Separable blade agitator assembly and disassembly method

• US 4,314,396 A
• Filed: 10/19/1979
• Issued: 02/09/1982
• Est. Priority Date: 03/05/1979
• Status: Expired due to Term

• Current Assignee: Pfaudler, Inc. (GMM Pfaudler Ltd.)
• Original Assignee: Sybron Corporation (Envista Holdings Corporation)
• Inventors: Nunlist, Erwin J., Harrison, Edward S., Coleman, Howard G.
• Primary Examiner(s): Crane, Daniel C.
• Application Number:
  US06/088,972
• Time in Patent Office: 844 Days
• Field of Search: 29/156.8 R, 29/252, 29/447, 403/273, 403/28, 403/30, 416/241 R, 366/343, 366/344, 366/349, 366/143, 366/144, 366/147, 366/326
• US Class Current: 29/889
• CPC Class Codes: B01F 27/071 Fixing of the stirrer to the shaft
• CPC Class Codes: B01J 19/0066 Stirrers mixing per se B01F
• CPC Class Codes: B01J 19/02 Apparatus characterised by being constructed of material selected for its chemically-resistant properties
• CPC Class Codes: B01J 2219/0209 of glass
• CPC Class Codes: B23P 11/025 by using heat or cold
• CPC Class Codes: B23P 6/00 Restoring or reconditioning objects straightening or restoring form of sheet metal, metal rods, metal tubes, metal profiles, or specific articles made therefrom B21D1/00, B21D3/00; repairing defective or damaged objects by casting techniques B22D19/10
• CPC Class Codes: F16D 1/0858 due to the elasticity of the hub (including shrink fits)
• CPC Class Codes: Y10T 29/49316 Impeller making
• CPC Class Codes: Y10T 29/49865 by temperature differential [e.g., shrink fit]
• CPC Class Codes: Y10T 403/48 Shrunk fit

Abstract

A separable blade agitator has a glass coated drive shaft and a glass coated impeller interference fitted to the end of the shaft in a gasketless, glass surface to glass surface joint. The interference fitting of the impeller to the shaft is accomplished by super cooling the end of the shaft with nitrogen or the like so that it can be inserted into a glass coated bore in the impeller.

Claims

1. A method of replacing, in situ within a vessel, the separable impeller of a separable blade agitator comprising the steps of:

a. providing a vessel with a separable blade agitator suspended therein, the agitator having a separable impeller portion fixed to the lower end of a vertically oriented hollow drive shaft, said drive shaft having its lower end closed and its outer surface exposed to the contents of the vessel including said lower end provided with a glass coating, said separable impeller having a hub with a bore therethrough, the hub surface defining the I.D. of said bore also being provided with a glass coating wherein the glass coated lower end of said drive shaft extends through said glass coated bore to join said separable impeller and shaft in an interference fitted, gasketless, glass surface-to-glass surface connection;

b. introducing a cooling fluid into said drive shaft adjacent said lower end to cool shrink the O.D. thereof to loosen the interference fit between said glass coated lower end and said glass coated bore;

c. lowering said impeller to remove the same from said shaft;

d. wrapping the glass coated lower end of said shaft with a removable, protective wrap immediately after the removal of said impeller;

e. locating a replacement impeller below said shaft, said replacement impeller having a bore therethrough axially aligned with said shaft, the surface of said impeller defining the I.D. of said bore being glass coated and sized to provide an interference fit about 0.0025 to 0.0075 inches per inch of diameter with said shaft O.D. when said shaft and impeller have equalized in temperature;

f. removing the wrap from the lower end of said shaft;

g. raising said replacement impeller until the lower end of said shaft passes through said bore; and

h. terminating the introduction of cooling fluid and supporting said replacement impeller in said raised position until said lower end and said impeller bore have equalized in temperature to provide a gasketless, glass surface-to-glass surface interference fitted connection.

2. A method of releasably assembling an impeller having a glass lined bore to a closed end of a hollow glass coated drive shaft in order to provide a gasketless, glass surface-to-glass surface releasable connection therebetween comprising the steps of:

a. providing a hollow glass coated drive shaft having a closed end;

b. sizing the outside diameter of said glass coated shaft end and the inside diameter of said glass lined bore to provide an interference fit therebetween of about 0.00025 to 0.00075 inches per inch of diameter, the amount of the interference being selected within a range which is

i. sufficiently great enough to transmit a desired torque from said drive shaft to said impeller when said shaft and impeller are equalized in temperature and

ii. sufficiently small enough to free said shaft from said bore when said shaft and impeller are at a predetermined differential temperature;

c. cooling said shaft end internally of said shaft to produce said differential temperature and shrink the outside diameter of said shaft end by an amount sufficient to permit said shaft end to pass through said bore;

d. moving said impeller relative to said shaft end until said shaft end is located within said bore; and

e. equalizing the temperature said shaft end and impeller so that the outside diameter of said glass coated shaft end expands into an interference fit engagement with said glass lined bore.

3. A method of releasably joining an impeller to an agitator drive shaft in situ within a reactor vessel comprising the steps of:

a. providing a hollow elongated drive shaft and suspending it within the vessel so that its upper end is fixed to drive means without said vessel, the lower end of said shaft being closed and the outer surface of said shaft exposed to the contents of the vessel being provided with a glass coating;

b. carrying into said vessel an impeller having a hub with a bore therethrough, the entire surface of said impeller including the surface defining the I.D. of said bore being glass coated, the I.D. of said bore and the O.D. of said shaft lower end being sized to provide an interference fit therebetween of about 0.00025 to 0.00075 inches per inch of diameter when said shaft end and impeller are at the same temperature;

c. creating a temperature differential between said lower end and impeller hub by introducing a cooling fluid into said shaft at a point outside of the vessel and directing said fluid within and through said shaft from said point to said lower end for cooling said lower end from within and shrinking the O.D. thereof by an amount sufficient to permit the entry of said lower end into said glass coated hub bore;

d. locating said impeller beneath said shaft lower end and thereafter lifting said impeller to a raised position to locate said cooled shaft end within said hub bore; and

e. terminating the introduction of cooling fluid to said shaft lower end and supporting said impeller in said raised position until the temperature of said shaft end has risen by an amount sufficient to expand the O.D. thereof into an interference fitted, glass surface-to-glass surface connection with the I.D. of said bore.