Rubber Bonding | Rubber Metal Bonding

Rubber Bonding To Metal

 

Production of high-quality bonded parts begins with two choices: the elastomer and the adhesive system.

 

1. Elastomer- The first choice is the elastomer. The gumstock type and the details of its formulation will be predicated by the intended function of the bonded assembly. The rubber for a highly engineered automobile engine mount will be selected for its dynamic performance in controlling vibrations and for its ability to endure under-the-hood operating conditions. Conversely, the elastomer for an engine seal must provide superb resistance to attack by engine fluids.

 

2. Adhesive System- The second choice is the adhesive system. The adhesive system must provide an excellent bond under the specified vulcanization conditions, as well as maintain its bond under service conditions.

 

Elastomers

Natural rubber and many synthetic elastomers make up the range of rubber polymers that are available for fabrication. Factors to consider when selecting the elastomer are performance requirements of the part, ease of mixing, processing and molding.

The largest percentage of vulcanization bonded assemblies makes use of:

 

• Natural rubber (NR)
• Styrene-butadiene copolymers (SBR)
• Polychloroprene (CR)
• Acrylonitrile-butadiene copolymers (NBR)

Other commonly used synthetic elastomers include:

• Butyl rubber (IIR)
• Isoprene, synthetic (IR)
• Polybutadiene (BR)
• Chlorosulfonated polyethylene (CSM)
• Polyacrylate (ACM)
• Ethylene-acrylate ester types (AEM)
• Various castable polyurethanes (AU or EU)

 

High and ultra-high performance elastomers are specified where durability and extreme service conditions are mandated. These include various fluoroelastomer (FKM) and silicone (MQ) types, and hydrogenated NBR (HNBR).

Part designers are beginning to use melt-processable or thermoplastic elastomers for assemblies whose main function is cushioning or shock control. These elastomers include various polyolefins (TPO), styrene-butadiene block copolymers, and thermoplastic polyurethanes. These materials are atypical for bonded assemblies as they do not require vulcanization, but they are easy to process, and waste can be recycled. End-uses generally require service at ambient temperatures.

 

Many of the above mentioned elastomers have features which satisfy specific end-use requirements: oil and organic fluid resistance, heat resistance, resistance to chemical attack, high strength, superior dynamic properties, and/or ease of processing.

 

Compounding Effects

Data generated by LORD technical service laboratories, combined with customer input, provides the information needed for understanding compounding variables and bonding. These formulation guidelines pertain mainly to the non-polar diene elastomers: EPDM, IIR, and NR, and to a lesser extent, the easier to bond and more polar types, such as CR and NBR.

The following compounding ingredients, cure system, fillers, extender oils/plasticizers, and antidegradants all affect “bondability” to varying degrees. The effects of these ingredients are listed below:

 

• Sulfur Levels – The amount of sulfur in the compound has a significant role: sulfur levels of one p.h.r. or higher have a favorable effect on bondability. Little or no sulfur results in a compound that is more difficult to bond.
• Accelerators – Of the more commonly used accelerators, MBT generally allows good bondability. ZDMC and the ultra-accelerators such as TMTD detract from bond-ability, particularly in “EV” or “semi-EV” cure systems. The prevulcanization inhibitor (PVI) is often added to fast-vulcanizing stocks to increase processing safety. However, when using ultra-accelerators. High levels of PVI in NR formulations are detrimental to bonding. Amounts of PVI below 0.15 p.h.r. usually allow satisfactory bonding.
• Fillers – The type and amount of filler is critical. Compounds with 40 to 80 p.h.r. of carbon black are easier to bond than those with lower black levels. Non-black fillers, such as clays and silicas, also facilitate bonding.
• Waxes and Oils – Waxy or oily compounding ingredients that migrate to the vulcanizing elastomer surface cause bonding difficulties. These include low molecular-weight polyolefin auxiliaries, (i.e., low-melting polyethylene and polypropylene processing aids/lubricants), aromatic oils and fatty acid esters (i.e., ricinoleates). Naphthenic or paraffinic oils are less problematic.
• Phthalate Ester Plasticizers – Although phthalate esters such as dioctyl phthalate are often recommended for maintaining the mechanical properties of polyolefinic elastomers (EPDM and IIR) in low-temperature, end-use applications, they are detrimental for bonding. Using phthalate esters can compromise the bondability of NBR stocks. However, incorporating high surface area, inorganic fillers, such as silicas, can sometimes neutralize the negative effects of phthalate ester plasticizers.
• Anti-ozonants – High levels of anti-ozonants and certain antioxidants, particularly the p-phenylene diamine type, may detract from bondability.
• Non-diene Elastomers – Elastomers not cured with sulfur and accelerators are easier to bond through inclusion of high surface area fillers. They become more difficult to bond when compounded with certain oils, plasticizers and waxes.

 

Elastomer Blends

Blends of two or more gumstocks (e.g., NR-SBR mixtures, NBR mill-mixed with IR) are chosen so the most desirable features or properties of each component are available. Blends are also selected in an effort to improve raw material economics, without compromising finished part quality.

Elastomer blends are almost always heterophase systems, i.e., dispersions of one type of elastomer in a continuum or matrix of the other. This heterogeneity is because most elastomer pairs are not mutually soluble. Blending results in less-than-uniform distribution of the compounding ingredients, which often causes one of the elastomers to be preferentially vulcanized by the sulfur and accelerators.

The overall effects of elastomer blending can impact bondability and adhesive selection. For example, blends of NBR and NR will be more difficult to bond than compounds comprised entirely of nitrile elastomer. 

 

Additional Considerations

The finer points of adhesive selection include considerations regarding the design of the part, the molding method and the compound formulation.

 

• Part Design – The design or geometry of the assembly will influence bonding and how well that part will withstand service environments. Fluid engine mounts or bushings (i.e., those with contained fluid) may place atypical demands on the environmental resistance of the cured adhesive. If the elastomer-metal interface is exposed to a confined fluid such as hot glycol/water mixture, the adhesive system will need to withstand this particular service exposure.
• Molding Method – The molding method will affect the tendency for undesirable wiping or sweeping of the adhesive. This phenomenon sometimes results when a molten elastomer compound moves across the adhesive-coated metal part surfaces prior to vulcanization. Under these conditions, some adhesives can be swept away from the interfaces where they are needed. 
• Prebaking – Prebake tolerance is the adhesive’s ability to withstand high-temperature exposure before it contacts the vulcanizing elastomer. Bonding is dependent on chemical reactions that occur at elevated temperatures between the adhesive and the vulcanizing elastomer compound (i.e., across the adhesive-elastomer interface). If chemical reactions begin in the adhesive before elastomer contact, a significant amount of the adhesive’s bonding capability can be lost. Reaction of key adhesive ingredients from the adhesive-coated metal surface can cause the adhesive to lose some of its bonding activity. Reaction may result in migration of highly reactive species to the compound surface. Pre-reaction of key ingredients can then occur at the outer layer of the elastomer, before adhesive elastomer contact.

 

Bonding Process

There are four stages to the bonding process:

1. Substrate Preparation
2. Primer and Adhesive Application
3. Elastomer Preparation
4. Molding, Curing, and Finishing

Rubber Bonding | Rubber Metal Bonding

Supplier	:	Rugaval Rubber Sdn Bhd
Email	:	rugavalrubber@gmail.com
Phone	:	60351918961
Fax	:	60351915961
Location	:	Selangor, Malaysia

Send us your enquiry if you have questions or comments about our products and services.