US3161935A

US3161935A - Tamping mechanism

Info

Publication number: US3161935A
Application number: US809456A
Authority: US
Inventors: Carl W Chanlund
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-04-28
Filing date: 1959-04-28
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

Dec. 22, 1964 c. w. CHANLUND 3,161,935

TAMPING MECHANISM Filed April 28, 1959 5 Sheets-Sheet l INVENTOR.

14 TTOENEYS Dec. 22, 1964 c. w. CHANLUND TAMPING MECHANISM 5 Sheets-Sheet 2 Filed April 28. 1959 622! W CZazzhzzd BY A TTOF/VEYS Dec. 22, 1964 c. w. CHANLUND 3,161,935

TAMPING MECHANISM Filed April 28, 1959 5 Sheets-Sheet 3 8 F5 041% M 6M 87 if wg \m 66 J BY g m a? a w 66 3 6 ATTORNEYS Dec. 22, 1964 c. w. CHANLUND TAMPING MECHANISM 5 Sheets-Sheet 4 Filed April 28, 1959 yea A TTOENEYS Dec. 22, 1964 c. w. CHANLUND TAMPING MECHANISM Filed April 28, 1959 I sma/A 5 Sheets-Sheet 5 INVENTOR.

BY gmy m ATTORNEYS United States Patent 3,161,935 TAMPING MECHANISIVI Carl W. Chanlund, 412 Maple St, Nampa, Idaho Filed Apr. 28, 1959, Ser. No. 8ll&,456 tjlm'rns. (Cl. 2537) This invention relates to a mechanism for tamping a concrete mix during placing of the mix into a mold to thereby displace air or other gases from the mold and produce a tightly packed, high strength product free from voids.

More specifically, the invention relates to a tamping device for general use in concrete pipe making machines for tamping a concrete mix while it is being placed in a vertical, rotating mold having a core. The core may or may not have a vibrator associated therewith, as desired. Moreover, the present vertical tamping device may be used with a mold having a bell end, with such bell end either down or up.

In accordance with the present invention, the form is preferably placed upright so that it rests on one end, with the bell end upward. A central core is inserted in the form, and the annular space between the form and the core is gradually filled with concrete of a suitable mix and consistency supplied by way of a hopper and discharge chute. During such filling operation, the freshly deposited stratum of the concrete mix is continuously tamped, and consequently compacted, by a shoe secured to the lower end of a pair of tamping sticks. Simultaneously therewith, the mold is rotated and the core is preferably, although not necessarily, vibrated at a high frequency. The mold is supported by a table, which is slowly rotated to present different parts of the mold under the discharge chute and to the tarnping shoes for filling and compacting the mix in the mold. After the mold has been filled, the bell end is finished by a forming head applied thereto under pressure. Thereafter, the core is removed through the lower end of the pipe, while the mold is stationary and the core is rotating, to provide the pipe WltL a smooth, troweled, inner surface. The mold is then removed from the machine and transferred to a drying room.

The present disclosure is concerned primarily with the tamping device of the machine and, accordingly, said device is llustrated and described herein in full detail; whereas, only so much of the remainder of the machine has been included as is necessary to a full understanding of the construction and operation of the tamping device.

An object of the invention is to provide a camping device or mechanism of unitary construction that may readily be placed in operative position relative to a concrete pipe making machine, or removed for repair or replacement.

Another object is to provide a camping device having one or more tamping units that are readily adjustable relative to the mold so that the tamping device can be used, without change of parts, in connection with the manufacture of concrete pipe of a lar e range of diameters.

Still another object is to provide, in a tamping device, an improved friction box in which a fluid pressure actuated bellows replaces the conventional compression spring to provide an accurately regulable frictional resistance to the upward movement of the tamping stick as the mold is being filled, whereby a predetermined, uniform tamping force can be applied to the mix in the mold.

