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Fast-Cure Urethane – An Alternative to MMAs for Composite Assembly

( 07/22/2020 ) Written by: Steve Webb

Manufacturers have been using methacrylate adhesives (MMAs) for bonding composites due to their strength and rapid cure.  While perfectly suited for open-mold fiberglass components, MMAs have traditionally had difficulties in bonding some composites such as SMC or had read-through issues due to shrinkage and high temperature exotherm when bonding thermoplastic structures and thin composites. A historic barrier to urethane adhesive adoption, however, has been its slower rate of cure. Specifically, most urethane adhesives have a linear relationship of open time to cure time, so urethanes that offer reduced handling time also present a very short open time, leaving inadequate time for product assembly. Conversely, adequate open times are associated with slow cure times. In this way, polyurethanes have traditionally been at a disadvantage compared to the fast rate of cure which allows for quicker production rates when using MMAs. Adding heat to cure urethanes has been a common solution, but this adds the cost of heated tooling to the manufacturing costs as well as creating potential quality issues with ‘cold spots’ in heated tooling as some polyurethanes require heat to fully cure.

A step-change in addressing this situation is LORD 7800 fast-curing structural polyurethane adhesive. The LORD 7800 family has a range of four different open time product options followed by a rapid cure. The product family’s cure profile is like an MMA and cures at room temperature. It readily accepts low heat from heated fixtures and can help solve cold spot quality issues in heated tooling. Examples of time savings offered by this new generation of urethane adhesive includes lowering cycle time and tooling temperatures in heavy-duty truck hood manufacturing, meeting the challenges of automotive lightweighting bonding LGF-PP and removing long work-in-progress queues in automotive manufacturing with pressure testing in as little as five minutes. Further, bulk dispensing of LORD 7800 using meter-mix-dispense equipment is more cost effective versus MMAs because the upfront investment is considerably lower due the pourable consistency of the adhesive. 
 

ABOUT THE AUTHOR MORE BY THIS AUTHOR
Steve Webb

Steve Webb is an Application Engineer at LORD Corporation and is focused on current and next-generation adhesive development.
He collaborates with customers to design and implement adhesives into their manufacturing processes for optimal efficiency.

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