BS EN 302-7-2004 pdf download.Adhesives for load-bearing timber structures Test methods Part 7: Determination of the conventional working life.
This part of EN 302 specifies a method for determining the conventional working life for adhesives for load- bearing timber structures, by a viscosity test.
This method is not suitable for determining the conventional working life of a multi-component adhesive whose actual working life is very short.
This document is only intended for obtaining a reliable basis for comparison between adhesives. The method gives results which cannot be applied to the safe manufacture of timber structures without modifications for the influences of factory temperature and relative air humidity.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 923:1998, Adhesives — Terms and definitions
EN ISO 2555:1999, Plastics — Resins in the liquid state or as emulsions or dispersions — Determination of apparent viscosity by the Brook field test method (iSO 2555:1989)
3 Terms and definiflons
For the purposes of this document, the terms and definitions given in EN 923:1998 and the following apply.
3.1
conventional working life
period of time at 20 °C during which an adhesive, prepared for application, increases in apparent viscosity to
25000 mPa s
NOTE The test procedure is that described in this document.
4 Principle
The viscosity of a specified volume of adhesive at 20 °C is monitored using a Brookfield type viscometer, until it reaches 25 000 mPa s.
5 Safety
Persons using this document shall be familiar with normal laboratory practice.
— the viscometer body;
— seven removable, interchangeable spindles, numbered 1 to 7;
— a support which holds the viscometer and moves It into the vertical plane;
— a removable guard stirrup which is not use in this method.
NOTE A RVF model Is suitable for most of the commercial adhesives used fo the gluing of load-bearing timber structures.
6.3 Temperature regulated water bath, capable of maintaining the mixture to be tested at 20 ‘C with an accuracy of± 2 °C.
6.4 Thermometer, graduated to 0,1 ‘C, to measure the temperature of the adhesive being tested.
7 Procedure
7.1 Handle the adhesive components in accordance with the instructions of the manufacturer of the adhesive, Ensure that, at the start of the test, all the components have a temperature of (20 ± 0.5) ‘C. Ensure that during the test, the relative humidity of the air in the testing room remains at (65 ± 5) %.
NOTE It is a common practice to store the components at (20 ±2) C for 1 night before testing
7.2 Set up, calibrate and operate the viscometer in accordance with the Instructions of the instrument manufacturer. Choose a rotational frequency of 20 mm1. Spindles shall be chosen such that the instrument reading is in the range from 20 % to 95 % of the full scale value.
7.3 Prepare a sufficient amount of the glue mix In the beaker (6.1) to fill 213 of its volume, in accordance with the specifications of the manufacturer. Start to record the time at the moment (t0) the component that initiates the reaction is added.
7.4 Gently stir the mixture manually for 5 mm at (20 ± 2) ‘C, In order to allow any exothermic reaction to proceed normally, do not place the beaker in the water bath during this operation and avoid heating the mixture by body heat through the hand.
7.5 Place the beaker in the water bath (6.3) adjusted at (20 ± 2) ‘C for the rest of the procedure. Adjust the water level of the water bath so that it is slightly above that of the adhesive in the beaker (6.1). Keep the beaker uncovered throughout the test.
7.6 Determine the viscosity of the adhesive system at 15 mm intervals from the initial time to. About one minute before each reading, gently stir the sample for 15 s to ensure homogeneity.BS EN 302-7-2004 pdf download.