The Adhesive Selection Module

RATIONALE

Probably one of the most daunting areas to consider when using and designing with adhesives is the selection of the most suitable adhesive for the job. There are over 18 different generic types of adhesives to choose from of which there are numerous sub-types and hybrids (please refer to Adhesives - an overview for further information). When this is then coupled with the fact that there are thousands of commercial grades of adhesives to choose from and hundreds of suppliers to contact the task is enormous.

With this in mind we have set about to develop a module that enables the user to make an informed choice as to the most likely generic adhesive types that could be used for a particular application.

For those of you who do not require any further introduction to this area please feel free to go directly to the module by clicking HERE.

MODULE OVERVIEW

This module is built on the process of de-selection from an initial list of all adhesives under consideration. This first iteration considers a total of eight of the most common adhesives types:

• Toughened Acrylic
• Anaerobic Acrylic
• Cyanoacrylate
• One Part Epoxy
• Two Part Epoxy
• Hot Melt
• Polyurethane
• Polyvinyl Acetate
• Silicone Rubber

The module is designed to be expandable so this initial list can be expanded to include not only other generic adhesive types but specific commercial grades should the data be available. In theory therefore, the list could include every adhesive in existence.

The selection criteria are therefore based upon how each adhesive scores through a number of questions or performance limits. At present this has been split into four pages covering the areas of:

Material Information - this looks at the substrates/adherends to be bonded and enables the user to select a combination of two materials taking into account the possible fact that the surface may differ from the bulk material. Three levels of selection accuracy is offered ranging from most suitable to possibly suitable. The selection is based upon knowledge of preferred substrates for each particular adhesive type. It is recognised that as each adhesive family can be very broad in terms of chemical and physical properties there will inevitably be exceptions to these selection criteria. This limitation could easily be addressed should specific adhesive types be included into the module.

Joint and Loading Conditions - this area considers SHEAR loading only for both the internal loading conditions i.e. mass of unsupported adherend (e.g. a structure stuck to a vertical surface) and external loads. The loads are combined in a simple additive fashion. Complex load combinations are not addressed at this time. However consideration is made of the potential effect of creep and impact loading on the adhesives under consideration. For this version a simple screening value of 10MPa IN SHEAR is applied in each case. It is accepted that this is a very crude approach but at least it does offer some guidance as to what adhesives are susceptible to such loads. It is envisaged that the user in subsequent versions of this software could input some type of load level.

Operating Environment - some simple questions are asked to ascertain operating temperature ranges that the joint will experience and also whether the joint will see a high humidity environment. The filters for this selection process are relatively simple but could be more complex in future versions.

Manufacturing Information - the final selection of a suitable type of adhesive my also depend upon a range of manufacturing criteria, the main ones relating to cure rates and H&S issues. As for the earlier pages it is envisaged that more detail could be included here such as specific types of cure mechanism, dispensing needs etc.

At the end of each page, the outcome of the search is displayed in terms of those adhesives that have passed and those that have failed. To aid the user in understanding why an adhesive has been rejected, the key failure question is provided, enabling the user to adjust their input accordingly. This is especially relevant in the latter stages of the selector where the effect of cure rate on handling strength etc may not be fully appreciated. It also enables the user to extend or reduce the range of possible adhesives.

Finally the module finishes with a summary of the adhesives that fit the initial selection criteria and details of the options selected. In addition links are provided to give help with adhesive types and surface preparation.

This module is the first iteration of what is planned to be a useful selection tool for adhesive users. It is designed to be both expandable and versatile and could include a much wider range of both adhesives and adherends. It is anticipated that subsequent versions of this module will be developed as and when sufficient time and resource become available.

It must be stressed however that this selector is extremely generic in nature and there undoubtedly will be exceptions to the results that are generated. Should you wish to make further comment on this or any other module in the toolkit please feel free to contact us at adhesivestoolkit@twi.co.uk or via the forum groups on this site.