US3728825A

US3728825A - Cryogenic deflashing apparatus and operating system for same

Info

Publication number: US3728825A
Application number: US00188488A
Authority: US
Inventors: C Barrett
Original assignee: BURDETT OXYGEN CO Inc
Current assignee: BURDETT OXYGEN CO Inc
Priority date: 1971-10-12
Filing date: 1971-10-12
Publication date: 1973-04-24
Anticipated expiration: 1990-04-24

Abstract

An apparatus for removing the molding flash from normally soft or resilient molded parts, such as rubber, which utilizes a nonsymmetrical tumbling barrel for tumbling and mixing the parts to be deflashed. Low temperature fluid is fed into the barrel to cause freezing or embrittlement of the molded parts to a predetermined extent and temperature-responsive speed control is used for rotation of the tumbling barrel to achieve uniform results and improved efficiency in the cost and effectiveness of the deflashing operation. The temperature sensing probe is isolated from the parts being tumbled, but is so located as to more accurately reflect the temperature of the parts, rather than the temperature of the atmosphere in the barrel. The electric motor utilized to drive the tumbling barrel is disposed in the path of exhaust flow of the cryogenic gas so as to be cooled thereby to reduce the heat factor and consequently the power requirements.

Description

Waited States Patent Barrett, Jr. Apr. 24, 1973 v 7 [54} CRYOGENIC DEFLASHHNG 3,528,201 9 1970 Jones ..5l/l64 APPARATUS AND OPERATING SYSTEM FOR SAME Primary ExaminerHar0ld D. Whitehead [75] Inventor: Charles D. Barrett, Jr., Mentor, AUOmeyTISIer and Omstem 10 7] ABSTRACT [73] Assignee: Burdett Oxygen Co. of Cleveland,

Inc. Cleveland, Ohio An apparatus for removing the molding flash from normally soft or resilient molded parts, such as rubber, [22} Filed: Oct. 12, 1971 Appl. No.: 188,488

Related US. Application Data which utilizes a non-symmetrical tumbling barre] for tumbling and mixing theparts to be deflashed. Low temperature fluid is fed into the barrel to cause freezing or embrittlement of the molded parts to a predetermined extent and temperature-responsive speed control is used for rotation of the tumbling barrel to achieve uniform results and improved efficiency in the cost and effectiveness of the deflashing operation. The temperature sensing probe is isolated from the parts being tumbled, but is so located as to more accurately reflect the temperature of the parts, rather than the temperature of the atmosphere in the barrel. The electric motor utilized to drive the tumbling barrel is disposed in the path of exhaust flow of the cryogenic gas so as to be cooled thereby to reduce the heat factor and consequently the power requirements.

3 Claims, 7 Drawing Figures Patented April 24, 1973 5 Sheets-Sheet 2 o o o M o ,/////4// a i m INVENTOR. CHARLES Q B aacT-r JR.

' Armani-:95.

Patented A ril 24, 1973 5 SheetsSheet f5 INVENTOR. Gummy, D. BARRETTJR.

k1 TORNEYS.

Patented A ril 24, 1973 v 2 3,728,825

I 5 Sheets-Sheet 4.

ua-svaeo REVEKSE HPSPEED FORWARD CREE? FORWAQD v CREE? REVERfi D INVENTOR.

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ATTORNE Patented April 24, 1973 5 Sheets-Sheet 5 INVENTOR.

CHAN-E9 .BAKRETTJR Fig? BY ATTORNEYS.

CRYOGENIC DEFLASI-IING APPARATUS AND OPERATING SYSTEM FOR SAME CROSSREFERENCES TO RELATED APPLICATIONS This application is a substitute for my prior filed application Ser. No. 23,875 carrying the same title and now abandoned.

BACKGROUND OF THE INVENTION Molded products, particularly those which are injection or pressure molded, often are produced with flash, a thin section of excess material, which must be removed to provide a finished part. Various techniques, including the use of tumbling barrels, are known to the art for effecting removal of the flash from the parts. In contrast to rigid molded parts of metal or the like where the flash is brittle, the removal of the flash from molded elastomers or the like has always posed a special problem because of the resilient or yielding characteristic of the flash. It is not rigid or sufficiently brittle to respond to the conventional tumbling barrel techniques at ordinary temperatures.

