Trouble shooting for mechanically jammed Serpentine oven

This is a recent incident in one of the plant with an Auto-bake Serpentine oven. A picture of the Serpentine oven is downloaded from the Auto-bake website as shown below.

Picture downloaded from Auto-Bake Website for illustration only

The picture above shown only a Serpentine oven. The advantage of having a Serpentine oven is the same oven drive chain can be lengthen and passing through multi compartment with different environmental condition and make into a full production line, except packaging.

As shown in the sketch below, the production line that was mechanically jammed has an Infeed section, an Oven, a Cooling section and an Outfeed section. The width of the line is approximately 1.5 meter. It has two double pitch roller chains running at both side of the line with carriers hanging in between the two roller chains.

Both roller chains are a few hundred meters in length passing through multi loops as shown in the sketch. Thus the whole line is running with two motors (drive 1 & drive 2). There is a synchronizing encoder in between the two drives, sensing the tension condition of the chain and controlling the speed on drive 2 in related to drive 1. This serves to share the whole line load between the two motors.

The incident started with an alarm, "drive 1 mechanically overloaded". The production team reported the issue to engineering team and they started the trouble shooting process. 

The engineering team first noted that there was no output from the variable frequency drive unit of motor 2. Hence they thought it was the faulty variable frequency drive that causes motor 2 not working which lead to mechanical overload alarm of drive 1.  With this finding, they planned to check into the variable frequency drive unit and replace if necessary.

When I was informed on such issue, I stopped them from any work on the variable frequency drive but ask them to check into the position of synchronizing encoder. I explain to them that the variable frequency drive 2 might have no output if the synchronizing encoder indicates that the section of roller chains driven by motor 2 are tight. The check was carried out and proven right. The synchronizing encoder was fully retracted because the sections of rollers chains for "cooling" was tight.

I ask the team to check on any obvious mechanical jam, especially by the ends of all loops because a straight run of chain normally should not jam. The team finally reported thaty there was no obvious jam and they are running out of idea on how to check further.

Then I decided to manually pull stretches of rollers chain in various sections of the production lines, with the intention to feel if there is any difference in tension. The tensioner on the outfeed end for both roller chains are released before the "feeling process". 

The "feel" of both rollers chains (both sides of the production line) in the cooling section are quite even. The same goes to those roller chains in the oven. When it came to the infeed end, the roller chain on the left hand side seems to be tighter as compare to the right hand side. The difference became more obvious on the return path of the roller chain. The difference was very slight and I decide to get the executives, engineers and supervisors to feel the difference too as a matter of On-Job-Training.

Finally when it came to feeling the roller chains on the return path of the outfeed section, a greater difference in tension was found. With this "feel" action, we finally manage to trace toward the jammed sprocket as shown in the sketch.

Removing baking trays from the section and climbed into the suspection area, we then found the little M6 X 10 Counter sunk screw jamming in one of the sprocket.

With such a small piece of screw jamming in one of the sprocket which is not easily accessible, the tracing technique is important or else it would be difficult to find even though the problem is truely minor. Hence I decided to share it in my blog here and hope that readers who had read this will be able to lear the little practice of "feeling the machine" during trouble shooting.

Chiller Unit tripped with "No Flow" alarm

On passing by the Chilled water system and glycol chiller units in the plant this morning, I saw the supervisor and technician are working there for some problem faced. On checking with them, I was informed that the chiller unit tripped with "Glycol no flow" alarm. It runs back to normal after resetting.

I decided to ask if they understand what possible caused the tripping and I was informed that the level in the glycol tank is low. With doubt in mind, I decided to go with them to check the glycol tank level and noticed that the level was not "too low" as what they explained.

Hence decided to explain to them on how to trace for the possible root cause on such system trip issue. As I always highlighted to the team, a successful man always slice a large problem into smaller pieces and then tacker them one by one. In no time, the problem will be solved. The same apply to engineering trouble shooting.

Hence the first step is to trace the part of the whole system that giving alarm "glycol no flow to chiller unit". The following snip set of the glycol system related is capture and atteched here for reference.

Using the glycol tank as a starting point, we noted that there are three pumps (PP1, PP2, and PP3) taking their supply from Glycol tank and discharge into a common line to send for chilling into two chiller units (Chiller 1 and Chiller 2) and then back to glycol tank. Two of the pumps will be running at any one time with the third pump on standing by. There is another circuit with two pumps (PP4 and PP5) taking suction from glycol, sending through Chiller 3 and then back to the tank. For this circuit, one pump will be running and the other on standing by too.

After check and confirm the level of glycol in glycol tank is normal. I noticed that the running pumps are PP2, PP3 and PP4. The pressure gauges readings were PG2 zero PSI, PG3 80 PSI and PG4 50 PSI.

