LORD Chemlok® rubber-to-metal adhesives were first introduced in 1956. While much has changed during this time, one thing remains constant: the quality of Chemlok adhesives. The Chemlok brand is recognized globally as the industry leader in rubber-to-metal adhesives. When manufacturers have a critical application that demands a proven rubber-to-metal adhesive, they look to LORD Chemlok products.
Although a premium adhesive is the basis of a quality bond, it’s only the beginning; proper application is essential for maximum results. Whether you’re dipping or spraying, you’ll learn how to maximize efficiency and optimize results.
Chemlok solvent-based adhesive systems are available in several sizes to accommodate varying production requirements. Choose from one of these convenient packages:
One of the most important factors influencing adhesion in the bonding process is surface preparation. To ensure optimum bond performance and long-term environmental resistance, substrates must be free of organic and inorganic contaminants. Organic materials include grease, dirt and oils which can be removed by solvent or alkaline cleaning. Common inorganic contaminants are rust, scale and oxide layers. These can be cleaned by either mechanical or chemical processes, or a combination of both.
There are a number of ways to prepare substrates for adhesive application; however, the methods can be broadly divided into mechanical and chemical. Regardless of which method you choose, the essentials of all good surface preparations include:
Mechanical Preparation – Mechanical preparation involves physically removing surface contamination and increasing surface area and substrate profile. These methods include:
Chemical Preparation – Chemical processes, on the other hand, utilize organic and inorganic chemicals to dissolve, suspend or eliminate soils and surface contaminants. Preparation methods include:
Special Note About Degreasers – Although chlorinated solvents like trichloroethylene and perchloroethylene are still used for degreasing, many companies have discontinued use due to environmental and health-related issues. As a result, many environmentally friendly alternatives have been developed, which produce surfaces clean enough for use with adhesive systems. Popular alternatives to chlorinated solvent degreasers include:
To determine which preparation method best suits your needs, consider:
Maintaining optimum surface cleanliness is essential until adhesive application is complete. To accomplish this:
The water break test can be used to check for oil and grease removal. If a surface can support an unbroken film of deionized water for 60 seconds or more, it is considered essentially free from grease or oil.
The following three-step process is the preferred mechanical surface preparation technique.
Degreasing Grit-blasting Degreasing
The above methods produce excellent surfaces for bonding most substrates. Sometimes, more elaborate chemical methods may be needed for certain substrates or for improved environmental resistance. For more information, please contact us for assistance. Details on each specific method mentioned above are described under the heading for the specific substrate. Regardless of the system, selected parts must remain clean when being removed from the cleaning tank. Water break tests such as ASTM F22 should be performed regularly to check cleaning effectiveness.
Although the general principles are the same for preparing all substrates, some materials require special attention. Outlined below are guidelines for surface preparation of specific substrates:
Steel (Mechanical Preparation)
Grit blasting (with steel or aluminum oxide) is widely used for preparing steel surfaces. It is especially effective for metals covered with rust, scale, oxide layers and similar corrosion compounds. Steel preparation usually involves:
Consult the manufacturers of blasting equipment, abrasive media and alkaline cleaning units for specific information concerning equipment for this process.
Steel (Chemical Preparation)
Chemical treatments for steel typically include iron phosphate or zinc phosphate conversion coatings. For rubber-to-metal bonding applications, calcium-modified, microcrystalline zinc phosphate (film weight of 125-450 mg/ft2) is recommended. Zinc phosphate treatment consists of:
Hot caustic clean Water rinse Phosphoric acid pickle Water rinse Zinc phosphate Cold water rinse Hot water rinse Hot air dry
This type of surface treatment provides on-the-shelf corrosion protection of the uncoated part as well as improved under-bond corrosion protection. For detailed information and names of representative suppliers, consult manufacturers of phosphating treatments and other chemical treatments.
Stainless Steel (Mechanical Preparation)
Preparing stainless steel with mechanical methods includes:
Stainless Steel (Chemical Preparation)
Chemical treatment for the passivation of stainless steel involves the following:
Immersion times, solution concentrations and operating temperatures may be adjusted to suit conditions and alloys.
The preferred mechanical method for preparing aluminum is blasting. This includes:
Chromate alodizing of aluminum also produces excellent bonds. This involves:
Solvent degrease or aqueous clean Water rinse Deoxidizer Water rinse Chromate conversion treatment Water rinse Warm air dry
Consult the manufacturers of the proprietary materials used in these processes for more information. Aluminum surfaces may also be prepared by anodizing (electrolytic deposition of aluminum oxide).