To attain these objects, a preferred form of the invention includes one or more tamping units or devices carried by a carriage, which is movable on a bridge comprising a pair of rails placed above the mold in which the concrete pipe is to be cast. Each tamping device is a self-contained unit including an electric motor, a transice mission unit including mechanism to change the rotary motion of the motor into a rapid reciprocating motion of at least one tamping stick, and a friction box, which frictionally carries the tamping stick to enable the tamping shoe and tamping stick to progressively move upwardly as the mold is filled. By removing a few bolts, the entire tamping device may be readily removed from the carriage for repair or replacement. These bolts engage slots in the carriage and permit a quick adjustment of each tamping device relative to the mold, whereby the tamping device may be readily adapted for use'with molds for casting different diameter pipes. It is preferred to use two tamping devices simultaneously, since this produces a more tightly packed pipe than would result from the use of one tamping device.

Other objects and advantages of the invention, together with certain details of construction and combination of parts, will be apparent from the following detailed description and accompanying drawings.

In the drawings, wherein for purposes of illustration a preferred embodiment of the invention is shown:

FIG. 1 is a fragmentary side elevation of a machine for the manufacture of concrete pipe including two tamping units made in accordance with the principles of the present invention;

FIG. 2 is an enlarged fragmentary, horizontal sectional view through the mold and one of the tamping sticks, taken on the line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary plan view of the machine taken on the line 3-3 of FIG. 1 and particularly showing the relative position of the two tamping units;

FIG. 4 is an enlarged fragmentary, vertical sectional view through one of the tarnping devices and the carriage, taken on the line 4-4 of FIG. 3

FIG. 5 is an enlarged fragmentary, horizontal sectional view through one of the friction boxes, taken on the line 5-5 of FIG. 4;

FIG. 6 is a horizontal sectional view through the transmission unit or gear housing taken on the line 66 of FIG. 4;

PEG. 7 is an enlarged fragmentary, vertical sectional view through one of the friction boxes, taken on line 77 of FIG. 6;

FIG. 8 is an enlarged horizontal sectional view, similar to FIG. 5, but showing a modified friction box housing accommodating a pair of tamping sticks;

FIG. 9 is a fragmentary view, partly in section, of another modified friction box structure featuring a combined wear member, and bellows and pressure or friction wearplate retainer;

FIG. 10 is a plan view of the friction box structure shown in PEG. 9;

FIG. 11 is a vertical sectional view taken on the line lit-11 of FIG. 9;

FIG; 12 is a horizontal sectional view taken on line l212 of FIG. 9.

FIG. 13 is a perspective view of the combined wear member, bellows and wearplate retainer shown in FIGS. 9, 10 and 11;

FIG. 14 is a diagrammatic view illustrating the manner in which a flattened tube is slotted to form the retainer of FIG. 13; and

FIG. 15 is a perspective view of the wearplate shown in FIGS. 9, 10 and 11.

Referring to the several figures of the drawings, wherein the same reference numerals are used to designate the same element:

With reference to FIG. 1, which illustrates a portion of a machine for manufacturing concrete pipe, the numeral 10 designates a floor or base for supporting a pair of upstanding standards 11 and 12. The standard 11 is A carriage C is mounted for movement along the rails 13. The carriage C comprises a top plate 17, a bottom plate 17 and a pair of slide plates 18, supported by upper rollers 19 and lower rollers 1%, which engage the top and bottom, respectively, of rails 13 to assure stability and ease in movement. Upper plate 17 is provided with a pair of lateral extensions 2% which serve as brackets to support a pair of tamping devices T, as described more fully hereinafter. A plurality of triangular gussets 2t), welded to the extensions 26 and side plates 13, provide reinforcement for the brackets.

Cylindrical standard 12 serves as a main column for a mold transfer and indexing device designated generally by the reference numeral 22 and including a sleeve 23 'rotatably supported by the standard 12. The transfer device 22 includes a turret structure 22 mounted on the sleeve 23 and adapted to support a pair of pipe forming molds 2%, which are shown at a mold loading and unloading station A, and at a mold filling, vibrating and tamping station B. The details of the mold transfer and indexing device 22 form no part of the present invention.