To overcome this problem, a cryogenic technique has been developed for artificially creating brittleness and rigidity in elastomeric flash by a low temperature freezing process utilizing highly compressed or liquified gases or other cryogenic media. In the early stages of this development, carbon dioxide was favored for the cooling medium. More recently, liquid nitrogen has come to the fore for this purpose.

The problem factors involved in such cryogenic tumbling systems are essentially the following:

a. Excessive costs incurred from inefficient use of the cryogenic fluid.

b. The increased time factor involved in the deflashing operation due to the necessity of waiting for adequate freezing of the flash to be achieved.

c. The inability to accurately determine and sense the temperature point at which the flash is sufficiently rigid for effective removal by tumbling, even though the main body of the part is not so frozen and is not required to be.

d. Adequate control means to avoid undesirable embrittlement of the main body of the part.

e. Difficulty in obtaining uniformity of freezing action of the individual parts in the tumbling barrel f. Difficulty in exposing all parts uniformly to the tumbling action.

g. Difficulty in effectively sealing the tumbling barrel against the escape of debris.

The invention is directed to overcoming these problem factors, as well as others, for improved quality and efficiency of operation.

SUMMARY OF THE INVENTION It has been found that the utilization of a two-speed cycle for the freezing and deflashing operation contributes to greatly improved results and the invention is directed in part to this concept.

The invention is also directed to the concept of a non-symmetrical barrel structure for obtaining more uniform exposure of the parts to the freezing and deflashing cycle.

Improvements have also been made in the disposition and location of the temperature sensing probe for greater sensitivity of control and in an improved control system and circuitry for the operating cycle.

Additionally, a closure for the tumbling barrel has been provided which effectively resists deformation resulting from the wide temperature differential between the interior of the tumbling barrel and the exterior of the tumbling barrel during the cryogenic process. This is accomplished by a redesign of the heat transfer characteristics of the closure for the barrel.

A flow pattern for the cryogenic exhaust gases has been provided which effective cools the motor drive mechanism and permits the use of smaller motors and less power input.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a view in front elevation of the cryogenic deflashing apparatus embodying the features of the invention.

FIG. 2 is an enlarged fragmentary cross-sectional view of a portion of the apparatus, taken as indicated on line 22 of FIG. 1.

FIG. 3 is an enlarged fragmentary cross-sectional view of a portion of the apparatus, taken as indicated on line 33 of FIG. 1.

FIG. 4 is an enlarged fragmentary view showing details of construction of the edge portion of the closure or door of the tumbling barrel.

FIG. 5 is a diagrammatic representation of the control circuitry for the various operating cycles of the DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to FIGS. 1, 2 and 3 of the drawings, there is shown a tumbling barrel 10 having a suitable closure or door 1 1 which can be swung open to gain access to the interior of the barrel. The illustrated barrel is provided with six tumbling sides or planes and will be so described hereinafter. However, it will be understood that the number of sides may be more or less than the example described.

The barrel 10 is mounted for rotation about a central horizontally extending axis and is positioned within a safety enclosure 12 to prevent injury or accident, as well as serving to maintain the barrel in an elevated position above ground level for convenience in loading and unloading. The hinged door 13 of the safety enclosure is maintained in closed position during operation of the tumbling barrel and is opened only when access is desired to the barrel. In its closed position, the safety door 13 engages and closes a normally open limit switch 14 which is an element of the control circuit. If the safety door 13 is not fully closed, the limit switch 14 remains open and prevents operation of the deflashing apparatus.

