Feedability issues can cause you to spend time, money, and countless resources to alleviate the problem. The best way to prevent these issues is to be proactive in the early stages of design. Addressing any potential problems before they happen is the best way to ensure a smooth production run.
Below are some things to contemplate regarding assembly and automated feeding.
Considering Materials
The material type used in the automated feedability process is paramount. For example, rubber seals feed differently than metal or plastic components. Plastic and metal seals have physical properties to remain rigid in a feeder. Since rubber has different properties, such as elasticity, it can lead to rubber distortion if fed like metal and plastic.
Silicone is a popular choice for seal molding because of its significant chemical resistance, superb mechanical properties, and unparalleled temperature resistance. The catch is silicone’s sticky surface which, when packaged too tightly or fed too closely, can cause the sides of their seals to stick, conform, or even break in automation.
Before beginning the automated manufacturing process, you should consider if the customer’s chosen material has the physical properties to endure automation. If it does not, then think if another material should be used for the product design, or if alterations can be made to the automated system to allow feedability. These types of situations are important to contemplate in the design stage to prevent potential feedability issues once the automation process is running.
Static Solutions
Static in automatic feeding systems is another challenge. Charged ions–known as static–are generated from the friction of seals and o-rings moving through vibratory bowl feeders. When feeding materials like silicone, static can cause product pieces to cling to each other and the surfaces of the feeding system. This cling may seem innocuous, but it can cause machines to jam and ruin or damage both the products and machines.
To solve static issues, special ionizers can be added to automated feeding systems to blow charged air into the system and remove charged ions. Surface treatments or coatings like Teflon, Parylene and silicone top coat can smooth surfaces to reduce static.
One factor you may not think about regarding static is humidity. In the production environment, low humidity may stop some rubber surfaces from sticking to each other, but at the cost of generating more static. High humidity environments create less static, but cause some rubber compounds to stick together. For packaging, anti-static bags can be an option to avoid static cling.
Beating Stiction
Stiction, which is friction that prevents stationary surfaces from being set in motion, is typically found in low-durometer, flexible parts like many rubber products. Stiction mostly affects parts with flat, smooth surfaces because of the increased surface contact between the machine parts and the product. Additionally, stiction can have some rubber products like seals stick together or to production equipment as they are molded or fed into machinery.
An effective way to combat stiction is for the manufacturer to apply a special surface finish or special coating to the surfaces of the mold or feeder system. This creates non-stick surfaces to reduce friction and improve movement of the rubber products in the automated system.
A common misconception with customers is that a dull o-ring will not perform well. An o-ring does not need a high polish finish to be effective; as long as it is properly designed, leak paths will be nonexistent. Any parts with rough finishes will still seal if they are well-designed and accurately fitted.
For customers requiring a tailor-made finishing process, manufacturers can use a high-energy finishing machine to roughen up the surface of a final part. If a tacky material has difficulty sliding through the feeding assembly, the finishing machine will break up the seal surface and allow the parts to move better during assembly.
Choosing the Right Hardness
Although rubber is a tough material, not all grades of durometer or rubber hardness can resist automation. While silicone has a low durometer, it can cause problems with automatic feeding due to sticky and soft physical characteristics. On the other hand, high-durometer, hard rubber parts like urethane always feed better in the automation process than low-durometer, softer parts.
For an o-ring to successfully be used in an automatic feeding system, it should be stiff enough to stand on end but flexible enough to stretch over the part. This is good to keep in mind for materials with durometers measuring approximately 70 Shore or greater.
Softer rubber compounds measuring 30 Shore or less may not be viable for a product produced during automation. However, those softer rubber compounds may be used with the help of coatings, surface finishes or changes to the production environment like humidity controls or temperature.
Smart Packaging
Another issue to keep in mind with automated feeding is packaging. Some o-rings, like ones with a large inner diameter and small cross sections, will deform when stored for long durations. The o-ring will develop a curve from the weight of the other o-rings in the packaging, causing a “potato chip” appearance. Seal stickiness can be worsened by factors including vacuum sealing, material choice and humidity changes. If o-rings are shipped overseas, they may be packed tightly and left in boxes for long durations of time, compounding the issue. Also, highly static compounds like silicone will build a static charge during shipment, causing o-rings to stick together.
A way to solve the packaging problem is to keep in mind the shape of the seal to ensure there are no places where parts can fit together. When working with rubber parts, distortion must be compensated for. Ensure there are no facets to round, and if needed, add channels or dimples to the seals to prevent parts from touching or sticking in the packaging stage. Consider placing fewer parts in a loose bag and then inducing air before sealing, as this minimizes the chance of seals to warp or scrunch. Although fewer parts per bag may require dividers, more shipping space and higher shipping costs, it may be worth it in the long run, as it will improve seal life and reduce pricey manufacturing issues once production starts.
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