Mold 24, at station E, is supported upon a table 25 carried by a guide 25 and which table can be raised and lowered in a deep pit P formed in base 16, by piston rods 25 The table 25 is adapted to be raised sufiiciently to take the weight of the mold off the turret 22 during filling of the mold. The table 25 includes gearing connected to a drive shaft (not shown) for slowly rotating it while the mold is being filled and tamped. The details of the table rotating mechanism form no part of the present invention, and are disclosed in full and claimed in the application, supra.

The carriage C supports a mechanism for forming the bell end on a pipesection while in the mold 24, such mechanism being designated generally by the numeral 26, FEGS. 1 and 3, and including a hydraulically operated forming head 27, supported on the lower end of a rod, not shown, which extends through the carriage C. The details of the bell end forming mechanism "form no part of the present invention, but are disclosed in full and claimed in the application, supra.

Referring to FIGS. 1 and 2, it will be seen that the mold 24 includes an outer cylindrical shell 28, and an inner cylindrical core 29, which is fixed to the table 25 and insertable into the mold 24- through its lower end. The core 2? is provided on its outer face with a sheet metal liner 3%) so as to present a smooth surface. The outer shell 28 and core 29 are disposed in spaced, concentric, relation to provide an annular channel into which a concrete mix 33 is poured by means of a chute 32, FIG. 1. Chute 32 discharges concrete from a hopper 31 disposed adjacent the mold 24 and supported by a stand 31% only a portion of which is shown in FIG. 1. 'The discharge of the concrete mix is continuous during the mold filling operation.

A tamping shoe 34 is attached to the lower end of a tamping stick 36 by screws 35, FIG. 2. The camping stick 36 extends into the annular space of the mold 24 between the shell 28 and core 29, and is rapidly reciprocated during the filling operation of the mold by the tamping device T, which will be described later. The upper stratum of the concrete is thereby continually tamped, which operation removes air, eliminates voids, and produces a very compact mass of concrete in the mold. Compacting of the concrete is further facilitated by a vibrator (not shown) mounted within the core 29 and having a frequency of about 3600 vibrations per minute and an amplitude of inch to /8 inch.

Referring to FIGS. 3 and 4, it will be noted that the movable carriage C supports two independent tamping units T and is provided with an elongated slot 37 through which the tamping sticks 36 extend. A pair of spaced, vertical, bowed plates 38, welded as shown at 38 to the upper and

lower plates

17 and 17 form side walls for said slot 3' 7.

The slot 37, FIG. 3, is defined by three sections designated as 37 37 and 37 The

sections

37 and 37 are inclined at the same angle to the longitudinal axis L of the carriage C. The center lines of slot sections 37* and 37 intersect at the point 37 which lies along the longitudinal axis of the carriage C. Slot section 37 extends perpendicularly to the longitudinal axis L of carriage C and connects the inner ends of slot sections 3'? and 37 From the foregoing, it is evident that when the carriage is moved into a position in which the point 3'7 lies directly above the axis of mold 24, as shown in FIG. 3, the center lines of the slot sections 3'," and 37 will coincide with a radius of the mold. In this position, it will be seen that adjustment of the tamping devices T along the center lines of the slot section 3&7 or 37*, as described later, will enable the tamping devices T to be used with pipes of various diameters.

A servomotor 39, FIG. 1, is provided to move carriage C along the rails 13. The cylinder of the servomotor is pivoted at 39 to a bracket 39 fixed to the supporting rails 13. A pair of fluid pressure lines 46 and til is connected to the cylinder at opposite sides of a piston ll slidable in said cylinder. Piston 4?. is mounted on one end of a pistol rod 41 which is connected at 42 to the carriage C. In order to move carriage C to the right, fluid pressure (preferably hydraulic) is applied through line 4%) to the left-hand side of piston 4i and exhausted through line 4th from the right-hand side. Movement of the carriage to the right is limited by adjustable stops 19* mounted on the rails 13. If it is desired to move carriage C to the left, i'luid pressure is applied to the right-hand side of piston ll and exhausted from the lefthand side.