Mounted exteriorly of the safety enclosure 12 is a control panel 15 by means of which the operating conditions for the deflashing apparatus are established and observed. By way of example, the control panel includes a temperature indicating and control device 16, an adjustable cycle timer mechanism 17 with provision for automatic reset, an elapsed time indicator 18 for recording the operative usage of the apparatus, an adjustable speed control 19 for selectively setting the speed of the electric motor which drives the tumbling barrel, and a series of pushbutton operated switches whose functions will be described in more detail by reference to the circuit diagram of FIG. 5. There are nine of such switches shown for the preferred control circuitry which will be described, but it will be understood that if even greater versatility of the control circuit is desired, additional switches might be added. Conversely, if some of the functions performed by the described switches are not necessary in particular production applications of the invention, some of the switches might be eliminated. As shown and described, the nine switches are a power on switch 20, a power off switch 21, an automatic cycle switch 22, a manual cycle switch 23, a cycle reset switch 24, a cycle off switch 25, a creep forward switch 26, a creep reverse switch 27 and a high speed reverse switch 28. The socalled creep switches 26 and 27 are for extremely low speed operation on the order of less than rpm of the tumbling barrel. The adjustable speed control knob 19 would ordinarily be associated only with the high speed control circuit to the motor, as this speed adjustment is the one that would be most frequently used in the operation of the deflashing apparatus. The adjustment of the creep speed, which is rarely needed, could be provided for interiorly of the control panel or, if desired, a creep speed control 29 could be provided on the control panel.

It is also desirable that the control panel include a warning light 30 to give visual indication when the power is on to the apparatus.

Also mounted exteriorly of the safety enclosure 12 is the drive mechanism for rotation of the tumbling barrel which includes an electric motor 31 connected to a gear reducer 32, both of which are suitable supported on a platform-or shelf 33. Either a sprocket and chain drive or a belt drive 34 can be used to transmit rotation from the gear reducer 32 to a hollow shaft 35 which is suitable affixed, as by welding or the like, centrally ofa plate 36. The plate 36 may be a separate turn plate which is secured to an end face on the exterior of the tumbling barrel or, as here shown, it may be the end plate itself of the exterior shell of the tumbling barrel. The shaft 35 is suitable journalled for rotation in a bearing 37 which is secured interiorly of the wall 38 of the safety enclosure 12. The drive unit is completely enclosed in a housing 39 which is provided with one or more screened or louvered openings 40 for the cooling ventilation which will be hereinafter described.

Another hollow shaft 41 is similarly affixed centrally of the opposite end plate 42 of the tumbling barrel and is journalled for rotation in a bearing 43 mounted on the opposite end wall 44 of the safety enclosure. The shaft 41 is coaxial with the shaft 35 and, in combination, these two shafts define a horizontal axis of rotation for the tumbling barrel 10.

The tumbling barrel includes an inner container or receptacle of polygonal cross-section having six tumbling walls or surfaces, one of which is provided by the interior surface of the door 10. Three of such adjacent walls or surfaces, indicated by the

reference characters

45, 46 and 47, are of equal length and disposed-at an angle of 120 to each other. Another wall 48 adjoins the wall 45 at an angle of 120, but is of greater length than the wall 45. The fifth wall 49 intersects the wall 47 at an angle of 120 in convergent relationship to the wall 48 and is equal in length to the wall 48. The sixth tumbling wall is defined by the interior face or surface 50 of the sealing plate 69 which forms a portion of the closure or door 11. The length of the surface or wall 50 is less than that of any of the other five tumbling walls previously described which define the container or inner shell 52.

Spaced outwardly from and surrounding the inner shell 52 is an outer shell 53 which corresponds generally to the configuration of the inner shell. The outer shell is secured, as by welding, to a flange 54 which extends outwardly from the opening 55 which is provided for the door 10 in the inner shell 52. The outer shell includes the previously described end plates 36 and 42 which are spaced outwardly from the

end walls

56 and 57 of the inner shell 52. There is thus provided an air space 58 between the inner and outer shells which is preferably filled with any suitable form of insulating material for cryogenic purposes.

In addition to the previously described securement of the outer shell 53 to the flange 54, it will be understood that additional securing means may be provided between the

shells

52 and 53 in the form of welded studs or spacers or channels or the like which traverse the air space 58 at spaced locations to give rigidity to the tumbling barrel.

