Vacuum System Overview to Product Handling
Chris Alto - Product Specialist
Vacuum is commonly used in the manufacturing industry. For example: holding parts in place, seal testing, picking and placing. In tandem, vacuum technology is becoming more efficient, leaving us many different options. This article will walk through the main considerations and what to look for when configuring a vacuum system.
In order to size vacuum cups, we need to know the properties of the part(s) being handled. This helps us determine the vacuum cup style, size, and material. Other elements to consider –
• Height, length, width • Weight • Is the part wet or oily? o This can cause flat cups to slide around. Cleats or “feet” help stabilize the cup position • Temperature? o Too hot and the vacuum cup can melt. Too cold and the cup will stiffen. Different materials accommodate for the right temperature.
In addition, we need to know information about your process:
• What is the available space to contact the part? If the part has gaps or holes, it’s important to grip on the solid cross-section and/or outside edges. Let’s say we are gripping a box. Are we limited to a narrow side with the potential for instability? • Is the surface sealed or porous/leaky? • Does it need to be grabbed horizontally from top/bottom, or vertically from its side? Vertical holds require more grip force due to gravity and side holding (shear force). • Gripping multiple parts at once? • Cycles per minute? • The time required from pick point to drop point?
Some products are simple to handle like boxes and sheet metal. There are many creative ways to effectively handle wrinkly bags, concave/convex shapes, and other irregular surfaces.
• How much holding force is required? • What is the vacuum cup size limitation? • How much is the End-of-Arm tool going to weigh? • Could the part peel off with fast movement?
Once cup size and orientation are determined, the pump can be sized.
Venturi style vacuum generators are operated by passing compressed air over a constricted area. This results in a decreased pressure, causing a vacuum to be pulled through the restriction and into the compressed flow path.
Venturi generators excel at frequent cycling and decentralized systems.
Electric vacuum pumps are commonly used in very high-flow applications.
In a facility that has a house vacuum system plant-wide, a localized vacuum generator is not required provided a centralized system is ok for the application.
All pumps create a vacuum; the different sizes mainly affect the flow capability. The smallest pump can create a deep vacuum on a huge vacuum cup with a tight seal but reaching the required vacuum level won’t be abrupt. An oversized pump may cause inefficiency and loss of performance. An undersized pump cannot keep up with leakage. If the part handled is porous or leaky, the pump must be sized to compensate for the air flow rate of the leak.
A centralized system has one vacuum source for multiple cups. Although fewer components, a mispicked cup will result in a leak and a large pressure drop in the system.
A decentralized system is commonly most effective with multiple cups. Each cup has its own pump so the other cups maintain their holding force in case of one cup not sealing. A properly sized decentralized system commonly accomplishes the fastest cycle rates, lowest energy consumption, and safest method of product handling.
Accessories Lastly, what accessories do you need? Vacuum sensors, blow-off for faster part release, on/off valving, tubing, and fittings are all common needs.
Avoid as many 90-degree angles as possible to avoid turbulence. Also, the fastest flow will be limited by the smallest restriction.
Aim to have your vacuum cups/seal as close to the pump as possible. This will improve response time. Also, flow restrictions and pressure drop become apparent with longer tubing.
Common Troubleshooting Q&A
My parts keep peeling off the cups. My vacuum gauge shows 24” Hg and should have 4x the needed holding force.
What is the vacuum level with no product on the cups? Let’s say you see 16” Hg, your effective holding force is 24-16 = 8” Hg (one-third of the holding force expectation). This can be caused by an oversized pump, undersized tubing (creating restriction), or both. It is important to check the vacuum level at both the pump and the cup, as there can be pressure loss through long airlines and elbows.
My vacuum system isn’t releasing the parts fast enough.
How far is the vacuum source to the vacuum seal? All the tubing volume takes time to release. The more volume, the longer it takes. One of the best solutions is to incorporate a short, pressurized blow-off to bring the vacuum lines back to atmospheric pressure.
The suction cups are wearing out too quickly.
One thing to consider is the quality of the cup material. A cheaper cup may save a few bucks, but how much is being spent on ordering, inventory, and downtime replacement? Also, be sure the cup is making clean linear contact with the product. Any sliding will wear out the rubber or potentially roll the lip.
When in doubt, call Automation, Inc. for application assistance and sizing. We have testing capabilities to identify the best solution for your vacuum handling application.