Strange Anealling Oven behavior

Your issues seem to be in a part other than the elements. Temp controller contacts, main power contacts, sounds like one of the phase feeds is not coming on. Time to dig deeper into the oven.

Just a guess however.

Thank you , You think maybe the latching current on the SCR's my not be enough or possibly the SCR not opening perhaps

I would suspect a bad SCR, or at least an intermittent problem. Since it works and it doesn't , just occurred has anyone bothered to document exactly when this happens? Time and date of each incident? The cause may be external to the plant, perhaps a poorly balanced circuit on the local utility grid? New construction in the area say 3 years ago?

Just guessing again, dig deeper.

Yes I believe it is alldocumented through the P sheets for each coil that goes in the ovens and also I have all 6 bases linked to a Honeywell VRX100 Data logger and digital chart recorder. Thank you

How do you measure the temp of each oven? Thermocouple or a pyrometer. Could this be an instrumentation issue?

I am using Omega Type K thermocouple with "Honeywell UDC2500 controller. I have checked the programs and the relays center and the nitrogen switches and the water seal switches and all operate as they should. It's very odd how these ovens are behaving like this and as I said before I have been told they seems to do this at least once or twice a month

The Honeywell UDC's are a very good instrument. I like them, and literally have hundreds of them. Do you have a calibration schedule in place?

Type K thermocouples need to be replaced often. I've had problems with them going out of calibration when they have been cycled over a period of time.

Presently, I'm converting everything that I can to type N, as it's much more stable. However, type S, platinum, 10% platinum rhodium, is the most stable, but very expensive.

Your UDC's can be programmed to handle all the thermocouple types. Of course, you would have to run new extension wire.

I find this a very interesting subject. Please keep us posted!

Yes I am aware of the inherent issues with the Type K thermocouples. Their range to 1400 C is great for my applications and the cost of replacment is cheaper than the S or R ( I use a select amount of R thermocouples when higher heat is needed) The problem with the Honeywell's is the factory limits for each thermocouple are set to low. The 2500 series and most all honeywell controllers only allow 1316 C for K types and the thermocouple can go to 1400C. The type R thermocouples and style of head we use in the Annealing ovens are very very expensive. Round 1800 each I think . I have been thinking about replacing all the honeywells with the Athena series C or their Platnium series which allow type K thermocouples to achive temps to around 1365 C.

1400C is way to hot for a Type K TC. Your only choice is a type S or type R. Yes, they are expensive. However, they last, and stay in calibration a very long time.

We buy the wire and fabricate them in house, (type S). Platinum wire has come way down in price.

You could look into the M-Geo sheath type:

http://www.geocorpinc.com/products/thermo-mgeo-style.htm

The platinum wire inside is of a very small diameter, so the prices are quite reasonable.

Of course, you will need new extension wire, not very expensive as it's copper compensated. Your UDC is easily programmed to handle type S or type R.

"The problem with the Honeywell's is the factory limits for each thermocouple are set to low. The 2500 series and most all honeywell controllers only allow 1316 C for K types and the thermocouple can go to 1400C."

1400C is beyond the published range of type K:

http://www.watlow.com/reference/refdata/0310.cfm

Anyway, others have given you some good places to look for problems.

Please keep us posted.

Thanks Brick Yes I stand corrected(thank you ) on the upper limits of the K TC it is actually 1250C. Nevertheless, I do have plenty of other thermocouple types and wire and heads and cermaic sheaths yadda yadda, I can fabricate most of them here( it's just dedicating the time ) easier to order you know. I do have some R type open wire which I slip into specialized dual chambered small diameter ceramic sleeves but the head of maintenance(who doesn't do electrical anymore now) still thinks he has to do everything dealing with the thermocouples. Should have that sorted out here shortly with a few diplomatic meetings with the other management ( that's the goal anyhow). I would like to switch the higher temp areas to type R/S but the ones on the oven issue at hand only need to get as high as 960C for annealing purposes. I have no control over setting up they just telll me what they want to do at what and I program things accordinglly. By the way we currently recieve our K TC's from Omegatron , I guess best deal there again I am out of that loop right now . I have heard of a Ice Bath type calibration at the old juction refcerence point but would that be at the head junction or at the end of the leads at the temp controller. Thanks again (if anyone knows how to perform the ice-bath calibration on the honeywell UDC2500 I would greatly appreciate the knowledge Thanks again

Well, the ice bath calibration will only give you your "zero", but what is most important is the "span" adjustment. Basically, your concern is calibration in the range of your process.

To do it right, you need one of these:

I like this instrument, as it has in "in, out" function. About $1300.

There are many other company's that can provide you with calibrated TC's in the temp. range that you deal with.

I know little of your process, and don't know what your tolerances are.