A conduit for the liquified or highly compressed fluid, such as nitrogen, extends through the interior of the hollow shaft 41 and traverses the end plate 42 and the end wall 57 so as to communicate with the interior of the inner shell 52. A solenoid-operated valve 60 is provided on the conduit 59 exteriorly of the tumbling barrel for controlling the passage of fluid therethrough from a suitable source of supply (not shown). The conduit 59 may revolve with the tumbling barrel and the shaft 41 by utilization of a suitable swivel joint connection (not shown) or, if desired, it may be free of attachment to the shaft or tumbling barrel and be maintained in a fixed posture. Any suitable form of nozzle or fitting may be provided on the end of the conduit 59 to diffuse or direct the discharged cryogenic medium in a desired discharge pattern into the interior of the tumbling barrel.

A suitable support housing 61 for a thermocouple or temperature-sensing probe 62 extends through the ho]- low drive shaft 35 and through the end plate 36 and the end wall 56 into the interior of the inner shell 52 so as to project the probe 62 downwardly in proximity with the periphery of the inner shell and closely adjacent to the interior face of the end wall 56. An anchor bracket 63 is secured to the support housing 61, exteriorly of the tumbling barrel 10, for maintaining the support housing and its probe 62 in a fixed position during the rotation of the tumbling barrel. Thereby, the probe maintains its downwardly directed location near the bottom of the tumbling barrel, as indicated in FIG. 2 of the drawings, during the rotation of the barrel.

A plurality of spaced vent openings 64 are provided in the end wall 56 in registry with like openings 65 provided in the end plate 36 of the outer shell 53. The

openings

64 and 65 are isolated from the air space 58 between the inner and outer shells by means of hollow spacers or tubes 66 which are welded between the inner and outer shells to interconnect each pair of

openings

64 and 65. These hollow spacers 66 also serve to provide part of the additional securement means between the inner and outer shells, which were previously mentioned.

A partition wall 67 is secured to the interior of the inner shell in parallel spaced relationship to the end wall 56 so as to isolate the temperature sensing probe 62 from physical contact with the parts being processed in the tumbling barrel. The partition wall 67 is perforated by a plurality of minute openings 68 which are small enough to prevent passage of the deflashing debris, but will still permit circulation and flow of the atmosphere within the tumbling barrel.

The interior of the tumbling barrel is cooled by the cryogenic medium to a temperature which may approach approximately 320F., whereas the external room temperature may be on the order of 80F. This produces a temperature gradient of approximately 400F. between the inner and outer faces of the closure or door 11. The closures heretofore used have consisted of hollow box-like metal structures, filled with insulating material, and provided with a compressible gasket for seating the closure against the metal flange surface provided on the tumbling barrel. Due to the magnitude of the temperature gradient involved and the thermal conductivity between the inner and outer faces of such closures, thermal stress and deformation of the closure could not be avoided and proper sealing of the tumbling barrel, if attainable at all, required frequent replacement of the gasket material.

In order to overcome this problem, the closure 11 consists of a metal plate 69 which overlies the flange 54 and provides a metal-to-metal seal therewith when it is clamped into position. This seal is not subject to deterioration or to variations in compressibility, as is the gasket seal heretofore utilized. A hollow box-like shell 70. of thin gauge metal or other suitable material is secured to the exterior face of the door plate 69 by suitable fasteners 71, as indicated. A resilient or compressible insulating gasket 72 is interposed between the undersurface of the peripheral flange 73 of the door shell 70 and the portion of the plate 69 which underlies it. The hollow interior of the shell 70 is filled with suitable insulating material. In this manner, the exterior face of the plate 69 is isolated from metal-to-metal contact with the insulating shell 70 so that there is no appreciable heat transfer between these two thermally conductive elements of the closure 11. To the extent that there is a cryogenic temperature effect on the door plate 69 which results in contraction, such contraction is uniformly dissipated throughout the plate 69 without bowing or deformation of the plate which would otherwise interfere with the metal-to-metal closure seal. The securement between the insulating shell 70 and the plate 69 is such that the plate may contract or expand and shift relatively to the shell 70 without being restrained by any rigid securement between the plate 69 and the insulating shell 70. Inasmuch as the shell 70 does not act as a restraint upon the cryogenic contraction of the sealing plate 69, there is no tendency for the plate to deform. It remains in planar abutment and sealing engagement with the flange 54 of the tumbling barrel. Any suitable means may be provided for securing the closure 11 in place. The means here illustrated are toggle clamps 741 which are secured to the tumbling barrel and adapted to engage one of a pair of spaced rods 75 mounted on the exterior of the insulating shell 70. The ends of the other rod 75 are releasably retained in elongated camming slots 76 provided on marginal portions of the end plates 36 and 42.

