Silicone Repair Methods
Many applications for reusable silicone blankets involve the blanket being bonded or otherwise attached to a metal support frame. When a tear or leak develops in the membrane, a repair that does not require removal of the blanket from the frame is desirable. This can be readily accomplished with uncured silicone patch material when a heat source is available or with RTV Silicone Adhesive if a room temperature cure is necessary. Both methods are outlined below.
Heat Curable Silicone Patch Method
- This method uses uncured Mosites #1453 Silicone as the patch compound. Other
uncured silicone sheet compounds will work in the same manner (#14248 Maroon, #1495 Clear, #14116 Gray, etc.).
- Inspect the torn area of the blanket. Remove any shredded or loose material. If possible, make a pattern that will cover all the damaged area. Avoid making square corners – rounded or oval patches reduce stress areas from developing in the corners. Remove the damaged area covered by the pattern with a sharp knife or blade. Transfer the pattern to your uncured silicone patch material and cut it slightly larger – to extend ½ inch on all sides.
- Clean the surface of the cured silicone thoroughly (MEK, alcohol, etc.). Place a piece of Teflon or FEP release film under the repair/patch area. Lay the uncured silicone patch into position and rub down firmly to remove entrapped air. Skive or feather the edges of the patch.
- Cover the patch with a layer of release film. Place a metal plate -aluminum is preferred – on both sides of the repair area. Use a “C”clamp or vise grip pliers to apply light contact pressure to the metal plates.
- Use a heat gun to apply heat to the metal plate. Be careful not to allow the silicone blanket to contact the heat gun nozzle or be exposed directly to the extreme temperature of the gun. A distance of approximately 6 inches from the plates will result in a temperature of 300 – 350 degrees F. Maintain this temperature for at least 15 minutes. (A thermocouple or monitor at the blanket patch is ideal.) After the cure time has elapsed, the clamping fixture can be removed and the blanket inspected and placed back into service.
Mosites TCT-6 Heater Kit for Silicone Repair
The heater kit described in this paragraph consists of a silicone heater blanket, capable of producing a temperature of 300 degrees F, bonded to a layer of thermally conductive silicone rubber with a face cover of 5 mil Teflon film. The heater blankets can be made in various sizes, but TCT-6 refers to a 6 inch diameter heater. The unit works on standard 110 volt electrical outlets and produces the desired temperature without the necessity of a transformer. The Teflon film face cover allows easy clean-up and prevents unwanted adhesion of patch materials. The conductive silicone layer provides uniform dispersion of the temperature supplied by the strip heaters in the silicone heater blanket. This kit can be used in the repair procedure outlined above, and eliminate the need for a heat gun. The metal plates and a source of light clamping pressure are still necessary.
Room Temperature Cure Silicone Patch Method
- Clean the silicone surface in the area that is to be repaired with solvent (MEK, acetone, alcohol, etc.)
- Examine the damaged area. A linear cut can be repaired with a 2 inch wide “batten strip” of 1/32 inch thick cured silicone sheet. Allow 1 inch of patch material to extend on each side of the cut. Apply the patch on the outside of the blanket to avoid mark-off on the part. Use a uniform coating of GE – RTV -108 Silicone Adhesive on the cured silicone patch material. Lay it into position, press it down to remove entrapped air, remove any excess RTV that exudes from the edges, use a skive or spatula to feather the edges. Allow the repair to cure at ambient temperature for at least 24 hours before using.
- If the tear is jagged or material is missing, make a pattern of the repair area that will remove all the damaged silicone. If possible avoid square corners – rounded corners or oval patches help reduce stress areas from forming. Transfer the pattern to the blanket and to a piece of cured silicone of the same thickness. Use a sharp knife or scissors to cut the rubber. Check the patch for fit in the blanket; mark the side of the patch that will face the tool.
- Lay the patch on the 1/32 inch thick cured silicone sheet. Cut the 1/32 inch thick sheet oversize by 1 inch per side. Use RTV -108 Adhesive to bond the patch to the 1/32 sheet. A bond layer of 15 to 25 mils is sufficient for good adhesion. Apply light pressure to remove air from the RTV. Remove any excess adhesive from the perimeter of the patch and allow the RTV to cure at room temperature for 2-3 hours or until the laminate can be handled.
- Apply RTV-108 Adhesive to the 1 inch border of the 1/32 inch sheet and place the patch into position on the blanket. Use light pressure to exclude air from the patch. Excess RTV can be removed and the patch edges feathered to make a smooth transition.
The RTV-108 Adhesive requires at least 24 hours at room temperature before stress can be placed on the bond joint. Optimum cure usually develops in 3 to 7.