I have many furnaces about the size of a barn. Some, in accordance with AMS-2759D, must be surveyed, every 6 months, with 48 thermocouples. The tolerance is +-10F, as the product is aerospace forgings.

That said, I'm sorry for you that you have to deal with in-house politics. I'm the department leader, and have to deal with the knee-jerk, a-hole, with out a clue, not knowing a forging from a football, bean-counters.

They just don't understand that a failed Nadcap audit can and will shut you down.

All that said, it doesn't sound like your problem is all instrumentation. As stated by others in this thread, you have a lot of other things to check out.

Please keep us posted.

Yes, very good point North. If it was me, I'd check the calibration of everything involved.

How are you measuring the temp? What do you have for a controller? What is the primary element?

You should run some type of a survey in the furnace. Set up some test thermocouples to run with the load. Basically here, you have no idea what the actual temp is.

Your solution, the only solution, is to run a test, and find out what is really going on. Never trust a single reading from a single instrument. You need independent conformation of the process from several test setups.

1. Check the calibration of the controller.

2. Check calibration of the primary sensor.

3. Verify those readings with a test setup, using independent instrumentation.

4. Monitor and record every process variable that you can. Time, temp., current, everything.

I work with large industrial furnaces, used for the heating of, and heat treating, aerospace forgings.

We have to comply to AMS2750D, a very tight spec. The slightest and smallest thing can throw your process out of whack.

You have your homework cut out for you. Your solution is to check, and record, every process variable.

So, implement a test procedure for every run. The solution is in the details.

Have you monitored the draw on each phase.

You need to know if you have a power source prob,

a control prob, or a sensor prob.

Yes ,well given I am the only electrician for the whole 120,000 sq. foot plant I have over 50 current readings to check and log when I get in first thing in the morning. I have found through searching the file cabinets around the plant some information on the average Current draws for both types of ovens and have checked them when I can usually about once per day if I am there during the correct cycle time (timing is everything with these things)!! I feel that the most important information I can retrieve fromthe current readings would apply to the first 2 hours of cycle start to see weather the ovens are taking full draw at start up or are they cutting out at a certain point. As noted before I have already tore into these ovens and checked the resistance of the elements and both have some issuses. As far as being able to monitor the starting of the cycle with a amp meter I am trying to time it right , prob not till WED of this week, ( I will be replacing 10 elements on the newer Denton oven on Mon or Tue. I have to lean towards the power supply possibility over control, other than the known bad elements. I did however read the article on the 2750D requirments for calibration and was interesting to see that they only allow 3-4 months of use for the thermocouples. At my plant common practice is not to replace unless it's broke policy, but like I said before I am farely new here and implementing new policies is a painstakingly process.

Is there any consistency on when it is that a given oven takes longer to reach temp? I.E. base #2 for the Denton is a problem 3 runs out of five.

What about environmental concerns? Is there a gas purge into these ovens of a blanket gas? What about local barometric air pressure? What about a possible exothermic component to this issue?

I would get a trio of clamp on amp meters connected to a data logger and watch the current draw over the whole run of each oven while on each base.

I would do the same thing with respect to temperature. Get an pyrometer rigged up so it can see the heated process and connect it to a data logger as well. Then compare the indicated versus actual to see what is going on.

I'm not questioning your skills so do not think I am, but, do you really have an issue or does it only look like you do? Wonky instrumentation has often time caused a good in control process to look like it is not.

Hello North, There is no real consistency to the directed issue,it seems to come and go as it may.The older GE oven is only for Bases 1-3, and the Denton (pad elements) is for use on bases 4-6 only. The inner bell style of the two different types limits which furnace for the base. Standard strat is as follows (I don't operate them but know the process somewhat) After two 6,000 lb coils are stacked and loaded the innner bell is lowered to respective base(each base 1-6 all have their own innner bells) but share the oven. 2. The purge cycle begins before heating by means of a water seal and Nitrogen gas is pumped in to force out O2, this maintains the atmosphere to prevent the copper rod from absorbing any oxygen into the product. 3. After purge cycle is complete the ovens should start the cook cycle and depending on which cycle (i.e A-F ) determines the Cooktemp and Cook time between full temp and cool down. The rest doesn't matter cause power is cut out after certain time anyways. The matter of the rise time doesn't matter which base it is on . I have repaired and replaced every plug pin on bases 1-3 including the oven plugs themselves. I have physically checked every inch of the hard wiring from socket to controller, the controller's wiring and the contactors . I don't know what the actual barmetric pressure is or where to measure it (building or inside the oven) a pyrometer is no where on site and getting one prob not gonna happen either I have one thermocouple inside through the bottom of base th read temp inside bell, and two thermocouples on the ovens themselves (one for low and one for high, overtemp) All thermocouples SEEM to be working fine I have tested the controller AND physically can see the contactors sucked in and the output of the controller is working fine. I have heard about using a ICE bath to recalibrate the Honeywell controllers but there is not sufficent down time on the controller to be able to do this ( And I have never done that particular test before either) would like to learn it though because I have about 15 controllers through out the plant I am sure haven't been calibrated for years. There is no PM structure in place (YET) this is what I am trying to implement, also remeber most of the equipment in here is around 15-30 years old and most of them have no PM guidelines so I have to make them as I go. Also about 3 years ago the Ex-plant manager put the company almost into bankruptcy becaus eof very poor decisions and inferior machine parts replacement trying to save a buck on parts for equipment and cost us around 5 million in bad returned product that we couldn't even use for remelt and had to sell for scrap. nevertheless he is gon bout 1 1/2 years now and things are rough but getting better every week. So because of the major setback by old manager there is little capitol for parts and no capitol for any new repair equipment or test euqipment. However it is getting better like I stated earlier, so all is not lost one other item though what are you refering to by "possible exothermic component to this issue?" Thank to all for your help