Depending upon the required environmental resistance, preparation of magnesium surfaces varies. Blasting with sand or aluminum oxide provides a good bonding surface, but the bond will not provide outstanding environmental resistance. For best results, use chemical methods such as chromic pickling or anodizing. The chrome-pickle process consists of:
Vapor degrease and/or alkaline clean Cold water rinse Chrome-pickle Cold water rinse Hot water rinse
Brass and Copper
In addition to blasting with sand or aluminum oxide, brass and copper surfaces may be treated with chemical methods including ammonium persulfate etching. This method involves:
In addition to ammonium persulfate etching, there are a number of commercially available etchants. Consult the manufacturers of these specific products for product selection and processing information.
Lead – Mechanical methods are used almost exclusively with lead and are usually satisfactory. If the lead surface is freshly abraded and an oxide film has not had time to form, surface preparation may not be required.
Zinc – Zinc surfaces are almost always prepared mechanically. However, be careful when bonding directly to zinc-plated, galvanized or electrogalvanized surfaces. Typically, hot dip-galvanized substrates can not be adhered to, whereas some electrogalvanized surfaces may be bondable.
Plated Metals – Two unique problems are often encountered when preparing and bonding plated metals:
Since the plating process produces a clean, bondable surface, freshly plated surfaces often do not require additional preparation. Keep in mind, however, that plating changes surface properties such as adhesion, porosity and surface stress of the metal deposit. Current density, composition of the plating bath (including brightener content) and temperature of the bath also affect the bondability of the plated surface. When mechanical pretreatment is used, abrade the surface lightly. Fine grades of sand or abrasive paper will minimize penetration. The correct chemical treatment depends upon the type of metal which is deposited during the plating process. If the plating does not adhere tightly to the base metal, the plating process itself should be investigated. Application of Chemlok 205 or 207 primer, 5.1-10.2 micron (0.2-0.4 mil) dry film thickness, often improves adhesion to plated metals.
Rubber can be adhesive bonded to many rigid plastics. To prepare plastic surfaces:
A rough surface can be molded into the plastic by using a mold that has been textured. Use only internal plastic mold releases. Further details concerning the proper treatments of many engineered plastics are available on request.
The principles outlined in this guide can be adapted to the surface preparation of almost any rigid material for bonding. The essentials of proper surface preparations include:
Also, high surface profiles [as high as 50.8-76.2 micron (2-3 mil)] from mechanical blasting generally bond better than those with low surface profiles [less than 12.7 micron (0.5 mil)].
Temperature – Temperature affects the viscosity of Chemlok primers and covercoats. If stored cold, allow them to return to the usual working temperature before using. For drums, this may take as long as 48 hours. Recommended storage temperature is 21- 27°C (70-80°F). Cold storage is not recommended.
Dilution – Regardless of dilution amounts, it is important in all cases that the appropriate diluent be added to the primer or adhesive while stirring. Depending upon the application, dilution of both the primer and covercoat may be required. Mixing guidelines are listed in data sheets that come with each Chemlok product.
Pails, Single Gallons and Smaller Containers – Hand stir in a “figure 8” motion with a wooden paint stick. For gallon containers, paint shakers may also be used with solvent-based adhesives. Fifteen minutes is usually sufficient. Continue mixing until all settled material is removed from the bottom and the solution has a uniform appearance. Stir frequently during use. To minimize solvent loss, replace the container lid when not in use. Solvent loss reduces ingredient solubility, and increases solids content and viscosity. Caution: If used, electric mixers should have spark-proof motors.
Drums – Chemlok products are available in standard 55-gallon drums as well as 55-gallon units with built-in agitators. The standard drum has two openings [3/4-inch and 2-inch (1.91 cm and 5.08 cm)] in the drum head, while the agitator drum has a 2-inch (5.08 cm) side opening near the drum head outer edge. Regardless of type, all steel drums have protective interior coatings that have been tested for safe storage. Most Chemlok products are available in agitator units, which have a double-blade agitator accessible through a bung in the center of the drum head. Initially, a steel hand crank should be used to loosen settled material. The adhesive should be agitated at least three to four hours at 40 to 60 rpm prior to use; eight hours is recommended length of time. For continuous agitation, a variable speed, air-driven motor is typically used. Caution: Electric motors should not be used because of spark and fire hazard. To prevent sparks from static electricity, drums should be properly grounded.
