Operation | Calculations | Troubleshooting | Capacities and Prices

INTRODUCTION TO THREAD ROLLING

Rolled threads are produced in a single pass at speeds far in excess of those used to cut threads.

The thread is formed by the axial flow of material in the work piece. The grain structure of the material is not cut, but is distorted to follow the thread form. No chips or swarf should be produced.

The resultant thread is very much stronger than a cut thread. It has a greater resistance to mechanical stress and an increase in fatigue strength. Also the surface is burnished and work hardened. There are no pits at the crest or cracks at the core, which often occur with cut threads.

The material to be rolled must have a minimum elongation of 12% and a tensile strength no greater than 110kg/sq.mm. Most steels fall into this category including tool and stainless steels, aluminium, malleable cast iron, brass with at least 60% copper, and light alloys.

Thread rolling heads can be axial or tangential. Axial heads can be rotary or stationary, and can be shank or flange mounted. They are used for producing threads on the end of a component.

Tangential heads are used to produce threads behind a shoulder, or in the middle of a component. They can also produce threads either side of a shoulder simultaneously, within certain criteria.

Both axial and tangential heads can be used to produce knurls and serrations.

Tangential heads are fixed and are used from the cross slide. Axial heads have an automatic opening mechanism.

A4-A6 TYPE

We are sole U.K. distributors for Alco S.A. , manufacturers of a range of Thread Rolling Heads. We stock heads for right and left hand threads as listed in the tables below. We also stock the entire range of associated standard thread rolls, (see ‘CHASERS AND ROLLS’). We can supply special rolls for standard heads on request, and special heads to customer’s requirements. We stock a range of parts, many of which are also suitable for ‘Fette’ type heads. A catalogue is available on request.

We can sometimes supply reconditioned heads as available, or we can recondition your equipment. Please enquire.

OPERATION – AXIAL HEADS

Fitting the rolls

To fit the rolls, first remove the front plate. Remove any rolls already fitted taking care not to drop the needle rollers or carbide bushes.

Fit the rolls in a clockwise direction with either 1,2,3 or A,B,C face up for right hand threads. If a left hand thread is to be rolled a special head is required, and the rolls are fitted anti-clockwise. Heads for left hand threads are suffixed ‘IZQ’ e.g. A2 IZQ.

The rolls are fitted to the eccentric pins using either needle roller bearings or carbide bushings. Needle bearings are much cheaper but take longer to fit, tend to wear, and can allow ingress of foreign matter, which can damage the eccentric pins. When fitting or removing needle bearings it is best to pack the gap between the rolls and the eccentric pins with grease. Always fit the correct amount of needle bearings, ensure that they are not worn or dirty, and that the rolls move freely on them.

The thread rolls have a chamfer ground on each end, which determines the length of the lead. There are two basic leads; 2K (normal long) and 1K (normal short). Special leads; 0.6K (very short) and 3K (very long) are available at extra cost. Always use the longest practical lead to prolong the life of the rolls.

Rolls for head sizes A1 and bigger can normally be reground.

Adjusting the head – A0 to A34

Refer to the figure. Assemble the head on the machine, ensuring that the scale on the black spring housing (2) is visible with the head closed. Slacken the hexagon nuts (15) enough to allow the spring housing to rotate against the backplate (3). Close the head using the handle (9). The head can now be set using a threaded setting piece or plain setting piece at the thread core diameter. Insert the setting piece between the rolls and rotate the backplate against the spring housing until the rolls are fully engaged with the setting piece. Tighten the hexagon nuts(15) and check that the head will open by pulling the front forward from the shank. The head should rotate a little and the rolls should retract from the setting piece.

If the head cannot be adjusted to the diameter required, and assuming that diameter is within the capacity of the head, carry out the following procedure:-

Remove the 3 hexagon nuts, and rotate the front of the head as far to the left as possible. Withdraw the front of the head from the spring housing taking care not to disturb the gears attached to the eccentric spindles. When completely separated, rotate the front of the head 120 degrees, in either direction, and refit to the spring housing. Try to adjust to size again. If unsuccessful, try the third position. If still unsuccessful, the head or the rolls are faulty.

This setting up procedure is not guaranteed to give the accuracy that may be required, and minor adjustments may still be necessary, depending on the type, tensile strength and elongation of the material being rolled.

Thread length is preset with the head open, and for short or medium lengths may be set using the end stop assembly. Longer lengths may be preset using the machine stops. When the stop is reached, the shank is arrested but the front of the head moves forward to the work piece until the opening mechanism operates.

Operating the head. A0, A1, A12, A2, A23, A233400, A3, A34

Before operating the head the correct machine speeds and feeds must be selected. Operating at too low a speed can cause poor threads to be produced and may even cause damage to the rolls and the head. Details of how to calculate these parameters are given later but if in doubt remember that higher speeds produce a more favourable effect.

