TM 1006:2010

Determination of the sagging behaviour of a polyurethane foam and the maximal joint width

Final version: 06/10/2010

Background and purpose

One of the most important physical properties of a One Component Foam (OCF) is the ability to set itself in a cavity and fill the joint. This property is dependent upon the temperature of the canister, the environment and the dimensions of the joint. It is particularly important for vertical joints.
This method has two objectives:
a) To judge the sagging behaviour of an OCF for given conditions: canister, ambient temperature and the joint width.
b) To define the maximum joint width for the usability of the OCF at given temperatures to ensure the foam does not slide down (sag).

Apparatus and material

• Several pairs of wooden boards (or alternative materials such as carton or wood wrapped with paper) with dimensions of 900 mm x 90 mm x 10 mm (length x width x thickness), to build the flanks of the test joint.
• Multiple pairs of spacers with different thicknesses (typically from 30 mm upwards in 5 mm steps).
• Screw clamps
• Climate chamber

Procedure

Preparation

a) Store the test canister for at least 24 hours at the desired canister test temperature, e.g. 5 °C.
b) In order to avoid overfilling and overexpansion of the foam, it is helpful to draw two orientation lines on the inner sides of both boards. The lines should be placed along the long side of the board, each 2 cm from the long edges.
c) Sagging behaviour at given joint width: Build a joint with the desired width using the boards and spacers (see Pic. 2).

Evaluation of maximal joint width: Build several joints beginning  with the smallest width (typically 30 mm) up to the  largest   anticipated width in suitable 5 or 10 mm steps

d) Acclimatize the joints for at least 24 hours in the climate chamber at the selected ambient test temperature e.g. – 10 ºC.

Testing procedure description

e) Shake the canister thoroughly and spray the foam into the joint. Fill the joint from the bottom to the top, leaving the last 5 cm at the top free to avoid bonding with the top surface. Foam without interruption until you reach the top. The amount of foam for filling should be chosen to initially fill the joint to approximately 50 - 60% of its depth (use the orientation lines). The initial filling should be as uniform as possible to ensure that the foam-surface is as straight as possible and allow more precise measurement in subsequent steps. The dispensing speed should be about 50 - 70 g/min for gun-foam and 150 – 200 g/min for straw-foam.  If the flow rates cannot be achieved, lower rates   are acceptable.
f) Store the filled joints at the desired ambient test temperature for a further 24 hours.
g) After this time examine each joint  to judge the behaviour of the foam as follows:
Grade 1 No sagging.
The foam is still equally spread and set in the joint
Grade 2 Slight sagging.
The foam is still set in the joint but shows some sagging towards the bottom (see the F Pic. 4). At the bottom the foam is build not more than ?=3cm above the rest of the foam. Measuring points for building this difference value should be  about 5 cm (d_down) and about 70 cm (d_up) from the bottom of the joint and ? = (d_down – d_up) / 2.
Grade 3 Strong sagging
The foam is not set equally in the joint. It has sagged partly
(i.e. Δ > 3cm) or has flowed/sagged completely out of the joint.

h) Definition of maximal joint width: Find the joint with the greatest width where the foam is judged to be at least Grade 2. The size of this joint is referred to as the maximal acceptable joint width for the foam application at the given conditions.

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