Handling Quick Tips for Solvent-Based Adhesives:
Handling Quick Tips for Aqueous Adhesives:
Chemlok solvent-based adhesives may be applied by brushing, dipping, spraying or roll coating. General recommendations are:
Hand Brushing – Chemlok solvent-based adhesives are suitable for hand brushing straight from the can. When using this method, wear cloth gloves and work in a clean environment. Also make sure there are no dirty or greasy objects within reach. When working from small, open containers, solvent evaporation may increase adhesive solids. This is particularly true with large brushes, which carry a substantial volume of adhesive in the brush body. This adhesive dries and, in some cases, becomes pasty. If brush strokes become visible on painted parts, dilute the adhesive to the original viscosity. Brushing is easiest when the viscosity is correct. Primers and covercoats usually dry in 30 to 60 minutes at 21°C (70°F). Higher temperatures and/or increased air circulation will accelerate drying time.
Dip Application – Hand-dipping Chemlok adhesives is recommended when only a small number of parts need to be coated or when factory conditions prohibit mechanical units. To avoid excess coating, sags and drips, withdraw parts from the adhesive slowly. Also be sure to control the viscosity and agitate the adhesive frequently.
Mechanical Dipping – There are two primary mechanical dipping applications: conveyor equipment and dip tanks.
Conventional conveyor equipment is classified as either monorail or bar conveyor systems. The monorail system is a single-chain unit; the bar conveyor is a double-chain assembly with bars running horizontally between the chains. Selection of a conveyor unit depends on the size and number of parts to be dipped. For best results, arrange the conveyor’s dipping section so parts are withdrawn at an angle rather than straight up and down. By removing the parts at an angle, the conveyor’s forward motion provides a gradual vertical lift, which allows excess fluid to drain evenly from parts.
When using dip tanks, the adhesive should be agitated continuously, ensuring a good top-to-bottom turnover. The constant motion prevents skinning and sweeps air bubbles to the side. Circulating pumps or submerged impeller agitators are very effective. Because of the filler content, diaphragm pumps, if used, should be dual-diaphragm models. Tank depth should only accommodate the largest part to be dipped. Additional depth only increases the volume of the tank and lessens the likelihood of adhesive turnover. Also, the tank bottom should be slanted so that immer-sion depth of the parts and the tank depth both decrease as parts move up and out at an angle. To facilitate adhesive changing and minimize down-time, tanks should be mobile. If parts are to be partially dipped or if the conveyor’s low point is not adjustable, provisions will be needed for raising or lowering the tank. A drip pan behind the dip tank is also recommended. If excess droplets from the parts have not hardened, they may be returned to the tank. However, if the material has solidified, it should be discarded. Other suggestions include:
Chemlok adhesives may be agitated or pumped continuously over indefinite periods without damage. However, over-mixing can cause solvent loss.
Depth of Immersion – As a general rule, avoid immersing parts deeper than absolutely necessary. This minimizes adhesive build-up. For parts that require only partial coating, adjust the conveyor line height or immersion tank level to suit your needs. It’s also important to clean part-hanging hooks prior to use. And when a variety of parts will be processed by the same dipping equipment, various hook sizes may be needed.
Design of Metal Parts – To ensure successful dipping, a metal contour or hole should be designed in the part’s upper body for securing it to a conveyor hook. The part should hang so drainage is toward a point where the adhesive tear will not interfere with the molding process. Air entrapment can be avoided by changing positions on the conveyor hook. Protruding stud heads that have been welded or swaged into flat plates frequently trap air where the weld is not completely filled. If the stud is at a high stress point, the small void can be the first spot of bond failure. Hand touch-up of critical points may be needed to prevent solvent entrapment.
Perforated Metals – When parts with small perforations are dipped, adhesive is frequently trapped in the holes, causing webbing or sagging. You may need to “touch up” these areas with a paint brush. Withdrawing parts slowly from the dip tank helps prevent these problems.
Precautions with Threaded Parts – Soft, rubber caps or thimbles for externally threaded studs, or a cork for tapped holes, are often used to protect threads from adhesive coating. Unfortunately, these protective devices are not always effective. Do not dip if it is important to the function of the part that threads be clean.
