Thermo Control for Polytetraflon® Bath Heaters
PTFE or PFA coated tubular heaters, fluoroplastic coated heaters and PFA or FEP coated heater cables have been in the market for years. The units all bear extremely similar names and all claim to meet high safety standards. However, reality in the field of coated tubular heaters often looks alarmingly different when it comes to safety.
It is hard for the user to differentiatethe technical details and often an ‘attractive’ priceor a high heating performance leads to a hasty purchasing decision. The purchaser may not be involved in the process and will thus hardly be in a position to identify serious safety deficiencies and considerable differences in lifetime.
The Polytetraflon® series PH 1 – PH 2 – aswell as PH 9 heaters already developed and patented by us in 1991 are now also available with an optional thermo control unit. A thermo element (FeCuNi type „J“) can be fitted on one side, just below the welding spot on the PTFE head, to measure the inner temperature of the heater.
Purchasing and installing an according temperature control provides the possibility to set a temperature limit and thus shut down the heater before it overheats, e.g., due to running dry.
In case that the temperature within the heater rises to thislimit, the heater is shut down by the control unit. The defaultcan be solved and in most cases the heater can be used againthereafter. However, in any case the system must be checkedfor possible damage.
Several heaters may also be controlled via plc by fitting according analysis units. According to the bath operating temperature, the density and the specific heat capaciy of the medium the control should be set approx. 30 °C higher than the desired bath temperature. The control’s function is not tocontrol the bath temperature. This must be done by meansof a further separate control.
In Europe fires initiated by electric bath heatings cause damages amounting to several millions every year. An uncontrolled faulty heater can reach temperatures between 700 °C and800 °C.
Typical reasons for defaults are:
- Installation of too high heating performances intoo little space
- Application of heaters with too highspecific surface load capacities in media with specific heat capacities other than that of water or with very high densityor media tending to form incrustations or deposits.
- Lowering the bath level at continued heating resp. simultaneous lowering of the level when shutting down the heater
- Non-application of bath temperature control and/or level monitor
- Incrustations of the level monitor
- Non-application of earth-leakage circuitbreakers
- Clogging up by sludge on the floor
- Contact to otheritems in the bath caused by heavy turbulences
- Running dry
Andthere are many other possible causes for defaults that mayoccur and that nobody may have thought of so far such as,e.g., human failure. PH type Polytetraflon® heaters arethe non plus ultra in respect to quality, longliveity andsafety. They very well bear comparison with any competitive heatersworldwide. Only the best materials from renowned manufacturers are applied.
The heater coating is made exclusively from a special PFA type. The material may be 3 times as expensive as PTFE, butit provides considerably superior characteristics. PFA hasa much higher alternating bending resistance than PTFE anddoes not show „white breaking“ like the sintermaterial PTFE. In addition, PFA’s water steam permeabiltyrate is lower.
The connection cables consist of fully PFA coated and PTFE insulated individual strands, thus limiting air inclusionsin the cable to a minimum. The area above the bath level is especially critical because of the high humidity here and the possibility of condensate formation caused by a vacuum effect. The expensively manufactured PFA cable provides the necessary safety. The formation of condensate from water can be reduced to a minimum. Also air inclusions between the tubular heater body and the PFA coating are reduced to a minimum. This is achievedby a specially developed, expensive manufacturing process.
The included air expands when heating up and thus produces over pressure in the heater. As long as the heaters are continuously operated, there will not be serious problems, but when the baths cool down resp. when the heaters are switched on or shutdown by the bath temperature control the overpressure decreases, thus producing a vacuum. The vacuum again attracts humidty. This problem is almost excluded by the application of the saidmaterials and processes.
Polytetraflon® heaters are much lesssensitive to cold/hot changes than other heaters of comparable design.
The head of all our PH series heaters is made of massive PTFE without any mechanical connections. Connecting cables – heatercoating and head are welded together water tight and can be immersed completely.
In addition, the geometry of the head is designed in such a way as to enable firm and stable installation of the heaters in the baths, a considerable step towards safety.Furthermore, a heater type may be used for any level, because the so-called ‚cold ends’ are practically notrequired. The only important point is that the head mustbe fully immersed. Holders are available at competitive pricesor may even be manufactured by the operator himself. Allthis eliminates the requirement to keep different heater types on stock.
Tests in chromic acid and copper baths havebeen running over several years and have proven the troublefree function over many thousands of operating hours.
Since 1991 thousands of Polytetraflon® heatershave been put into operation and are running worldwide, especially where critical media are used.
Another novelty, which a.o. we applied for patent also in the USA, is a Coex® PFA heater coating.
This is a coextrudedPFA tube, which is fitted with PFA/carbongraphite on the inside towards the heater. The outer layertowards the medium consists of PFA natural, so that the heattransfer from the inside is approx. 30 % times better than it is the case with standard PFA or PTFE while keeping the universal chemical resistance on the outside, which would not be the case if it was fully carbon or graphite filledPFA or PTFE.
The Coex® type also has a considerablylower permeability than common virgin types.
Polytetraflon® PH 1 - PH 2 – PH 9 types with PFA natural or PFA Coex® can be produced with different specific surface load capacities at identical designs:
2.5 W/cm² only in Coex® - 2.2 W/cm² - 1.5 W/cm² -1.0 W/cm² for PFA natural.