How small changes eliminate conveyor jams
It’s all in the details
Conveyor jams insights
- Conveyor jams can cause safety, quality, customer service risk and can be quite expensive for manufacturers.
- These challenges can be alleviated if companies put them in the proper location, know how to level them and have a good understanding of physics.
I’m an industrial engineer by education and continuous improvement consultant by trade. Over the years, I have had the opportunity to visit hundreds of factories. In many of those that used conveyers, hourly operators were fighting the same problem – downtime caused by conveyer jams. These jams caused safety, quality, customer service risk and cost quite a bit of money.
For many years of my career, I worked with a product that acted as if it was two-dimensional: ceiling tile. I could watch the square and rectangular tiles travel along conveyers and turn and skew at transitions. The skewed tiles would then jam in places that weren’t designed to pass tiles through unless they came in squarely and properly located.
I spent a lot of time helping teams identify and eliminate the root cause of the skewing. There are three key factors:
- Proper location of the tiles with respect to the process they were designed to enter
- Levelness and squareness of the conveyers with respect to each other and the process
- Understanding and applying basic physics principles.
Once I was able to improve product flow and reduce jams in two dimensions, I wanted to show it could be done with “three dimensional” products. As fate would have it, I had that opportunity once I started my consulting business. Some of my clients were experiencing similar flow and jam issues with products in bottles, boxes, and other product configurations. I have applied these same principles to three-dimensional products with similar results. Let’s explore the three key factors to reduce jams in more detail:
1. Proper location of the product with respect to the process
Many processes are designed to be balanced with respect to the product being produced. Examples include: punch presses, packaging, bagging, painting, welding and others. When conveying a product through a process, it’s best to bring the center of the product through the center of the process. I have seen those very products conveyed up to an inch off-center. It can be devastating to the flow. Therefore, we need to have a way to assure products are properly centered.
One way to do this is through conveyer guiding. My preference is to position a conveyer guide parallel to the direction of flow. The edge of the guide should be located using the center of the process, plus the width of the product and an additional 1/16”. This allows for product size variation. The conveyer rollers or belts should pull the product over to the guide and let it settle into place in a straight line, well before it enters the process:
I believe that it’s best to bring the product over to the “operator” side, so s/he can easily see what’s happening. Also, if we must adjust the guide location for different product sizes, it can be done from where the operator is naturally working, reducing effort and downtime. Once we establish ideal location(s) for the various product sizes, they should be made as error-proof as possible, using pins, marking, or other means for repeatability.
Finding the center of the process can be done with string or laser and two people. The human eye can see differences of <=1/8” over a 50-foot span, when focused and properly trained. Don’t forget to shut down and lock out the line when doing this work, which can take as much as one hour.
Many factories don’t use parallel guides and choose to use “funnel” guides that look as shown in figure 1.
The problem with this approach is the product can easily turn and doesn’t flow under control when it enters the process. Another problem is the end points of the funnel may create a pinch point, especially if the product has turned coming through the funnel. This can increase jams and downtime. Guides tend to wear down faster in this configuration and decrease the chance for the product to be properly positioned as it enters the process. You wouldn’t believe how many other engineers have challenged me on the removal of funnels. I guess being an industrial engineer didn’t give me the credibility I thought I deserved with my mechanical engineering friends. The results did, however. (See figure 2)
Once process center and conveyer guides have been established, it’s time to move on to leveling and squaring.
2. Levelness and squareness of conveyers with respect to each other and the process
When a new line is installed in a factory or equipment is replaced, there is a certain amount of leveling that occurs. Most engineers and contractors I have worked with believe everything is level when things are within ½ inch of each other. Unfortunately, this is not good enough. With just a little more tweaking we could prevent jams from occurring in the first place. When a product makes a transition from one conveyer to another with a height difference of ½ inch, the leading-edge acts like a ski used by a downhill racer. It wants to turn as it hits the transition. This situation worsens if there is a speed differential between conveyers. Most problematic is if there is side to side variation in the conveyers. The more the product turns, the more likely it will jam.
As before, start with the process that the product is designed to enter. Identify the pass line. This is the vertical location of the base of the product as it travels through the process. Ideally, all conveyers should be leveled to the pass line.
Make sure that the process is level side to side and then throughout the process that will be acting on the product. This isn’t always possible, as elevation changes might be required throughout the process. But, make sure critical areas are level front to back and side to side. Once the process levelness has been established, level the entry and exit conveyers to the process. Bring all conveyer transitions to 1/16” or less with respect to each other. If an elevation change is required between conveyers, make the prior conveyer higher than the next conveyer, to minimize corner or edge damage of the product (See figure 3).
Use a torpedo level to check conveyer transitions and measure the differential by placing shims underneath the level. It’s quick and as accurate as you need it to be. When you achieve levelness with a shim that’s .015” or less, you have a low jam potential process. Figure 4 illustrates the difference between using a torpedo and standard level and the critical placement for measurements:
Most teams of two persons can level a section of conveyer in 5 – 10 minutes. This work must be done safely, with the line properly locked out. If you have 10 conveyer sections, plan being down for two hours or so. Good planning and communication will minimize the impact of this downtime.
3. Understanding and applying basic laws of physics
I told you earlier that I was an industrial engineer. Therefore, physics isn’t a strong part of my background. Luckily, some laws of physics are simple enough to apply and can’t really be argued, no matter who’s the smartest person in the room. That’s why they’re called laws, after all!
Gravity wins. What this means to me is that processes should be designed to work with gravity and not fight against it. Moving things to a lower position, rather than a higher position takes less energy. It’s easier to drop something, rather than lift it. Stacking things downward. Using the stored energy in a process to convey things from point A to point B. All I know is that sometimes it appears that we have designed our conveying systems to fight gravity. Given a choice, I let gravity assist the flow of materials around a production line.
An object in motion will stay in the direction of its motion unless a force acts on it. If I want something to travel in a straight line, I should avoid putting anything in contact with it. When I bring things to a guide, I try to manage the flow so that the product settles to the guide in a straight line, while the guide is positioned in parallel to the direction of the flow. If the product is coming out of a curve, I it to fully clear the curve before it flows to the guide, or else I’ll be dealing with many forces that are fighting each other and may turn the product in an undesirable way.
For every action, there is an equal and opposite reaction. Avoid banging product against walls or guides, if possible. If the product isn’t perfectly flat, there’s no guarantee it will transfer at the expected angle. You may also damage the edges or corners of the product or its packaging. Options to avoid direct contact include conveyer timing, curves, and jumps. Design the line to minimize direct contact and transfers of energy between the system and the product.
To summarize, jams and downtime can be significantly reduced in a process if you pay strict attention to detail and utilize simple techniques to properly locate products, convey them in a level manner and apply simple laws of physics. Size or speed or shape of the product doesn’t matter. What matters is your resolve to do the right thing for your people and reduce the risk of jams.
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