Withdrawing Parts From the Adhesive – Removing metal parts slowly from the adhesive is critical to dipping success. If removed too quickly, an excessive amount of adhesive may cling to the part. This excess adhesive drains slowly and unevenly, forming tears, sags and lips on the edges. Collectively, these imperfections reduce aesthetics, prolong drying time and, ultimately, affect the overall molding operation. For optimum results, remove parts slowly and evenly. This allows uniform adhesive drainage, helping eliminate bond defects. A vertical withdrawal rate of 3 feet (91 cm) per minute is usually satisfactory.
Dip/Spin Coating – Dip/spin coating may be used on small parts, but appearances are not as uniform as dipping. Despite reduced aesthetics, this method is satisfactory for many applications, including rubber-encapsulated inserts. When dip/spin coating, place parts in a dip/spin barrel, dip in the appropriate primer, then spin in the drum at a high rpm until excess primer is removed. Coated parts can then be dumped onto a screen or open conveyor to dry at room temperature or in warm, dry, circulating air. The same procedures can be used when applying the adhesive covercoat.
Spray Application – Spray application of adhesives is particularly applicable when coating one side or certain areas of a part. When spraying, however, it is impor¬tant that the adhesive reach the substrate wet. If drying occurs before reaching the metal, adhesion will be poor. Hand-held guns may be used for small runs, while conveyorized or automated units are effective for large production operations. To reduce overspray, electrostatic units can be employed. And for small, intricate parts, an air brush may be used. Regardless of size, properly adjusted equipment ensures delivery of uniform films – without sags and tears. During hand-spray operations, parts are often assembled on racks that incorporate masks wherever needed. If the application requires overall coating, parts can be rotated in front of the spray gun. Chain-on-edge conveyors can be programmed to automatically rotate metals as they pass the guns.
Spray Equipment – Many manufacturers make paint guns that are also suitable for applying Chemlok adhesives. The preferred system includes:
Removal of oil and water is critical to preventing contamination. Therefore, the entire spray system should be easy to dismantle and clean. In instances of low-flow equipment, should settling of diluted adhesive in a flow-restricted area become a problem, it may be necessary to install plumbing which switches to a clean-out solvent every eight hours. When spraying Chemlok adhesives, it is also important to continuously agitate the supply tank. If liquid lines have too small a diameter, for instance where the diameter is smaller than 3/8 inch (9.5 mm), the lines should be short to provide rapid flow rate and prevent dead spots where settling can occur.
Electrostatic Spray Equipment – A number of devices may be used for electrostatic spray applications, including electrostatic and conventional electrostatic air hand guns, and spinning disc and mini-bell electrostatic applicators. (The controls and adjustments on electrostatic and conventional electrostatic guns are similar except for the necessity of a remote power-pack.) When using these applicators, a small amount of Methyl Ethyl Ketone (MEK), or other polar solvent such as diacetone alcohol or cyclohexanone, may be needed to increase covercoat polarity. Slow-evaporating aromatic solvents may also be added to primers to improve the spray’s wrap quality. Do not, however, exceed 15% ketone by volume when diluting a topcoat that will be sprayed over an uncured primer. This eliminates the chance of re-solvating the primer. Because of the high dilution typically used with primers and adhesives, both must be continuously agitated. Also, hose and piping lengths should be minimized, and precautions should be taken against adhesive settling in the lines during extended shut-downs.
Coverage – Estimating coverage of sprayed adhesives is difficult, as the quantity used depends largely upon the amount of overspray. In many cases, it may be as much as 50%. With electrostatic spraying, however, transfer efficiency may be as high as 75%; therefore, a much higher coverage rate can be expected.
Controlling Atomizing Air Pressure – Maintaining atomizing air pressure is important to successful spray application. If the pressure is too high, adhesive droplets may disperse and dry before reaching the metal, leaving a dry, dusty appearance. Threads of material will also be seen floating in the spray booth, otherwise known as “cobwebbing.” You can control the problem by reducing atomization pressure, further dilution or by using a higher boiling solvent.
Controlling Premature Drying – Spray-coated parts dry much more quickly than dipped parts, as partial drying occurs during atomization. To properly wet the metal, the adhesive must be fluid when it reaches the substrate. If multiple guns are used, ensure each is applying a wet coat. Do not apply a dry coat with the first gun then cover it with a wet coat.