. The tamping devices '1 are shown in detail in FIGS. 3- to 8. Two tamping devices are shown, but it should be understood that the invention can be carried out with a single tamping device, although two tamping devices produce more effective compacting of the concrete in the mold 24. As the two tamping devices are identical in construction and in operation, the description which follows'is applicable to both devices.

Each tamping device T includes a gear housing designatedgenerally by the reference numeral 43. The housing 43 includes side walls 4%, a bottom wall 4-4 and a removable cover plate 4-5 held in place by bolts 415. Four gussets 47, FIG. 6, disposed Within the housing 43 and Welded to the bottom wall 44* and side walls td, serve to reinforce the housing. The housing 3 is adapted to contain gear lubricant 46, as shown in PEG. 4. Cover plate 45, FIG. 3, is provided with a filling plug 49, and the bottom wall 44 FIG. 6, is provided with a drain plug Sll.

A power input or drive shaft 51, FIG. 4, is rotatably supported in ball bearings 52 and 53 carried by hearing

supports

54 and 55 mounted in openings 5d and 55 respectively, and bolted at 56 to opposite side walds 4a of the housing 43. A pair of helical driving gears 8 and 59 are secured to drive shaft 51 to rotate therewith. It will be noted that the

openings

54 and 55* are larger than the

gears

58 and 5%, so that these gears and the shaft 51 can be preassemoled and inserted into the housing 3 through either opening The helical gears 58 and 59 are pitched in opposite directions for the purpose of rotating cooperating helical gears 6t? and 61, respectively, in opposite directions and to counterbalance the end thrust on bearings 52 and 5'3. The helical gears es and d1 mounted on driven or output shafts s2 and 63, respec tively. Driven

shafts

62 and 63 extend at ri ht angles to drive shaft 51 and are disposed above the drive shaft as shown in FIG. 4. One end of

shafts

62 and 63 rotates in ball bearings 64, FIG. 6, carried by bearing supports 65 mounted in openings 65 in the rear side wfll 4t) and secured by bolts 66. The other end of

shafts

62 and 63 rotates in ball bearings 67 mounted in openings 67 in the front side wall 44 and held in place by a retaining plate 68 and bolts 70. Lock nuts 69 retain bearings 67 against a shoulder 67 on

shafts

62 and 63. Retaining plates 68 are each provided with a lubricant seal 71, which surrounds

shafts

62 and 63 to prevent loss of lubricant. One end of each of

shafts

62 and 63 extends through the front side wall 44 and one of the retaining plates 68, and secured to the extension thereof, as by a key 73, is a crank 72. Each crank 72 is provided with a crank arm 74- and a counterweight 75. A link 76 is secured to each crank arm by a pivotal connection 77 including a roller bearing 73. Lubricant passages 79 are provided in the

shafts

62 and 63 to permit the passage of lubricant 48 from the housing 43 to the roller bearings 73, as shown in FIG. 6. The links 76 form a double connecting rod on the tamping unit.

One end of drive shaft 51 extends through an opening in bearing support 55, FIG. 4, to receive a driving pulley 89. A power element 31, shown as an electric motor, is mounted on cover plate 45 by bolts 84. The mounting means for motor 31 includes the usual slots, not shown, to permit adiustment of the motor 81 on cover plate 45. The shaft 8% of motor 8'1 is provided with a pulley 82. Power from pulley 82 is transmitted to pulley Si} by a pair of V-belts 83.

The lower end of the links 76 is attached to a friction box, generally designated by the numeral 85, in a manner described later. As shown in FIGS. 4 and 5, the friction box comprises an elongated sleeve-like housing member 86 of rectangular cross-section, preferably made of aluminum to reduce its inertia. A pair of steel wear plates 87 is secured to opposed inner walls of the housing 85 as by rivets S7. A friction element 88, made of laminated tough leather, or aluminum, is secured to another inner wall by rivets 88 Tamping stick 36, which is usually made of seasoned hickory Wood, passes through the friction box 35 and engages a friction face $8 of the friction element $8. In order to adjustably urge tamping stick 36 and friction element 8%; into frictional engagement, a floating, aluminum pressure plate 89 is interposed between stick 36 and a rubber bellows o-r diaphragm 9t engaged with the inner face of the wall of housing $6 which is opposite friction element 88. A bolt 91 maintains bellows in position in the friction box 85.

