Hello again all!

[wade88]

Hello again ladies and gentleman,

To those who vaguely remember who I am from my last posts maybe 24 months or so ago and those who of course don't (98%) - HI!

Hope you're well and its really nice to see the forum still going strong, servicing the needs of the incapable, wising up the DIY'ers to the hazards of using 1.5mm flex for shower circuits and generally arguing among yourselves for sport. Top stuff.

Since my last post (which I haven't actually bothered to go back and see what was) i have long since given up the electrical game per-se, and have been working as an Operations and Health and safety manager for a large manufacturing firm based in Hampshire. I am still very actively involved in the plant machinery side of this business and am the on site maintenance tech for any breakdowns but in regards to electrical installs etc I'm leaving that behind - for now.

However - what brings me back to the forum i hear you ask, other than to bore you with the summary history of my employment status...

I am the head liaison for any engineering projects that are taken on here (bespoke machine builds, structural, machine fabrication etc) and we are currently mid way through a new build of a line that we will bringing in to commission end of June, but we have hit a small hiccup on the way.

The engineer currently building the line is not electrical bias and is currently trying to figure out how to put together an infra-red heating section (polycarbonate moulds to be pre-heated before filling) that consists of:

24 x 0.5kw infra-red cassettes.

He was asking me my opinion on the best way to do this and at this stage (being well aware of the thought pattern of most of the elders on this forum) NO I AM NOT BUILDING THIS LINE far from it. We are paying for this build to be out sourced and built in Glasgow I am merely a guide to the engineers as to our requirements and some design aspects, i find myself on the forum today looking to better my own knowledge and understand HVAC and process heating control a little better.

My initial thought would have been to separate the 24 IR cards into 3 groups of 8. Break down a 3/phase supply and utilise a phase per group to keep a common source of singular isolation and lower the current demand and connect each group to a dedicated channel of a 3 channel PID temp controller with integrated SSR, Looking to run at around 90-100 degrees C so a type J thermocouple will suffice nicely, although i am unsure of whether the same and singular thermocouple will service all 3 channels individually? Would independent means of temperature measurement be needed for each channel? I dont really want control of each group independently, just a common means of temp control for all 24.

Sorry for the mammoth post, would really appreciate the feedback as always guys - i hope you're well and still fighting the good fight.

Kind regards,

Ben

 

[Darkwood]

Hello again and yes I remember that ugly mug ...

Its easy to design a heating bank with PID control but the job it does can be effected by many factors, the tolerances you have with temp variation, the effects of ambient cooling, the effects of IR card failure etc ...also the positioning of thermocouples or other forms of temp' measurement can also effect design... without knowing the details of the production process, the proposed design of the line and the material/product tolerances, it is very hard to give any real constructive advice and only really can give blanket basic control advice.

Im coincidently building a few Temp' PID control kits to update a couple of heat presses but I have a wide playing field as product has a wide tolerance band and thermocouple positions and heating elements are already existing.

 

[Richard Burns]

Welcome back.
I was thinking you would need more back up for the system, and was wondering on physical size, but Darkwood has put it a lot better.

 

[wade88]

Hi Again Gents,

Thanks for the swift replies.

So the machine in summary is as follows. If you imagine a chocolate molding line - A number (114 in this case) of polycarbonate molds travelling around a track way being subjected to different process at different points in time. Typically, most basic lines will index via a quantity of servo drives controlled by a PLC program designed around the operation blah blah.

Our line is no different although the line movement is generated pneumatically with 8 concentrically actuating pistons of different bores and stroke lengths depending on the direction of travel. At certain points different processes will take place to:

a) fill the moulds
b) vibrate the moulds to settle the product
c) clean the mould tops of excess product
d) Chill the moulds ready for de-cast
e) turn the moulds over so they face upside down and attempt via some pneumatic force, to empty the moulds of their contents

We as a company are the largest manufacturer in the UK of rodenticide products and this machine max wax block bait. Some of you may be familiar with this if you have ever had domestic rat problems.

So the material in its molten form is quite viscous, runny flapjack for example.

Before the moulds enter the floodfill, they need to be pre-heated to allow the paraffin wax content of the slurry to adhere to the mould edges which in turn will produce this high gloss finish, similar to what is seen with chocolate bars of some variety. The chocolate moulding industry plant is almost identical to what we have.

So the IR cassette bank is the tray pre-heat process of the operation. The indexing time of the line will be 5 seconds, and the pre-heat section is circa 800mm long (moulds are 400mm long) so each tray will spend a total of 10 seconds under it being warmed before entering the flood fill - we need the trays to bhit about 90-100 degrees surface temeprature in that 10 second period. The polycarbonate melting point is 146 degrees C so we have plenty of tolerance on that side.