A customer of ours had similar problems with stress relieving furnaces.

Eventually it was traced to burnt contacts on the contactors,which could intermittently drop one or more phases to the elements.There was no evidence of this except that the contactors had a high temperature as before failure the contacts had a relatively,but difficult to measure high resistance. In retrospect perhaps we should have measured voltage drop over the contact when on load.

We replaced one contactor to keep the plant going,and stripped and dressed or installed new contacts (moving and fixed) progressively until all contactors had been repaired.

Please let us know how you get on,and like the rest of us sparks, keep one hand in your pocket!

I dont have any experience of exothermic materials but our respected colleague refers to a furnace load that initially generates heat by chemical action after warming starts the reaction.

Three phase SCRs are phase dependent so when you change bases I would check that phase rotation was the same.

it's non-mechanical phase rotation shouldn't matter? Also I should mentionthat the GE(older oven) has two (2) 3 ph plugs and the Denton has one (1)

While it does seem funny (or not) - We do in situ PWHT of large vessel, steam generators. Part of the equipment is 3-phase SCR controls and not contractors. I had one of our technicians call me and said that there was a big difference in amp readings phase to phase on the output. It slipped my mind that the heating equipment was phase sensitive and I called another eng and he reminded me that was what happened when the phases were not correct.

It has to do with the way the three phase SCRs trigger.

Anyway check it out - don't cost much - and it can save you a lot of time.

HEy Jmart23, I was just reading your post and thanks I wasn't even thinkg of phasing because it was just elements(big toaster oven) BUT............ The GE (older oven) has two (2) three phase plegs and the Denton(newer) oven only has one. If I remember correctly I think I believe I saw a reference diagram ( hand drawn and faded ofcourse) of the phasing and wiring lay out fromthe original designs. I know I have replaced the pins on the recepticles and the wiring is as such the phases hace to go back in the same way ........But on the plugs on the other hand they can easily get out of sync with the plugs once disassembled for servicing and/or repair. So I guess at this point my next step is to verify the phasing of the recepticles and plugs are in order and to also verify that they are in compliance with the original schematics. I also plan on removing the bus bar covers (big suckers) and removing all sections of the bus and clean and polish them on a wire wheel, replacing the hardware with new bolts with lock washers this time , (I observed a few bolts that wouldn't loosen and frozen threads, so might as replace them all 20 I think) at the same time also verify that the wires from the plugs are also connected to the appropriate locations on the bus sections. And as if that wasn't a long enough day I should take time to inspect the SCR cabinet I think it is a Spang or something. Thanks again all

First see what insulation material you have. If they are refractory bricks-they use more energy, heat, time to get to temp AND to cool down when compared to a mineral wool type material. Have a look and see what you have.

I am not sure as to what type of elements you were refering to, BUT if you are using a Iron or Nickel Chrome type element in your oven and you are purging with nitrogen, I always tell the client to run the oven 3 times normally and then run it once to 3/4 temp empty as the nitrogen purge does not allow the Iron Chrome elements to oxidise, hence reducing element life span and eventual required temp. (In house tests)

Also check your temp controller and SCR's parameters, sometimes we cut one or both the temp controller and SCR's outputs back, Furnace label says "70kW 380-400V 3P" but we cut it back to say "55-60kW" due to amperage available.

Post a pic of your elements, either old, damaged or new so we can have a look see.

Yes as soon as I get permission you must understand that because of certain aspects of our work I am not at liberty to go into much detail about certain things , meaning I might not be allowed to use an outside source camera. Yet we do have a Digital camera in house and will get use of it and then download the to my email and then post, I doubt that would be too much to ask because I am trying to help resolve an issue with them. Prob take a few days to get it together though Thanks for everyone's input thus far