The bolt 91 has an axial bore 2 passing partially therethrough and opening into the interior of bellows t). A radial bore $3 in bolt 91 places axial bore 92. in communication with an annular groove 94 in the outer surface of said bolt. Housing 86 has a passage 95, which communicates with an air pressure line 95. Line 96 is selectively connectable to a source of air under pressure or to the atmosphere by conventional valve means, not shown. By selectively operating such valve means, the pressure of the air in bellows 90 may be varied, as desired, in order to produce a controlled frictional force between tarnping stick 36 and friction element 88. The floating pressure plate 8? is disposed between bellows 9t and tamping stick 36. The plate 89 has horizontally projecting lugs 8%, FIG. 7, at its upper and lower ends, which cooperate with the corresponding ends of friction box housing 86 to prevent relative vertical movement of said plate relative to said box while permitting said plate to be freely moved toward tamping stick 36. The pressure plate 39 is preferably assembled with the housing 86 by inserting it diagonally into the opening thereof until the lugs 39 are clear of said opening, and then turned in said opening into parallelism with the front wall of the housing. The friction element 88 and the Wear plates 87 are thereafter assembled with and riveted to the housing 86. The housing 86 is provided, about midway of its length, with a pair of opposed lobes 97 towhich the lower end of links 76 are pivotally connected by pins 98.

A guide bracket 99, FIGS. 4 and 6, is secured to the front side wall 44 of gear housing 43. The bracket 99 is provided with a pair of vertically extending, parallel guide tracksldd, which cooperate with a guide roller m1 attached to a wall of the housing 86 of the friction box 85, as shown in FIG. 6. The bracket 99 has an elongated slot 162 (FIG. 4) at its upper end and two such slots 102 at its lower end through which bolts 103 pass, to provide for proper alignment of said bracket on the gear housing 43. The roller 101 guides the housing 86 for vertical reciprocating movement relative to the gear housing 43.

The gear housing 43 is secured to upper plate 17 (FIGS. 3 and 4) of carriage C and extension 20 by a plurality of bolts 1%, which pass through lugs M5 at the base of said housing and through elongated slots 1% in plate 17 and extension 26*. The slots 1% extend parallel with and in spaced relation on opposite sides of the center line of slot 37, which arrangement permits the adjustment of the tamping units T along the axis of said slot 37 for tamping pipes of different diameter.

FIG. 8 illustrates a modified form of friction box for accommodating two tamping sticks. In this modification, an aluminum housing 86 is provided, on opposed inner walls, with a pair of steel wear plates $7 secured thereto by rivets 37*. One inner wall has secured thereto a friction element 88 of leather or aluminum. A friction element 8n similar to the floating pressure plate 89, is engaged by bellows A pair of tamping sticks 36 and 36 spaced apart by a floating wear plate 89 (similar to plate 89), pass between the friction elements $8 and 38 in frictional engagement with the

surface

38 and 38 thereof, respectively. The bellows W is connected with a source of air under pressure in the same manner as the bladder 9t? in FIG. 5, and the corresponding parts in FIG. 8 have been identified by the same reference numerals.

FIGS. 1 and 3 illustrate the parts in operative position for filling and tamping a concrete mix in the pipe mold 24. As shown, the pipe mold 2 5- rests on table 25 at station B and another pipe mold 24 is shown at the loading andunloading station A. Carriage 'C occupies the righthand position in which the rollers 19 engage the stops 19*. In this position, the point 37 is directly over the center of mold form 24 and core 29 and the axes of

portions

37 and 37 of slot 37 lie along radii of the mold. End-former 27 is positioned to one side of the center of form 24, as shown.

