INDUSTRIAL A N D ENGINEERING CHEMISTRY
October, 1927
1151
Soft-Rubber Filter-Press Plates and Frames' By H. E. Fritz and J. H. Clark, Jr. THEB. F. GOODRICH RUBBERCOMPANY, AKRON,OHIO, A N D T.SWRIVER & eo., HARRISON, N. J.
M
ANY attempts have been made to construct those parts of a filter press with which the durry to be filtered comes in contact from a material suitable for handling very corrosive substances. At present the most outstanding material for this service is a standard filter-press skeleton filled with wooden plates and frames. While wooden plates and frames have proved comparatively satisfactory in many installations, their disadvantages are well known to all users. The high cost of maintenance in some cases has driven operators and engineers to other types of filtration equipment which have not proved satisfactory. Requirements of Filter Press for Handling Corrosive Materials The requirements of a filter press for handling corrosive materials, with reference to the material for plates and frames therein, are briefly as follows: (1) It must not be disintegrated by corrosives. ( 2 ) It must not be fragile. (3) It should be impervious t o materials handled, b u t not heavy or cumbersome. (4) It must have sufficient tensile strength to withstand the press-closing pressure and operating pressure. ( 5 ) It must have sufficient life t o warrant the cost of installation. (6) Upkeep and maintenance should be low. (7) It should not require much attention during periods of inactivity.
Advantages of Rubber for This Purpose Reviewing the field of corrosives and materials resistant to them, one finds that rubber is the material best suited for this purpoie. Rubber, however, will not meet all the service requirements involved in all corrosive filtration problems, but it has the greatest spread of all known materials of construction. Temperature is one of its limiting factors. Common interpretation of rubber may mean one of a variety of compounds ranging from a bone-hard product to materials such as rubber bands. The harder yarieties of rubber, while having greater resistance to corrosives, are subject to cold flow and to breakage from rough handling, whereas the softer stocks have not the rigidity to be satisfactory for sewice as plates and frames. The intermediate stocks, which might be called semi-hard, are the best suited for use as filter-press plates and frames. Design of Plates and Frames After a series of experiments in which a variety of rubber compounds were tested under conditions resembling those prevailing in actual filtering operations, a certain stock was chosen and full-sized plates and frames made up for the purpose of solving the engineering problems involved in the molding operation. These plates and frames have been designed as closely as possible in accordance wTith standard wooden plates and frames, in respect to width of joint surface, design of drainage surface, location of eyes and ports, etc. Any changes made in no way affect the general operating conditions or filtration efficiencies. These test plates and frames were operated under pressures up to 65 pounds per square inch and showed very little distortion. The soft contacting areas between the plates Received August 13, 1927.
and frames made a perfect seal, SO that no leakage occurred. They were used in a standard filter-press skeleton designed for wooden plates and frames. Rubber-lined pipes through the press head, rubber-lined plates against the press head and follower, and rubber-lined valves to control the flow were used. I n this way the material being filtered comes in contact with rubber only. It is possible to arrange the ports in these plates and frames for washing or non-washing and open or closed delivery. The thickness of the frames may be varied if so desired. Materials Handled The accompanying table lists some of the chemicals and the conditions under which the press plates and frames will operate successfully. For materials not listed the manufacturer should be consulted. CONCENTRATION BY WEIGHT Pev cent
MAXIMUM TEMPERATURES
F.
LIQUID ACIDS
Hydrobromic Hydrofluoric Hydrofluosilicic Muriatic (hydrochloric) Phosphoric Sulfuric Carbonic Pyroligneous Sulfurous
Any concentration Any concentration Any concentration Any concentration u p to 75 Up to 50 Any concentration Any concentration Any concentration
100 150 150 150 125 150 150 150 150
SOLUTIONS
Caustic soda and potash Calcium chloride Calcium hypochlorite Copper sulfate Sodium acid sulfate Milk of lime Zinc chloride Aqua ammonia Ferrous sulfate Sodium chloride Zinc sulfate Aluminum sulfate (alum)
Up to saturation Up to saturation
U p to saturation
Up t o saturation Up to saturation Any concentration 50 Any concentration Saturation Saturation Saturation Saturation
150 1.50 100 150 150
125 100 125 150
150 150 150
O R G A N I C LIQUIDS
Acetone Ethyl alcohol Methanol
Any concentration Any concentration
130 140 150
Other Rubber-Lined Parts The method of feeding a press under these conditions also presents some difficulties; a satisfactory solution is offered through use of rubber-lined blow cases in which the air is also used for agitation, diaphragm pumps with rubberlined liquid ends and rubber-lined pipe and valves. Advantages of Rubber over Other Materials The advantages of rubber press plates and frames over other corrosion-resisting materials of construction are: (1) (2) (3) (4) (5)
Rubber is tough, rigid, and non-breakable. It has long life and replacement is infrequent. It has low density and is light and easy to handle. A perfect seal is obtained between plates and frames. It is inexpensive.
Conclusion
As in most all other new developments, misapplication will probably be the greatest drawback to the progress of this development, and in all cases where there is no reliable past service record as regards rubber in the service in question a reliable manufacturer should be consulted and preliminary tests made.