I basically want the engineers building the line to incorporate some digital temperature control into the system to prevent the operators from free heating the IR bank and subsequently burning our moulds which are not only expensive, but have a huge lead time.

But with my limited knowledge of such control systems, my first post was the best I could come up with on the fly to provide a basic level of control.

Cheers

 

[Richard Burns]

Generally I am not a good person to be responding here Darkwood will do it much better.

However you only need to specify to the constructors the functionality that you need, it is then up to them to design a compliant system.
I would expect on that basis that you would need to know that the temperature was not exceeding say 140°C during the heating section to protect the moulds and so have a cut off for this purpose.
Depending on how the moulds move from heating to fill the best place to measure the mould surface temperature would be just prior to the fill as they may have cooled down after leaving the heaters, here you would need to ensure above 90°C.
Depending on your method of controlling the temperature (presumably there is no option to delay the line speed) as it heats you would need temperature measurement and control during heating.
If you have 24 cassettes and two cassettes per mould presumably you have a parallel 12 moulds on the line, each of the 12 moulds may need monitoring dependent on the process variability across the line.

If you specify this sort of control and require it to be complaint with British standards then the constructors can implement the required safety and back up protocols required to ensure it is fail safe.

It maybe passing the buck, but it passes to a competent group, and it prevents you specifying something non complaint and having to bear the blame!

 

[Darkwood]

As infra-red is an harder concept to measure heat wise as it does not heat the ambient air but the product itself and the product will convect heat to raise ambient air temp, also you cannot simply fit a thermocouple to it as absorbtion rates of fixed equipment subject to the IR may vary and build up to give a non reflective value of what the actual product is doing. Their may be an option to laser temp' measure that will look directly at the product or mold or look at both with independent lasers - although I pesonally haven't been involved with IR set-ups it would be my first line of enquiry.

A laser on the product to get accurate temp readout and one on the mold as a redundancy measure if the first one fails and the moulds get too hot.

Voltage regulated supplys to the IR cards could increase and decrease the intensity of IR to control the temp' but this may be already in the design concept.

 

[gnuuser]

As infra-red is an harder concept to measure heat wise as it does not heat the ambient air but the product itself and the product will convect heat to raise ambient air temp, also you cannot simply fit a thermocouple to it as absorbtion rates of fixed equipment subject to the IR may vary and build up to give a non reflective value of what the actual product is doing. Their may be an option to laser temp' measure that will look directly at the product or mold or look at both with independent lasers - although I pesonally haven't been involved with IR set-ups it would be my first line of enquiry.

A laser on the product to get accurate temp readout and one on the mold as a redundancy measure if the first one fails and the moulds get too hot.

Voltage regulated supplys to the IR cards could increase and decrease the intensity of IR to control the temp' but this may be already in the design concept.

i agree with darkwood
controlling the temp would require having a good backup control and monitoring system and you may also consider ambient temp control as well.
surface temp can differ if the ambient temperature is much colder than the product and could have an undesirable affect.
submersible thermocouple can give you the temp of the product but should not be relied upon alone
having a laser as well will give you a better monitoring
as the differences can be taken into account for designing purposes

 

[Darkwood]

I would also be looking up Pyrometers ... there are various ones out there even IR ones which are pretty accurate. Another thought is the absorbtion or reflective traits of the wax you wish to melt... has anyone actually confirmed its an effective method to heat the wax up?

 

[wade88]

Guys,

Thanks for all your replies.

The sole purpose of this IR heat set up is to simply "Pre-heat" the polycarbonate tray BEFORE it is filled with the wax slurry (this process has already been taken care of - we have a working line in house that has been commissioned for the last 3 years, this new engineer is building a new line based on existing "known to work" principles).

The idea behind IR was its immediate heat up and cool down capability - the problem currently is the engineer commissioned to undertake this new build is not in any way familiar with the electrical requirements be it design or install. So having a reasonable but FAR from crystal knowledge, i said i would look into it for him to set him on the right path before he forks out at great expense for a professional..... don't shoot the messenger lads, i know exactly what i would prefer being the client here. I would sooner see someone come in and build a temperature control panel for me from the ground up but money being tight and the situation as it is, i thought i would explore this avenue first as i remembered what an outstanding group of intellectuals and Samaritans you all are and have helped me immensely in the past

I trust you all had good weekends, back to the grind on another glorious Monday!

Cheers, Ben