Assuming that it is desired to make a concrete pipe of a given diameter, the tamping sticks 36 of tamping units T are held in raised position by bellows 99 to clear the mold 24, and the tamping units are then adjusted along slots 37 to the proper position to enable the tamping sticks 36 to enter the annular space in the mold between the core 29 and outer shell 23. The fluid pressure in bellows 99 is released by allowing the fluid therein to escape to the atmosphere. Tamping sticks 36 andthe tamping shoes 34 attached to the lower ends thereof then drop by gravity to the bottom of form 24. Pressure is then restored in the bellows 90 to frictionally oppose upward movement of the tamping sticks 36 during filling of the mold 224. The rotating table 25', the vibrator (not shown) in the core 29 and tamping units T are set into operation, and simultaneously chute 32 is brought into position, preferably mechanically (by means not shown) to feed concrete into the mold. A fairly dry concrete mix is preferably used. As the concrete is poured into the mold, the core 29 is vibrated at a high frequency and the table 25 is simultaneously slowly rotated. The tamping sticks 36 are reciprocated at a rate of about 750 to 1000 (preferably about 800) impacts per minute and are successively brought against different portions of the upper strata of the concrete as the form rotates, preferably at a peripheral speed of about 175 feet per minute. This action removes air and other gases which may be entrained in the concrete, prevents the formation of voids, and compacts the concreteto produce a verydense, tightly packed pipe of high quality. The pressure in bellows 99 is preset at a suitable value to provide the desired friction between tamping sticks 36 and friction element to cause the tamper feet 34 to deliver an impact blow of the desired degree, for example, about ISO-7f per sq. in. It will be seen that, as the level of the concrete in the mold 24 increases, the tamping sticks 36 will slide upwardly through friction boxes 55, but due to the pressure of the bellows applied against the tamping sticks, there will be a constant resistance to such upward movement, resulting in'uniform tamping of the mix. This operation continues until the concrete has been poured to the required level in the mold, whereupon the pouring and tamping-are discontinued. A tamping stick stroke of about four inches will produce good results. 1

Tamping sticks 36 are thenraised to clear the mold, and fluid pressure is admitted to the right-hand side of piston 41 in servomotor 39 to move the carriage C to its left-hand position, which brings end-former 27 directly .over. the core.- The rotating table and core vibrator are kept in operation and the end-former 2'7 is then lowered and applied under pressure to the bell end of the pipe (by means not shown) to produce the desired shape on such end of the newly molded pipe. End-former 2'? is raised, table is then lowered to transfer the weight of the mold 24 to the turret structure 22*, and thereafter core 29 is rotated and removed through the lower end ofthe pipe, by means not shown. The indexing mechanism then rotates the turret structure 22 to move the filled form 24 from station 3 to station A, and to present an empty form to station B, whereupon the operation is repeated.

It is frequently necessary to make pipe having an annu lar, wire mesh, reinforcing member. When such pipes are poured, a friction box of the character shown in FIG.

8 is preferably employed, in which tamping sticks 3-6 and 36* extend into the mold on opposite sides of the reinforcing member to uniformly compact the mix in the mold and around the reinforcing member.

From the foregoing, it will be seen that I have provided a unitary camping device in which all of the parts of the mechanism are carried by gear housing 43, which gear housing is also provided with guide means to maintain the friction box in its proper operative position relative to a mold. By loosening bolts 1%, the tamping device can be quickly and accurately adjusted along the center line of slot 37 to handle molds for different diameter pipes. The bolts 1% may also be removed, whereby the entire tamping unit may be removed from the machine for repair or replacement, thereby avoiding needless and long shutdowns as in thecase of mechanical failure of parts of prior art tamping devices. a

By the provision of the elongated bellows 9t instead of the usual spring element, it is possible to provide a large pressure area acting on the tamping sticks in which the pressure at all points is the same, and by varying the pressure of the air in the bellows, any desired frictional force between the friction surface of the friction elements and the t-amping sticks may be obtained. The frictional force may be varied by a remotely positioned valve (not shown) without the necessity of stopping the tamping device as in the case in adjusting the usual spring means. This arrangement is also conducive to maintaining a can stant frictional force onthe tamping sticks and to a longer life of the various elements of the device.

it also avoids needless shut-downs and resulting loss of time. More- ;over, the pressure in the bell ws Eli) can be released by .ment

beginning of a tamping operation, thus further saving time and labor in'the use of the device.