Referring more particularly to FIG. 5 of the drawings, the control system and method of operation of the cryogenic deflashing apparatus will now be described. When the power line switches are closed, a transformer 77 is energized and power is supplied from the secondary of the transformer through the normally closed power off" switch 21 to one terminal of the power on switch button 20. The

switches

20 and 21 are interlocked so that the opening of the switch 21 causes the opening of the switch 20. Power is also supplied to one side of the normally open contacts 79 of an electro-magnetic contactor 78.

When the switch button 20 is closed, the contactor 78 is energized to close the contacts 79 and energize the SCR motor control unit 80. A fan 81 for the cooling of the motor control unit is also energized. Additionally, the temperature control unit 16 is energized, the warning light 30 is energized and power is supplied to one side of all the relays and push button controls of the circuit. The molded parts to be deflashed are placed in the tumbling barrel, the closure 1 1 is secured in place to seal the opening 55 and the tumbling barrel is now ready to be operated in any one of several modes of operation which are permitted by the control system. However, it is necessary that the door 13 of the safety enclosure 12 by closed, as the limit switch 14 must be closed before the control circuit is operable.

If the manual cycle switch button 23 is now pressed, the normally open contacts 82 of a relay 83 are closed as are the normally open contacts 84 of a relay 85. The pressing of the manual cycle switch button 23 also closes the circuit to the timer 17 which has previously been set to the selected timing interval desired. The relay 86, having normally open contacts 87, is also energized and causes opening of the normally closed solenoid operated valve 60. The circuit to the relay86 is controlled by the contacts 88 of the temperature control unit 16, which in turn responds to the temperature sensed by the thermocouple probe 62 in the interior of the tumbling barrel. A circuit is established through the adjustable high speed control 19 of the motor control circuit and the tumbling barrel is caused to rotate in one direction at that selected high speed, which for example may be on the order of 40 rpm.

When the temperature of the interior of the tumbling barrel drops to a predetermined value to which the temperature control 16 has been set, the normally closed contact 88 is opened by the temperature control unit 16 to de-energize the relay 86, causing contact 87 to open and de-energize the solenoid valve '60, restoring it to its normally closed position. If the temperature within the barrel should increase beyond the selected range established by the temperature control unit 16,

the contacts 88 would again close to energize the relay 86 to close the contacts 87 and open the valve 60 to permit the cryogenic medium to be discharged through the conduit 59 into the interior of the tumbling barrel.

If for any reason, the operator wishes to inspect the parts within the tumbling-barrel before the deflashing cycle is completed, the cycle can be interrupted by opening the door 13 of the safety enclosure, which causes the opening of the door limit switch 14 to stop the rotation of the tumbling barrel and arrest the timing cycle of the timer 17 at the point of interruption, without any resetting of the timer. Therefore, when the door is again closed and the switch 14 re-establishes the circuit, the timer 17 will continue its timing function from the point of interruption to the completion of the cycle. Similarly, the cycle can be interrupted without causing resetting of the timer 17, by depressing the cycle off switch button 25.

The cycle is completed when the pre-set timing interval of the timer 17 has elapsed. When this occurs, the normally closed contact 89 of the timer is opened to de-energize the clutch 90 of the timer, permitting the timer to reset, and establishing the circuit for the next cycle. During the time that the relay 85 is energized, the elapsed time indicator 18 is also energized to record the running time cumulatively.