Hence my first advice to the technician and supervisor is to ensure all presure gauges are working correctly. The pressure gauge that indicating 0 PSI is definitely faulty or blocked. Assuming pressure Gauge PG4 is correct at 50PSI, then pressure gauge PG3 with pressure of 80 PSI may be faulty too, or there may be some blockage on the line. Hence, I advice them to check on any possibility of partial iced up in the heat exchanger of the running chiller unit. The system may have to be shut down for a short while to let the iced glycol melt.

A further action is required to check the glycol bridge. It may happen that the bridge is too low, or else the glycol should not iced up in the heat exchanger.

After ensuring that both the supervisor and technician understand the explanation above, they were then left to continue with their action to rectify the issue accordingly.

NOTE:
"NO FLOW" alarm is activated by the differential pressure switch PS connected across the inlet and outlet of the heat exchanger. Hence an alarm basically indicate possibly blockage of the heat exchanger. 

Example in setting up SOP for electrode boiler feed water de-ionization system

In the past, we normally carry out training to our subordinate with hands holding practice. But with new management style of educated management team today, a lot of SOP with standard format are requested. The amount of paperwork also increased tremendously, to the extend that wometimes there is no time to spend in production floor.

Below is an SOP prepared to train my engineering subordinate on maintenance of de-ionization system for electrode boiler. It is posted for sharing, and as a record that I so this now. 😂

1.0 PURPOSE
To provide as training material for basic understanding on why de-ionization system is required for our electrode boiler and to provide a clear guide on how to maintain the system effectively.

2.0 SCOPE
To cover a brief explanation on the importance of de-ionization system with regards to electrode boiler.

To explain detail procedures in checking functionality of de-ionization column together with conductivity meter function.

3.0 RESPONSIBILITY
3.1 Engineers/Executives

3.2 Engineering Supervisors

4.0 DISTRIBUTION LIST
4.1 CONTROLLED COPY to be kept by HOD

4.2 UN-CONTROLLED COPY to be kept in [Engineering FOM Folder]

5.0 APPLICABLE DOCUMENTS
5.1 Refer to EQUIPMENT LOG AND FILING PROCEDURE for how to manage completed log sheets.

5.2 Electrode Steam Boiler Log.

5.3 ROC CCT-3300 series Conductivity Controller Operation Manual

6.0 BACKGROUND INFORMATION
Total Dissolved Solids (TDS) are the total amount of movable charged ions, including positively charged Cations and negatively charged Anions. These ions are originated from dissolved minerals, salts or metals in a given volume of water. It is expressed in units of mg per unit volume of water (mg/L), also referred to as parts per million (ppm).

TDS is directly related to the purity and quality of water. Water with higher content of TDS is known as hard water. If we boil hard water, after the water being evaporated, the dissolved solids will be depositing on heating surface and form scale on the surfaces. More deposit will be formed when we boil water with higher TDS.

Water fed into boiler must be with high quality with minimum TDS. This is to ensure that no or minimum scale will be built up on the heating surfaces. Formation of scale on heating surfaces will retard heat transfer rate and if the rate of heat transfer is too low, then the heating elements will be overheated and burnt easily.

As conductivity is easier to measure, it is used in algorithms estimating salinity and TDS, both of which affect water quality. Depending on the steaming rate, the quality of water required will be different. Our electrode boiler steaming rate is comparatively low and thus only ion exchange columns are used for our de-ionization process to improve water quality.

Deionization is the process by which mineral ions in water are removed. Using specific ion-exchange resins (an insoluble matrix usually found in a bead shape), the ions in water can be drawn out and replaced. First, water flows through a certain resin that will cause the cations in the water to be drawn out, replacing the cations with hydrogen ions (cations) instead. The water, now very acidic, runs through another resin that will absorb the anions in the water, replacing these ions with hydroxide anions. The hydrogen and hydroxide will then combine to form water in a chemical reaction, leaving mineral-free water with very low TDS which will then minimize scaling of heating elements in our electrode boilers.

When the hydrogen and hydroxide ions are depleted in the resins column, the de-ionization effect will be low. In such case TDS will be increased and the conductivity measured will be higher too. This means that the de-ionization column would have to be sent for regeneration.
One important point to take note is that water flow rate passing through ion exchange column plays an important part in efficiency of ion exchange.

7.0 IPORTANT SETTINGS
Parameters Setting as below:

Parameter order	Description	Setting
1	Electrode Constant	0.100
2	Radis point setting	1.000
3	Measurement Unit	microSimens/CM
4	4mA transfer value setting	0.5
5	20mA transfer value setting	200
6	Alarm High Limit	1.0
7	Alarm Release	0.1

Note: The conductivity meter we used on the boiler feed water system is ROC CCT-3300 series conductivity controller (our unit is CCT-3200T for display only).  Refer to the CCT-3300 Series conductivity controller manual for detail on how to set the parameters.

