Cold pilger tube mills for extra thin wall precision

 

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A significant amount of cold rolled tubes, especially thin-walled, of small diameter from heat resisting, stainless grades as well as alloys on the basis of zirconium, titanium and nickel with increased requirements to accuracy, quality of finished surface and metal structure is required for the power, machine-building and chemical industries. For production of these tubes, two-, three- and four-rolls mills with lever type synchronization are recommended.

CPM 30 for rolling of extra thin wall precision tubes, equipped with 2-rolls, 3-rolls, 2-rollers and 3-rollers stands.

 

Hot tests of CPM 30 on the manufacturer's site

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Key parameters of the mills providing performance of specified quality, accuracy and output requirements are listed below:

Technical characteristics of cold pilger mills for rolling extra thin-walled tubes

Offered mill sizes

Mill size P A R A M E T E R S
Maximum shell diameter, mm Finished tube diameter, mm Finished tube WT, mm Stand stroke, mm Number of double strokes per min., not more Capacity, m/h Main drive power, kW, not more
Single strand mills
CPM 25 25 6-20 0,1-2 300 160 50-100* 30
CPM 40 40 10-35 0,15-3 500 120 50-150* 80
CPM 80 80 30-70 0,3-5 700 80 50-150* 120
Double strand mills
CPM 2-25 25 8-20 0,2-2 300 120 60-200* 50
CPM 2-40 40 12-35 0,3-3 500 100 60-250* 110
CPM 2-80 80 30-70 0,5-5 700 60 60-250* 150


* depending on rolling pass schedule and quality requirements

 

Design features of the CPM main units for rolling extra thin-walled precise tubes

 

Arrangement. Mills are delivered in a single or double-strand option. In double-strand mills, adjustment of dies on rolling tube size and adjustment of mandrel position in working zone are provided individually in each strand than quality of finished tube is reached equivalent with single-strand mills.

The mills are designed with end face loading with two shell chucks and with two mandrel rod chucks. Considering specific character of thin-walled tube production, for some tubes to use arrangement with end face loading with stop in shell end face is reasonable.

Rolling technological scheme. The basic variant of the rolling technological scheme is double turn and double feed with rolling at back and forth strokes. In particularly critical cases, for providing maximum uniformity of metal structure (for instance, production of extra thin-walled tubes with small diameter from zirconium alloys) technological rolling scheme with exclusion of deformation under backward stroke of dies is reasonable.

Working stand. Working stand of the mill is made with movable forced housing and movable roll cassette with ring type dies. Depending on assortment of finished tubes, working stand can be designed with two, three or four rolls.

Three rolls type universal working stand can be equipped as with variable profile groove dies or with constant profile groove rollers and profile support beams as well. Synchronization of cassette and forced housing motion is provided with help of levers system.

Exclusion of deformation under backward stroke is performed by additional device in the synchronization line of forced housing and cassette motion.

Feed and turn mechanism. For the mills with end face loading with stop in shell in end face, mechanical converter of continuous rotation into impulsive rotation of screw and chucks spindles is used. Feed and turn mechanism of the mills is made on the base of epicyclic crank type converter of continuous rotation into a intermittent momentum.

Converter of continuous rotation into interrupt motion of feed and turn has been made as planetary-crank mechanism connected by its driven link to the transmission from the mill main drive to synchronous electrical mill shaft via gears which provide the rotation frequency of satellites with cranks two time more than the working strokes number. During the one turn of satellite with crank, the driven link of the converter gets an impulse to turn to 90° while the crank of the mill drive turns to 50 – 60°. During the rest time of the cycle, the driven link remains practically unmovable.

Via the gear system including changeable gears, impulse is transferred to the screws the rotation of which provides replacement of the shell chucks into set accurate replacement of the feed by changeable gears within limits of from 0.5 up to 10 mm per one cycle.

For the mills with end face loading having two shell chucks and two rod chucks as converters of continuous rotation into intermittent motion is used program control by motors in step mode is used.

Being coordinated with the Customer, mills can be delivered for the maximum shell length of from 5 up to 15 m and with finished tube receiving table with length necessary for production requirements.

 

Working stand and cassette travel drive. Working stand and cassette travel drive is made of planetary-crank type with rectilinear motion of crank with rotating counterweight balancing of dynamic forces and moments system that allows to decrease energy consumption significantly during mill operation.

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