The automatic cycle differs from the previously described manual cycle by introducing a creep speed interval of operation before the high speed stage of rotation of the tumbling barrel occurs. When the automatic cycle switch button 22 is depressed to close the circuit, the relay 83 and another relay 91 are energized to complete a circuit to the motor control unit 80 through the adjustable creep speed control unit 29. This causes the tumbling barrel to be rotated in the same direction as previously described, but at a greatly reduced speed on the order of rpm. or less. As previously described, the relay 86 is also energized to cause the control valve 60 to open and supply cryogenic fluid to the interior of the tumbling barrel. The creep speed circuit will remain operative until such time as the temperature in the interior of the tumbling barrel has reached the predetermined value as established by the temperature control 16. When this low temperature point is reached the relay 86 is de-energized to cause closing of the valve 60, and at the same time the relay 85 is energized through the contacts 88 to cause the motor of the timer 17 to be started. The energization of the relay 85 establishes a high speed operating circuit to the motor control unit 80 through the high speed control unit 19 and the tumbling barrel now is caused to rotate at the previously established high speed. This high speed rotation will continue for the duration of the time established by the timer 17. Upon completion of the time cycle, the motor circuit will be interrupted and the timer clutch 90 will be released to reset the timer and place the circuit in condition for operation of the next cycle. The cycle may be interrupted if desired in the same manner as previously described with respect to the manual cycle of operation.

The function of the creep speed cycle is to permit freezing of the flash uniformly without causing any roll-over" or deformation of the flash which would impede the subsequent deflashing process. Ordinarily, if the parts to be deflashed are vigorously tumbled at relatively high speed during the initial lowering of the temperature of the tumbling barrel, the flash tends to deform or fold back upon the main body of the part due to the turbulence and impact forces in the tumbling barrel which act upon the flash before it has yet achieved rigidity. It has heretofore been attempted to overcome this problem by initially utilizing a cycle of intermittent high speed rotation of the tumbling barrel during the preliminary freezing process. However, this approach has failed to overcome the problem because the parts are alternately at rest and then in a state of high speed tumbling, so that no uniformityof freezing of the flash is obtained. By using a continuous low speed tumbling action during the initial stages of freez ing of the parts and then automatically switching over to the high speed tumbling action in response to the dropping of the temperature to the desired value, the desired extent of preliminary freezing is attained uniformly and without any significant roll-over or deformation of the flash which would interfere with its subsequent easy removal through the high speed tumbling action.

Inasmuch as the duration of the creep speed cycle is related directly to the rate of temperature change which occurs in the interior of the barrel as determined by the mass, density and thermal absorption characteristics of the parts being processed, the duration of this cycle will vary with the particular characteristics of the load being processed. The duration of the creep speed cycle is customarily less than two minutes and will more often be less than 1 minute long. The high speed cycle will ordinarily have a duration of less than 15 minutes and more often approximately 10 minutes.

It will be noted that the temperature-sensing probe 62 is disposed out of the direct path of the incoming cryogenic gas and is shielded from false temperature responses by the perforate partition wall 67. Furthermore, the probe 62 is positioned adjacent the bottom of the tumbling barrel where the parts being processed normally tend to accumulate. Thereby, the probe more accurately reflectsthe temperature of the parts themselves, rather than the temperature of the incoming cryogenic gas, although the probe is protected from injury by the tumbling parts by the partition wall 67.

Again referring to FIG. 5 of the drawings, there are manual control means additional to the manual cycle and the automatic cycle previously described. If it is desired to position the tumbling barrel for loading or unloading purposes, either the creep forward switch button 26 or the creep reverse switch button 27 may be pressed to slowly rotate the barrel to the desired posture. None of the previously described relays are energized during the operation of either of these manually controlled creep speed circuits. When the switch button 26 or the switch button 27 is released, the rotational motion of the tumbling barrel ceases.

The high speed reverse switch button 28 is provided for manually controlling the rotation of the tumbling barrel in a direction opposite to its normal direction of high speed rotation. When this switch button closes the circuit, a relay 92 having contacts 93 is energized and completes a circuit to the motor control unit through the adjustable high speed control unit 19. The holding circuit established by the contacts 93 is opened when the cycle ofi'" switch button 25 is pressed.

