Coming In From The Cold
Here in North Carolina, the winter has been exactly as the National Weather Service predicted: warm and dry, a typical result of the La Nina weather pattern in the Pacific. This morning we awoke to birds singing, announcing that spring nesting season is coming soon.
But that’s not the case everywhere, and many of our customers along the Great Lakes and in the Northeast have to deal with the effects of severe cold weather on plants and equipment. Flame hardening systems are not immune to these effects, so I thought our February blog was a good time to highlight some issues to be aware of as we enter the dead of winter.
We see temperature-related problems in three areas of flame hardening:
- Cold quenches causing cracks, particularly in the surface of parts
- Cold fuel gas delivery systems losing pressure, reducing the temperature of the flame and failing to achieve the necessary hardness level
- Cold parts left in unheated shop areas being exposed too suddenly to high temperatures, resulting in uneven depths
I’ll address each of these with some tips on how you can minimize the issue.
Probably the most significant of these issues is the quench temperature. Quench that is too cold for the heating process causes cracks and failures. Especially in the dead of winter, you need to monitor your quench temperature!
We had one customer with a plant on Lake Michigan. They could draw lake water directly into the plant. That’s a great, cost effective way to run water through your production lines, but when the customer started experiencing cracks in their rope drums in the wintertime, we quickly traced the root of their problem to their water source: 60 degree lake water that wasn’t being heated before coming into contact with the drums.
Depending on your flame hardening setup, this problem can be solved fairly easily:
- If you’re using a closed system put a heater in the quench tank.
- If you’re taking water from the city or directly from a body of water outside (lake or a pond), build your own tank inside your facility with a pump. That way the holding tank allows the water to warm up close to the air temperature inside the building. Alternatively, install a hot water heater on the line coming in from the outside and raise the temperature of incoming water accordingly.
In cases of customers using propane gas to fuel their flame hardening systems, we find that winter temperatures cause challenges because of the pressure drop that can occur with outside propane gas delivery systems. The vaporization rate, based on a number of factors including air temperature, tank temperature and humidity, all play a part in the equation that determines your rate of vaporization, and how that effects the level of pressure at the torch. Geek out on that process with this educational paper by Emerson Process Management.
For the rest of us, here’s the bottom line: cold fuel gas delivery systems reduce the quantity of gas you’re pulling through the line. If it’s reduced enough, the flame coming out at the torch will not be as hot – so the quality of the hardness depth and pattern can be negatively affected.
Again, this problem can be addressed fairly easily:
- If you have propane tanks on the outside of your facility, realize that delivery is going to be lower in cold weather. If the tanks are small enough to be moved, you could bring them into a controlled temperature environment to keep them above freezing.
- If that’s not possible due to tank size or regulatory compliance for your facility, you could increase the gas pressure on the regulator to allow more flow to compensate for the change in temperature.
- And always, in winter, make sure the tank is as full as possible.
The third way winter temperatures can interfere with quality flame hardening is when parts don’t get stored in climate controlled facilities. Yes, the starting temperature of steel matters when it comes to heat treating, especially a localized, high heat process like the kind of surface hardening you get with flame hardening. If heat is turned off over a weekend and parts drop to 50 degrees, it makes a difference – especially if it’s a big part like a 10 or 12 inch crane wheel that absorbs a lot of heat fast as you heat it up.
Before you do any localized hardening on parts below 60 degrees:
- If you have some sort of tempering or batch oven, put the parts in a warm oven before flame hardening them. It doesn’t have to be high – 400 degrees for an hour should suffice.
- If you don’t have an oven, use a blast torch (carefully) to warm up the parts before localized hardening with flame or induction.
I hope the rest of your winter keeps the cold where it should be and the warmth where it needs to be. If you find any of these temperature problems are giving you headaches, don’t hesitate to email me at firstname.lastname@example.org. Or call me at 919-956-5208. It might take me some time but I will get back to you! Thanks for visiting our website.