Roll Coating – Roll coating may be used to coat cylindrical or flat objects. Shafts and pipes can be coated by holding them momentarily between two rotating felt rolls that have been dipped in adhesive. A mohair fabric paint roller can be used to coat large, flat surfaces. However, short nap rollers are preferred.
Reverse Roll Coating – Reverse roll coating is used to apply Chemlok solvent-based products to coil steel, coil aluminum or coil stainless. If you do not have two coating units that can run in tandem, the primer must be cover-coated at a later time. When reverse roll coating, pump the primer (or adhe¬sive) from a drum into a coating pan. A pick-up roll then transfers the adhesive to an applicator roll that the coil metal passes over at a line speed of 100 to 150 feet (30 to 46 m) per minute. Adjust the primer or adhesive flow rate so it overflows the coating pan into a slanted trough, which then returns the material to the drum. This system ensures constant agitation.
All Chemlok solvent-based adhesives can be dried at room temperature – 30 to 60 minutes at 21°C (70°F) is sufficient. If faster drying is necessary, use a circu-lating air dryer at 66-93°C (150-200°F). Be sure there is adequate air circulation, though, because the fastest drying occurs when the solvent is removed and begins diffusing through the surface. Air may be recirculated, provided there is enough exhaust to prevent excessive solvent build-up. With closed systems, care must be taken to prevent explosive solvent build-ups. For this reason, conveyorized dryers with open ends and crosswise air circulation are most often used. Gas-fired ovens may also be used if they are designed properly. It’s also important to purge solvent vapors and unburned gas before restarting gas ovens. Do not operate ovens over 110°C (230°F).
Handling Coated Parts – Coated areas that will receive high levels of stress should be protected or retouched if damaged. Removing adhesive from these areas may cause premature bond failure. Both clean metal parts and coated materials should be kept free of contamination. Because fingerprints can adversely affect adhesion, gloves are highly recommended. Thin, white, cotton gloves are satisfactory, as they show soil easily, are economical enough to be discarded when necessary, and are thin and porous enough to be comfortable.
Coated Parts Layover Stability – Mold as soon as possible, but store all coated parts properly to ensure maximum layover. Typically, this entails sealing adhesive-treated metals in a clean plastic container and storing the package in a cardboard box. These precautions ensure parts are not exposed to UV light, and are protected from airborne contaminates.
Temperature variations encountered during shipping and storage typically do not affect the performance of Chemlok solvent-based primers and adhesives. However, freezing temperatures may increase viscosity, and some products may gel. All products should be warmed to room temperature before using. Refer to product literature for additional information. Summer storage and shipping temperatures, on the other hand, may exceed safe limits for Chemlok products. Shipping and storage temperatures of 21-27°C (70-80°F) to are recommended, and temperatures greater than 38°C (100°F) should be avoided. Also, avoid storing Chemlok products near heating units and in upper racks of non-air conditioned warehouses. Cool and well-ventilated storage areas are ideal and should be used whenever possible. Special handling and storage precautions, when necessary, will be clearly marked on drums.
One of the most important steps in the manufacturing process is molding. During this phase, the adhesive-coated metals and elastomer are placed in the mold cavity, and under proper conditions of time, temperature and pressure the bonded assembly is formed. Controlling each step in the molding process is critical to bond success. Major variations in any step will cause bond failures. Minor alterations, though not detrimental individually, can collectively result in poor or marginal adhesion and above-average scrap rates. For ideal bonding, maintain maximum mold pressure with minimum elastomer viscosity. This pressure/viscosity ratio, typically obtained with the specified time and temperature conditions, ensures peak wetting at the adhesive-elastomer interface. It also optimizes physical properties of the elastomer being cured. Other considerations include:
Following part bonding, additional treatments are usually required. However, exercise caution throughout the process, especially during the following situations:
Proper handling of Chemlok adhesives is essential for safe and effective application. Although many of the safety concerns can be avoided by using aqueous Chemlok systems, we recommend these procedures be followed when using any Chemlok product:
As an extension of our product development efforts, LORD Corporation has invested in an aqueous adhesives applications laboratory in Erie, PA. By simulating customers’ applications, we can provide detailed technical support and more thoroughly evaluate optimum application characteristics of new products. Up to 1,000 pieces can be coated on the current equipment, which can support the following processes:
For more information, please contact us for assistance.