 020 series of Quality Assurance Procedures


For more information email us at info@cpm-uk.com or call +44 161 865 6161

Self Priming Centrifugal Pumps

(03/02/2010)

Are ‘Self Priming’ Pumps what they say?


Most maintenance personnel who work with centrifugal pumps have been trained to never start a pump unless it is primed. We were told that this could score the seal or packing or cause permanent damage when the suction liquid level is below the pump. We are then told about ‘self priming’ pumps and we think, is all this caution necessary?


The fact is that no ‘self priming pump is truly self priming in suction head situations and so in all instances the seal(s) should be protected against overheating at all times. That requires more than just a cooling mechanism as seals and packing rely upon a small amount of liquid to migrate between the faces in order to lubricate them.


Protecting the Seals


A properly primed pump would use the pumped media or a flushing liquid to cool and lubricate the seal. Centrifugal pumps that are classified ‘self priming’ normally have 2 a double seal with a barrier fluid in a chamber between the two seals. It is this fluid which protects the seals when starting the pump dry. Assuming the seal has been provided with adequate cooling and lubrication the concern now is whether the pumped media is above the flooded suction or below the pump.


The task is to create sufficient suction to lift the pumped media into the pump. The impeller can’t do that. The impeller is designed to create a pressure differential with the pumped media in the impeller and pump housing. Common media is in the form of liquids and is up to 800 times as dense as air. Centrifugal pumps will not pump air.


Two Common Approaches


There are two common approaches to the problem. The most straight forward is to provide the pump with an auxiliary pumping device which will remove the air and draw the media in. It is assumed that the suction pipe is submerged in the media causing an air seal. Similarly the discharge must also have an air seal which is normally in the form of a valve which prevents air being drawn into the impeller and pump housing from the discharge line.


The secondary method of ‘air pump’ is in the form of a diaphragm or educator pump which can be electrically, mechanical or pneumatically driven. With the pump suction and discharge sealed, the secondary pump will pump air out and draw the media in. When the media is drawn up to the level of the impeller, the impeller begins to pump, forcing the valve open. A pressure switch would then normally switch off the secondary air pump.


Another approach is to build the pump housing in such a way as the media would remain in the housing when both suction and discharge valves are drained. Suction and discharge pipes can be built where they are above the impeller thus creating a ‘tank’ below that houses the impeller and volute. A valve on the suction or discharge pipes may avoid the media siphoning out of the ‘tank’ when the pump is stopped.


When the pump is restarted, the media in the ‘tank’ may be sufficient to create suction lift and draw the media into the pump ‘tank’ and impeller and to purge the air out of the discharge. The pump is said to ‘digest’ the air. This approach requires that on the initial installation of the new or rebuilt pump there must be an initial prime loaded into the pump. If for any reason the pump ‘tank’ is drained the pump will fail to pump. So, the self priming feature of this pump is only effective after an initial prime. This style of pump can be referred to as a ‘re-priming pump’.


For more information email us at info@cpm-uk.com or call +44 161 865 6161

Vibrator Motor Repairs

(02/02/2010)
Unusual application calls for special considerations and handling


One of the unique motor applications were often called upon to service is the vibrator motor. These are mechanically robust electric motors, fitted with large eccentric weights, designed to deliberately vibrate – a lot. The unusual application calls for some special considerations when repairing these motors.


When dismantling the motor, the first step is to document the position of the eccentric weights on both ends, relative to each other, so the performance characteristics remain unchanged. Many of these are fitted with two weights on each end and only one of the weights is keyed. The second weight can be shifted relative to the first to allow adjustment of the unbalance to suit the application. In some applications, for example, when shaking a product through a hopper, the weights might be adjusted to different settings to move materials of different density.


Shift weights to opposite sides


While there are designs where the weights on both ends are offset in the same direction, it is sometimes more effective to shift the weights to opposing sides. The resulting structure movement is more conducive to energy transfer when the ends of the motor undulate. Installing the eccentric both on the same side (e.g. both ends of the motor have the eccentric weights in the 6:00 position at the same time) produces a more violent movement that is more likely to break welds and do structural damage#


It is critical that the eccentric adjustment of the counterweights on both ends be identical. Setting the offset on opposite ends to different force will result in transverse forces that are very likely to result in destruction of the mounting supports, or the shaker screen duty motor itself.


All that shaking requires a massive shaft and oversized bearings as well as special bearing fits for the housing and bearing journal. In layman’s terms, the shaft fit is a slip fit and the housing fit is tight. As you might imagine, so much radial load requires special bearings. Aside from the relatively large bearing for the kW rating, the internal clearance of the bearings is always greater than C3. A bearing with C4 internal clearance is most common for vibrator motors


Repair Methods


Not all journal repair methods are appropriate for the extreme duty of the application. Electro-plating is the preferred option to restore an undersized bearing journal. Metal spraying should be avoided; it may fracture under the pounding forces. Welding should also be avoided, as the shaft has been known to become brittle and break. A severely damaged shaft should be replaced, and the replacement shaft should match the original material.


The bearing fits are typically a looser than usual shaft fit, with a tight housing fit. Some older bearing fit tables refer to these as “rotating housing, stationery shaft” tolerances. Bearing manufacturers differ slightly in their tolerance recommendations.


NJ Roller Bearings


Some shaker screen duty motors are fitted with NJ roller bearings, which have a locating shoulder on only one side of the inner race. The inner race is specially ground or “crowned” to provide the necessary internal clearance for a vibrator motor. The bearing numbers may be hand engraved on the bearing.