FIGS. 9 to 15, inclusive, illustrate a further modified form of friction box lltl comp-rising a housing 111 made of aluminum or other suitable light-weight metal. The ho ising Till has lateral extensions or robes 112., similar to the lobes 9'7, adapted to be connected to the links ?e-i d. A rectangular opening 113 in the housing 111 is defined by side walls 114, a front wall 11S and a rear wall 116. An aluminum wear or friction element 117, similar to the friction element 83 of FIG. 5, is disposed in the opening H3 and'secured against the inner face of front wall 115 by a plurality of countersunk bolts 118.

A combined wear member, and bellows wearplate retainer 119 comprises an elongated oval portion 129, FIG. 13, having straight, parallel wear elements l2l.l2l projecting therefrom. Theoval portion 326 is defined by straight side portions l22l22 connected together by semicircular, arcuate end portions 123-423. The combined width of each of the side portions 122 122 and wear elements l2 l12l is slightly less than the distance between the front wall 115 and the rear wall 116 of the housing Elli, so that when the retainer ll? is positioned in the-openmgjli the wearplate lll'is disposed between the extremities of the wear elements -l2ll2ll. The overall distance from the outer face of one friction ele- 121 tothe outer face of the other is approximately equal to the dimension of the opening 113 between the side walls li t. Thus, the overall exterior cross-sectional dimensions of the retainer 119 are approximately equal to the transverse dimensions of the opening 113. Countersunlt openings '124 are drilled in the wear elements l21. 121 to receive countersunk bolts 125 to secure said elements against theinner face of the side walls 114 of the housing 111.

The retainer 119 is formed in a very simple manner. Thus, as diagrammatically shown in FIG. 14, a section of circular tubing T is flattened into the elongated oval shape of the portion 1241*, FIG. 13. The arcuate ends of the tened tube T are then slit transversely at 1245 and axially at two points l2'7l27 to form tongues 12%. The metal M between the slits 127-127 is discarded as waste. The tongues 128 are then straightened out into alignment with the flat sides of the tube T to form the friction elements 1Zl3l2l, FIG. 12. The extremities of the tongues l28128 lie in a plane common to the crest of the rounded ends l23123.

A rubber bellows or diaphragm 12% of elongated oval shape is complemental in size to, and is positioned within, the retainer 119 against the inner face of the rear wall 116 of the housing 111. A bolt and nut assembly 13d, identical in construction and purpose to that shown in FIG. 5, secures the bellows to the wall 136 and provides for admission and exhaust of operating fluid through passage 131 in said wall.

A floating pressure plate 132 of aluminum or other suitable material is positioned in the retainer 119 between the bellows and a tamp stick 36. The plate 132 is complemental in shape to the oval portion Frill of the retainer 119 and is restrained thereby from vertical and lateral movement relative thereto, but is free for axial movement in said retainer, toward and away from the tamp stick 36.

it will be noted from FIG. 12 that the housing Jill is protected against wear by the tamp stick 35 through the provision of the wearplate 117 and the wear elements l2ll2l, which are provided for contact with the front and side surfaces, respectively, of the tamp stick. Frictional pressure is applied to the temp stick by the floating friction plate 132 in accordance with the pressure of the operating fluid introduced into the bellows 129, in the same manner described hereinbefore in connection with the bellows 96. It will be understood from FIGS. 9, 11

I and 12 that the retainer 11% confines the bellows within the oval portion 1% and prevents undue stress and expansion thereof when subjected to internal pressures which effect inflation thereof.

A guide roller 133, similar to the roller 101, is mounted at the upper end of the housing 111 for cooperation with the guide tracks 100.

