Adhesives are used everywhere! A breakfast box is glued shut, a paper towel tube is spiral glued, can labels are glued on, furniture is laminated, etc. To meet the demand of the wide variety of adhesive applications, there are many materials in play that make up the adhesive itself. Without knowing the properties of the adhesive you’re pumping, you'll likely get "stuck" somewhere in the pump selection process. Read on to learn about the raw materials that make up adhesives, then explore the properties of adhesives that affect pump selection.
- Elastomeric (rubber-like) materials – Covers adhesives made with neoprene, nitrile, and natural rubber. These generally have good resistance to many liquids and are most useful in bonding fabrics and rubber products.
- Epoxy resin – Epoxies are known for a strong, tough bond with good chemical resistance properties.
- Phenol formaldehyde resins – These resins are used extensively for making plywood and veneers, and are by far the oldest of the synthetic resins used for adhesives.
- Polyvinyl acetate – This polymer is commonly found in adhesives because it can bond to just about any material. They can be combined with wood chips, sawdust, clay and other granular products as a binder for many different products, like ceiling tile and wall board.
- Sodium silicate (water glass) – A water soluble silicate glass that is widely used for bonding paper and cardboard products. Sodium silicates are low cost, require little preparation, are nonflammable and will not deteriorate.
- Hot melt – Hot melts do not contain any solvents. Heat application turns hot melt into a liquid and in this state it sets the surfaces to which it is applied as it cools and forms a bond between the two materials.
Viscosity is the most common property affecting adhesive pump selection. Viscosity directly correlates with the level of flow resistance as a fluid moves through a pump. A lower viscosity (thin fluid) will have the least resistance, and vice versa.
For example, rubber cement adhesive is at the higher end of the viscous scale, while polyvinyl acetates and sodium silicates are less viscous. Remember that all pumps are not created equal when it comes to viscous material. You can read about Why Viscous Material is the Centrifugal Pump’s Kryptonite on our blog.
A corrosive adhesive can quickly eat away at certain pump materials of construction, so it’s important to determine the corrosive nature of the adhesive and its raw materials by considering its pH level.
Rubber cements, phenolics, epoxy, and sodium silicate are generally handled with iron or carbon steel. Acid starches are best handled with bronze fitted or stainless steel. The polyvinyl acetate family requires stainless steel construction for best pump life. It’s also important to remember that some systems are flushed with water or other solvents, which may also have an effect on the pump materials of construction.
Although not a property of an adhesive, it is necessary to control the temperature of the adhesive to keep it in a solution or "pumpable" form. In essence, temperature is directly related to the viscosity level of the fluid. When the adhesive is at a higher temperature viscosity drops, while lower temperatures increase the viscosity.
Along with the above three properties, consider the likelihood of the adhesive's tendency to deteriorate if left stagnant, harden with heat, or "ball up", which can ultimately create system issues if not appropriately planned for.
Special consideration should also be made when selecting mechanical seals for adhesive applications because mechanical seals themselves generate heat. If too much heat is generated a slew of issues can occur, including material degradation, and other issues like "balling up". Rubber cement has tendencies to "ball up" in between mechanical seal faces, pushing the faces far enough apart to cause seal leakage and eventual failure. (Curious about other reasons why mechanical seals fail? Read our post, 6 Reasons Why Mechanical Seals Fail.)
All in all, adhesives can be tough to pump!
What other properties do you consider when selecting a pump for adhesives?
If you're struggling with moving an adhesive in your plant, contact us today! We're happy to provide assistance to businesses in Wisconsin and upper Michigan.