38 THE DISTRIBUTOR’S LINK Anthony Di Maio Anthony E. Di Maio attended Wentworth Institute and Northeastern University. In 1962 he started working with Blind Fasteners as Vice-President of Engineering & Manufacturing for two blind rivet manufacturers. He has been Chairman of the Technical Committee of the Industrial Fasteners Institute (IFI) and is still involved in the writing of IFI specifications. In 1991, he started ADM Engineering and is working with Fastener Manufacturers developing new fasteners and special machinery. He can be reached at ADM Engineering, 6 Hermon Ave., Haverhill, MA 01832; phone and fax 978-521-0277; e-mail: tdimaio@verizon.net. THE CHARACTERISTICS OF BLIND RIVETS The blind rivet has features and characteristics that no other fastener has. A blind rivet is a two-part fastener consisting of a rivet body and mandrel. Rivet Body The rivet body upsets when the mandrel is pulled and it is the rivet body that fastens the work pieces together. Mandrel Head Upset Mandrel The mandrel is the setting force of the rivet body. When the mandrel is pulled the mandrel head will push against the barrel of the rivet body and enter the rivet body and expand and upset the barrel of the rivet body. The mandrel will continue to be pulled by the setting tool until the mandrel head upsets the rivet body against the work pieces, until the mandrel head meets a resistance then the mandrel will break. The mandrel will break at a pre-determined position of the mandrel and at a pre-determined tensile strength. Breakpoint PROPERLY SET RIVET Workpiece The pre-determined tensile break-load strength is listed in the Industrial Fasteners Institute (IFI) standards book under IFI specifications IFI-114. IFI lists the minimum and the maximum mandrel tensile strengths for all diameter mandrels and all alloys. Example: Grade #30 in IFI-114 is for blind rivets having a steel rivet body and steel mandrel. Let us look at the 1/8 diameter, steel/steel combination, mandrel diameter of 0.076 (nominal) alloy carbon steel. Minimum mandrel tensile is 600lbs and maximum of 800lbs. Therefore, for 1/8 diameter blind rivets made with a steel body and steel mandrel the mandrel tensile will be between 600 and 800lbs if the blind rivet is manufactured to IFI specifications. The minimum and maximum tensile strengths values are critical to the performance of the blind rivet. Minimum mandrel tensile ensures the user that the mandrel will have the proper tensile strength to set the blind rivet and fasten the work pieces securely together. The mandrel tensile strength is the clamping force of the blind rivet. If mandrels have a tensile strength below the minimum values of the IFI specifications, the work pieces will not be properly fastened together. When this occurs, it is called “premature mandrel breaking” and the blind rivet application is not correct. Very surprising to me is that ISO does not list any minimum mandrel tensile specifications in their blind rivet specifications. This is a very harmful and serious omission to their blind rivet specifications. Low mandrel tensile strengths can be caused by incorrect tooling that makes the mandrel and improper heat treatment of certain aluminum mandrels. If a user is setting blind rivets manufactured to ISO standards and the blind rivet mandrels have a “premature mandrel break” the user has no recourse with the manufacturer because ISO blind rivet specifications have no minimum mandrel tensile requirements in their blind rivet specifications. Maximum tensile requirement is also critical. If a blind rivet mandrel has a tensile strength above the IFI maximum specifications, the mandrel head, when the blind rivet is set could enter the rivet body barrel and travel through the work piece. When the mandrel does finally break, you will see mandrel material protruding outside the flange of the blind rivet body. please turn to page 147
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