The BK 3 Speed Drying Recorder has been used widely in the coatings industry throughout the world for several decades. A needle carrier holding six hemispherical ended needles travels the length of the six 305 x 25 mm test strips in 6, 12 or 24 hours. Other speeds are available to special order. A time scale on the side cover is graduated to suit the three different travel times.
The BK 6 and BK 10 Recorders have independently operating tracks allowing tests to be made at different start times. Pairs of tracks operate at the same speed, and a wide range of travel times are available. Travel times of 6, 12, 24 and 48 hours are all considered as standard. A time scale on the front cover is graduated to suit the instrument’s drying time ranges. Each pair of tracks has its own individual operating switch.
Stages in the Drying Process Defined as:
The first stage is a pear-shaped impression corresponding to the time taken for evaporation of solvent.
The second stage is the cutting of a continuous track, corresponding to a sol-gel transition.
The third stage is an interrupted track corresponding to the surface-dry time.
A fourth stage is where the needle no longer penetrates the film, corresponding to the final drying time.
A typical white enamel would have a drying time expressed as follows: 1-1/4 —-3-1/2—-4 (hours)
Although all stages recorded are significant it is often sufficient to express a drying time in terms of set-time and hard-dry time, thus: 1-1/4 – 4 (hours). Brass weights, each weighing 5 g, may be used to apply greater pressure on the needles and thus record the through-drying properties of alkyds, varnishes and paints. The 3-SPEED BK DRYING RECORDER will give useful information about the gelation times of many two component surface coating materials and about the properties of such films.
Method of Use
Select the required speed by turning the speed control knob in a clockwise direction and sliding in or pulling out to the required speed. Release knob.
Apply film to the test strips and place them on the Recorder.
Lift the release lever on the back of the needle carrier and slide it to the starting position.
Lower the needles on to the test strips.
Switch on and the needles will now commence the run along the strips. On reaching the end of the travel, the carrier automatically stops. Switch off.
Individual glass strips may be removed from the machine simply by depressing one end at the strip so
that the opposite end tilts clear at the holder.
Determination of Drying Time
The drying time of alkyds, varnishes or paints is determined by adding the requisite drier and thinning to a viscosity at which the material is normally applied. The finish is allowed to stand at room temperature for 24 hours to “mature”. A test strip measuring 12″ x 1″ (which may be of plain or ground glass or of other suitable material) is prepared by casting a film upon it by means of a special applicator which is accurately ground at one end to deposit a wet film thickness of 1.5 mils and 3 mils at the other. The test strips are placed on the table in their holders and the instrument is then operated as indicated below.