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Efficient Laminating of Structural Insulated Panels or SIPs

Background

Many residential and some commercial building projects are making good use of Structural Insulated Panels, specifically for sidewalls and roofs. These panels, also referred to as SIP’s, are usually made up of OSB (oriented strand board) laminated to both sides of an EPS (expanded polystyrene) core using a water-based emulsion adhesive. The core material is typically 4’ X 8’ and the skins are either 4’ or 8’ wide, in lengths up to 24’, or in some cases, 28’. By laminating these under controlled factory conditions, it is possible to accurately predict the “in-service” performance of the product. 

Panels of this type are quickly and easily installed and offer great energy savings over conventional construction methods. Factory cut panels allow a variety of architectural designs previously thought to be impractical.

Some other panels, as may be used for patio enclosures, in-plant offices and other such applications, may be produced by laminating aluminum or FRP directly onto the EPS core material. In this case, since the skins are a non-porous material, a one-part liquid moisture cured urethane is used, but the overall production of panels is similar.  

A common requirement of all panels of this type is that they need to have a non-creep structural bond, they need to be flat and they need to be manufactured to a specific thickness dimension in order to match up with other components.

Adhesive Types

The two adhesives commonly used for making SIP panels are the two-part, water emulsion adhesive, used for laminating panels with porous skins, and the one-part, liquid urethane adhesive used for laminating non-porous skins directly to the EPS. Either of these adhesives can provide the necessary moisture, creep, and temperature resistance required of a structural adhesive. A manufacturer of SIP panels should work with the appropriate certifying agency to make sure the product selected matches the job requirement.

The press time with the emulsion type adhesive is about 45 to 60 minutes, and with the liquid urethane adhesive can vary from 1-1/2 to 2 hours. This needs to be taken into account when choosing an adhesive system.

Cold Press Laminating System

While different methods have been used for making SIP panels, many manufacturers choose using a Glue Spreader and one or more Air Pod Platen presses for making this type of panel. Our drawing below shows such a line layout, using a 56” wide Glue Spreader to apply adhesive to the core components and one 24′ Air Pod Press, with provision for adding a second press at a later date.

Although the two basic pieces of equipment are the Glue Spreader for applying the adhesive, and the Press for application of pressure while the glue line “sets”, auxiliary handling equipment, conveyors, carts, etc., will complete the system and make the operation more efficient. The system shown can produce (80) 4′ x 24′ panels per day based on nominal 6″ thick panels using an emulsion adhesive with a press time of 60 minutes.

Adhesive Application

The Black Bros. #775 Adhesive Spreader will quickly and effectively apply a uniform coating of glue to both the top and bottom surfaces of the core stock with one pass through the machine. The Adhesive Spreader is normally specified with a special opening to allow gluing up to 12″ thick foam cores. Grooved Neoprene coating rolls are used for the emulsion adhesive and smooth EPDM rolls are used for the liquid moisture cured urethane.

Accurate control of glue application is important for several reasons. First, an accurate application rate will help to control the cost of the glue used. It can also be adjusted to compensate for in‑plant conditions to help give the proper amount of lay‑up time. Of course, most important is the assurance of getting a good bond. Your glue supplier will give you a good guideline for the amount to apply, based on the stock, the lay‑up time for the load, differing in‑plant conditions, etc. We welcome the opportunity to discuss your requirements with them to insure you of good results in your laminating operation.

Glue Spreader rolls should be maintained in good condition to assure accurate control of the glue spread. We suggest that the rolls be reground and regrooved at least once a year when the machine is operated on a single shift, 40-hour work week. The cost of maintaining the rolls in good condition will more than offset in glue savings, and, in addition, the quality of the bond line will be better, resulting in few, if any, rejects.

