AGMA 6015-A13

This Standard provides a method for determining the power rating of gear sets used in main mill drives, pinion stands, and combination units used for the reduction of material size in metal rolling mills.

Applicability

Applications include but are not limited to, hot mills and cold mills, roughing and finishing stands: reducing, increasing, and 1:1 ratio sets. Auxiliary drives, including drives listed in ANSI/AGMA 6013-A06, such as bridles, coilers, uncoilers, edge trimmers, flatteners, loopers (accumulators), pinch rolls, scrap choppers, shears, and slitters are not covered by this document.

This standard includes a method by which different gear tooth designs can be rated and compared at extended life cycles typical for these applications, up to 175 000 hours.

Extended face widths in excess of the 40 inch limit contained within ANSI/AGMA 2001-D04 and ANSI/AGMA 6013-A06 are accommodated. Single helical designs with face widths as large as 60 inches and double helical designs with effective face widths as large as 90 inches are not uncommon in these applications. A calculation method is included for the load distribution factor, K_m, using a modification to the factors defined in ANSI/AGMA 2001-D04 for these extended face widths.

The standard addresses the range of load spectra experienced by these drives and defines load sharing for two and three high mill pinion stands.

Rating formulae

The formulae included determine the allowable fatigue ratings for pitting resistance and bending strength of steel gears with machined single or double helical external involute gear teeth only. Use of these formulae does not assure the performance of assembled gear drive systems, as numerous other design and operational factors are involved that are beyond the scope of this document.

The formulae evaluate gear tooth capacity as influenced by the major factors which affect gear tooth pitting and gear tooth fracture at the root fillet, when operating within design criteria for alignment and lubrication.

Where empirical values for rating factors are given by curves, curve-fitting equations are provided to facilitate computer programming. The constants and coefficients used in curve fitting often have significant digits in excess of those inferred by the reliability of the empirical data. Experimental data from actual gear unit measurements are seldom repeatable within a plus or minus 10 percent band.

This standard is intended for use by experienced gear designers capable of selecting reasonable values for the rating factors. It is not intended for use by the engineering public at large. Values for factors assigned in other standards are not applicable to this standard nor are the values assigned in this standard applicable to other standards. Mixing values from other standards with those from this standard could lead to erroneous ratings.

The gear designer or manufacturer is not responsible for the total system unless such a requirement is clearly identified in the contractual agreement.

It is imperative that the overall system designer be satisfied that the system of connected rotating parts is compatible, free from critical speeds and from torsional or other vibrations within the specified speed range, no matter how induced.

CAUTION: Compliance with this standard does not constitute a warranty of the rating of the gear set under installed field service conditions.

Limitations

The formulae of this standard are not applicable to other types of gear tooth deterioration such as wear, case crushing, and welding. They are also not applicable when vibratory conditions exceed the limits specified for the normal operation of the gears, see ANSI/AGMA 6000-B96.

This standard is not applicable when any of the following conditions exist:

• Transmission accuracy level, A_v, is more than 10 (Q_v less than 7);

• Teeth have been surface hardened by nitriding or flame hardening;

• Transverse contact ratio, m_p, is greater than 2.0;

• Diametral pitch is finer than 5.0;

• Teeth are damaged, e.g., cracked, worn, pitted, scuffed or plastically deformed;

• Interference exists between tooth tips and root fillets;

• Teeth are pointed. For most designs covered by this standard, pointed teeth are defined as those with normal chordal top land thickness, t_o, less than 0.25/P_nd. Smaller top lands require additional review;

• Operating backlash is insufficient;

• Normal gear mesh temperature is less than 32°F or greater than 250°F.

• Undercut exists in an area above the theoretical start of active profile.

• The root profiles are stepped or irregular. The J factor calculation uses the stress correction factors developed by Dolan and Broghamer [1]. These factors may not be valid for root forms which are not smooth curves. For root profiles which are stepped or irregular, other stress correction factors may be more appropriate.

Scuffing criteria are not included in this standard. A method to evaluate scuffing risk can be found in AGMA 925-A03.

Design considerations to prevent fractures emanating from stress risers on the tooth profile, tip chipping, and failures of the gear blank through the web or hub should be analyzed by general machine design methods.

Edition:

A13

Published:

09/23/2013

ANSI:

ANSI Approved

Number of Pages:

67

File Size:

1 file , 2.2 MB