Fishscaling of porcelain/vitreous enamel coatings

Fishscaling

Fishscaling is an enameling defect, which is characterized by small enamel particles chipping off.

Chipping off may happen directly after firing when cooling down or sometimes even days later.

example of enamel defect called fishscaling

Effected products may usually not be repaired. Due to this reason, this defect is still one of the most described topics within the international enameling industry.
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Thermal imaging of enameling furnaces

The performance of industrial enameling furnaces may gradually decline over time.

This may result in higher energy consumption (read increased enameling cost) and reduced quality of the coated surface.

In extreme cases the enameling furnace may even unexpectedly break down, because insulation has been damaged and/or worn out.

Therefore we suggest regular inspections & thermal imaging to identify major heat bridges and other spots with possible insulation issues.

Thermal imaging of industrial enameling furnace roof at hotzone near 180 degree turn
Thermal imaging of industrial enameling furnace roof
Thermograph inspection of enameling furnace door
Heat bridges at clean out door

Ultrasonic thickness measurement

With ultrasonic thickness measurement, you may detect the thickness of individual layers within a multi layer coating.

This may be of great help, when troubleshooting e.g. a two coats / one fire vitreous enameling process.

See our webshop for more details about this and other film thickness gauges.

ultrasonic thickness gauge
ultrasonic thickness gauge

 

Temperature profiling and analyzing at industrial enameling furnaces

Introduction

Firing is a critical process step at every enameling shop, because it determines the esthetical and functional properties of the fused enamel coating.

In order to continuously achieve good enameling results, it is important to maintain the actual firing conditions at the enameling furnace within strict tolerances.

Regular verification of the actual temperature profile measured on the enamelled object is therefore a common procedure at industrial enameling plants with ISO 9000 quality assurance systems.

Companies with only one enameling furnace and a verification frequency of once per year, will typically outsource these temperature surveys to a specialized company.

Ditmer Trading & Consulting BV has the necessary equipment to measure temperature profile(s) at your enameling plant.

Companies with multiple furnaces and/or a high verification frequency, may consider to perform this test inhouse and purchase a state-of-the-art furnace tracker via our webshop.

Firing curve / temperature profile

Beneath a typical example of a temperature profile at a double hooked U-type continuous enameling furnace for cooker components.

temperature profile of continuous enameling furnace

Important aspects of firing curves are :

  • Top temperature
  • Time at top temperature
  • Time above soaking temperature
  • Temperature differences between top & bottom
  • Temperature increase/decline at preheating & cooling zone

Equipment for measuring actual firing temperature

Traditionally temperature measurement within continuous enameling furnaces was done with a so-called Bozsin box.


These large & heavy insulated boxes contained a full-size working temperature recorder with paper printer, which was connected via one or multiple thermocouples to an object while both being suspended at the furnace conveyor and passing thru the enameling furnace.

Thermal barrier for temperature profiling of industrial enameling furnaces

Over time electronics became smaller & smarter and nowadays furnace temperatures profiles are recorded by means of a data logger which is placed in a much smaller thermal barrier. (see picture above)

Upon completion of the test run this data logger is connected with a laptop or PC and the collected data may be processed & analyzed with advanced software. See our webshop for more details.

Optionally it is even possible to have real time data transmitted from the furnace tracker.

Furnace surveys

As mentioned previously, DTC may perform furnace surveys and measure temperature profiles at your facilities.

Contact us for a cost estimation

Troubleshooting enameling defects

Resolving enamel defects during an industrial manufacturing process requires a structured three steps approach.

Step I Identify the right defect.
This may sound silly, but it is sometimes not easy to determine what is the exact defect. Incorrect identification will lead to the wrong causes & remedies.
Step II Evaluate possible causes.
Focus your attention on the most logical ones first.
Step III Implement appropriate remedies.

 

Due to the relative complex nature of enameling processes, it might not be easy to resolve an enamel defect.

Please feel free to contact us, if you require any further information and/or hands-on assistance.