An important consideration for any glue application has to do with the residue generated at the end of the day, both in unused glue and in the waste water generated as a result of cleaning the Adhesive Spreader. A few years ago, Black Bros. introduced the automatic roll cleaning system for use with water-based adhesives. We have supplied this on many machines and it works well. The operator only has to wipe the ends of the rolls and clean the end seals to complete the clean‑up operation.

The automatic roll cleaning system is operated by a programmable controller that controls the forward and reverse action of the rolls as well as spraying water on the rolls at the appropriate time for most effective cleaning action. The most obvious result of using this feature is that it eliminates the need for an operator to manually perform the cleaning operation. This frees the operator to do other duties. Another advantage is that the machine is cleaned the same each time. This assures that the rolls will give the maximum results for the longest time. It also generates much less wastewater, perhaps 1/2 to 1/3 of what would be generated using manual cleaning methods. This alone can quickly justify the cost of the automatic roll-cleaning feature.

Stock Lay-Up

After adhesive is applied, a stack is laid up, starting with a carrier or caul board, then a piece of facing material, then the core, covered with glue on both sides. The second face is then applied.  This procedure is continued until the entire stack is assembled. A top caul board is applied and the stack is ready to go to the laminating press.

Structural insulated panels are often used with other components. With this in mind, some customers use core material sized slightly smaller than the surface material to eliminate cutting out this material after laminating. If this is done, appropriate alignment devices are made by these customers to facilitate lay-up.

Because of the relatively light weight of SIP panels, and the fact that most of the core material is limited to 4’ X 8’ size, many customers simply build the stack on a roller conveyor. When building panels with large skins, methods other than manual are sometimes used, for example, the use of a vacuum lift above the work area to handle these skins is common. Large or heavy panels can be laid up on a scissors lift if necessary. This is also helpful since it keeps the lay-up at a constant height.

Using caul boards is always recommended. Caul boards protect the panels from damage as the stack is handled, they also help uniform the pressure across the surface during laminating. If one press is used, the stack can be loaded directly into the press; however, because of the thickness of the panels, it is common to use more than one press. When using more than one press, a transfer cart is used to move loads from the lay-up area to the appropriate press.

Pressing

Air Pod Presses have important advantages over other laminating methods. Two specific advantages are accurate control of laminating pressure for uniform thickness panels with a complete glue bond, as well as the inherently flat panels produced with a platen press. Air Pod Presses are virtually maintenance free as long as the air supply is kept relatively clean. No scheduled maintenance is required, and pod replacement is virtually nil.

Using multiple air pods, evenly distributed across the load, gives very uniform distribution of pressure. When laminating a stack of pieces, there can be some variation in stack height, due to the normal tolerance of the components. The platen on an Air Pod Press can move slightly to compensate for such variations. An important advantage when using Air Pod Presses is that the laminating pressure remains consistent as the glue line “sets”, that is, there is constant follow up. This is particularly important when laminating wood products with a water based glue as there will be some dimensional  change during the laminating operation.

Too little pressure on SIP panels can result in poor glue bonds. Too much pressure can crush the core and result in a thin panel. When manufacturing this type of product, we suggest the use of our 10 to 20 PSI presses, which will develop sufficient pressure for bonding the materials, but can be controlled so as not to crush the foam core. These Presses were designed specifically for bonding stressed skin insulated core panels. On the 10-PSI press, each 10-PSI on the gauge is equal to about 1 PSI on the load, which makes it very easy to control the laminating pressure. An air regulator controls this pressure.

The use of one or more Black Bros. Air Pod Presses will provide an economical solution to producing high quality panels. You can start with one Press and later add to your production capacity simply by adding another Press. If you select the 4′ x 24′ Press for your operation, it allows you the capability of doing various size pieces in the same press. For example, you could laminate (3) stacks of 8′ simultaneously, (2) stacks of 12′, (1) stack of 8′ and (1) stack of 16′, (1) stack of 24′ long panels.

For more information, please contact us via your sales associate, our contact form, our toll-free number 800-252-2568, or email us at [email protected].