To reset an interrupted cycle, the cycle reset switch button 24 is pressed to de-energize relay 83 and the timer 17 to cause the clutch 90 of the timer to release and reset the timer. The operation of the cycle off switch button 25 has previously been described.

When the power off switch button 21 is pressed it breaks the power on holding circuit established by the contacts 79 of the electro-rnagnetic contactor 78 and the entire control circuit is then de-energized.

Thus, an extremely versatile control system has been provided for the cryogenic deflashing apparatus, which provides for selected manual control whenever desired as well as a completely automatic cycle and a semi-automatic cycle which has been referred to as the manual cycle. Temperature values, timer duration, rate of creep speed, and rate of high speed are all adjustable so that the control system can be pre-set to that combination of variable time, speed and temperature factors which through experience or empirically will best serve to give optimum results in the particular cryogenic deflashing operation which is encountered.

Referring again to FIGS. 1-3 of the drawings, it will be noted that the interior of the tumbling barrel is customarily not pressurized, but instead the injected cryogenic gas is permitted to diffuse through the partition wall 67 and exhaust to atmosphere through the

vent openings

64 and 65 in the inner and outer shells respectively. When the cryogenic gas exhausts, it is still well below ambient room temperature and has a considerable latent capacity for additional cooling. To obtain the benefit of this available cooling effect of the exhaust gases, a deflector element or shroud 94 of circular configuration is affixed to the interior face of the wall 38 of the safety enclosure so as to capture the exhaust gas being discharged from the vent openings 65 and funnel or direct it through one or more openings 95 in the wall 38 to the interior of the housing 39, within which the drive mechanism for the tumbling barrel is contained. The cold exhaust gas circulates within the housing 39 and is vented out of the housing through the louvered openings 40, thus serving to artificially cool the electric motor 31 and reduce its operating temperature to a point which is sufficiently low to permit the use of a lower-rated motor requiring less power than would otherwise be required in the absence of the cooling effect of the cryogenic exhaust gas.

Referring now to FIGS. 6 and 7 of the drawings, FIG. 6 is a diagrammatic representation of the flow pattern of the parts within the tumbling barrel when they are dropping from the tumbling wall 50 which is most remote from the axis of rotation of the barrel. FIG. 7 is a diagrammatic representation of this flow pattern of the parts when they are falling from the tumbling wall 46 which is considerably closer to the axis of rotation of the barrel than the wall 50. It will be noted that the tumbling pattern of the load changes as the tumbling barrel moves from the angular position shown in FIG. 6 to the angular position shown in FIG. 7. This change in the tumbling pattern minimizes the possibility that the same strata or layer of parts will fairly consistently occupy the same place in the tumbling pattern. As the tumbling pattern is varied, the parts change their position in the flow pattern so that during any single revolution of the tumbling barrel all of the parts are exposed to substantially the same processingtreatment.

This variation of the flow pattern IS in contrast to that utilized. In such a symmetrical configuration, there is no significant variation or change in the flow pattern of the parts as all the tumbling surfaces are equi-distant from the axis of rotation of the tumbling barrel. Consequently, each strata of parts tends to retain its relative position in the flow pattern during the rotation of the tumbling barrel and the parts are unequally and non-uniformly exposed to the tumbling treatment. This results in non-uniformity of results in the deflashing procedure. By utilizing a non-symmetrical polygonal configuration of tumbling walls which are disposed at non-uniform-distances from the axis of rotation of the barrel, a continually recurring variation in the tumbling pattern is generated for optimum uniformity of results.

Having thus described my invention, I claim:

1. In a control system for a cryogenic deflashing apparatus having a power-driven rotatable tumbling barrel, the combination of a drive control circuit for initiating rotation of said barrel at a creep speed, temperature-sensing means disposed in said barrel, means for cooling the interior of said barrel to a selected low temperature, and means responsive to the attainment of said selected temperature for establishing a high speed drive control circuit to cause rotation of said barrel at a speed substantially greater than said creep speed.

2. A combination as defined in claim 1, wherein said high speed is at least twice as great as said creep speed.

3. A combination as defined in claim 1, including valve means responsive to the attainment of said selected temperature for arresting the operation of said cooling means.