When rewinding vibrator motors, the winder is aware that the magnetic flux densities are often lower than usual. It is not desirable for the motor to accelerate too quickly; that can cause structural damage to the installation. It takes time to establish the required movement of the hopper or structure, and too rapid acceleration might break welds near the motor mounting. The motor frame could even be damaged over the course of numerous starts.


Use extreme-pressure grease


Extreme-pressure grease is required to accommodate the large radial load on the bearings. Standard ball bearing grease can break down under the operating conditions


In a good design, the end brackets and retaining bolts are also more substantial that those of similar kW ratings. Bolt torque is of increased performance as is the importance of lock washers, thread-locker compounds when recommended, and lock nuts on designs where the bolt is not threaded into a trapped frame. Through-bolts are less suitable than designs with a substantial frame tapped for thread engagement of (at least) twice the bolt diameter.


The installer should be aware that these bolts must be of the same size; the use of under-sized base bolts can result in catastrophic damage to the motor and driven equipment as well as increased risk of injury to personnel. Washers, when used, must be hardened washers to prevent distortion, which would result in loosening of the fasteners


Lugs should be crimped and soldered for the added security. The lead opening/terminal box must be packed with material to prevent chafing of the leads against other surfaces. Suitable materials include vermiculite, electrical compound or pump packing. Never use silicone sealant, which makes it difficult to access the leads when the motor is next removed from service.


Final Test Run


The final test run is performed without the counterweights, for practical reasons as well as safety. Bearings and no-load current along with all dynamic tests are performed in accordance with CPM’s OPN 020 series of Quality Assurance Procedures


For more information email us at info@cpm-uk.com or call +44 161 865 6161

Changes to Electric Energy Efficiency Motor Markings

(01/02/2010)
CEMEP (European Committee of Manufacturers of Electrical Machines and Power Electronics) are withdrawing the Voluntary Agreement for marking motor Efficiency Classes, EFF1, EFF2 and EFF3. The termination date is 10 February 2010.


From that date new motors manufactured are not allowed to use the CEMEP EFF-trademarks, EFF1, EFF2 and EFF3. They will be using the new efficiency classes in accordance with IEC 60034-30


The changes will be as follows:


Previous motor efficiency classes in EuropeNew international motor efficiency classes
EFF3 = Low Efficiency 
EFF2 = Improved EfficiencyIE1 = Standard Efficiency (comparable to EFF2)
EFF1 = High EfficiencyIE2 = High Efficiency (comparable to EFF1 )
 IE3 = Premium Efficiency

Please see further information here


For more information email us at info@cpm-uk.com or call +44 161 865 6161

Summer Swelter Avoided

(09/07/2009)
CPM recently helped a facilities management company to save office workers from getting hot under the collar when they removed, repaired and refitted a heating and ventilation fan in a 14 storey office block.


One of the North West’s leading Facilities Management Companies recently called CPM for assistance when a large major fan failed in a 14 storey office block.

 

The heating and ventilation fan was situated on the top floor of the building and had tripped resulting in loss of services to the building. The location and restrictive access to the fan posed a problem which was overcome by innovative handling equipment

 

A CPM Engineer diagnosed a short circuit with in the electric motor driving the fan. A full risk assessment of the project was carried out and submitted to the client together with a comprehensive method statement. 

 

A team of CPM engineers subsequently attended site and stripped out the fan unit from the building using specialist lifting equipment and a hired crane.

 

The fan was repaired at CPM’s Manchester works which consisted of a full motor rewind and fan overhaul and dynamic balancing.  The unit was refitted and commissioned to the satisfaction of the customer over a weekend slot with a 2 year warranty, thus avoiding any further inconvenience to the Facilities Management Company and their client.

 

Under Pressure

(09/07/2009)
CPM design and machine a cabinet for pressurised testing in a controlled environment


CPM recently received a call from a North West based Specialist Printing company.  They needed to perform product testing within a controlled pressurised environment and sought advice on how to achieve their objective in the quickest possible time with the least investment. 


CPM’s response was to meet with the client, draw up the specification and working together to achieve the operating conditions, design a machine cabinet.  The designs were produced on a CAD based package and submitted to the client for approval.  A quotation was then submitted for the manufacture of the design and once approved the manufacture could proceed.


The manufacture was achieved within days of approval and included the doors, inspection access and shelving.  Once the manufacture was complete a team of CPM Engineers erected the equipment on site and commissioned to the customers satisfaction.  The project from start to finish was 2 weeks and so meeting the customers deadline for production.

 

Another example of CPM’s engineering skills put to innovative use.

Predictive Maintenance Averts Disaster

(09/07/2009)
How CPM used ultrasound to detect and 'nurse' a failing bearing


One of the North West leading Paper Manufacturers averted a potential lengthy and costly stoppage when CPM Reliability Engineers identified a bearing on a large paper roll that was entering the early stages of failure. The problem was identified using Ultrasound technology which is particularly good at finding problems on relatively slow moving equipment.

 

CPM Engineers routinely monitor critical assets on the plant and having identified the problem and were able to advise the customer of the seriousness of the situation and predicted time to failure.

 

No spare roll was available for 3 weeks so it was decided to ‘nurse’ the bearing through until the new assembly was delivered to site and when time could be made available for a ‘production window’.

 

By carrying out regular monitoring with Ultrasound and re-greasing using the ultrasound reading as a guide the precise amount of grease was applied to the bearing and the plant was able to run at virtually full production. savings in production were in access of £30,000 and the cost of no-urgent repairs and labour costs estimated at £1,800.00.

 

CPM Engineers were able to assist the customer in the fitting of the replacement roll and the refurbishment of the failed roll.

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