The head is closed manually or automatically, by pushing on the closing handle. The head should be offered up to the work piece (or vice-versa) in a positive but not sudden manner, and not with excessive force. Sudden engagement causes work hardening of the blank and possible damage to the rolls. Excessive force may damage the threads being produced.

The thread will be produced automatically as soon as the rolls engage the work piece. When the preset length is reached the head will automatically open, and may be traversed at speed to the start position ready for the next pass.

Cooling and lubrication

These are important to ensure good output, and to prolong the life of the rolls. If possible coolant should be conveyed to each roll from the front. With rotary heads splash guards may be required.

The coolant must be free from swarf and other particles to avoid damage to the rolls and needle bearings, tanks with partitions to allow settling and magnetic separators are recommended.

Wear on the eccentric pins can be reduced by the application of molykote or a colloidal graphite.

Adjusting the head. A4, A45, A5, A56, A6

Refer to figure 2. Slacken the hexagon nuts, 29, allowing the gear ring, 5, to rotate against the spring housing, 4. Close the head and introduce the setting piece between the rolls. Displace the gear ring, 5, against the spring housing until the rolls rest against the setting piece. Tighten the nuts, 29. Preset the thread length with the head open.

This is identical to operation of a normal shank mounted fixed head, except that opening is by the internal limit stop. If the head is only to be used in this mode a shank mounted version, the RN, may be used. Standard rotating heads are flange mounted.

Operating the head, Rotary mode

The head is mounted as in figure 3, with the operating ring (figure 2 item 3) connected to a pivoted clevis. Before rolling ensure that the head is closed by drawing it back until the closing stop operates. The head is then fed forward to commence rolling. At the desired thread length the opening stop causes the clevis to pivot opening the head. The head can now be withdrawn, operating the closing stop once more.

THREAD ROLLING PARAMETERS

Correct selection of the rolling speed is essential to ensure a good thread quality and long roll life. The required speed depends on elongation of the material, thread form, machine capability and the tensile strength of the material to be rolled in Kg/sq.mm.

Recommended speeds are:-

Carbon steels to 70 Kg/sq.mm	30-60 m/min
Heat treatable steels to 100 Kg/sq.mm	30-70 m/min
Stainless steels	40-70 m/min
High speed steels & High alloy steels	30-50 m/min
Non ferrous metals, light alloys and brass with more than 60% copper.	60-90 m/min

NOTE:- IF THE QUALITIES OF THE MATERIAL ARE UNKNOWN NEVER ROLL BELOW 30 M/MIN, OR ROLL BREAKAGE MAY OCCUR.

Formulae for calculating parameters.

Rolling speed V =	D x 3.14 x N meters per minute 1000
Rolling time T =	60 x L seconds N x P
Rolling power N =	C x P x O x V x 1.35 horse power 1800
Rolling speed N =	1000 x V rpm D x 3.14
Where:	D = Thread diameter in mm. P = Thread pitch. L = Thread length in mm. T = Rolling time in seconds. N = Spindle speed in rpm. V = Rolling speed in m/min. C = 1 for 'v' form thread, 2 for square form thread. O = Tensile strength of material in Kg/sq.mm.

TROUBLE SHOOTING

Truncated threads
Head incorrectly set.
Head adjustment loose (tighten nuts).
Blank diameter too small.

Rough finish/scale formation
Material too brittle, or enlongation too low.
Coolant contaminated.

Head fails to open
Machine stops incorrectly adjusted or loose.
Rolls sticking due to contaminated coolant.
Work piece loose.
Spring or gear broken in head.

Material bends
Already bent.
Material requires stress relieving.
Work piece running out.
Chamfering not concentric.
Work piece overhang too long.

Burrs generated
Head engaging work piece too quickly or too slowly.
Correct chamfer required on work piece.

Double thread generated
Rolls incorrectly assembled on head.

Rolls damage or wear quickly
Attempting more than one rolling pass on same piece.
Head approaches work piece at wrong speed.
Rolling pressure excessive, blank diameter too great.
Rolling speed too low.
Needle rollers worn or dirty.
Machine power too low.

Tapering
Soft material at small diameter, blanks may need to be ground.
Spring housing worn or spring weak.

ALCO AXIAL THREAD ROLLING HEADS PRICES

SHANK MOUNTED FOR STANDARD COARSE THREADS

Enquire for Reconditioned Heads

Stationary Axial Head Rotary (G) Axial Head

SHANK MOUNTED FOR FINE THREADS

FLANGE MOUNTED

These heads are all rotary. Those marked * can also be used fixed. Heads marked (FT) are for fine threads, otherwise they are for standard coarse threads.