8.0 PROCEDURE
8.1 How to carry out spot check on functionality of de-ionization system.

8.2 The engineering supervisor should go up to boiler platform and carry out the following check as a spot check to the effectiveness of technician in carry out their duty in logging boiler log.

8.3 It is advisable for the supervisor to shut the feed water supply to de-ionization system and feed water tank for 30 minutes to create some room before carrying out the following trial.

8.4 Check inlet and outlet connections to both de-ionization column and make sure that they are connected to the correct inlet and outlet holes. Take note on the IN and OUT marking on the cap.

8.5 Check all fittings in and out from the boiler, including those for the boiler gauge glass. Any deposit of white particle on the fittings indicates some minor steam leakage and the white particle that deposit after evaporation of steam or water is an indication of high TDS water.

8.6 After the water level in the feed water tank drop approximately 1 inch, the room in the tank would be good enough for the following test.

8.7 Turn on the supply valve to de-ionization system again and confirmed that water pressure drop across the system is lesser than 1.0 bar.

8.8 Partially close the valve toward the flow meter and set it to approximately 6 LPM (Litres per minute).

8.9 Check the conductivity meter and confirm that the conductivity is lower than 1µS/CM (microSimens per CM).

8.10 Set the flow rate back to approximately 6 LPM and let the system run back to normal.

8.11 During the above spot check, if the conductivity of feed water goes beyond 1µS/CM and the related technician who carry out boiler log did not report. Please guide accordingly. In case of repeated mistake, please carry out necessary disciplinary action.

8.12 Carry out the following procedures if the conductivity goes beyond 1µS/CM.

8.13 Change over to use the other column and carry out all above steps to double check that the new column is performing as expected.

8.14 Removed the exhausted column from system and replaced it with the standing by new unit.

8.15 Report to Engineer/Executive immediately for arrangement to re-generate the exhausted de-ionization column.

8.16 The duty is not end. Make sure you follow up within the week that the PR and PO are issued, old column removed to regenerate and regenerated column sent back to our plant.

8.17 The responsibility of supervisor only ends after the stand by unit of de-ionization column had been set back to stand by.

Power supply to control system

With the introduction of  PLC (Programmable Control Logic) into industrial automation, the use of 24 VDC power supply become a norm.

Industrial automation company such as Allen Bradley and Siemens, together with others companies like Phoenix, Omron and etc. do supply high quality power supply units. These are normally quite high in cost and they are claimed to be "more safe and stable".

After all,

1. Are this claims justify the duty they provided?
2. What is the differences between this and normal 24 Volts DC power supply unit?
3. Is there any possibility that we can repair the power supply unit ourselves?

On browsing the internet, I come across this Power Supply Repair E-Handbook and believe it will give you the answer. You can checkout here to buy the product.

Note: sometimes, the links provided might be not accessible due to some WIFI setting. In such case, try it again when you are in a different WIFI coverage.

High technology problem after a electrical power shutdown

A recent expansion called for incoming electrical power shutdown for installation of new VCB (Vacuum Circuit Breaker).

It had been a normal practice that engineering team has to standby to rectify issues caused by power shutdown. I always refer to this as the "high technology problem", because this type of problem seldom happen to the traditional equipment with hard wired control circuit.

As the digital technology advanced, a lot of control had been digitized. More and more companies are now promoting the "4th Industrial Revolution". I believe that this is the right direction but sometimes I cannot stop myself doubting on how many of those involved really understand the practical problems behind this development.

Digitizing means more electronic components are used in plant automation. The advantages for electronic components are low power consumption, higher flexibility in equipment production and modification.  Nevertheless, digitizing also means that higher chances of component failure caused by electrical surge.

With a high number of PLCs and VFDs used in the plant automation, it had been a norm that a few VFD fail after power shutdown. This time, five VFDs need to be replaced.

The same happen to earth leakage and over current relays. One unit is replaced this time.

There may be someone thinking that it is caused by unhealthy electrical quality. The fact is we had carried out various electrical quality check and the same problem never end.

One other problem that frequently faced is the Ethernet communication used for production line PLCs and VFDs. The lines are fully auto, with ability to set in recipe which is known as flexibility. But the system tends to lost communication. Sometimes problem is rectified by replacement if Ethernet switches, but quite often the issue is solved by a few restarting of the control system and/or unplugging and plugging of Ethernet cables. We believe this is not a professional method, but it works.

 

New start to an old blog

This blog had been created for sometimes. For various reasons, it had not been updated effectively.

