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DESIGN OF A FLUIDISING (FLUIDIZING) TANK (best viewed on 800 x 600 screen)

Tanks should be at least 150mm larger in each direction than the dimensions of the largest item to be coated. This allows for some movement of the item, which is required to avoid pinholes or voids. The exact dimesions must be decided on the basis of the shape of the item and amount of movement required to ensure a pinhole-free coating.

The tank is designed as such:

Text Box: Reinforcing bars

The reinforcing bars must be designed to prevent bowing of the filter media.

For tanks designed to hold up to 1 tonne of powder:-

The reinforcing bars should be 30-50mm bar by 0.5 - 1.0mm square section. If the edges can be rounded off this will help to prevent big bubbles.
The mesh should be made of wire mesh with a minimum diameter of 3mm with 2.5 to 3 cm square holes.

Larger tanks will require greater reinforcement, and perhaps thicker wire mesh. The exact requirements will depend on the dimensions of the tank.

The filter paper should be chosen to give a pressure difference ratio between the plenum chamber and the bottom of the powder tank. P₂ = 3 : P₁ = 1.

In practice for tanks up to 1 tonne of powder, 4 to 6 sheets of filter paper will do this. Plascoat paper has a "grammage" of 280g/M² and an air resistance of 3000Pa. The paper can be obtained from Gravatom Engineering Systems Ltd., Clayland Road, Bishops Waltham, Hampshire SO32 1BH, UK. Tel: +44 (0) 1489 896 010, fax: +44 (0) 1489 894 382.

The Blower required will need to be able to deliver both the pressure and the air flow calculated using the worksheet below. The blower must be fitted with a dust filter at the air inlet to prevent the fluid bed diffuser from becoming blocked with air-borne dust particles.

Alternative filter Mediums

10 to 15 sheets of canvas (cotton sailcloth) with a grammage of 330g/m^2.The larger number of sheets is required because this sort of canvas has less air resistance. This can be obtained from Deeptron Ltd., Sevenoaks House, Portsmouth Road, Ripley, Surrey, GU23 6EJ, UK. Tel: +44 (0) 1483 224 764, fax: +44 (0) 1483 211 958.

Another alternative is a single sheet of 'Fluitex'. The grade will depend on the powder in the tank. 'Fluitex Airslide' fabrics are produced by Muhlen and Sohn, PO Box 1165, D-89130 Blaustein, Germany. Tel: +49 (0) 7304 801 00, fax: +49 (0) 7304 801 23.

BLOWER REQUIREMENTS FOR FLUID BED POWDERS

STANDARD 550 BOX CONTAINING PPA 571

AIRFLOW REQUIREMENT = 80 M³/Hr PER M² SURFACE AREA OF BED

PRESSURE REQUIRED = 2 to 2.5 x HEIGHT x BULK DENSITY x 100 mbar

Example:Standard 550 Fluidising tank

BED WIDTH	LENGTH	AREA	AIR FLOW REQUIRED
Metres	Metres	m²	m³/hr	Ft³/Min
1.67	0.91	1.52	121.58	71.55

POWDER HEIGHT	POWDER TYPE	BULK DENSITY	PRESSURE REQUIRED
Metres		g/cc = kg/L	mbar	ins water gauge
0.84	PPA/LDPE	0.36	75.6	30.35

Fill in the blue cells marked and then click anywhere on the page to calculate your blower requirements

Insert bed width	metres	Insert bed length		metres
Insert bed height	metres	Insert powder bulk density		g/cc

Select powder grade
PPA 571	PPA 691 for battery boxes		Other grades

Area in m²=		Air flow requirement
			m³/hr
			ft³/min
		Pressure requirement
			mbar
			ins water gauge

Volume of powder required assuming full un-fluidised tank =			m³
Weight of powder required assuming full un-fluidised tank =			kgs

Plascoat Systems Ltd.

Trading Estate,

Farnham, Surrey

GU9 9NY, UK

Tel: +44 (0) 1252 733777, Fax: +44 (0) 1252 721250

email: sales@plascoat.com