Adhesive/Sealant, Polyacrylate, Room Temperature Vulcanizing, Alcohol Cure for Engine Sealing
Publication Date: 03/01/2016 - Complete Document *
Material Description. This Polyacrylate adhesive/sealant requires no catalyst or heat to cure. When applied it reacts with moisture in the air releasing an alcohol by-product and fully cures to an elastomeric product, adhering to most clean surfaces without need of a primer. Adhesively bonded and fully cured adhesive/sealant acts as a barrier against oil migration across mating surfaces.
Symbols. Not applicable.
Applicability. Formed-In-Place Gasket (FIPG) for sealing engine covers, pans or mating of other components for oil seal integrity or to restrict dust or unwanted air and water intrusion. This sealant was not developed for engine coolant joints.
Application Temperature and Assembly Sequence. Unless otherwise specified by the adhesive/sealant manufacturer, apply this adhesive/sealant on the intended surface whose temperature is from 20 °C to 40 °C (68 °F to 104 °F). Below 20 °C adhesion and cure rate slows. It is the responsibility of the applicator and the adhesive/sealant manufacturer to establish the accepted conditions, e.g., process time from applied bead to assembly to air test, temperature and adhesive/sealant cure rate to provide acceptable adhesion and leak test performance. See Assembly, Sealing and Fastening Bill of Materials (BOM) Level II for minimum process time.
Continuous Usage Temperature. Up to +150 °C as defined by SAE J2236 (see 188.8.131.52 and Table 5). Use temperature is a material strength measurement, not related to adhesion performance.
Other Surface Treatments. The adhesive/sealant approved to this standard must be applied after paint or coated part treatments (e.g., Electro Coat Paint Operation (ELPO)/Uniprime coatings of stamped steel covers). It is the responsibility of the applicator and the adhesive/sealant manufacturer to establish the accepted conditions, e.g., time, temperature and coating cure to provide acceptable adhesion and leak test performance.
Cleanliness of Mating Joint Surfaces. It is the responsibility of the applicator and the adhesive/sealant manufacturer to establish the accepted surface conditions, e.g., washer cleaner concentrations, drying time, and storage protection from airborne contaminants to provide acceptable adhesion and leak test performance.
Monitoring Cleaning/Washing System Changes on Adhesion. It is the responsibility of the sealant applicator to evaluate changes in chemical cleaning/washing systems over time for parts where sealant is applied. Changes must be supported by lap shear data to evaluate the effect on sealant adhesion. Run the appropriate Table 2 test panels through the relevant washer system changes in production scale or in a pilot size operation. The values must meet or exceed Table 5 values. Any joints receiving plasma treatment as a surface preparation method in production, do not require data monitoring of a change in cleaner/washer.
Gap Limitations. Adhesive/sealant is capable of sealing a gap from 0.1 mm to 0.5 mm (the blowout test determines the maximum gap).
Product Advantages. Unlike silicone sealant chemistry, polyacrylate sealant poses no contamination risk to oxygen sensors or increased oil foaming due to oil absorption and extraction during curing.
Remarks. The words must, shall or will as used in this document mean a mandatory requirement.
Cost. Unless otherwise specified, pricing shall be based on 20 kg (5 gal) pails compared with existing products. Material cost comparison is sealant price per mass (grams) times specific gravity. The quantity of sealant per pail varies with manufacturer. Cost comparison for decision making must be from engine specific use (grams per component, engine) and annual volumes.
Polyacrylate (ACM) sealant will cost more per engine versus current production silicone sealants. Once production costs are developed more accurate information will be provided.
Cure Rate. This adhesive/sealant is slower than most silicone adhesive/sealants from 10% to 100% Relative Humidity (RH). Depth of cure inward from an exposed 1 mm edge for seven (7) days at 25 °C, 50% RH is 10 mm
Open Time to Joint Assembly. All Room Temperature Vulcanizing (RTV) silicone sealant joints must be closed and clamped within 15 minutes of the sealant application to the mating flange. Clamped is defined as having a minimum of 80% of the fasteners tightened to the final torque with no two (2) adjacent fasteners untightened. Until production experience provides better information
Shelf-Life Limitations. This sealant is packaged in service and repair cartridges with foil sealed ends. With proper storage the un-opened sealed packaging has a nine (9) month shelf-life. Once opened, shelf-life is limited by how well the opened container is protected against moisture before it is emptied.
Large Scale Operations. Due to the moisture sensitivity of this sealant, use small pails (20 L/5 gal maximum) with strict limits on storage stock rotation. Product left in delivery lines over extended holiday periods may require a purge.
GM Materials engineering recommends all RTV adhesive/sealant (regardless of cure system) be used in a ventilated area.
Joint Performance. This adhesive/sealant has low lateral joint movement (onset of cohesive or adhesive failure) on metal substrates due to its low elongation. The shear strength in mega-pascals is high to achieve separation compared to silicone sealants suggesting good bond strength.
Follow these joint strategies (see 1.4.3a thru 1.4.3d) when using this sealant to reduce leak risk.
a. Machined surfaces to tight tolerances. Avoid joints with high stack tolerance variation as the maximum recommended gap is 0.5 mm. Higher gaps (1.0 mm) are possible with the use of surface treatments and/or wider flanges (8 mm or more).
b. Joint metals with low thermal expansion behavior.
c. Wide flange joints with close bolt patterns. The joint flange width shall be 5 mm or more with bolt pattern width not exceeding 80 mm between any two bolts centers on the joint.
d. A step chamfer is recommended by the adhesive/sealant manufacturer to maximize joint movement capabilities of the sealant
Proper Use of Test Methods. Testing for this standard is based on coupon surfaces and conditions different from those of assembly or service. Standard tests permit comparison between products while attempting to represent a worse case condition related to end use. Testing actual production processes, design (chamfer) and surfaces is necessary before actions are taken. Use the test matched with the desired property/definition.
Note: For example; Lap Shear strength may be used to measure the effect of sealant and/or process variation (e.g., ineffective surface cleanliness, build variations, etc.,) on bond strength provided it mimics the actual production application with all its known variables. Lap shear is a cured property, not a wet uncured characteristic.
Surface Treatments to Promote Joint Adhesion. Demanding and enforcing part cleaning control through cleaning process specifications is necessary for optimum sealant to joint bond life. Surface treatment chemicals (e.g., Henkel Bonderite) formulated for specific base metals are applied in washer systems or by liquid soaked applicator to maximize bond performance. These are not cleaners, as they are only effective on a washed surface, but properly applied and protected may be globally shipped and perform long after the application.
Fuel Dilution in Engine Oil. This sealant lap shear testing to GMW16678 Test Condition A, Fuel E fuel dilution, (see Table 5, Note 1) produced the desired cohesive separation on the two (2) test panel substrates used. Since standard lap shear test panels don’t specifically represent production surfaces, testing of production surfaces for adhesion evaluation is mandatory for engine joints where the fluid level is above the joint whether the engine is on or off. The results on engine joints exposed to measured fuel dilution conditions will dictate use.
Adhesive Failure. This sealant lap shear testing to the indicated substrates (see Table 5, Note 1) produced adhesive not cohesive separation from the test panel substrates. Testing of production surfaces for adhesion evaluation is mandatory for engine joints. The results on engine joints exposed to production intent conditions will dictate use.
Document Type : Complete Document
Edition : Issue 1
Language : English
Page Count : 14
Publication Date : 03/01/2016
Revision : 1
Status : Current
Title : Adhesive/Sealant, Polyacrylate, Room Temperature Vulcanizing, Alcohol Cure for Engine Sealing