Today, I had decided to re-design its outlook and you can notice a lot of books appeared as its background on the bookshelf. This is one of the main reason because there are so much to share and yet there is so little time to write post.

Believing that Rome is not built in one day, with this new start, I will post idea as it appears and will progress to share any information which I find useful and believe they will help my audiences as it progress. Any comment will be welcome and I will try my best to improve along the way.

Think "dynamic" in Engineering

Production executive who has basic engineering knowledge asked me about a recent problem faced with regards to the LPG supply line.

In the plant, we have a few LPG storage tanks, passing through two units of evaporators into a common main supply line. This main line is then branches into four sub-lines, supplying to four production lines.

It is Malaysia's industrial practice that the main petroleum gas (PG) supply line into any building must be set at a pressure not more than 18 psi. This 18 psi line pressure will then be a standard to work on for normal equipment operation.

Our four PG lines comprise of three oven with ribon burners and a thermo oil heater unit with industrial burner. Recent problem faced is the industrial burner did not manage to switch into high fire during operation. This was traced and I noted the minimum gas pressure switch was activated on low pressure when the system changed from low fire to high fire mode.

My explaination to the team is simple. The gas supply rate is not sufficient to maintain industrial burner at high firing rate. Thus I arranged for the team to check and clean the supply line filters for any possibility of blockage. Meanwhile,  a detail trace was then carried out and noted that it was a cool day and one of the LPG evaporator unit was malfunction because it is electrically operated and the heater unit was out of order.

Below are questions by the production executive and my answers:

Why we have four lines but only the thermo oil heater is affected?
Answer: The firing rates are different. Ribon fire burners are having low firing rate, thus minor supply line pressure fluctuation is not an issue on individual burner. As for industrial burner, the firing rate is higher and thus gas supply rate is important to maintain efficient firing. Thus a minimum gas pressure switch was there to ensure gas pressure prior to combustion is above the minimum requirement. It was this minimum gas pressure switch being activated that leading to shutting down of burner.

We do have a pressure regulator supplying to thermal oil unit industrial burner, the upstream pressure was still higher than down stream and the down stream was seemed to maimtain at its normal reading, why there was still tripping?
Answer: The normal line pressure was 18PSI. With only one evaporator, especially in a cool day, the line pressure drop to 16PSI when the consumption is high. Even the down stream pressure was tegulated to only 3 PSI, the actual flow rate of gas across the regulator opening was lower due to lower upstream pressure. Thus eventhough the regulator still manage to regulate to set pressure finally, there was a minor time lag. Too bad that this time lag was long enough to activate the minimum pressure switch which finally shut down the burner.

On the second query, I took opportunity to highlight to the team on what is so called "theory and practical are different". Theoretically we normally apply some assumptions, which sometumes are so obvious and yet negligible, thus we do not highlight them specifically.  Nevertheless, in practical world, this assumption is normally what causing an issue. Hence it is important as an engineer to observe this and remember, engineering is working with dynamic condition and we should not apply theory learnt statically.

For this incident, I was glad that the productuin executives are now paying more attention on understanding the root causes of "equipment breakdown". With extra knowledge or experience gained, they would be able to understand that it is not an equipment issue but a system issue. With this understanding, they will then be more appreciating on why a certain preventive task was carry out not directly on an equipment.

2015-07-Another busy day

Due to the problem faced amidnight on roll oven, I can carried out another training to the staffs on the ignition cycle of the burners system on the Baker Thermal Roll oven.

Starting on the importance of purging cycle related to safety issue. Follow up with the reason of having zero pressure regulator again to minimize gas leakage potential into the plant.

As gas pressure is at zero atmospheric pressure, then the function of air fuel mixing valve, and to "suck" gas into the burner.

The cycle of igniting follow by flame detection system was explained too.

After that, get related personnel to carry out necessary service to rectify problem of oven firing up to temperature slow.

Another training carried out today is to train three existung engineer on linking notebook to HMI, uploading runtime program from HMI, import to AB factory talk view studio, converting into latest version of runtime and download back to HMI.

Trouble shooting steps were trained to another team on the refrigeration system and how to check the signal feed back from pressure transducer.

2015-07-08, train on panelview plus

I was reported that the AllenBradley panelview plus 600 on two of the packing machines.

On checking with them, the message displayed was FATAL FAULT 3A.

While tracing, noted the terminal status indicator has blinking green comm and stead red Fault. As per manual, advice to replace the panelview.

I further check and found that fault 3A is a start up fault and related to stuck touch. Thus I think it may means the touch screen.

Notices that they were some old units of same panel view. Thus decide to dismantle and make use of the old panel view touch screen.

After the action, I managed to re use one of the unit.

With such action, a saving of RM1200 for suck repair because buying and replacing the unit will cost that much.