It will be understood that various changes may be made in the details of construction and in the arrangement of the parts of the tamping units, the carriage, the elevated track therefor, etc., shown herein, without departing from the principles of the invention or the scope of the annexed claims.

I claim:

1. In a pipe molding machine having means adapted to support a mold, in combination: an elevated track; a carriage mounted for movement along said track to a position directly over a mold for material to be tamped; a pair of gear housings supported in spaced relation on said carriage, each housing including an input shaft and an output shaft and connecting gearing within the housing, each output shaft including a crank arm supported by a wall of said housing; a separate power element for each gear housing mounted on the respective housings; a pair of tamping sticks; a driving connection between each crank arm and a separate one of said tamping sticks, said driving connections including a friction box enclosing a tamping stick and cooperating means carried by each gear housing and friction box for guiding its associated friction box, said gear housings being disposed with their respective output shaft axes at obtuse angles with each other and coinciding with radii of the axis of said mold supporting means, and with the tamping sticks disposed in the space between the gear housings, whereby either of said tamping sticks may be used independently of the other.

2. In a pipe molding machine having means adapted to support a mold, in combination: a tamping device including a tamping stick for tamping concrete in a cylind-rical pipe mold carried by said support means; a carriage supported for movement along a line in a horizontal plane above said mold, said carriage having a horizontally elongated slot having an axis forming an angle with the line of movement of said carriage, said tamping stick extending through said slot, said slot being capable, upon movement of the carriage, of being aligned with a radius of a pipe mold on said mold support means; and means for adjustably mounting said tamping device along the axis of said slot, whereby said tamping stick may be adjusted for tamping pipes of various diameters.

3. In a pipe molding machine having means adapted to support a mold, in combination: a plurality of tamping devices, each provided with a tamping stick for tamping concrete in a cylindrical pipe mold; a carriage, means supporting said carriage for movement along a line in a horizontal plane above the mold, said carriage having elongated slot means including portions having axes extending along different lines and forming an angle with the line of movement of said carriage and with the axis of each other, said tamping sticks extending through said slot portions, said slot portions being capable, by movement of said carriage, of aligning with radii of pipe molds of different diameters in said mold support means; and means adjust-ably mounting said tamping devices along said slot portions, whereby the tamping sticks may be adjusted for tamping pipes of various diameters.

4. A friction box for a tamping device, comprising: a housing having a rectangular passage extending therethrough, a tamping stick of rectangular cross-section extending through said passage; a member having a flat friction surface within said housing disposed adjacent one side of said tamping stick; an elongated fluid pressure actuated inflatable member within said housing to urge said frictional surface and tamping stick into frictional engagement one with another; and a retainer in said friction box, said retainer having a contour conforming with the peripheral contour of said inflatable member and forming an enclosure for confining the outer edge of said inflatable member, said retainer including spaced friction elements engageable by opposite edges of said tamping stick.

5. A friction box as defined in claim 4, in which the retainer includes an oval portion defined by opposed flat sides interconnected by arcuate end portions, and wherein the inflatable member is complemental in shape to said oval portion of said retainer, and wherein the flat sides of the retainer each carry one of the friction elements, and wherein the cross-sectional configuration of the retainer conforms to the shape of the rectangular passage in the housing.

References Cited in the file of this patent UNITED STATES PATENTS 1,037,189 Allen Sept. 3, 1912 1,095,104 Glenn Apr. 28, 1914 1,453,269 Buente May 1, 1923 1,799,076 Andelt Mar. 31, 1931 2,134,614 Laffenty Oct. 25, 1938 2,185,613 Tuerck Ian. 2, 1940 2,196,874 Ruegy Apr. 9, 1940 2,229,922 Heinze Ian. 28, 1941 2,242,690 Wallace May 20, 1941 2,308,403 Terry et al. Ian. 12, 1943 2,712,679 Everhart et al. July 12, 1955 2,893,099 Trautman July 7, 1959 FOREIGN PATENTS 233,145 Germany Mar. 28, 1911