Standard sensors and equipment won’t survive for very long in automated welding environments where high temperatures, flying sparks and weld spatter can quickly damage them. Here are some questions to consider when choosing the sensors that best fit such harsh conditions:
- How close do you need to be to the part?
- Can you use a photoelectric sensor from a distance?
- What kind of heat are the sensors going to see?
- Will the sensors be subject to weld large weld fields?
- Will the sensors be subject to weld spatter?
- Will the sensor interfere with the welding process?
Some solutions include using:
- A PTFE weld spatter resistant and weld field immune sensor
- A high-temperature sensor
- A photoelectric diffuse sensor with a glass face for better resistance to weld spatter, while staying as far away as possible from the MIG welding application
A recent customer was going through two sensors out of four every six hours. These sensors were subject to a lot of heat as they were part of the tooling that was holding the part being welded. So basically, it became a heat sink.
The best solution to this was to add water jackets to the tooling to help cool the area that was being welded. This is typically done in high-temperature welding applications or short cycle times that generate a lot of heat.
- Solution 1 was to use a 160 Deg C temp sensor to see if the life span would last much longer.
- Solution 2 was to use a plunger prob mount to get more distance from the weld area.
Using both solutions was the best solution. This increased the life to one week of running before it was necessary to replace the sensor. Still better than two every 6 hours.
Taking the above factors into consideration can make for a happy weld cell if time and care are put into the design of the system. It’s not always easy to get the right solution as some parts are so small or must be placed in tight areas. That’s why there are so many choices.
Following these guidelines will help significantly.
When installing sensors into a harsh environment, for example a weld cell application, protecting the sensor is a crucial step in the installation process. These sensors are exposed to extreme heat, weld slag and sometimes impact. In order to reduce sensor usage, the sensor needs to be protected from the harsh area of exposure. This can be achieved by using a complete sensor protection method that includes proper sensor selection such as sensors that have a weld slag resistant coating, proper mounting and cable protection. If you follow these steps the end result will be longer sensor life.
- Step 1
- Identify form factor (size of sensor)
- Output polarity (DC 3wire PNP, NPN etc.)
- Identify special sensor characteristics (Slag resistant coating, SteelFace, F1 etc.)
- Step 2
- Select your mechanical protection system (ProxMount etc.)
- Step 3
- TPE cable
- WeldRepel tubing and wrap
So, by simply implementing the three step total solution into your harsh or extreme application you can protect and lengthen the life of the sensors and cables providing less downtime. For more information on the total solution, check out this whitepaper on Increasing Sensor Life and Production Productivity.
Let’s start with a question: Could a pair of slip-joint pliers be used to drive a nail into a 2 x 4? Sure it could. It requires persistence, and there’s often a great deal of profanity involved, but it can be done. Don’t ask me how I know this. The pliers get the job done, but quite obviously, they’re not the right tool for the job.
But this isn’t a DIY carpentry blog, it’s a blog about industrial sensors. So what does any of this have to do with industrial sensors? Just as it’s important to select the right tool to pound a nail into a piece of wood, it’s also important to choose the right sensor when faced with a sensing task.
For example, let’s say you have an application that requires a position sensor that is going to be subjected to regular, high-pressure wash down. Could you use a standard, IP67-rated sensor? Sure you could, it would work just fine…For a while. And then the profanity would begin again. Fortunately, there are purpose-built sensors designed for just such applications. Or, let’s say you use sensors as part of a welding process, and the weld slag build-up is murdering your sensors. Rather than trying to drive nails with pliers, why not select a hammer right from the start? The right tool for the job.
Continue reading “If I had a Hammer…”
It’s another day at the plant, and the “Underside Clamp Retracted” sensor on Station 29, Op 30 is acting up again. Seems to be intermittently functioning…the operator says that the line is stopping due to “Error: Underside Clamp Not Retracted”.
You think to yourself, “Didn’t we just replace that prox last week?” A quick check of the maintenance log confirms it: that prox was indeed replaced last week. In fact, that particular prox has been replaced seven times in the last six months. Hmm….the frequency of replacement looks like it’s going up…four of the seven replacements were performed in the last two months.
What’s going on here? Is it really possible that seven defective proxes just all happened to end up at Station 29, Op 30, Underside Clamp Retract? Not likely!
Continue reading “Broken sensors that won’t stay fixed!”
Inductive proximity sensors in a welding environment face a variety of hazards. Hot metal particles – called weld spatter – are ejected from the welding process and can melt or burn their way through unprotected plastic sensor faces. Built-up weld spatter (often called weld slag) can eventually cause a sensor to trigger on falsely. If the slag can’t be removed, the sensor has to be replaced.
One solution to these issues is sensors made with tough ceramic faces. The ceramic face stands up to the hot weld spatter without melting, and doesn’t provide a good surface for slag adhesion. Even if slag does build up on a ceramic face, it can typically be removed during maintenance without the need for sensor replacement.
Continue reading “Ceramic-faced Sensors Stand up to Welding Processes”