FYI. Curing different colors at the same time..

[boink]

I noticed the other day that if sometime you have a small batch of more than one color in the oven at the same time, you may want to check the temps.

I had a chrome piece and a black piece in at the same time and the temps were definately different. The chrome piece was reading around 320-340 degrees while the black was hovering over 400. Not the ideal for curing them right.

I guess it has to do with the reflectiveness of the chrome and the absorbing properties of black.

[CaptainChauncy]

Do you have any problems with the oven blowing one color powder onto a different colored part? I have always only cured one color at a time because I didnt want powder to get on other parts.

[sdold]

How are you measuring the temps?

Last summer I was solution heat-treating some 2124 aluminum, and I needed to get the temps as accurate as possible. I experimented with an infrared thermometer, the kind with the LED that you aim at the part. I found that it had fairly accurate readings on dark objects, but on bare aluminum it read about 30% low. I measured the actual temps of the parts using special paints that melt at certain temps, and the areas measured were shielded from the heating elements, so I trust the paint, and don't really trust the infrared thing that much anymore.

[boink]

I was curing some small parts for use in the garage.. not customer's parts.

I used the laser thermometer which seems to be pretty accurate, but I suppose the reflectiveness may have a little to do with it...

As far as parts getting contaminated, I haven't seen it...BUT these were small parts and I might have just gotten lucky and no free floating particles were floating around.

[HobbyTalk]

Different objects have differnet emissivity levels. Your IR gun should have given you instructions on that. Below are part of the instructions on the gun that I have.

MEASURING TIPS: For the most accurate measurements, follow these tips when using the FlashPoint temperature gauge:
Always point the sensor directly at the object being measured at a 90 degree angle. Try not to have the gauge tilted at a different angle in relation to the object being measured.

It may be a good idea to re-measure the temperature of an object at a slightly different location on the object, to reconfirm the accuracy of the reading.

Try to avoid allowing sunlight or other artificial light from beaming in-between the gauge and object being measured, as heat from such light could skew actual readings. For the same reason, also try to prevent wind from blowing in-between the gauge and object being measured.

Generally, higher air or ambient temperatures lend to more accurate readings. Cold ambient temperatures can result in inaccurate readings. Ambient or air temperature refers to the area around the infrared temperature gauge, the higher the temperature the more accurate the reading, the lower the temperature the less accurate the readings.

Many external forces can cause errors in how temperatures are measured by infrared temperature gauges such as FlashPoint. This is because infrared temperature gauges do not make physical contact with the heated object. In fact, it is not unusual for the temperature measurement of an infrared temperature gauge to be different than that of a thermometer which makes physical contact with the heated object - even when they are measuring the exact same point! There is a way to adjust how infrared temperature gauges read temperatures that can make up for these unwanted external forces, and make temperature readings more accurate.

Emissivity is the way that any object emits heat energy into the air. Emissivity is always rated by a numerical value. Different types of materials have different emissivity values. An object’s emissivity is dependent on its surface condition, material type, temperature and wavelength of temperature measurement. Adjusting the infrared temperature gauge to compensate for the emissivity values of different objects is the key in getting the most accurate temperature readings.

In general, an object having perfect heat dissipation characteristics has an emissivity value of 1.00 (think of this like saying 100%) this is the absolute maximum possible emissivity value. Thus, the higher an objects’ emissivity rating the better FlashPoint will be able to make an accurate reading without any adjustments. The lower an objects emissivity rating, the more inaccurate FlashPoint will be and adjustment of FlashPoint's emissivity setting might be needed. The absolute lowest possible emissivity rating is 0.01.

FlashPoint's factory default emissivity value is 0.95, displayed as 95E which will provide accurate temperature measurements for most materials. Many metals, especially those having very shiny or clean surfaces have emissivity values that vary in value. For example, the emissivity rating of shiny metals such as copper can be extremely low. If you measured the temperature of copper using an infrared temperature gauge the reading could be MUCH lower than the temperature measured using a thermometer which makes physical contact with the copper. This is because the emissivity value of copper is extremely low at 0.05. Adjusting FlashPoint’s emissivity value for materials having very low emissivity values might be desirable to get the most accurate temperature measurements.

Note: Non-contact infrared temperature gauges are not recommended for use in measuring the temperature of shiny or polished metals.

Some common emissivity settings:
1) Aluminum: Sandblasted set the emissivity at 21E.
2) Aluminum: Anodized set the emissivity at 77E.

[sdold]

Thanks for posting that, I never had the instructions for the IR thermometer I was using and didn't know they had a correction for emissivity. That makes perfect sense.

Thinking more about this, it doesn't sound good to have the oven heating element exposed to the parts, since the direct IR from the element would heat up dark parts much faster (and hotter) than light parts. Things absorb heat at the same rate that they emit it (Kirchoff?). I guess this is reason for convection ovens.